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Allocation of blade surface area to meiospore production in annual and perennial representatives of the.. 1985

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ALLOCATION OF BLADE SURFACE AREA TO MEIOSPORE PRODUCTION I N ANNUAL AND PERENNIAL REPRESENTATIVES OF THE GENUS LAMINARIA By TERRIE KLINGER A.B., U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y , 1979 A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF BOTANY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF B R I T I S H COLUMBIA O c t o b e r 1984 © T e r r i e K l i n g e r 1984 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 -6 (3/81) ABSTRACT A l l o c a t i o n of blade surface area to meiospore production was q u a n t i f i e d for semelparous and iteroparous representatives of the genus Laminaria (Phaeophyta: Laminariales) at each of two s i t e s i n Barkley Sound, Vancouver Island, B.C. The annual semelparous sporophyte Laminaria ephemera produced s o r i between A p r i l and J u l y ; a maximum mean percentage of 31.7% of t o t a l vegetative blade area was devoted to sorus production, and 100% of the in d i v i d u a l s were reproductive within at least one sample. The perennial iteroparous sporophyte Laminaria s e t c h e l l i i produced s o r i throughout the year; a maximum mean percentage of 30.4% of t o t a l blade area was devoted to sorus production, and a maximum of 54% of the i n d i v i d u a l s were reproductive within any sample. These r e s u l t s are discussed i n the context of l i f e h istory evolution. Concentric rings are v i s i b l e i n cross-section of the stipes of Laminaria s e t c h e l l i i . These rings were demonstrated to form annually, and thereby permitted estimation of ind i v i d u a l age and of age structure among populations of L. s e t c h e l l i i at two si t e s i n Barkley Sound. Age structures were d i s s i m i l a r between populations, and showed no evidence of s t a b i l i t y . The twelve year age class was most abundant at one s i t e (Wizard Rock), and the two and three year age classes were most abundant at a second s i t e (Execution Bay). - i i i - TABLE OF CONTENTS page Chapter 1. General Introduction 1 Chapter 2. Seasonal Patterns of Recruitment i n Laminaria ephemera 17 Introduction 17 Materials and Methods 18 Results 19 Discussion 20 Chapter 3. A l l o c a t i o n to Meiospore Production i n Laminaria ephemera 26 Introduction 26 Materials and Methods 26 Results 29 Discussion 31 Chapter 4. A l l o c a t i o n to Meiospore Production i n Laminaria s e t c h e l l i i 45 Introduction 45 Materials and Methods 45 Results 47 Discussion 51 Chapter 5. Age Structure among Populations of Laminaria s e t c h e l l i i 67 Introduction 67 Materials and Methods 68 Results 69 Discussion 71 - i v - TABLE OF CONTENTS, cont. Chapter 6. General Discussion 80 Bibliography 84 Appendix 1 90 Appendix 2 91 - v - LIST OF TABLES Table T i t l e Page 2.1. Tagged cobble a t t r i t i o n rate. 25 3.1. Sampling schedule, Laminaria ephemera. 35 4.1. Sampling schedule, Laminaria s e t c h e l l i i . 55 A . l . Results of gametophyte culture experiments. 96 - v i - L I S T OF FIGURES F i g u r e T i t l e Page 2.1. Map o f B a r k l e y Sound, B.C. 24 3.1. V e g e t a t i v e and s o r a l s u r f a c e a r e a , C a b l e B e a c h . 36 3.2. V e g e t a t i v e and s o r a l s u r f a c e a r e a , E x e c u t i o n Bay. 37 3.3. P e r c e n t a g e o f s o r a l p l a n t s , C a b l e B e a c h . 38 3.4. P e r c e n t a g e o f s o r a l p l a n t s , E x e c u t i o n Bay. 39 3.5. S i z e c l a s s d i s t r i b u t i o n , C a b l e B e a c h . 40 3.6. S i z e c l a s s d i s t r i b u t i o n , E x e c u t i o n Bay. 41 3.7. S i z e c l a s s d i s t r i b u t i o n , r e p r o d u c t i v e p l a n t s , C a b l e B e a c h . 42 3.8. S i z e c l a s s d i s t r i b u t i o n , r e p r o d u c t i v e p l a n t s . E x e c u t i o n Bay. 43 3.9. R a t i o o f s o r a l s u r f a c e a r e a t o v e g e t a t i v e s u r f a c e a r e a . 44 4.1. V e g e t a t i v e and s o r a l s u r f a c e a r e a , W i z a r d Rock. 56 4.2. R a t i o o f s o r a l s u r f a c e a r e a t o v e g e t a t i v e s u r f a c e a r e a . 57 4.3. P e r c e n t a g e o f s o r a l p l a n t s , W i z a r d Rock. 58 4.4. V e g e t a t i v e and s o r a l s u r f a c e a a r e a , E x e c u t i o n Bay. 59 4.5. P e r c e n t a g e o f s o r a l p l a n t s , E x e c u t i o n Bay. 60 4.6. R e p r o d u c t i v e p l a n t s v e r s u s age, W i z a r d Rock. 61 4.7. R e p r o d u c t i v e p l a n t s v e r s u s age, E x e c u t i o n Bay. 62 4.8. S t i p e volume v e r s u s age, W i z a r d Rock, 05 A u g u s t 1982. 63 4.9. S t i p e volume v e r s u s age, W i z a r d Rock, 18 November 19 82. 64 - v i i - LIST OF FIGURES, cont. 4.10. Stipe volume versus age, Execution Bay, 28 October 1982. 65 4.11. Stipe volume versus age, Execution Bay, 10 November 1982. 66 5.1. Size class d i s t r i b u t i o n , Wizard Rock. 74 5.2. Age class d i s t r i b u t i o n , Wizard Rock, 18 November 1982. 75 5.3. Age class d i s t r i b u t i o n , Wizard Rock, pooled samples. 76 5.4. Size class d i s t r i b u t i o n , Execution Bay. 77 5.5. Age class d i s t r i b u t i o n , Execution Bay, 10 Novmeber 1982. 78 5.6. Age class d i s t r i b u t i o n , Execution Bay, pooled samples. 79 A . l . Stipe cross-section, Laminaria s e t c h e l l i i . 93 - v i i i - ACKNOWLEDGEMENTS Sincere thanks are due Dr. R.E. DeWreede for h i s encouragement, guidance, and unflagging patience through the completion of t h i s project. Thanks are also due Drs. P.J. Harrison and R. Turkington for valuable discussion and comment, and for re a l expediency i n the c r i t i c a l review of t h i s thesis. The administrative e f f o r t s of Dr. K. Cole are g r a t e f u l l y acknowledged. Dr. R.F. Scagel and the Department of Botany, U.B.C, graciously provided for laboratory use at Bamfield Marine Station. Thanks to Dr. L.D. Druehl for interested discussion and for general help with kelp. Thanks are also extended to Robin Boal, K i t t y Lloyd, Ann Lindwall, and Shirley Smith-Pakula. Dr. R.E. DeWreede, Lynn Yip, Dr. M.W. Hawkes and Stuart Arkett gave comprehensive assistance and support i n the subtidal. Additional and welcome support i n the f i e l d was provided by John Versendaal, Herb Vandermeulen, Serge Villeneuve, Iddamaria Germann, Harry Goldberg, Ron Smith, Rick Cohen, E r i c Cabot, Ray Lewis, Rick Schuller, Steve Fain, Joel E l l i o t , Adrienne Forest, and Joel P e c c h i o l i . Serge Villeneuve and Dr. L.D. Druehl kindly loaned the f a c i l i t i e s of the In s t i t u t e for the Enhancement of Photosynthesis, Bamfield, B.C. Dr. Wm.J. Emery made available the LSI-11 computer and d i g i t i z e r of the Dept. of Oceanography, U.B.C. Thanks to Sharon and Rob DeWreede, Denise Bonin and Mike Hawkes, Iddamaria Germann and U l i Hoeger for unending kindness and h o s p i t a l i t y . Big thanks to Lynn Yip for everything shared and accomplished subaerially. - 1 - CHAPTER 1 GENERAL INTRODUCTION Benthic marine algae exhibit l i f e h i s t o r y c h a r a c t e r i s t i c s which deviate strongly from many of the l i f e h i s t o r y phenomena described for higher plants and animals. S c i e n t i f i c treatment of alga l l i f e h i s t o r i e s has t r a d i t i o n a l l y been of a taxonomic or phylogenetic nature, rather than quantitive or the o r e t i c a l (but for exceptions see Clayton, 1982; Searles, 1980). Evaluation of algal l i f e h i s t o r i e s i n the context of population dynamics and reproductive strategies i s timely and germane to the study of l i f e h istory evolution. The kelps (order Laminariales) comprise a taxonomically well-defined group d i s t r i b u t e d throughout the northern and southern Hemispheres. Members of the order exhibit a heteromorphic a l t e r n a t i o n of generations, i n which the macroscopic sporophyte l i b e r a t e s meiospores which germinate to produce microscopic filamentous gametophytes. Gametophytes mature to produce either oogonia or antheridia; f e r t i l i z a t i o n i s oogamous, and r e s u l t s i n sporophyte i n i t i a t i o n (Eain, 1979, and references t h e r e i n ) . Sporophytes t y p i c a l l y are large and show varying degrees of morphological complexity ( c f . Setc h e l l and Gardner, 1925). Some perennial species (e.g. Laminaria s e t c h e l l i i S i l v a , Pterygophora c a l i f o r n i c a Rupr., Eisenia arborea Aresch.) maintain a woody stipe; other perennial species (e.g. Macrocystis p y r i f e r a (L.) C. Ag. , Laminaria groenlandica Rosenv.), as well as most annual species (e.g. Nereocvstis luetkeana (Mert.) Post, et Rupr.) maintain slender, more p l i a n t stipes. Stipes may be elongate, shortened, or absent e n t i r e l y . Blades may be single or multiple, and may be entire or variously dissected. Blades produced by annual species are usually maintained for the - 2 - duration of the season, while blades produced by many of the perennial species (e.g. Laminaria s e t c h e l l i i , Pleurophycus gardneri) are deciduous; that i s , new blades are formed annually and remnants of old blades are not retained. Blade growth i s indeterminate i n most species. Meiosporangia are produced i n sporangial s o r i on the terminal blade (Laminariaceae) or on sp e c i a l i z e d blades or sporophylls (Alariaceae, Lessoniaceae). Paraphyses and ultimately sporangia originate from m i t o t i c d i v i s i o n s of meristodermal c e l l s (Walker, 1980; Eain, 1979). Both paraphyses and sporangia are pigmented ( i b i d . ) , as are l i b e r a t e d meiospores (Eain, 1964). From 16 to 64 spores may be produced per sporangium. Members of the genus Laminaria are reported to consistently produce thirty-two spores per sporangium (Eain, 1979). The r a t i o of female to male spores produced per sporangium i s reportedly 1:1 (Eain, 1979). Spores germinate wi t h i n about twenty-four hours of l i b e r a t i o n (Eain, 1964); there i s no evidence that spores remain planktonic for an extended period. Nutrients are assimilated across the blade surface from the surrounding medium. Photosynthesis occurs along the length of the t h a l l u s , though rates of carbon f i x a t i o n may vary with distance from the t r a n s i t i o n zone (Kuppers and Kremer, 1978). The capacity for carbohydrate t r a n s l o c a t i o n has been reported for a number of species (Lobban, 1978b; Buggeln, 1977; Schmitz and Lobban, 1976; Schmitz and Srivastrava, 1975; Luning e t . a l . , 1972); tra n s l o c a t i o n i s generally u n i d i r e c t i o n a l , and towards meristematic regions. Translocation towards reproductive regions has not been reported for members of the Laminariaceae, but may occur among some more s p e c i a l i z e d members of the Lessoniaceae (Lobban, 1978b). - 3 - Kelp gametophytes are known primarily from laboratory studies, although they have occasionally been found i n the f i e l d (Moss e t . a l . , 1981; Klinger and Moe, unpubl.). Gametophytes are dioecious and sexes are normally heteromorphic (Kain, 1979; Cole, 1968; Hollenberg, 1939; Clare and Herbst, 1938; McKay, 1933; Harries, 1932). Female gametophytes may become reproductive at an early, s i n g l e - c e l l e d stage, or may grow to become tufted filaments, each c e l l of which p o t e n t i a l l y can be transformed into an oogonium. Oogonium formation i s dependent, i n the laboratory, upon temperature and l i g h t q u a l i t y (Luning, 1980; Luning and Neushul, 1978; Luning and Dring, 1975; Luning and Dring, 1972; Hsiao and Druehl, 1971). Male gametophytes grow to filamentous t u f t s of few to many c e l l s before becoming f e r t i l e (Luning and Neushul, 1978). In the laboratory, both male and female vegetative filamentous gametophytes may be fragmented, resuspended, and subsequently cultured to produce multiple reproductive i n d i v i d u a l s . The persistence and reproductive behavior of gametophytes i n the f i e l d i s lar g e l y unknown. In one exceptional study, Hsiao and Druehl (1973) outplanted labeled gametophytes of Laminaria saccharina i n order to follow t h e i r seasonal development. They reported continual oogenesis and sporophyte i n i t i a t i o n for the study period of July 1968, to June 1971, but observed development of sporophytes only i n the l a t e winter and i n the early f a l l . The authors concluded that establishment of macroscopic sporophytes i s l i m i t e d by the action of environmental e f f e c t s on the embryosporophytes, rather than by environmental