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Macroalgae as microhabitat : seaweed traits and wave action as predictors of invertebrate epifaunal diversity 2007

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M A C R O A L G A E A S M I C R O H A B I T A T : S E A W E E D T R A I T S A N D W A V E A C T I O N A S P R E D I C T O R S OF I N V E R T E B R A T E E P I F A U N A L D I V E R S I T Y by C O L I N R O B E R T B A T E S 1 B . S c , Simon Fraser University, 1997 M.Sc . , University of New Brunswick Fredericton, 2002 A THESIS S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF D O C T O R OF P H I L O S O P H Y in T H E F A C U L T Y OF G R A D U A T E S T U D I E S (Botany) The University of British Columbia October 2007 © Col in Robert Bates, 2007 ABSTRACT In many coastal environments, anthropogenic stressors yield changes in seaweed biodiversity. Here, I describe three studies addressing how such floristic changes might affect provision of habitat by seaweeds for small mobile invertebrate epifauna. In chapter 2, I used observational and manipulative (transplant) experiments to test how changes in seaweed biodiversity influenced, biodiversity of associated invertebrates. I found that invertebrate epifaunal richness and abundance were not affected by changes in seaweed biodiversity. Invertebrate assemblage structure was, in most cases, not influenced by changes in seaweed composition; only when algal assemblages were composed of monocultures of species with 'foliose' morphologies did I observe a change in invertebrate assemblage structure. Correlations between algal functional composition and invertebrate assemblage structure were observed, but not between algal species composition and invertebrate assemblage structure. These results suggest that changes in seaweed biodiversity will have implications for invertebrate epifauna only under specific scenarios of algal change. In Chapter 3, I tested the performance of host taxonomic relatedness and functional (i.e. morphological) group affiliation as predictors of associated invertebrate epifauna. Neither general framework performed well; invertebrate assemblages found on congeneric host species were as similar as those found on hosts classified in different kingdoms, and taxon richness and abundance of invertebrates varied substantially within seaweed functional groups. Species identity was identified as a key predictor of the performance of seaweeds as hosts for invertebrate epifauna. In chapter 4, I examined the context dependence of these host identity effects by testing how host morphological complexity and maximum wave velocity interacted to determine local invertebrate diversity. Three types of host species were identified: a) morphologically 'simple' thalli that were minimally utilized as habitat under any of the tested wave regimes, b) thalli that were coarsely branched and were utilized by invertebrates under relatively benign wave conditions but became less utilized under higher wave action, and C) 'complex' algal hosts that supported diverse invertebrate assemblages under all tested wave conditions. Together, these studies support the view that invertebrates that use seaweeds as habitat are host-generalists, a n d t h e r e f o r e c o n s e q u e n c e s for i n v e r t e b r a t e s of c h a n g e s in s e a w e e d b i o d i v e r s i t y a r e l ikely to b e m i n i m a l . K e y w o r d s : b i o d i v e r s i t y , Br i t i sh C o l u m b i a , c o m m u n i t y e c o l o g y , e p i f a u n a , fac i l i ta t ion , f u n c t i o n a l g r o u p , h a b i t a t - p r o v i s i o n , intert idal , i n v e r t e b r a t e , m a r i n e , m o r p h o l o g y , s e a w e e d , t a x o n o m y , w a v e e x p o s u r e TABLE OF CONTENTS TABLE OF CONTENTS iv LIST OF TABLES vii LIST OF FIGURES viii ACKNOWLEDGEMENTS x CO-AUTHORSHIP STATEMENT xi Chapter 1: General Introduction 1 1.1 Conceptual framework 2 1.1.1 Changing world, changing biodiversity 2 1.1.2 Changes in seaweed biodiversity 2 1.1.3 Habitat modification 3 1.2 Community ecology as a predictive science 3 1.2.1 Biodiversity-ecosystem function relationships 4 1.2.2 Functional group diversity 5 1.2.3 Phylogenetic / taxonomic perspectives in community ecology 5 1.2.4 Functional trait performance along environmental gradients 6 1.3 Objectives of this thesis 7 1.3.1 Questions 7 1.4 The study system 7 1.4.1 Seaweeds 8 1.4.2 Invertebrate epifauna 8 1.4.3 Study sites 9 1.5 Literature cited..„ 13 Chapter 2: Do changes in seaweed biodiversity influence associated invertebrate epifauna? 17 2.1 Introduction 18 2.2 Materials and methods 20 2.2.1 Defining seaweed functional groups 20 2.2.2 Observational study 21 2.2.3 Manipulative experiment 21 2.2.4 Experimental treatments 21 iv 2.2.5 Seaweed transplants 23 2.2.6 Sample processing 24 2.2.7 Statistical analysis 24 2.3 Results 26 2.3.1 Observational study 26 2.3.2 Manipulative experiment 26 2.4 Discussion 27 2.4.1 Observational versus manipulative results 29 2.4.2 Implications for invertebrates of changes in seaweed biodiversity 29 2.5 Literature cited 36 Chapter 3: A comparison of host taxonomic relatedness and functional-group affiliation as predictors of seaweed-invertebrate epifaunal associations 40 3.1 Introduction 41 3.2. Materials and methods 44 3.2.1 Study Sites 44 3.2.2 Sample collections 44 3.2.3 Algal taxonomy & taxonomic distance ...44 3.2.4 Algal functional groups 45 3.2.5 Statistical analysis 45 3.2.5.1 Taxonomic distance analyses 45 3.2.5.2 Functional group analyses 46 3.3 Results 46 3.3.1 General results 46 3.3.2 Algal taxonomic distance 47 3.3.3 Across algal functional groups 47 3.3.4 Within algal functional groups 47 3.4 Discussion 48 3.4.1 Taxonomic relatedness of seaweed host 48 3.4.2 Seaweed functional groups 50 3.4.3 Is there hope for generalizations about seaweed-epifauna associations? 52 3.5 Literature cited 62 Chapter 4: Do facilitator traits interact with an environmental gradient to determine local species diversity? 68 v 4.1 Introduction 69 4.1.1 Ecosystem engineering, species traits, & environmental gradients 69 4.1.2 Wave action as a moderator of algal-invertebrate interactions 70 4.2 Materials and methods 71 4.2.1 Study sites 71 4.2.2 Measurement of maximum wave forces 72 4.2.3 Sampling of seaweeds and epifauna ....72 4.2.4 Statistical analyses 74 4.3 Results 75 4.3.1 Invertebrate abundance and taxon richness 75 4.3.2 Invertebrate composition 75 4.4 Discussion 76 4.4.1 How do seaweeds protect invertebrates from wave action? 77 4.4.2 Performance of the Bruno and Bertness model 79 4.4.3 Implications 80 4.5 Literature cited 90 Chapter 5: General Summary 95 5.1 Recapitulation of thesis objectives 96 5.2 Summary of study findings 96 5.3 Consequences for small mobile invertebrate epifauna of changes in seaweed biodiversity 97 5.4 Community ecology as a predictive science 98 5.5 Byproducts 99 5.6 Hindsight and future directions 99 5.7 Literature cited 101 Appendices 102 Appendix A: Taxonomic affiliations of invertebrate voucher specimens collected for the studies described in this thesis 103 vi LIST OF TABLES T a b l e 2 .1 : L is t o f a l g a l s p e c i e s i n c l u d e d in th is s t u d y , with f u n c t i o n a l g r o u p a s s i g n m e n t a n d w h e t h e r t h e y w e r e e n c o u n t e r e d in the o b s e r v a t i o n a l s t u d y ( O ) , u s e d in t h e m a n i p u l a t i v e s t u d y ( M ) o r bo th (B) 3 0 T a b l e 2.2: D e s c r i p t i o n o f a l g a l a s s e m b l a g e p a r a m e t e r s u s e d to c o m p o s e c o n t r o l a n d e x p e r i m e n t a l p lo t s . N = 4 for e a c h t r e a t m e n t ; e a c h t r e a t m e n t h a d f o u r a s s o c i a t e d con t ro l p lo ts 31 T a b l e 2 .3 : A N O S I M r e s u l t s for m a n i p u l a t i v e e x p e r i m e n t : C o m p a r i s o n s o f s p e c i f i c t r e a t m e n t s to c o n t r o l p lo t s for a l g a l t a x o n o m i c c o m p o s i t i o n (A) , a l g a l f u n c t i o n a l c o m p o s i t i o n ( B ) , a n d c o m p o s i t i o n of a s s o c i a t e d m o b i l e i n v e r t e b r a t e e p i f a u n a ( C ) . 3 2 T a b l e 2.4: S u m m a r y of d i f f e r e n c e s in a b u n d a n c e o f m a j o r i n v e r t e b r a t e t a x a f o u n d o n c o n t r o l p lo ts v e r s u s m o n o c u l t u r e s of f o l i o s e s e a w e e d ( G r o u p T 2 ) 3 3 T a b l e 2 .5 : S p e a r m a n r a n k c o r r e l a t i o n v a l u e s for t e s t s o f c o n g r u e n c e b e t w e e n t w o s e a w e e d a s s e m b l a g e d e s c r i p t o r s v s . a s s e m b l a g e s t r u c t u r e o f a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a 3 4 T a b l e 3 .1 : F u n c t i o n a l g r o u p af f i l ia t ions , n u m b e r of c o l l e c t e d thal l i , a n d t a x o n o m i c h i e r a r c h y u s e d to c a l c u l a t e t a x o n o m i c d i s t a n c e s b e t w e e n s e a w e e d s p e c i e s . T a x o n o m i c a u t h o r i t i e s a r e a v a i l a b l e f r o m A l g a e B a s e ( w w w . A l g a e B a s e . o r g ) 5 3 T a b l e 3 .2: R e s u l t s o f A N O S I M test for d i f f e r e n c e s in i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e a c r o s s s ix a l g a l f u n c t i o n a l g r o u p s . B o l d f a c e text i n d i c a t e s n o d i f f e r e n c e b e t w e e n g r o u p s (p > 0 . 0 5 ) 5 4 T a b l e 3 .3 : R e s u l t s o f A N O S I M t e s t s c o m p a r i n g i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e s a c r o s s a l g a l s p e c i e s wi th in s ix f u n c t i o n a l g r o u p s . B o l d f a c e text h i g h l i g h t s n o d i f f e r e n c e b e t w e e n s p e c i e s (p > 0 .05) 5 5 T a b l e 4 . 1 : R e l a t i o n s h i p s b e t w e e n m a x i m u m w a v e v e l o c i t y ( r a n g i n g f r o m - 1 m/s - 6 m/s) v e r s u s i n v e r t e b r a t e a b u n d a n c e a n d r a r e f i e d i n v e r t e b r a t e r i c h n e s s a s s o c i a t e d with t w e l v e s e a w e e d s p e c i e s . B o l d f a c e text i n d i c a t e s s i g n i f i c a n t (p < 0 . 0 5 ) i n f l u e n c e o f w a v e v e l o c i t y , a n d all s i g n i f i c a n t r e l a t i o n s h i p s a r e n e g a t i v e 8 2 vii LIST OF FIGURES F i g u r e 1.1: T h e l o w e r intert idal z o n e o f N u d i b r a n c h Po in t , B a r k l e y S o u n d , Br i t i sh C o l u m b i a is d o m i n a t e d b y a w i d e d i v e r s i t y o f s e a w e e d f o r m s . T h i s l u s h c o v e r is t y p i c a l o f l o w e r intert idal s h o r e s in t h e r e g i o n 10 F i g u r e 1.2: A s e l e c t i o n o f t h e d i v e r s e a r r a y o f s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a f o u n d o n s e a w e e d s in s o u t h e r n B a r k l e y S o u n d , Br i t i sh C o l u m b i a 11 F i g u r e 1.3: M a p o f s t u d y a r e a in s o u t h e r n B a r k l e y S o u n d , Br i t i sh C o l u m b i a , i n d i c a t i n g s ix s t u d y s i t e s : N u d i b r a n c h P o i n t (a : e x p o s e d ; b: s h e l t e r e d ) , S c o t t ' s B a y (c: e x p o s e d ; d : s h e l t e r e d ) , a n d D i x o n Is land (e: e x p o s e d ; f: s h e l t e r e d ) . Inset b o x s h o w s V a n c o u v e r I s l a n d , Br i t i sh C o l u m b i a , C a n a d a 12 F i g u r e 2 .1 : n M D S p lo t s of B r a y - C u r t i s S imi la r i ty b a s e d o n : A ) s e a w e e d t a x o n o m i c c o m p o s i t i o n , B ) s e a w e e d f u n c t i o n a l c o m p o s i t i o n , a n d C ) a s s o c i a t e d m o b i l e i n v e r t e b r a t e e p i f a u n a , f r o m 2 0 0 3 & 2 0 0 4 . C : C o n t r o l , T 1 : m i x e d p o l y c u l t u r e , T 2 : s i m p l e m o n o c u l t u r e , T 3 : s i m p l e p o l y c u l t u r e , T 4 : c o m p l e x m o n o c u l t u r e , T 5 : c o m p l e x p o l y c u l t u r e . D a s h e d l ine i n d i c a t e s that T r e a t m e n t g r o u p is d i f f e ren t f r o m c o n t r o l g r o u p ( A N O S I M p < 0 . 0 5 ; T a b l e 2.4) 3 5 F i g u r e 3 .1 : D e n d r o g r a m i l lustrat ing t a x o n o m i c r e l a t i o n s h i p s b e t w e e n a l g a l s p e c i e s i n v e s t i g a t e d a s h o s t s for s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a . T a x o n o m i c r e l a t i o n s h i p s t a k e n f r o m G a b r i e l s o n ef al. ( 2 0 0 6 ) 5 8 F i g u r e 3.2: A N O S I M R - v a l u e s i n d i c a t i n g s imi lar i ty o f i n v e r t e b r a t e a s s e m b l a g e s b e t w e e n a l g a l s p e c i e s wi th in s e v e n g r o u p s of i n c r e a s i n g t a x o n o m i c d i s t a n c e . N o d i f f e r e n c e s w e r e o b s e r v e d b e t w e e n g r o u p s (p = 0 . 4 4 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) 5 9 F i g u r e 3 .3 : C o m p a r i s o n s of r a r e f i e d i n v e r t e b r a t e t a x o n r i c h n e s s ( u p p e r p a n e l ) a n d i n v e r t e b r a t e a b u n d a n c e ( l o w e r p a n e l ) a c r o s s s e v e n a l g a l f u n c t i o n a l g r o u p s . S h a r e d let ters ( u p p e r p a n e l ) i n d i c a t e n o s ign i f i can t d i f f e r e n c e b e t w e e n g r o u p s (p > 0 . 0 5 ) . I n v e r t e b r a t e a b u n d a n c e d id not d i f fer a c r o s s a l g a l f u n c t i o n a l g r o u p s (p = 0 . 0 8 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) 6 0 F i g u r e 3.4: C o m p a r i s o n s of r a r e f i e d i n v e r t e b r a t e t a x o n r i c h n e s s ( u p p e r p a n e l ) a n d i n v e r t e b r a t e a b u n d a n c e ( l o w e r p a n e l ) for a l g a l s p e c i e s w i th in s e v e n a l g a l f u n c t i o n a l g r o u p s . H o r i z o n t a l b a r s i n d i c a t e t h e m e a n v a l u e fo r e a c h f u n c t i o n a l g r o u p . A s t e r i s k viii (*) i n d i c a t e s tha t t h e s p e c i e s m e a n d i f fers f r o m t h e f u n c t i o n a l g r o u p m e a n (p < 0 . 0 5 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) 61 F i g u r e 4 . 1 : C o n c e p t u a l m o d e l i l lustrat ing h o w a m b i e n t s t r e s s l e v e l s a n d fac i l i ta tor traits a r e p r o p o s e d to i n t e r a c t to d e t e r m i n e l e v e l s o f l o c a l s p e c i e s d i v e r s i t y . F i g u r e r e p r o d u c e d f r o m B r u n o a n d B e r t n e s s ( 2 0 0 1 ) , u s e d with p e r m i s s i o n 8 4 F i g u r e 4 . 2 : P h o t o g r a p h s o f t w e l v e s e a w e e d s p e c i e s s t u d i e d a s h o s t s for s m a l l m o b i l e i n v e r t e b r a t e s : a ) Alaria marginata, b) Chondracanthus exasperatus, c ) Codium fragile, d) Cryptosiphonia woodii, e ) Endocladia muricata, f) Fucus distichus s u b s p . evanescens, g ) Gastroclonium subarticulatum, h ) Mastocarpus ( ' P e t r o c e l i s ' p h a s e ) , i) Mazzaella splendens, j) Polysiphonia hendryi, k) Prionitis lyallii, a n d I) Ulva lactuca 8 5 F i g u r e 4 . 3 : R e l a t i o n s h i p b e t w e e n m a x i m u m w a v e v e l o c i t y ( o v e r 2 4 h o u r s ) a n d a b u n d a n c e o f s m a l l m o b i l e i n v e r t e b r a t e s a s s o c i a t e d wi th t w e l v e s p e c i e s o f h o s t s e a w e e d . * i d e n t i f i e s a s i g n i f i c a n t i n f l u e n c e o f w a v e v e l o c i t y ; r e g r e s s i o n s ta t i s t i cs a r e l i s ted in T a b l e 4.1 8 6 F i g u r e 4 .4 : R e l a t i o n s h i p b e t w e e n m a x i m u m w a v e v e l o c i t y ( o v e r 2 4 h o u r s ) a n d t a x o n r i c h n e s s ( r a r e f i e d to 2 0 i n d i v i d u a l s ) of s m a l l m o b i l e i n v e r t e b r a t e s a s s o c i a t e d with t w e l v e s p e c i e s o f h o s t s e a w e e d . A n a s t e r i s k (*) iden t i f i e s a s i g n i f i c a n t i n f l u e n c e o f w a v e v e l o c i t y ; r e g r e s s i o n s ta t i s t i cs a r e l i s ted in T a b l e 4 .1 8 7 F i g u r e 4 . 5 A : C h a n g e s in a v e r a g e a b u n d a n c e of i n v e r t e b r a t e t a x a a s s o c i a t e d with s ix h o s t s e a w e e d s p e c i e s a c r o s s a m a x i m u m w a v e v e l o c i t y g r a d i e n t . E r r o r b a r s w e r e o m i t t e d a n d l i n e s j o i n i n g p o i n t s w e r e a d d e d for c lar i ty . F i g u r e l e g e n d is in t h e t o p - left b o x . N o t e t h e d i f fe rent y - a x i s s c a l e s 8 8 F i g u r e 4 . 5 B : C h a n g e s in a v e r a g e a b u n d a n c e o f i n v e r t e b r a t e t a x a a s s o c i a t e d with s i x h o s t s e a w e e d s p e c i e s a c r o s s a m a x i m u m w a v e v e l o c i t y g r a d i e n t . E r r o r b a r s w e r e o m i t t e d a n d l i n e s j o i n i n g p o i n t s w e r e a d d e d for c lar i ty . F i g u r e l e g e n d is in t h e t o p - m i d d l e b o x . N o t e t h e d i f fe rent y - a x i s s c a l e s 8 9 ix ACKNOWLEDGEMENTS R o b D e W r e e d e , t h a n k y o u for all y o u r e n c o u r a g e m e n t , s u p p o r t , a n d g u i d a n c e , in B a m f i e l d , B a n g k o k a n d b e y o n d , I e n j o y e d o u r t a l k s a b o u t s c i e n c e a n d e v e r y t h i n g e l s e . T h a n k y o u a l s o to S a n d r a L i n d s t r o m , D i a n e S r i v a s t a v a , R o y T u r k i n g t o n , G a r y B r a d f i e l d a n d T o m T o m a s c i k for y o u r t i m e a n d h e l p f u l s u g g e s t i o n s . S ta f f , g r a d u a t e s t u d e n t s , a n d f ie ld a n d l a b h e l p e r s f r o m t h e B a m f i e l d M a r i n e S c i e n c e s C e n t r e m a d e m y l o n g h o u r s s o m e w h a t s h o r t e r : L e a h H a s s a l l , R i a n D i c k s o n , J u l i e C o l l e n s , N a t e J u e , H o n g N g u y e n , S h a w n P a r r i e s , K r i s t e n R u t l i d g e , R a c h e l S a r a g a , D a v e T a y l o r , S c o t t T o e w s , L a u r a W h i t e , T a s i a Y i m , S o p h i e B o i z a r d , S h a r o n J e f f e r y , S h i r l e y P a k u l a , a n d Cl i f f H a y l o c k . F r i e n d s a l s o h e l p e d m e a l o n g t h e w a y : J e r s e y , R i a n D i c k s o n , S a r a h D o n a l d , J o h n H u g h e s , N a o m i M a n ' I n ' T ' V e l d t , Dary l l M i l n e , M a r k S t o k o e , S c o t t T o e w s , T a r a M a c D o n a l d , R o d n e y W i t h a l l , B r i a n S t a r z o m s k i , J o n S h u r i n , S a r a h T y n e , a n d D e n n i s M o r g a n . C o r r e s p o n d e n c e with M i c h a e l B o i l e r h e l p e d m e to u n d e r s t a n d a l g a l r e c o n f i g u r a t i o n , a n d S p e n c e r W o o d w a s pa t ien t a n d h e l p f u l wi th m y s ta t i s t i c s q u e s t i o n s . T h a n k y o u a l s o to t h e H u u - A y - A h t F i rs t N a t i o n fo r g r a n t i n g a c c e s s to the i r t rad i t iona l l a n d . T h e N a t i o n a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l , t h e U n i v e r s i t y of Br i t i sh C o l u m b i a , a n d t h e B a m f i e l d M a r i n e S c i e n c e s C e n t r e p r o v i d e d f i n a n c i a l s u p p o r t for th is w o r k . x CO-AUTHORSHIP STATEMENT Chapter 2: Do changes in seaweed biodiversity influence associated invertebrate epifauna? I h a d t h e i d e a fo r th i s s t u d y , a n d I s e t u p , s a m p l e d , a n d a n a l y z e d t h e d a t a . I a c k n o w l e d g e t h e c o n t r i b u t i o n s o f R o b e r t D e W r e e d e to t h e c o n c e p t u a l d e v e l o p m e n t a n d m e t h o d s u s e d for th is e x p e r i m e n t . I w r o t e t h e first draf t o f t h e m a n u s c r i p t , a n d c o m m e n t s b y R o b D e W r e e d e a n d t w o a n o n y m o u s r e v i e w e r s c o n t r i b u t e d to t h e r e a d a b i l i t y a n d r igor o f t h e f inal repor t . A v e r s i o n o f th is c h a p t e r is p u b l i s h e d : B a t e s , O R . a n d R . E . D e W r e e d e ( 2 0 0 7 ) Journal of Experimental Marine Biology and Ecology 344: 2 0 6 - 2 1 4 . xi Chapter 1: General Introduction 1.1 Conceptual framework 1.1.1 Changing world, changing biodiversity As global human populations increase, our collective influence on the earth's biota becomes more profound. In the majority of populated regions, human actions are responsible for both extirpating and introducing species and for causing changes in biological composition (Hooper ef al. 2005). Such changes are happening at levels of organization from genes to communities (Grosberg and Cunningham 2001), and invasive species are problematic in many ecosystem types (Kaiser 1999). Awareness of these changes has led to concerns about the consequences of altered biodiversity for community and ecosystem processes (Naeem et al. 1994). In the marine environment, coastal zones are particularly threatened (Gray 1997) because an estimated 67% of the world's human population lives within 60 km of the coast (Hammond 1992). Examples of anthropogenic stressors on coastal biodiversity include climate change, resource over-harvesting, toxic pollutants, eutrophication, coastal habitat alteration, tourism, introduced species, and marine litter (Suchanek 1994, Gray 1997, Crowe ef al. 2000, Bax ef al. 2003). The greatest threat to marine biodiversity is habitat loss (Gray 1997). 1.1.2 Changes in seaweed biodiversity Seaweeds, the benthic marine algae, are susceptible to impacts by human activities (Schramm and Nienhuis 1996, Scott and Tittley 1998, Ducrotoy 1999). The work described in this thesis was motivated in part by my previous studies of the dynamics of marine algae in the Bay of Fundy (Bates 2002, Bates ef al. 2005, 2007). My observations there of degraded seaweed assemblages, in conjunction with my perception that seaweeds are typically overlooked in coastal conservation and management plans, prompted an interest in understanding the consequences of anthropogenic changes in biodiversity of marine algae. Of the many functions that benthic marine algae perform, I chose to study their role as "habitat modifying 2 o r g a n i s m s " ( H M O s ) ( B r u n o a n d B e r t n e s s 2 0 0 0 ) in intert idal e n v i r o n m e n t s . S e a w e e d s p r o v i d e hab i ta t to a w i d e a r r a y o f o r g a n i s m s , t h e b u l k o f w h i c h a r e s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a ( T a y l o r 1 9 9 8 ) . 1.1.3 Habitat modification T h e r a m i f i c a t i o n s of c h a n g e s in b i o d i v e r s i t y a r e c o m p o u n d e d w h e n t h e a f f e c t e d s p e c i e s a r e p r o v i d e r s o f b i o g e n i c hab i ta t for o t h e r s p e c i e s . A l t h o u g h s u c h p o s i t i v e i n t e r a c t i o n s h a v e l o n g b e e n k n o w n to i n f l u e n c e c o m m u n i t y s t r u c t u r e , r e c e n t y e a r s h a v e s e e n i n c r e a s e d i n t e r e s t in u n d e r s t a n d i n g the b i o l o g i c a l a n d p h y s i c a l f a c t o r s that r e g u l a t e b i o g e n i c h a b i t a t p r o v i s i o n ( B e r t n e s s a n d L e o n a r d 1 9 9 7 , S t a c h o w i c z 2 0 0 1 , B r u n o et al. 2 0 0 3 ) . H a b i t a t m o d i f i c a t i o n is t h o u g h t to b e i m p o r t a n t in c i r c u m s t a n c e s w h e r e a H M O c a n a m e l i o r a t e a b i o t i c o r b iot ic s t r e s s o r s that w o u l d o t h e r w i s e p r e v e n t t h e c o e x i s t e n c e o f a s s o c i a t e d s p e c i e s o r a s s e m b l a g e s ( C r a i n a n d B e r t n e s s 2 0 0 6 ) . H a b i t a t m o d i f y i n g s p e c i e s h a v e b e e n v a r i o u s l y r e f e r r e d to a s ' f o u n d a t i o n s p e c i e s ' ( D a y t o n 1 9 7 2 ) , ' e c o s y s t e m e n g i n e e r s ' ( J o n e s etal. 1 9 9 7 ) , a n d ' k e y s t o n e f a c i l i t a t o r s ' ( H a c k e r a n d G a i n e s 1 9 9 7 ) . H a b i t a t m o d i f i c a t i o n c a n b e a c t i v e , m e d i a t e d b y t h e a c t i o n s of a n H M O , for e x a m p l e w h e n b e a v e r s fall t r e e s to c r e a t e d a m s ( W r i g h t e t al. 2 0 0 2 ) , o r hab i ta t m o d i f i c a t i o n c a n o c c u r p a s s i v e l y , w h e r e t h e s i m p l e p r e s e n c e of t h e hab i ta t m o d i f i e r a c t s to a m e l i o r a t e s t r e s s o r s . T h i s latter p r o c e s s is o f i n t e r e s t h e r e . 1.2 Community ecology as a predictive science E c o l o g i s t s a r e i n c r e a s i n g l y a s k e d to p r e d i c t t h e c o n s e q u e n c e s of c h a n g e s in b i o d i v e r s i t y ( H a w k i n s 1 9 9 9 , B e n e d e t t i - C e c c h i et a l . 2 0 0 1 ) . P r e d i c t i n g t h e c o n s e q u e n c e s of b iot ic c h a n g e s is no t a s i m p l e task ; s u c h p r e d i c t i o n s a r e h i n d e r e d b y s e v e r a l c o n c e p t u a l a n d p r a c t i c a l l im i ta t ions . B i o l o g i c a l a s s e m b l a g e s c a n b e h i g h l y v a r i a b l e in s p a c e a n d t i m e ( B e n e d e t t i - C e c c h i 2 0 0 1 ) , s o the s c a l e of i n v e s t i g a t i o n c a n i n f l u e n c e resu l t s a n d c o n c l u s i o n s . A s we l l , " s t a n d a r d " e c o l o g i c a l p r o c e d u r e s m a y not b e su f f i c ient to a d d r e s s t h e s c i e n t i f i c a n d p r e d i c t i v e n e e d s o f m a n a g e r s a n d p o l i c y m a k e r s ( L a w t o n 1 9 9 9 ) . In p r a c t i c e , m o s t e c o l o g i s t s h a v e s t u d i e d p a i r w i s e c o m p a r i s o n s of s p e c i e s 3 i n t e r a c t i o n s , a n d t h e c o n c l u s i o n s of t h e s e s t u d i e s a r e o f t e n s p e c i f i c to t h e s i t e s , d a t e s , a n d o r g a n i s m s e x a m i n e d ( M c G i l l e f al. 2 0 0 6 ) . S e v e r a l r e v i e w s h a v e l a m e n t e d the "fa i lures" a n d l a c k of g e n e r a l i t i e s o f c o m m u n i t y e c o l o g y ( L a w t o n 1 9 9 9 , S i m b e r l o f f 2 0 0 4 ) , d r a w i n g t h e p o s s i b i l i t y that c o m m u n i t y e c o l o g y m a y not b e a b l e to p r o v i d e a n s w e r s a b o u t t h e c o n s e q u e n c e s o f c h a n g e s in b i o d i v e r s i t y that a r e c o n s i s t e n t a c r o s s d i f ferent s p a t i a l a n d t e m p o r a l s c a l e s , d i f fe rent s p e c i e s o r e c o s y s t e m s . H o w e v e r , t h e r e a r e s e v e r a l r e c e n t l y p r o p o s e d a p p r o a c h e s that h o l d p r o m i s e for c o m m u n i t y e c o l o g y a s a p r e d i c t i v e s c i e n c e ( M c G i l l e f al. 2 0 0 6 ) . In t h e f o l l o w i n g s e c t i o n s , I br ief ly o u t l i n e s e v e r a l c o n c e p t s that a l l o w i n v e s t i g a t o r s to l o o k p a s t s p e c i e s ident i ty t o w a r d s m o r e g e n e r a l p r e d i c t i v e f r a m e w o r k s : b i o d i v e r s i t y - e c o s y s t e m f u n c t i o n r e l a t i o n s h i p s , f u n c t i o n a l d i ve rs i t y , p h y l o g e n e t i c / t a x o n o m i c p e r s p e c t i v e s in c o m m u n i t y e c o l o g y , a n d t h e s t u d y of f u n c t i o n a l trait p e r f o r m a n c e a l o n g e n v i r o n m e n t a l g r a d i e n t s . 1.2.1 Biodiversity-ecosystem function relationships T o u n d e r s t a n d t h e c o n s e q u e n c e s of c h a n g e s in b i o d i v e r s i t y o n e c o s y s t e m p r o c e s s e s , i n v e s t i g a t o r s h a v e c r e a t e d or m a n i p u l a t e d a s s e m b l a g e s a l o n g a g r a d i e n t o f b i o d i v e r s i t y ( v a r i o u s l y i n c o r p o r a t i n g s p e c i e s r i c h n e s s , f u n c t i o n a l r i c h n e s s , a n d c o m p o s i t i o n o f t a x o n o m i c a n d f u n c t i o n a l g r o u p s ) a n d m e a s u r e d s u b s e q u e n t c h a n g e s in e c o s y s t e m p r o p e r t i e s ( L o r e a u e f al. 2 0 0 1 , N a e e m a n d W r i g h t 2 0 0 3 ) . D e s p i t e e a r l y d e b a t e s a b o u t p r o b l e m s o f e x p e r i m e n t a l d e s i g n s a n d m e c h a n i s m s u n d e r p i n n i n g o b s e r v e d p a t t e r n s , b i o d i v e r s i t y - e c o s y s t e m f u n c t i o n r e s e a r c h h a s o f f e r e d s e v e r a l g e n e r a l i n s i g h t s a b o u t t h e r e l a t i o n s h i p b e t w e e n d i v e r s i t y a n d e c o s y s t e m p r o p e r t i e s ( H o o p e r e f al. 2 0 0 5 ) . H o w e v e r , i n v e s t i g a t i o n s a b o u t t h e r e l a t i o n s h i p s b e t w e e n b i o d i v e r s i t y a n d f u n c t i o n in m a r i n e e n v i r o n m e n t s w e r e re la t i ve ly s c a r c e ( D u a r t e 2 0 0 0 ) until r e c e n t l y ( B o l a m e f al. 2 0 0 2 , S t a c h o w i c z ef al. 2 0 0 2 , S o l a n e f al. 2 0 0 4 , B r u n o ef al. 2 0 0 5 ) . 4 1.2.2 Functional group diversity R e c o g n i t i o n that s p e c i e s c a n p l a y s i m i l a r r o l e s wi th in a s s e m b l a g e s h a s g i v e n r i se to the i d e a that t a x a c a n b e g r o u p e d t o g e t h e r into f u n c t i o n a l g r o u p s ( G i t a y a n d N o b l e 1 9 9 7 ) . I n h e r e n t in t h e i d e a o f f u n c t i o n a l g r o u p s is that s p e c i e s c a n b e f u n c t i o n a l l y e q u i v a l e n t o r r e d u n d a n t : l o s s o f a par t i cu la r s p e c i e s c a n b e c o m p e n s a t e d for b y the p r e s e n c e o f f u n c t i o n a l l y s i m i l a r s p e c i e s . E v i d e n c e e x i s t s to s u g g e s t that f u n c t i o n a l g r o u p d i v e r s i t y is i m p o r t a n t to e c o s y s t e m p r o c e s s e s ( T i l m a n et al. 1 9 9 7 , D i a z a n d C a b i d o 2 0 0 1 , P e t c h e y a n d G a s t o n 2 0 0 2 , D i a z et al. 2 0 0 3 ) . H o w e v e r , t h e r e is c o n s i d e r a b l e d e b a t e a b o u t t h e b e s t w a y to d e l i n e a t e f u n c t i o n a l g r o u p s ( G i t a y a n d N o b l e 1 9 9 7 ) , a n d to w h e t h e r o r not s p e c i e s c a n rea l ly b e c o n s i d e r e d r e d u n d a n t ( R o s e n f e l d 2 0 0 2 , L o r e a u 2 0 0 4 ) . A s wi th b i o d i v e r s i t y - e c o s y s t e m f u n c t i o n r e s e a r c h , m o s t o f the d a t a a v a i l a b l e o n f u n c t i o n a l d i v e r s i t y a r e not f r o m m a r i n e e n v i r o n m e n t s ( G r a y 1 9 9 7 ) . T h e i d e a of f u n c t i o n a l g r o u p i n g s r e m a i n s a n intr igu ing a p p r o a c h to a s s e s s i n g c h a n g e s in b iod ive rs i t y , a n d for u n d e r s t a n d i n g the c o n s e q u e n c e s o f t h e s e c h a n g e s for e c o s y s t e m a n d c o m m u n i t y - l e v e l p r o p e r t i e s . 1.2.3 Phylogenetic / taxonomic perspectives in community ecology P h e n o t y p e s a r e , to a l a r g e ex tent , d r i v e n b y g e n o t y p e s . In a n e c o l o g i c a l c o n t e x t , it m a k e s s e n s e that c l o s e l y r e l a t e d s p e c i e s , t h r o u g h s h a r e d g e n o t y p e s , will exh ib i t s i m i l a r p h e n o t y p e s , a n d t h e r e f o r e f u n c t i o n s im i l a r l y ( W e b b et al. 2 0 0 2 ) . A s t a x o n o m i c r e l a t i o n s h i p s a r e i n c r e a s i n g l y r e s o l v e d , r e l a t e d n e s s c a n b e u s e d to g e n e r a t e h y p o t h e s e s a b o u t e c o l o g i c a l p e r f o r m a n c e b a s e d o n re la t i ve t a x o n o m i c o r g e n e t i c d i s t a n c e s . T h i s a p p r o a c h is still qu i te n e w , h o w e v e r i n te res t is g r o w i n g . R e c e n t l y d e v e l o p e d m e t r i c s o f t a x o n o m i c s imi lar i ty ( C l a r k e et al. 2 0 0 6 ) m a k e it p o s s i b l e to c a l c u l a t e t a x o n o m i c d i s t a n c e s b a s e d o n a L i n n a e a n c l a s s i f i c a t i o n s c h e m e , s o a d v a n c e d k n o w l e d g e a b o u t p h y l o g e n e t i c t r e e r e c o n s t r u c t i o n is not n e c e s s a r y to tes t h y p o t h e s i s b a s e d o n t a x o n o m i c r e l a t e d n e s s . 5 1.2.4 Functional trait performance along environmental gradients. P a r t o f t h e l a c k o f g e n e r a l i t y of c o m m u n i t y e c o l o g y s t e m s f r o m t h e u s e o f n o m e n c l a t u r a l l y l i n k e d ( i .e. s p e c i e s i d e n t i t y - b a s e d ) s t a t e m e n t s that c o u l d b e m o r e e f f e c t i v e if t h e y f o c u s e d o n t h e f u n c t i o n a l traits o f t h e o r g a n i s m s u n d e r s t u d y ( M c G i l l ef al. 2 0 0 6 ) . F u n c t i o n a l traits a r e m e a s u r a b l e p r o p e r t i e s o f o r g a n i s m s that s t r o n g l y i n f l u e n c e p e r f o r m a n c e ( M c G i l l ef al. 2 0 0 6 ) , a n d trait d i v e r s i t y c a n u n d e r p i n t h e r e l a t i o n s h i p b e t w e e n b i o d i v e r s i t y a n d e c o s y s t e m f u n c t i o n ( W a l k e r et al. 1 9 9 9 ) . T h e e n v i r o n m e n t s in w h i c h o r g a n i s m s l ive a r e r a r e l y c o n s t a n t , y e t m o r e o f t e n t h a n not, c o m m u n i t y e c o l o g y r e s e a r c h d o e s not a c k n o w l e d g e e n v i r o n m e n t a l g r a d i e n t s ( M c G i l l etal. 2 0 0 6 , but s e e B e l c h e r etal. 1 9 9 5 , P e l t z e r etal. 1 9 9 8 , H e l m u t h etal. 2 0 0 2 , P u i j a l o n a n d B o m e t t e 2 0 0 4 ) . E x a m p l e s o f e n v i r o n m e n t a l g r a d i e n t s i n c l u d e t e m p e r a t u r e , nutr ients , m o i s t u r e , a n d h y d r o d y n a m i c r e g i m e . G r a y ( 1 9 9 7 ) s u g g e s t s , r ightly s o , that "no e c o l o g i c a l s y s t e m c a n b e s t u d i e d in i so la t i on f r o m t h e e n v i r o n m e n t in w h i c h it ex is ts" . T h e r e c o g n i t i o n o f g r a d i e n t s is a n i m p o r t a n t e l e m e n t to i n c r e a s i n g t h e r e a l i s m o f e c o l o g i c a l s t u d i e s , a n d to u n d e r s t a n d i n g h o w s p a t i a l v a r i a t i o n i n f l u e n c e s e c o l o g i c a l p r o c e s s e s . M c G i l l et al. ( 2 0 0 6 ) s u g g e s t that, in part, s t u d y i n g f u n c t i o n a l traits a c r o s s e n v i r o n m e n t a l g r a d i e n t s c o u l d h e l p to t r a n s f o r m c o m m u n i t y e c o l o g y into a m o r e quant i t a t i ve a n d p r e d i c t i v e s c i e n c e . T h i s w o u l d i m p r o v e o u r abi l i ty to p r o v i d e i n f o r m a t i o n r e l e v a n t to u n d e r s t a n d i n g the r a m i f i c a t i o n s of s t r e s s o r s o f a n t h r o p o g e n i c o r ig in , s u c h a s g l o b a l c l i m a t e c h a n g e . T h e s e d e v e l o p m e n t s in c o m m u n i t y e c o l o g y a r e i n t e r e s t i n g a n d p r o g r e s s i v e . H o w e v e r , t h e r e is a l s o c u r r e n t r e s e a r c h s u g g e s t i n g that s p e c i e s ident i ty is i m p o r t a n t to e c o s y s t e m p r o c e s s e s ( B r u n o ef al. 2 0 0 5 , O ' C o n n o r a n d C r o w e 2 0 0 5 ) . D e s p i t e c r i t i c i s m s of c o m m u n i t y e c o l o g y ( L a w t o n 1 9 9 9 ) , it is diff icult to a v o i d s t u d y i n g c o m m u n i t i e s o f o r g a n i s m s ; in o r d e r to s t u d y c o m m u n i t y e c o l o g y , w e m u s t s t u d y s p e c i f i c c o m m u n i t i e s ( S i m b e r l o f f 2 0 0 4 ) . 