suppression of gametogenesis. Kain (1964) recognized that filamentous vegetative growth of female gametophytes p o t e n t i a l l y allows gametophytes to "become perennial with i n d e f i n i t e gamete production". Luning and Neushul (1978) argue that - 4 - "optimal" conditions of temperature and l i g h t q u a l i t y promote oogenesis among s i n g l e - c e l l e d females, but note that such conditions may be lacking i n coastal waters. The possible existence of a dynamic trade-off between precocious development of a single oogonium and delayed production of multiple oogonia has implications for fecundity which can be argued analogously to Charnov and Schaffer's (1973) discussion regarding semelparous versus iteroparous s t r a t e g i e s ; b r i e f l y , those authors a t t r i b u t e advantage to early production of fewer of f s p r i n g , rather than to delayed production of a greater number of off s p r i n g , for the case of the expanding population. The capacity for fragmentation among filamentous gametophytes renders such gametophytes f u n c t i o n a l l y equivalent to iteroparous organisms. The apparent p l a s t i c i t y of gametophyte reproductive behavior i s important i n that f a c u l t a t i v e expression of either semelparity or i t e r o p a r i t y has not been previously considered i n the l i t e r a t u r e . The instantaneous rate of population increase (r) describes the rate at which a given population i s expanding or declining, and i s a measure of f i t n e s s i n that i t r e f l e c t s the successful production of o f f s p r i n g by members of a population. " r " i s a function of the p r o b a b i l i t i e s of survival and reproduction, as defined by the Euler equation: where l(x)=the p r o b a b i l i t y of survival to age x from b i r t h , m(x)=the instantaneous b i r t h rate, and dx=time i n t e r v a l T to T+l (cf. Michod and Anderson, 1980; Stearns, 1976; Lotka, 1956). Observed values of l(x) and m(x) may be presented as elements of a Leslie-type matrix, i n which p r o b a b i l i t i e s of age-specific fecundity comprise the elements of the f i r s t row vector, and age-specefic p r o b a b i l i t i e s of 1(x) m(x) dx = 1 (1) - 5 - survival are l i s t e d on the sub-diagonal ( L e s l i e , 1945). A l l other matrix elements are zero. The matrix may be solved for the dominant eigenvalue, X i then: r = lnX. (2) The L e s l i e matrix has been widely used i n p r o j e c t i o n of population growth rates, and has been applied, for example, to populations of humans ( L e s l i e , 1945), and trees (Usher, 1966). The assumptions inherent i n construction of the matrix for the purposes of population p r o j e c t i o n may be constraining, however. For c a l c u l a t i o n of rate of increase, the matrix model demands that the population be at the stable age d i s t r i b u t i o n , and that empirical determination of l(x) and m(x) be possible. Leslie-type models constructed for the purposes of population p r o j e c t i o n are suited l a r g e l y to d i p l o n t i c organisms without complexity of l i f e h i s t o r y , such as humans. There exist, however, a number of p r o j e c t i o n models which consider complexity within the d i p l o n t i c l i f e h i s t o r y . These t y p i c a l l y are t a i l o r e d to insect populations with stage-specific dynamics ( M i l l s , 1981a; 1981b), or to populations of higher plants i n which several demographically- d i s s i m i l a r stages occur within the l i f e h istory (Hubbell and Werner, 1979). Common to both non-complex and complex l i f e h i s t o r y models i s the assumption that a single ploidy l e v e l (usually 2n) i s maintained throughout the l i f e h i s t o ry, and that alternate ploidy l e v e l s (usually In) are r e s t r i c t e d to transient episodes of sexual reproduction i n which syngamy clo s e l y follows meiosis. Further, f i t n e s s (as " r " or X) i s determined by the demographic parameters ( l ( x ) , m(x)) of the stage of p r e v a i l i n g ploidy. Mortality occurring w i t h i n the stage of t r a n s i t i o n a l ploidy i s incorporated into the fecundity term of the stage of p r e v a i l i n g ploidy. For the d i p l o n t i c l i f e - 6 - history, no fecundity occurs i n the stage of t r a n s i t i o n a l ploidy, by d e f i n i t i o n . A simple example may be i l l u s t r a t i v e . For a sexually reproducing human, m(x) describes the number of daughters born to a female aged x during the time period T to T+l. The value taken by m(x) i s therefore the product of the following q u a n t i t i e s : 1. number of female gametes produced; 2. p r o b a b i l i t y of survival of female gametes to f e r t i l i z a t i o n ; 3. p r o b a b i l i t y of f e r t i l i z a t i o n X (0.5); 4. p r o b a b i l i t y of zygote survival to b i r t h . The second and t h i r d terms above r e f e r to events occurring within the stage of t r a n s i t i o n a l ploidy ( i n t h i s example. In). " M o r t a l i t y " i n either of these terms (eg. death of female gametes p r i o r to f e r t i l i z a t i o n ) has the eff e c t of reducing the observed fecundity. For d i p l o n t i c organisms, each of the foregoing terms i s absorbed into the complex term m(x) because of the very small temporal window i n which they occur, and, more importantly, because at no point during the stage of t r a n s i t i o n a l ploidy can the absolute number of of f s p r i n g produced exceed the absolute number of meiotic products m u l t i p l i e d by (0.5). B i r t h of twins constitutes a special case and w i l l not be considered here. The elaboration of the haploid stage i n the kelp l i f e history renders models such as those c i t e d above in t r a c t a b l e i n p r e c i s e l y describing kelp population dynamics. The i n t e r p o s i t i o n of an indeterminate number of mitoses between meiosis and syngamy allows the absolute number of d i p l o i d o f f s p r i n g produced to exceed the number of o r i g i n a l meiotic products X (0.5), i f these haploid m i t o t i c products are ultimately transformed to oogonia. An important consequence of t h i s p o s s i b i l i t y i s the potential for p r o l i f e r a t i o n of a " s u c c e s s f u l " haploid genotype p r i o r to recombination. The average f i t n e s s of a population tends to be increased by the action of s e l e c t i v e pressures on the net reproductive rates of i n d i v i d u a l s w i t h i n the population. Relevant changes i n the parameters of age-specific fecundity and mortality can be estimated by construction of the appropriate Leslie-type matrices from empirical data. For diplohaplonts such as the kelps i t i s therefore tenable that changes i n f i t n e s s may r e s u l t from the action of s e l e c t i v e pressures upon fecundity and mortality i n either stage; that i s , change i n f i t n e s s may be effected w i t h i n either the gametophyte or sporophyte stage. Under varying s e l e c t i v e regimes, the haploid gametophyte and d i p l o i d sporophyte may contribute d i f f e r e n t i a l l y to o v e r a l l (zygote-to-zygote) f i t n e s s . If the p o t e n t i a l for population increase e x i s t s within the In stage independently of and i n a d d i t i o n to the potential for increase w i t h i n the 2n stage, then the construction of l i f e tables and L e s l i e matrices should be possible for both stages independently, i f the q u a l i f y i n g assumptions of the L e s l i e formulation are met. The observable rate of population increase should then be some product of the p r o b a b i i t i e s of the two independently-constructed matrices. I n t e r s p e c i f i c v a r i a t i o n i n the l i f e h istory of the kelp sporophyte i s well documented (Luning, 1980; Kain, 1979). Sporophytes may be ephemeral (Laminaria ephemera S e t c h e l l ) , annual (Cymathere t r i p l i c a t a (Post, et Rupr.) J. Ag.) s h o r t - l i v e d perennial (Laminaria groenlandica Rosenv.), or l o n g - l i v e d perennial (Laminaria s e t c h e l l i i S i l v a ) . It i s reasonable to expect that - 8 - gametophytes of d i f f e r e n t taxa also exhibit v a r i a t i o n i n l i f e h istory parameters. Selective pressures should act to maximize the average p r o b a b i l i t y of successful reproduction by members of a population, and for the kelps, such maximization should occur within sporophyte and gametophyte populations independently. It i s tempting to reduce the complexities of kelp population dynamics by combining m u l t i p l i c a t i v e l y the independently-constructed Leslie-type matrices of the sporophyte and gametophyte populations. Schmidt and Lawlor (1983) have j u s t i f i e d reduction of the "complex" l i f e h i s t o r y of an annual plant with a seedbank: by wisely chosing t h e i r sampling time, they have reduced the sporophyte matrix to a column vector, and have m u l t i p l i e d t h i s vector by the a g e - c l a s s i f i e d seedbank matrix. The r e s u l t s are then used to test d i f f e r e n t i a l s e n s i t i v i t y of X to changes i n l i f e - h i s t o r y parameters. Such a manipulation may have some l i m i t e d a p p l i c a b i l i t y to the kelp l i f e h i s t o r y , e s p e c i a l l y i n the case of an annual sporophyte a l t e r n a t i n g with an age-structured gametophyte population. The formulation, however, would require empirical determination of both sporophyte and gametophyte survivorship and fecundity, and these q u a n t i t i e s are u n i d e n t i f i a b l e for the gametophyte stage i n the f i e l d . Fischer (1931) introduced the concept of reproductive value i n order to express the value of future production of of f s p r i n g discounted to the present. For an expanding population, N of f s p r i n g produced at time T+0 are more valuable than the same number of of f s p r i n g produced at time T+l. For a declining population the converse may be true. - 9 - Schaffer (1974) and Taylor e t . a l . (1974) have independently argued that, for s t r i c t l y age-structured populations, maximizing f i t n e s s i s equivalent to maximizing reproductive value at each age, subject to the constraints that change i n reproductive e f f o r t with time has no e f f e c t on o f f s p r i n g produced i n previous reproductive episodes. Caswell (1982) has further shown that, for s t a g e - c l a s s i f i e d populations with complex l i f e h i s t o r i e s of a c e r t a i n form, maximizing f i t n e s s i s equivalent to maximizing reproductive value at each stage; Caswell treats the a g e - c l a s s i f i e d models of Schaffer and Taylor e t . a l . as a special case of h i s more generalized model. The models of Schaffer, Taylor e t . a l . , and Caswell, when applied to the kelp l i f e h i s t o r y , are forced to accommodate age structure, stage complexity, and vegetative as well as sexual reproduction i n at least one stage (gametophyte). Of the three models, Caswell's may be modified most e a s i l y i n order to accomodate these added parameters, by construction of a l i f e - c y c l e graph which i s d e s c r i p t i v e of the diplohaplontic l i f e h i s t o r y and which remains consistent with the stated assumptions of the model. Models dependent upon s t a g e - c l a s s i f i c a t i o n are applied to the kelps with d i f f i c u l t y . Stage c l a s s i f i c a t i o n s have been developed expressly i n order to describe more p r e c i s e l y populations i n which s t r i c t age c l a s s i f i c a t i o n has l i t t l e bearing on schedules on fecundity and survivorship. Stage c l a s s i f i c a t i o n i s therefore meant to replace age c l a s s i f i c a t i o n . For the kelps, the stage c l a s s i f i c a t i o n which may be invoked i n order to describe the sporophyte/gametophyte a l t e r n a t i o n may have superimposed upon i t at least one, and perhaps two, age structures. That i s , any age structure expressed by the sporophyte or gametophyte populations e x i s t s i n addition to stage complexity. The complexity inherent i n the kelp l i f e h i s t o r y i s therefore not analogous to - 10 - the "complexities" of higher plant and insect populations considered by- other authors. L i f e history theory i s predicated on the assumption of resource l i m i t a t i o n ( S n e l l and King, 1977; Gadgil and Bossert, 1970; Cody, 1966; Williams, 1966). That i s , a f i n i t e and l i m i t i n g amount of resources are available to i n d i v i d u a l s , and i n d i v i d u a l s must therefore p a r t i t i o n the available