6 1.3 Objectives of this thesis I h a v e a t t e m p t e d to a c k n o w l e d g e t h e s e d e v e l o p m e n t s in c o m m u n i t y e c o l o g y w h e n d e f i n i n g m y r e s e a r c h q u e s t i o n s . T h e s t u d i e s d e s c r i b e d in th i s t h e s i s a r e un i f i ed not o n l y by a c o m m o n s t u d y s y s t e m , but a l s o b y a n in te res t in g a i n i n g a b r o a d e r u n d e r s t a n d i n g a b o u t t h e v a l u e of s t u d y i n g s p e c i e s v e r s u s g e n e r a l i z i n g a c r o s s t a x a . In d o i n g s o , I c a n d e v e l o p ins igh t not o n l y into the ro le o f s e a w e e d s a s hab i ta t for i n v e r t e b r a t e e p i f a u n a a n d the c o n s e q u e n c e s of c h a n g e s in s e a w e e d a s s e m b l a g e s , but a l s o a b o u t s e v e r a l n e w p a r a d i g m s for c o m m u n i t y e c o l o g y . 1.3.1 Questions T h r e e g e n e r a l q u e s t i o n s a r e a d d r e s s e d in th is t h e s i s ; I l o o k h e r e at h o w c h a n g e s in s e a w e e d b i o d i v e r s i t y , s e a w e e d s p e c i e s ident i ty a n d a n e n v i r o n m e n t a l g r a d i e n t (i .e. w a v e v e l o c i t y ) i n f l u e n c e i n v e r t e b r a t e b i o d i v e r s i t y . S p e c i f i c a l l y , I a s k : 1) H o w d o c h a n g e s in b i o d i v e r s i t y o f h a b i t a t - f o r m i n g s e a w e e d s i n f l u e n c e the b i o d i v e r s i t y o f i n v e r t e b r a t e e p i f a u n a u s i n g th is b i o g e n i c h a b i t a t ? ( C h a p t e r 2) 2) H o w d o s e a w e e d t a x o n o m i c r e l a t e d n e s s a n d f u n c t i o n a l g r o u p aff i l iat ion p e r f o r m a s p r e d i c t o r s of hab i ta t a s s o c i a t i o n s b e t w e e n s e a w e e d s a n d m o b i l e i n v e r t e b r a t e e p i f a u n a ? ( C h a p t e r 3) 3) H o w d o e s s e a w e e d a r c h i t e c t u r a l c o m p l e x i t y in te rac t with a g r a d i e n t o f w a v e f o r c e to d e t e r m i n e p a t t e r n s of i n v e r t e b r a t e d i v e r s i t y ? ( C h a p t e r 4) 1.4 The study system T h e s e q u e s t i o n s w e r e a d d r e s s e d u s i n g a n intert idal s e a w e e d - e p i f a u n a s y s t e m . T h e intert idal is a n e x c e l l e n t s t u d y e n v i r o n m e n t in w h i c h to a d d r e s s m y r e s e a r c h q u e s t i o n s ; d i v e r s e a s s e m b l a g e s o f s e a w e e d s a n d i n v e r t e b r a t e s p e r s i s t a c r o s s s e v e r a l 7 e n v i r o n m e n t g r a d i e n t s o f ( e . g . t e m p e r a t u r e , d e s i c c a t i o n , w a v e f o r c e ) that o c c u r a c r o s s s h o r t d i s t a n c e s ( H a w k i n s 1 9 9 9 ) . 1.4.1 S e a w e e d s S e a w e e d s , t h e m a c r o s c o p i c m a r i n e a l g a e , a r e a m o r p h o l o g i c a l l y a n d p h y l o g e n e t i c a l l y d i v e r s e g r o u p of o r g a n i s m s . T h e y r a n g e f r o m s m a l l , u n d i f f e r e n t i a t e d f i l a m e n t s a n d s i m p l e b l a d e s to l a r g e a n d c o m p l e x , h i g h l y d i f f e r e n t i a t e d thall i with s p e c i a l i z e d s t r u c t u r e s for a t t a c h m e n t , r e p r o d u c t i o n , p h o t o s y n t h e s i s , a n d f lotat ion ( G r a h a m a n d W i l c o x 2 0 0 0 ) . S e a w e e d s a r e a p o l y p h y l e t i c g r o u p , e n c o m p a s s i n g a v a s t a r r a y of g e n e t i c d i v e r s i t y a n d s p a n n i n g two k i n g d o m s o f life. T h e r e a r e t h r e e m a j o r t a x o n g r o u p s of s e a w e e d s , the r e d s ( P h y l u m R h o d o p h y t a ) , g r e e n s ( P h y l u m C h l o r o p h y t a ) , a n d b r o w n s ( C l a s s P h a e o p h y c e a e ) . S e a w e e d s c o m p r i s e t h e d o m i n a n t b i o m a s s in m a n y t e m p e r a t e r o c k y n e a r s h o r e e c o s y s t e m s ( F i g u r e 1.1), a n d t h e y a r e e c o l o g i c a l l y i m p o r t a n t c o m p o n e n t s of a m i l i eu r e g u l a t e d b y c o m p l e x s p e c i e s i n t e r a c t i o n s a n d a c o n s t a n t l y f l uc tua t ing e n v i r o n m e n t . 1.4.2 I n v e r t e b r a t e e p i f a u n a S m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a a r e a s u b s e t of i n v e r t e b r a t e s d e f i n e d by the i r vagi l i ty , hab i ta t a n d s i z e r a n g e (0.2 m m to 3 0 . 0 m m ) r a t h e r t h a n the i r t a x o n o m i c affinity. M o b i l e e p i f a u n a a r e f r e e to m o v e b e t w e e n h o s t s , un l i ke s e s s i l e e p i f a u n a s u c h a s b r y o z o a n s o r b a r n a c l e s . T h r o u g h o u t th is t h e s i s , s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a will b e r e f e r r e d to a s ' a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a ' , o r s i m p l y ' e p i f a u n a ' . E p i f a u n a a r e a h igh ly d i v e r s e g r o u p , r e p r e s e n t i n g a w i d e a r r a y of i n v e r t e b r a t e t a x a . C o m m o n l y e n c o u n t e r e d p h y l a i n c l u d e : A r t h r o p o d a , M o l l u s c a , A n n e l i d a , E c h i n o d e r m a t a , a n d N e m a t o d a ( F i g u r e 1.2). E p i f a u n a f o u n d o n s e a w e e d s m a y o r m a y not u s e the i r h o s t s a s a f o o d s o u r c e ( A r r o n t e s 1 9 9 9 ) . 8 1.4.3 S t u d y s i t e s T h e s e s t u d i e s w e r e u n d e r t a k e n in s o u t h e r n B a r k l e y S o u n d , B r i t i sh C o l u m b i a , C a n a d a ( F i g u r e 1.3). C o l l e c t i o n s w e r e t a k e n at s ix s i t e s ; t w o s i t e s w e r e l o c a t e d at e a c h of N u d i b r a n c h P o i n t (48°48'53" N, 125°10'20" W ; 48°48'53" N , 125°10'19" W ) , S c o t t ' s B a y ( 4 8 ' 5 0 ' 0 5 " N, 125°05'39"W; 48°50'04"N, 125°05'38"W) a n d D i x o n I s l a n d (48°51'07"N, 1 2 5 T J 5 ' 2 5 " W ; 4 8 ' 5 1 ' 1 2 " N , 125°05'20"W). T h e s e s i t e s a r e " typ ica l" s h o r e s for the a r e a , s u b j e c t e d to a g r a d i e n t o f w a v e e x p o s u r e , a n d a r e l o c a t e d wi th in two k i l o m e t r e s of t h e B a m f i e l d M a r i n e S c i e n c e s C e n t r e . F o u r o f t h e s i t e s w e r e s e l e c t e d b a s e d o n p r e - e x i s t i n g m e a s u r e m e n t s of w a v e e x p o s u r e ( B a t e s et al., u n p u b l i s h e d d a t a ) , with two a d d i t i o n a l s i t e s a d d e d to b r o a d e n t h e g e o g r a p h i c r a n g e a n d to fill in the s p e c t r u m of p o s s i b l e w a t e r m o t i o n m e a s u r e m e n t s . 9 F i g u r e 1.1: T h e l o w e r intert idal z o n e o f N u d i b r a n c h P o i n t , B a r k l e y S o u n d , Br i t i sh C o l u m b i a is d o m i n a t e d b y a w i d e d i v e r s i t y o f s e a w e e d f o r m s . T h i s l u s h c o v e r is t y p i c a l o f l o w e r intert idal s h o r e s in t h e r e g i o n . F i g u r e 1.2: A s e l e c t i o n o f t h e d i v e r s e a r r a y o f s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a f o u n d o n s e a w e e d s in s o u t h e r n B a r k l e y S o u n d , Br i t i sh C o l u m b i a . 11 125 15' F i g u r e 1.3: M a p of s t u d y a r e a in s o u t h e r n B a r k l e y S o u n d , Br i t i sh C o l u m b i a , i n d i c a t i n g s ix s t u d y s i t e s : N u d i b r a n c h P o i n t (a : e x p o s e d ; b: s h e l t e r e d ) , S c o t t ' s B a y (c: e x p o s e d ; d : s h e l t e r e d ) , a n d D i x o n Is land (e: e x p o s e d ; f: s h e l t e r e d ) . Inset b o x s h o w s V a n c o u v e r I s l a n d , Br i t i sh C o l u m b i a , C a n a d a . 12 1.5 L i t e r a t u r e c i t e d A r r o n t e s , J . 1 9 9 9 . O n t h e e v o l u t i o n of i n t e r a c t i o n s b e t w e e n m a r i n e m e s o h e r b i v o r e s a n d a l g a e . B o t a n i c a M a r i n a 4 2 : 1 3 7 - 1 5 5 . B a t e s , C . R. 2 0 0 2 . M o n i t o r i n g s e a w e e d b i o d i v e r s i t y in t h e B a y o f F u n d y , N e w B r u n s w i c k , C a n a d a . M a s t e r s t h e s i s . U n i v e r s i t y o f N e w B r u n s w i c k , F r e d e r i c t o n . B a t e s , C . R., G . W . S a u n d e r s , a n d T . C . C h o p i n . 2 0 0 5 . A n a s s e s s m e n t of t w o t a x o n o m i c d i s t i n c t n e s s i n d i c e s for d e t e c t i n g s e a w e e d a s s e m b l a g e r e s p o n s e s to e n v i r o n m e n t a l s t r e s s . B o t a n i c a M a r i n a 4 8 : 2 3 1 - 2 4 3 . B a t e s , C . R., G . W . S a u n d e r s , a n d T . C . C h o p i n . 2 0 0 7 . H i s t o r i c a l v s . c o n t e m p o r a r y m e a s u r e s o f s e a w e e d b i o d i v e r s i t y in the B a y o f F u n d y . C a n a d i a n J o u r n a l o f B o t a n y (in review). B a x , N. , A . W i l l a m s o n , M . A g u e r o , E . G o n z a l e z , a n d W . G e e v e s . 2 0 0 3 . M a r i n e i n v a s i v e a l i e n s p e c i e s : a t h r e a t to g l o b a l b i o d i v e r s i t y . M a r i n e P o l i c y 2 7 : 3 1 3 - 3 2 3 . B e n e d e t t i - C e c c h i , L. 2 0 0 1 . V a r i a b i l i t y in a b u n d a n c e o f a l g a e a n d i n v e r t e b r a t e s at d i f fe rent s p a t i a l s c a l e s o n r o c k y s e a s h o r e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 2 1 5 : 7 9 - 9 2 . B e n e d e t t i - C e c c h i , L., F. P a n n a c c i u l l i , F. Bu l le r i , P. S . M o s c h e l l a , L. A i r o l d i , G . Re l i n i , a n d F. C i n e l l i . 2 0 0 1 . P r e d i c t i n g the c o n s e q u e n c e s of a n t h r o p o g e n i c d i s t u r b a n c e : l a r g e s c a l e e f f e c t s o f l o s s of c a n o p y a l g a e o n r o c k y s h o r e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 2 1 4 : 1 3 7 - 1 5 0 . B e r t n e s s , M . D., a n d G . H . L e o n a r d . 1 9 9 7 . T h e ro le o f p o s i t i v e i n t e r a c t i o n s in c o m m u n i t i e s : l e s s o n s f r o m intert idal h a b i t a t s . E c o l o g y 7 8 : 1 9 7 6 - 1 9 8 9 . B o l a m , S . G . , T . F. F e r n a n d e s , a n d M . H u x h a m . 2 0 0 2 . D i v e r s i t y , b i o m a s s , a n d e c o s y s t e m p r o c e s s e s in t h e m a r i n e b e n t h o s . E c o l o g i c a l M o n o g r a p h s 7 2 : 5 9 9 - 6 1 5 . B r u n o , J . F., a n d M . D. B e r t n e s s . 2 0 0 1 . H a b i t a t m o d i f i c a t i o n a n d fac i l i ta t ion in b e n t h i c m a r i n e c o m m u n i t i e s . P a g e s 5 6 0 in M . D. B e r t n e s s , S . D. G a i n e s , a n d M . E . H a y , e d i t o r s . M a r i n e c o m m u n i t y e c o l o g y . S i n a u e r A s s o c i a t e s Inc. B r u n o , J . F., K. E . B o y e r , J . E . Du f fy , S . C . L e e , a n d J . S . K e r t e s z . 2 0 0 5 . E f f e c t s o f m a c r o a l g a l s p e c i e s ident i ty a n d r i c h n e s s o n p r i m a r y p r o d u c t i o n in b e n t h i c m a r i n e c o m m u n i t i e s . E c o l o g y L e t t e r s 8 : 1 1 6 5 - 1 1 7 4 . B r u n o , J . F., J . J . S t a c h o w i c z , a n d M . D. B e r t n e s s . 2 0 0 3 . I n c l u s i o n o f fac i l i ta t ion into e c o l o g i c a l t h e o r y . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 8 : 1 1 9 - 1 2 5 . 13 C l a r k e , K. R., P. J . S o m e r f i e l d , a n d M. G . C h a p m a n . 2 0 0 6 . O n r e s e m b l a n c e m e a s u r e s for e c o l o g i c a l s t u d i e s , i n c l u d i n g t a x o n o m i c d i s s i m i l a r i t i e s a n d a z e r o - a d j u s t e d B r a y - C u r t i s c o e f f i c i e n t for d e n u d e d a s s e m b l a g e s . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 330:55-80. C r a i n , C . M. , a n d M . D. B e r t n e s s . 2 0 0 6 . E c o s y s t e m e n g i n e e r i n g a c r o s s e n v i r o n m e n t a l g r a d i e n t s : I m p l i c a t i o n s for c o n s e r v a t i o n a n d m a n a g e m e n t . B i o s c i e n c e 56:211- 2 1 8 ! C r o w e , T . P., R. C . T h o m p s o n , S . B r a y , a n d S . J . H a w k i n s . 2 0 0 0 . I m p a c t s o f a n t h r o p o g e n i c s t r e s s o n r o c k y intert idal c o m m u n i t i e s . J o u r n a l o f A q u a t i c E c o s y s t e m S t r e s s a n d R e c o v e r y 7 : 2 7 3 - 2 9 7 . D a y t o n , P. K. 1 9 7 2 . T o w a r d a n u n d e r s t a n d i n g of c o m m u n i t y r e s i l i e n c e a n d t h e potent ia l e f f e c t s o f e n r i c h m e n t s to the b e n t h o s at M c M u r d o S o u n d , A n t a r c t i c a . P a g e s 8 1 - 9 6 in B. C . P a r k e r , ed i tor . P r o c e e d i n g s o f t h e C o l l o q u i u m o n C o n s e r v a t i o n P r o b l e m s in A n t a r c t i c a . A l l e n P r e s s , L a w r e n c e . D i a z , S . , a n d M . C a b i d o . 2 0 0 1 . V i v e la d i f f e r e n c e : p lan t f u n c t i o n a l d i v e r s i t y m a t t e r s to e c o s y s t e m p r o c e s s e s . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 6 :646-655. D i a z , S . , A . J . S y m s t a d , F. S . C h a p i n III, D. A . W a r d l e , a n d L. F. H u e n n e k e . 2 0 0 3 . F u n c t i o n a l d i v e r s i t y r e v e a l e d by r e m o v a l e x p e r i m e n t s . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 8 :140-146. D u a r t e , C . M . 2 0 0 0 . M a r i n e b i o d i v e r s i t y a n d e c o s y s t e m s e r v i c e s : a n e l u s i v e link. J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 2 5 0 :117-131. D u c r o t o y , J . P. 1 9 9 9 . I n d i c a t i o n s of c h a n g e in t h e m a r i n e f l o ra o f t h e N o r t h S e a in t h e 1 9 9 0 s . M a r i n e P o l l u t i o n Bu l le t in 3 8 :646-654. G i t a y , H . , a n d I. R. N o b l e . 1 9 9 7 . W h a t a r e f u n c t i o n a l t y p e s a n d h o w s h o u l d w e s e e k t h e m ? P a g e s 3 8 3 in T . M . S m i t h , H . H . S h u g a r t , a n d F. I. W o o d w a r d , e d i t o r s . P l a n t F u n c t i o n a l T y p e s - T h e i r R e l e v a n c e to E c o s y s t e m P r o p e r t i e s a n d G l o b a l C h a n g e . C a m b r i d g e U n i v e r s i t y P r e s s , C a m b r i d g e . G r a h a m , L. E. , a n d L. W . W i l c o x . 2 0 0 0 . A l g a e . P r e n t i c e H a l l , U p p e r S a d d l e R i v e r , N e w J e r s e y . G r a y , J . S . 1 9 9 7 . M a r i n e b i o d i v e r s i t y : p a t t e r n s , t h r e a t s a n d c o n s e r v a t i o n n e e d s . B i o d i v e r s i t y a n d C o n s e r v a t i o n 6 : 153-175 . G r o s b e r g , R., a n d C . W . C u n n i n g h a m . 2 0 0 1 . G e n e t i c s t r u c t u r e in t h e s e a : f r o m p o p u l a t i o n s to c o m m u n i t i e s , in M . D. B e r t n e s s , S . D . G a i n e s , a n d M . E . H a y , e d i t o r s . M a r i n e C o m m u n i t y E c o l o g y . S i n a u e r A s s o c i a t e s Inc., S u n d e r l a n d , M a s s a c h u s e t t s . H a c k e r , S . D., a n d S . D. G a i n e s . 1 9 9 7 . S o m e i m p l i c a t i o n s of d i r e c t p o s i t i v e i n t e r a c t i o n s for c o m m u n i t y s p e c i e s d ive rs i t y . E c o l o g y 7 8 : 1 9 9 0 - 2 0 0 3 . 14 H a m m o n d , A . 1 9 9 2 . W o r l d R e s o u r c e s 1 9 9 2 - 1 9 9 3 : T o w a r d s S u s t a i n a b l e D e v e l o p m e n t . O x f o r d U n i v e r s i t y P r e s s , O x f o r d . H a w k i n s , S . J . 1 9 9 9 . E x p e r i m e n t a l e c o l o g y a n d c o a s t a l c o n s e r v a t i o n : c o n f l i c t s o n r o c k y s h o r e s . A q u a t i c c o n s e r v a t i o n : m a r i n e a n d f r e s h w a t e r e c o s y s t e m s 9 : 565-572 . H o o p e r , D. U . , F. S . C h a p i n , J . J . E w e l , A . H e c t o r , P. I n c h a u s t i , S . L a v o r e l , J . H . L a w t o n , D. M . L o d g e , M . L o r e a u , S . N a e e m , B. S c h m i d , H . S e t a l a , A . J . S y m s t a d , J . V a n d e r m e e r , a n d D. A . W a r d l e . 2 0 0 5 . E f f e c t s o f b i o d i v e r s i t y o n e c o s y s t e m f u n c t i o n i n g : A c o n s e n s u s of c u r r e n t k n o w l e d g e . E c o l o g i c a l M o n o g r a p h s 75:3-35. J o n e s , C . G . , J . H . L a w t o n , a n d M . S h a c h a k . 1 9 9 7 . P o s i t i v e a n d n e g a t i v e e f f e c t s o f o r g a n i s m s a s p h y s i c a l e c o s y s t e m e n g i n e e r s . E c o l o g y 7 8 : 1946-1957 . K a i s e r , J . 1 9 9 9 . S t e m m i n g t h e t ide of i n v a d i n g s p e c i e s . S c i e n c e 2 8 5 :1836-1841. L a w t o n , J . H . 1 9 9 9 . A r e t h e r e g e n e r a l l a w s in e c o l o g y ? O i k o s 8 4 :177-192. L o r e a u , M . 2 0 0 4 . D o e s f u n c t i o n a l r e d u n d a n c y e x i s t ? O i k o s 104 :606-611. L o r e a u , M. , S . N a e e m , P. I n c h a u s t i , J . B e n g t s s o n , J . P. G r i m e , A . H e c t o r , D. U . H o o p e r , M . A . H u s t o n , D. G . R a f f a e l l i , B. S c h m i d , D. T i l m a n , a n d D. A . W a r d l e . 2 0 0 1 . B i o d i v e r s i t y a n d e c o s y s t e m f u n c t i o n i n g : c u r r e n t k n o w l e d g e a n d f u t u r e c h a l l e n g e s . S c i e n c e 294:804-808. M c G i l l , B. J . , B. J . E n q u i s t , E . W e i h e r , a n d M. W e s t o b y . 2 0 0 6 . R e b u i l d i n g c o m m u n i t y e c o l o g y f r o m f u n c t i o n a l traits. T r e n d s in E c o l o g y a n d E v o l u t i o n 2 1 :178-185. N a e e m , S . , L. J . T h o m p s o n , S . P. L a w l e r , J . H . L a w t o n , a n d R. M . W o o d f i n . 1 9 9 4 . D e c l i n i n g b i o d i v e r s i t y c a n a l ter the p e r f o r m a n c e o f e c o s y s t e m s . N a t u r e 368:734- 7 3 7 . N a e e m , S . , a n d J . W r i g h t . 2 0 0 3 . D i s e n t a n g l i n g b i o d i v e r s i t y e f f e c t s o n e c o s y s t e m f u n c t i o n i n g : d e r i v i n g s o l u t i o n s to a s e e m i n g l y i n s u r m o u n t a b l e p r o b l e m . E c o l o g y L e t t e r s 6 : 5 6 7 - 5 7 9 . P e t c h e y , O . L., a n d K. J . G a s t o n . 2 0 0 2 . E x t i n c t i o n a n d t h e l o s s o f f u n c t i o n a l d i ve rs i t y . P r o c e e d i n g s o f t h e R o y a l S o c i e t y o f L o n d o n B 2 6 9 :1721-1727. R o s e n f e l d , J . S . 2 0 0 2 . F u n c t i o n a l r e d u n d a n c y in e c o l o g y a n d c o n s e r v a t i o n . O i k o s 9 8 :156-162. S c h r a m m , W . , a n d P. H . N i e n h u i s , e d i t o r s . 1 9 9 6 . M a r i n e B e n t h i c V e g e t a t i o n : R e c e n t c h a n g e s a n d t h e E f f e c t s of E u t r o p h i c a t i o n . S p r i n g e r - V e r l a g , B e r l i n H e i d e l b e r g N e w Y o r k . 15 S c o t t , G . W . , a n d I. T i t t ley . 1 9 9 8 . C h a n g e s in the M a r i n e F l o r a o f t h e N o r t h S e a . C e n t r e for E n v i r o n m e n t a l R e s e a r c h into C o a s t a l I s s u e s , S c a r b o r o u g h . S i m b e r l o f f , D. 2 0 0 4 . C o m m u n i t y e c o l o g y : is it t i m e to m o v e o n ? T h e A m e r i c a n N a t u r a l i s t 163:787-799. S o l a n , M. , B. J . C a r d i n a l e , A . L. D o w n i n g , K. A . M . E n g e l h a r d t , J . L. R u e s i n k , a n d D. S . S r i v a s t a v a . 2 0 0 4 . E x t i n c t i o n a n d E c o s y s t e m F u n c t i o n in t h e M a r i n e B e n t h o s . S c i e n c e 306:1177-1180. S t a c h o w i c z , J . J . 2 0 0 1 . M u t u a l i s m , fac i l i ta t ion , a n d t h e s t r u c t u r e o f e c o l o g i c a l c o m m u n i t i e s . B i o s c i e n c e 51:235-246. S t a c h o w i c z , J . J . , H . F r i e d , R. W . O s m a n , a n d R. B. W h i t l a t c h . 2 0 0 2 . B i o d i v e r s i t y , i n v a s i o n r e s i s t a n c e , a n d m a r i n e e c o s y s t e m f u n c t i o n : R e c o n c i l i n g pa t te rn a n d p r o c e s s . E c o l o g y 83:2575-2590. S u c h a n e k , T . H . 1 9 9 4 . T e m p e r a t e c o a s t a l m a r i n e c o m m u n i t i e s : b i o d i v e r s i t y a n d t h r e a t s . A m e r i c a n Z o o l o g i s t 34:100-114. T a y l o r , R. B. 1 9 9 8 . D e n s i t y , b i o m a s s , a n d p r o d u c t i v i t y o f a n i m a l s in f o u r s u b t i d a l r o c k y r e e f h a b i t a t s : t he i m p o r t a n c e o f s m a l l m o b i l e i n v e r t e b r a t e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 172:37-51. T i l m a n , D., J . K n o p s , D. W e d i n , P. R e i c h , M . R i t c h i e , a n d E . S i e m a n n . 1 9 9 7 . T h e i n f l u e n c e o f f u n c t i o n a l d i v e r s i t y a n d c o m p o s i t i o n o n e c o s y s t e m p r o c e s s e s . S c i e n c e 277:1300-1302. W a l k e r , B., A . K i n z i g , a n d J . L a n g r i d g e . 1 9 9 9 . P l a n t at t r ibute d i v e r s i t y , r e s i l i e n c e , a n d e c o s y s t e m f u n c t i o n : t h e n a t u r e a n d s i g n i f i c a n c e o f d o m i n a n t a n d m i n o r s p e c i e s . E c o s y s t e m s 2 :95-113. W e b b , C . O . , D. D. A c k e r l y , M . A . M c P e e k , a n d M . J . D o n o g h u e . 2 0 0 2 . P h y l o g e n i e s a n d c o m m u n i t y e c o l o g y . A n n u a l R e v i e w of E c o l o g y a n d S y s t e m a t i c s 33:475-505. W r i g h t , J . P., C . G . J o n e s , a n d A . S . F l e c k e r . 2 0 0 2 . A n e c o s y s t e m e n g i n e e r , t he b e a v e r , i n c r e a s e s s p e c i e s r i c h n e s s at the l a n d s c a p e s c a l e . O e c o l o g i a 132:96-101. 16 Chapter 2: Do changes in seaweed biodiversity influence associated invertebrate epifauna? A v e r s i o n of th is c h a p t e r h a s b e e n pub l i s hed : Ba t e s , C R . a n d R .E . D e W r e e d e (2007 ) D o c h a n g e s in s e a w e e d b iod i ve r s i t y i n f l uence a s s o c i a t e d inver tebra te e p i f a u n a ? J o u r n a l of E x p e r i m e n t a l Ma r i n e B i o l o gy a n d E c o l o g y 344 : 206 - 214 . 17 2 . 1 Introduction L o c a l b i o d i v e r s i t y is o f ten p o s i t i v e l y i n f l u e n c e d b y t h e p r e s e n c e o f h a b i t a t - f o r m i n g or hab i ta t m o d i f y i n g o r g a n i s m s ( T h o m p s o n et al. 1 9 9 6 , S t a c h o w i c z 2 0 0 1 ) . T h e i m p o r t a n c e of b i o g e n i c h a b i t a t p r o v i s i o n a n d of p o s i t i v e i n t e r a c t i o n s in g e n e r a l is i n c r e a s i n g l y a c k n o w l e d g e d , par t i cu la r l y in m a r i n e s y s t e m s ( B e r t n e s s et al. 1 9 9 9 , B r u n o a n d B e r t n e s s 2 0 0 0 , S t a c h o w i c z 2 0 0 1 , B r u n o et al. 2 0 0 3 ) . B i o g e n i c hab i ta t p r o v i s i o n is m o s t o f ten i n v e s t i g a t e d a s t h e c r e a t i o n o r m o d i f i c a t i o n o f hab i ta t b y o n e s p e c i e s for a g r o u p of o t h e r s p e c i e s ( C a s t i l l a ef al. 2 0 0 4 , W o n h a m et al. 2 0 0 5 ) . H o w e v e r , m a n y s i t u a t i o n s ex i s t w h e r e h a b i t a t - f o r m i n g s p e c i e s a r e c o m p o n e n t s o f a s s e m b l a g e s of t a x a that c a n c o l l e c t i v e l y a c t a s hab i ta t ( B r u n o a n d B e r t n e s s 2 0 0 0 , S t a c h o w i c z 2 0 0 1 , B r u n o et al. 2 0 0 3 ) . I n v e s t i g a t i o n s into a s s e m b l a g e - l e v e l i n f l u e n c e o n b i o g e n i c hab i ta t p r o v i s i o n a r e m u c h l e s s f r e q u e n t a n d , w h e r e a v a i l a b l e , h a v e y i e l d e d m i x e d r e s u l t s , s h o w i n g pos i t i ve , n e g a t i v e , a n d n e u t r a l r e l a t i o n s h i p s b e t w e e n fac i l i ta tor d i v e r s i t y a n d d i v e r s i t y of a s s o c i a t e d o r g a n i s m s ( B r u n o a n d B e r t n e s s 2 0 0 0 ) . T h e s e m i x e d r e s u l t s c o n c e r n i n g hab i ta t p r o v i s i o n b y m u l t i - s p e c i e s c o m m u n i t i e s m a y s t e m f r o m p r o b l e m s of d e f i n i n g fac i l i tator d ivers i ty , b e c a u s e v a r i o u s c o m p o n e n t s o f d ive rs i t y ( e . g . , r i c h n e s s , c o m p o s i t i o n ) c a n a f fec t p r o c e s s e s d i f fe rent ia l l y ( D i a z a n d C a b i d o 2 0 0 1 , N a e e m 2 0 0 2 ) a n d it c a n b e diff icult to s e p a r a t e t h e e f f e c t s o f d i f ferent c o m p o n e n t s o f d i v e r s i t y ( N a e e m a n d W r i g h t 2 0 0 3 ) . B i o d i v e r s i t y , a s it r e l a t e s to e c o s y s t e m f u n c t i o n i n g , c a n b e d e f i n e d in a va r i e ty o f d i f f e ren t w a y s , i n c o r p o r a t i n g t h e n u m b e r o f s p e c i e s ( M a g u r r a n 1 9 8 8 , P e t c h e y 2 0 0 0 ) , t h e f u n c t i o n a l r o l e s o f t h e s p e c i e s ( T i l m a n et al. 1 9 9 7 , D i a z a n d C a b i d o 2 0 0 1 , P e t c h e y a n d G a s t o n 2 0 0 2 ) , a n d the ident i ty of t he s p e c i e s o r t h e f u n c t i o n a l g r o u p s that c o m p o s e t h e a s s e m b l a g e . W h i l e m u c h w o r k in b i o d i v e r s i t y r e s e a r c h h a s f o c u s e d o n s p e c i e s r i c h n e s s a s the i n d e p e n d e n t v a r i a b l e , t h e r e is d e b a t e a b o u t the re la t ive i m p o r t a n c e of s p e c i e s r i c h n e s s , f u n c t i o n a l r i c h n e s s a n d s p e c i e s o r f u n c t i o n a l g r o u p ident i ty ( T i l m a n et al. 1 9 9 7 , B r u n o ef al. 2 0 0 5 ) . H e r e , I d e s c r i b e m y ef for ts to a d d r e s s t h e s e c o n c e p t s in a n intert idal s t u d y s y s t e m , w h e r e I tes t h o w v a r i a t i o n in f o u r s e a w e e d a s s e m b l a g e - l e v e l p a r a m e t e r s ( i .e. s e a w e e d s p e c i e s r i c h n e s s , f u n c t i o n a l g r o u p r i c h n e s s , s p e c i e s c o m p o s i t i o n , a n d f u n c t i o n a l g r o u p c o m p o s i t i o n ) i n f l u e n c e s a s s o c i a t e d s m a l l m o b i l e e p i f a u n a . U n d e r s t a n d i n g t h e re la t i ve i n f l u e n c e o f t h e s e d i f fe rent c o m p o n e n t s o f b i o d i v e r s i t y o n b i o g e n i c hab i ta t p r o v i s i o n is b e c o m i n g i n c r e a s i n g l y i m p o r t a n t a s h u m a n ac t i v i t i es 18 c o n t i n u e to a l ter c o m p o s i t i o n of b i o l o g i c a l c o m m u n i t i e s a n d r e d u c e d i v e r s i t y ( C o l e m a n a n d W i l l i a m s 2 0 0 2 ) . H a b i t a t l o s s h a s b e e n p i n p o i n t e d a s t h e m a j o r c a u s e of d e c l i n i n g b i o d i v e r s i t y ( T i l m a n e f al. 1 9 9 4 ) , a n d the i m p l i c a t i o n s a r e c o m p o u n d e d if h a b i t a t - f o r m i n g s p e c i e s a r e lost . A n t h r o p o g e n i c c h a n g e s in s e a w e e d d i v e r s i t y h a v e b e e n o b s e r v e d in n e a r s h o r e m a r i n e e n v i r o n m e n t s f r o m m a n y r e g i o n s t h r o u g h o u t t h e w o r l d , m o s t n o t a b l y in E u r o p e ( S c h r a m m a n d N i e n h u i s 1 9 9 6 ) a n d in e a s t e r n C a n a d a ( L o t z e a n d M i l e w s k i 2 0 0 4 , B a t e s ef al. 2 0 0 5 ) . A n t h r o p o g e n i c s t r e s s o r s that resu l t in c h a n g e s in s e a w e e d a s s e m b l a g e s i n c l u d e e u t r o p h i c a t i o n , silt d e p o s i t i o n , t r a m p l i n g , h a b i t a t a l t e r a t i o n , a n d h a r v e s t o f p r e d a t o r s o r h e r b i v o r e s . T h e s e s t r e s s o r s a c t by c o m p r o m i s i n g t h e b a s i c r e q u i r e m e n t s of m a r i n e a l g a e , w h i c h i n c l u d e s u b s t r a t e to a t t a c h to, l ight a n d n u t r i e n t s fo r p h o t o s y n t h e s i s , a n d po ten t i a l for s u c c e s s f u l d i s p e r s a l a n d r e c r u i t m e n t . A s a resul t , s t r e s s e d a l g a l a s s e m b l a g e s o f t e n shift f r o m m o s a i c s o f l o n g e r - l i v e d , p e r e n n i a l a l g a e to a s s e m b l a g e s d o m i n a t e d b y e p h e m e r a l , f a s t g r o w i n g , nut r ient s c a v e n g i n g a n n u a l s ( L o t z e ef al. 1 9 9 9 ) , o f t e n r e f e r r e d to a s ' g r e e n - t i d e s ' . T h e s e o b s e r v e d c h a n g e s i n v o l v e d i f ferent c o m p o n e n t s o f b i o d i v e r s i t y , i n c l u d i n g the n u m b e r a n d ident i ty of s e a w e e d s p e c i e s a n d f u n c t i o n a l g r o u p s . B e c a u s e s e a w e e d s a r e vital b i o g e n i c h a b i t a t p r o v i d e r s for s m a l l m o b i l e i n v e r t e b r a t e s , a n u n d e r s t a n d i n g o f t h e r e l a t i o n s h i p s b e t w e e n d i f ferent c o m p o n e n t s of s e a w e e d d i v e r s i t y a n d i n v e r t e b r a t e d i v e r s i t y is i m p o r t a n t for p r e d i c t i n g the i m p l i c a t i o n s o f m a r i n e f lor ist ic c h a n g e . H e r e , I a s k (1) Is s e a w e e d s p e c i e s r i c h n e s s p o s i t i v e l y c o r r e l a t e d with i n v e r t e b r a t e s p e c i e s r i c h n e s s a n d a b u n d a n c e ? (2) Is s e a w e e d f u n c t i o n a l r i c h n e s s p o s i t i v e l y c o r r e l a t e d wi th i n v e r t e b r a t e s p e c i e s r i c h n e s s a n d a b u n d a n c e ? (3) D o e s s p e c i e s c o m p o s i t i o n of h o s t s e a w e e d a s s e m b l a g e s c o r r e l a t e with i n v e r t e b r a t e a s s e m b l a g e s t r u c t u r e ? a n d (4) D o e s f u n c t i o n a l c o m p o s i t i o n o f h o s t s e a w e e d a s s e m b l a g e s c o r r e l a t e with i n v e r t e b r a t e a s s e m b l a g e s t r u c t u r e ? 19 2.2 Materials and methods I in i t iated th is s t u d y with o b s e r v a t i o n a l c o l l e c t i o n s to d e t e r m i n e n a t u r a l l e v e l s o f s e a w e e d d i v e r s i t y a n d s t r u c t u r e o f a s s o c i a t e d m o b i l e e p i f a u n a . I t h e n p e r f o r m e d m a n i p u l a t i v e e x p e r i m e n t s o v e r two y e a r s to d e t e r m i n e t h e i m p l i c a t i o n s o f v a r i e d c o m b i n a t i o n s o f s e a w e e d s p e c i e s r i c h n e s s , f u n c t i o n a l r i c h n e s s , a n d s p e c i e s a n d f u n c t i o n a l c o m p o s i t i o n o n t h e s t r u c t u r e o f a s s o c i a t e d m o b i l e e p i f a u n a l a s s e m b l a g e s . T h i s s t u d y w a s d o n e in J u n e to A u g u s t o v e r t w o y e a r s ( 2 0 0 3 - 2 0 0 4 ) at N u d i b r a n c h Pt . ( F i g u r e 1.3). N u d i b r a n c h Pt . is a re la t ive ly pr is t ine s i te with g e n t l y s l o p i n g , s e m i w a v e - e x p o s e d r o c k y r e e f s , a n d a r ich a s s e m b l a g e of s e a w e e d s ( T a b l e 2 .1) . S i t e p r e p a r a t i o n took p l a c e in A p r i l a n d M a y 2 0 0 3 a n d o b s e r v a t i o n a l a n d m a n i p u l a t i v e q u a d r a t s m e a s u r e d 16 x 4 7 c m , o r i e n t e d p e r p e n d i c u l a r to t h e w a t e r l ine . T h i s q u a d r a t s i z e w a s c h o s e n a s a m a n a g e a b l e a r e a to s a m p l e , a n d m a d e e f f i c ient u s e o f t r a n s p l a n t m a t e r i a l s . C u r r e n t t a x o n o m i c a u t h o r i t i e s c a n b e f o u n d b y c o n s u l t i n g G a b r i e l s o n et al. ( 2 0 0 6 ) . 2.2.1 Defining seaweed functional groups T o a s s i g n s e a w e e d s p e c i e s into f u n c t i o n a l g r o u p s ( T a b l e 2 .1) , I u s e d f u n c t i o n a l f o r m g r o u p i n g s f o l l o w i n g S t e n e c k a n d D e t h i e r ( 1 9 9 4 ) . O w i n g to t h e l imi ta t ions of the t r a n s p l a n t m e t h o d ( d e s c r i b e d b e l o w ) , I u s e d o n l y f o u r o f a p o s s i b l e s e v e n s e a w e e d f u n c t i o n a l g r o u p s ( T a b l e 2 .1) : f o l i o s e , c o r t i c a t e d f o l i o s e , l e a t h e r y , a n d c o r t i c a t e d te re te (i.e. r o u n d e d in c r o s s s e c t i o n ) . A s a s s e r t e d b y F a r i n a ef al. ( 2 0 0 3 ) , t he f u n c t i o n a l / m o r p h o l o g i c a l a p p r o a c h in m a r i n e a l g a e h a s h a d v a r i a b l e s u p p o r t for a gradient o f f u n c t i o n a l p e r f o r m a n c e a c r o s s g r o u p s , but t h e endpoints are w e l l e s t a b l i s h e d , r a n g i n g f r o m f a s t g r o w i n g o p p o r t u n i s t i c ' s i m p l e ' f o r m s (i .e. t h e f o l i o s e g r o u p ) at o n e e n d , to t h e s l o w e r - g r o w i n g , t yp i ca l l y later s u c c e s s i o n a l s p e c i e s with ' c o m p l e x ' thall i ( i .e. c o r t i c a t e d te re te) at t h e o t h e r e n d . M y d i s c u s s i o n of s e a w e e d f u n c t i o n a l c o m p o s i t i o n c o n c e n t r a t e s o n t h e d i f f e r e n c e s b e t w e e n t h e s e e n d p o i n t s . 2 0 2.2.2 Observational study T h e p u r p o s e o f t h e o b s e r v a t i o n a l s t u d y w a s t w o - f o l d : to d e t e r m i n e na tu ra l l e v e l s of s e a w e e d s p e c i e s r i c h n e s s , f u n c t i o n a l r i c h n e s s , a n d total s e a w e e d b i o m a s s to a id in the c r e a t i o n of rea l i s t i c ' con t ro l s ' for t r a n s p l a n t e d s e a w e e d c o m m u n i t i e s ; a n d to o b t a i n b a s e l i n e d e s c r i p t i o n s of t h e r e l a t i o n s h i p s b e t w e e n s e a w e e d c o m m u n i t y p a r a m e t e r s a n d i n v e r t e b r a t e d i v e r s i t y . T e n o b s e r v a t i o n a l q u a d r a t s w e r e s a m p l e d in M a y 2 0 0 3 by h a r v e s t i n g a p a t c h l o c a t e d 5 0 c m to t h e right o f t e n r a n d o m l y s e l e c t e d m a n i p u l a t i v e q u a d r a t s ( d e s c r i b e d b e l o w ) . W i t h i n e a c h o b s e r v a t i o n a l q u a d r a t , e a c h s e a w e e d s p e c i e s p r e s e n t , a l o n g with a s s o c i a t e d i n v e r t e b r a t e s , w a s c o l l e c t e d a n d i m m e d i a t e l y p l a c e d into s e p a r a t e z i p p e r e d c o l l e c t i o n b a g s . S a m p l e s w e r e t h e n f r o z e n for a m i n i m u m of 2 4 h o u r s to e u t h a n i z e e p i f a u n a b e f o r e p r o c e s s i n g . 