resources between the a l t e r n a t i v e processes of growth and reproduction. Resource p a r t i t i o n i n g thus implies the existence of a reproduction-associated cost. This cost function i s usually estimated as the increased r i s k of i n d i v i d u a l mortality r e s u l t i n g from d i v e r s i o n of resources from growth processes to reproductive processes. The cost hypothesis i n turn allows the p r e d i c t i o n that adult survival w i l l vary inversely with fecundity ( B e l l , 1980). The existence of such an inverse r e l a t i o n s h i p between fecundity and survivorship i s testable by both i n t e r s p e c i f i c and i n t r a s p e c i f i c comparisons, though documentation of the inverse r e l a t i o n s h i p i s not i t s e l f s u f f i c i e n t to prove the existence of reproduction-associated cost ( B e l l , 1984). The cost hypothesis can be used to evaluate some parameters of the kelp l i f e h i s t o r y . We can assume, for the time being, that fecundity i n kelps i s sol e l y a function of meiospore production, and that gametophytes do not contribute to o v e r a l l fecundity. The kelp sporophyte i s thus rendered f u n c t i o n a l l y equivalent to a d i p l o n t i c organism. We can then go on to predict that sporophyte fecundity and survivorship are inversely related, and can test t h i s p r e d i c t i o n at both i n t e r s p e c i f i c and i n t r a s p e c i f i c l e v e l s . - 11 - The evolution of delayed maturity has sometimes been a t t r i b u t e d to se l e c t i o n for increased fecundity which may accompany a delay i n developmental time-to-maturity (Ste arns and Crandall, 1981; B e l l , 1980; Gadgil and Bossert, 1970; Tinkle, 1969). A postulated increase i n fecundity with an associated decrease i n developmental time i s testable i n the context of the kelp l i f e h i s t o ry, i f fecundity and developmental time-to-maturity can be estimated. The hypotheses of reproduction-associated cost and of delayed maturity thus allow two testable predictions to be made for populations of kelp sporophytes: 1) that the annual semelparous sporophyte w i l l exhibit a greater fecundity than the perennial iteroparous sporophyte; and 2) that developmental time-to-maturity w i l l be shorter for the semelparous sporophyte, provided i t exhibits a greater fecundity than the iteroparous sporophyte. Several authors have argued that reproductive e f f o r t should generally increase with age among iteroparous organisms (Pianka and Parker, 1975; Schaffer, 1974; Gadgil and Bossert, 1970). The r a t i o of reproductive tissue to vegetative tissue per in d i v i d u a l can be used as a measure of reproductive e f f o r t (Pianka and Parker, 1975). For the kelps, then, one can estimate reproductive e f f o r t by measuring sorus production r e l a t i v e to t o t a l (vegetative) blade production. This formulation permits a t h i r d testable p r e d i c t i o n that the r a t i o of sorus production to t o t a l blade production w i l l increase with age among iteroparous sporophytes. Two congeneric species were chosen for the purposes of a comparative study. Laminaria ephemera Setc h e l l i s a short-lived,semelparous sporophyte - 12 - found i n lower i n t e r t i d a l and subtidal habitats of the eastern P a c i f i c . L. s e t c h e l l i i S i l v a i s a lo n g - l i v e d iteroparous sporophyte of roughly the same habitat and d i s t r i b u t i o n . These species may be found growing adjacent to one another at many s i t e s i n Barkley Sound, Vancouver Island, B.C. Sporophyte populations of the two species do not intermix, each being r e s t r i c t e d to s l i g h t l y d i f f e r e n t substrata. Laminaria ephemera was o r i g i n a l l y described from c o l l e c t i o n s made i n Monterey County, C a l i f o r n i a p r i o r to 1901. The species i s distinguished from i t s congeners by the presence of a d i s c o i d holdfast, and by the absence of mucilage ducts from both the stipe and blade (Druehl, 1968). The species i s reportedly d i s t r i b u t e d from Volga Island, Alaska to Monterey County, C a l i f o r n i a (Abbott and Hollenberg, 1976), but extends at least to San Luis Obispo County i n the south (pers. obs.). Laminaria ephemera sporophytes display rather simple morphology. The di s c o i d holdfast i s small and without haptera, the stipe f l e x i b l e and terete, the blade single (but sometimes dissected). The sorus i s reportedly l i n e a r i n formation (Abbott and Hollenberg, 1976; Druehl, 1968), though soral patches may i n fact be as broad as the width of the blade (S e t c h e l l , 1901; and pers. obs.). Sori are formed asynchronously on either side of the blade, and the sorus formed on one side i s usually much larger than that formed on the other. Sorus formation i s i n i t i a t e d proximally to the t r a n s i t i o n zone and proceeds d i s t a l l y . Laminaria ephemera sporophytes are a highly seasonal component of the kelp f l o r a of Barkley Sound, B.C. Juvenile sporophytes are f i r s t i d e n t i f i a b l e i n March, depending upon the s i t e and p r e v a i l i n g weather conditions. Most sporophytes disappear by lat e June or early July. Sporophytes may be - 13 - i n t e r t i d a l , but are more commonly subtidal, and are often confined to substrata of cobble or small boulders underlain by soft bottoms of pebble or coarse sand. Individuals are only r a r e l y found on the subtidal g r a n i t i c pavements and outcrops t y p i c a l of Barkley Sound. Laminaria s e t c h e l l i i S i l v a i s a woody-stiped perennial species of the eastern P a c i f i c , d i s t r i b u t e d from Yakutat, Alaska (Druehl, 1968) to Ensenada, Baja C a l i f o r n i a , Me xico (Abbott and Hollenberg, 1976). The species i s characterized by a well-developed, erect stipe and large, repeatedly dissected blade, and by the presence of mucilage ducts i n both the stipe and blade. The holdfast i s hapterous and ramifying. The nomenclature of S i l v a (1957) and of Druehl (1968; 1979) w i l l be followed throughout. Laminaria dentigera (Nicholson, 1976) i s not considered to be conspecific with L. s e t c h e l l i i , and the former s p e c i f i c epithet i s reserved for a species of Alaskan Laminaria, according to Druehl (1979). Laminaria s e t c h e l l i i commonly inhabits stable and permanent substrata along exposed, wave-swept rocky shores. Mature plants exist i n nearly monospecific stands, and may form dense canopies. Juveniles (1 to 2 years old) are found among stands of adults of the species, but may also occur along the peripheries of populations and on newly-available substrata remote from adult populations. V i s i b l e rings formed by seasonal development of a secondary cortex are obvious i n basal cross-section of the s t i p e . Similar rings are common to other woody-stiped species, including Laminaria hyperborea (Gunn.) F o s l i e (Eain, 1963), Pterygophora c a l i f o r n i c a Ruprecht (Frye, 1918), and Ecklonia radiata (C. Ag.) J. Ag. (Novaczek, 1981). - 14 - The blade of Laminaria s e t c h e l l i i i s deciduous. A single blade i s i n i t i a t e d from the meristematic region at the t r a n s i t i o n zone, normally i n the months of September through December, depending upon the population and upon the s i t e . The blade develops and p e r s i s t s for about twelve months, at which time i t may be shed e n t i r e l y , leaving a bladeless stipe with a l a t e n t l y active meristematic region. A l t e r n a t i v e l y , the e x i s t i n g blade may be retained u n t i l seasonal i n i t i a t i o n of new blade tissues form the t r a n s i t i o n zone. In t h i s l a t t e r case, remnants of the older blade are e n t i r e l y sloughed shortly a f t e r i n i t i a t i o n of the new blade. Seasonal retention or los s of the e x i s t i n g blade seems to be independent of population and of s i t e . There i s , however, some age-dependent expression of t h i s t r a i t among the populations studied. A l l f i r s t and second year plants shed the e x i s t i n g blade e n t i r e l y , and 'overwinter' as bare stipes. Most t h i r d and fourth year plants also shed the e x i s t i n g blade. Older plants (5 and more years of age) generally r e t a i n at least some portion of the e x i s t i n g blade beyond i n i t i a t i o n of the new blade. A small percentage of older plants do, however, lose the e x i s i t n g blade e n t i r e l y , and p e r s i s t temporarily as bladeless stipes. Luning (1969; 1971) has reported a si m i l a r ontogney for the seasonal renewal of the blade of Laminaria hyperborea. I t appears, however, that the e x i s t i n g blade of L. hyperborea i s always maintained beyond new blade i n i t i a t i o n . The occurence of-bladeless stipes has not been reported for L. hyperborea. Small soral patches are generally i n i t i a t e d d i s t a l l y on well-developed fronds of Laminaria s e t c h e l l i i , and usually form synchronously and symmetrically on either side of the blade. As sorus development progresses, the sorus extends i n a proximal d i r e c t i o n and ultimately adjoins the - 15 - t r a n s i t i o n zone. Not a l l plants, however, produce such extensive s o r i . Eain (1971) has described s i m i l a r development of s o r i for Laminaria hyperborea. In the f a l l months, when remnants of the old blade p e r s i s t and are d i s t a l to newly-formed blade tissues, functional s o r i may be produced concomitantly along proximal regions of the old blade and d i s t a l regions of the new blade. The observation of simultaneous sorus formation on new and o l d blades of Laminaria s e t c h e l l i i indicates that sorus i n i t i a t i o n and development are independent of the age of the blade tissues. In the f i e l d , s o r i have been observed on fronds estimated to be l e s s than one month old. Blade surface area i s deemed the most appropriate parameter for i n t e r p s e c i f i c comparisons of meiospore production w i t h i n the genus Laminaria. Blade anatomy i s consistent along the length of the blade, and the entire blade i s pigmented, with meristodermal and upper-cortical c e l l s containing chloroplasts. Sorus formation i s the product of m i t o t i c transformations of the meristoderm. Vegetative and reproductive (soral) areas along the blade can be e a s i l y distinguished and evaluated with l i t t l e ambiguity. Fecundity can be estimated by q u a n t i f i c a t i o n of the number of spores produced per unit sorus area. Comparison of dry weight of the blade tissues i s considered inappropriate for the purposes of the present study. Euppers and Eremer (1978) have demonstrated for two species of Laminaria that dry weight per unit area v a r i e s along the length of the blade; dry weight per unit area may change seasonally as w e l l . Spatial and seasonal inconsistencies i n dry weight per unit area r e f l e c t energetic processes and constraints, e s p e c i a l l y i n terms of storage and u t i l i z a t i o n of carbohydrates. However, use of dry weight as a comparative parameter i n the present study p o t e n t i a l l y confounds the processes of - 16 - c a r b o h y d r a t e m e t a b o l i s m w i t h t h o s e o f m e i o s p o r e p r o d u c t i o n . A d d i t i o n a l l y , o b s e r v a t i o n s o f d r y w e i g h t n e c e s s a r i l y i n c l u d e t h e e x t r a n e o u s c o n t r i b u t i o n o f e p i p h y t e s t o t o t a l w e i g h t . D r y w e i g h t i s t h e r e f o r e n o t u s e d f o r t h e p u r p o s e s o f t h i s s t u d y . - 17 - CHAPTER 2 SEASONAL PATTERNS OF RECRUITMENT IN LAMINARIA EPHEMERA INTRODUCTION The cobble and boulders supporting dense populations of Laminaria ephemera at Cable Beach and at Execution Bay were unstable and subject to seasonal b u r i a l . The seasonal recurrence of s h o r t - l i v e d sporophytes on such unstable substrata i s of i n t e r e s t . Disallowing that recruitment of L. ephemera sporophytes occurs beyond the s e t t l i n g of meiospores, the L. ephemera gametophyte or embryosporophyte must p e r s i s t for at least 7 months. Success i n the following season requires that gametophytes or embryosporophytes are not overgrown by other algae, grazed by herbivores, or scoured away. Kelp gametophytes are generally capable of survival i n the dark (Kain, 1964; and pers. obs.). I t might be possible, therefore, that gametophytes can survive b u r i a l for extended periods of 7 months or more, i f the overlying sediment i s of a grain size s u f f i c i e n t to permit oxygenation within the sediment. Gametophytes or embryosporophytes could subsequently emerge to produce macroscopic sporophytes upon seasonal uncovering of the substratum. Such a scenario p o t e n t i a l l y obviates problems of overgrowth, grazing, and scouring, and conceivably leads to the production of dense, nearly monospecific stands of L. ephemera. Such high densities of L. ephemera have been repeatedly observed i n the f i e l d (pers. obs.). Few or no other kelp species i n Barkley Sound are reproductive simultaneously with Laminaria ephemera. Species such as Pterygophora c a l i f o r n i c a , A l a r i a marginata, and Cymathere t r i p l i c a t a tend to be - 18 - reproductive l a t e r i n the season than L. ephemera. This temporal difference i n reproduction, when coupled with seasonal b u r i a l and emergence of substrata, reduces the p r o b a b i l i t y of overgrowth or exclusion of L. ephemera by other kelp gametophytes, i f b u r i a l occurs p r i o r to spore production by kelps other than L. ephemera. In an attempt to document the observed seasonal pattern of Laminaria ephemera sporophyte recruitment, cobbles were tagged in s i t u and monitored for an 18 month period (June 1981 through November 1982). Three questions were addressed: 1) i n which months were cobbles supporting L. ephemera sporophytes buried and subsequently uncovered? 2) when did meiospore production occur r e l a t i v e to cobble b u r i a l ? and 3) would L. ephemera sporophytes reappear i n the following season on cobbles which had been previously buried? MATERIALS AND METHODS Thirty-nine cobbles were tagged and numbered i n Execution Bay (re: Figure 2.1) on 27 June 1981. Cobbles included i n the study were within an area of 2 les s than 50 m , on a sandy bottom, at 4-5 m depth. Cobbles chosen for 3 tagging were of minimum dimensions 15 cm , and supported at least 5 Laminaria ephemera sporophytes at the time of tagging. Other alg a l species were present on some cobbles, including j u v e n i l e Pterygophora c a l i f o r n i c a , A l a r i a marginata, and Cymathere t r i p l i c a t a . Tags were f i x e d in s i t u by a p p l i c a t i o n of underwater epoxy putty to the upper surface of each cobble. Five additional epoxy tags were f i x e d on rock walls bordering the study s i t e ; these were to serve as ind i c a t o r s of tag l o s s . - 19 - Forty-eight hours were allowed for curing of the applied epoxy. T h i r t y - six of the o r i g i n a l 39 tags were well-cured a f t e r 48 hours, and the experiment was begun with these 36 cobbles. On 29 June 1981, and at approximately monthly i n t e r v a l s thereafter, recovery of the tagged cobbles was attempted by underwater survey of the study s i t e . During these surveys, the presence or absence of Laminaria ephemera and of other alg a l species on the tagged cobbles was recorded, and the reproductive condition of Laminaria ephemera was noted. RESULTS Laminaria ephemera sporophytes were reproductive upon i n i t i a t i o n of the study (29 June 1981). Observations at Execution Bay have indicated that meiospore production may begin as early as A p r i l and may continue u n t i l July (re: Chapter 3). No Laminaria ephemera sporophytes remained on tagged cobbles, or w i t h i n the study area, on 05 August 1981, and L. ephemera sporophytes did not reappear on these cobbles at any time during the subsequent surveys. On 05 August 1981, the holdfasts of j u v e n i l e Pterygophora c a l i f o r n i c a remaining on some cobbles were buried beneath approximately 1 cm of sand. On 28 August 1981, there was evidence of tumbling of tagged cobbles, judged by p o s i t i o n of the tags and by o r i e n t a t i o n of stipes of P. c a l i f o r n i c a . Evidence of such tumbling p e r s i s t e d through the subsequent surveys of 25 September, 29 October, and 26 November 1981. Surveys made aft e r 26 November 1981 f a i l e d to recover any tagged cobbles. This f a i l u r e i s a t t r i b u t e d to b u r i a l of the study s i t e beneath 20-30 cm of sand and pebble. Surveys were continued through November 1982; tagged cobbles - 20 - were not uncovered during t h i s entire period. The disappearance of tagged cobbles i s assumed to r e f l e c t b u r i a l rather than tag l o s s ; epoxy tags applied to rock walls bordering the study s i t e were observable throughout the 18 month study period. B u r i a l was estimated as the rate of cobble disappearance, and i s expressed as the percentage of tagged cobbles not recovered during surveys. Values are given i n Table 2.1. Estimated b u r i a l for every survey p r i o r to 26 November 1981 was 11.1% or l e s s ; b u r i a l was estimated to be 69.4% for the survey of 26 November 1981. No tags were recovered during the survey made 11 December 1981, or at any time thereafter. DISCUSSION The b u r i a l of cobbles w i t h i n the study s i t e i s a seasonal phenomenon. Most cobbles exposed i n the early summer (June) remain exposed u n t i l the l a t e f a l l (November-December), at which time b u r i a l occurs. B u r i a l seems to r e s u l t from sand and pebble transport by water motion associated with winter storms. Summer hydrographic conditions remove the previously-deposited sand and pebble, again exposing cobbles, but removal may not occur i n the season immediately following b u r i a l . That i s , the cycle of b u r i a l and emergence may be of duration i n excess of one year, as indicated by the r e s u l t s of t h i s study. Meiospore production by Laminaria ephemera occurs p r i o r to cobble b u r i a l , by as much as 4 months, assuming that meiospores are produced i n July and cobbles are buried i n November. However, tumbling of cobbles and sand deposition may begin as early as August, cl o s e l y following meiospore - 21 - production by Laminaria ephemera. Pterygophora c a l i f o r n i c a , A l a r i a marginata. and Cymathere t r i p l i c a t a generally reproduce i n August or l a t e r . Laminaria ephemera sporophytes i n Barkley Sound grow at high densities (re: Chapter 3) and bear s o r i on single blades which are usually retained on the parent plant through the period of spore release. Sorus-bearing blades have no means of f l o t a t i o n , and no apparent means of long-distance d i s p e r s a l . Dispersal of kelp spores a f t e r l i b e r a t i o n from the sporangium i s reported to minimal (Anderson and North, 1967). I t i s therefore reasonable to assume that most l i b e r a t e d spores of Laminaria ephemera s e t t l e and germinate on cobbles nearby the parent sporophyte. Data presented here and repeated personal observations indicate that these gametophyte-bearing cobbles are subject to seasonal b u r i a l . That the cobbles tagged during t h i s study were buried but not subsequently uncovered allows only speculation regarding the fate of Laminaria ephemera gametophytes. I t i s possible that some proportion of gametophytes buried for 12 months or more remained v i a b l e . This i s suggested by the observation, at an adjacent s i t e , of Laminaria ephemera sporophyte development upon emergence of cobbles which had been buried for 8-12 months pr i o r to sporophyte i n i t i a t i o n . None of these cobbles were tagged, however, and qua n t i t a t i v e data are not a v a i l a b l e . In culture, Laminaria ephemera gametophytes are lon g - l i v e d . Gametophtyes germinated from s o r i c o l l e c t e d i n Barkley Sound have been retained i n culture 2 at low l i g h t (<50 uE/cm / s e c ) , or i n the dark with intermittent l i g h t breaks, for three years (Klinger, unpubl. obs.). There i s no reason to assume reduced gametophyte longevity i n the f i e l d , though the p r o b a b i l i t y of gametophyte mortality .in s i t u may be s u b s t a n t i a l l y enhanced. - 22 - Other algal species growing i n sandy habitats i n B r i t i s h Columbia may possess means of non-sexual reproduction, which are presumably of adaptive value i n sand-inundated environments. Harkham (1968) has demonstrated sporophyte i n i t i a t i o n by vegetative propagation of haptera i n Laminaria s i n c l a i r i i . Hathieson (1967) has reported 'direct development' among sporophytes of Phaeostrophion i r r e g u l a r e , i n which unispores l i b e r a t e d by sporophytes give r i s e to new sporophytes d i r e c t l y , thereby eliminating the microscopic sexual gametophyte from the l i f e h i s t o r y . Newroth and Markham (1972) have proposed that carpospores of Gymnogongrus l i n e a r i s may develop parthenogentically, and tetrasporophytes have not been reported for t h i s species. Parthenogenesis among l i b e r a t e d carpospores does not avoid the r i s k of mortality incumbent upon germlings i n sandy habitats, but does reduce the r i s k inherent i n reproduction by eliminating the tetrasporophyte stage from the l i f e h i s t o r y . In addition, Harkham and Newroth (1972) have noted that branches of G. l i n e a r i s which bear cystocarps may be abcised from the parent plant p r i o r to carpospore release, and that such branches may aid d i s p e r s a l , ostensibly to substrata temporarily free from sand and therefore conducive to carpospore settlement and germination. The capacity for vegetative propagation, non-sexual reproduction, or long-distance dispersal reduces or elimates the r i s k of gamete or zygote mortality due to sand scour and b u r i a l . Laminaria ephemera d i f f e r s from other sandy-habitat species such as Laminaria s i n c l a i r i i , Phaeostrophion i r r e g u l a r e , and Gymnogongrus l i n e a r i s i n that the species maintains an obligatory microscopic sexual stage, has no a l t e r n a t i v e means of non-sexual reproduction, and has no apparent means of long-distance d i s p e r s a l . - 23 - A v a i l a b i l i t y of hard substratum i s c r i t i c a l for successful meiospore settlement. Laminaria ephemera produces s o r i during the early summer (re: Chapter 3), when sand l e v e l s i n the subtidal are lowest, and when cobbles are exposed. This confers the greatest p r o b a b i l i t y of meiospore settlement success. S i m i l a r l y , Markham (1968) has noted that Laminaria s i n c l a i r i i i n B r i t i s h Columbia produces s o r i during the winter months, when sand l e v e l s i n the i n t e r t i d a l are lowest. It i s clear that the microscopic gametophyte or embryosporophyte of Laminaria ephemera must p e r s i s t f o r at least 7 months i n a habitat subject to sand scour and b u r i a l . I t i s conceivable that b u r i a l actually enhances gametophyte survivorship i n sandy habitats, by reducing scour, and by reducing or eliminating grazing by herbivores and overgrowth by other algae. The seasonal timing of meiospore release and settlement are therefore c r i t i c a l , both i n the a v a i l a b i l i t y to the meiospores of suitable hard substratum and i n the po t e n t i a l for successful germination p r i o r to b u r i a l . The success of Laminaria ephemera i n sandy habitats may consequently be a t t r i b u t a b l e to i t s truncated sporophyte generation, precise period of meiospore l i b e r a t i o n , and persistent gametophyte generation. - 24 - F i g u r e 2.1. Map o f B a r k l e y Sound, Vancouver I s l a n d , showing 3 st u d y s i t e s : W i z ard Rock, C a b l e Beach, and E x e c u t i o n Bay. - 25 - TABLE 2.1. DATE PERCENT 29 June 1981 2.77% 05 August 1981 11.11% 28 August 1981 . . 0% 28 September 1981 11.11% 29 October 1981 5.55% 26 November 1981 69.44% Table 2.1. Number of tagged cobbles not recovered i n each o f s i x surveys, expressed as a percentage of the number of cobbles i n i t i a l l y tagged (n=36). - 26 - CHAPTER 3 ALLOCATION TO MEIOSPORE PRODUCTION IN LAMINARIA EPHEMERA INTRODUCTION Sporophytes of Laminaria ephemera are annual and semelparous. The general phenology of the species i n Barkley Sound i s given i n Chapter 1. For the semelparous species, we can predict a r e l a t i v e l y high fecundity and a short time-to-maturity, according to arguments presented i n Chapter 1. In addition, a comparison of reproductive e f f o r t between populations of Laminaria ephemera can be made. Fecundity among sporophytes can be estimated by determination of the number of spores produced per i n d i v i d u a l , where the number of spores i s proportional to the surface area of the sorus produced. The surface area of the sorus can be measured graphically. Reproductive e f f o r t can be estimated as the r a t i o of vegetative to reproductive (soral) blade surface area. MATERIALS AND METHODS Laminaria ephemera was repeatedly harvested from each of two si t e s along the M i l l s Penninsula, Barkley Sound, B.C. (Figure 2.1). Dates of sampling are presented i n Table 3.1. An east-facing promontory forms the western boundary of Cable Beach. This rock wall extends v e r t i c a l l y to a depth of about 5 m, and meets a soft bottom punctuated by rocky outcrops. The s i t e i s subject to l i t t l e wave action, but high surge accompanies winds from the southeast or from the north. The study s i t e comprised a patch roughly 3 m , at 3 m depth, l i m i t e d on two sides by rock w a l l , and characterized by small boulders and large cobble on a s h i f t i n g , pebbly bottom. Execution Bay i s situated between the promontories of Execution Rock and Nudibranch Point. The back of the bay consists of rocky pavements extending to a bottom of sand and pebble. The study s i t e constituted an area of about 5 2 m , at 3 m depth, among cobble and boulders. 