2.2.3 Manipulative experiment T o s e p a r a t e t h e i n f l u e n c e of s e a w e e d s p e c i e s r i c h n e s s , f u n c t i o n a l r i c h n e s s , a n d f u n c t i o n a l c o m p o s i t i o n o n a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a , I c r e a t e d s e a w e e d c o m m u n i t i e s that v a r i e d e a c h o f t h e s e p a r a m e t e r s w h i l e h o l d i n g t h e o t h e r v a r i a b l e s c o n s t a n t . I u s e t h e a p p r o a c h of ' s y n t h e t i c r e m o v a l e x p e r i m e n t s ' a s d e s c r i b e d b y S c h m i d et al. ( 2 0 0 2 ) , w h e r e t h e e x p e r i m e n t a l d e s i g n i n c l u d e s intact c o m m u n i t i e s a n d t h e n o m i t s c e r t a i n s p e c i e s o r g r o u p s of s p e c i e s to d e t e r m i n e the i r e f f e c t s . P r i o r to e a c h t r a n s p l a n t e x p e r i m e n t , q u a d r a t s w e r e s c r a p e d c l e a r o f e x i s t i n g b i o t a . I t h e n e s t a b l i s h e d s ix t r e a t m e n t s . 2.2.4 Experimental treatments T h r e e v a r i a b l e s w e r e c o n s i d e r e d w h e n d e t e r m i n i n g c o m p o s i t i o n of s e a w e e d t r e a t m e n t q u a d r a t s : S e a w e e d s p e c i e s r i c h n e s s (S) , s e a w e e d f u n c t i o n a l r i c h n e s s , (F) , a n d s e a w e e d f u n c t i o n a l c o m p o s i t i o n ( F C ) . A four th p a r a m e t e r , s e a w e e d s p e c i e s c o m p o s i t i o n , w a s i n c o r p o r a t e d b y r a n d o m l y s e l e c t i n g s p e c i e s wi th in f u n c t i o n a l g r o u p s 21 a c c o r d i n g to t h e g u i d e l i n e s d e s c r i b e d b e l o w . T o d e s c r i b e t h e f u n c t i o n a l c o m p o s i t i o n of s e a w e e d q u a d r a t s , I c l a s s i f i e d a s s e m b l a g e s a s s i m p l e (on ly ' f o l i o se ' f o r m s p r e s e n t ) , c o m p l e x (on ly ' c o r t i c a t e d te re te ' f o r m s p r e s e n t ) , o r m i x e d (all f o u r f u n c t i o n a l g r o u p s p r e s e n t ) . T h e t r e a t m e n t s d e s c r i b e d b e l o w a r e s u m m a r i z e d in T a b l e 2 .2 . T r e a t m e n t 1 ( T 1 ) : S = 4, F = 4, F C = m i x e d . In t h e ' m i x e d p o l y c u l t u r e ' t r e a t m e n t , f o u r s e a w e e d s p e c i e s w e r e i n c l u d e d in e a c h q u a d r a t . O n e s p e c i e s w a s r a n d o m l y s e l e c t e d f r o m e a c h s e a w e e d f u n c t i o n a l g r o u p , e n s u r i n g all f u n c t i o n a l g r o u p s w e r e r e p r e s e n t e d . T h i s t r e a t m e n t t e s t e d for t h e c o n s e q u e n c e s o f r e d u c e d s p e c i e s r i c h n e s s w i t h o u t t h e l o s s o f f u n c t i o n a l r i c h n e s s . T r e a t m e n t 2 ( T 2 ) : S = 1, F = 1, F C = f o l i o s e . In the ' s i m p l e m o n o c u l t u r e ' t r e a t m e n t , o n e s p e c i e s ( p e r q u a d r a t ) w a s r a n d o m l y s e l e c t e d f r o m the s ix a v a i l a b l e s p e c i e s in t h e ' fo l iose ' f u n c t i o n a l g r o u p . T h i s t r e a t m e n t is c o m p a r a b l e to the ' g r e e n t ide ' p h e n o m e n o n , w h e r e s e a w e e d a s s e m b l a g e s a r e c o m p o s e d of f a s t g r o w i n g , o p p o r t u n i s t i c a l g a e typ i ca l l y f r o m t h e C h l o r o p h y t e o r d e r U l v a l e s ( M i d d e l b o e a n d S a n d - J e n s e n 2 0 0 0 ) . T r e a t m e n t 3 ( T 3 ) : S = 6, F = 1, F C = f o l i o s e . In t h e ' s i m p l e p o l y c u l t u r e ' t r e a t m e n t , p o l y c u l t u r e s w e r e e s t a b l i s h e d u s i n g all s ix s p e c i e s s e l e c t e d f r o m t h e ' fo l iose ' m o r p h o t y p e . T h i s t r e a t m e n t t e s t s for t h e i n f l u e n c e o f a l ow f u n c t i o n a l r i c h n e s s but h i g h s p e c i e s r i c h n e s s . T r e a t m e n t 4 ( T 4 ) : S = 1, F = 1, F C = c o r t i c a t e d t e r e t e . In t h e ' c o m p l e x m o n o c u l t u r e ' t r e a t m e n t , o n e s p e c i e s (per q u a d r a t ) w a s r a n d o m l y s e l e c t e d f r o m the e i g h t a v a i l a b l e s p e c i e s f r o m t h e ' c o r t i c a t e d t e r e t e ' f u n c t i o n a l g r o u p . T h i s t r e a t m e n t is c o m p a r a b l e to a l a t e - s u c c e s s i o n a l s e a w e e d a s s e m b l a g e , w h e r e a s l o w e r - g r o w i n g , c o m p e t i t i v e l y d o m i n a n t , r o b u s t m o r p h o t y p e is f o u n d , s u c h a s the Chondracanthus canaliculatus m o n o c u l t u r e s d e s c r i b e d b y D e a n a n d C o n n e l l ( 1 9 8 7 b ) . T r e a t m e n t 5 ( T 5 ) : S = 6, F = 1, F C = c o r t i c a t e d t e r e t e . In t h e ' c o m p l e x p o l y c u l t u r e ' 2 2 t r e a m e n t , p o l y c u l t u r e s w e r e e s t a b l i s h e d with s ix s p e c i e s s e l e c t e d f r o m the ' c o r t i c a t e d t e r e t e ' m o r p h o t y p e . T r e a t m e n t 6 ( C ) : S = 8, F = 4, F C = m i x e d . C o n t r o l q u a d r a t s w e r e b a s e d o n the c o m m u n i t i e s e n c o u n t e r e d in t h e o b s e r v a t i o n a l s t u d y , a n d e a c h w a s c o m p o s e d o f e i g h t s e a w e e d s p e c i e s r a n d o m l y s e l e c t e d a c r o s s f o u r f u n c t i o n a l g r o u p s . T r e a t m e n t s 1 a n d 2 w e r e run in 2 0 0 3 a n d t r e a t m e n t s 3 to 5 w e r e run in 2 0 0 4 , a n d n = 4 p e r t r e a t m e n t . T r e a t m e n t 6 w a s run b o t h 2 0 0 3 a n d 2 0 0 4 , a n d n = 8 for 2 0 0 3 a n d n = 12 for 2 0 0 4 . 2 .2 .5 S e a w e e d t r a n s p l a n t s I u s e d t h e t r a n s p l a n t a p p r o a c h o f S h a u g h n e s s y a n d D e W r e e d e ( 2 0 0 1 ) to c r e a t e c o m p o s i t e c o m m u n i t i e s . T o p r e p a r e for t r a n s p l a n t s , q u a d r a t s w e r e first c l e a r e d o f the e x i s t i n g f lo ra a n d f a u n a , f i ve h o l e s w e r e dr i l led into t h e r o c k y s u b s t r a t u m , a n d m a s o n r y a n c h o r s w e r e e m b e d d e d . T h e a n c h o r s p r o v i d e d a m e a n s of a t t a c h i n g m a l l e a b l e w i re g r i d s to t h e inter t ida l . S e a w e e d thall i s e l e c t e d for t r a n s p l a n t i n g w e r e c o l l e c t e d f r o m within t h e s t u d y s i te a n d d e f a u n a t e d by d i p p i n g in f r e s h w a t e r a n d s h a k i n g , f o l l o w e d b y v i s u a l i n s p e c t i o n a n d m a n u a l r e m o v a l o f r e m a i n i n g e p i f a u n a ( K e l a h e r 2 0 0 2 ) . H o l d f a s t s of a l g a e w e r e w o v e n into th ree - tw is t P V C r o p e , a n d t h e n a t t a c h e d to t h e w i r e g r i d s with n y l o n z i p t i es . M e a n b i o m a s s o f all t r a n s p l a n t e d q u a d r a t s w a s a p p r o x i m a t e l y e q u a l (dry b i o m a s s = 1 0 . 2 5 g +/- 0 . 9 4 g) a n d w a s e q u i v a l e n t to t h e s e a w e e d b i o m a s s of the o b s e r v a t i o n a l q u a d r a t s ( 1 2 . 8 4 g +/- 2 .00 g ) . A l g a l p e r c e n t c o v e r w a s g r e a t e r t h a n 9 5 % in all q u a d r a t s . Q u a d r a t s w e r e e s t a b l i s h e d o v e r t h r e e d a y s a n d left for 3 0 d a y s . P l a n t s w e r e t h e n h a r v e s t e d b y c o l l e c t i n g the total b i o m a s s of e a c h s p e c i e s f r o m e a c h q u a d r a t into s e p a r a t e z i p p e r e d c o l l e c t i o n b a g s . S a m p l e s w e r e f r o z e n for a m i n i m u m of 2 4 h o u r s to e u t h a n i z e e p i f a u n a b e f o r e p r o c e s s i n g . 2 3 2.2.6 Sample processing T o r e m o v e the e p i f a u n a f r o m the h o s t a l g a , e a c h f r o z e n s e a w e e d t h a l l u s w a s r e m o v e d f r o m its b a g a n d t h a w e d in a d i s h with 5 0 0 m L o f s e a w a t e r . M o s t e p i f a u n a s a n k to t h e b o t t o m o f t h e d i s h , but e a c h s a m p l e w a s a l s o r u b b e d a n d v i s u a l l y i n s p e c t e d to r e m o v e r e m a i n i n g e p i f a u n a . Tha l l i with d e n s e b r a n c h i n g o r f o l d i n g w e r e p r o c e s s e d with a d d i t i o n a l a t t e n t i o n . T h i s a p p r o a c h w a s h i g h l y e f f e c t i v e , a n d v i s u a l i n s p e c t i o n with a d i s s e c t i n g m i c r o s c o p e r e v e a l e d f ew , if a n y , e p i f a u n a r e m a i n i n g o n t h e thal l i . B e c a u s e s e s s i l e i n v e r t e b r a t e i n d i v i d u a l s w e r e re la t ive ly s c a r c e ( typ ica l l y b r y o z o a n s o r b a r n a c l e s ) a n d diff icult to q u a n t i f y a s a n u m b e r o f i n d i v i d u a l s (in t h e c a s e o f t h e c o l o n i a l b r y o z o a n s ) , m y a n a l y s e s a r e l imi ted to m o b i l e e p i f a u n a . S a m p l e s w e r e s i e v e d t h r o u g h a 0.2 m m s c r e e n to re ta in e p i f a u n a , a n d t h e n p r e s e r v e d in a 1.5 m L E p p e n d o r f t u b e c o n t a i n i n g 9 5 % e t h a n o l . I n v e r t e b r a t e s w e r e t h e n e n u m e r a t e d a s m o r p h o s p e c i e s ( O l i v e r a n d B e a t t i e 1 9 9 6 ) a n d later k e y e d to the l o w e s t t a x o n o m i c l eve l p o s s i b l e . H o s t thall i w e r e d r i e d at 80° C for 2 4 h o u r s , a n d t h e n w e i g h e d to t h e n e a r e s t 0.01 g to q u a n t i f y h o s t b i o m a s s . 2.2.7 Statistical analysis T e s t s for t h e i n f l u e n c e o f s e a w e e d s p e c i e s a n d f u n c t i o n a l r i c h n e s s w e r e p e r f o r m e d u s i n g o r d i n a r y l e a s t s q u a r e s r e g r e s s i o n for t h e o b s e r v a t i o n a l s t u d y , a n d o n e - w a y A N O V A s for t h e m a n i p u l a t i v e s t u d y , in bo th c a s e s u s i n g i n v e r t e b r a t e t a x o n r i c h n e s s a n d a b u n d a n c e a s r e s p o n s e v a r i a b l e s . G r o u p s o f c o n t r o l q u a d r a t s w e r e not d i f ferent wi th in y e a r ( P > 0 . 2 5 ) s o c o n t r o l s w e r e p o o l e d a c r o s s t r e a t m e n t s wi th in e a c h y e a r ( U n d e r w o o d 1 9 9 7 ) . I n v e r t e b r a t e a s s e m b l a g e s a s s o c i a t e d with c o n t r o l p lo ts w e r e d i f ferent ( P < 0 . 0 5 ) b e t w e e n 2 0 0 3 a n d 2 0 0 4 , s o t r e a t m e n t s w e r e c o m p a r e d to con t ro l q u a d r a t s f r o m t h e s a m e y e a r in w h i c h the t r e a t m e n t w a s d o n e . T o a c c o u n t for i n c r e a s e d l i k e l i h o o d o f T y p e 1 s tat i s t i ca l e r r o r s , I u s e d B o n f e r r o n i c o r r e c t e d cr i t ical a l p h a v a l u e s in c a s e s w h e r e m u l t i p l e c o m p a r i s o n s w e r e p e r f o r m e d ( Z a r 1 9 9 9 ) . F o r p a r a m e t r i c t e s t s , d a t a w e r e t e s t e d for n o r m a l i t y ( A n d e r s o n - D a r l i n g test) a n d fo r h o m o g e n e i t y o f v a r i a n c e u s i n g C o c h r a n ' s C ( U n d e r w o o d 1 9 9 7 ) . If d a t a d id not c o n f o r m , a p p r o p r i a t e 2 4 t r a n s f o r m a t i o n s w e r e a p p l i e d ( Z a r 1 9 9 9 ) . P a r a m e t r i c t e s t s w e r e c a r r i e d ou t u s i n g J M P 4 . 0 . 4 ( S A S Institute Inc.). N o n - p a r a m e t r i c m u l t i v a r i a t e a p p r o a c h e s ( C l a r k e 1 9 9 3 ) w e r e u s e d to tes t for the i n f l u e n c e o f s e a w e e d t a x o n o m i c a n d f u n c t i o n a l c o m p o s i t i o n o n i n v e r t e b r a t e c o m p o s i t i o n . T o d o w n - w e i g h t t h e con t r ibu t i on of a b u n d a n t t a x a to m e a s u r e s o f b e t w e e n - s a m p l e s imi la r i ty ( C l a r k e 1 9 9 3 ) , a b u n d a n c e d a t a e i t h e r f o u r t h - r o o t t r a n s f o r m e d ( i n v e r t e b r a t e s ) o r r o o t - t r a n s f o r m e d ( s e a w e e d ) . T h e d e g r e e o f t r a n s f o r m a t i o n d i f f e red b e t w e e n i n v e r t e b r a t e s a n d s e a w e e d s b e c a u s e i n v e r t e b r a t e s w e r e c o u n t e d a s i n d i v i d u a l s ( r a n g i n g f r o m z e r o to 1 0 0 0 ) a n d s e a w e e d s w e r e s a m p l e d a s p e r c e n t c o v e r ( r a n g i n g f r o m z e r o to 1 0 0 ) . S im i la r i t y of s p e c i e s c o m p o s i t i o n of i n v e r t e b r a t e s a m p l e s a n d s e a w e e d t r a n s p l a n t q u a d r a t s w a s c a l c u l a t e d u s i n g B r a y - C u r t i s s im i l a r i t i es ( B r a y a n d C u r t i s 1 9 5 7 ) , w h i c h is a m e a s u r e of s a m p l e s imi lar i ty that r a n g e s b e t w e e n z e r o (no s p e c i e s in c o m m o n ) a n d 1 0 0 ( s p e c i e s c o m p o s i t i o n a n d a b u n d a n c e a r e e q u i v a l e n t b e t w e e n s a m p l e s ) . T h e s e s a m p l e s imi lar i t ies w e r e t h e n v i s u a l i z e d u s i n g n o n - m e t r i c m u l t i d i m e n s i o n a l s c a l i n g ( n M D S ) . T o c a l c u l a t e s e a w e e d f u n c t i o n a l c o m p o s i t i o n , total p e r - q u a d r a t b i o m a s s of e a c h s e a w e e d s p e c i e s w a s s u m m e d into t h e a p p r o p r i a t e f u n c t i o n a l g r o u p b e f o r e a p p l y i n g root t r a n s f o r m a t i o n a n d c a l c u l a t i n g B r a y - C u r t i s s imi lar i ty . T w o t e c h n i q u e s w e r e u s e d to a s s e s s t h e i m p l i c a t i o n s o f t h e d i f fe rent t r e a t m e n t s for i n v e r t e b r a t e c o m p o s i t i o n : a) for t h e m a n i p u l a t i v e e x p e r i m e n t , d i rec t c o m p a r i s o n s b e t w e e n t r e a t m e n t s a n d c o n t r o l s w e r e m a d e u s i n g A n a l y s i s of S i m i l a r i t i e s ( A N O S I M ; C l a r k e 1 9 9 3 ) , a n d b) for bo th the o b s e r v a t i o n a l a n d m a n i p u l a t i v e c o m p o n e n t s , a s s e s s m e n t s o f o v e r a l l c o n g r u e n c e in m u l t i v a r i a t e s imi la r i ty p a t t e r n s b e t w e e n s e a w e e d f u n c t i o n a l a n d s p e c i e s c o m p o s i t i o n v s . I n v e r t e b r a t e s p e c i e s c o m p o s i t i o n w e r e m a d e u s i n g M a n t e l t e s t s ( Z a r 1 9 9 9 ) ; h e r e I c a l c u l a t e d S p e a r m a n r a n k c o r r e l a t i o n ( Z a r 1 9 9 9 ) b e t w e e n s imi lar i ty m a t r i c e s . W h e r e s i g n i f i c a n t d i f f e r e n c e s b e t w e e n t r e a t m e n t a n d c o n t r o l s w e r e i n d i c a t e d by the A N O S I M t e s t s , t h e b i o t a r e s p o n s i b l e for d i f f e r e n c e s b e t w e e n g r o u p s w e r e ident i f ied u s i n g S im i la r i t y P e r c e n t a g e s ( S I M P E R ; C l a r k e 1 9 9 3 ) . M u l t i v a r i a t e a n a l y s e s w e r e c a r r i e d ou t u s i n g P R I M E R s o f t w a r e ( V e r s i o n 5.2, P r i m e r - E , w w w . p r i m e r - e . o r g ) . 2 5 2.3 Results 2.3.1 Observational study F o r the o b s e r v a t i o n a l c o l l e c t i o n s , n o s i g n i f i c a n t c o r r e l a t i o n s w e r e o b s e r v e d b e t w e e n a n y o f t h e m e a s u r e d v a r i a b l e s , h o w e v e r n o l o w - d i v e r s i t y s e a w e e d q u a d r a t s w e r e e n c o u n t e r e d ; a v e r a g e s e a w e e d s p e c i e s r i c h n e s s w a s 6.1 (+/- 0 . 4 9 S E ) a n d a v e r a g e s e a w e e d f u n c t i o n a l r i c h n e s s w a s 2 . 9 0 (+/- 0 . 2 3 ) . T h e r e w a s n o c o r r e l a t i o n b e t w e e n s e a w e e d s p e c i e s r i c h n e s s a n d i n v e r t e b r a t e s p e c i e s r i c h n e s s ( P = 0 .64 , r 2 = 0 .17) o r i n v e r t e b r a t e a b u n d a n c e ( P = 0 . 6 5 , r 2 = 0 . 0 2 ) , o r b e t w e e n s e a w e e d f u n c t i o n a l r i c h n e s s a n d i n v e r t e b r a t e r i c h n e s s ( P = 0 . 7 3 , r 2 = 0 . 0 3 ) a n d i n v e r t e b r a t e a b u n d a n c e ( P = 0 . 5 7 , r2 = 0 . 0 4 ) . F u r t h e r , n o c o r r e l a t i o n w a s o b s e r v e d b e t w e e n i n v e r t e b r a t e a s s e m b l a g e s t r u c t u r e a n d e i t h e r s e a w e e d a s s e m b l a g e s t r u c t u r e ( S p e a r m a n r a n k c o r r e l a t i o n ( r s = 0 . 1 1 1 , P = 0 . 2 3 2 ) or s e a w e e d f u n c t i o n a l s t r u c t u r e (r s = 0 . 0 1 9 , P = 0 . 4 6 9 ) . A n a v e r a g e of 3 0 1 . 7 (+/- 6 3 . 5 S E ) i n v e r t e b r a t e s w e r e f o u n d p e r q u a d r a t , with a total o f 3 0 1 7 e p i f a u n a i n d i v i d u a l s a c r o s s 61 i n v e r t e b r a t e t a x a a c r o s s all q u a d r a t s . 2.3.2 Manipulative experiment N o n e o f t h e f ive s e a w e e d t r e a t m e n t s r e s u l t e d in d i f f e r e n c e s in i n v e r t e b r a t e r i c h n e s s o r i n v e r t e b r a t e a b u n d a n c e c o m p a r e d to c o n t r o l q u a d r a t s ( A N O V A , P2003 > 0 . 0 2 5 , P2004 > 0 . 0 1 7 ; cr i t ica l a l p h a v a l u e s d e t e r m i n e d b y B o n f e r r o n i c o r r e c t i o n ) . A c r o s s all t r e a t m e n t q u a d r a t s , a total o f 9 5 9 3 i n v e r t e b r a t e i n d i v i d u a l s w e r e e n c o u n t e r e d a c r o s s 6 6 t a x a . M e a n p e r - q u a d r a t i n v e r t e b r a t e t a x o n r i c h n e s s r a n g e d f r o m 1 5 to 2 5 , a n d m e a n p e r - q u a d r a t a b u n d a n c e r a n g e d f r o m 1 1 0 to 3 3 8 i n d i v i d u a l s . I n v e r t e b r a t e c o m p o s i t i o n in m o s t o f the t r e a t m e n t s v a r i e d i n d e p e n d e n t l y o f s e a w e e d c o m p o s i t i o n . I n v e r t e b r a t e a s s e m b l a g e s f r o m m i x e d p o l y c u l t u r e s ( T 1 ) w e r e not s ign i f i can t l y d i f fe rent f r o m t h e 2 0 0 3 c o n t r o l s ( A N O S I M P > 0 . 0 2 5 ) , a n d s i m p l e p o l y c u l t u r e s ( T 3 ) , c o m p l e x m o n o c u l t u r e s ( T 4 ) , a n d c o m p l e x p o l y c u l t u r e s ( T 5 ) w e r e not s ign i f i can t l y d i f f e ren t f r o m t h e 2 0 0 4 c o n t r o l s ( A N O S I M P > 0 . 0 1 7 ; F i g . 2.1 C a n d T a b l e 2 . 3 C ) . In o n l y o n e t r e a t m e n t ( s i m p l e m o n o c u l t u r e s , T 2 ) d id c o m p o s i t i o n of i n v e r t e b r a t e 2 6 a s s e m b l a g e s d e p e n d o n t h e ident i ty of the s e a w e e d t r e a t m e n t ( A N O S I M , R = 0 . 5 2 0 , P < 0 . 0 0 1 ; F i g . 2.1 C a n d T a b l e 2 . 3 C ) . S I M P E R a n a l y s i s i n d i c a t e d that d i f f e r e n c e s in the a b u n d a n c e o f a m p h i p o d s a c c o u n t e d for 4 2 % of t h e o b s e r v e d a s s e m b l a g e d i ss im i l a r i t y b e t w e e n T 2 a n d t h e c o n t r o l q u a d r a t s , f o l l o w e d b y h a r p a c t i c o i d c o p e p o d s ( - 1 6 % ) , s n a i l s ( - 1 0 % ) a n d l i m p e t s , m i t e s , a n d p o l y c h a e t e s , w h i c h e a c h a c c o u n t e d for l e s s t h a n 5% of the d i f f e r e n c e s ( T a b l e 2 .4) . O v e r a l l p a t t e r n s ( i .e. r a n k o r d e r of s imi lar i ty r e l a t i o n s h i p s wi th in m a t r i c e s ) b e t w e e n s e a w e e d t a x o n o m i c c o m p o s i t i o n a n d i n v e r t e b r a t e t a x o n o m i c c o m p o s i t i o n ( F i g . 2 .1 , T a b l e 2.5) w e r e not c o r r e l a t e d in 2 0 0 3 (r s = 0.111, P = 0 . 2 3 9 ) or in 2 0 0 4 (r s = 0 . 1 0 3 , P = 0 . 1 3 9 ) . H o w e v e r , o v e r a l l p a t t e r n s of s e a w e e d f u n c t i o n a l c o m p o s i t i o n w e r e c o r r e l a t e d with p a t t e r n s o f i n v e r t e b r a t e t a x o n o m i c c o m p o s i t i o n in b o t h 2 0 0 3 (r s = 0 . 2 7 5 , P = 0 . 0 1 3 ) a n d 2 0 0 4 (r s = 0 . 1 9 6 , P = 0 . 0 1 7 ) . 2.4 Discussion I f o u n d that m a n y of the t e s t e d c o m p o n e n t s o f s e a w e e d d i v e r s i t y h a d n o o b s e r v a b l e i n f l u e n c e o n d i v e r s i t y of a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a . In all c a s e s , i n v e r t e b r a t e r i c h n e s s a n d a b u n d a n c e v a r i e d i n d e p e n d e n t l y of t h e m a n i p u l a t e d qua l i t i e s of h o s t a l g a l a s s e m b l a g e s . Inver tebra te a s s e m b l a g e s t r u c t u r e w a s d i f fe rent b e t w e e n con t ro l q u a d r a t s a n d a l g a l a s s e m b l a g e s c o m p o s e d o f s i m p l e m o n o c u l t u r e s , but u n d e r n o n e of the o t h e r t e s t s c e n a r i o s . C o n g r u e n c e of p a i r w i s e s a m p l e s im i l a r i t i es w a s d e t e c t e d b e t w e e n a l g a l f u n c t i o n a l s t r u c t u r e a n d i n v e r t e b r a t e a s s e m b l a g e s , but not b e t w e e n a l g a l t a x o n o m i c s t r u c t u r e a n d i n v e r t e b r a t e a s s e m b l a g e s . W h e n c o m p a r e d at t h e s p e c i e s l eve l , a l g a e v a r y in q u a l i t y o f h a b i t a t p r o v i s i o n for e p i f a u n a , with c o m p l e x l y b r a n c h i n g a l g a l s p e c i e s t y p i c a l l y h a v i n g a h i g h e r d i ve rs i t y of a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a a s c o m p a r e d to a l g a e with s i m p l e m o r p h o l o g i e s ( G e e a n d W a r w i c k , 1 9 9 4 , C h e m e l l o a n d M i l a z z o 2 0 0 2 ) . In th is s t u d y I e x a m i n e d i n v e r t e b r a t e s a s s o c i a t e d with v a r i o u s t y p e s of s e a w e e d c o m m u n i t i e s . A l l s e a w e e d q u a d r a t s c o m p o s e d of m o r e t h a n o n e s p e c i e s h a d a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e s that w e r e not d i f f e ren t f r o m con t ro l q u a d r a t s that c o n t a i n e d e i g h t s e a w e e d s p e c i e s . W h e n s e a w e e d q u a d r a t s w e r e c o m p o s e d of o n l y o n e s p e c i e s , r e s u l t s of e p i f a u n a c o m p a r i s o n s d e p e n d e d o n the f u n c t i o n a l ident i ty o f t h e s e a w e e d m o n o c u l t u r e . T h i s 2 7 latter resu l t is c o n s i s t e n t with p r e v i o u s i n v e s t i g a t i o n s that l ink i n v e r t e b r a t e d i v e r s i t y to s e a w e e d h o s t ident i ty ( G e e a n d W a r w i c k 1 9 9 4 , C h e m e l l o a n d M i l a z z o 2 0 0 2 ) a n d s i m i l a r to t h o s e r e p o r t e d b y P a r k e r et al. ( 2 0 0 1 ) , w h o s h o w e d that wi th in a s u b t i d a l N o r t h e a s t A t l a n t i c e s t u a r i n e s e a g r a s s / d r i f t s e a w e e d c o m m u n i t y , p lan t c o m p o s i t i o n w a s a s t r o n g p r e d i c t o r o f i n v e r t e b r a t e c o m m u n i t y s t ruc tu re , w h i l e p lan t r i c h n e s s s h o w e d o n l y a w e a k p o s i t i v e c o r r e l a t i o n with d i v e r s i t y o f i n v e r t e b r a t e e p i f a u n a . M y r e s u l t s c o n t r a s t with s im i l a r s t u d i e s u n d e r t a k e n in terrest r ia l h a b i t a t s . H a d d a d et al. ( 2 0 0 1 ) r e p o r t e d that i n s e c t s p e c i e s r i c h n e s s w a s p o s i t i v e l y c o r r e l a t e d with p l a n t s p e c i e s a n d f u n c t i o n a l r i c h n e s s in g r a s s l a n d e c o s y s t e m s , a n d P e m e r ef al. ( 2 0 0 3 ) r e p o r t e d that a f ter the c e s s a t i o n of po l l u t i on , h e r b i v o r e r i c h n e s s w a s p o s i t i v e l y i n f l u e n c e d b y s u b s e q u e n t i n c r e a s e s in p l a n t s p e c i e s a n d f u n c t i o n a l r i c h n e s s . G i v e n that s t r o n g e r r e l a t i o n s h i p s h a v e b e e n o b s e r v e d b e t w e e n d i v e r s i t y of p l a n t s a n d i n v e r t e b r a t e s in te r res t r ia l s y s t e m s , it is l o g i c a l to a s k w h y m a r i n e a l g a l d i ve rs i t y a n d a s s o c i a t e d e p i f a u n a a r e not m o r e tightly l i n k e d . T e r r e s t r i a l i n s e c t s a r e o f t e n s p e c i a l i z e d to the i r h o s t ( J a n z et al. 2 0 0 1 ) , w h e r e a s m a r i n e i n v e r t e b r a t e s t e n d to b e m u c h m o r e g e n e r a l i z e d in the i r h o s t u s a g e ( A r r o n t e s 1 9 9 9 ) , a l t h o u g h e x a m p l e s of m a r i n e h o s t s p e c i a l i z a t i o n d o ex i s t ( S o t k a 2 0 0 5 ) . In the a b s e n c e of w i d e s p r e a d h o s t - s p e c i a l i z a t i o n , m a r i n e e p i f a u n a a r e l ikely m o r e a m e n a b l e t h a n i n s e c t s to s w i t c h to a n e w h o s t w h e n h o s t c o m p o s i t i o n o r r i c h n e s s c h a n g e . W h y d id i n v e r t e b r a t e s a s s o c i a t e d with s i m p l e m o n o c u l t u r e s d i f fer c o m p a r e d to the c o n t r o l s ? T h e major i ty o f s t u d i e s re lat ing h o s t a r c h i t e c t u r a l c o m p l e x i t y to e p i f a u n a d ive rs i t y c o n c l u d e that h o s t p l a n t s that a r e bet ter at p r o v i d i n g p r e d a t o r - f r e e s p a c e will h a v e the h i g h e s t a s s o c i a t e d i n v e r t e b r a t e d i ve rs i t y ( A r r o n t e s 1 9 9 9 ) . T h e s p e c i e s i n c l u d e d in t h e f o l i o s e f u n c t i o n a l g r o u p t e n d to b e of l ow s t r u c t u r a l c o m p l e x i t y , with m a n y s p e c i e s l a c k i n g b r a n c h e s o r s p e c i a l i z e d s t r u c t u r e s . T h i s l a c k of c o m p l e x i t y m a y p r o v i d e f e w e r s p a c e s for e p i f a u n a to h i d e f r o m p r e d a t o r s , w h i c h c o u l d e x p l a i n t h e d i f ferent c o m p o s i t i o n of a m p h i p o d s , h a r p a c t i c o i d c o p e p o d s , g a s t r o p o d s , l i m p e t s , m i t e s , a n d p o l y c h a e t e w o r m s o b s e r v e d in s i m p l e m o n o c u l t u r e s c o m p a r e d to c o n t r o l s ( T a b l e 2.4). H o w e v e r , s t ruc tu ra l c o m p l e x i t y c a n b e diff icult to d e f i n e in a s t r a i g h t f o r w a r d m a n n e r , a n d o t h e r c h a r a c t e r i s t i c s b e s i d e s b r a n c h i n g m a y i n f l u e n c e a n a l g a l h o s t ' s abi l i ty to p r o v i d e p r e d a t o r - f r e e s p a c e . S e v e r a l o f t h e f o l i o s e s e a w e e d s p e c i e s ( e . g . Porphyra s p p . , Ulva lactuca) exh ib i t h i g h l y f o l d e d m o r p h o l o g i e s , w h i c h c a n a l s o p r o v i d e e f f ec t i ve s h e l t e r for i n v e r t e b r a t e e p i f a u n a . F i g u r e 2.1 C s h o w s that s e v e r a l o f the s i m p l e 2 8 m o n o c u l t u r e q u a d r a t s h a d a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e s that g r o u p c l o s e l y with t h o s e f r o m t h e c o n t r o l q u a d r a t s . T h i s s u g g e s t s that f u n c t i o n a l g r o u p i n g s , a s cu r ren t l y d e f i n e d , m a y not b e the m o s t re l i ab le m e t h o d of p r e d i c t i n g a s e a w e e d s p e c i e s p e r f o r m a n c e a s a h o s t f o r i n v e r t e b r a t e e p i f a u n a . E v i d e n c e e x i s t s to s u g g e s t that h o s t s p e c i e s ident i ty is p a r t i c u l a r l y i m p o r t a n t w h e n a b i o t i c c o n d i t i o n s a r e s t r e s s f u l . F o r e x a m p l e , L i l l ey a n d S c h i e l ( 2 0 0 6 ) f o u n d that o n N e w Z e a l a n d s h o r e s e x p o s e d to t h e r m a l s t r e s s , r e m o v a l o f a d o m i n a n t c a n o p y f o r m i n g s p e c i e s , Hormosira banksii ( T u r n e r ) D e c a i s n e , h a d s i g n i f i c a n t i n f l u e n c e o n a s s e m b l a g e s t r u c t u r e o f n e a r b y a n d a s s o c i a t e d o r g a n i s m s . 2.4.1 Observational versus manipulative results R e s u l t s f r o m m y m a n i p u l a t i v e s t u d y s u g g e s t that o n l y u n d e r p a r t i c u l a r s c e n a r i o s of a l g a l c h a n g e will c o m p o s i t i o n of a s s o c i a t e d e p i f a u n a b e i n f l u e n c e d . T h e r e f o r e , it is not s u r p r i s i n g tha t m y o b s e r v a t i o n a l s t u d y d i d no t r e v e a l a n y l i n k a g e s b e t w e e n a l g a l b i o d i v e r s i t y a n d e p i f a u n a l d ivers i ty , b e c a u s e n o l o w - d i v e r s i t y s e a w e e d a s s e m b l a g e s w e r e e n c o u n t e r e d in o b s e r v a t i o n a l q u a d r a t s . 2.4.2 Implications for invertebrates of changes in seaweed biodiversity U n d e r m o s t s c e n a r i o s , it a p p e a r s that i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e s a r e r o b u s t to c h a n g e s in s e a w e e d b i o d i v e r s i t y . H o w e v e r , a n i n t e r e s t i n g o b s e r v a t i o n is that the ' s i m p l e m o n o c u l t u r e ' t r e a t m e n t , w h i c h h a r b o r e d a l o w e r d i v e r s i t y o f i n v e r t e b r a t e e p i f a u n a , is s i m i l a r in c o m p o s i t i o n to the i n c r e a s i n g l y f i e l d - o b s e r v e d ' g r e e n t ide ' p h e n o m e n o n . T h i s s u g g e s t s that if g r e e n t i d e s c o n t i n u e to b e c o m e m o r e w i d e s p r e a d , t h e r e is po ten t i a l for c h a n g e s in s e a w e e d b i o d i v e r s i t y to a l ter l o c a l d i v e r s i t y a n d c o m p o s i t i o n of i n v e r t e b r a t e a s s e m b l a g e s . It is a l s o w o r t h n o t i n g that e v e n t h o u g h h o s t - spec i f i c i t y d o e s not a p p e a r s t r o n g in th is s y s t e m , s e a w e e d s d o p r o v i d e hab i ta t for m y r i a d i n v e r t e b r a t e s a n d if s e a w e e d c o v e r w e r e to b e ent i re ly lost , th is c o u l d b e d e t r i m e n t a l to a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a ( W a l k e r a n d K e n d r i c k 1 9 9 8 ) , a n d to l a rge r i n v e r t e b r a t e s a n d f i sh that f e e d o n s e a w e e d - a s s o c i a t e d e p i f a u n a . 2 9 T a b l e 2.1: L is t o f a l g a l s p e c i e s i n c l u d e d in th is s t u d y , wi th f u n c t i o n a l g r o u p a s s i g n m e n t a n d w h e t h e r t h e y w e r e e n c o u n t e r e d in t h e o b s e r v a t i o n a l s t u d y ( O ) , u s e d in t h e m a n i p u l a t i v e s t u d y (M) or bo th (B) . T a x o n F u n c t i o n a l G r o u p I n c l u s i o n Ahnfeltiopsis leptophyllus L e a t h e r y O Analipus japonicus C o r t i c a t e d t e r e t e B Callithamnion pikeanum F i l a m e n t o u s 0 Ceramium pacificum C o r t i c a t e d t e r e t e 0 Ceramium s p . C o r t i c a t e d t e r e t e 0 Chondracanthus exasperatus L e a t h e r y M Fucus distichus s u b s p . evanescens L e a t h e r y B Gastroclonium subarticulatum C o r t i c a t e d t e r e t e M Halosaccion glandiforme F o l i o s e B Mastocarpus jardinii L e a t h e r y M Mastocarpus papillatus L e a t h e r y B Mazzaella affinis C o r t i c a t e d f o l i o s e B Mazzaella splendens C o r t i c a t e d f o l i o s e B Microcladia borealis C o r t i c a t e d t e r e t e O Microcladia coulteri C o r t i c a t e d t e r e t e 0 Neorhodomela larix C o r t i c a t e d t e r e t e M Odonthalia flocossa C o r t i c a t e d t e r e t e B Osmundea spectabilis L e a t h e r y 0 Porphyra s p . F o l i o s e B Prionitis lyallii C o r t i c a t e d t e r e t e B Sargassum muticum C o r t i c a t e d t e r e t e M Ulva lactuca F o l i o s e B Ulva intestinalis F o l i o s e M Ulva linza F o l i o s e B Ulva californica F o l i o s e B 30 T a b l e 2.2: D e s c r i p t i o n o f a l g a l a s s e m b l a g e p a r a m e t e r s u s e d to c o m p o s e contro l a n d e x p e r i m e n t a l q u a d r a t s . N = 4 for e a c h t r e a t m e n t ; e a c h t r e a t m e n t h a d four a s s o c i a t e d con t ro l q u a d r a t s . T r e a t m e n t Identity S p e c i e s F u n c t i o n a l F u n c t i o n a l Y e a r R i c h n e s s (S) R i c h n e s s (F) C o m p o s i t i o n ( F C ) T 1 : M i x e d P o l y c u l t u r e 4 4 M i x e d 2 0 0 3 T 2 : S i m p l e M o n o c u l t u r e 1 1 F o l i o s e 2 0 0 3 T 3 : S i m p l e P o l y c u l t u r e 6 1 F o l i o s e 2 0 0 4 T 4 : C o m p l e x M o n o c u l t u r e 1 1 C o r t i c a t e d te re te 2 0 0 4 T 5 : C o m p l e x P o l y c u l t u r e 6 1 C o r t i c a t e d te re te 2 0 0 4 C : C o n t r o l 8 4 M i x e d 2 0 0 3 & 2 0 0 4 T a b l e 2 .3 : A N O S I M r e s u l t s for t h e m a n i p u l a t i v e e x p e r i m e n t : C o m p a r i s o n s of s p e c i f i c t r e a t m e n t s to con t ro l q u a d r a t s for a l g a l t a x o n o m i c c o m p o s i t i o n (A) , a l g a l f u n c t i o n a l c o m p o s i t i o n (B), a n d c o m p o s i t i o n of a s s o c i a t e d m o b i l e i n v e r t e b r a t e e p i f a u n a ( C ) . T r e a t m e n t C o m p a r e d to C o n t r o l A : A l g a l S p e c i e s C o m p o s i t i o n A N O S I M R P v a l u e B: A l g a l F u n c t i o n a l C o m p o s i t i o n A N O S I M R P v a l u e C : Inver tebrate S p e c i e s C o m p o s i t i o n A N O S I M R P v a l u e T 1 T 2 T 3 T 4 T 5 - 0 . 0 1 2 0 . 8 6 5 0 . 9 5 4 0 . 8 9 6 0 . 9 0 3 0 . 4 7 6 0 . 0 0 5 0 .001 0 .001 0 .001 -0 .071 0 . 3 1 7 0.271 0 . 7 3 3 0.491 0 . 6 0 5 0 . 0 4 3 0 . 0 0 9 0 . 0 0 2 0 . 0 0 2 0 . 2 5 0 0 . 5 2 0 0 . 2 8 2 0 . 2 1 3 - 0 . 0 5 5 0 .071 0 .001 0 . 0 4 2 0 . 1 4 9 0 . 5 7 3 CO T a b l e 2.4: S u m m a r y of d i f f e r e n c e s in a b u n d a n c e of m a j o r i n v e r t e b r a t e t a x a f o u n d o n cont ro l q u a d r a t s c o m p a r e d m o n o c u l t u r e s o f f o l i o s e s e a w e e d ( G r o u p T 2 ) . O r d e r C o n t r o l G r o u p T 2 A v e r a g e A v e r a g e A b u n d a n c e A b u n d a n c e A m p h i p o d a 1 9 8 . 1 7 1 1 8 . 2 5 H a r p a c t i c o i d a 3 9 . 5 0 1 9 . 2 5 G a s t r o p o d a 4 1 . 1 7 2 3 . 5 0 P a t e l l o g a s t r o p o d a 1 3 . 5 0 2 .50 A c a r i d a 1 4 . 0 0 8 . 2 5 P o l y c h a e t a 9 . 5 0 6 . 