2 High i n i t i a l plant densities (0.98 per cm ) and small areal extent of each of these two s i t e s allowed the subjective designation of a l l conspecific i n d i v i d u a l s within a s i t e as members of a single population. No genetic inferences are made by use of the term "population" here or i n the discussion that follows. Plants were harvested from each s i t e for a twelve week period i n A p r i l through July, 1982. The sampling period at each s i t e was determined by the developmental status of plants at that s i t e . Sampling was i n i t i a t e d when juve n i l e sporophytes attained s u f f i c i e n t size for taxonomic i d e n t i f i c a t i o n (about 1 cm blade length), and was continued u n t i l fewer than f i f t y i n d i v i d u a l s remained wi t h i n the study area. The small size of pre-reproductive i n d i v i d u a l s necessitated use of a compressed a i r driven a i r l i f t sampler. The a i r l i f t allowed thorough sampling of the harvested area, without los s of i n d i v i d u a l s of smaller size classes. A i r l i f t sampling was replaced by hand-collection of plants i n samples taken l a t e r i n the season. 2 Each sample consisted of a l l plants removed from an area of about 1 m . Plants were transported to the laboratory i n mesh bags, and maintained i n - 28 - trays of flowing seawater. Blade and sorus perimeter were traced for a l l in d i v i d u a l s w i t h i n each sample. Larger plants were traced while fresh; smaller plants were pressed and dried p r i o r to tracing. A correction factor of 1.78% was calculated was the mean of 68 r e p l i c a t e s , for use i n standardizing surface area measurements of pressed and dried plants with those of fresh plants. F i f t y plants were randomly selected from each sample. Total vegetative surface area and t o t a l sorus surface area were calculated f o r each plant by means of integrating the area beneath the traced perimemters, using a d i g i t i z i n g t ablet i n tandem with an LSI-11 computer. Values were recorded to 2 + 0.01 cm . Operator accuracy was estimated to be -0.19%, calculated as the mean of twenty-two t r i a l s . Sorus samples were taken from 5 mature sporophytes from each of 2 study s i t e s (Cable Beach and Execution Bay). One piece of approximately 1 cm was excised from each plant, from the region immediately d i s t a l to the t r a n s i t i o n zone. Pieces of sorus were preserved i n 4% formalin s o l u t i o n i n seawater, and l a t e r sectioned i n both lon g i t u d i n a l and transverse planes; sections from each plane were prepared and viewed independently. Preparations were examined microscopically for determination of number of spores per sporangium, and of number of sporangia per unit blade surface area. Five observations were made per preparation, on r e p l i c a t e d sections, for a t o t a l of f i f t y observations per population. One-way analysis of variance was performed according to Sokal and Rohlf (1969) subsequent to B a r t l e t t ' s test for homogeneity of variance. Transformation of values p r i o r to analysis was performed when appropriate, and i s indcated i n the text. - 29 - RESULTS Mean vegetative surface area at Cable Beach decreased from 293.0 cm (09 2 A p r i l 1982) to 116.6 cm (13 June 1982; Figure 3.1). Mean soral surface area 2 9 decreased from 48.4 cm (09 A p r i l 1982) to 22.6 cm (13 June 1982). 2 Individual values ranged from a vegetative surface area of 0.2 cm (09 A p r i l 2 2 1982) to 452.4 cm (09 A p r i l 1982); and from a soral surface area of 0.1 cm 2 (13 June 1982) to 124.4 cm (09 A p r i l 1982). No plants remained at the study s i t e on the fourth sampling date of 05 July 1982. 2 Mean vegetative surface area at Execution Bay decreased from 687.6 cm (19 A p r i l 1982) to 115.7 cm2 (05 July 1982; Figure 3.2). Mean soral surface 2 2 area declined from 100.6 cm (19 A p r i l 1982) to 40.6 cm (05 July 1982). 2 Individual values ranged from a vegetative surface area of 0.3 cm (19 A p r i l 1982) to 999.3 cm2 (19 May 1982), and from a soral surface area of 0.7 cm2 (13 June 1982) to 245.1 cm2 (13 June 1982). Ninety-two percent of the sample at Cable Beach was reproductive on the f i n a l sampling date of 13 June 1982 (Figure 3.3). One-hundred percent of the sample at Execution Bay was reproductive on the f i n a l sampling of 05 July 1982 (Figure 3.4). Samples from Cable Beach and from Execution Bay both showed 92% reproductive plants on the common sampling date of 13 June 1982. The greatest percentage of every sample at Cable Beach f e l l within the 2 smallest (0.1-100.0 cm ) size class (Figure 3.5). No plants remained within 2 the largest (400.1-500 cm ) size class at the l a t e r sampling dates of 04 May and 13 June 1982). - 30 - The greatest percentage of each sample at Execution Bay f e l l within the smallest size class, except for that sample taken on 28 May 1982, i n which the greatest percentage f e l l among the second, t h i r d , and f i f t h size classes (Figure 3.6). Plants were found among the largest size classes (800.1-900.0 2 and 900.1-1000.0 cm ) only on the sampling dates of 19 May and 28 May 1982. 2 By 05 July 1982, no harvested plants exceeded 400.00 cm . At Cable Beach, many plants among the larger size classes (up to 100%) were reproductive at a l l sampling dates (Figure 3.7). Few plants among the 2 smallest size class (0.1-100.0 cm ) were reproductive at early sampling dates; 83.3% of t h i s size class was reproductive at the l a t e s t sampling date (13 June 1982). At Execution Bay, a maximum of 100% of the plants among some larger size classes were reproductive even i n the e a r l i e s t samples (19 A p r i l 1982 and 19 May 1982; Figure 3.8). There were no reproductive i n d i v i d u a l s within the 2 smallest size class (0.1-100.0 cm ) on 19 A p r i l 1982, and the percentage of reproductive i n d i v i d u a l s w i t h i n t h i s size class remained r e l a t i v e l y low u n t i l the f i n a l sampling date of 05 July 1982, at which time a l l plants were reproductive. The mean r a t i o of sorus surface area to vegetative surface area at Cable Beach increased from 13.2% (09 A p r i l 1982) to 19.8% (13 June 1982; Figure 3.11). Individual values for samples from Cable Beach ranged from 0.3% (13 June 1982) to 83.1% (13 June 1982). Mean values for samples from Execution Bay increased from 14.7% (19 A p r i l 1982) to 31.7% (05 July 1982; Figure 3.11). Individual values ranged from 1.9% (28 March 1982) to 92.2% (05 July 1982). - 31 - A l l mature sporangia observed contained 32 spores per sporangium. Presumably, 16 of these 32 spores were female, and 16 were male (Kain, 1964). No attempt was made i n t h i s study to determine sex r a t i o of spores. Microscopic examination of plants from Cable Beach gave a mean value of 7.72 sporangia per 0.012 cm (n=50; S.D.=0.93). This quantity i s equivalent to 5 2 4.14 X 10 sporangia per cm . For plants from Execution Bay, a mean value of 8.02 sporangia per 0.012 cm (n=50; S.D.=0.77) was obtained; t h i s i s equivalent 5 2 to 4.47 X 10 sporangia per cm . Analysis of variance showed no s i g n i f i c a n t difference between the number of sporangia per unit length for plants from 7 these two s i t e s . Estimated mean numbers of spores produced were 1.32 X 10 2 7 2 spores per cm (Cable Beach), and 1.43 X 10 spores per cm (Execution Bay). A conservative estimate of sporophyte fecundity can be made by combining minimum mean soral surface area with estimates of spores produced per unit g area X 0.5. The r e s u l t i n g fecundity estimates are 1.49 X 10 spores (Cable g Beach) and 2.90 X 10 spores (Execution Bay). DISCUSSION Sporophytes c o l l e c t e d from both Cable Beach and from Execution Bay exhibited several c h a r a c t e r i s t i c s which may be expected of semelparous plants. These include l i t t l e development of supportive tissues, r e l a t i v e l y short time-to-maturity, and high percentage of reproductive plants within the population. At least two c h a r a c t e r i s t i c s were exhibited which are generally not expected of strongly-semelparous plants; these include a p o t e n t i a l l y high pre-reproductive mortality and a low reproductive e f f o r t , judged by r e l a t i v e l y low mean a l l o c a t i o n of blade tissue to sorus formation. - 32 - The development of l i t t l e supportive tissue i s evident from inspection of the plant t h a l l u s , and of blade and stipe cross-sections (cf. Druehl, 1968). Stipes are t h i n and barely—corticated, and lack mucilage ducts. The holdfast i s small and without haptera. Blades are thin, with l i t t l e c o r t i c a t i o n and with s l i g h t development of medullary tiss u e s . The occasional formation of s o r i along the stipe (pers. obs.) indicates that stipe tissues may not be highly d i f f e r e n t i a t e d from blade tissues. Sorus formation along the stipe has not been reported for any other kelp species. Individual time-to-maturity was not measured i n t h i s study, but can be estimated from f i e l d observation of the populations. Small (le s s than 10 cm blade area) sporophytes were f i r s t observed at Cable Beach and at Execution Bay on 14 and IS March, 1982; by 24 March, some plants at Cable Beach had become reproductive. By May, more than 25% of the plants harvested from both s i t e s had produced s o r i (re: Figures 3.3 and 3.4), and by July, 100% of the harvested plants displayed s o r i and showed signs of i n c i p i e n t necrosis (Execution Bay), or a l l plants had disappeared (Cable Beach). Sporophyte l i f e - s p a n i s therefore conservatively estimated to be 5 months, and i s probably much less than that for an i n d i v i d u a l within a population. Developmental time-to-maturity may be as short as 1.5 to 2 months. A very high percentage (Cable Beach: 92%; Execution Bay: 100%) of harvested plants were reproductive at the end of the season. These data do not indicate, however, that 92% or 100% of the i n i t i a t e d sporophytes became reproductive w i t h i n the season, and there i s no estimate available for the number of plants w i t h i n a population which do not survive to reproductive maturity. - 33 - F i e l d observations indicate that pre-reproductive mortality may i n fact 2 be high. Densities of very small sporophytes (less than 2 cm blade surface 2 area) were estimated to be 4.3 per cm early i n the season; such high densities were never observed among reproductive plants l a t e r i n the season. Further, mortality occurring i n the period between zygote formation and growth to i d e n t i f i a b l e size was not qu a n t i f i e d , but i s p o t e n t i a l l y high. The r a t i o of soral surface area to vegetative surface area can be used as an estimate of reproductive e f f o r t (Pianka and Parker, 1975). This r a t i o averaged from 13% to 17%, with one outstanding mean value of 32%. Individual values, however, ranged from less than 1% to almost 93%. It appears, therefore, that almost the entire blade i s developmentally capable of transformation to sorus t i s s u e ; consequently, the r e l a t i v e l y low average values of 13% and 17% are unexpected i n that they r e f l e c t a generally low reproductive e f f o r t . Two explanations are immediately apparent: 1) that f i t n e s s i s not s i g n i f i c a n t l y enhanced by increasing the a l l o c a t i o n of reproductive tissue to, say, 90%, and therefore no sel e c t i v e pressure favors such an increase; 2) that there ex i s t s some cost (sensu B e l l , 1980 and 1984; Cody, 1966) associated with sorus production, and that t h i s cost reduces the amount of sorus which can viabl y and p r o f i t a b l y be produced without jeopardizing future s u r v i v a l . However, the existence of such a trade-off between enhanced sorus production and future survival seems untenable for the ephemeral sporophyte, i n which survival beyond the end of the present reproductive episode i s zero. There i s some evidence of both within- and between-site v a r i a t i o n i n l i f e h istory t r a i t s . At both Cable Beach and Execution Bay, mean sorus size decreased with time. This trend i s due to a small group of plants w i t h i n each - 34 - population which grew very quickly, reached a large size, and produced a large sorus. These large and precocious plants were absent from l a t e r samples, which were comprised predominantly of plants of smaller size and smaller sorus area. Sporophytes at Cable Beach were reproductive e a r l i e r i n the season, and became senescent e a r l i e r i n the season, than those at Execution Bay. Mean plant size at Execution Bay was greater, i n a l l samples, than mean plant size for roughly concurrent samples from Cable Beach; a greater percentage of plants among the f i n a l sample was reproductive at Execution Bay than at Cable Beach; and reproductive e f f o r t (as the mean r a t i o of soral surface area to vegetative surface area) was, on average, greater at Execution Bay than at Wizard Rock. The population at Cable Beach, then, reproduced e a r l i e r , achieved a smaller mean tha l l u s size, exhibited a lower average fecundity and a smaller average reproductive e f f o r t , and became senescent e a r l i e r i n the season than the population at Execution Bay. It i s impossible, however, from these data, to discriminate between the contributions of genotypic v a r i a t i o n and phenotypic expression i n determination of these s i t e - s p e c i f i c t r a i t s . - 35 - TABLE 3.1. CABLE BEACH: 09 A p r i l 1982 EXECUTION BAY: 19 A p r i l 1982 04 May 1982 19 May 1982 13 June 1982 28 May 1982 13 June 1982 05 J u l y 1982 Table 3.1. Dates of harvests made at each of two s i t e s , Cable Beach and Execution Bay. - 36 - CM E <_> o Ci) OJ u O in 400 200 100 50 20h 7 1 / V t i m e F i g u r e 3.1. S e m i - l o g a r i t h m i c p l o t o f mean v e g e t a t i v e s u r - f a c e a r e a ( f i l l e d c i r c l e s ) and mean s o r a l s u r f a c e a r e a (open c i r c l e s ) , + 1 S.E., among r e p r o d u c t i v e p l a n t s w i t h i n samples c o l l e c t e d from C a b l e Beach. (09 A p r i l : n=5; 04 May: n=19; 13 J u l y : n=46; v a r i a b l e n r e s u l t s from the v a r i a b l e number o f r e p r o d u c t i v e p l a n t s w i t h i n each sample o f 50 i n - d i v i d u a l s ) . - 37 - 1000 r - ^ 500 - a o 00 200 100 50 0 20 AV ^ t i m e F i g u r e 3.2. S e m i - l o g a r i t h m i c p l o t of mean v e g e t a t i v e s u r - f a c e a r e a ( f i l l e d c i r c l e s ) and mean s o r a l s u r f a c e a r e a (open c i r c l e s ) , + 1 S.E., among r e p r o d u c t i v e p l a n t s w i t h i n samples c o l l e c t e d from E x e c u t i o n Bay. (19 A p r i l : n=2; 19 May: n=2 8 ; 28 May: n=44; 13 June: n=46; 05 J u l y : n=50; v a r i a b l e n r e - s u l t s from t h e v a r i a b l e number o f r e p r o d u c t i v e p l a n t s w i t h i n each sample of 50 i n d i v i d u a l s ) . - 38 - 100 80 § 60 CL AO 20 h > < ^ V V t i m e F i g u r e 3.3. P e r c e n t a g e of s o r a l p l a n t s among samples from C a b l e Beach. - 3 9 - 100 80 60 - AO - 20 t ime 7-^ ^7- F i g u r e 3.4. P e r c e n t a g e of s o r a l p l a n t s among samples from E x e c u t i o n Bay. - 40 - c <_> D - 80 60 40 20 60 AO 20 4 0 - 2 0 - s u r f a c e a r e a (cm2) F i g u r e 3.5. P e r c e n t a g e o f p l a n t s f a l l i n g w i t h i n 100 cm s i z e c l a s s e s , f o r t h r e e s a m p l e s f r o m C a b l e B e a c h ; a b o v e : 09 A p r i l ; m i d d l e : 04 May; b e l o w : 13 J u n e , 1 9 8 2 . - 41 - c 8 0 - 6 0 - 4 0 - 20 - 40 - 2 0 - 20- i 2 0 - 40 - 20 - c£ C?> c£ r $ c £ C?> C?> c£ ^ r\r \P & <\Q -> surface area (cm') F i g u r e 3.6. P e r c e n t a g e of p l a n t s f a l l i n g w i t h i n 100 cm s i z e c l a s s e s , f o r f i v e samples from E x e c u t i o n Bay; from t o p : 19 A p r i l ; 19 May; 28 May; 13 June; 05 J u l y , 1982. - 42 - 100-| c u !_ CU Q. 100-, 60 - 2 0 - 1 0 0 n 6 0 - 2 0 - 7 7- surface area (cm2) F i g u r e 2 3 . 7 . P e r c e n t a g e of r e p r o d u c t i v e p l a n t s w i t h i n each 100 cm ( s u r f a c e area) s i z e c l a s s , f o r samples from C a b l e Beach. Above: 19 A p r i l ; m i d d l e : 04 May; below: 13 June, 1982. - 43 - 100-1 6 0 - 2 0 - 100-i 60 - 2 0 - 100 - i § 6 0 - <u CL - 20-' 100 - 6 0 - 2 0 - 100" 6 0 - 2 0 - & ^ ^ ^ c £ c £ surface area (cm2) Figure ?3.8. Percentage of reproductive plants within each 100 cm (surface area) s i z e c l a s s , f o r samples from Execu- t i o n Bay. From top: 19 A p r i l ; 19 May; 28 May; 13 June; 05 J u l y , 1982. - 44 - cu o > £ 0.6 r 0.4 0.2 J L J 09 19 04 19 28 13 05 A P R I L MAY J U N E JULY time F i g u r e 3.9. Mean r a t i o ( e x p r e s s e d as a d e c i m a l v a l u e ) of s o r a l s u r f a c e a r e a t o v e g e t a t i v e s u r f a c e a r e a , + 1 S.D., f o r samples from C a b l e Beach (open c i r c l e s ) and from E x e c u t i o n Bay ( f i l l e d c i r c l e s ) . - 45 - CHAPTER 4 ALLOCATION TO ME10SPORE PRODUCTION IN LAMINARIA SETCHELLII INTRODUCTION Sporophytes of Laminaria s e t c h e l l i i are perennial and iteroparous. The general phenology of the species i n Barkley Sound has been presented i n Chapter 1. According to the argument presented i n Chapter 1, we can predict that the iteroparous species w i l l exhibit a r e l a t i v e l y low annual fecundity, prolonged time-to-maturity, and increasing reproductive e f f o r t with age. Fecundity among sporophytes can be estimated by determination of the number of spores produced per i n d i v i d u a l , where the number of spores produced i s proportional to the surface area of the sorus. Reproductive e f f o r t can be estimated as the r a t i o of vegetative to reproductive (soral) blade surface area. MATERIALS AND METHODS Laminaria s e t c h e l l i i was repeatedly harvested i n Barkley Sound, B.C., from each of two s i t e s . Wizard Rock and Execution Bay (re: Figure 2.1). Wizard Rock i s a small, low island, the long axis of which runs roughly east to west. The northwest shore of the is l a n d i s subject to l i t t l e wave action, but high surge and strong currents accompany winds from the southeast or north. The rocky margin of the i s l a n d extends to about 8 m depth, where i t meets a sloping g r a n i t i c pavement. L. s e t c h e l l i i occupies the s u b l i t t o r a l fringe, from about the 0 m tide l e v e l to 4 m depth. - 46 - The study population comprised an area of roughly 12 m by 2 m along the upper-subtidal margin. Estimated average density of L. s e t c h e l l i i at t h i s 2 s i t e was 11.2 i n d i v i d u a l s per 0.25 m (S.D.=1.55), calculated as the mean of 2 10 haphazardly placed 0.25 m quadrats. A l l conspecific i n d i v i d u a l s within the study s i t e were subjectively designated as members of a single population. No genetic inferences are made here by use of the term "population" here or i n the discussion that follows. Execution Bay has been previously described i n Chapter 2. Laminaria s e t c h e l l i i occurs along the s u b l i t t o r a l margins of Execution Bay, as well as along the margins of wash-rocks and pinnacles i n the center of the bay. The study population consisted of plants growing along a 10 m by 2 m length of rocky pavement at the back of the bay. Estimated average plant density for L. 2 s e t c h e l l i i at t h i s s i t e was 13.2 i n d i v i d u a l s per 0.25 m (S.D.=1.48), 2 calculated as the mean of 5 haphazardly placed 0.25 m quadrats. Again, a l l conspecific i n d i v i d u a l s within the study area were designated as members of a single population. Plants were harvested from each study s i t e for a 12 month period beginning i n October, 1981 (Wizard Rock) and November, 1981 (Execution Bay). For each harvest, a course perpendicular to shore was chosen. Plants along t h i s course were removed at the holdfast or at the juncture of the holdfast and s t i p e . No discrimination was made between plants of d i f f e r e n t size classes during harvesting. A l l plants encountered along the course were harvested u n t i l a t o t a l sample of more than 55 i n d i v i d u a l s had been obtained. An undisturbed area of at least 0.5 m width was allowed between successively harvested courses. Courses were chosen sequentially, i n order to avoid sampling of previously harvested areas. - 47 - Samples were returned to the laboratory and maintained i n flowing sea water p r i o r to processing. For each plant, the blade was removed from the stipe at the t r a n s i t i o n zone. The perimeter of the entire blade was then traced onto paper. D i s t i n c t i o n was made between old or residual blade tissue and newly-generated blade tissue. Blades were examined for the presence of s o r i ; i f present, s o r i were excised and these perimeters were also traced. Blades were discarded a f t e r tracing. F i f t y traced plants were randomly chosen from each sample. Total vegetative and t o t a l soral surface area was calculated for each plant as described i n Chapter 3. The diameter at the base and the t o t a l length of each stipe harvested was measured and recorded. The volume of each stipe was calculated as the volume 2 of a cylinder (volume=TTr X height). Basal portions of a l l stipes were retained and immediately frozen for l a t e r sectioning, for purposes of age determination. Sorus samples were taken from 5 reproductive sporophytes from each study 2 s i t e . One piece of approximately 1 cm was excised from each i n d i v i d u a l , from a region midway along the frond. Each excised piece was preserved and l a t e r sectioned and examined microscopically as previously described i n Chapter 3. RESULTS Mean vegetative surface among reproductive plants at Wizard Rock ranged 2 2 from 299.4 cm (28 January 1982) to 5254.4 cm (18 June 1982; Figure 4.1). No d i s c r i m i n a t i o n between age or size class was made i n c a l c u l a t i n g these mean 2 values. Individual values among reproductive plants ranged from 55.7 cm (19 - 48 - 2 November 1982) to 8136.6 cm (05 August 1982). Analysis of variance performed on log-transformed values showed s i g n i f i c a n t differences (p<.001 level) i n mean vegetative surface area between samples taken on 19 November and 12 December 1981, and 28 January, 29 A p r i l , 18 June, and 05 August 1982. Samples taken on 15 October 1981 and 15 March 1982 were excluded from t h i s analysis because of the small number of i n d i v i d u a l s (n=0 and n=2, respectively) within these samples. Further analysis of between-group differences showed s i g n i f i c a n t difference (p<.001 lev e l ) between Group 1 (12 December 1981 and 28 January 1982) and Group 2 (29 A p r i l , 18 June, and 05 August 1982). There was no s i g n i f i c a n t difference between samples wi t h i n Group 2. 2 Mean soral surface areas at Wizard Rock ranged from 28.1 cm (28 January 1982) to 109.2 cm2 (05 August 1982); Figure 4.1). Individual values ranged 2 2 from 0.02 cm (18 June 1982) to 1202.3 cm (19 November 1981). Analysis of variance performed on log-transformed values showed no s i g n i f i c a n t difference (p<.001 lev e l ) between six samples taken 19 November and 12 December 1981, and 28 January, 29 A p r i l , 18 June, and 05 August 1982. Samples taken 15 October 1981 and 15 March 1982 were omitted from t h i s analysis, as noted above. Mean r a t i o s of soral surface area to vegetative surface area at Wizard Rock ranged from 1.25% (18 June 1982) to 18.54% (19 November 1981; Figure 4.2). Individual values ranged from 0.01% (18 June 1982) to 44.80% (19 November 1981). Analysis of variance was performed a f t e r a r c - s i n transformation of decimal values. Results showed a s i g n i f i c a n t difference (p<.001 lev e l ) i n the r a t i o of soral surface area to vegetative surface area between samples. Further analysis of between-group variance showed s i g n i f i c a n t difference (p<.001 level) between Group 1 (19 November 1981) and Group 2 (12 December 1981, 28 January, 29 A p r i l , 18 June, and 05 August 1982). - 49 - There was no s i g n i f i c a n t difference between samples within Group 2. The percentage of harvested plants bearing s o r i at Wizard Rock ranged from 0% percent (15 October 1981) to 54% (05 August 1982; Figure 4.3). The greatest number of soral plants was found on 12 December 1981 (34%) and on 05 August 1982 (54%). The smallest number of soral plants was found on 15 October 1982 (0%) and on 15 March 1982 (4%). Mean vegetative surface areas among reproductive plants at Execution Bay ranged from 341.2 cm2 (25 November 1981) to 5026.4 cm2 (28 May 1982; Figure 4.4). No discrimination between age or size class was made i n c a l c u l a t i o n of these values. Individual values among reproductive plants ranged from 74.6 2 2 cm (28 January 1982) to 81.9 cm (28 May 1982). Analysis of variance performed on log-transformed values showed a s i g n i f i c a n t difference (p<.001 leve l ) between samples. Further analysis showed a s i g n i f i c a n t difference (p<.05 lev e l ) between Group 1 (15 March and 28 October 1982) and Group 2 (28 May 1982). 