7 5 A v e r a g e D iss imi la r i ty / % cont r ibu t i on to D iss imi la r i ty S D o v e r a l l d i ss imi la r i ty 1 9 . 8 3 1.38 4 2 . 1 5 7.41 1.44 1 5 . 7 5 4 . 6 8 1.19 9 . 9 5 2.21 1.60 4 .71 2 .19 2 .22 4 . 6 5 1.93 2 .60 4 . 1 0 oo co T a b l e 2.5: S p e a r m a n r a n k c o r r e l a t i o n v a l u e s for t e s t s o f c o n g r u e n c e b e t w e e n two s e a w e e d a s s e m b l a g e d e s c r i p t o r s c o m p a r e d to a s s e m b l a g e s t r u c t u r e o f a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a . O b s e r v a t i o n a l C o l l e c t i o n s M a n i p u l a t i v e E x p e r i m e n t E p i f a u n a s imi lar i ty c o m p a r e d to: r s P r s ( T i - T 2 ) P<TI-T2) rS(T3-T5) P(T3-TS) S e a w e e d t a x o n o m i c s imi lar i ty 0 .111 0 . 2 3 2 0 .111 0 . 2 3 9 0 . 1 0 3 0 . 1 3 9 S e a w e e d f u n c t i o n a l s imi lar i ty 0 . 1 9 0 . 4 6 9 0 . 2 7 5 0 . 0 1 3 0 . 1 9 6 0 . 0 1 7 co T1 & T2 (2003) A: S e a w e e d T a x o n o m i c Similarity T3 - T5 (2004) / — S t r e s s = .14 / T 2 - N A ^ \ 1 1 1 V? - T2 X / X ^ B: S e a w e e d Funct iona l Similarity r c c c v £ C Stress = .06 (T4\ C: Invertebrate T a x o n o m i c Similarity Stress = .11 T2' c / Stress = .02 /c A \ c\ c \ \\ (c \ r \ T 5 _ \ j 4 - - T3 \I3/ F i g u r e 2 .1 : n M D S p lo t s o f B r a y - C u r t i s S im i l a r i t y b a s e d o n : A ) s e a w e e d t a x o n o m i c c o m p o s i t i o n , B ) s e a w e e d f u n c t i o n a l c o m p o s i t i o n , a n d C ) a s s o c i a t e d m o b i l e i n v e r t e b r a t e e p i f a u n a , f r o m 2 0 0 3 & 2 0 0 4 . C : C o n t r o l , T 1 : m i x e d p o l y c u l t u r e , T 2 : s i m p l e m o n o c u l t u r e , T 3 : s i m p l e p o l y c u l t u r e , T 4 : c o m p l e x m o n o c u l t u r e , T 5 : c o m p l e x p o l y c u l t u r e . D a s h e d l ine i n d i c a t e s that T r e a t m e n t g r o u p is d i f ferent f r o m c o n t r o l g r o u p ( A N O S I M p < 0 . 0 5 ; T a b l e 2 .4) . 3 5 2.5 L i t e r a t u r e c i t e d A r r o n t e s , J . 1 9 9 9 . O n t h e e v o l u t i o n of i n t e r a c t i o n s b e t w e e n m a r i n e m e s o h e r b i v o r e s a n d a l g a e . B o t a n i c a M a r i n a 4 2 : 1 3 7 - 1 5 5 . B a t e s , C . R., G . W . S a u n d e r s , a n d T. C . C h o p i n . 2 0 0 5 . A n a s s e s s m e n t o f t w o t a x o n o m i c d i s t i n c t n e s s i n d i c e s for d e t e c t i n g s e a w e e d a s s e m b l a g e r e s p o n s e s to e n v i r o n m e n t a l s t r e s s . B o t a n i c a M a r i n a 4 8 : 2 3 1 - 2 4 3 . B e r t n e s s , M . D., G . H . L e o n a r d , J . M . L e v i n e , P. R. S c h m i d t , a n d A . O . I n g r a h a m . 1 9 9 9 . T e s t i n g t h e re la t i ve c o n t r i b u t i o n of p o s i t i v e a n d n e g a t i v e i n t e r a c t i o n s in r o c k y intert idal c o m m u n i t i e s . E c o l o g y 8 0 : 2 7 1 1 - 2 7 2 6 . B r a y , J . R., a n d J . T . C u r t i s . 1 9 5 7 . A n o r d i n a t i o n of the u p l a n d f o r e s t c o m m u n i t i e s o f S o u t h e r n W i s c o n s i n . E c o l o g i c a l M o n o g r a p h s 2 7 : 3 2 5 - 3 4 9 . B r u n o , J . F., a n d M . D. B e r t n e s s . 2 0 0 0 . H a b i t a t m o d i f i c a t i o n a n d fac i l i ta t ion in b e n t h i c m a r i n e c o m m u n i t i e s . P a g e s 5 6 0 in M . D. B e r t n e s s , S . D. G a i n e s , a n d M . E . H a y , e d i t o r s . M a r i n e c o m m u n i t y e c o l o g y . S i n a u e r A s s o c i a t e s Inc. B r u n o , J . F., K. E . B o y e r , J . E . Duf fy , S . C . L e e , a n d J . S . K e r t e s z . 2 0 0 5 . E f f e c t s o f m a c r o a l g a l s p e c i e s ident i ty a n d r i c h n e s s o n p r i m a r y p r o d u c t i o n in b e n t h i c m a r i n e c o m m u n i t i e s . E c o l o g y L e t t e r s 8 : 1 1 6 5 - 1 1 7 4 . B r u n o , J . F., J . J . S t a c h o w i c z , a n d M. D. B e r t n e s s . 2 0 0 3 . I n c l u s i o n o f fac i l i ta t ion into e c o l o g i c a l t h e o r y . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 8 : 1 1 9 - 1 2 5 . C a s t i l l a , J . C , N . A . L a g o s , a n d M . C e r d a . 2 0 0 4 . M a r i n e e c o s y s t e m e n g i n e e r i n g by the a l i e n a s c i d i a n Pyura praeputialis o n a mid- in ter t ida l r o c k y s h o r e . M a r i n e E c o l o g y P r o g r e s s S e r i e s 2 6 8 : 1 1 9 - 1 3 0 . C h e m e l l o , R., a n d M . M i l a z z o . 2 0 0 2 . E f f e c t of a l g a l a r c h i t e c t u r e o n a s s o c i a t e d f a u n a : s o m e e v i d e n c e f r o m p h y t a l m o l l u s c s . M a r i n e B i o l o g y 1 4 0 : 9 8 1 - 9 9 0 . C l a r k e , K. R. 1 9 9 3 . N o n - p a r a m e t r i c mu l t i va r i a te a n a l y s i s o f c h a n g e s in c o m m u n i t y s t r u c t u r e . A u s t r a l i a n J o u r n a l o f E c o l o g y 1 8 : 1 1 7 - 1 4 3 . C o l e m a n , F. C , a n d S . L. W i l l i a m s . 2 0 0 2 . O v e r e x p l o i t i n g m a r i n e e c o s y s t e m e n g i n e e r s : po tent ia l c o n s e q u e n c e s for b i o d i v e r s i t y . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 7 : 4 0 - 4 4 . D e a n , R. L., a n d J . H . C o n n e l l . 1 9 8 7 . M a r i n e i n v e r t e b r a t e s in a l g a l s u c c e s s i o n . III. M e c h a n i s m s l ink ing hab i ta t c o m p l e x i t y with d ive rs i t y . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 1 0 9 : 2 4 8 - 2 7 3 . 3 6 D i a z , S . , a n d M . C a b i d o . 2 0 0 1 . V i v e la d i f f e r e n c e : p lan t f u n c t i o n a l d i v e r s i t y m a t t e r s to e c o s y s t e m p r o c e s s e s . T r e n d s in E c o l o g y a n d E v o l u t i o n 16:646-655. F a r i n a , J . M. , J . C . C a s t i l l a , a n d F. P. O j e d a . 2 0 0 3 . T h e " i d i o s y n c r a t i c " e f f ec t o f a " s e n t i n e l " s p e c i e s o n c o n t a m i n a t e d r o c k y intert idal c o m m u n i t i e s . E c o l o g i c a l A p p l i c a t i o n s 13:1533-1552. G e e , J . M. , a n d R. M . W a r w i c k . 1 9 9 4 . M e t a z o a n c o m m u n i t y s t r u c t u r e in re la t ion to the f rac ta l d i m e n s i o n of m a r i n e m a c r o a l g a e . M a r i n e E c o l o g y P r o g r e s s S e r i e s 103 :141-150. H a d d a d , N . M. , D. T i l m a n , J . H a a r s t a d , M . R i t c h i e , a n d J . M . H . K n o p s . 2 0 0 1 . C o n t r a s t i n g e f f e c t s o f p lan t r i c h n e s s a n d c o m p o s i t i o n o n i n s e c t c o m m u n i t i e s : a f ie ld e x p e r i m e n t . T h e A m e r i c a n Na tura l i s t 158:17-35. J a n z , N. , K. N y b l o m , a n d S . N y l i n . 2 0 0 1 . E v o l u t i o n a r y d y n a m i c s o f h o s t - p l a n t s p e c i a l i z a t i o n : a c a s e s t u d y of the tr ibe N y m p h a l i n i . E v o l u t i o n 5 5 :783-796. K e l a h e r , B. P. 2 0 0 2 . I n f l u e n c e of p h y s i c a l c h a r a c t e r i s t i c s o f c o r a l l i n e turf o n a s s o c i a t e d m a c r o f a u n a l a s s e m b l a g e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 232 :141-148. L i l ley , S . A . , a n d D. R. S c h i e l . 2 0 0 6 . C o m m u n i t y e f f e c t s f o l l o w i n g t h e d e l e t i o n of a h a b i t a t - f o r m i n g a l g a f r o m r o c k y m a r i n e s h o r e s . O e c o l o g i a 148 :672-681. L o t z e , H . K., a n d I. M i l e w s k i . 2 0 0 4 . T w o c e n t u r i e s o f mu l t i p l e h u m a n i m p a c t s a n d s u c c e s s i v e c h a n g e s in a N o r t h A t l a n t i c f o o d w e b . E c o l o g i c a l A p p l i c a t i o n s 1 4 : 1428-1447 . L o t z e , H . K., W . S c h r a m m , D. S c h o r i e s , a n d B. W o r m . 1 9 9 9 . C o n t r o l o f m a c r o a l g a l b l o o m s at e a r l y d e v e l o p m e n t a l s t a g e s : Pilayella littoralis v e r s u s Enteromorpha s p p . O e c o l o g i a 119:46-54. M a g u r r a n , A . E . 1 9 8 8 . E c o l o g i c a l d i ve rs i t y a n d its m e a s u r e m e n t . P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n . M i d d e l b o e , A . L., a n d K. S a n d - J e n s e n . 2 0 0 0 . L o n g - t e r m c h a n g e s in m a c r o a l g a l c o m m u n i t i e s in a D a n i s h e s t u a r y . P h y c o l o g i a 3 9 :245-257. M o n t e i r o , L. R., B . B o r d i n , a n d S . F u r t a d o d o R e i s . 2 0 0 0 . S h a p e d i s t a n c e s , s h a p e s p a c e s a n d t h e c o m p a r i s o n o f m o r p h o m e t r i c m e t h o d s . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 5 :217-220. N a e e m , S . 2 0 0 2 . D i s e n t a n g l i n g the i m p a c t s o f d i v e r s i t y o f e c o s y s t e m f u n c t i o n i n g in c o m b i n a t o r i a l e x p e r i m e n t s . E c o l o g y 8 3 :2925-2935 . 3 7 N a e e m , S . , a n d J . W r i g h t . 2 0 0 3 . D i s e n t a n g l i n g b i o d i v e r s i t y e f f e c t s o n e c o s y s t e m f u n c t i o n i n g : d e r i v i n g s o l u t i o n s to a s e e m i n g l y i n s u r m o u n t a b l e p r o b l e m . E c o l o g y L e t t e r s 6:567-579. P a r k e r , J . D., J . E . Duf fy , a n d R. J . O r t h . 2 0 0 1 . P l a n t s p e c i e s d i v e r s i t y a n d c o m p o s i t i o n : e x p e r i m e n t a l e f f e c t s o n m a r i n e e p i f a u n a l a s s e m b l a g e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 224:55-67. P e r n e r , J . , W . V o i g t , R. B a h r m a n n , W . H e i n r i c h , R. M a r s t a l l e r , B. F a b i a n , K. G r e g o r , D. L i ch te r , F. W . S a n d e r , a n d T . H . J o n e s . 2 0 0 3 . R e s p o n s e s o f a r t h r o p o d s to p lant d i ve rs i t y : c h a n g e s a f ter po l lu t ion c e s s a t i o n . E c o g r a p h y 26:788-800. P e t c h e y , O . L. 2 0 0 0 . S p e c i e s d ivers i ty , s p e c i e s e x t i n c t i o n , a n d e c o s y s t e m f u n c t i o n . T h e A m e r i c a n N a t u r a l i s t 1 5 5 : 6 9 6 - 7 0 2 . P e t c h e y , O . L., a n d K. J . G a s t o n . 2 0 0 2 . E x t i n c t i o n a n d the l o s s o f f u n c t i o n a l d i ve rs i t y . P r o c e e d i n g s o f t h e R o y a l S o c i e t y o f L o n d o n B 269:1721-1727. S h a u g h n e s s y , F. J . , a n d R. E . D e W r e e d e . 2 0 0 1 . S i z e , s u r v i v a l a n d t h e potent ia l for r e p r o d u c t i o n in t r a n s p l a n t s o f Mazzaella splendens a n d Mazzaella linearis ( R h o d o p h y t a ) . M a r i n e E c o l o g y P r o g r e s s S e r i e s 222:109-118. S c h m i d , B., A . H e c t o r , M . A . H u s t o n , P. Inchaus t i , I. Ni js , P. W . L e a d l e y , a n d D. T i l m a n . 2 0 0 2 . T h e d e s i g n a n d a n a l y s i s of b i o d i v e r s i t y e x p e r i m e n t s . P a g e s 6 1 - 7 5 in M . L o r e a u , S . N a e e m , a n d P. I n c h a u s t i , e d i t o r s . B i o d i v e r s i t y a n d e c o s y s t e m f u n c t i o n i n g - S y n t h e s i s a n d p e r s p e c t i v e s . O x f o r d U n i v e r s i t y P r e s s . S c h r a m m , W . , a n d P. H . N i e n h u i s , e d i t o r s . 1 9 9 6 . M a r i n e B e n t h i c V e g e t a t i o n : R e c e n t c h a n g e s a n d t h e E f f e c t s o f E u t r o p h i c a t i o n . S p r i n g e r - V e r l a g , B e r l i n H e i d e l b e r g N e w Y o r k . S o t k a , E . E . 2 0 0 5 . L o c a l a d a p t a t i o n in h o s t u s e a m o n g m a r i n e i n v e r t e b r a t e s . E c o l o g y L e t t e r s 8 : 4 4 8 - 4 5 9 . S t a c h o w i c z , J . J . 2 0 0 1 . M u t u a l i s m , fac i l i ta t ion , a n d the s t r u c t u r e o f e c o l o g i c a l c o m m u n i t i e s . B i o s c i e n c e 5 1 : 2 3 5 - 2 4 6 . S t e n e c k , R. S . , a n d M . N. D e t h i e r . 1 9 9 4 . A f u n c t i o n a l g r o u p a p p r o a c h to the s t r u c t u r e of a l g a l - d o m i n a t e d c o m m u n i t i e s . O i k o s 69:476-498. T h o m p s o n , R. E. , B. J . W i l s o n , M . L. T o b i n , A . S . Hil l , a n d S . J . H a w k i n s . 1 9 9 6 . B i o l o g i c a l l y g e n e r a t e d hab i ta t p r o v i s i o n a n d d i v e r s i t y o f r o c k y s h o r e o r g a n i s m s at a h i e r a r c h y o f s p a t i a l s c a l e s . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 202:73-84. 3 8 Tilman, D., J . Knops, D. Wedin, P. Reich, M. Ritchie, and E. Siemann. 1997. The influence of functional diversity and composition on ecosystem processes. Science 277:1300-1302. Tilman, D., R. M. May, C. L. Lehman, and M. A. Nowak. 1994. Habitat destruction and the extinction debt. Nature 371:65-66. Underwood, A. J . 1997. Experiments in ecology: their logical design and interpretation using analysis of variance. Cambridge University Press, Cambridge. Walker, D. I., and G . A. Kendrick. 1998. Threats to macroalgal diversity: marine habitat destruction and fragmentation, pollution and introduced species. Botanica Marina 41:105-112. Wonham, M. J . , M. O'Connor, and C. D. G. Harley. 2005. Positive effects of a dominant invader on introduced and native mudflat species. Marine Ecology Progress Series 289:109-116. Zar, J . H. 1999. Biostatistical Analysis, 4th edition. Prentice Hall, Upper Saddle River, New Jersey, USA. 39 Chapter 3: A comparison of host taxonomic relatedness and functional-group affiliation as predictors of seaweed-invertebrate epifaunal associat ions. A ve r s i on of th is c h a p t e r wi l l be subm i t t ed to Marine Ecology Progress Series. 3.1 Introduction F o r s m a l l m o b i l e i n v e r t e b r a t e s , s e a w e e d s a r e a r e f u g e f r o m s t r e s s f u l c o n d i t i o n s a s s o c i a t e d wi th life o n r o c k y intert ida l s h o r e s . S e a w e e d p r o v i d e c o o l , we t , a n d p r o t e c t i v e c a n o p i e s a n d i n t e r s t i c e s ( H a y w a r d 1 9 8 0 , 1 9 8 8 ) a n d c a n a m e l i o r a t e the i n f l u e n c e of r a p i d c h a n g e s in t e m p e r a t u r e , u l t rav io let r a d i a t i o n , d e s i c c a t i o n , a n d h y d r o d y n a m i c f o r c e s c a u s e d b y t w i c e - d a i l y e m e r s i o n a n d i m m e r s i o n b y s e a w a t e r . A t h igh t i des , s e a w e e d s c a n a l s o of fer s h e l t e r f r o m p r e d a t i o n b y f i sh ( H o l m l u n d ef al. 1 9 9 0 , M a r t i n - S m i t h 1 9 9 3 , N o r d e r h a u g et al. 2 0 0 5 ) . M y r i a d i n v e r t e b r a t e t a x a u s e s e a w e e d s a s hab i ta t ( C o l m a n 1 9 3 9 ) , a n d in s o m e c a s e s a s a f o o d s o u r c e ( H a w k i n s a n d Har tno l l 1 9 8 3 , A r r o n t e s 1 9 9 9 ) . E p i f a u n a c o m p o s i t i o n , t a x o n r i c h n e s s , a n d a b u n d a n c e o f ten di f fer a c r o s s s p e c i e s o f h o s t s e a w e e d ( C o l m a n 1 9 3 9 , S e e d a n d O ' C o n n o r 1 9 8 1 , T a y l o r a n d C o l e 1 9 9 4 ) . In th is s t u d y , I e x p l o r e s e v e r a l g e n e r a l f r a m e w o r k s that h o l d p r o m i s e for p r e d i c t i n g s u c h p a t t e r n s o f i n v e r t e b r a t e b i o d i v e r s i t y b a s e d o n s e a w e e d traits. H a y w a r d ( 1 9 8 8 ) s t a t e d that it is c l e a r that d i s t r i b u t i o n s o f e p i f a u n a resu l t f r o m b e h a v i o r a l c h o i c e s b y i n v e r t e b r a t e s to f ind a n d r e m a i n in t h e hab i ta t m o s t s u i t a b l e . C r i t e r i a for e p i f a u n a h o s t c h o i c e i n c l u d e f a c t o r s in terna l to s e a w e e d s : m a t e r i a l p r o p e r t i e s s u c h a s ce l l s t r u c t u r e a n d ce l l wal l c o m p o n e n t s , e n e r g e t i c s t o r a g e p r o d u c t s a n d d e f e n s i v e b i o c h e m i s t r y ( H a y et al. 1 9 8 7 , G r a h a m a n d W i l c o x 2 0 0 0 , P a d i l l a a n d A l l e n 2 0 0 0 , V a n A l s t y n e a n d H o u s e r 2 0 0 3 ) . T h e s e p r o p e r t i e s c a n v a r y a c r o s s s e a w e e d s , r e s u l t i n g in d i f f e r e n c e s in nutrit ive v a l u e a n d pa la tab i l i t y ( P a i n e a n d V a d a s 1 9 6 9 , H a w k i n s a n d H a r t n o l l 1 9 8 3 ) . In a d d i t i o n to n e g a t i v e l y a c t i n g to d i rec t l y d e t e r e p i f a u n a ( H a y et al. 1 9 8 7 ) , a l g a l d e f e n s i v e b i o c h e m i s t r y c a n a c t p o s i t i v e l y , to p r o m o t e e p i f a u n a by c o n f e r r i n g a s s o c i a t i o n a l d e f e n s e s : e . g . u n p a l a t a b l e a l g a e a r e a v o i d e d b y o m n i v o r o u s f i s h e s , a n d e p i f a u n a t h e r e f o r e e s c a p e p r e d a t i o n ( H a y et al. 1 9 9 0 ) . A l o n g with t h e s e in te rna l s e a w e e d f e a t u r e s , e p i f a u n a a l s o s e l e c t s e a w e e d h o s t s b a s e d o n e x t e r n a l f e a t u r e s . A r c h i t e c t u r a l c o m p l e x i t y o f o v e r a l l s e a w e e d f o r m h a s w i d e l y b e e n l i n k e d to a b u n d a n c e a n d r i c h n e s s of i n v e r t e b r a t e s ( D e a n a n d C o n n e l l 1 9 8 7 a , G e e a n d W a r w i c k 1 9 9 4 , T a y l o r a n d C o l e 1 9 9 4 , D a v e n p o r t e f al. 1 9 9 6 , Hu l l 1 9 9 7 , C h e m e l l o a n d M i l a z z o 2 0 0 2 ) . C o m p a r e d to " s i m p l e " f o r m s s u c h a s u n b r a n c h e d b l a d e s a n d c r u s t s , " c o m p l e x " , h i g h l y b r a n c h i n g s e a w e e d s c a n bet ter p r o v i d e p r e d a t o r - f r e e s p a c e for 41 e p i f a u n a ( D u f f y a n d H a y 1 9 9 1 ) , s t a y m o i s t to limit d e s i c c a t i o n e f f e c t s (Ji a n d T a n a k a 2 0 0 2 ) , a n d p r o v i d e i n c r e a s e d s u r f a c e a r e a a n d m i c r o h a b i t a t v a r i e t y ( C h r i s t i e e f al. 2 0 0 3 , N o r d e r h a u g etal. 2 0 0 5 ) . A t p r e s e n t , s c i e n t i f i c p e r c e p t i o n a b o u t the qua l i t y o f d i f fe rent s e a w e e d s a s h o s t s for s m a l l m o b i l e e p i f a u n a a r e b a s e d o n a b o d y of s t u d i e s that c o m p a r e p e r f o r m a n c e of re la t ive ly f e w s e a w e e d s p e c i e s , t yp i ca l l y b e t w e e n two ( K r a u f v e l i n a n d S a l o v i u s 2 0 0 4 , W i k s t r o m a n d K a u t s k y 2 0 0 4 ) a n d s e v e n ( H o l m l u n d et al. 1 9 9 0 ) , but s o m e t i m e s u p to t e n ( T a y l o r a n d C o l e 1 9 9 4 , T a y l o r a n d S t e i n b e r g 2 0 0 5 ) . H o w e v e r , a k e y g o a l o f c o m m u n i t y e c o l o g y is to e s t a b l i s h g e n e r a l p r i n c i p l e s that d e s c r i b e h o w biot ic a n d ab io t i c f a c t o r s s t r u c t u r e b i o l o g i c a l a s s e m b l a g e s ( M a c A r t h u r 1 9 7 2 ) . T o a l l e v i a t e the n e e d to c o m p a r e t h e p e r f o r m a n c e o f p a r t i c u l a r a l g a l s p e c i e s a s h o s t s for e p i f a u n a , a m o r e g e n e r a l p r e d i c t i v e f r a m e w o r k is d e s i r a b l e . T h e o b j e c t i v e o f t h e c u r r e n t s t u d y is to c o m p a r e t w o s u c h g e n e r a l f r a m e w o r k s : s e a w e e d t a x o n o m i c r e l a t e d n e s s a n d s e a w e e d f u n c t i o n a l f o r m g r o u p i n g s . E c o l o g i s t s a r e i n c r e a s i n g l y r e c o g n i z i n g that t a x o n o m i c r e l a t i o n s h i p s b e t w e e n s p e c i e s c a n i n f o r m p r e d i c t i o n s a b o u t s p e c i e s p e r f o r m a n c e in a n e c o l o g i c a l c o n t e x t ( W e b b et al. 2 0 0 2 ) . S p e c i e s that a r e c l o s e l y r e l a t e d a r e m o r e l ikely to s h a r e traits (i .e. s imi lar i ty b y c o m m o n d e s c e n t ) , a n d t h u s p e r f o r m s i m i l a r l y in e c o l o g i c a l s c e n a r i o s . T a x o n o m i c r e l a t e d n e s s m a y i n f o r m p r e d i c t i o n s o f s e a w e e d - h o s t p e r f o r m a n c e b e c a u s e in terna l f e a t u r e s o f s e a w e e d s (mater ia l p r o p e r t i e s , nutr i t ive v a l u e , d e f e n s i v e c h e m i s t r y ) t e n d to b e c o n s e r v e d wi th in t a x o n o m i c l i n e a g e s . H o w e v e r , a p r o p e r t y that c o u l d c o n f o u n d t h e u s e o f s e a w e e d t a x o n o m i c r e l a t e d n e s s a s a p r e d i c t o r o f a s s o c i a t e d e p i f a u n a is tha t e x t e r n a l m o r p h o l o g y in s e a w e e d s c a n v a r y s e e m i n g l y i n d e p e n d e n t l y o f t a x o n o m i c aff inity. I n d e e d , s o m e g e n e r a s u c h a s Codium a n d Caulerpa c o n t a i n a w i d e a r r a y o f m o r p h o l o g i e s ( S i l v a 1 9 9 2 ) , w h i l e c o n v e r g e n t e v o l u t i o n h a s r e s u l t e d in s t r ik ing ly s i m i l a r f o r m s s h a r e d b y a l g a e c l a s s i f i e d a s d i s tant l y a s s u b k i n g d o m ( e . g . Ulva lactuca, a g r e e n a l g a f r o m S u b k i n g d o m V i r i d i p l a n t a e a n d Porphyra s p p . , r e d a l g a e f r o m the S u b k i n g d o m B i l i phy ta) a n d k i n g d o m ( e . g . Analipus japonicus, a b r o w n a l g a ( K i n g d o m C h r o m i s t a ) a n d Cumagloia andersonii, a r e d a l g a ( K i n g d o m P l a n t a e ) . T h i s s imi lar i ty in m o r p h o l o g y a c r o s s t a x o n o m i c g r o u p i n g s h a s b e e n f o r m a l l y r e c o g n i z e d s i n c e the e a r l y 1 9 8 0 ' s , a n d l ed to t h e p r o p o s a l o f m o r p h o l o g i c a l l y b a s e d " func t i ona l f o r m " g r o u p i n g s u n d e r w h i c h p r e d i c t i o n s o f e c o l o g i c a l a n d e c o p h y s i o l o g i c a l p e r f o r m a n c e o f s e a w e e d s c o u l d b e m a d e (Litt ler a n d Litt ler 1 9 8 0 , S t e n e c k a n d W a t l i n g 1 9 8 2 , S t e n e c k a n d D e t h i e r 4 2 1 9 9 4 ) . T h e u s e of te r res t r ia l p lant f u n c t i o n a l g r o u p s h a s a l s o b e c o m e c o m m o n in r e c e n t t i m e s ( L a v o r e l et al. 1 9 9 7 , D i a z a n d C a b i d o 2 0 0 1 ) . In a r e c e n t r e v i e w of the p e r f o r m a n c e o f a l g a l f u n c t i o n a l g r o u p s , P a d i l l a a n d A l l e n ( 2 0 0 0 ) w e r e cr i t ica l o f p r e v i o u s a p p l i c a t i o n s o f s e a w e e d f u n c t i o n a l f o r m m o d e l s , h i g h l i g h t i n g a l a c k o f e m p i r i c a l s u p p o r t for m o s t o f t h e m o d e l p r e d i c t i o n s d e s p i t e w i d e s p r e a d a c c e p t a n c e o f the i r u s e . T h e y d id , h o w e v e r , m a k e a po in t o f s u g g e s t i n g the p r o m i s e o f f u n c t i o n a l f o r m g r o u p i n g s for p r e d i c t i n g s t r u c t u r e o f hab i ta t for a s s o c i a t e d o r g a n i s m s . T h i s i d e a r e m a i n s u n t e s t e d , a l t h o u g h s e e H a c k e r a n d S t e n e c k ( 1 9 9 0 ) w h o d i s c u s s e d s e v e r a l h a b i t a t - p r o v i d i n g a l g a l s p e c i e s b a s e d o n the i r f u n c t i o n a l g r o u p p l a c e m e n t . I n h e r e n t in t h e c o n c e p t o f u s i n g f u n c t i o n a l g r o u p i n g s to p r e d i c t e c o l o g i c a l o r e c o p h y s i o l o g i c a l p r o p e r t i e s is the i d e a that s p e c i e s g r o u p e d t o g e t h e r will p e r f o r m s imi la r ly . T h i s p r e m i s e h a s b e e n d i s c u s s e d in t e r m s of ' f u n c t i o n a l r e d u n d a n c y ' ( N a e e m 1 9 9 8 , F o n s e c a a n d G a n a d e 2 0 0 1 , R o s e n f e l d 2 0 0 2 , L o r e a u 2 0 0 4 ) . T h i s c o n c e p t is r e l e v a n t to d i s c u s s i o n s a b o u t the c o n s e q u e n c e s o f c h a n g e s in b i o d i v e r s i t y b e c a u s e l o s s of p a r t i c u l a r s p e c i e s c o u l d b e c o m p e n s a t e d for b y f u n c t i o n a l l y e q u i v a l e n t c o e x i s t i n g s p e c i e s . T h i s b u f f e r i n g c a p a c i t y o f s p e c i e s r ich a s s e m b l a g e s h a s b e e n v i e w e d a s a f o r m of " b i o l o g i c a l i n s u r a n c e " ( T h e b a u l t a n d L o r e a u 2 0 0 6 ) ; h o w e v e r , to d a t e , d i rec t t e s t s of the f u n c t i o n a l e q u i v a l e n c e o f s e a w e e d s a s h o s t s for i n v e r t e b r a t e s a r e l imi ted to c o m p a r i s o n s o f o n l y t w o s e a w e e d t a x a s u c h a s Cladophora glomerata a n d Fucus vesiculosus ( K r a u f v e l i n a n d S a l o v i u s 2 0 0 4 ) . T o tes t t he e f f i c a c y o f s e a w e e d t a x o n o m i c r e l a t e d n e s s a n d f u n c t i o n a l g r o u p affinity a s p r e d i c t o r s o f s e a w e e d - i n v e r t e b r a t e e p i f a u n a a s s o c i a t i o n s , I a s k t h r e e q u e s t i o n s : a ) is s imi lar i ty o f i n v e r t e b r a t e a s s e m b l a g e s p o s i t i v e l y c o r r e l a t e d with a l g a l h o s t t a x o n o m i c r e l a t e d n e s s ; b) d o e s i n v e r t e b r a t e a s s e m b l a g e s t r u c t u r e d i f fer a c r o s s s e a w e e d f u n c t i o n a l g r o u p s ; a n d c) is the p e r f o r m a n c e o f s e a w e e d s p e c i e s a s hab i ta t for s m a l l m o b i l e i n v e r t e b r a t e s s i m i l a r with in a l g a l f u n c t i o n a l g r o u p s ? 4 3 3.2. Materials and methods 3.2.1 Study Sites C o l l e c t i o n s of h o s t a l g a e a n d a s s o c i a t e d i n v e r t e b r a t e s w e r e t a k e n at s ix r o c k y intert idal s i t e s a l o n g s o u t h e r n B a r k l e y S o u n d , Br i t i sh C o l u m b i a , C a n a d a ( F i g u r e 1.3). E a c h s i te w a s s a m p l e d o n c e p e r m o n t h o v e r e l e v e n m o n t h s ( M a r c h 2 0 0 5 - J a n u a r y 2 0 0 6 ) d u r i n g s p r i n g t i d e s . 3.2.2 Sample collections A t e a c h s a m p l i n g e v e n t (site p e r d a t e ) , r e p r e s e n t a t i v e s o f t h r e e to s e v e n a l g a l s p e c i e s w e r e h a p h a z a r d l y c o l l e c t e d a l o n g a h o r i z o n t a l belt t r a n s e c t that m e a s u r e d 1 m x 3 0 m, c e n t r e d at 1 m a b o v e c h a r t d a t u m . I s a m p l e d e i g h t i n d i v i d u a l thall i p e r a lga l s p e c i e s , a n d e a c h t h a l l u s w a s s e a l e d in a z i p p e r e d c o l l e c t i o n b a g . A l g a l s p e c i e s w e r e s e l e c t e d if t h e y w e r e a b u n d a n t at the s i te, a n d a l s o to m a x i m i z e t a x o n o m i c a n d f u n c t i o n a l r e p r e s e n t a t i o n wi th in t h e o v e r a l l d a t a se t . In tota l , 1 6 5 2 a l g a l thall i w e r e c o l l e c t e d a c r o s s 3 2 a l g a l s p e c i e s ( T a b l e 3.1) . S a m p l e s w e r e f r o z e n to e u t h a n i z e e p i f a u n a b e f o r e p r o c e s s i n g , a n d t h e n p r o c e s s e d a s d e s c r i b e d in s e c t i o n 2 .2 .6 . 3.2.3 Algal taxonomy & taxonomic distance T a x o n o m i c a f f i l ia t ions of the 3 2 i n c l u d e d s p e c i e s o f h o s t a l g a e ( T a b l e 3 .1) w e r e o b t a i n e d f r o m G a b r i e l s o n et al. ( 2 0 0 6 ) . T a x o n o m i c r a n k s r a n g e d f r o m s p e c i f i c e p i t h e t s to K i n g d o m . T a x o n o m i c d i s t a n c e b e t w e e n s e a w e e d h o s t s w a s c a l c u l a t e d b y c o u n t i n g the n u m b e r of " s t e p s " t h r o u g h a d e n d r o g r a m of the L i n n a e a n t a x o n o m i c h i e r a r c h y ( F i g u r e 3 .1) . F o r s e v e r a l t a x o n o m i c r a n k s (T r ibe , S u b f a m i l y , S u b p h y l u m , I n f r a k i n g d o m , a n d S u b k i n g d o m ) t h e r e w a s a) o n l y o n e t a x o n in th is d a t a s e t c l a s s i f i e d to th is l eve l ( e . g . T r i b e C e r a m i a e ) , o r b) l a c k of mul t ip le s u b c l a d e s at that r a n k ( e . g . S u b k i n g d o m ) . T h e s e r a n k s w e r e not i n c l u d e d in c a l c u l a t i o n s of t a x o n o m i c d i s t a n c e . 44 3.2.4 Algal functional groups A l t h o u g h s e v e r a l s e a w e e d f u n c t i o n a l g r o u p c l a s s i f i c a t i o n s ex i s t (Littler a n d Littler 1 9 8 0 , S t e n e c k a n d W a t l i n g 1 9 8 2 , S t e n e c k a n d D e t h i e r 1 9 9 4 ) , t h e g r o u p i n g s a r e v e r y s imi la r . I c h o s e to u s e t h e a l g a l f u n c t i o n a l g r o u p s e r e c t e d b y S t e n e c k a n d D e t h i e r ( 1 9 9 4 ) b e c a u s e t h e y i n c l u d e d e i g h t g r o u p s c o m p a r e d to t h e o t h e r t w o m o d e l s , w h i c h u s e d s ix . B a s e d o n s imi lar i ty in g r o s s m o r p h o l o g y , S t e n e c k a n d D e t h i e r g r o u p e d a l g a e into m i c r o a l g a e , f i l a m e n t o u s , f o l i o s e , c o r t i c a t e d f o l i o s e , c o r t i c a t e d t e r e t e , l e a t h e r y , g e n i c u l a t e c a l c a r e o u s , a n d c r u s t o s e . I u s e s e v e n o f t h e s e g r o u p s ( m i c r o a l g a e a r e not c o n s i d e r e d ) , a n d f u n c t i o n a l g r o u p aff i l iat ion of e a c h s p e c i e s is l i s ted in T a b l e 3 .1 . 3.2.5 Statistical analysis Al l i n v e r t e b r a t e a b u n d a n c e s w e r e four th - root t r a n s f o r m e d b e f o r e mu l t i va r i a te a n a l y s e s to d o w n w e i g h t t h e c o n t r i b u t i o n of h i g h l y a b u n d a n t i n v e r t e b r a t e s p e c i e s to m e a s u r e s o f s a m p l e s imi lar i ty ( C l a r k e 1 9 9 3 ) . 3.2.5.1 Taxonomic distance analyses P a i r w i s e c o m p a r i s o n s of i n v e r t e b r a t e a s s e m b l a g e s imi la r i ty b e t w e e n a l g a l thalli w e r e c a l c u l a t e d u s i n g t h e B r a y - C u r t i s s imi lar i ty m e a s u r e ( B r a y a n d C u r t i s 1 9 5 7 ) . A n a l y s i s o f S i m i l a r i t i e s ( A N O S I M ; C l a r k e 1 9 9 3 ) w a s u s e d to a s s e s s t h e d e g r e e of i n v e r t e b r a t e a s s e m b l a g e s imi lar i ty b e t w e e n h o s t s p e c i e s . T h e A N O S I M test s tat is t ic (R) r a n g e s b e t w e e n - 1 a n d 1, with v a l u e s c l o s e to z e r o i n d i c a t i n g n o d i f f e r e n c e b e t w e e n s a m p l e g r o u p s . V a l u e s c l o s e r to 1 i n d i c a t e a g r e a t e r d i f f e r e n c e b e t w e e n g r o u p s t h a n with in g r o u p s , w h e r e a s v a l u e s c l o s e r to - 1 i n d i c a t e a g r e a t e r d i f f e r e n c e wi th in g r o u p s t h a n b e t w e e n g r o u p s . T h e r e s u l t a n t R - v a l u e s w e r e t h e n p lo t ted a g a i n s t t a x o n o m i c d i s t a n c e of the t w o h o s t s b e i n g c o m p a r e d . T h e R - v a l u e s w e r e not n o r m a l l y d i s t r i b u t e d but e x h i b i t e d h o m o g e n e o u s v a r i a n c e s (Bart lett 's test , F = 0 . 4 7 p = 0 . 8 6 ) , s o the n o n p a r a m e t r i c W i l c o x o n s i g n e d - r a n k s p r o c e d u r e w a s u s e d to tes t for d i f f e r e n c e s in i n v e r t e b r a t e a s s e m b l a g e s imi lar i ty a m o n g t a x o n o m i c l e v e l s . 4 5 3.2.5.2 Functional group analyses A c r o s s a l g a l f u n c t i o n a l g r o u p s , I u s e d A N O S I M to tes t for d i f f e r e n c e s in c o m p o s i t i o n o f i n v e r t e b r a t e a s s e m b l a g e s a n d A N O V A to tes t for d i f f e r e n c e s in i n v e r t e b r a t e a b u n d a n c e s a n d t a x o n r i c h n e s s . T o c o n t r o l for r i c h n e s s d i f f e r e n c e s c a u s e d by d i f f e r e n c e s in i n v e r t e b r a t e a b u n d a n c e , I r a r e f i e d s p e c i e s r i c h n e s s to 2 0 i n d i v i d u a l s ( M a g u r r a n 1 9 8 8 ) . I u s e d the m e a n of e a c h a l g a l s p e c i e s to r e p l i c a t e wi th in f u n c t i o n a l g r o u p , a n d , b e c a u s e v a l u e s of i n v e r t e b r a t e a b u n d a n c e a n d r a r e f i e d r i c h n e s s v i o l a t e d a s s u m p t i o n s of n o r m a l i t y a n d h o m o g e n e i t y of v a r i a n c e , I u s e d M o n t e C a r l o r a n d o m i z a t i o n p r o c e d u r e s ( M a n l y 1 9 9 1 ) to d e t e r m i n e t h e l e v e l o f s i g n i f i c a n c e of d i f f e r e n c e s a c r o s s f u n c t i o n a l g r o u p s . S p e c i f i c a l l y , ident i ty of a l g a l s p e c i e s w a s s h u f f l e d a c r o s s f u n c t i o n a l g r o u p s , a n d the o r ig ina l F -s tat is t i c w a s c o m p a r e d to a null d i s t r ibut ion of F -s ta t i s t i cs c r e a t e d t h r o u g h 4 9 9 9 of t h e s e r a n d o m i z e d p e r m u t a t i o n s . W i t h i n f u n c t i o n a l g r o u p s , I u s e d A N O S I M to tes t a c r o s s a l g a l s p e c i e s for d i f f e r e n c e s in i n v e r t e b r a t e a s s e m b l a g e s . T o test for d i f f e r e n c e s in v a l u e s o f i n v e r t e b r a t e a b u n d a n c e a n d r a r e f i e d r i c h n e s s , M o n t e C a r l o r a n d o m i z a t i o n p r o c e d u r e s ( M a n l y 1 9 9 1 ) w e r e a g a i n u s e d to tes t for b e t w e e n - s p e c i e s d i f f e r e n c e s . S p e c i f i c a l l y I t e s t e d if, for e a c h s p e c i e s c o m p a r i s o n , M e a n s p e c i e s x - M e a n species Y ( w h e r e (X, Y ) r e p r e s e n t all p a i r w i s e c o m b i n a t i o n s of s p e c i e s with in f u n c t i o n a l g r o u p s ) , d i f f e r e d s i g n i f i c a n t l y f r o m a null d i s t r ibut ion c r e a t e d t h r o u g h 4 9 9 9 r a n d o m i z a t i o n s (with r e p l a c e m e n t ) of t h e v a l u e s for bo th g r o u p s . M u l t i v a r i a t e r e s u l t s a n d t a x o n o m i c d i s t a n c e s w e r e o b t a i n e d u s i n g P R I M E R s o f t w a r e ( V e r s i o n . 6 .1 .6 , P r i m e r - E , w w w . p r i m e r - e . o r g ) . P a r a m e t r i c u n i v a r i a t e a n a l y s e s w e r e p e r f o r m e d u s i n g J M P i n ( V e r s i o n 4 .0 .4 , S A S Institute Inc.), a n d r a n d o m i z a t i o n p r o c e d u r e s w e r e a c h i e v e d u s i n g P o p T o o l s ( H o o d 2 0 0 6 ) . 3.3 Results 3.3.1 General results A total o f 5 4 , 7 7 6 i n d i v i d u a l s w e r e s a m p l e d a c r o s s 9 8 t a x a o f m o b i l e i n v e r t e b r a t e e p i f a u n a . T h e ma jo r i t y of t h e s e i n d i v i d u a l s c a m e f r o m a s m a l l n u m b e r of h i g h e r t a x a , 4 6 i n c l u d i n g g a m m a r i d a m p h i p o d s ( 4 7 . 9 % ) , h a r p a c t i c o i d a n d c a l a n o i d c o p e p o d s ( 1 8 . 4 % ) , j u v e n i l e b i v a l v e m o l l u s k s ( 1 2 . 2 % ) , g a s t r o p o d m o l l u s k s (5 .0 % ) , i s o p o d s (4 .0 % ) , m i t e s (3.6 % ) , p o l y c h a e t e w o r m s (2 .8 %) a n d n e m a t o d e s (2 .2 % ) . 3.3 .2 Algal taxonomic distance S im i l a r i t y o f i n v e r t e b r a t e a s s e m b l a g e s d id not d e c r e a s e a s t a x o n o m i c d i s t a n c e s b e t w e e n s e a w e e d h o s t s i n c r e a s e d ; i n v e r t e b r a t e a s s e m b l a g e s w e r e a s s i m i l a r b e t w e e n c o n g e n e r i c a l g a l h o s t s a s b e t w e e n a l g a l s p e c i e s in d i f fe rent k i n g d o m s ( W i l c o x o n , C h i - S q u a r e = 6 . 9 3 , d f = 7, p = 0 .44 ; F i g u r e 3 .2) . 3.3 .3 Across algal functional groups I n v e r t e b r a t e a s s e m b l a g e s w e r e d i f ferent a c r o s s m o s t a l g a l f u n c t i o n a l g r o u p s ( A N O S I M R = 0 . 2 0 9 , p < 0 . 0 0 1 ; T a b l e 3.2) . H o w e v e r , g e n i c u l a t e c o r a l l i n e a l g a e h a d s i m i l a r i n v e r t e b r a t e c o m p o s i t i o n to l e a t h e r y , c o r t i c a t e d t e r e t e , c o r t i c a t e d f o l i o s e , a n d f o l i o s e f u n c t i o n a l g r o u p s . A s w e l l , c r u s t o s e a n d c o r t i c a t e d f o l i o s e f u n c t i o n a l g r o u p s h a r b o r e d s i m i l a r l y s p a r s e a s s e m b l a g e s . I n v e r t e b r a t e t a x o n r i c h n e s s w a s d i f ferent a c r o s s s o m e , but not al l , a l g a l f u n c t i o n a l g r o u p s (p < 0 . 0 0 2 , F i g u r e 3 .3, u p p e r p a n e l ) . T h e f i l a m e n t o u s , f o l i o s e , c o r t i c a t e d f o l i o s e , a n d c o r t i c a t e d t e r e t e f u n c t i o n a l g r o u p s w e r e not d i f fe rent (p > 0 .05) . T h e c r u s t o s e g r o u p w a s d i f fe rent b e c a u s e it h a d f ew , if a n y , t a x a a s s o c i a t e d with it, a n d the l e a t h e r y a n d g e n i c u l a t e c o r a l l i n e f u n c t i o n a l g r o u p s w e r e not d i f f e ren t f r o m e i ther the f o r m e r o r t h e latter s e t of f u n c t i o n a l g r o u p s . N o d i f f e r e n c e s a c r o s s a l g a l f u n c t i o n a l g r o u p s w e r e n o t e d for a b u n d a n c e of i n v e r t e b r a t e s ( F i g u r e 3 .3 , l o w e r p a n e l ) , a l t h o u g h t h e r e s u l t s w e r e m a r g i n a l l y n o n s i g n i f i c a n t (p = 0 . 0 8 1 ) . 3 .3 .4 Within algal functional groups T h e r e w a s little e v i d e n c e to s u p p o r t the p r e d i c t i o n that a l g a l s p e c i e s wi th in the s a m e f u n c t i o n a l g r o u p w e r e f u n c t i o n a l l y e q u i v a l e n t . C o m p o s i t i o n o f i n v e r t e b r a t e 4 7 a s s e m b l a g e s ( T a b l e 3 .3) w a s d i f fe rent for m o s t p a i r w i s e c o m p a r i s o n wi th in m o s t o f the f u n c t i o n a l g r o u p s . O n l y f i ve ou t o f 2 8 p o s s i b l e p a i r w i s e c o m p a r i s o n s w e r e n o n s i g n i f i c a n t in the f i l a m e n t o u s f u n c t i o n a l g r o u p . T h e c o r t i c a t e d f o l i o s e g r o u p s h o w e d o n e n o n s i g n i f i c a n t resu l t o u t o f t e n , c o r t i c a t e d te re te s h o w e d o n e ou t o f 3 6 , l e a t h e r y s h o w e d o n e out o f s ix . W i t h i n t h e f o l i o s e g r o u p a n d t h e g e n i c u l a t e c o r a l l i n e g r o u p s , all o f t h e s p e c i e s h a d d i f f e ren t i n v e r t e b r a t e a s s e m b l a g e s , w h e r e a s in t h e c r u s t o s e g r o u p , the t w o s p e c i e s h a d t h e s a m e t y p e o f a s s e m b l a g e . F o r r a r e f i e d i n v e r t e b r a t e t a x o n r i c h n e s s a n d i n v e r t e b r a t e a b u n d a n c e ( F i g u r e 3 .4) , m o s t a l g a l s p e c i e s h a d a m e a n r i c h n e s s a n d a b u n d a n c e that d i f f e r e d f r o m the f u n c t i o n a l g r o u p m e a n (p < 0 . 0 5 ) . N o t a b l e e x c e p t i o n s i n c l u d e t h e f i l a m e n t o u s g r o u p for w h i c h r a r e f i e d i n v e r t e b r a t e r i c h n e s s w a s c o n s i s t e n t with t h e f u n c t i o n a l g r o u p m e a n for m o s t t a x a , a l t h o u g h Polysiphonia senticulosa a n d Rhizoclonium riparium w e r e , r e s p e c t i v e l y , w e l l b e l o w a n d a b o v e t h e f i l a m e n t o u s g r o u p m e a n . H o w e v e r , d e s p i t e th is re la t ive c o n s i s t e n c y in t a x o n r i c h n e s s , i n v e r t e b r a t e a b u n d a n c e w a s v a r i a b l e a c r o s s the f i l a m e n t o u s g r o u p . R a r e f i e d r i c h n e s s a n d c o m p o s i t i o n w e r e t h e s a m e for s p e c i e s with in the c o r a l l i n e a n d c r u s t o s e g r o u p s ; h o w e v e r o n l y two s p e c i e s w e r e r e p r e s e n t e d in e a c h f u n c t i o n a l g r o u p . 3.4 Discussion 3.4.1 Taxonomic relatedness of seaweed host K n o w l e d g e o f t h e i n f l u e n c e o f h o s t r e l a t e d n e s s o n a s s o c i a t e d f a u n a is potent ia l l y i m p o r t a n t to t h e e s t i m a t i o n o f g l o b a l s p e c i e s d i v e r s i t y ( O d e g a a r d et al. 2 0 0 5 ) , for p r e d i c t i n g t h e e c o l o g i c a l p e r f o r m a n c e o f h o s t s p e c i e s , a n d u n d e r s t a n d i n g c o m m u n i t y a s s e m b l y . H o w e v e r , a l t h o u g h s e v e r a l r e c e n t s t u d i e s e x a m i n e t h e i n f l u e n c e o f g e n e t i c d i ve rs i t y o n a s s o c i a t e d m a r i n e i n v e r t e b r a t e s with in s i n g l e h o s t s p e c i e s ( H u g h e s a n d S t a c h o w i c z 2 0 0 4 , J o h n s o n e f al. 2 0 0 6 ) , c r o s s - s p e c i e s t e s t s o f l i n k a g e s b e t w e e n h o s t p lant r e l a t e d n e s s a n d a s s o c i a t e d f a u n a a r e not c o m m o n (Fa r re l l a n d Mi t ter 1 9 9 0 , L o s o s 1 9 9 6 , K e l l y a n d S o u t h w o o d 1 9 9 9 , O d e g a a r d etal. 2 0 0 5 , W e i b l e n etal. 2 0 0 6 ) . T h e resu l t s of t h e c u r r e n t s t u d y s h o w that s e a w e e d h o s t t a x o n o m i c r e l a t e d n e s s d o e s not in fo rm p r e d i c t i o n s a b o u t d i f f e r e n c e s in d ive rs i t y o f a s s o c i a t e d s m a l l m o b i l e 4 8 i n v e r t e b r a t e s . I f o u n d that m o b i l e i n v e r t e b r a t e a s s e m b l a g e s w e r e a s d i f fe rent o n s ib l i ng a lga l s p e c i e s a s o n h o s t s c l a s s i f i e d in d i f fe rent k i n g d o m s ( F i g u r e 3 .2) . W h e r e h o s t r e l a t e d n e s s o f terrestr ia l p l a n t s h a s b e e n i n v e s t i g a t e d a s a p r e d i c t o r of d i ve rs i t y o f a s s o c i a t e d p h y t o p h a g o u s i n s e c t s , s o m e p r e d i c t i v e v a l u e o f h o s t t a x o n o m i c r e l a t e d n e s s h a s b e e n d e m o n s t r a t e d . Insec t a s s e m b l a g e s a r e m o r e s i m i l a r o n p lant h o s t s f r o m t h e s a m e g e n u s a n d fami ly , but no t at h i g h e r t a x o n o m i c d i s t a n c e s ( 0 d e g a a r d et al. 2 0 0 5 , W e i b l e n et al. 2 0 0 6 ) , a n d h o s t s p e c i f i c i t y is i n v o k e d a s a n e x p l a n a t i o n for th is r e l a t i o n s h i p . C o n g r u e n c e in p a t t e r n s o f d i v e r s i f i c a t i o n b e t w e e n h o s t a n d h e r b i v o r e c l a d e s i n d i c a t e that s p e c i a l i z a t i o n c o u l d b e a resu l t o f c o e v o l u t i o n b e t w e e n h o s t p l a n t s a n d s p e c i a l i s t f e e d e r s (Far re l l a n d Mit ter 1 9 9 0 ) . T h e r e l a t i o n s h i p b e t w e e n h o s t p h y l o g e n y a n d p h y t o p h a g o u s i n s e c t s m a k e s s e n s e b e c a u s e h e r b i v o r o u s i n s e c t s p r e f e r c l o s e l y r e l a t e d p l a n t s that a r e s i m i l a r in c h e m i s t r y a n d r e s o u r c e p r o v i s i o n . In the m a r i n e s y s t e m e x a m i n e d in the c u r r e n t s t u d y , th is is not t h e c a s e ; m a n y s e a w e e d e p i f a u n a d o not c o n s u m e the i r h o s t ( A r r o n t e s 1 9 9 9 ) , a n d t h e r e f o r e t e n d to b e m o r e g e n e r a l in the i r h o s t u s e p a t t e r n s . A s s u g g e s t e d in the i n t r o d u c t i o n to this c h a p t e r , m a r i n e i n v e r t e b r a t e e p i f a u n a s e l e c t s e a w e e d h o s t s b a s e d o n in te rna l a n d e x t e r n a l f e a t u r e s , y e t s e a w e e d f o r m h a s b e e n s h o w n to b e a s t r o n g e r r e g u l a t o r o f i n v e r t e b r a t e e p i f a u n a t h a n pa la tab i l i t y o r d e f e n s i v e c h e m i s t r y ( D e a n a n d C o n n e l l 1 9 8 7 a , N o r d e r h a u g 2 0 0 4 ) . It is t h e r e f o r e not s u r p r i s i n g that s e a w e e d t a x o n o m i c r e l a t e d n e s s w a s not c o n g r u e n t with o b s e r v e d p a t t e r n s o f a s s o c i a t e d i n v e r t e b r a t e s . A d d i t i o n a l s u p p o r t for t h e lack o f i n f l u e n c e o f h o s t t a x o n o m i c r e l a t e d n e s s o n a s s o c i a t e d i n v e r t e b r a t e s is p r o v i d e d by the o b s e r v a t i o n that a s i n g l e s p e c i e s exh ib i t ing a n a l t e r n a t i o n o f h e t e r o m o r p h i c g e n e r a t i o n s , Mastocarpus papillatus, s h o w s that e v e n wi th in t h e s a m e s p e c i e s , f u n c t i o n a l l y d i f fe rent f o r m s s u p p o r t d i f ferent i n v e r t e b r a t e a s s e m b l a g e s ( F i g u r e 3 .4) . It is i m p o r t a n t to n o t e that s e a w e e d t a x o n o m y is c u r r e n t l y in flux, a n d e v e n m a j o r g r o u p s l ike t h e R h o d o p h y t a a r e s u b j e c t to s u b s t a n t i a l h i g h e r - l e v e l t a x o n o m i c r e a r r a n g e m e n t ( S a u n d e r s a n d H o m m e r s a n d 2 0 0 4 ) . F u r t h e r m o r e , g e n e t i c d i s t a n c e s b e t w e e n s e a w e e d t a x a c l a s s i f i e d to the s a m e t a x o n o m i c r a n k s a r e not a l w a y s e q u a l . H o w e v e r , g i v e n t h e o f t e n - d e m o n s t r a t e d l i n k a g e s b e t w e e n a l g a l h o s t m o r p h o l o g y a n d i n v e r t e b r a t e d i v e r s i t y ( M a r t i n - S m i t h 1 9 9 3 , D a v e n p o r t etal. 1 9 9 6 , Attrill etal. 1 9 9 9 , D a v e n p o r t et al. 1 9 9 9 , M c A b e n d r o t h ef al. 2 0 0 5 ) , it is u n l i k e l y that m y c o n c l u s i o n s w o u l d c h a n g e g i v e n a r e v i s e d a l g a l t a x o n o m y . 4 9 3.4.2 Seaweed functional groups D i f f e r e n c e s w e r e o b s e r v e d a c r o s s s e v e r a l a l g a l f u n c t i o n a l (i .e. m o r p h o l o g i c a l ) g r o u p s for i n v e r t e b r a t e c o m p o s i t i o n , y e t f e w e r b e t w e e n - g r o u p d i f f e r e n c e s w e r e n o t e d for n u m b e r of i n v e r t e b r a t e t a x a a n d n o d i f f e r e n c e s w e r e s e e n for i n v e r t e b r a t e a b u n d a n c e ( T a b l e 3.2, F i g u r e 3 .3) . M o r p h o l o g i c a l l y b a s e d a l g a l f u n c t i o n a l g r o u p s h a v e h a d v a r i a b l e s u c c e s s for p r e d i c t i n g s e a w e e d - i n v e r t e b r a t e i n t e r a c t i o n s ( H a w k i n s a n d Har tno l l 1 9 8 3 , A r r o n t e s 1 9 9 0 , D u f f y a n d H a y 1 9 9 1 , W a k e f i e l d a n d M u r r a y 1 9 9 8 ) , a n d P a d i l l a a n d A l l e n ' s ( 2 0 0 0 ) s u g g e s t i o n that a l g a l f u n c t i o n a l f o r m g r o u p s c o u l d b e a p p l i e d to hab i ta t p r o v i s i o n w a s not we l l s u p p o r t e d h e r e . O b s e r v a t i o n s of i n v e r t e b r a t e r i c h n e s s a c r o s s f u n c t i o n a l g r o u p s t e n d , o n a v e r a g e , to fo l low c o m m o n p e r c e p t i o n s a b o u t r e l a t i o n s h i p s b e t w e e n a l g a l t h a l l u s c o m p l e x i t y a n d i n v e r t e b r a t e d i ve rs i t y . S p e c i f i c a l l y , the c o m p l e x l y b r a n c h i n g f i l a m e n t o u s a n d c o r t i c a t e d t e r e t e f u n c t i o n a l g r o u p s t e n d e d to h a v e t h e m o s t a s s o c i a t e d i n v e r t e b r a t e s , w h e r e a s s i m p l e g r o u p s ( i .e. flat b l a d e s f r o m the c o r t i c a t e d f o l i o s e a n d l e a t h e r y g r o u p s , a n d c r u s t o s e g r o u p s ) t e n d e d to h a v e the l eas t ( F i g u r e 3 .3) . H o w e v e r , t h e r e w a s s u b s t a n t i a l v a r i a t i o n wi th in f u n c t i o n a l g r o u p s ( F i g u r e 3.4), s u g g e s t i n g that f u n c t i o n a l g r o u p p e r f o r m a n c e a c t u a l l y i n d i c a t e s little a b o u t the p e r f o r m a n c e o f t h e c o n s t i t u e n t s p e c i e s . H a y ( 1 9 9 4 ) s u g g e s t e d that if, in g e n e r a l , e c o l o g i c a l l y m e a n i n g f u l s e a w e e d f u n c t i o n a l g r o u p s c o u l d b e e r e c t e d , t h e s e p a t t e r n s o f s imi lar i ty c o u l d t h e n l e a d natura l l y to d i s c u s s i o n s of s p e c i e s d i f f e r e n c e s . H o w e v e r , b a s e d o n m y o b s e r v a t i o n s a c r o s s a l a r g e n u m b e r of s p e c i e s , it a p p e a r s that i n v e r t e b r a t e s e l e c t i o n o f s e a w e e d h o s t is l a rge ly d e p e n d a n t u p o n t h e ident i ty of the h o s t s p e c i e s , no t t h e f u n c t i o n a l g r o u p . W h i l e t h e r e is n o q u e s t i o n that a l g a l m o r p h o l o g y i n f l u e n c e s d i v e r s i t y o f a s s o c i a t e d i n v e r t e b r a t e s , it a p p e a r s that the r e l a t i o n s h i p b e t w e e n h o s t m o r p h o l o g y a n d i n v e r t e b r a t e a s s e m b l a g e s is not s t r a i g h t f o r w a r d (i .e. i n c r e a s e d a r c h i t e c t u r a l c o m p l e x i t y d o e s not d i rec t ly l e a d to h i g h e r d i v e r s i t y of a s s o c i a t e d i n v e r t e b r a t e s ) , a p h e n o m e n o n that is not u n c o m m o n w h e n c o n s i d e r i n g q u e s t i o n s of f u n c t i o n a l m o r p h o l o g y ( K o e h l 1 9 9 6 ) . S e v e r a l p o s s i b l e e x p l a n a t i o n s ex i s t to e x p l a i n the v a r i a b l e p e r f o r m a n c e of h o s t s p e c i e s with in a l g a l f u n c t i o n a l g r o u p s . F i rst , o n c e i n v e r t e b r a t e s c h o o s e a h o s t b a s e d o n g r o s s m o r p h o l o g y , h o s t s e l e c t i o n d e c i s i o n s m a y b e r e f i n e d b a s e d o n in terna l f e a t u r e s o f s e a w e e d s . W h i l e I h a v e not d i rec t l y t e s t e d a n y in terna l v a r i a b l e s h e r e , I d o s h o w that c o m p l e x l y b r a n c h i n g 5 0 a l g a e with v e r y s i m i l a r e x t e r n a l f e a t u r e s c a n h o s t d i f fe rent i n v e r t e b r a t e a s s e m b l a g e s . F o r e x a m p l e , s p e c i e s wi th in f i l a m e n t o u s a n d c o r t i c a t e d t e r e t e g r o u p s ( F i g u r e 3.4) , a n d e v e n c o n g e n e r i c a l g a e with v e r y s i m i l a r f o r m s ( e . g . Acrosiphonia coalita v e r s u s Acrosiphonia arcta) h a v e a v e r y d i f fe rent n u m b e r o f a s s o c i a t e d i n v e r t e b r a t e s . T h i s latter resu l t is s i m i l a r to o b s e r v a t i o n s that the i n v a s i v e s p e c i e s Fucus evanescens C . A g . is ut i l ized l e s s b y e p i f a u n a t h a n t h e n a t i v e c o n g e n e r Fucus vesiculosus L. a l o n g E u r o p e a n c o a s t s ( W i k s t r o m a n d K a u t s k y 2 0 0 4 ) . T h e s e t y p e s o f o b s e r v a t i o n s d r a w into q u e s t i o n e v e n the u s e of s e a w e e d a r c h i t e c t u r a l c o m p l e x i t y a s a p r e d i c t o r o f a s s o c i a t e d i n v e r t e b r a t e s ; th is o f t e n - c i t e d r e g u l a t o r o f s e a w e e d - e p i f a u n a a s s o c i a t i o n s d o e s not a p p e a r to b e w h o l l y r e l i a b l e c r i te r ion for g e n e r a l i z a t i o n . S e c o n d , s e a w e e d f u n c t i o n a l g r o u p s a r e t rad i t iona l ly d e l i n e a t e d b a s e d o n m o r p h o l o g i c a l f e a t u r e s o f i n d i v i d u a l thalli ( S t e n e c k a n d D e t h i e r 1 9 9 4 ) . H o w e v e r , c o m p l e x i t y o f m o r p h o l o g y is a p a r a m e t e r that c a n v a r y a c r o s s s c a l e s o f o b s e r v a t i o n ( K i n g s f o r d 1 9 9 5 , M c A b e n d r o t h e r a / . 2 0 0 5 ) . F o r e x a m p l e , at t h e s m a l l ( i .e. a l g a l tha l lus) s c a l e , a r c h i t e c t u r a l c o m p l e x i t y m a y b e c o n s i d e r e d a s b r a n c h i n g c o m p l e x i t y ( C h e m e l l o a n d M i l a z z o 2 0 0 2 ) , w h e r e a s at b r o a d e r (i .e. s e a w e e d s t a n d ) s c a l e s , a r r a n g e m e n t o f the ind iv idua l thall i in s p a c e i n f l u e n c e s i n v e r t e b r a t e hab i ta t c h o i c e s ( G o o d s e l l a n d C o n n e l l 2 0 0 2 , G o o d s e l l etal. 2 0 0 4 , G o o d s e l l a n d C o n n e l l 2 0 0 5 , R o b e r t s a n d P o o r e 2 0 0 5 ) . T h e s e t w o s c a l e s o f a r c h i t e c t u r a l c o m p l e x i t y c a n d i f fe rent ia l l y a f f e c t v a r i o u s t y p e s o r s i z e s o f s e a w e e d - a s s o c i a t e d i n v e r t e b r a t e s ( H a c k e r a n d S t e n e c k 1 9 9 0 ) , o r m o d i f y the e f f e c t s o f d i f f e ren t a b i o t i c a n d b io t i c s t r e s s o r s . It is p o s s i b l e that t h e f u n c t i o n a l g r o u p s e r e c t e d b y S t e n e c k a n d D e t h i e r ( 1 9 9 4 ) a r e not d e f i n e d a c c o r d i n g to p a r a m e t e r s that a r e r e l e v a n t to hab i ta t u s e by s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a . P a d i l l a a n d A l l e n ( 2 0 0 0 ) s u g g e s t e d that a l g a l f u n c t i o n a l g r o u p s s h o u l d b e b a s e d not o n g r o s s m o r p h o l o g y , but o n p a r t i c u l a r f u n c t i o n s , a n d t h e n t e s t e d b e f o r e b e i n g g e n e r a l l y a p p l i e d a c r o s s t a x a . H o w e v e r , in e x a m i n i n g t h e s u i t e o f s p e c i e s t e s t e d h e r e , it s e e m s un l i ke l y that m e a n i n g f u l f u n c t i o n a l g r o u p s c o u l d b e d e f i n e d ; w h i l e t h e r e is a n a p p a r e n t g r a d i e n t o f hab i ta t u s e by i n v e r t e b r a t e s , n o c l u s t e r s o f s im i l a r l y f u n c t i o n i n g a l g a l s p e c i e s w e r e o b s e r v e d ( F i g u r e 3 .4) . A s s u c h , r e p l a c e m e n t s b y ' e q u i v a l e n t ' o r ' r e d u n d a n t ' t a x a a p p e a r un l ike ly . 51 3 . 4 . 3 Is there hope for generalizations about seaweed-epifauna associations? T h e t w o f r a m e w o r k s t e s t e d h e r e ( t a x o n o m i c r e l a t e d n e s s a n d a l g a l f u n c t i o n a l g r o u p aff i l iat ion) d o not a p p e a r u s e f u l for i n f o r m i n g p r e d i c t i o n s o f h a b i t a t u s e by i n v e r t e b r a t e e p i f a u n a . H o w e v e r , s e v e r a l o p t i o n s still ex i s t a s p o s s i b i l i t i e s for g e n e r a l i z i n g a b o u t s e a w e e d - e p i f a u n a a s s o c i a t i o n s ; I o f fer h e r e s e v e r a l s u g g e s t i o n s for fu ture r e s e a r c h . F i rst , t he m a r i n e s y s t e m s t u d i e d h e r e e m b o d i e s a m u c h w i d e r t a x o n o m i c b r e a d t h in b o t h h o s t p l a n t s a n d a s s o c i a t e d i n v e r t e b r a t e s c o m p a r e d to te r res t r ia l i n s e c t - h o s t p lant s y s t e m s . I n v e r t e b r a t e f u n c t i o n a l g r o u p s , b a s e d o n f e e d i n g a n d b i o t u r b a t i o n t y p e s , h a v e b e e n s u c c e s s f u l e l s e w h e r e ( M e r m i l l o d - B l o n d i n et al. 2 0 0 2 , R a b e n i era/. 2 0 0 5 ) a n d m a y o f fer s o m e r e s o l u t i o n in th is m a r i n e s y s t e m . For e x a m p l e , m a r i n e i n v e r t e b r a t e m e s o h e r b i v o r e s m a y s h o w a s t r o n g e r affinity for s p e c i f i c a l g a l h o s t s t h a n w a s r e v e a l e d by t h e b r o a d , c o m m u n i t y - w i d e a s s e s s m e n t of i n v e r t e b r a t e e p i f a u n a d e s c r i b e d h e r e . S e c o n d , g i v e n the o b s e r v e d g r a d i e n t of h o s t u s e a c r o s s a l g a l t a x a , it w o u l d b e i n t e r e s t i n g to l o o k for p a r t i c u l a r a l g a l traits that c o u l d b e m e a s u r e d o n a c o n t i n u o u s s c a l e , i n s t e a d o f d i s c r e t e g r o u p s that i n tegra te s u i t e s of a l g a l traits . C h e m e l l o a n d M i l a z z o ( 2 0 0 2 ) e x a m i n e d v a r i a t i o n in n i n e m o r p h o l o g i c a l traits a c r o s s s ix b r o w n a l g a l s p e c i e s , a n d s h o w e d that d e g r e e of b r a n c h i n g a l o n e e x p l a i n e d o v e r 6 0 % of the v a r i a t i o n in p l a n t - m o l l u s c a s s e m b l a g e s . T h i s a p p r o a c h h o l d s p r o m i s e , a l t h o u g h d i f f icu l t ies c a n a r i s e w h e n l o o k i n g for m o r p h o l o g i c a l traits that a r e s h a r e d a c r o s s a b r o a d s p e c t r u m of a l g a l m o r p h o l o g i e s . L a s t l y , t h e s m a l l p r o p o r t i o n o f v a r i a n c e e x p l a i n e d by t h e s e a w e e d traits t e s t e d h e r e s u g g e s t s that f a c t o r s o t h e r t h a n s e a w e e d traits a r e i n f l u e n c i n g h a b i t a t c h o i c e s b y s m a l l m o b i l e i n v e r t e b r a t e s . It is h i g h l y l ikely that a b i o t i c e n v i r o n m e n t a l c o n d i t i o n s a r e a l s o i n t e g r a t e d into hab i ta t c h o i c e s by e p i f a u n a , a n d a m a j o r f e a t u r e of intert idal e x i s t e n c e is a d d r e s s e d in t h e n e x t c h a p t e r : h y d r o d y n a m i c r e g i m e . 5 2 T a b l e 3 . 1: F u n c t i o n a l g r o u p af f i l iat ions, n u m b e r of c o l l e c t e d thall i , a n d t a x o n o m i c h i e r a r c h y u s e d to c a l c u l a t e t a x o n o m i c d i s t a n c e s b e t w e e n s e a w e e d s p e c i e s . T a x o n o m i c author i t i es a r e a v a i l a b l e f r o m G a b r i e l s o n et al. ( 2 0 0 6 ) Functional Group N Genus & Species Family Order Subclass Class Phylum Kingdom f i lamentous 8 Acrosiphonia arcta Acros iphon iaceae Cod io la les U lvophyceae Chlorophyta P lantae f i lamentous 8 Acrosiphonia coalita Acros iphon ia ceae Cod io la les U lvophyceae Chlorophyta P lantae leathery 54 Alaria marginata A la r i aceae Laminar ia les P h a e o p h y c e a e Ochrophyta Chromis ta cort icated 36 Analipus japonicus Scy tos iphonaceae Ectocarpa les P h a e o p h y c e a e Ochrophyta Chromis ta f i lamentous 42 Ceramium pacificum C e r a m i a c e a e Ceramia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae cort icated fol iose 107 . Chondracanthus exasperatus Gigar t inaceae Gigart inales Rhodymen iophyc idae Flor ideophycidae Rhodophyta P lantae f i lamentous 8 Cladophora Columbians C l a d o p h o r a c e a e C ladophora les C ladophorophyceae Chlorophyta P lantae cort icated 46 Codium fragile C o d i a c e a e Bryops ida les Bryops idophyceae Chlorophyta P lantae coral l ine 8 Corallina officinalis var. chilensis Cora l l i naceae Coral l ina les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lantae coral l ine 16 Corallina vancouvehensis Cora l l i naceae Coral l ina les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lantae c rus tose 8 Coralline Crust Cora l l i naceae Cora l l ina les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae leathery 8 Costaria costata C o s t a r iaceae Laminar ia les P h a e o p h y c e a e Ochrophyta Chromis ta cort icated 39 Cryptosiphonia woodii Dumont iaceae Gigart inales Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae cort icated 8 Desmarestia ligulata Desmares t i aceae Desmarest ia les Phaeophyceae Ochrophy ta Chromis ta cort icated 62 Endocladia muricata Endoc lad iaceae Gigart inales Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae leathery 396 Fucus distichus subsp . evanescens F u c a c e a e Fuca les P h a e o p h y c e a e Ochrophyta Chromis ta cort icated 74 Gastroclonium subarticulatum C h a m p i a c e a e Rhodymenia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lantae cort icated fol iose 8 Halosaccion glandiforme Pa lmar iaceae Palmar ia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lantae cort icated fol iose 8 Leathesia difformis Chorda r iaceae Ectocarpa les P h a e o p h y c e a e Ochrophyta Chromis ta cort icated fol. / c rus tose 8 / 3 9 Mastocarpus papillatus Phy l lophoraceae Gigart inales Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae cort icated fo l iose 84 Mazzaella splendens Gigar t inaceae Gigart inales Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae cort icated 8 Nemalion elminthoides L iagoraceae Nemal ia les Nemal iophyc idae Flor ideophycidae Rhodophy ta P lan tae cort icated 35 Neorhodomela larix R h o d o m e l a c e a e Ceramia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae f i lamentous 35 Polysiphonia hendryi R h o d o m e l a c e a e Ceramia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae f i lamentous 15 Polysiphonia paniculata R h o d o m e l a c e a e Ceramia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lantae f i lamentous 7 Polysiphonia senticulosa R h o d o m e l a c e a e Ceramia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae fo l iose 64 Porphyra abbottiae B a n g i a c e a e Bangia les Bang iophyc idae Bang iophyceae Rhodophy ta P lan tae cort icated 80 Prlonitis lyallii Ha lymen iaceae Halymenia les Rhodymen iophyc idae Flor ideophycidae Rhodophy ta P lan tae f i lamentous 8 Rhizoclonium riparium Cladopho raceae C ladophora les C ladophorophyceae Chlorophyta P lan tae cort icated 46 Sargassum muticum S a r g a s s a c e a e Fuca les Phaeophyceae Ochrophy ta Chromis ta fol iose 270 Ulva lactuca Ulvaceae Ulvales U lvophyceae Ch lorophyta P lantae fo l iose 8 Ulva intestinalis Ulvaceae Ulva les U lvophyceae Ch lorophyta P lan tae co T a b l e 3 .2: R e s u l t s o f A N O S I M test for d i f f e r e n c e s in i n v e r t e b r a t e e p i f a u n a a s s e m b l a g e a c r o s s s ix a l g a l f u n c t i o n a l g r o u p s . B o l d f a c e text i n d i c a t e s n o d i f f e r e n c e b e t w e e n g r o u p s (p > 0 . 0 5 ) . Functional Group Comparison R- Statistic P -Value f o l i o s e , l e a t h e r y 0 . 1 2 2 < 0 .001 f o l i o s e , c o r t i c a t e d 0 . 1 1 3 < 0 .001 f o l i o s e , c o r t i c a t e d f o l i o s e 0 . 1 4 7 < 0 .001 f o l i o s e , f i l a m e n t o u s 0 . 3 5 8 < 0 .001 f o l i o s e , c r u s t o s e 0 . 5 4 2 < 0 .001 f o l i o s e , c o r a l l i n e 0 . 0 9 0 < 0 . 0 4 8 l e a t h e r y , c o r t i c a t e d t e r e t e 0 . 2 0 8 < 0 .001 l e a t h e r y , c o r t i c a t e d f o l i o s e 0 . 1 7 2 < 0 . 0 0 1 l e a t h e r y , f i l a m e n t o u s 0 . 4 1 9 < 0 .001 l e a t h e r y , c r u s t o s e 0 . 2 0 0 < 0 .001 l ea thery , c o r a l l i n e 0 . 0 6 7 0.098 c o r t i c a t e d t e r e t e , c o r t i c a t e d f o l i o s e 0 . 2 3 3 < 0 . 0 0 1 c o r t i c a t e d t e r e t e , f i l a m e n t o u s 0 .151 < 0 .001 c o r t i c a t e d t e r e t e , c r u s t o s e 0 . 5 9 3 < 0 .001 c o r t i c a t e d t e r e t e , c o r a l l i n e 0 .041 0.194 c o r t i c a t e d f o l i o s e , f i l a m e n t o u s 0 . 3 7 3 < 0 . 0 0 1 c o r t i c a t e d f o l i o s e , c r u s t o s e 0 . 0 4 4 0.088 c o r t i c a t e d f o l i o s e , c o r a l l i n e 0 . 0 3 6 0.203 f i l a m e n t o u s , c r u s t o s e 0 . 8 5 9 < 0 .001 f i l a m e n t o u s , c o r a l l i n e 0 . 3 2 0 < 0 .001 c r u s t o s e , c o r a l l i n e 0 . 8 8 4 < 0 . 0 0 1 T a b l e 3.3: R e s u l t s o f A N O S I M t e s t s c o m p a r i n g i n v e r t e b r a t e e p i f a u n a a s s e m b l a g a c r o s s a l g a l s p e c i e s wi th in s ix f u n c t i o n a l g r o u p s . B o l d f a c e text h i g h l i g h t s n o d i f f e r e n c e b e t w e e n s p e c i e s (p > 0.05). A. Filamentous (Global R = 0.431, p < 0.001) Species comparisons R- Statistic P-Value Polysiphonia senticulosa, Polysiphonia hendryi 0.321 < 0.001 Polysiphonia senticulosa, Acrosiphonia arcta 0.379 0.005 Polysiphonia senticulosa, Polysiphonia paniculata 0.133 0.064 Polysiphonia senticulosa, Acrosiphonia coalita 0.867 0.002 Polysiphonia senticulosa, Ceramium pacificum 0.881 < 0.001 Polysiphonia senticulosa, Rhizoclonium riparium 0.897 < 0.001 Polysiphonia senticulosa, Cladophora columbiana 0.995 < 0.001 Polysiphonia hendryi, Acrosiphonia arcta 0.007 0.510 Polysiphonia hendryi, Polysiphonia paniculata 0.237 < 0.001 Polysiphonia hendryi, Acrosiphonia coalita 0.012 0.422 Polysiphonia hendryi, Ceramium pacificum 0.374 < 0.001 Polysiphonia hendryi, Rhizoclonium riparium 0.256 0.007 Polysiphonia hendryi, Cladophora columbiana 0.419 < 0.001 Acrosiphonia arcta, Polysiphonia paniculata 0.073 0.168 Acrosiphonia arcta, Acrosiphonia coalita 0.575 < 0.001 Acrosiphonia arcta, Ceramium pacificum 0.702 < 0.001 Acrosiphonia arcta, Rhizoclonium riparium 0.594 < 0.001 Acrosiphonia arcta, Cladophora columbiana 0.963 < 0.001 Polysiphonia paniculata, Acrosiphonia coalita 0.133 0.080 Polysiphonia paniculata, Ceramium pacificum 0.56 < 0.001 Polysiphonia paniculata, Rhizoclonium riparium 0.173 0.038 Polysiphonia paniculata, Cladophora columbiana 0.296 0.015 Acrosiphonia coalita, Ceramium pacificum 0.178 0.024 Acrosiphonia coalita, Rhizoclonium riparium 0.442 < 0.001 Acrosiphonia coalita, Cladophora columbiana 0.881 < 0.001 Ceramium pacificum, Rhizoclonium riparium 0.607 < 0.001 Ceramium pacificum, Cladophora columbiana 0.697 < 0.001 Rhizoclonium riparium, Cladophora columbiana 0.74 < 0.001 B. Foliose (Global R = 0.113, p < 0.001) Species comparisons R- Statistic P-Value Ulva lactuca, Porphyra 0.12 < 0.001 Ulva lactuca, Ulva intestinalis 0.191 0.028 Porphyra, Ulva intestinalis 0.41 < 0.001 C. Corticated foliose (Global R = 0.269, P < 0.001) Species comparisons R- Statistic P-Value Mazzaella splendens, Chondracanthus exasperatus 0.176 < 0.001 Mazzaella splendens, Leathesia difformis 0.913 < 0.001 Mazzaella splendens, Mastocarpus papillatus 0.469 < 0.001 Mazzaella splendens, Halosaccion glandiforme 0.74 < 0.001 Chondracanthus exasperatus, Leathesia difformis 0.414 < 0.001 Chondracanthus exasperatus, Mastocarpus papillatus 0.067 0.188 Chondracanthus exasperatus, Halosaccion glandiforme 0.281 < 0.001 Leathesia difformis, Mastocarpus papillatus 0.966 < 0.001 Leathesia difformis, Halosaccion glandiforme 0.83 < 0.001 Mastocarpus papillatus, Halosaccion glandiforme 0.556 < 0.001 D. Corticated terete (Global R = 0.255, P < 0.001) Species comparisons Sargassum muticum, Gastroclonium subarticulatum Sargassum muticum, Neorhodomela larix Sargassum muticum, Codium fragile Sargassum muticum, Prionitis lyallii Sargassum muticum, Cryptosiphonia woodii Sargassum muticum, Analipus japonica Sargassum muticum, Endoctadia muricata Sargassum muticum, Nemalion elminthoides Gastroclonium subarticulatum, Neorhodomela larix Gastroclonium subarticulatum, Codium fragile Gastroclonium subarticulatum, Prionitis lyallii Gastroclonium subarticulatum, Cryptosiphonia woodii Gastroclonium subarticulatum, Analipus japonica Gastroclonium subarticulatum, Endocladia muricata Gastroclonium subarticulatum, Nemalion elminthoides Neorhodomela larix, Codium fragile Neorhodomela larix, Prionitis lyallii Neorhodomela larix, Cryptosiphonia woodii Neorhodomela larix, Analipus japonica Neorhodomela larix, Endocladia muricata Neorhodomela larix, Nemalion elminthoides Codium fragile, Prionitis lyallii Codium fragile, Cryptosiphonia woodii Codium fragile, Analipus japonica Codium fragile, Endocladia muricata Codium fragile, Nemalion elminthoides Prionitis lyallii, Cryptosiphonia woodii Prionitis lyallii, Analipus japonica R- Statistic P-Value 0.235 < 0.001 0.272 < 0.001 0.431 < 0.001 0.164 < 0.001 0.207 < 0.001 0.259 < 0.001 0.361 < 0.001 0.736 < 0.001 0.158 < 0.001 0.626 < 0.001 0.306 < 0.001 0.282 < 0.001 0.347 < 0.001 0.368 < 0.001 0.831 < 0.001 0.468 < 0.001 0.115 < 0.001 0.132 < 0.001 0.255 < 0.001 0.18 < 0.001 0.791 < 0.001 .04 0.061 0.322 < 0.001 0.344 < 0.001 0.285 < 0.001 0.181 0.036 0.097 0.005 0.143 0.003 56 Prionitis lyallii, Endocladia muricata 0.193 < 0.001 Prionitis lyallii, Nemalion elminthoides 0.165 0.037 Cryptosiphonia woodii, Analipus japonica 0.109 < 0.001 Cryptosiphonia woodii, Endocladia muricata 0.118 0.002 Cryptosiphonia woodii, Nemalion elminthoides 0.449 < 0.001 Analipus japonica, Endocladia muricata 0.132 0.003 Analipus japonica, Nemalion elminthoides 0.481 < 0.001 Endocladia muricata, Nemalion elminthoides 0.32 0.004 E. Leathery (Global R = 0.339, P < 0.001) Species comparisons R- Statistic P-Value Fucus distich us, Desmarestia ligulata 0.442 < 0.001 Fucus distichus, Alaria marginata 0.312 < 0.001 Fucus distichus, Costaria costata 0.434 < 0.001 Desmarestia ligulata, Alaria marginata -0.095 0.829 Desmarestia ligulata, Costaria costata 0.763 < 0.001 Alaria marginata, Costaria costata 0.337 0.003 F. Geniculate coralline (Global R = 0.33, P = 0.003) Species comparisons R- Statistic P-Value Corallina vancouveriensis, Corallina officinalis 0.337 0.003 G. Crustose (Global R = -0.066, P = .100) N o s p e c i e s c o m p a r i s o n s r e q u i r e d " O O TO 0) CO '<_> Q . CO CO _TO (_) r3 CO CO CO _TO O >-, ct L o -c •c fiatosacc-ion giandiforme Gastrocloniuni subattKUlatum MazzaeHa spiendens Chondracanihus exa sp e tu s Mastocatpus papiflatus Endocladia muricata Cryptosiptioma woodii Polysiphonia pankulata Polysiphonia hendryi Polysiphonia senticutosa Meorhodorneia la fix Ceramium pacificism Prionitis iyailii Corallina vancouveriensis Coraiiina officinafisvar. chihnsis Coralline Crust NemaHon elminthoides Porphyra abtottiae Ut/a intestinaHs Uka lactuca Acrosiphonia coaita Acrospiionia arcta Rhizoclonium riparium 0ladophora columbiana Codium fragile Sargassum muticum Fucus distichussuhsp. evanescens L&athesia difformis Analipus japonicus Costaria costata Alaria rnarginata Desmarestia Igulata F i g u r e 3 .1 : D e n d r o g r a m i l lustrat ing t a x o n o m i c r e l a t i o n s h i p s b e t w e e n a l g a l s p e c i e s i n v e s t i g a t e d a s h o s t s f o r s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a . T a x o n o m i c r e l a t i o n s h i p s f o l l o w G a b r i e l s o n etal. ( 2 0 0 6 ) . 