2 Mean soral surface areas at Execution Bay ranged from 40.5 cm (15 March 2 1982) to 1116.3 cm (28 October 1982; Figure 4.4). Individual values ranged 2 2 from 1.1 cm (28 May 1982) to 4206.7 cm (28 October 1982). Analysis of variance performed on log-transformed values showed a s i g n i f i c a n t difference (p<.001 lev e l ) between samples. Further analysis of between-group differences showed a s i g n i f i c a n t difference (p<.001 l e v e l ) between Group 1 (25 November 1981, 28 January, 15 March, and 28 May, 1982) and Group 2 (28 October 1982). There was no s i g n i f i c a n t difference between samples within Group 1. The mean r a t i o s of soral surface area to vegetative surface area at Execution Bay ranged from 1.74% (28 May 1982) to 30.48% (28 October 1982; Figure 4.2). Individual values ranged from 0.04% (28 May 1982) to 83.6% (25 November 1981). Analysis of variance performed on a r c - s i n transformed values showed a s i g n i f i c a n t difference (p<.001 lev e l ) between samples. Further analysis showed a s i g n i f i c a n t difference (p<.001 lev e l ) between Group 1 (25 November 1981 and 28 October 1982) and Group 2 (28 January, 15 March, and 28 May 1982). There was no s i g n i f i c a n t difference between samples wit h i n either group. The percentage of plants bearing s o r i at Execution Bay ranged from 6% (15 March 1982) to 48% (28 October 1982; Figure 4.5). The greatest number of soral plants were found on 28 May 1982 (34%) and on 20 October 1982 (48%), and the smallest number was found on 15 March 1982 (6%). C o r r e l a t i o n analysis (Spain, 1982) of soral surface area versus age showed no s i g n i f i c a n t c o r r e l a t i o n between these two parameters. C o r r e l a t i o n analysis of the percentage of reproductive plants w i t h i n each sample versus age at Wizard Rock and at Execution Bay showed a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n (p<.001 lev e l ) between these two parameters (Figures 4.6 and 4.7). Differences i n the shape of the b e s t — f i t curve between these two s i t e s i s not considered to be important u n t i l confirmed by further sampling and analysis. The r e s u l t s of the analysis indicate that, for sporophytes among the populations samples, the p r o b a b i l i t y of becoming reproductive increases with age. C o r r e l a t i o n analysis of stipe volume versus age showed s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n (p<.001 lev e l ) between these two parameters (Figures 4.8-4.11). The c o e f f i c i e n t of determination obtained by analysis i s not of s u f f i c i e n t magnitude to allow confident p r e d i c t i o n of age by observation of stipe volume. These data do indicate, however, that stipe volume increases - 51 - with age, and t h i s observation implies the occurrence of energetic processes which may have importance to other energetic aspects of the sporophyte l i f e h i s t o r y . A l l mature sporangia observed contained 32 spores per sporangium. A 1:1 sex r a t i o smong spores i s assumed (cf. Kain, 1964). A mean value of 7.82 sporangia per l i n e a r centimeter (n=50; S.D.=0.87) was obtained for samples 5 2 from Wizard Rock. This value i s equivalent to 4.25 X 10 sporangia per cm . For samples from Execution Bay, a mean value of 6.36 spores per l i n e a r centimeter (n=50; S.D.=1.44) was obtained; t h i s i s equivalent to 2.81 X 105 2 sporangia per cm . Analysis of variance showed that there exists a s i g n i f i c a n t difference (p<.001 lev e l ) i n number of sporangia per l i n e a r centimeter between samples from Wizard Rock and Execution Bay. A conservative estimate of annual sporophyte fecundity can be made by combining minimum mean soral surface area with estimates of the number of spores produced per unit surface area X (0.5). The r e s u l t i n g estimates are 8 8 1.91 X 10 spores (Wizard Rock) and 1.80 X 10 spores (Execution Bay). This formulation assumes that each plant surviving to reproduce produces a sorus equivalent to the observed minimum mean soral surface area i n at least one reproductive period. The lack of a g e - s p e c i f i c i t y i n the c a l c u l a t i o n of t h i s estimate precludes assignment of any reproductive value to estimated fecundity. DISCUSSION Among the populations studied, there exists a strong seasonality to the processes of blade generation and stipe-holdfast generation, though the - 52 - precise timing of these processes may be somewhat s i t e - s p e c i f i c . New blade tissues are generally i n i t i a t e d i n October and November (Wizard Rock) or i n January (Execution Bay); blade i n i t i a t i o n and expansion are followed by stipe elongation and increase i n g i r t h , and by production of new haptera, i n March and A p r i l (both s i t e s ) . Sorus production may occur throughout the year, but i s greatest i n summer months (Wizard Rock) and i n the f a l l (Execution Bay). E x i s t i n g blades deteriorate and are sloughed i n the early f a l l (Wizard Rock) and i n the l a t e f a l l and early winter (Execution Bay). Populations of Laminaria s e t c h e l l i i at two s i t e s i n Barkley Sound show several l i f e h istory c h a r a c t e r i s t i c s which are consistent with those expected of iteroparous species. These c h a r a c t e r i s t i c s include delayed maturity, substantial development of supportive tissues, and an average reproductive e f f o r t which i s low i n comparison with maximum values for i n d i v i d u a l reproductive e f f o r t , where reproductive e f f o r t i s estimated as the r a t i o of sorus surface area to vegetative surface area. Age of f i r s t reproduction i n Laminaria s e t c h e l l i i i s generally delayed u n t i l the second or t h i r d year, though i n d i v i d u a l s are capable of reproduction i n the f i r s t year. Beyond the age of f i r s t reproduction, there e x i s t s no apparent c o r r e l a t i o n between age and the magnitude of sorus production i n any season. There does ex i s t , however, a p o s i t i v e c o r r e l a t i o n between age and the p r o b a b i l i t y of sorus production within a season. The observations of a p o s i t i v e c o r r e l a t i o n between age and stipe volume, and of no c o r r e l a t i o n between age and fecundity, suggest d i f f e r e n t i a l a l l o c a t i o n of resources to these to functions. That i s , stipe maintenance and growth may constitute consevative physiological functions which predictably demand a proportion of annual resources, whereas fecundity, with no observable - 53 - age-dependent c o r r e l a t i o n be yond the age of f i r s t reproduction, may only occasionally demand resource a l l o c a t i o n , t h i s a l l o c a t i o n being independent of ind i v i d u a l age and perhaps a response to other (unidentified) signals. I m p l i c i t i n t h i s argument i s the existence of within-plant competition for resources; t h i s may not be a j u s t i f i a b l e assumption for the kelps, i n which stipe, holdfast, blade, and sorus tissues are a l l pigmented and p o t e n t i a l l y capable of photosynthesis and nutrient a s s i m i l a t i o n . Generation of new stipe and holdfast tissues i s greatest during March and A p r i l ; observed sorus production i s minimal during these months. The r a t i o of sorus surface area to vegetative surface area can be used as a measure of reproductive e f f o r t (Pianka and Parker, 1975). The mean r a t i o s (Wizard Rock: 18.54%; Execution Bay: 30.48%) are small when compared with the corresponding maximum indi v i d u a l values (Wizard Rock: 44.80%; Execution Bay: 83.63%). This indicates that reproductive e f f o r t i s generally low, and that actual a l l o c a t i o n to sorus production i s less than that which i s p h y s i o l o g i c a l l y possible. Values obtained for i n d i v i d u a l and mean sorus production may r e f l e c t error inherent i n the discrete sampling of a continuous v a r i a b l e . That i s , sorus production was not measured through time for any single i n d i v i d u a l ; r e s u l t i n g values r e f l e c t an instantaneous measurement and may i n fact underestimate sorus production. I t should be noted, however, that vegetative surface area also constitutes a continuous v a r i a b l e . Expressing sorus surface area as a f r a c t i o n of vegetative surface area should therefore reduce t h i s error, and values obtained are considered to be strongly i n d i c a t i v e of actual values. - 54 - Reproductive i n d i v i d u a l s were found among populations throughout the year, and only one sample (Wizard Rock: 15 October 1981) contained no reproductive plants. Abundance of reproductive plants v a r i e d both seasonally and between populations. At Wizard Rock, soral plants were most abundant i n summer months (June and August 1982) and i n the winter (December 1981), and were les s abundant i n the f a l l and spring. At Execution Bay, reproductive plants were most abundant i n the l a t e spring (May 1982) and i n the f a l l (October 1982). The proportion of reproductive plants was l e s s than 50% i n a l l samples but one (Wizard Rock, 05 August 1982: 54%). This r e s u l t contrasts sharply with the observed high proportions of reproductive i n d i v i d u a l s found among populations of a congeneric annual species (re: Chapter 3). I t i s possible, however, that for Laminaria s e t c h e l l i i , the summed proportion of reproductive i n d i v i d u a l s for any annual period i s greater than the values obtained here. The manner i n which these data were c o l l e c t e d precludes confident p r e d i c t i o n of the t o t a l number of i n d i v i d u a l s reproducing annually. There i s evidence of s i t e - s p e c i f i c differences i n expression of l i f e h istory c h a r a c t e r i s t i c s among populations of Laminaria s e t c h e l l i i . Timing and magnitude of reproductive events v a r i e d between the two populations, as discussed above. It i s impossible from these data to d i s t i n g u i s h between genotypic differences and phenotypic p l a s t i c i t y i n the determination of s i t e - s p e c i f i c t r a i t s . - 55 - TABLE 4.1. WIZARD ROCK: 15 October 1981 19 November 1981 28 January 1982 29 March 1982 18 June 1982 05 August 1982 EXECUTION BAY: 25 November 1981 28 January 1982 15 March 1982 28 May 1982 18 October 1982 Table 4.1. Dates o f harvests made a t each o f two s i t e s , Wizard Rock and Execution Bay. - 56 - CM E O CD 1000 A 4 (_> o 3 01 100 t f Co t i m e F i g u r e 4.1. S e m i - l o g a r i t h m i c p l o t o f mean v e g e t a t i v e s u r - f a c e a r e a (open c i r c l e s ) and mean s o r a l s u r f a c e a r e a ( f i l - l e d c i r c l e s ) , + 1 S.E., among r e p r o d u c t i v e p l a n t s w i t h i n samples c o l l e c t e d from Wizard Rock. (19 Nov.: n=5; 12 D e c : n=17; 28 J a n . : n=4; 29 A p r i l : n=5; 18 June: n=19; 05 Aug.: n=27; v a r i a b l e n r e s u l t s from the v a r i a b l e number of r e p r o - d u c t i v e p l a n t s w i t h i n each sample of 50 i n d i v i d u a l s ) . - 57 - 0.6-1 3 0.4 a > E o T3 o 0.2 - ' 7 7 7 c f 41 o I A 0 — 7 7 7 7 7 „ - t i m e F i g u r e 4 . 2 . Mean r a t i o ( e x p r e s s e d as a d e c i m a l v a l u e ) of s o r a l s u r f a c e a r e a t o v e g e t a t i v e s u r f a c e a r e a , + 1 S.D., f o r samples from W i z a r d Rock (open c i r c l e s ) and E x e c u t i o n Bay ( f i l l e d c i r c l e s ) . - 58 - 60-, I AOH CL 20A / ^ / / 4? * *?