1.0 t 0.8 CD en 0.6 4, 0.4 H T 1 0.2 0.0 to C CD O E "E O TO O CO V) tA TO o E 3 E o C T a x o n o m i c D i s t a n c e F i g u r e 3.2: A N O S I M R - v a l u e s i n d i c a t i n g s imi lar i ty of i n v e r t e b r a t e a s s e m b l a g e s b e t w e e n a l g a l s p e c i e s wi th in s e v e n g r o u p s of i n c r e a s i n g t a x o n o m i c d i s t a n c e . N o d i f f e r e n c e s w e r e o b s e r v e d b e t w e e n g r o u p s (p = 0 . 4 4 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) . 7 -, 5 H ab ab 3 H 2 H b 100 H 80 60 H 40 H 20 T IS o '•c o o Algal Functional Group F i g u r e 3 .3 : C o m p a r i s o n s o f r a r e f i e d i n v e r t e b r a t e t a x o n r i c h n e s s ( u p p e r p a n e l ) a n d i n v e r t e b r a t e a b u n d a n c e ( l o w e r p a n e l ) a c r o s s s e v e n a l g a l f u n c t i o n a l g r o u p s . S h a r e d let ters ( u p p e r p a n e l ) i n d i c a t e n o s ign i f i can t d i f f e r e n c e b e t w e e n g r o u p s (p > 0 .05) . I n v e r t e b r a t e a b u n d a n c e d id not dif fer a c r o s s a l g a l f u n c t i o n a l g r o u p s (p = 0 . 0 8 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) . F i g u r e 3.4: C o m p a r i s o n s o f r a r e f i e d i n v e r t e b r a t e t a x o n r i c h n e s s ( u p p e r p a n e l ) a n d i n v e r t e b r a t e a b u n d a n c e ( l o w e r p a n e l ) for a l g a l s p e c i e s wi th in s e v e n a l g a l f u n c t i o n a l g r o u p s . H o r i z o n t a l b a r s i n d i c a t e the m e a n v a l u e for e a c h f u n c t i o n a l g r o u p . A s t e r i s k (*) i n d i c a t e s that t h e s p e c i e s m e a n d i f fe rs f r o m t h e f u n c t i o n a l g r o u p m e a n (p < 0 . 0 5 ) . B a r s r e p o r t m e a n v a l u e s (+/- S E ) . 6 1 3.5 L i t e r a t u r e c i t e d A r r o n t e s , J . 1 9 9 0 . D ie t , f o o d p r e f e r e n c e , a n d d i g e s t i v e e f f i c i e n c y in intert ida l i s o p o d s i n h a b i t i n g m a c r o a l g a e . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 1 3 9 : 2 3 1 - 2 4 9 . A r r o n t e s , J . 1 9 9 9 . O n t h e e v o l u t i o n o f i n t e r a c t i o n s b e t w e e n m a r i n e m e s o h e r b i v o r e s a n d a l g a e . B o t a n i c a M a r i n a 4 2 : 1 3 7 - 1 5 5 . AttnII, M . J . , J . A . S t r o n g , a n d A . A . R o w d e n . 1 9 9 9 . A r e m a c r o i n v e r t e b r a t e c o m m u n i t i e s i n f l u e n c e d b y s e a g r a s s s t ruc tura l c o m p l e x i t y ? E c o g r a p h y 2 3 : 1 1 4 - 1 2 1 . B r a y , J . R., a n d J . T . C u r t i s . 1 9 5 7 . A n o r d i n a t i o n o f t h e u p l a n d f o r e s t c o m m u n i t i e s o f S o u t h e r n W i s c o n s i n . E c o l o g i c a l M o n o g r a p h s 2 7 : 3 2 5 - 3 4 9 . C h e m e l l o , R., a n d M . M i l a z z o . 2 0 0 2 . E f f e c t of a l g a l a r c h i t e c t u r e o n a s s o c i a t e d f a u n a : s o m e e v i d e n c e f r o m p h y t a l m o l l u s c s . M a r i n e B i o l o g y 1 4 0 : 9 8 1 - 9 9 0 . C h r i s t i e , H . , N . M . J o r g e n s e n , K. M . N o r d e r h a u g , a n d E . W a a g e - N i e l s e n . 2 0 0 3 . S p e c i e s d i s t r i bu t i on a n d h a b i t a t e x p l o r a t i o n o f f a u n a a s s o c i a t e d wi th t h e k e l p (Laminaria hyperborea) a l o n g t h e N o r w e g i a n c o a s t . J o u r n a l o f t h e M a r i n e B i o l o g i c a l A s s o c i a t i o n o f t h e U n i t e d K i n g d o m 8 3 : 6 8 7 - 6 9 9 . C l a r k e , K. R. 1 9 9 3 . N o n - p a r a m e t r i c mu l t i var ia te a n a l y s i s o f c h a n g e s in c o m m u n i t y s t r u c t u r e . A u s t r a l i a n J o u r n a l o f E c o l o g y 1 8 : 1 1 7 - 1 4 3 . C o l m a n , J . 1 9 3 9 . O n t h e f a u n a s i n h a b i t i n g intert idal s e a w e e d s . J o u r n a l o f t h e M a r i n e B i o l o g i c a l A s s o c i a t i o n o f t h e U n i t e d K i n g d o m 2 4 : 1 2 9 - 1 8 3 . D a v e n p o r t , J . , A . But le r , a n d A . C h e s h i r e . 1 9 9 9 . E p i f a u n a l c o m p o s i t i o n a n d f rac ta l d i m e n s i o n s o f m a r i n e p l a n t s in re la t ion to e m e r s i o n . J o u r n a l of t h e M a r i n e B i o l o g i c a l A s s o c i a t i o n o f the U n i t e d K i n g d o m 7 9 : 3 5 1 - 3 5 5 . D a v e n p o r t , J . , P . J . A . P u g h , a n d J . M c K e c h n i e . 1 9 9 6 . M i x e d f r a c t a l s a n d a n i s o t r o p y in s u b a n t a r c t i c m a r i n e m a c r o a l g a e f r o m S o u t h G e o r g i a : i m p l i c a t i o n s for e p i f a u n a l b i o m a s s a n d a b u n d a n c e . M a r i n e E c o l o g y P r o g r e s s S e r i e s 1 3 6 : 2 4 5 - 2 5 5 . D e a n , R. L., a n d J . H . C o n n e l l . 1 9 8 7 . M a r i n e i n v e r t e b r a t e s in a l g a l s u c c e s s i o n . II. T e s t s of h y p o t h e s e s to e x p l a i n d i v e r s i t y with s u c c e s s i o n . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 1 0 9 : 2 1 7 - 2 4 7 . D i a z , S . , a n d M . C a b i d o . 2 0 0 1 . V i v e la d i f f e r e n c e : p l a n t f u n c t i o n a l d i v e r s i t y m a t t e r s to e c o s y s t e m p r o c e s s e s . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 6 : 6 4 6 - 6 5 5 . Duf fy , J . E . , a n d M . E . H a y . 1 9 9 1 . F o o d a n d s h e l t e r a s d e t e r m i n a n t s o f f o o d c h o i c e by a n h e r b i v o r o u s m a r i n e a m p h i p o d . E c o l o g y 7 2 : 1 2 8 6 - 1 2 9 8 . 6 2 F a r r e l l , B . D., a n d C . Mit ter . 1 9 9 0 . P h y l o g e n e s i s o f insec t/p lan t i n t e r a c t i o n s : H a v e P h y l l o b r o t i c a l e a f b e e t l e s ( C h r y s o m e l i d a e ) a n d t h e L a m i a l e s d i v e r s i f i e d in p a r a l l e l ? E v o l u t i o n 4 4 : 1 3 8 9 - 1 4 0 3 . F o n s e c a , C . R., a n d G . G a n a d e . 2 0 0 1 . S p e c i e s f u n c t i o n a l r e d u n d a n c y , r a n d o m e x t i n c t i o n s , a n d stabi l i ty o f e c o s y s t e m s . J o u r n a l o f E c o l o g y 8 9 :118-125. G a b r i e l s o n , P . W . , T . B . W i d d o w s o n a n d S . C . L i n d s t r o m . 2 0 0 6 . K e y s to t h e S e a w e e d s a n d S e a g r a s s e s o f S o u t h e a s t A l a s k a , Br i t i sh C o l u m b i a , W a s h i n g t o n , a n d O r e g o n , P h y c o l o g i c a l C o n t r i b u t i o n N o . 7. G e e , J . M . , a n d R. M . W a r w i c k . 1 9 9 4 . M e t a z o a n c o m m u n i t y s t r u c t u r e in re la t ion to t h e f rac ta l d i m e n s i o n o f m a r i n e m a c r o a l g a e . M a r i n e E c o l o g y P r o g r e s s S e r i e s 103:141-150. G o o d s e l l , P . J . , a n d S . D. C o n n e l l . 2 0 0 2 . C a n h a b i t a t l o s s b e t r e a t e d i n d e p e n d e n t l y o f h a b i t a t c o n f i g u r a t i o n ? I m p l i c a t i o n s f o r r a r e a n d c o m m o n t a x a in f r a g m e n t e d l a n d s c a p e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 239:37-44. G o o d s e l l , P . J . , a n d S . D. C o n n e l l . 2 0 0 5 . H i s t o r i c a l c o n f i g u r a t i o n o f h a b i t a t i n f l u e n c e s t h e e f f e c t s o f d i s t u r b a n c e o n m o b i l e i n v e r t e b r a t e s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 299:79-87. G o o d s e l l , P. J . , M . J . F o w l e r - W a l k e r , B. M . G i l l a n d e r s , a n d S . D . C o n n e l l . 2 0 0 4 . V a r i a t i o n s in t h e c o n f i g u r a t i o n o f a l g a e in s u b t i d a l f o r e s t s : I m p l i c a t i o n s for i n v e r t e b r a t e a s s e m b l a g e s . A u s t r a l E c o l o g y 2 9 :350-357. G r a h a m , L. E . , a n d L. W . W i l c o x . 2 0 0 0 . A l g a e . P r e n t i c e H a l l , U p p e r S a d d l e R i v e r , N e w J e r s e y . H a c k e r , S . D., a n d R. S . S t e n e c k . 1 9 9 0 . H a b i t a t a r c h i t e c t u r e a n d t h e a b u n d a n c e a n d b o d y - s i z e - d e p e n d e n t hab i ta t s e l e c t i o n of a p h y t a l a m p h i p o d . E c o l o g y : 2 2 6 9 - 2 2 8 5 . H a w k i n s , S . J . , a n d R. G . H a r t n o l l . 1 9 8 3 . G r a z i n g o f intert ida l a l g a e b y m a r i n e i n v e r t e b r a t e s . O c e a n o g r a p h y a n d M a r i n e B i o l o g y : a n A n n u a l R e v i e w 21 :195-282. H a y , M . E. , J . E . D u f f y , V . J . P a u l , P. E . R e n a u d , a n d W . F e n i c a l . 1 9 9 0 . S p e c i a l i s t h e r b i v o r e s r e d u c e the i r s u s c e p t i b i l i t y to p r e d a t i o n b y f e e d i n g o n t h e c h e m i c a l l y d e f e n d e d s e a w e e d Avrainvillea longicaulis. L i m n o l o g y a n d O c e a n o g r a p h y 3 5 :1734-1743. H a y , M . E . , J . E . D u f f y , C . A . P f i s ter , a n d W . F e n i c a l . 1 9 8 7 . C h e m i c a l d e f e n s e a g a i n s t d i f fe rent m a r i n e h e r b i v o r e s : a r e a m p h i p o d s i n s e c t e q u i v a l e n t s ? E c o l o g y 68:1567- 1 5 8 0 . 6 3 H a y w a r d , P. J . 1 9 8 0 . I n v e r t e b r a t e e p i p h y t e s o f c o a s t a l m a r i n e a l g a e . P a g e s 7 6 1 - 7 8 7 in J . H . P r i c e , D . E . G . Irvine, a n d W . F. F a r n h a m , e d i t o r s . T h e S h o r e E n v i r o n m e n t , V o l . 2: E c o s y s t e m s . A c a d e m i c P r e s s , L o n d o n a n d N e w Y o r k . H a y w a r d , P. J . 1 9 8 8 . A n i m a l s o n S e a w e e d . R i c h m o n d P u b l i s h i n g C o . L td . , R i c h m o n d S u r r e y . H o l m l u n d , M . B., C . H . P e t e r s o n , a n d M. E . H a y . 1 9 9 0 . D o e s a l g a l m o r p h o l o g y a f fec t a m p h i p o d s u s c e p t i b i l i t y to f i sh p r e d a t i o n ? J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 1 3 9 : 6 5 - 8 3 . H o o d , G . M . 2 0 0 6 . P o p T o o l s v e r s i o n 2 .7 .5 . A v a i l a b l e o n t h e in ternet . U R L h t t p : / / w w w . c s e . c s i r o . a u / p o p t o o l s . H u g h e s , A . R., a n d J . J . S t a c h o w i c z . 2 0 0 4 . G e n e t i c d i v e r s i t y e n h a n c e s t h e r e s i s t a n c e o f a s e a g r a s s e c o s y s t e m to d i s t u r b a n c e . P r o c e e d i n g s o f t h e N a t i o n a l A c a d e m y of S c i e n c e s U S A 1 0 1 : 8 9 9 8 - 9 0 0 2 . Hu l l , S . L. 1 9 9 7 . S e a s o n a l c h a n g e s in d ivers i ty a n d a b u n d a n c e o f o s t r a c o d s o n four s p e c i e s o f intert ida l a l g a e wi th d i f fer ing s t r u c t u r a l c o m p l e x i t y . M a r i n e E c o l o g y P r o g r e s s S e r i e s 1 6 1 : 7 1 - 8 2 . J i , Y . , a n d J . T a n a k a . 2 0 0 2 . E f f e c t o f d e s i c c a t i o n o n t h e p h o t o s y n t h e s i s o f s e a w e e d s f r o m t h e intert idal z o n e in H o n s h u , J a p a n . P h y c o l o g i c a l R e s e a r c h 5 0 : 1 4 5 - 1 5 3 . J o h n s o n , M . T . J . , M . J . L a j e u n e s s e , a n d A . A . A g r a w a l . 2 0 0 6 . A d d i t i v e a n d in te rac t i ve e f f e c t s o f p lan t g e n o t y p i c d i v e r s i t y o n a r t h r o p o d c o m m u n i t i e s a n d p lant f i t n e s s . E c o l o g y L e t t e r s 9 : 2 4 - 3 4 . Ke l l y , C . K., a n d T . R. E . S o u t h w o o d . 1 9 9 9 . S p e c i e s r i c h n e s s a n d r e s o u r c e ava i lab i l i ty : a p h y l o g e n e t i c a n a l y s i s o f i n s e c t s a s s o c i a t e d with t r e e s . P r o c e e d i n g s o f the N a t i o n a l A c a d e m y of S c i e n c e s U S A 9 6 : 8 0 1 3 - 8 0 1 6 . K i n g s f o r d , M . J . 1 9 9 5 . Drift a l g a e : a c o n t r i b u t i o n to n e a r - s h o r e h a b i t a t c o m p l e x i t y in the p e l a g i c e n v i r o n m e n t a n d a n at t rac tant for f i s h . M a r i n e E c o l o g y P r o g r e s s S e r i e s 1 1 6 : 2 9 7 - 3 0 1 . K o e h l , M . A . R. 1 9 9 6 . W h e n d o e s m o r p h o l o g y m a t t e r ? A n n u a l R e v i e w of E c o l o g y a n d S y s t e m a t i c s 2 7 : 5 0 1 - 5 4 2 . K r a u f v e l i n , P., a n d S . S a l o v i u s . 2 0 0 4 . A n i m a l d i ve rs i t y in B a l t i c r o c k y s h o r e m a c r o a l g a e : c a n Cladophora glomerata c o m p e n s a t e for lost Fucus vesiculosus? E s t u a r i n e , C o a s t a l a n d S h e l f S c i e n c e 6 1 : 3 6 9 - 3 7 8 . L a v o r e l , S . , S . M c l n t y r e , J . L a n d s b e r g , a n d T . D . A . F o r b e s . 1 9 9 7 . P l a n t f u n c t i o n a l c l a s s i f i c a t i o n s : f r o m g e n e r a l g r o u p s to s p e c i f i c g r o u p s b a s e d o n r e s p o n s e to d i s t u r b a n c e . T r e n d s in E c o l o g y a n d E v o l u t i o n 1 2 : 4 7 4 - 4 7 8 . 6 4 Littler, M . M. , a n d D. S . Littler. 1 9 8 0 . T h e e v o l u t i o n o f t h a l l u s f o r m a n d s u r v i v a l s t r a t e g i e s in b e n t h i c m a r i n e m a c r o a l g a e : f ie ld a n d l a b o r a t o r y t e s t s o f a f u n c t i o n a l f o r m m o d e l . T h e A m e r i c a n N a t u r a l i s t 116:25-44. L o r e a u , M . 2 0 0 4 . D o e s f u n c t i o n a l r e d u n d a n c y e x i s t ? O i k o s 104:606-611. L o s o s , J . B. 1 9 9 6 . P h y l o g e n e t i c p e r s p e c t i v e s o n c o m m u n i t y e c o l o g y . E c o l o g y 77:1344- 1 3 5 4 . M a c A r t h u r , R. H . 1 9 7 2 . G e o g r a p h i c a l E c o l o g y : P a t t e r n s in t h e D i s t r i b u t i o n o f S p e c i e s . P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n , N e w J e r s e y . M a g u r r a n , A . E . 1 9 8 8 . E c o l o g i c a l d i v e r s i t y a n d its m e a s u r e m e n t . P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n . M a n l y , B. F. J . 1 9 9 1 . R a n d o m i z a t i o n a n d M o n t e C a r l o m e t h o d s in b i o l o g y . C h a p m a n a n d H a l l , L o n d o n . M a r t i n - S m i t h , K. M . 1 9 9 3 . A b u n d a n c e of m o b i l e e p i f a u n a : t h e ro le o f hab i ta t c o m p l e x i t y a n d p r e d a t i o n b y f i s h e s . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 174:243-260. M c A b e n d r o t h , L., P. M . R a m s a y , A . F o g g o , D. R u n d l e , a n d D. T . B i l t on . 2 0 0 5 . D o e s m a c r o p h y t e f rac ta l c o m p l e x i t y d r i v e i n v e r t e b r a t e d i v e r s i t y , b i o m a s s a n d b o d y s i z e d i s t r i b u t i o n s . O i k o s 111:279-290. M e r m i l l o d - B l o n d i n , F., M . G e r i n o , M . C r e u z e d e s C h a t e l l i e r s , a n d V . D e g r a n g e . 2 0 0 2 . F u n c t i o n a l d i v e r s i t y a m o n g 3 d e t r i t i v o r o u s h y p o r h e i c i n v e r t e b r a t e s : a n e x p e r i m e n t a l s t u d y in m i c r o c o s m s . J o u r n a l o f the N o r t h A m e r i c a n B e n t h o l o g i c a l S o c i e t y 2 1 :132-149. N a e e m , S . 1 9 9 8 . S p e c i e s r e d u n d a n c y a n d e c o s y s t e m rel iabi l i ty . C o n s e r v a t i o n B i o l o g y 12:39-45. N o r d e r h a u g , K. M . 2 0 0 4 . U s e of r e d a l g a e a s h o s t s b y k e l p - a s s o c i a t e d a m p h i p o d s . M a r i n e B i o l o g y 144:225-230. N o r d e r h a u g , K. M. , H . C h r i s t i e , J . H . F o s s a , a n d S . F r e d r i k s e n . 2 0 0 5 . F i s h - m a c r o f a u n a i n t e r a c t i o n s in a k e l p (Laminaria hyperborea) f o r e s t . J o u r n a l o f t h e M a r i n e B i o l o g i c a l A s s o c i a t i o n o f the U n i t e d K i n g d o m 8 5 :1279-1286. 0 d e g a a r d , F., O . H . D i s e r u d , a n d K. 0 s t b y e . 2 0 0 5 . T h e i m p o r t a n c e o f p lan t r e l a t e d n e s s for h o s t ut i l i zat ion a m o n g p h y t o p h a g o u s i n s e c t s . E c o l o g y L e t t e r s 8 :612-617 . P a d i l l a , D. K., a n d B. J . A l l e n . 2 0 0 0 . P a r a d i g m lost: r e c o n s i d e r i n g f u n c t i o n a l f o r m a n d g r o u p h y p o t h e s e s in m a r i n e e c o l o g y . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 250:207-221. 6 5 P a i n e , R. T . , a n d R. L. V a d a s . 1 9 6 9 . C a l o r i f i c v a l u e s of b e n t h i c m a r i n e a l g a e a n d the ir p o s t u l a t e d re la t ion to i n v e r t e b r a t e f o o d p r e f e r e n c e . M a r i n e B i o l o g y 4:79-86. R a b e n i , C . F., K. E . D o i s y , a n d L. D. Z w e i g . 2 0 0 5 . S t r e a m i n v e r t e b r a t e c o m m u n i t y f u n c t i o n a l r e s p o n s e s to d e p o s i t e d s e d i m e n t . A q u a t i c S c i e n c e s 67:395-402. R o b e r t s , D. A . , a n d A . G . B. P o o r e . 2 0 0 5 . Hab i ta t c o n f i g u r a t i o n a f f e c t s c o l o n i s a t i o n o f e p i f a u n a in a m a r i n e a l g a l b e d . B i o l o g i c a l C o n s e r v a t i o n 127:18-26. R o s e n f e l d , J . S . 2 0 0 2 . F u n c t i o n a l r e d u n d a n c y in e c o l o g y a n d c o n s e r v a t i o n . O i k o s 98:156-162. S a u n d e r s , G . W . , a n d M . H. H o m m e r s a n d . 2 0 0 4 . A s s e s s i n g r e d a l g a l s u p r a o r d i n a l d i v e r s i t y a n d t a x o n o m y in the c o n t e x t o f c o n t e m p o r a r y s y s t e m a t i c d a t a . A m e r i c a n J o u r n a l o f B o t a n y 91:1494-1507. S e e d , R., a n d R. J . O ' C o n n o r . 1 9 8 1 . C o m m u n i t y o r g a n i z a t i o n in m a r i n e a l g a l e p i f a u n a s . A n n u a l R e v i e w of E c o l o g y a n d S y s t e m a t i c s 12:49-74. S i l v a , P. C . 1 9 9 2 . G e o g r a p h i c p a t t e r n s o f d ive rs i t y in b e n t h i c m a r i n e a l g a e . P a c i f i c S c i e n c e 46:429-437. S t e n e c k , R. S . , a n d M . N . D e t h i e r . 1 9 9 4 . A f u n c t i o n a l g r o u p a p p r o a c h to the s t r u c t u r e o f a l g a l - d o m i n a t e d c o m m u n i t i e s . O i k o s 69:476-498. S t e n e c k , R. S . , a n d L. W a t l i n g . 1 9 8 2 . F e e d i n g c a p a b i l i t i e s a n d l imitat ion o f h e r b i v o r o u s m o l l u s c s : a f u n c t i o n a l g r o u p a p p r o a c h . M a r i n e B i o l o g y 68:299-319. T a y l o r , R. B., a n d R. G . C o l e . 1 9 9 4 . M o b i l e e p i f a u n a o n s u b t i d a l b r o w n s e a w e e d s in n o r t h e a s t e r n N e w Z e a l a n d . M a r i n e E c o l o g y P r o g r e s s S e r i e s 115:271-282. T a y l o r , R. B., a n d P. D. S t e i n b e r g . 2 0 0 5 . H o s t u s e b y A u s t r a l a s i a n s e a w e e d m e s o g r a z e r s in re la t ion to f e e d i n g p r e f e r e n c e s o f l a r g e r g r a z e r s . E c o l o g y 86:2955-2967. T h e b a u l t , E . , a n d M . L o r e a u . 2 0 0 6 . T h e r e l a t i o n s h i p b e t w e e n b i o d i v e r s i t y a n d e c o s y s t e m f u n c t i o n i n g in f o o d w e b s . E c o l o g i c a l R e s e a r c h 21:17-25. V a n A l s t y n e , K. L., a n d L. T . H o u s e r . 2 0 0 3 . D i m e t h y l s u l f i d e r e l e a s e d u r i n g m a c r o i n v e r t e b r a t e g r a z i n g a n d its ro le a s a n a c t i v a t e d c h e m i c a l d e f e n s e . M a r i n e E c o l o g y P r o g r e s s S e r i e s 250:175-181. W a k e f i e l d , R. L., a n d S . N . M u r r a y . 1 9 9 8 . F a c t o r s i n f l u e n c i n g f o o d c h o i c e b y the s e a w e e d - e a t i n g m a r i n e s n a i l Norrisia norrisi ( T r o c h i d a e ) . M a r i n e B i o l o g y 130:631-642. W e b b , C . O . , D. D. A c k e r l y , M . A . M c P e e k , a n d M . J . D o n o g h u e . 2 0 0 2 . P h y l o g e n i e s a n d c o m m u n i t y e c o l o g y . A n n u a l R e v i e w of E c o l o g y a n d S y s t e m a t i c s 33:475-505. 6 6 W e i b l e n , G . D., C . O . W e b b , V . N o v o t n y , Y . B a s s e t , a n d S . E . Mi l le r . 2 0 0 6 . P h y l o g e n e t i c d i s p e r s i o n of h o s t u s e in a t rop i ca l i n s e c t h e r b i v o r e c o m m u n i t y . E c o l o g y 87 Supplement:S62-S75. W i k s t r o m , S . A . , a n d L. K a u t s k y . 2 0 0 4 . I n v a s i o n of a h a b i t a t - f o r m i n g s e a w e e d : e f f e c t s o n a s s o c i a t e d b i o t a . B i o l o g i c a l I n v a s i o n s 6 : 1 4 1 - 1 5 0 . 6 7 Chapter 4 : Do facilitator traits interact with an environmental gradient to determine local species diversity? A version of this chapter will be submitted to Ecology. 68 4.1 Introduction 4.1.1 Ecosystem engineering, species traits, & environmental gradients M a n y h a b i t a t - p r o v i d i n g o r g a n i s m s p r o m o t e the c o e x i s t e n c e o f o t h e r s p e c i e s by d i rec t ly o r ind i rec t ly a m e l i o r a t i n g t h e n e g a t i v e e f f e c t s o f i n h o s p i t a b l e e n v i r o n m e n t s ( T h o m p s o n etal. 1 9 9 6 , K e l a h e r e f a / . 2 0 0 1 , B r a d s h a w etal. 2 0 0 3 ) . T h i s p r o c e s s , k n o w n a s e c o s y s t e m e n g i n e e r i n g ( J o n e s ef al. 1 9 9 4 ) , c a n e x p a n d the r e a l i z e d n i c h e o f a s s o c i a t e d s p e c i e s ( C r a i n a n d B e r t n e s s 2 0 0 6 , M c G i l l e f al. 2 0 0 6 ) , a n d p r o v i d e a f o u n d a t i o n for en t i re c o m m u n i t i e s . T h e s e fac i l i tat ive i n t e r a c t i o n s a r e c o m m o n in n a t u r e a n d a l t h o u g h l o n g r e c o g n i z e d , e c o l o g i s t s h a v e o n l y r e c e n t l y b e g u n to f o r m a l l y i n c l u d e fac i l i tat ion into m o d e l s o f t h e m a j o r f a c t o r s that s t r u c t u r e b iot ic a s s e m b l a g e s ( B r u n o a n d B e r t n e s s 2 0 0 0 , M e n g e 2 0 0 0 , S t a c h o w i c z 2 0 0 1 , B r u n o etal. 2 0 0 3 ) . G i v e n u n c e r t a i n t y a b o u t t h e c o n s e q u e n c e s o f c h a n g e s in b i o d i v e r s i t y o f h a b i t a t - p r o v i d i n g s p e c i e s ( B e n e d e t t i - C e c c h i e f al. 2 0 0 1 , H o o p e r ef al. 2 0 0 5 , E w e r s a n d D i d h a m 2 0 0 6 , T h e b a u l t a n d L o r e a u 2 0 0 6 , W i n f r e e et al. 2 0 0 7 ) , t he c u r r e n t c h a l l e n g e is to d e t e r m i n e t h e c i r c u m s t a n c e s u n d e r w h i c h e c o s y s t e m e n g i n e e r i n g is i m p o r t a n t ( C r a i n a n d B e r t n e s s 2 0 0 6 ) . S e v e r a l f a c t o r s h a v e b e e n s u g g e s t e d to c o n t r o l t h e c o n t e x t u n d e r w h i c h s p e c i e s c a n a c t a s hab i ta t p r o v i d e r s ( B r u n o a n d B e r t n e s s 2 0 0 0 , C r a i n a n d B e r t n e s s 2 0 0 6 , M c G i l l e f al. 2 0 0 6 ) , two of w h i c h I f o c u s o n h e r e : h o s t s p e c i e s traits a n d e n v i r o n m e n t a l g r a d i e n t s . S p e c i e s traits h a v e r e c e n t l y b e e n s u g g e s t e d a s i m p o r t a n t r e g u l a t o r s o f hab i ta t p r o v i s i o n ( B r u n o a n d B e r t n e s s 2 0 0 0 ) , ye t " . . . r e m a r k a b l y little w o r k h a s b e e n d o n e o n the traits i n v o l v e d in e c o s y s t e m e n g i n e e r i n g . . . " ( B o u m a ef al. 2 0 0 5 ) . It m a k e s s e n s e that h o s t s p e c i e s traits s h o u l d i n f l u e n c e e c o s y s t e m e n g i n e e r i n g , b e c a u s e not all hab i ta t - p r o v i d i n g s p e c i e s a r e c r e a t e d e q u a l . T o e f fec t i ve l y a m e l i o r a t e the i n f l u e n c e o f e n v i r o n m e n t a l s t r e s s , h o s t s p e c i e s m u s t p o s s e s s traits that a c t u a l l y h a v e a n i n f l u e n c e o n p r e v a i l i n g s t r e s s o r s ( B r u n o a n d B e r t n e s s 2 0 0 0 ) . S o m e ( M c G i l l et al. 2 0 0 6 ) h a v e a r g u e d that a s t u d y o f f u n c t i o n a l traits is a p r a g m a t i c a p p r o a c h to i m p r o v i n g the p r e d i c t i v e p o w e r o f c o m m u n i t y e c o l o g y . E n v i r o n m e n t a l g r a d i e n t s m a y b e d e t e r m i n a n t s o f t h e s t r e n g t h a n d i m p o r t a n c e of pos i t i ve i n t e r a c t i o n s ( B e r t n e s s a n d C a l l a w a y 1 9 9 4 , J o n e s etal. 1 9 9 7 , C a l l a w a y et a l . 6 9 2 0 0 2 , C r a i n a n d B e r t n e s s 2 0 0 6 , M c G i l l etal. 2 0 0 6 ) a l t h o u g h t h e m e c h a n i s m s of s t r e s s a m e l i o r a t i o n a r e h y p o t h e s i z e d to di f fer d e p e n d i n g o n t h e l e v e l o f e n v i r o n m e n t a l s t r e s s ( B r u n o e t al. 2 0 0 3 ) . In h a r s h e n v i r o n m e n t s , e c o s y s t e m e n g i n e e r i n g is p r e d i c t e d to b e i m p o r t a n t b e c a u s e o f t h e a m e l i o r a t i o n o f abiotic s t r e s s o r s ( B e r t n e s s a n d C a l l a w a y 1 9 9 4 ) , w h e r e a s in b e n i g n e n v i r o n m e n t s , h a b i t a t - p r o v i d i n g o r g a n i s m s t e n d to p r o v i d e resp i te f r o m ' n e g a t i v e ' biotic i n t e r a c t i o n s s u c h a s c o m p e t i t i o n a n d p r e d a t i o n ( C r a i n a n d B e r t n e s s 2 0 0 5 , 2 0 0 6 ) . H o w e v e r , o n l y a f e w s t u d i e s ( W r i g h t a n d J o n e s 2 0 0 4 , C r a i n a n d B e r t n e s s 2 0 0 5 ) h a v e exp l i c i t ly e x a m i n e d e c o s y s t e m e n g i n e e r i n g a l o n g s t r e s s g r a d i e n t s ( C r a i n a n d B e r t n e s s 2 0 0 6 ) . S p e c i e s traits a n d e n v i r o n m e n t a l c o n t e x t u n d o u b t e d l y w o r k in c o n c e r t to d e t e r m i n e t h e o u t c o m e of p o s i t i v e i n t e r a c t i o n s b e t w e e n c o e x i s t i n g s p e c i e s ( M c G i l l et al. 2 0 0 6 ) . B r u n o a n d B e r t n e s s ( 2 0 0 0 ) p r o p o s e d a m o d e l s u m m a r i z i n g the i r p r e d i c t i o n s a b o u t h o w trait v a l u e s a n d s t r e s s l e v e l s m i g h t in teract to d e t e r m i n e l o c a l s p e c i e s d i ve rs i t y ( F i g u r e 4 . 1 ) . T h e y s u g g e s t that u n d e r low s t r e s s s c e n a r i o s , b y de f in i t ion , s t r e s s is not a c t i n g to p r e v e n t a s s o c i a t e d s p e c i e s f r o m i n h a b i t i n g a p a r t i c u l a r p a t c h . T h e r e f o r e , fac i l i tat ion is not r e q u i r e d to m a i n t a i n l oca l s p e c i e s d i ve rs i t y . In m o d e r a t e l y s t r e s s f u l s c e n a r i o s , fac i l i tat ing s p e c i e s that l a c k the traits a p p r o p r i a t e to a m e l i o r a t e s t r e s s o r s s h o u l d h a v e a l o w e r d i v e r s i t y o f a s s o c i a t e d o r g a n i s m s c o m p a r e d to fac i l i ta tors with h i g h trait v a l u e s . L a s t l y , in h i g h s t r e s s s c e n a r i o s , B r u n o a n d B e r t n e s s ( 2 0 0 0 ) p r e d i c t that a s s o c i a t e d o r g a n i s m s will b e a b s e n t f r o m p a t c h e s u n l e s s fac i l i ta tors with traits su f f i c ient to a m e l i o r a t e s t r e s s a r e p r e s e n t . T h e o b j e c t i v e o f t h e c u r r e n t s t u d y is to tes t h o w e c o s y s t e m e n g i n e e r i n g is i n f l u e n c e d b y fac i l i ta tor traits a l o n g a s t r e s s g r a d i e n t in a m u l t i - s p e c i e s intert idal s e a w e e d - e p i f a u n a s y s t e m . S p e c i f i c a l l y , I e x a m i n e h o w the s t r e s s e s i m p o s e d by c r a s h i n g w a v e s in te rac t with s e a w e e d m o r p h o l o g y to d e t e r m i n e hab i ta t p r o v i s i o n for s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a . 4.1.2 Wave action as a moderator of algal-invertebrate interactions W a v e a c t i o n is a m a j o r f o r c e dr iv ing the e c o l o g y a n d e v o l u t i o n o f n e a r s h o r e b e n t h i c o r g a n i s m s (Be l l a n d D e n n y 1 9 9 4 , D e n n y a n d G a y l o r d 2 0 0 2 , K o e h l 2 0 0 6 ) . W a t e r m o v e m e n t e x p e r i e n c e d at a s i te c a n i n f l u e n c e o r g a n i s m a l s i z e a n d m o r p h o l o g y 7 0 (Gutierrez and Fernandez 1992, Blanchette 1997, Milligan and DeWreede 2000, Denny and Gaylord 2002), physiology (Hurd 2000), large and small-scale organismal distributions (Bustamante and Branch 1996, DeFelice and Parrish 2001, Guerra-Garcia 2001, Hovel et al. 2002), and mortality, survival and population structure (Carrington 1990, McQuaid and Lindsay 2000, Duggins etal. 2001, Pratt and Johnson 2002). For small mobile invertebrates, which can include amphipods, isopods, gastropods, and copepods, among other taxa, bare rock substrate provides little refuge from hydrodynamic forces imposed by crashing waves (Thompson ef al. 1996). However, biogenic structures such as mussel beds and algal cover can provide protection for a wide array of invertebrate epifauna. Quality of habitat provision varies across algal hosts (Chapter 3), and evidence exists to suggest that morphological properties of host algae can underpin observed differences in diversity of associated invertebrates (Colman 1939, Seed and O'Connor 1981, Taylor and Cole 1994). Habitat provision by single host algal species across wave gradients has been investigated several times (Domrmasnes 1968, Fenwick 1976, DeFelice and Parrish 2001, Arroyo ef al. 2004), however no cross-species comparisons have been undertaken. To test if facilitator traits (i.e. algal morphology) and an environmental gradient (i.e. wave action) interact to regulate local species diversity (of small mobile invertebrates), I ask here three questions: a) how do individual algal species perform as habitat-providing organisms across a wave exposure gradient; b) how does habitat use by invertebrate epifauna compare across host algal species as wave impact increases; and c) do these observations fit the predictions made by Bruno and Bertness (2000) regarding how facilitator traits and environmental stress could interact to determine local species diversity? 4.2 Materials and methods 4.2.1 Study sites Algae and associated invertebrates were collected monthly from February 2005 to March 2006 at six rocky intertidal sites in southern Barkley Sound, British Columbia. 71 S t u d y a r e a s w e r e d e l i n e a t e d a s 3 0 m of r o c k y intert idal s h o r e at a s h e l t e r e d a n d e x p o s e d s i te at e a c h o f D i x o n Is land , S c o t t ' s B a y , a n d N u d i b r a n c h P o i n t ( F i g u r e 1.3). 4.2.2 Measurement of maximum wave forces A s w a v e s m o v e into B a r k l e y S o u n d t h e r e is, in g e n e r a l , a g r a d i e n t o f d e c r e a s i n g w a v e he ight , a l t h o u g h w i n d d i r e c t i o n a n d loca l t o p o g r a p h y c a n g r e a t l y i n f l u e n c e r e a l i z e d w a v e i m p a c t o n d i f fe rent s h o r e s . A t e a c h of m y s t u d y s i t e s , w a v e i m p a c t w a s m e a s u r e d by d e p l o y i n g f ive m a x i m u m w a v e - f o r c e d y n a m o m e t e r s (Be l l a n d D e n n y 1 9 9 4 ) 2 4 h o u r s pr ior to c o l l e c t i o n o f a l g a e a n d a s s o c i a t e d i n v e r t e b r a t e s . D y n a m o m e t e r s w e r e p l a c e d a l o n g a 3 0 m t r a n s e c t at 1 m a b o v e c h a r t d a t u m (the s a m e a r e a a s t h e biot ic c o l l e c t i o n s , d e s c r i b e d b e l o w ) . D y n a m o m e t e r s i n d i c a t e o n l y t h e s t r o n g e s t w a v e to i m p a c t the s h o r e d u r i n g t h e p e r i o d o f d e p l o y m e n t , s o I fitted e a c h a p p a r a t u s with a s p r i n g of o n e of t h r e e s t r e n g t h s : w e a k (0.21 +/- 0 . 0 2 N/mm), m e d i u m ( 0 . 7 8 +/- 0 . 0 4 N/mm), o r s t r o n g (1 .8 +/- 0.21 N/mm) , c h o s e n a c c o r d i n g to p r e v a i l i n g w a v e c o n d i t i o n s . A p p a r a t i that w e r e s t r e t c h e d to t h e m a x i m u m s p r i n g e x t e n s i o n w e r e not i n c l u d e d in the a n a l y s i s (this o c c u r r e d o n l y f i ve t i m e s ou t of 2 9 5 d y n a m o m e t e r m e a s u r e m e n t s ) . S p r i n g e x t e n s i o n s w e r e c o n v e r t e d to m a x i m u m w a v e v e l o c i t i e s u s i n g e q u a t i o n s f r o m Be l l & D e n n y ( 1 9 9 4 ) . T o m i n i m i z e e f f e c t s o f wi th in-s i te ( t o p o g r a p h i c ) v a r i a t i o n in w a v e e x p o s u r e , d r o g u e s w e r e not d e p l o y e d n o r w e r e a l g a l c o l l e c t i o n s m a d e with in 2 m e t e r s o n e i ther s i d e o f t h e e n t r a n c e to s u r g e c h a n n e l s . 4.2.3 Sampling of seaweeds and epifauna T w e l v e d i f f e ren t a l g a l s p e c i e s w e r e e x a m i n e d ( F i g u r e 4 . 2 ) . It w a s not p o s s i b l e to a c h i e v e a ful ly c r o s s e d d e s i g n (i .e. all s p e c i e s f r o m all s i t e s at all d a t e s ) o w i n g to p a t c h y a l g a l d i s t r i b u t i o n s a n d s e a s o n a l i t y . S p e c i e s i n c l u d e d w e r e : Alaria marginata P o s t e l s & R u p r e c h t (54 i n d i v i d u a l s ) , Chondracanthus exasperatus ( H a r v e y & B a i l e y ) J . R . H u g h e y (107) , Codium fragile ( S u r i n g a r ) Har io t (46), Cryptosiphonia woodii ( J . A g a r d h ) J . A g a r d h (39), Endocladia muricata ( E n d l i c h e r ) J . A g a r d h (62) , Fucus distichus s u b s p . evanescens ( C . A g a r d h ) H .T . P o w e l l (396) , h e r e a f t e r r e f e r r e d to a s Fucus distichus, 7 2 Gastroclonium subarticulatum ( T u r n e r ) K u t z i n g (74), t he ' P e t r o c e l i s ' p h a s e of Mastocarpus (39) , Mazzaella splendens ( S e t c h e l l & N .L . G a r d n e r ) F r e d e r i c q (84), Prionitis lyallii H a r v e y (80) , Polysiphonia spp. (57) , a n d Ulva lactuca L i n n a e u s (270) . In total , 1 3 0 8 a l g a l thall i w e r e c o l l e c t e d , a n d the o n l y a l g a l s p e c i e s c o l l e c t e d at all s i t e s o n all s a m p l i n g d a t e s w a s Fucus distichus. T h e s e t w e l v e s p e c i e s c o m p r i s e a n a r r a y of m o r p h o l o g i e s that c a n b e a r r a n g e d in o r d e r o f i n c r e a s i n g a r c h i t e c t u r a l c o m p l e x i t y . T h e l eas t c o m p l e x s p e c i e s is a n epi l i th ic c r u s t ( 'Pe t roce l i s ' in F i g u r e 4 . 2 ) , a n d c o m p l e x i t y i n c r e a s e s with s e v e r a l c o r t i c a t e d f o l i o s e b l a d e s (A. marginata, C. exasperatus, M. splendens), a th in a n d h i g h l y f o l d i n g b l a d e (U. lactuca), s e v e r a l c o a r s e l y b r a n c h i n g s p e c i e s ( C . fragile, F. distichus, G. subarticulatum, P. lyallii), a n d t h e m o s t c o m p l e x thall i a r e r e p r e s e n t e d b y t h r e e m o r e h i g h l y b r a n c h i n g s p e c i e s ( C . woodii, E. muricata, P. hendryi). W h e n e n c o u n t e r e d , e i g h t i n d i v i d u a l s o f e a c h s t u d y s p e c i e s w e r e c o l l e c t e d at low t ide f r o m e a c h s i te , e a c h m o n t h d u r i n g s p r i n g t i d e s . A l g a l i n d i v i d u a l s w e r e h a p h a z a r d l y s e l e c t e d a l o n g a 1 m x 3 0 m h o r i z o n t a l b a n d t r a n s e c t , h o r i z o n t a l l y c e n t e r e d at o n e m e t e r a b o v e c h a r t d a t u m . T o m i n i m i z e the v a r i a t i o n c a u s e d b y v e r t i c a l sh i f ts in ab io t i c a n d b iot ic s t r u c t u r i n g f a c t o r s , s p e c i e s t yp i ca l o f t h e u p p e r intert ida l z o n e ( e . g . Fucus) w e r e c o l l e c t e d f r o m t h e b o t t o m of the i r ver t i ca l r a n g e , a n d l o w e r s p e c i e s ( e . g . Mazzaella a n d Chondracanthus) w e r e c o l l e c t e d at the u p p e r r e a c h e s o f the i r d i s t r i bu t ion . U p r i g h t tha l lo id a l g a e w e r e c o l l e c t e d b y p l u c k i n g f r o m the b a s e a n d e a c h w a s i m m e d i a t e l y p l a c e d into a n i n d i v i d u a l z i p p e r e d p las t i c b a g . C a r e w a s t a k e n not to s e l e c t i n d i v i d u a l s with e p i p h y t e c o v e r , a n d n o i n d i v i d u a l s w e r e s e l e c t e d f r o m t i d e p o o l s . I n v e r t e b r a t e s a m p l e s w e r e t a k e n f r o m ' P e t r o c e l i s ' c r u s t s b y v i s u a l l y a s s e s s i n g a 10 c m x 1 0 c m p a t c h for m a c r o i n v e r t e b r a t e s , t h e n r u b b i n g the s a m e a r e a with a c o t t o n s w a b to g a t h e r a n y m i c r o s c o p i c e p i f a u n a . A f t e r c o l l e c t i o n , all s a m p l e s w e r e l a b e l e d a n d f r o z e n for a m i n i m u m of 3 d a y s to e u t h a n i z e e p i f a u n a a n d p r e s e r v e s a m p l e s until p r o c e s s i n g c o u l d t a k e p l a c e . S a m p l e s w e r e p r o c e s s e d a n d i n v e r t e b r a t e e p i f a u n a w e r e r e m o v e d f r o m a l g a e a n d ident i f i ed a c c o r d i n g to p r o c e d u r e s d e s c r i b e d in s e c t i o n 2 .2 .6 . 7 3 4.2.4 Statistical analyses M a x i m u m w a v e v e l o c i t y m e a s u r e m e n t s w e r e a v e r a g e d a c r o s s t h e f i ve d y n a m o m e t e r m e a s u r e m e n t s f r o m e a c h s i te o n e a c h c o l l e c t i o n d a t e . F o r e a c h a l g a l h o s t s p e c i e s , i n v e r t e b r a t e a b u n d a n c e a n d t a x o n r i c h n e s s ( r a r e f i e d to 2 0 i n d i v i d u a l s ) w e r e p lo t ted a g a i n s t m a x i m u m w a v e ve loc i t y . S i g n i f i c a n c e o f t h e s e r e l a t i o n s h i p s w a s t e s t e d u s i n g a m i x e d - m o d e l u n i v a r i a t e A N O V A with o n e f i x e d f a c t o r ( m a x i m u m w a v e v e l o c i t y ) a n d t w o r a n d o m f a c t o r s (site a n d c o l l e c t i o n m o n t h ) . C o m p o s i t i o n of e p i f a u n a a s s e m b l a g e s w a s a l s o e x a m i n e d u s i n g n o n p a r a m e t r i c m u l t i v a r i a t e a p p r o a c h e s ( C l a r k e 1 9 9 3 ) . E p i f a u n a l a b u n d a n c e s w e r e four th - root t r a n s f o r m e d to d o w n w e i g h t t h e c o n t r i b u t i o n o f a b u n d a n t t a x a ( C l a r k e 1 9 9 3 ) , a n d s im i la r i t i es w e r e a s s e s s e d u s i n g the B r a y - C u r t i s s imi lar i ty m e a s u r e ( B r a y a n d C u r t i s 1 9 5 7 ) . T o tes t for d i f f e r e n c e s in c o m p o s i t i o n of i n v e r t e b r a t e e p i f a u n a a s w a v e a c t i o n i n c r e a s e s , w a v e v e l o c i t i e s w e r e g r o u p e d into s ix c a t e g o r i e s (< 2 .00 , 2 .00 - 2 .99 , 3 . 0 0 - 3 . 9 9 , 4 . 0 0 - 4 . 9 9 , 5 .00 - 5 .99 , a n d > 6 . 0 0 m e t e r s p e r s e c o n d ) , a n d t h e n for e a c h a l g a l h o s t , i n v e r t e b r a t e a s s e m b l a g e s f r o m a d j a c e n t c a t e g o r i e s ( i .e. < 2 . 0 0 v e r s u s 2 .00 - 2 . 9 9 ; 2 . 0 0 - 2 . 9 9 v e r s u s 3 . 0 0 - 3 . 9 9 a n d s o o n ) w e r e c o m p a r e d u s i n g A n a l y s i s o f S i m i l a r i t i e s ( A N O S I M ; C l a r k e 1 9 9 3 ) . T o d e t e r m i n e w h i c h h i g h e r i n v e r t e b r a t e t a x a w e r e m o s t i n f l u e n c e d b y w a v e a c t i o n o n e a c h a lga l h o s t s p e c i e s , I c o m p a r e d , u s i n g S imi la r i ty P e r c e n t a g e s ( S I M P E R ; C l a r k e 1 9 9 3 ) , e p i f a u n a a s s e m b l a g e s at the l o w e s t a n d h i g h e s t w a v e v e l o c i t i e s a v a i l a b l e for e a c h h o s t . T h i s a n a l y s i s i dent i f i ed w h i c h i n v e r t e b r a t e t a x a w e r e r e s p o n s i b l e for 9 0 % o f t h e var iab i l i ty in i n v e r t e b r a t e a s s e m b l a g e s t r u c t u r e a c r o s s t h e g r a d i e n t o f w a v e ve loc i t y . I t h e n p lo t ted t h e c h a n g e in a v e r a g e a b u n d a n c e s of t h e s e i n v e r t e b r a t e t a x a for e a c h a l g a l h o s t a l o n g t h e w a v e e x p o s u r e g r a d i e n t . U n i v a r i a t e a n a l y s e s w e r e d o n e u s i n g S P S S ( V e r s i o n 12, S P S S Inc.) a n d mu l t i va r i a te a n a l y s e s w e r e d o n e u s i n g P R I M E R ( V e r s i o n . 6 .1 .6 , P r i m e r - E L t d . , w w w . p r i m e r - e . o r g ) . 7 4 4.3 Results 4.3.1 Invertebrate abundance and taxon richness I n c r e a s e d w a v e v e l o c i t y r e s u l t e d in a d e c r e a s e in i n v e r t e b r a t e a b u n d a n c e o n Fucus distichus, but not o n a n y of the o t h e r t e s t e d h o s t s ( F i g u r e 4 . 3 ; T a b l e 4 . 1 ) . W a v e v e l o c i t y d e c r e a s e d i n v e r t e b r a t e t a x o n r i c h n e s s o n o n l y t h r e e of t h e t e s t e d s e a w e e d h o s t s ( F i g u r e 4 .4 ; T a b l e 4 . 1 ) . B a s e d o n this latter resul t , t h r e e g r o u p s of hab i ta t - p r o v i d i n g a l g a e w e r e i dent i f i ed , a n d t h e s e w e r e c o n g r u e n t with t h e re la t i ve a r c h i t e c t u r a l c o m p l e x i t y o f the h o s t s : low, m o d e r a t e , a n d h i g h c o m p l e x i t y thal l i . R i c h n e s s o f e p i f a u n a f o u n d o n s e a w e e d s of l ow c o m p l e x i t y (i .e. c r u s t s o r u n b r a n c h i n g b l a d e s s u c h a s ' P e t r o c e l i s ' , Alaria marginata, a n d Mazzaella splendens; F i g u r e 4 .2 h, a , i) a n d h i g h c o m p l e x i t y (i.e. h i g h l y f o l d e d , p a p i l l a t e d , o r b r a n c h e d thall i s u c h a s Ulva lactuca, Chondracanthus exasperatus Cryptosiphonia woodii, Endocladia muricata, a n d Polysiphonia s p p ; F i g u r e 4 . 2 I, b, d , e, j) w a s no t a f f e c t e d b y w a v e ve loc i t y . A l t e r n a t i v e l y , i n v e r t e b r a t e s l iving o n s e v e r a l s e a w e e d s o f m o d e r a t e a r c h i t e c t u r a l c o m p l e x i t y (i .e. c o a r s e l y o r s p a r s e l y b r a n c h i n g s p e c i e s : Fucus distichus, Gastroclonium subarticulatum, a n d Prionitis lyallii ( F i g u r e 4 . 2 f, g , k) w e r e r e d u c e d in i n v e r t e b r a t e t a x o n r i c h n e s s a s w a v e v e l o c i t y i n c r e a s e d . O n e e x c e p t i o n to th is latter g r o u p i n g w a s Codium fragile, w h i c h is a c o a r s e l y b r a n c h i n g g r e e n a l g a ( F i g u r e 4 .2 c) ; i n v e r t e b r a t e t a x o n r i c h n e s s o n C. fragile w a s not i n f l u e n c e d b y i n c r e a s e d w a v e v e l o c i t y . I n v e r t e b r a t e t a x o n r i c h n e s s w a s m o r e i n f l u e n c e d b y i n c r e a s i n g w a v e v e l o c i t y t h a n w a s i n v e r t e b r a t e a b u n d a n c e ; for two s e a w e e d h o s t s Prionitis lyallii and Gastroclonium subarticulatum ( F i g u r e 4 .2 k, g), i n v e r t e b r a t e t a x o n r i c h n e s s d e c r e a s e d with i n c r e a s i n g w a v e v e l o c i t y ( F i g u r e 4 .3) , w h e r e a s i n v e r t e b r a t e a b u n d a n c e ( F i g u r e 4 .4) d id not ( T a b l e 4 . 1 ) . 4.3.2 Invertebrate composition A s s e e n for i n v e r t e b r a t e t a x o n r i c h n e s s a n d a b u n d a n c e , t h e i n f l u e n c e of w a v e v e l o c i t y o n i n v e r t e b r a t e c o m p o s i t i o n (i .e. t he ident i t ies o f e p i f a u n a t a x a ) d e p e n d e d o n the ident i ty o f the h o s t s e a w e e d ( T a b l e 4 .2 a n d F i g u r e 4 . 5 ) . I n v e r t e b r a t e c o m p o s i t i o n o n 7 5 a l g a l h o s t s with s i m p l e m o r p h o l o g i e s ( 'Pet roce l i s ' , Alaria, a n d Mazzaella) w a s not i n f l u e n c e d by w a v e v e l o c i t y . F o r s e v e r a l s p e c i e s , Cryptosiphonia woodii, Prionitis lyallii a n d Ulva lactuca, c h a n g e s in i n v e r t e b r a t e c o m p o s i t i o n w e r e s e e n at l o w e r w a v e v e l o c i t i e s , but a s s e m b l a g e s s t a b i l i z e d a n d d id not c h a n g e a b o v e w a v e v e l o c i t i e s o f 3 m/s. F o r the r e m a i n i n g s p e c i e s , t he a s s e m b l a g e s a p p e a r to s t a b i l i z e at h i g h e r w a v e v e l o c i t i e s ( a b o v e 5 m/s). T h e m o s t a b u n d a n t i n v e r t e b r a t e t a x a f o u n d o n m o s t h o s t s p e c i e s w e r e a m p h i p o d s , c o p e p o d s , a n d b i v a l v e s ( F i g u r e 4.5). T h e i n f l u e n c e o f i n c r e a s e d w a v e v e l o c i t y o n e a c h o f t h e s e i n v e r t e b r a t e t a x a w a s v a r i a b l e for e a c h h o s t a l g a , a n d n o m o n o t o n i c r e l a t i o n s h i p s w e r e o b s e r v e d . A m p h i p o d s , t he m o s t a b u n d a n t g r o u p , i n c r e a s e d in a b u n d a n c e o n Chondracanthus exasperatus, but d e c r e a s e d o n Fucus distichus. B i v a l v e s ( typ ica l ly j u v e n i l e m u s s e l s , Mytilus s p p . ) w e r e a b u n d a n t o n o n l y a f e w a l g a l h o s t s , a n d a p p e a r e d e i t h e r u n a f f e c t e d b y i n c r e a s i n g w a v e v e l o c i t y ( e . g . o n Cryptosiphonia woodii) o r i n c r e a s e d in a b u n d a n c e ( e . g . o n Endocladia muricata). M a n y of the o t h e r i n v e r t e b r a t e t a x a w e r e p r e s e n t in s m a l l n u m b e r s a n d a p p e a r e d res i l ient to c h a n g e s in w a v e v e l o c i t y . 4.4 Discussion T h e r e s u l t s p r e s e n t e d h e r e s u p p o r t t he v i e w that traits o f h a b i t a t - p r o v i d i n g s p e c i e s c a n in te rac t with a n e n v i r o n m e n t a l g r a d i e n t to m o d e r a t e t h e i m p o r t a n c e of e c o s y s t e m e n g i n e e r i n g . I f o u n d that t h e t a x o n r i c h n e s s o f a s s o c i a t e d i n v e r t e b r a t e s d e p e n d e d o n t h e i n t e r a c t i o n b e t w e e n a r c h i t e c t u r a l c o m p l e x i t y o f h o s t s p e c i e s a n d the w a v e e x p o s u r e in tens i ty . T h r e e ' g r o u p s ' o f h o s t s p e c i e s w e r e i den t i f i ed , a n d t h e s e g r o u p s w e r e c o n g r u e n t with the re la t ive a r c h i t e c t u r a l c o m p l e x i t y o f the s e a w e e d hos t : a) ' s i m p l e ' thall i that w e r e m i n i m a l l y ut i l i zed a s hab i ta t u n d e r a n y o f t h e t e s t e d c i r c u m s t a n c e s , b) thall i that w e r e c o a r s e l y b r a n c h e d a n d w e r e ut i l i zed b y d i v e r s e i n v e r t e b r a t e a s s e m b l a g e s u n d e r re la t ive ly b e n i g n w a v e c o n d i t i o n s but b e c a m e l e s s ut i l i zed u n d e r h i g h e r w a v e a c t i o n , a n d C ) m o r e c o m p l e x o r h i g h l y f o l d i n g a l g a l h o s t s that a p p e a r e d to p r o v i d e e q u i v a l e n t hab i ta t to d i v e r s e i n v e r t e b r a t e a s s e m b l a g e s u n d e r all t e s t e d w a v e c o n d i t i o n s . T o u n d e r s t a n d h o w m o r p h o l o g y of s e a w e e d h o s t s c a n interact 7 6 with w a v e e x p o s u r e to r e g u l a t e i n v e r t e b r a t e d ivers i ty , it is u s e f u l to r e v i e w h o w s e a w e e d s h a v e a d a p t e d to c o p e with w a v e a c t i o n . 4.4.1 How do seaweeds protect invertebrates from wave action? T h e b e h a v i o r o f c r a s h i n g w a v e s o n a s h o r e is c o m p l e x , but t w o m a j o r f o r c e s a r e e x p e r i e n c e d b y a l g a e : brief, but i n t e n s e , i m p i n g e m e n t f o r c e s , a s we l l a s d r a g f o r c e s ( D e n n y a n d G a y l o r d 2 0 0 2 ) . T o c o p e with w a v e a c t i o n , m a n y a l g a l s p e c i e s h a v e e v o l v e d f lex ib le thall i that let t h e m r e c o n f i g u r e in f low, a l l o w i n g the a l g a to e x p e r i e n c e l o w e r f o r c e s t h a n w o u l d m o r e rigid o r g a n i s m s ( D e n n y a n d G a y l o r d 2 0 0 2 ) . In Chondrus crispus, two f a c e t s o f t h a l l u s r e c o n f i g u r a t i o n h a v e b e e n iden t i f i ed : a b e n d i n g of the s t ipe to a l l o w t h e a l g a to f lat ten a g a i n s t t he s u b s t r a t e a s we l l a s a c o m p a c t i o n of the c r o w n ( B o i l e r a n d C a r r i n g t o n 2 0 0 6 ) . W h e n t h e a l g a l h o s t f l a t tens d o w n th is l o w e r s t h e a s s o c i a t e d i n v e r t e b r a t e a s s e m b l a g e to the s u b s t r a t e w h e r e , in t h e o r y , t h e v e l o c i t y o f w a t e r s h o u l d b e s l o w e r a s c o m p a r e d to h i g h e r p o s i t i o n s in t h e w a t e r c o l u m n . H o w e v e r , for t u r b u l e n t f l o w s a n d s h a l l o w w a t e r (< 5 m e t e r s ) the d i f f e r e n c e s in v e l o c i t y b e t w e e n the s u b s t r a t e a n d w a t e r c o l u m n is n e g l i g i b l e ( D e n n y a n d G a y l o r d 2 0 0 2 ) , s o th is m e c h a n i s m is u n l i k e l y to c o n t r i b u t e to the o b s e r v e d r e l a t i o n s h i p s b e t w e e n i n v e r t e b r a t e d i ve rs i t y a n d w a v e v e l o c i t y . T h e a l g a l h o s t ' s p r o p e n s i t y to u n d e r g o c r o w n c o m p a c t i o n is m u c h m o r e l ikely to d i rec t ly i n f l u e n c e e p i f a u n a l i n v e r t e b r a t e s . T h i s c r o w n c o m p a c t i o n s e r v e s to s t r e a m l i n e the a l g a b y ' b r i n g i n g t o g e t h e r ' p a r t s o f t h e t h a l l u s a n d , in d o i n g s o , c a n p r o t e c t t he i n v e r t e b r a t e s f r o m b e i n g d i s l o d g e d by the w a t e r f low. H o w e v e r , t h e d e g r e e to w h i c h th is c o m p a c t i o n c a n p r o t e c t t h e i n v e r t e b r a t e s is d e p e n d a n t u p o n t h e m o r p h o l o g y of the h o s t a l g a ( B o i l e r a n d C a r r i n g t o n 2 0 0 7 ) . W h i l e I h a v e not d i rec t l y d e m o n s t r a t e d that m y s e a w e e d s t u d y s p e c i e s c a n u n d e r g o c r o w n c o m p a c t i o n , a r e c e n t c r o s s - s p e c i e s c o m p a r i s o n of r e c o n f i g u r a t i o n for t e n n o r t h w e s t A t l a n t i c s e a w e e d s ( B o i l e r a n d C a r r i n g t o n 2 0 0 7 ) s h o w e d that intert idal a l g a e with s i m i l a r m o r p h o l o g i e s r e c o n f i g u r e to a c o m p a r a b l e e x t e n t . It is t h e r e f o r e r e a s o n a b l e to g e n e r a l i z e to t h e t a x a t e s t e d in th is s t u d y . A l g a l c r u s t s (i .e. t he ' P e t r o c e l i s ' p h a s e of Mastocarpus) c a n n o t , o f c o u r s e , u n d e r g o c r o w n c o m p a c t i o n , s o t h e y d o not p r o v i d e c o v e r f r o m w a v e a c t i o n . A s a resul t , 7 7 t h e r e is a s p a r s e ( i .e. t y p i c a l l y n o n - e x i s t e n t ) i n v e r t e b r a t e a s s e m b l a g e a s s o c i a t e d with ' P e t r o c e l i s ' ( F i g u r e s 4 . 3 - 5 ) . F o r s i m p l e b l a d e s (i .e. Alaria a n d Mazzaella), w h i c h a r e no t wel l ut i l i zed by i n v e r t e b r a t e e p i f a u n a e v e n at l ow w a v e v e l o c i t i e s , r e c o n f i g u r a t i o n of the c r o w n is a c c o m p l i s h e d b y a n ' inrol l ing' of the b l a d e ( B o i l e r a n d C a r r i n g t o n 2 0 0 7 ) . I n v e r t e b r a t e s o n t h e ' i ns ide ' o f the ro l led b l a d e h a v e the p o t e n t i a l to b e p r o t e c t e d f r o m w a v e a c t i o n ( M . B o i l e r , p e r s o n a l c o m m u n i c a t i o n ) . F o r c o a r s e l y b r a n c h e d a l g a e , interstit ial s p a c e s a r e re la t ive ly l a r g e , s o c r o w n c o m p a c t i o n is u n l i k e l y to p r e v e n t w a t e r f r o m f l o w i n g t h r o u g h t h e i n t e r s t i c e s o f the t h a l l u s . A s a resu l t , i n v e r t e b r a t e s i nhab i t ing s p e c i e s s u c h a s Fucus distichus, Gastroclonium subarticulatum, a n d Prionitis lyallii are l ikely i n c r e a s i n g l y d i s l o d g e d a s w a t e r m o t i o n b e c o m e s f a s t e r ( F i g u r e 4 . 3 a n d 4 . 4 ) . F u r t h e r , B o i l e r a n d C a r r i n g t o n ( 2 0 0 7 ) s h o w e d that t h e s e c o a r s e l y b r a n c h i n g a l g a e r e c o n f i g u r e d to a l e s s e r e x t e n t a s c o m p a r e d to b l a d e d f o r m s , s o t h e a l g a e t e n d e d to e x p e r i e n c e h i g h e r d r a g . F o r h i g h l y b r a n c h i n g t a x a s u c h a s Polysiphonia s p p . a n d Cryptosiphonia woodii, interstit ial s p a c e s a r e re la t ive ly s m a l l , s o c r o w n c o m p a c t i o n resu l t s in a c o h e s i v e c o v e r that f o r m s o v e r the i n v e r t e b r a t e s . S i m i l a r l y , Ulva lactuca is a h igh ly f o l d e d b l a d e that c a n bu f fe r i n v e r t e b r a t e s f r o m w a v e f o r c e , s o t a x o n r i c h n e s s a n d a b u n d a n c e o f a s s o c i a t e d i n v e r t e b r a t e s a p p e a r r o b u s t to e l e v a t e d w a t e r v e l o c i t y . A n o t h e r s h a p e - c h a n g e m e c h a n i s m that a l g a e u s e to c o p e with w a v e a c t i o n is p h e n o t y p i c p las t i c i ty ( N o r t o n et al. 1 9 8 2 ) ; a l g a e f o u n d in w a v e - e x p o s e d a r e a s t e n d to b e s m a l l e r t h a n c o u n t e r p a r t s f o u n d in w a v e - s h e l t e r e d a r e a s ( B l a n c h e t t e 1 9 9 7 , F o w l e r - W a l k e r et al. 2 0 0 6 ) . D i f f e r e n c e s in m o r p h o l o g y a c r o s s a w a v e e x p o s u r e g r a d i e n t c a n o c c u r t h r o u g h d i f fe rent ia l g r o w t h ( F o w l e r - W a l k e r et al. 2 0 0 6 ) o r t h r o u g h tat ter ing of t h e t h a l l u s ( B l a n c h e t t e 1 9 9 7 ) . A l t h o u g h th is r e d u c t i o n in s u r f a c e a r e a c o u l d l e a d to a l o s s o f s p a c e for u s e b y i n v e r t e b r a t e s , th is m i g h t not d i rec t ly t r a n s l a t e to a l o s s o f i n v e r t e b r a t e d ivers i ty , for t w o r e a s o n s . F irst ly , e f f e c t s o f hab i ta t c o m p l e x i t y c a n a c t i n d e p e n d e n t l y o f s u r f a c e a r e a ( J o h n s o n et al. 2 0 0 3 , B e c e r r a - M u n o z a n d S c h r a m m 2 0 0 6 ) . F o r e x a m p l e , B e c k ( 2 0 0 0 ) f o u n d that g a s t r o p o d d i v e r s i t y i n c r e a s e d with t o p o g r a p h i c c o m p l e x i t y o f s u b s t r a t e w h e n s u r f a c e a r e a w a s h e l d c o n s t a n t . S e c o n d l y , d a m a g e to thall i c a n resu l t in i n c r e a s e d a d v e n t i t i o u s b r a n c h i n g ( V a n A l s t y n e 1 9 8 9 ) a n d t h u s ta t ter ing m a y e v e n t u a l l y l e a d to i n c r e a s e d t h a l l u s c o m p l e x i t y . T h i s latter i d e a r e m a i n s u n t e s t e d , h o w e v e r the c o n s e q u e n c e s o f a l g a l p h e n o t y p i c p las t i c i ty for i n v e r t e b r a t e h a b i t a t c h o i c e a r e a n in te res t ing a r e a for fu ture s t u d y . 7 8 T h e o b s e r v a t i o n that g r o u p s of i n v e r t e b r a t e t a x a w e r e d i f fe rent ia l l y i n f l u e n c e d by w a v e e x p o s u r e ( F i g u r e 4 .5) s u g g e s t s that, in a d d i t i o n to fac i l i ta tor traits , traits o f the fac i l i ta ted o r g a n i s m s a r e a l s o i m p o r t a n t for d e t e r m i n i n g t h e o u t c o m e o f p o s i t i v e i n t e r a c t i o n s in th is s y s t e m . D o m m a s n e s (1968) s t u d i e d t h e i n f l u e n c e of w a v e e x p o s u r e o n the m e i o f a u n a i n h a b i t i n g Corallina officinalis, a n d s u g g e s t e d that if e p i f a u n a l i n v e r t e b r a t e s h a d a p p e n d a g e s that w e r e wel l m a t c h e d to t h e m o r p h o l o g y of the i r h o s t s e a w e e d , th is w o u l d i m p r o v e the i r abi l i ty to w i t h s t a n d d i s l o d g e m e n t . T h i s i d e a a p p e a r s to b e s u p p o r t e d h e r e , pa r t i cu la r l y for the a m p h i p o d s . W i t h i n c r e a s i n g w a v e ve loc i t y , a m p h i p o d a b u n d a n c e d e c r e a s e d o n w i d e - b l a d e d h o s t s l ike Fucus distichus a n d Mazzaella spendens, but r e m a i n e d s i m i l a r (a lbei t v a r i a b l e ) o n m o r e f ine ly b r a n c h i n g h o s t s ( e . g . Endocladia muricata a n d Cryptosiphonia woodii), l ike ly re f l ec t ing the abi l i ty of a m p h i p o d s to be t te r g r a s p o n t o the t h i n n e r a x e s of t h e c o m p l e x l y b r a n c h i n g h o s t a l g a e . A b o v e w a v e v e l o c i t i e s o f 5 m/s, i n v e r t e b r a t e a s s e m b l a g e s a p p e a r e d to s t a b l i z e o n m a n y o f t h e h o s t a l g a e . H o w e v e r , it is diff icult to a s s e s s stabi l i ty b e c a u s e c o l l e c t i o n s t a k e n a b o v e 6 m/s w e r e not a v a i l a b l e for s e v e r a l h o s t s p e c i e s , a n d t h e r e is potent ia l for a s s e m b l a g e c h a n g e at h i g h e r w a v e v e l o c i t i e s t h a n w e r e m e a s u r e d in th is s t u d y . 4.4.2 Performance of the Bruno and Bertness model B r u n o a n d B e r t n e s s ( 2 0 0 0 ) p r o p o s e d a c o n c e p t u a l m o d e l that o u t l i n e d h o w fac i l i tator traits c o u l d in te rac t with a m b i e n t s t r e s s l e v e l s to d e t e r m i n e l o c a l s p e c i e s d i ve rs i t y ( F i g u r e 4 . 1 ) . In g e n e r a l the i r p r e d i c t i o n s w e r e s u p p o r t e d . H o w e v e r , m y r e s u l t s d id not m a t c h t h e s h a p e o f the i r p r e d i c t e d r e l a t i o n s h i p s in all c a s e s . T h e m o d e l p e r f o r m e d we l l for p r e d i c t i n g t h e i n f l u e n c e of s e a w e e d m o r p h o l o g y o n i n v e r t e b r a t e d i ve rs i t y at h i g h l e v e l s o f w a v e i m p a c t ; h o s t s p e c i e s with s i m p l e a r c h i t e c t u r e w e r e l e s s a b l e to bu f fe r i n v e r t e b r a t e s f r o m d i s l o d g e m e n t a s c o m p a r e d to h o s t s p e c i e s with m o r e c o m p l e x m o r p h o l o g i e s . H o w e v e r , at low l e v e l s o f s t r e s s , B r u n o a n d B e r t n e s s ( 2 0 0 0 ) p r e d i c t e d that l o c a l s p e c i e s d i v e r s i t y s h o u l d b e the s a m e o n all fac i l i ta tors . O n t h e c o n t r a r y , at low l e v e l s o f w a v e i m p a c t , t he s h a p e of the r e l a t i o n s h i p I o b s e r v e d w a s s i m i l a r to that at h i g h w a v e s t r e s s ; c o m p l e x s e a w e e d f o r m s p e r f o r m e d be t te r t h a n s i m p l e f o r m s . T h e r e a r e at l e a s t t w o r e a s o n s w h y t h e p r e d i c t i o n s o f B r u n o a n d 79 B e r t n e s s ' m o d e l d id not w o r k for p r e d i c t i n g i m p o r t a n c e of e c o s y s t e m e n g i n e e r i n g in low w a v e s t r e s s a r e a s . In intert idal e n v i r o n m e n t s , s t r e s s o r s ra re ly a c t a l o n e ; c o v a r y i n g s t r e s s o r s c o n f o u n d t e s t s o f i n d i v i d u a l s t r e s s g r a d i e n t s . W h e n c o n s i d e r i n g w a t e r m o t i o n , I h a v e f o c u s e d s o far o n l y o n t h e n e g a t i v e i m p l i c a t i o n s of i n c r e a s i n g h y d r o d y n a m i c f o r c e s . H o w e v e r , at t h e l o w e r e n d o f t h e w a t e r m o t i o n g r a d i e n t , o r g a n i s m s a r e s u b j e c t e d to s t r e s s e s a s s o c i a t e d with d e s i c c a t i o n , s u c h a s w a t e r s t r e s s a n d h i g h t e m p e r a t u r e s ( H e l m u t h et al. 2 0 0 2 ) . T h e s e a d d i t i o n a l s t r e s s o r s m a y e x p l a i n w h y , at l ow w a v e v e l o c i t i e s , s i m p l e a l g a l f o r m s h a d a low d ive rs i t y o f a s s o c i a t e d i n v e r t e b r a t e s c o m p a r e d to m o r e c o m p l e x f o r m s . A n o t h e r f a c t o r c o n f o u n d i n g the p r e d i c t i o n s of t h e B r u n o a n d B e r t n e s s m o d e l is t h e a s s u m p t i o n that t h e s t r e s s o r d o e s n ' t i n f l u e n c e t h e hab i ta t - p r o v i d i n g s p e c i e s ( B r u n o a n d B e r t n e s s 2 0 0 0 ) . T h i s a s s u m p t i o n is c l e a r l y v i o l a t e d in th is s t u d y s y s t e m b e c a u s e w a v e a c t i o n c a n m o d i f y t h e m o r p h o l o g y o f h o s t a l g a e . 4.4.3 Implications O n e p r e d i c t e d c o n s e q u e n c e of g l o b a l c l i m a t e c h a n g e is a n i n c r e a s e d f r e q u e n c y a n d in tens i ty o f s t o r m s , a n d t h u s o f w a v e a c t i o n ( C a r t e r a n d D r a p e r 1988, H o o z e m a n s a n d W i e r s m a 1 9 9 2 ) . T h e s e i n c r e a s e s in w a v e a c t i o n c a n in turn i n f l u e n c e t h e s u r v i v a l a n d d i s t r ibut ion of s e a w e e d s ( V a d a s et al. 1 9 9 0 , D i e z et al. 2 0 0 3 , J o n s s o n ef al. 2 0 0 6 ) . T h e f i n d i n g s of the c u r r e n t s t u d y s u g g e s t that in s o m e c a s e s , t h e s e sh i f t s in s e a w e e d c o m p o s i t i o n will h a v e r a m i f i c a t i o n s for i n v e r t e b r a t e s that u s e s e a w e e d s a s habi tat , po tent ia l l y l e a d i n g to c h a n g e s in c o m p o s i t i o n a n d a b u n d a n c e of f o o d s o u r c e s for b i rds a n d f i sh that f e e d o n s e a w e e d - d w e l l i n g i n v e r t e b r a t e s ( K e n d a l l e f al. 2 0 0 4 , V a n d e n d r i e s s c h e et al. 2 0 0 7 ) . If s c i e n t i s t s a n d m a n a g e r s h o p e to d e t e r m i n e w h i c h , a n d u n d e r w h a t c i r c u m s t a n c e s , e c o s y s t e m e n g i n e e r i n g is impor tan t , it is un l i ke l y that s i m p l e m o d e l s will e f f ec t i ve l y d e s c r i b e t h e c o n t e x t spec i f i c i t y o f s u c h p o s i t i v e i n t e r a c t i o n s . M y f i n d i n g s s u g g e s t that t h e r e l a t i o n s h i p s b e t w e e n fac i l i tator traits a n d e n v i r o n m e n t a l g r a d i e n t s a r e not s t r a i g h t f o r w a r d , a n d that k n o w l e d g e of s e v e r a l k e y f e a t u r e s will b e r e q u i r e d , i n c l u d i n g d e t a i l s a b o u t t h e d o m i n a n t s t r e s s o r s a c t i n g in t h e s y s t e m , t h e m e c h a n i s m s 8 0 t h r o u g h w h i c h t h e s e s t r e s s o r s n e g a t i v e l y i n f l u e n c e o r g a n i s m s p r e s e n t , a n d h o w hab i ta t - p r o v i d i n g o r g a n i s m s a m e l i o r a t e t h e e f f e c t s of t h e s e s t r e s s o r s . 81 T a b l e 4 . 1 : R e l a t i o n s h i p s b e t w e e n m a x i m u m w a v e v e l o c i t y ( r a n g i n g f r o m ~1 m/s - 6 m/s) v e r s u s i n v e r t e b r a t e a b u n d a n c e a n d r a r e f i e d i n v e r t e b r a t e r i c h n e s s a s s o c i a t e d with t w e l v e s e a w e e d s p e c i e s . B o l d f a c e text i n d i c a t e s s i g n i f i c a n t (p < 0 .05) i n f l u e n c e of w a v e ve loc i t y , a n d all s i gn i f i can t r e l a t i o n s h i p s a r e n e g a t i v e . Host Algal Species Invertebrate Abundance Invertebrate Richness F P F P Alaria marginata 0 . 0 9 5 0 .761 0 . 2 4 7 0 . 6 2 4 Chondracanthus exasperatus 0 . 9 7 6 0 . 3 4 4 3 . 5 2 5 0 . 0 6 4 Codium fragile 5 . 3 5 2 0 . 0 9 0 2 . 6 4 2 0 . 1 8 2 Cryptosiphonia woodii 0 . 2 0 3 0 . 6 8 3 0 . 1 1 4 0 . 7 6 4 Endocladia muricata 0 . 2 8 2 0 . 6 1 4 0 . 0 9 5 0 . 7 6 9 Fucus distichus s. evanescens 24.12 < 0.001 32.20 < 0.001 Gastroclonium subarticulatum 0 . 1 5 9 0 . 7 0 0 23.49 < 0.001 Mastocarpus ( ' P e t r o c e l i s ' p h a s e ) - 0 . 0 7 9 0 . 8 2 8 0 . 1 2 3 0 . 7 3 5 Mazzaella splendens 0 . 3 2 5 0 . 5 7 2 0 . 3 2 5 0 . 5 7 2 Polysiphonia s p p . 1.147 0 . 3 5 2 0 . 3 6 5 0 . 5 8 0 Prionitis lyallii 3 . 2 5 5 0 . 1 0 9 20.04 0.002 Ulva lactuca 4 . 2 3 4 0 . 0 5 4 0 . 0 0 3 0 . 9 5 9 T a b l e 4 . 2 : R e s u l t s o f A N O S I M t e s t s for d i f f e r e n c e s in c o m p o s i t i o n , a c r o s s a g r a d i e n t of m a x i m u m w a v e ve loc i ty , for i n v e r t e b r a t e s a s s o c i a t e d with t w e l v e h o s t a l g a l s p e c i e s . B o l d f a c e R - v a l u e s i nd i ca te a s ign i f i cant d i f f e r e n c e (p < 0 . 0 5 ) . G l o b a l R H o s t S e a w e e d S p e c i e s < 2 m/s 2 - 2.9 m/s 3 - 3.9 m/s 4 - 4 .9 m/s 5 - 5.9 m/s v e r s u s v e r s u s v e r s u s v e r s u s v e r s u s 2 - 2.9 m/s 3 - 3.9 m/s 4 - 4 . 9 m/s 5 - 5.9 m/s > 6 m/s 0 . 0 5 7 Alaria marginata - - - - - 0.158 Chondracanthus exasperatus 0.109 0.18 n d n d 0 . 1 2 2 * 0.254 Codium fragile n d n d 0.527 0.364 0 . 1 1 7 0.479 Cryptosiphonia woodii 0.544 0.403 n d 0 . 1 1 7 * nd 0.537 Endocladia muricata 0.473 0 . 1 2 0.924 n d n d 0.183 Fucus distichus s. evanescens 0.131 0 . 0 1 4 0.268 0 . 0 2 3 0 .121 0.276 Gastroclonium subarticulatum 0.329 0.19 0.571 0.283 nd - 0 . 0 3 3 Mastocarpus p e t r o c e l i s p h a s e ) - - - - - 0 . 0 2 4 Mazzaella splendens - - - - - 0.36 Polysiphonia sp. n d 0.385 0.8 0.259 nd 0.078 Prionitis lyallii n d 0.308 - 0 . 1 1 9 - 0 . 1 3 5 0 . 1 3 3 0.086 Ulva lactuca 0.282 0 . 0 6 5 - 0 . 0 7 5 0 . 0 4 4 0 . 1 7 3 (-) i n d i c a t e s that n o c o m p a r i s o n is n e c e s s a r y d u e to a n o n s i g n i f i c a n t G l o b a l A N O S I M test , (nd) i n d i c a t e s that n o d a t a a r e a v a i l a b l e for the c o m p a r i s o n . (*) i n d i c a t e s that c o m p a r i s o n w a s d o n e for c l o s e s t a v a i l a b l e ( lower) w a v e v e l o c i t y g r o u p . co CO Low i to tor not required 1 1 Facilitator largely / eliminates stress High / ' Stress too high and trait value too low for facilitator to affect diversity —___ ——• Facilitator trait/stress reduction F i g u r e 4 . 1 : C o n c e p t u a l m o d e l i l lustrat ing h o w t h r e e l e v e l s o f a m b i e n t s t r e s s ( low, m e d i u m , a n d h i g h ) a n d fac i l i ta tor traits a r e p r o p o s e d to in te rac t to d e t e r m i n e l e v e l s of l o c a l s p e c i e s d i v e r s i t y . F i g u r e r e p r o d u c e d f r o m B r u n o a n d B e r t n e s s ( 2 0 0 1 ) , u s e d with p e r m i s s i o n f r o m S i n a u e r A s s o c i a t e s , Inc. 8 4 F i g u r e 4 . 2 : P h o t o g r a p h s o f t w e l v e s e a w e e d s p e c i e s s t u d i e d a s h o s t s for s m a l l m o b i l e i n v e r t e b r a t e s : a ) Alaria marginata, b) Chondracanthus exasperatus, c) Codium fragile, d) Cryptosiphonia woodii, e ) Endocladia muricata, f) Fucus distichus s u b s p . evanescens, g) Gastroclonium subarticulatum, h) Mastocarpus ( ' P e t r o c e l i s ' p h a s e ) , i) Mazzaella splendens, j) Polysiphonia hendryi, k) Prionitis lyallii, a n d I) Ulva lactuca. 85 Alaria marginata Codium fragile , Cryptosiphonia woodii Endocladia muricata] * F u c u s distichus s. evanescens I—*-* 1 Gastroclonium subarticulatum] Mastocarpus ('Petrocelis' phase) Mazzaella splendens Prionitis lyallii Ulva lactuca HLMJL • 7 0 1 2 3 4 5 6 7 0 1 Maximum wave velocity (m/s) 2 3 4 5 6 7 F i g u r e 4 . 3 : R e l a t i o n s h i p b e t w e e n m a x i m u m w a v e v e l o c i t y ( o v e r a 2 4 h o u r p e r i o d ) a n d a b u n d a n c e o f s m a l l m o b i l e i n v e r t e b r a t e s a s s o c i a t e d with t w e l v e s p e c i e s o f h o s t s e a w e e d . A n a s t e r i s k (*) ident i f ies a s ign i f i can t i n f l u e n c e of w a v e v e l o c i t y . • mmm*m • • • • • • • tmtm • • • • 0 1 2 3 4 5 6 7 0 1 Maximum wave velocity (m/s) 2 3 4 5 6 7 0 1 2 3 4 5 6 7 F i g u r e 4 . 4 : R e l a t i o n s h i p b e t w e e n m a x i m u m w a v e v e l o c i t y ( o v e r a 2 4 h o u r p e r i o d ) a n d t a x o n r i c h n e s s ( r a r e f i e d to 2 0 i n d i v i d u a l s ) o f s m a l l m o b i l e i n v e r t e b r a t e s a s s o c i a t e d with t w e l v e s p e c i e s o f h o s t s e a w e e d . A n a s t e r i s k (*) ident i f i es a s i g n i f i c a n t i n f l u e n c e o f w a v e v e l o c i t y . 87 CD 1 c CO •a I 0 ca <D 50 CB CO S> 40 < 30 20 10 0 Alaria marginata Amphipods * Limpets •o Bivalves 0 Mites - - • Copepods - - - • • A Nematodes —A Diptera <? NucJibtanchs m Isopods • • Polychaetes — D Larvae — - O — Snails Cryptosiphonia woodii / / / V / ' - .. # °l •• 0 o ... fee <2 2-3 3-4 4-5 5-6 >6 Chondracanthus exasperatus Endocladia muricata / \ o / 0 I- < 2 2-3 3-4 4-5 5-6 >6 Max imum wave velocity (m/s) <2 2-3 3-4 4-5 5-6 >6 Figure 4.5A: C hange s in average abundance of invertebrate taxa assoc ia ted with six host seaweed spec ies ac ross a max imum wave velocity gradient. Error bars were omitted and lines joining points were added for clarity. Note the different Y -axes sca les . CO co Gastroclonium subarticulatum Polysiphonia spp. < 2 2-3 3-4 4-5 5-6 >6 Mastocarpus ('Petrocelis' phase) Amphipods Bivalves Copepods Diptera isopods Larvae Limpets Mites Nematodes Nudibranchs Polychaetes Snails <2 2-3 3 ^ 4-5 5-6 >6 Maximum wave velocity (m/s) Ulva lactuca - A » \ . r"—, "--r- - -r ^ <2 2-3 3-4 4-5 5-6 >6 Figure 4.6B: Changes in average abundance of invertebrate taxa associated with six host seaweed species across a maximum wave velocity gradient. Error bars were omitted and lines joining points were added for clarity. Note the different Y-axes scales. oo CD 4.5 Literature cited A r r o y o , N . L , M . M a l d o n a d o , R. P e r e z - P o r t e l a , a n d J . B e n i t o . 2 0 0 4 . D i s t r i b u t i o n p a t t e r n s o f m e i o f a u n a a s s o c i a t e d with a sub l i t tora l Laminaria b e d in the C a n t a b r i a n S e a ( n o r t h - e a s t e r n A t l an t i c ) . M a r i n e B i o l o g y 144 :231-242. 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T o w h a t e x t e n t d o e s u p r i g h t s e s s i l e e p i f a u n a a f fec t b e n t h i c b i o d i v e r s i t y a n d c o m m u n i t y c o m p o s i t i o n ? M a r i n e B i o l o g y 143 :783-791. B r a y , J . R., a n d J . T . C u r t i s . 1 9 5 7 . A n o r d i n a t i o n o f the u p l a n d f o r e s t c o m m u n i t i e s o f S o u t h e r n W i s c o n s i n . E c o l o g i c a l M o n o g r a p h s 2 7 :325-349. 9 0 B r u n o , J . F., a n d M . D. B e r t n e s s . 2 0 0 0 . H a b i t a t m o d i f i c a t i o n a n d fac i l i ta t ion in b e n t h i c m a r i n e c o m m u n i t i e s . P a g e s 5 6 0 in M . D. B e r t n e s s , S . D. G a i n e s , a n d M . E . H a y , e d i t o r s . M a r i n e C o m m u n i t y E c o l o g y . S i n a u e r A s s o c i a t e s Inc. B r u n o , J . F., J . J . S t a c h o w i c z , a n d M . D. B e r t n e s s . 2 0 0 3 . I n c l u s i o n o f fac i l i ta t ion into e c o l o g i c a l t h e o r y . T r e n d s in E c o l o g y a n d E v o l u t i o n 18:119-125. B u s t a m a n t e , R. H. , a n d G . M . B r a n c h . 1 9 9 6 . L a r g e s c a l e p a t t e r n s a n d t r o p h i c s t r u c t u r e o f S o u t h e r n A f r i c a n r o c k y s h o r e s : t h e r o l e s o f g e o g r a p h i c v a r i a t i o n a n d w a v e e x p o s u r e . J o u r n a l o f B i o g e o g r a p h y 23:339-351. C a l l a w a y , R. M. , R. W . B r o o k e r , P. C h o l e r , Z . K i k v i d z e , C . J . Lo r t i e , R. M i c h a l e t , L. P a o l i n i , F. I. P u g n a i r e , B. N e w i n g h a m , E . T . A s c h e h o u g , C . A r m a s , D. K i k o d z e , a n d B. J . C o o k . 2 0 0 2 . P o s i t i v e i n t e r a c t i o n s a m o n g a l p i n e p l a n t s i n c r e a s e with s t r e s s . N a t u r e 417:844-848. C a r r i n g t o n , E . 1 9 9 0 . D r a g a n d d i s l o d g m e n t o f a n intert idal m a c r o a l g a : c o n s e q u e n c e s of m o r p h o l o g i c a l v a r i a t i o n in Mastocarpus papillatus K u t z i n g . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 130:185-200. C a r t e r , D., a n d L. D r a p e r . 1 9 8 8 . H a s t h e n o r t h - e a s t A t l a n t i c b e c o m e r o u g h e r ? N a t u r e 332:494. C l a r k e , K. R. 1 9 9 3 . N o n - p a r a m e t r i c mu l t i var ia te a n a l y s i s o f c h a n g e s in c o m m u n i t y s t r u c t u r e . A u s t r a l i a n J o u r n a l o f E c o l o g y 18:117-143. C o l m a n , J . 1 9 3 9 . O n the f a u n a s inhab i t ing intert idal s e a w e e d s . J o u r n a l o f the M a r i n e B i o l o g i c a l A s s o c i a t i o n of the U n i t e d K i n g d o m 24 :129-183. C r a i n , C . M. , a n d M . D. B e r t n e s s . 2 0 0 5 . C o m m u n i t y i m p a c t s o f a t u s s o c k s e d g e : is e c o s y s t e m e n g i n e e r i n g i m p o r t a n t in b e n i g n h a b i t a t s ? E c o l o g y 8 6 :2695-2704. C r a i n , C . M. , a n d M . D. B e r t n e s s . 2 0 0 6 . E c o s y s t e m e n g i n e e r i n g a c r o s s e n v i r o n m e n t a l g r a d i e n t s : I m p l i c a t i o n s for c o n s e r v a t i o n a n d m a n a g e m e n t . B i o s c i e n c e 56:211- 2 1 8 . D e F e l i c e , R. O , a n d J . D. P a r r i s h . 2 0 0 1 . P h y s i c a l p r o c e s s e s d o m i n a t e in s h a p i n g i n v e r t e b r a t e a s s e m b l a g e s in r e e f - a s s o c i a t e d s e d i m e n t s o f a n e x p o s e d H a w a i i a n c o a s t . M a r i n e E c o l o g y P r o g r e s s S e r i e s 215:121-131. D e n n y , M. , a n d B. G a y l o r d . 2 0 0 2 . T h e m e c h a n i c s o f w a v e - s w e p t a l g a e . T h e J o u r n a l of E x p e r i m e n t a l B i o l o g y 205:1355-1362. D i e z , I., A . S a n t o l a r i a , a n d J . M . G o r o s t i a g a . 2 0 0 3 . T h e r e l a t i o n s h i p o f e n v i r o n m e n t a l f a c t o r s to t h e s t r u c t u r e a n d d is t r ibut ion o f s u b t i d a l s e a w e e d v e g e t a t i o n o f t h e w e s t e r n B a s q u e c o a s t (N S p a i n ) . E s t u a r i n e , C o a s t a l a n d S h e l f S c i e n c e 56:1041- 1 0 5 4 . 91 D o m m a s n e s , A . 1 9 6 8 . V a r i a t i o n s in the m e i o f a u n a o f Corallina officinalis L. with w a v e e x p o s u r e . S a r s i a 34:117-124. D u g g i n s , D., J . E . E c k m a n n , C . E . S i d d o n , a n d T . K l i n g e r . 2 0 0 1 . Interac t ive r o l e s of m e s o g r a z e r s a n d c u r r e n t f l o w in s u r v i v a l o f k e l p s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 223:143-155. E w e r s , R. M. , a n d R. K. D i d h a m . 2 0 0 6 . C o n f o u n d i n g f a c t o r s in t h e d e t e c t i o n o f s p e c i e s r e s p o n s e s to h a b i t a t f r a g m e n t a t i o n . B i o l o g i c a l R e v i e w s 81:117-142. F e n w i c k , G . D. 1 9 7 6 . T h e e f fec t o f w a v e e x p o s u r e o n t h e a m p h i p o d f a u n a o f the a l g a Caulerpa brownii. J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 25:1-18. F o w l e r - W a l k e r , M . J . , T . W e r n b e r g , a n d S . D. C o n n e l l . 2 0 0 6 . D i f f e r e n c e s in ke lp m o r p h o l o g y b e t w e e n w a v e s h e l t e r e d a n d e x p o s e d l oca l i t i e s : m o r p h o l o g i c a l l y p l a s t i c o r f i x e d tra i ts . M a r i n e B i o l o g y 148:755-767. G u e r r a - G a r c i a , J . M . 2 0 0 1 . H a b i t a t u s e of the C a p r e l l i d e a ( C r u s t a c e a : A m p h i p o d a ) f r o m C e u t a , N o r t h A f r i c a . O p h e l i a 55:27-38. G u t i e r r e z , L. M . , a n d C . F e r n a n d e z . 1 9 9 2 . W a t e r m o t i o n a n d m o r p h o l o g y in C h o n d r u s c r i s p u s ( R h o d o p h y t a ) . J o u r n a l o f P h y c o l o g y 28:156-162. H e l m u t h , B., C . D. G . H a r l e y , P. M . H a l p i n , M . O . O ' D o n n e l l , G . E . H o f m a n n , a n d C . A . B l a n c h e t t e . 2 0 0 2 . C l i m a t e c h a n g e a n d lat i tudinal p a t t e r n s o f intert ida l t h e r m a l s t r e s s . S c i e n c e 298:1015-1017. H o o p e r , D. U . , F. S . C h a p i n , J . J . E w e l , A . H e c t o r , P . I n c h a u s t i , S . L a v o r e l , J . H : L a w t o n , D . M . L o d g e , M . L o r e a u , S . N a e e m , B. S c h m i d , H . S e t a l a , A . J . S y m s t a d , J . V a n d e r m e e r , a n d D. A . W a r d l e . 2 0 0 5 . E f f e c t s o f b i o d i v e r s i t y o n e c o s y s t e m f u n c t i o n i n g : A c o n s e n s u s o f c u r r e n t k n o w l e d g e . E c o l o g i c a l M o n o g r a p h s 75:3-35. H o o z e m a n s , M . J . , a n d J . W i e r s m a . 1 9 9 2 . Is m e a n w a v e h e i g h t in t h e N o r t h s e a i n c r e a s i n g ? T h e H y d r o g r a p h i c J o u r n a l 63:13-15. H o v e l , K. A . , M . S . F o n s e c a , D. L. M y e r , W . J . K e n w o r t h y , a n d P. E . W h i t f i e l d . 2 0 0 2 . E f f e c t s o f s e a g r a s s l a n d s c a p e s t ruc tu re , s t ruc tu ra l c o m p l e x i t y a n d h y d r o d y n a m i c r e g i m e o n m a c r o f a u n a l d e n s i t i e s in N o r t h C a r o l i n a s e a g r a s s b e d s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 243:11-24. H u r d , C . L. 2 0 0 0 . W a t e r m o t i o n , m a r i n e m a c r o a l g a l p h y s i o l o g y , a n d p r o d u c t i o n . J o u r n a l o f P h y c o l o g y 36:453-472. J o h n s o n , M . P., N . J . F r o s t , M . W . J . M o s l e y , M . F. R o b e r t s , a n d J . H a w k i n s . 2 0 0 3 . T h e a r e a - i n d e p e n d e n t e f f e c t s o f hab i ta t c o m p l e x i t y o n b i o d i v e r s i t y v a r y b e t w e e n r e g i o n s . E c o l o g y L e t t e r s 6 :126-132. 9 2 J o n e s , C . G . , J . H . L a w t o n , a n d M. S h a c h a k . 1 9 9 4 . O r g a n i s m s a s e c o s y s t e m e n g i n e e r s . O i k o s 69:373-386. J o n e s , C . G . , J . H . L a w t o n , a n d M . S h a c h a k . 1 9 9 7 . P o s i t i v e a n d n e g a t i v e e f f e c t s o f o r g a n i s m s a s p h y s i c a l e c o s y s t e m e n g i n e e r s . E c o l o g y 78:1946-1957. J o n s s o n , M. , L. G r a n h a g , P . S . M o s c h e l l a , P. A b e r g , S . J . H a w k i n s , a n d R. C . T h o m p s o n . 2 0 0 6 . In te rac t i ons b e t w e e n w a v e a c t i o n a n d g r a z i n g c o n t r o l t he d is t r ibut ion o f intert idal m a c r o a l g a e . E c o l o g y 87:1169-1178. K e l a h e r , B. P., M . G . C h a p m a n , a n d A . J . U n d e r w o o d . 2 0 0 1 . S p a t i a l p a t t e r n s of d i v e r s e m a c r o f a u n a l a s s e m b l a g e s in c o r a l l i n e turf a n d the i r a s s o c i a t i o n s with e n v i r o n m e n t a l v a r i a b l e s . J o u r n a l of the M a r i n e B i o l o g i c a l A s s o c i a t i o n o f t h e U n i t e d K i n g d o m 81:917-930. K e n d a l l , M . A . , M . T . B u r r o w s , A . J . S o u t h w a r d , a n d S . J . H a w k i n s . 2 0 0 4 . P r e d i c t i n g the c o n s e q u e n c e s o f m a r i n e c l i m a t e c h a n g e o n the i n v e r t e b r a t e p r e y o f the b i rds o f r o c k y s h o r e s . Ibis 146:40-47 S u p p l e m e n t 4 1 . K o e h l , M . A . R. 2 0 0 6 . W a v e - s w e p t s h o r e : t he r igors o f life o n a r o c k y c o a s t . U n i v e r s i t y o f C a l i f o r n i a P r e s s , B e r k e l e y a n d L o s A n g e l e s , C a l i f o r n i a . M c G i l l , B. J . , B. J . E n q u i s t , E . W e i h e r , a n d M. W e s t o b y . 2 0 0 6 . R e b u i l d i n g c o m m u n i t y e c o l o g y f r o m f u n c t i o n a l traits. T r e n d s in E c o l o g y a n d E v o l u t i o n 21:178-185. M c Q u a i d , C . D., a n d T . L. L i n d s a y . 2 0 0 0 . E f f e c t of w a v e e x p o s u r e o n g r o w t h a n d morta l i ty r a t e s o f t h e m u s s e l Perna perna: B o t t o m - u p r e g u l a t i o n o f intert idal p o p u l a t i o n s . M a r i n e E c o l o g y P r o g r e s s S e r i e s 206:147-154. M e n g e , B. A . 2 0 0 0 . T e s t i n g t h e re la t ive i m p o r t a n c e o f p o s i t i v e a n d n e g a t i v e e f f e c t s o n c o m m u n i t y s t r u c t u r e . T r e n d s in E c o l o g y a n d E v o l u t i o n 15:46-47. M i l l i g a n , K.-L. D., a n d R. E . D e W r e e d e . 2 0 0 0 . V a r i a t i o n s in h o l d f a s t a t t a c h m e n t m e c h a n i c s wi th d e v e l o p m e n t a l s t a g e , s u b s t r a t u m - t y p e , s e a s o n , a n d w a v e e x p o s u r e for t h e intert idal k e l p s p e c i e s H e d o p h y l l u m s e s s i l e ( C . A g a r d h ) S e t c h e l l . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 254:189-209. N o r t o n , T . A . , A . C . M a t h i e s o n , a n d M . N e u s h u l . 1 9 8 2 . A r e v i e w o f s o m e a s p e c t s o f f o r m a n d f u n c t i o n in s e a w e e d s . B o t a n i c a M a r i n a 25:501-510. Pratt , M . C , a n d A . S . J o h n s o n . 2 0 0 2 . S t r e n g t h , d r a g , a n d d i s l o d g m e n t o f t w o c o m p e t i n g intert idal a l g a e f r o m two w a v e e x p o s u r e s a n d f o u r s e a s o n s . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 272:71-101. S e e d , R., a n d R. J . O ' C o n n o r . 1 9 8 1 . C o m m u n i t y o r g a n i z a t i o n in m a r i n e a l g a l e p i f a u n a s . A n n u a l R e v i e w of E c o l o g y a n d S y s t e m a t i c s 12:49-74. S t a c h o w i c z , J . J . 2 0 0 1 . M u t u a l i s m , fac i l i tat ion, a n d the s t r u c t u r e o f e c o l o g i c a l c o m m u n i t i e s . B i o s c i e n c e 51:235-246. 9 3 T a y l o r , R. B., a n d R. G . C o l e . 1 9 9 4 . M o b i l e e p i f a u n a o n s u b t i d a l b r o w n s e a w e e d s in n o r t h e a s t e r n N e w Z e a l a n d . M a r i n e E c o l o g y P r o g r e s s S e r i e s 115:271-282. T h e b a u l t , E . , a n d M . L o r e a u . 2 0 0 6 . T h e r e l a t i o n s h i p b e t w e e n b i o d i v e r s i t y a n d e c o s y s t e m f u n c t i o n i n g in f o o d w e b s . E c o l o g i c a l R e s e a r c h 21:17-25. T h o m p s o n , R. E. , B. J . W i l s o n , M . L. T o b i n , A . S . Hil l , a n d S . J . H a w k i n s . 1 9 9 6 . B i o l o g i c a l l y g e n e r a t e d hab i ta t p r o v i s i o n a n d d i v e r s i t y o f r o c k y s h o r e o r g a n i s m s at a h i e r a r c h y o f s p a t i a l s c a l e s . J o u r n a l o f E x p e r i m e n t a l M a r i n e B i o l o g y a n d E c o l o g y 202:73-84. V a d a s , R. L., W . A . W r i g h t , a n d S . L. Mi l ler . 1 9 9 0 . R e c r u i t m e n t o f A s c o p h y l l u m n o d o s u m : w a v e a c t i o n a s a s o u r c e o f morta l i ty . M a r i n e E c o l o g y P r o g r e s s S e r i e s 61:263-272. V a n A l s t y n e , K. L. 1 9 8 9 . A d v e n t i t i o u s b r a n c h i n g a s a h e r b i v o r e - i n d u c e d d e f e n s e in the intert idal b r o w n a l g a F u c u s distichus. M a r i n e E c o l o g y P r o g r e s s S e r i e s 56:169- 1 7 6 . V a n d e n d r i e s s c h e , S . , M . M e s s i a e n , S . O ' F l y n n , M . V i n c x , a n d S . D e g r a e r . 2 0 0 7 . H i d i n g a n d f e e d i n g in f loa t ing s e a w e e d s : F l o a t i n g s e a w e e d c l u m p s a s p o s s i b l e r e f u g e s or f e e d i n g g r o u n d s for f i s h e s . E s t u a r i n e , C o a s t a l a n d S h e l f S c i e n c e 71:691 - 7 0 3 . W i n f r e e , R., T . G r i s w o l d , a n d C . K r e m e n . 2 0 0 7 . E f f e c t o f h u m a n d i s t u r b a n c e o n b e e c o m m u n i t i e s in a f o r e s t e d e c o s y s t e m . C o n s e r v a t i o n B i o l o g y 21 :213-223. W r i g h t , J . P., a n d C . G . J o n e s . 2 0 0 4 . P r e d i c t i n g e f f e c t s o f e c o s y s t e m e n g i n e e r s o n p a t c h - s c a l e s p e c i e s r i c h n e s s f r o m p r i m a r y p roduc t i v i t y . E c o l o g y 8 5 :2071-2081. 9 4 Chapter 5: General Summary 5.1 Recapitulation of thesis objectives In r e s p o n s e to p e r s o n a l ( B a t e s 2 0 0 2 , B a t e s et a l . 2 0 0 5 , 2 0 0 7 ) a n d p u b l i s h e d ( S c h r a m m a n d N i e n h u i s 1 9 9 6 , S c o t t a n d Ti t t ley 1 9 9 8 ) o b s e r v a t i o n s of a n t h r o p o g e n i c c h a n g e s in s e a w e e d b i o d i v e r s i t y , t h e o b j e c t i v e of m y P h . D . r e s e a r c h w a s to i n v e s t i g a t e the p o s s i b l e c o n s e q u e n c e s o f t h e s e f lor ist ic sh i f ts for s m a l l m o b i l e i n v e r t e b r a t e e p i f a u n a that u s e s e a w e e d s a s hab i ta t . A c c o r d i n g l y , I e x a m i n e d h o w s e a w e e d traits at the a s s e m b l a g e l e v e l ( i .e. s e a w e e d b i o d i v e r s i t y ( C h a p t e r 2)) a n d t h e s p e c i e s l eve l ( t a x o n o m i c r e l a t e d n e s s a n d f u n c t i o n a l g r o u p aff inity ( C h a p t e r 3)) i n f l u e n c e d a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a . A s we l l , I e x a m i n e d h o w a n a b i o t i c e n v i r o n m e n t a l g r a d i e n t (i.e. m a x i m u m w a v e v e l o c i t y ) i n t e r a c t e d with s e a w e e d m o r p h o l o g y to d e t e r m i n e the o u t c o m e o f s u c h h a b i t a t - u s e ( C h a p t e r 4 ) . 5.2 Summary of study findings T h e m a j o r c o n c l u s i o n s of C h a p t e r 2, " D o c h a n g e s in s e a w e e d b i o d i v e r s i t y i n f l u e n c e i n v e r t e b r a t e e p i f a u n a ? " w e r e that: a) c h a n g e s in r i c h n e s s of a l g a l s p e c i e s a n d f u n c t i o n a l g r o u p s d o not i n f l u e n c e i n v e r t e b r a t e r i c h n e s s or a b u n d a n c e ; b) m o s t f lor ist ic c h a n g e s at the s e a w e e d a s s e m b l a g e l eve l d id not i n f l u e n c e i n v e r t e b r a t e c o m p o s i t i o n ; o n l y w h e n a l g a l a s s e m b l a g e s w e r e c o m p o s e d just of f o l i o s e s p e c i e s d id I o b s e r v e d i f f e r e n c e s in the a s s o c i a t e d i n v e r t e b r a t e a s s e m b l a g e s . In C h a p t e r 3, "A c o m p a r i s o n of h o s t t a x o n o m i c r e l a t e d n e s s a n d f u n c t i o n a l - g r o u p aff i l iat ion a s p r e d i c t o r s of s e a w e e d - i n v e r t e b r a t e e p i f a u n a a s s o c i a t i o n s " , I f o u n d that: a) t a x o n o m i c r e l a t e d n e s s of s e a w e e d h o s t s w a s no t c o r r e l a t e d with s imi lar i ty in i n v e r t e b r a t e c o m p o s i t i o n ; 9 6 b) the p e r f o r m a n c e o f s e a w e e d h o s t s p e c i e s a s hab i ta t w a s v a r i a b l e with in s e a w e e d f u n c t i o n a l g r o u p s . T h i s h i g h v a r i a t i o n wi th in f u n c t i o n a l g r o u p s led to m y c o n c l u s i o n that s p e c i e s ident i ty is m o r e u s e f u l t h a n f u n c t i o n a l g r o u p ident i ty for p r e d i c t i n g s e a w e e d p e r f o r m a n c e a s hab i ta t ; c) in g e n e r a l , p r e v a i l i n g p e r s p e c t i v e s a b o u t the r e l a t i o n s h i p b e t w e e n s e a w e e d a r c h i t e c t u r a l c o m p l e x i t y a n d i n v e r t e b r a t e hab i ta t u s a g e w e r e u p h e l d , h o w e v e r a r c h i t e c t u r a l c o m p l e x i t y w a s not a w h o l l y r e l i a b l e c r i te r ion for g e n e r a l i z i n g a b o u t a l g a l h o s t p e r f o r m a n c e ; s p e c i e s with t h e s a m e m o r p h o l o g y c a n h a v e v e r y d i f fe rent a s s e m b l a g e s of a s s o c i a t e d i n v e r t e b r a t e s . T h e m a j o r c o n c l u s i o n s o f C h a p t e r 4, " D o fac i l i ta tor traits i n t e r a c t with a n e n v i r o n m e n t a l g r a d i e n t to d e t e r m i n e loca l s p e c i e s d i v e r s i t y ? " w e r e : a) fac i l i ta tor traits (i .e. a l g a l m o r p h o l o g y ) d o in te rac t with a n e n v i r o n m e n t a l g r a d i e n t ( i .e. m a x i m u m w a v e v e l o c i t y ) to d e t e r m i n e l o c a l s p e c i e s d i v e r s i t y (of a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a ) . b) t h r e e c l a s s e s o f a l g a l h o s t w e r e ident i f ied : t h o s e that w e r e not ut i l i zed by i n v e r t e b r a t e s u n d e r a n y of the t e s t e d w a v e e x p o s u r e r e g i m e s , t h o s e that w e r e w e l l u t i l i zed u n d e r low v e l o c i t i e s but i n v e r t e b r a t e d i v e r s i t y d e c r e a s e d a s w a v e v e l o c i t y i n c r e a s e d , a n d h o s t s that w e r e wel l u t i l i zed u n d e r all o f the t e s t e d w a v e v e l o c i t i e s . c) s i m p l e m o d e l s that d e s c r i b e the i n t e r a c t i o n s b e t w e e n e n v i r o n m e n t a l s t r e s s a n d t r a i t - b a s e d s t r e s s a m e l i o r a t i o n a r e un l i ke l y to f o r e c a s t l o c a l s p e c i e s d i v e r s i t y . In par t i cu la r , t h e m o d e l that I t e s t e d ( B r u n o a n d B e r t n e s s 2000) w a s not c o n s i s t e n t with m y o b s e r v a t i o n s o f i n v e r t e b r a t e b i o d i v e r s i t y at low w a v e v e l o c i t i e s . 5.3 Consequences for small mobile invertebrate epifauna of changes in seaweed biodiversity A t t h e o u t s e t o f m y P h . D . r e s e a r c h , I h y p o t h e s i z e d t ight l i n k a g e s b e t w e e n i n v e r t e b r a t e s a n d the i r s e a w e e d h o s t s , a n d t h e r e f o r e I a n t i c i p a t e d that c h a n g e s in 9 7 s e a w e e d b i o d i v e r s i t y w o u l d resu l t in sh i f ts in b i o d i v e r s i t y o f e p i f a u n a l i n v e r t e b r a t e s . H o w e v e r , n e i t h e r o f t h e s e i d e a s w a s s t r o n g l y s u p p o r t e d b y m y o b s e r v a t i o n s o r m a n i p u l a t i o n s . It a p p e a r s that, a l t h o u g h ind iv idua l s e a w e e d s s u p p o r t e d d i f fe rent a s s e m b l a g e s of a s s o c i a t e d i n v e r t e b r a t e s ( F i g u r e 3 .4) , t h e r e w a s c o m m u n i t y - l e v e l bu f fe r ing of s m a l l - s c a l e c h a n g e s in s e a w e e d a s s e m b l a g e s t r u c t u r e ( F i g u r e 2 .1) . T h i s resu l t s u g g e s t s that s m a l l - s c a l e c h a n g e s in a l g a l b i o d i v e r s i t y a r e u n l i k e l y to i n f l u e n c e i n v e r t e b r a t e e p i f a u n a l d i ve rs i t y . O n e e x c e p t i o n to th is c o n c l u s i o n m i g h t o c c u r w h e n l a r g e r a r e a s of a l g a l c o v e r a r e lost o r r e d u c e d to " co ra l l i ne p a v e m e n t " , a s is the c a s e w h e n s e a u r c h i n s d e n u d e a l g a l c o v e r into "urch in b a r r e n s " ( H a r t a n d S c h e i b l i n g 1 9 8 8 ) . A l g a l c r u s t s s u p p o r t f e w or n o s m a l l m o b i l e i n v e r t e b r a t e s ( F i g u r e 3 .4) . T h e intert ida l e n v i r o n m e n t is a d y n a m i c a n d s o m e t i m e s h a r s h e n v i r o n m e n t , w h e r e a l g a l a s s e m b l a g e s c h a n g e d r a m a t i c a l l y t h r o u g h o u t t h e y e a r a n d e n v i r o n m e n t a l c o n d i t i o n s f l u c t u a t e s u b s t a n t i a l l y . T h i s t u m u l t u o u s e n v i r o n m e n t m a y h a v e s e l e c t e d i n v e r t e b r a t e s to b e h o s t - g e n e r a l i s t s . I n v e r t e b r a t e s u s i n g a l g a e a s hab i ta t a r e l ikely a d a p t e d to u n p r e d i c t a b l e c i r c u m s t a n c e s , s o t h e t y p e s o f c h a n g e s tha t I e x a m i n e d a r e within t h e s p e c t r u m of c o n d i t i o n s to w h i c h e p i f a u n a l i n v e r t e b r a t e s h a v e b e e n e x p o s e d . 5.4 Community ecology as a predictive science W h i l e s t u d y i n g t h e s e s e a w e e d - e p i f a u n a i n t e r a c t i o n s , I a t t e m p t e d to a d d r e s s the c r i t i c i sm that c o m m u n i t y e c o l o g y h a s fa i led a s a p r e d i c t i v e s c i e n c e b e c a u s e it l a c k s g e n e r a l l a w s ( L a w t o n 1 9 9 9 , M c G i l l et a l . 2 0 0 6 ) , a n d t h e r e s u l t s o f e c o l o g i c a l s t u d i e s a r e typ i ca l l y o r g a n i s m - a n d e n v i r o n m e n t - s p e c i f i c . I i n c o r p o r a t e d s e v e r a l a d v a n c e s in c o m m u n i t y e c o l o g y t h e o r y to a l l o w a c o m p a r i s o n of g e n e r a l v e r s u s s p e c i e s - i d e n t i t y b a s e d a p p r o a c h e s in th is s e a w e e d - e p i f a u n a s t u d y s y s t e m . T h e s e g e n e r a l a p p r o a c h e s i n c l u d e d a s t u d y o f b i o d i v e r s i t y - e c o s y s t e m f u n c t i o n r e l a t i o n s h i p s , f u n c t i o n a l g r o u p d ivers i ty , p h y l o g e n e t i c / t a x o n o m i c p e r s p e c t i v e s in c o m m u n i t y e c o l o g y , a n d t h e s t u d y of f u n c t i o n a l trait p e r f o r m a n c e a l o n g a n e n v i r o n m e n t a l g r a d i e n t . 9 8 I f o u n d that, e v e n wi th in th is s e a w e e d - e p i f a u n a l s t u d y s y s t e m , t h e potent ia l for g e n e r a l i z i n g a b o u t h o s t - e p i b i o n t i n t e r a c t i o n s w a s low. M y a t t e m p t s to d e p a r t f r o m t h e u s e of s e a w e e d s p e c i e s ident i ty ( e . g . by g r o u p i n g t h e m into f u n c t i o n a l g r o u p s , o r a s s u m i n g s e a w e e d s p e c i e s e q u i v a l e n c e by i n v o k i n g s p e c i e s r i c h n e s s ) w e r e not s u c c e s s f u l for p r e d i c t i n g b i o d i v e r s i t y o f a s s o c i a t e d i n v e r t e b r a t e e p i f a u n a ( C h a p t e r s 2 a n d 3). O n l y in C h a p t e r 4 d i d I o b s e r v e s o m e c o n g r u e n c e a c r o s s h o s t s p e c i e s , w h e r e s e a w e e d s with l ike m o r p h o l o g i e s r e s p o n d e d in s i m i l a r w a y s to c h a n g e s in w a t e r m o t i o n , resu l t i ng in s i m i l a r p a t t e r n s of i n v e r t e b r a t e r i c h n e s s a n d a b u n d a n c e . A s a resul t , it a p p e a r s that m o s t p r e d i c t i o n s a b o u t s e a w e e d - i n v e r t e b r a t e i n t e r a c t i o n s w o u l d s u f f e r if s e a w e e d s p e c i e s ident i ty w e r e not t a k e n into a c c o u n t . 5.5 Byproducts B y s t u d y i n g a l a r g e n u m b e r of i n v e r t e b r a t e a n d s e a w e e d t a x a , s o m e u s e f u l ' b y p r o d u c t s ' w e r e g e n e r a t e d . T h e C o n v e n t i o n o n B i o l o g i c a l D i v e r s i t y , o f w h i c h C a n a d a is a s i g n a t o r y n a t i o n , s t a t e s that pa r t i c i pa to ry n a t i o n s m u s t ident i fy a n d m o n i t o r their b i o l o g i c a l r e s o u r c e s . F e w s t u d i e s of s e a w e e d e p i f a u n a a r e a v a i l a b l e for t h e P a c i f i c c o a s t o f C a n a d a . M y d a t a s e t s d o c u m e n t i n v e r t e b r a t e hab i ta t u s a g e a c r o s s a w i d e a r r a y of h o s t s e a w e e d s . T h i s w o r k d o c u m e n t s b a s e l i n e i n f o r m a t i o n a b o u t t h e d y n a m i c s of i n v e r t e b r a t e hab i ta t u s e a c r o s s s p a c e a n d t i m e . I h a v e v o u c h e r c o l l e c t i o n s that I c a n c o n t r i b u t e to m u s e u m c o l l e c t i o n s , a n d I h a v e c o l l e c t i o n r e c o r d s , s o if i n v e r t e b r a t e b i o l o g i s t s a r e i n t e r e s t e d in f i n d i n g pa r t i cu la r t a x a , I c a n , at t h e v e r y l eas t , i n d i c a t e w h i c h a lga l h o s t o r c o l l e c t i o n s i te to start l o o k i n g at. 5.6 Hindsight and future directions T h e r e a r e s e v e r a l s h o r t c o m i n g s that a r e w o r t h y of m e n t i o n h e r e , t h i n g s that I w o u l d d o d i f fe rent ly if I c o u l d start a g a i n . A s with m o s t e c o l o g i c a l s t u d i e s , t he leve l o f r e p l i c a t i o n c o u l d h a v e b e e n i n c r e a s e d . In t h e s t u d y d e s c r i b e d in c h a p t e r 3, t h e r e a r e n u m e r o u s a l g a l s p e c i e s that 9 9 w e r e c o l l e c t e d o n l y a f e w t i m e s , s o resu l t s of c o m p a r i s o n s to we l l r e p l i c a t e d s p e c i e s c o u l d b e d r i v e n b y i d i o s y n c r a s i e s r e l a t e d to c o l l e c t i o n m e t h o d s , u n c o n t r o l l e d f a c t o r s , o r r a n d o m c h a n c e . I w o u l d m a k e a n a t t e m p t to m o r e e v e n l y r e p l i c a t e all a l g a l s t u d y s p e c i e s . In th is t h e s i s , I f r e q u e n t l y d i s c u s s the i m p l i c a t i o n s of a l g a l m o r p h o l o g y for i n v e r t e b r a t e hab i ta t u s a g e , but m y e s t i m a t e s of m o r p h o l o g i c a l c o m p l e x i t y a r e qua l i ta t i ve ; I d o not q u a n t i t a t i v e l y a d d r e s s s p e c i f i c m o r p h o l o g i c a l f e a t u r e s . O v e r the c o u r s e of m y P h . D . , I u n d e r t o o k s e v e r a l a t t e m p t s to m o r p h o m e t r i c a l l y q u a n t i f y d i f f e r e n c e s in a l g a l m o r p h o l o g y , but the i n t r i c a c i e s of c o m p a r i n g a l g a e with s u c h a w i d e a r r a y of f e a t u r e s e t s b e c a m e s tat i s t i ca l ly c o m p l e x . T h e l a n d m a r k m o r p h o m e t r i c m e t h o d s p o p u l a r t o d a y ( M o n t e i r o et a l . 2000) d o no t e a s i l y a c c o m m o d a t e m i s s i n g d a t a ( e . g . w h e r e f e a t u r e s s u c h a s b r a n c h i n g a r e not s h a r e d by all t a x a u n d e r c o m p a r i s o n ) . L a n d m a r k m o r p h o m e t r i e s a r e bet ter s u i t e d to c o m p a r i n g p h e n o t y p i c p last i c i ty or d e v e l o p m e n t wi th in t a x a . Q u a n t i f i c a t i o n of a c r o s s - s p e c i e s a l g a l m o r p h o l o g y r e m a i n s of in te res t to m e , a n d will b e par t o f m y o n g o i n g fu ture r e s e a r c h . D u e to c r y p t i c f e a t u r e s a n d c o m p l e x t a x o n o m y for s o m e i n v e r t e b r a t e t a x a , the leve l o f i dent i f i ca t ion for e p i f a u n a for s o m e t a x a ( e . g . n e m a t o d e s , s o m e a m p h i p o d s ) w a s c o a r s e . T h e c o n s e q u e n c e of s t u d y i n g s u c h a w i d e a r r a y o f t a x a (both for s e a w e e d s a n d for i n v e r t e b r a t e s ) is that e c o l o g i c a l d e t a i l s of i n v e r t e b r a t e s w e r e not c o n s i d e r e d in de ta i l . M y c o n c l u s i o n s o f i n v e r t e b r a t e hab i ta t g e n e r a l i s m a r e po ten t i a l l y o v e r s t a t e d ; if I i n t e g r a t e d the a u t e c o l o g y o f the i n v e r t e b r a t e s , m y c o n c l u s i o n s a b o u t t h e i m p l i c a t i o n s of c h a n g e s in s e a w e e d b i o d i v e r s i t y m i g h t b e d i f ferent . F u r t h e r m o r e , i n t e r a c t i o n s b e t w e e n the e p i f a u n a w e r e not a d d r e s s e d , n o r w e r e the i n f l u e n c e of e p i f a u n a o n t h e s e a w e e d h o s t s . W h i l e I d o not r e g r e t that I s t u d i e d s u c h a w i d e a r r a y of t a x a , I th ink t h e r e w o u l d b e v a l u e in r e t u r n i n g to s u b s e t s o f t a x a to e x a m i n e t h e m in m o r e d e t a i l . 100 5.7 Literature cited Bates, C. R. 2002. Monitoring seaweed biodiversity in the Bay of Fundy, New Brunswick, Canada. Masters thesis. University of New Brunswick, Fredericton. Bates, C. 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Bordin, and S. Furtado do Reis. 2000. Shape distances, shape spaces and the comparison of morphometric methods. Trends in Ecology and Evolution 15:217-220. Schramm, W., and P. H. Nienhuis, editors. 1996. Marine Benthic Vegetation: Recent changes and the Effects of Eutrophication. Springer-Verlag, Berlin Heidelberg New York. Scott, G . W., and I. Tittley. 1998. Changes in the Marine Flora of the North Sea. Centre for Environmental Research into Coastal Issues, Scarborough. 101 Appendices 102 Appendix A: Taxonomic affiliations of invertebrate voucher specimens collected for the studies described in this thesis. 103 A p p e n d i x A : T a x o n o m i c af f i l ia t ions of i n v e r t e b r a t e v o u c h e r s p e c i m e n s c o l l e c t e d for the s t u d i e s d e s c r i b e d in th is t h e s i s . T h e l is ted n u m b e r s a r e m y v o u c h e r ident i f ier c o d e s . If s p e c i f i c e p i t h e t o r g e n u s is not i n d i c a t e d , aff i l iat ion is l i s ted at t h e l e v e l o f P = P h y l u m ; C = C l a s s ; S C = S u b c l a s s ; O = O r d e r ; F = F a m i l y . 1) Harpacticoida (0) 46) Gammar idea (0) 88) Bivalvia (C) 2) Gammar idea (O) 47) Diptera (0) 89) Harpacticoida (0) 3) Polychaeta (C) 48) Acariformes (0) 90) Orthogastropoda (SC) 4) Flabellifera (SO) 49) Polychaeta (C) 91) Majidae (F) 5) Polyplacophora (C) 50) Coleoptera (0) 92) Ophiuroidea (C) 6) Orthogastropoda (SC) 51) Orthogastropoda (SC) 93) Bivalvia (C) 8) Orthogastropoda (SC) 52) Orthogastropoda (SC) 94) Unknown . 11) Amphipoda (O) 54) Gammaridea (0) 95) Orthogastropoda (SC) 12) Polychaeta (C) 55) Gammar idea (0) 96) Unknown 13) Patel logastropoda (0) 56) Polychaeta (C) 97) Bivalvia (C) 14) Orthogastropoda (SC) 58) Pugetia producta 98) Orthogastropoda (SC) 16) Majidae (F) 59) Calanoida (0) 99) Orthogastropoda (SC) 17) Asteroidea (C) 60) Acariformes (0) 100) Unknown 19) Orthogastropoda (SC) 62) Idotea wosnosenskii 101) Coleoptera (0) 20) Paguridae (F) 63) Polychaeta (C) 102) Orthogastropoda (SC) 21) Polychaeta (C) 64) Pantopoda (0) 103) Pantopoda (0) 23) Acariformes (0) 66) Polychaeta (C) 104) Bivalvia (C) 24) Patel logastropoda (0) 68) Harpacticoida (0) 105) Pseudoscorpionida (0) 25) Nudibranchia (SO) 69) Gammar idea (0) 106) Idoteidae (F) 26) Harpacticoida (O) 70) Polychaeta (C) 107) Orthogastropoda (SC) 27) Acariformes (0) 71) Diptera (0) 108) Orthogastropoda (SC) 28) Gammar idea (0) 72) Orthogastropoda (SC) 109) Polychaeta (C) 29) Asteroidea (C) 74) Orthogastropoda (SC) 110) Isopoda (SO) 30) Diptera (0) 76) Gammaridea (0) 111) Isopoda (SO) 31) Acariformes (0) 77) Orthogastropoda (SC) 112) Holothuroidea (C) 32) Nematoda (P) 78) Polyplacophora (C) 113) Platyhelminthes (P) 33) Gammar idea (0) 79) Idoteidae(F) 114) Platyhelminthes (P) 35) Acariformes (0) 80) Polychaeta (C) 115) Epicar idea (SO) 36) Harpacticoida (0) 81) Polychaeta (C) 116) Orthogastropoda (SC) 37) Polychaeta (C) 82) Polychaeta (C) 117) Unknown 38) Gastropoda (0) 83) Mytilus spp. 118) Orthogastropoda (SC) 39) Caprel l idea (SO) 84) Orthogastropoda (SC) 119) Flabellifera (SO) 40) Polyplacophora (C) 85) Gammar idea (0) 120) C u m a c e a (0) 41) Polychaeta (C) 86) Polychaeta (C) 121) Orthogastropoda (SC) 45) Gastropoda (0) 87) Orthogastropoda (SC) 122) Anisodoris nobilis 104

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