> O ^ 1981 1982 t i m e F i g u r e 4.3. P e r c e n t a g e of s o r a l p l a n t s among samples a t W i z a r d Rock. - 59 - rsi E o v. o <_> O" Z3 5 0 0 0 r 1 0 0 0 1 0 0 •> - 7 d> t i m e F i g u r e 4.4. S e m i - l o g a r i t h m i c p l o t o f mean v e g e t a t i v e s u r - f a c e a r e a ( o p e n c i r c l e s ) a n d mean s o r a l s u r f a c e a r e a ( f i l - l e d c i r c l e s ) , + 1 S.E., among r e p r o d u c t i v e p l a n t s w i t h i n s a m p l e s c o l l e c t e d f r o m E x e c u t i o n B a y . (25 N o v . : n=13; 28 J a n . : n=8; 15 M a r c h : n=3; 28 May: n=17; 28 O c t . : n = 2 4 ) . - 6 0 - ~ 4(H o S. 20 H - 7 - 1981 7 — 7 7 7 7 7 " ^ ^ *>V * ° 1982 time F i g u r e 4 . 5 . P e r c e n t a g e of s o r a l p l a n t s among samples from E x e c u t i o n Bay. - 61 - F i g u r e 4.6. B e s t - f i t c u r v e g e n e r a t e d by c o r r e l a t i o n a n a l y s i s o f p e r c e n t a g e of r e p r o d u c t i v e p l a n t s v e r s u s age, f o r samples from Wizard Rock. - 62 - age F i g u r e 4 . 7 . B e s t - f i t l i n e g e n e r a t e d by c o r r e l a t i o n a n a l y s i s o f p e r c e n t a g e o f r e p r o d u c t i v e p l a n t s v e r s u s age, f o r samples from E x e c u t i o n Bay. - 63 - F i g u r e 4.8. B e s t - f i t l i n e g e n e r a t e d by c o r r e l a t i o n a n a l y s i s o f s t i p e volume v e r s u s age a t Wizard Rock, 05 Aug. 1982. - 6 4 - F i g u r e 4.9. B e s t - f i t l i n e g e n e r a t e d by c o r r e l a t i o n a n a l y s i s o f s t i p e volume v e r s u s age a t W i z a r d Rock, 18 Nov. 1982. - 65 - F i g u r e 4.10. B e s t - f i t l i n e g e n e r a t e d by c o r r e l a t i o n a n a l y o f s t i p e volume v e r s u s age a t E x e c u t i o n Bay, 28 Oct. 1982. - 66 - F i g u r e 4.11. B e s t - f i t l i n e g e n e r a t e d by c o r r e l a t i o n a n a l y s i s o f s t i p e volume v e r s u s age a t E x e c u t i o n Bay, 10 Nov. 1982. - 67 - CHAPTER 5 AGE STRUCTURE AMONG POPULATIONS OF LAMINARIA SETCHELLII INTRODUCTION Among populations of perennial organisms, age-specific processes of reproduction and survivorship ultimately determine the population rate of increase. Q u a n t i f i c a t i o n of the rate of increase consequently demands that these age-specific processes are observable. I d e n t i f i c a t i o n of ind i v i d u a l age i s therefore a c r u c i a l f i r s t step i n the determination of population rate of increase. For the purposes of population projection, ' r ' , or instantaneous rate of increase, may be calculated as the natural logarithm of the eigenvalue of the age-structured matrix ( L e s l i e , 1945). Such matrix formulations demand that the age d i s t r i b u t i o n of the population be known, and usually require that t h i s age d i s t r i b u t i o n i s stable (Michod and Anderson, 1980; Caughley and B i r c h , 1971; L e s l i e , 1945). Age d i s t r i b u t i o n s among algal populations are lar g e l y unknown, due p r i n c i p a l l y to the lack of an adequate c r i t e r i o n by which to determine in d i v i d u a l age. However, Kain (1963), Novaczek (1981), and Dayton e t . a l . (1984) have used the concentric rings v i s i b l e i n the stipes of some kelps i n order to determine age; c o r r e l a t i o n a l evidence only has been used to show that such rings are annual i n formation. Estimates of in d i v i d u a l age and of population age d i s t r i b u t i o n for Laminaria s e t c h e l l i i have not been reported i n the l i t e r a t u r e . The present study describes the age d i s t r i b u t i o n of Laminaria - 68 - s e t c h e l l i i at two s i t e s i n Barkley Sound, Vancouver Island, B.C. MATERIALS AND METHODS Size class frequency by basal diameter was estimated i n a series of repeated, non-destructive measurements made on a single population of Laminaria s e t c h e l l i i at each of two study s i t e s . Wizard Rock and Execution Bay. Estimated average density of the population at Wizard Rock was 8.4 2 2 plants per .025 m (calculated as the mean of 5 haphazardly placed 0.25 m quadrats). The population was situated on an outcrop approximately 2.5 m X 2 m, at about 3 m depth. Observed t o t a l population size ranged from 99 to 122 in d i v i d u a l s for the sampling period of 25 August 1981 to 18 November 1982. Estimated average density of the population at Execution Bay was 7.4 2 2 plants per 0.25 m (calculated as the mean of f i v e haphazardly placed 0.25 m quadrats). The population was situated on an outcrop approximately 2.5 m X 1 m, at a depth of about 2.5 m. Observed t o t a l population size ranged from 75 to 92 i n d i v i d u a l s for the study period of 25 August 1981 to 02 November 1982. The basal diameter of a l l i d e n t i f i a b l e i n d i v i d u a l s of Laminaria s e t c h e l l i i within each population was measured. I n s i t u , at i n t e r v a l s of about six weeks. Measurements were made using p l a s t i c Vernier c a l i p e r s . Values were recorded to the mearest millimeter. Measurement error was estimated to be not more than 6.77%, calculated as the mean of 20 repeated measurements on tagged (therefore, i d e n t i f i a b l e ) i n d i v i d u a l s . This error quantity r e s u l t s primarily from the s l i g h t e c c e n t r i c i t y of the Laminaria s e t c h e l l i i stipe. Success i n l o c a t i n g and measuring each plant within the population at a single observation time was 96.1%, calculated as the mean of 4 sequential t r i a l s . - 69 - A l l plants remaining among the study populations at both study s i t e s were harvested i n November 1982. In the laboratory, the basal diameter of each plant was measured. The basal portion of each stipe was retained and frozen for l a t e r sectioning. Age class frequency among the sampled populations was determined by counting basal stipe rings i n cross section (re: Appendix A). Each stipe was sectioned at a distance of less than 0.5 cm from the holdfast. Entire cross sections were cut by hand, and these were examined beneath a dissecting microscope using a combination of transmitted and r e f l e c t e d l i g h t . The maximum number of annual growth rings were counted and recorded for each harvested plant. Age class frequencies were determined for one additional population each at Wizard Rock and at Execution Bay. Repeated harvests of 50 plants each were made between 19 November 1981 and 23 September 1982 (Wizard Rock), and between 25 November 1981 and 28 October 1982 (Execution Bay; re: Chapter 4 for harvesting methods). Stipes of a l l i n d i v i d u a l s were sectioned and maximum number of rings were counted, as above. Data obtained from repeated harvests at a single s i t e were pooled i n groups of 150-200, by date of harvest, for purposes of analysis. RESULTS Size class d i s t r i b u t i o n by 2 mm basal diameter increments was determined for a population at Wizard Rock (Figure 5.1). Diameters ranged from 1.0 mm (18 March, 07 July, 18 November 1982) to 28.0 mm (18 March 1982). More than 72% of the plants within within each sample f e l l among the 12-24 mm size classes. For the f i r s t three samples, the greatest percentage of plants f e l l w ithin the 17-18 mm size classes; t h i s peak s h i f t e d to the 19-20 mm size class - 70 - for a l l but one sample taken a f t e r 29 October 1981. The percentage of plants f a l l i n g within the smallest size class (1-2 mm basal diameter) may be some i n d i c a t i o n of recruitment during the sampling period. This quantity increased from 0% (29 October 1981) to 11% (11 June and 07 July 1982), and decreased again to 4% (18 November 1982). The age class d i s t r i b u t i o n for t h i s population at Wizard Rock was determined on 18 November 1982 (Fig. 5.2). Seventy percent of the population was of age 8-14 years. F i f t e e n percent were 1-2 years. The shape of the age class d i s t r i b u t i o n i s sim i l a r to that of the size class d i s t r i b u t i o n obtained for the same population on 18 November 1982. The age class d i s t r i b u t i o n s for eight harvests from Wizard Rock were pooled i n two groups according to date of harvest (Fig. 5.3). No single age class comprised more than 12.5% of the population. The peak of 11.5% at 11 years i n the f i r s t pooled group (19 November 1981 through 15 March 1982) s h i f t e d to 12.5% at 12 years i n the second pooled group (29 A p r i l through 23 September 1982). S i m i l a r l y , the minor peak of 8% at f i v e years i n the f i r s t group s h i f t e d to 9% at six years i n the second group. Size class d i s t r i b u t i o n by increments of 2 mm basal diameter was determined for a population at Execution Bay (Fig. 5.4). Stipe diameter ranged from 1.0 mm (11 December 1981, 25 July 1982) to 28.0 mm (02 November 1982). No single size class comprised more than 20% of the population, and no consistent peak size classes were apparent within t h i s population. The percentage of plants within the 1-2 mm size class increased from 0% (25 August, 26 September, 29 October 1981) to 11% (18 March, 25 July 1982), and decreased again to 1% (16 October 1982). The age class d i s t r i b u t i o n for t h i s population at Execution Bay was determined on 10 November 1982 (Fig. 5.5). Seventeen percent of the population was three years of age, and 9% were ten years of age. The age class d i s t r i b u t i o n s for seven harvests made at Execution Bay were pooled i n two groups according to date of sampling (Fig. 5.6). For the f i r s t pooled sample (25 November 1981 through 15 March 1982) 83% of the population was among the 1-5 year age classes, with the remaining seventeen percent d i s t r i b u t e d between the 6-14 year age classes. For the second pooled samples (28 May through 28 October 1982), 70% of the population was d i s t r i b u t e d among the 1-6 year age classes; the remaining 30% were d i s t r i b u t e d among the 7-17 year age classes. DISCUSSION Size class d i s t r i b u t i o n of Laminaria s e t c h e l l i i by basal diameter does not necessarily r e f l e c t the age class d i s t r i b u t i o n of the population. Size class frequency may, however, r e f l e c t populational t r a n s i t i o n s through time, and the frequencies of the smaller size classes may provide an estimate of recruitment into a population, when repeated measurements are made. The age class d i s t r i b u t i o n s presented for 4 populations at 2 s i t e s were neither s i m i l a r between populations at a single s i t e , nor between s i t e s . The roughly bimodal age class d i s t r i b u t i o n s exhibited by these populations indicate that the normal or stable age d i s t r i b u t i o n (sensu Lotka, 1922) has not been achieved. The stable age d i s t r i b u t i o n requires, by d e f i n i t i o n , that the age d i s t r i b u t i o n i s self-perpetuating, and that reversion to such a d i s t r i b u t i o n w i l l occur following disturbance (Lotka, 1922; 1956). The bimodal age d i s t r i b u t i o n i s i n t u i t i v e l y unstable i n that an age class e x h i b i t i n g a low- frequency at an intermediate age cannot generate an age class of greater frequency at a l a t e r age. For example, at Wizard Rock (Fig. 5.2), a frequency of 0% among the 3 year age class cannot give r i s e to a frequency of 14% among the 12 year age class, under conditions of s t a b i l i t y . Two processes may account for the observed age d i s t r i b u t i o n s . Annual f l u c t u a t i o n s i n sporophyte or gametophyte fecundity may produce v a r i a b l e numbers of zygotes and, i n turn, variable numbers of annual r e c r u i t s . Comparison of the very high numbers of spores produced (re: Chapter 4) with the small numbers of r e c r u i t s observed within these populations does not, however, support t h i s argument. S p e c i f i c a l l y , the high number of spores produced by a population i s not l i k e l y to l i m i t recruitment into that population. It i s more l i k e l y that the observed age d i s t r i b u t i o n s are the product of episodic recruitment and v a r i a b l e survivorship among r e c r u i t s . I t has been demonstrated (Kirkman, 1981; Pearse and Hines, 1979; Lobban, 1978a) that recruitment beneath an established canopy i s minimal. Successful recruitment may depend upon the creation of newly-available space. Patch size and the temporal window of space a v a i l a b i l i t y would therefore determine recruitment success within a canopy; these two factors are s u f f i c i e n t to explain both the observed differences i n age structure between the populations studied, and the absence of the normal age d i s t r i b u t i o n among these populations. Kain (1971; 1963) has reported age d i s t r i b u t i o n s for populations of Laminaria hyperborea i n the North A t l a n t i c . The reported age d i s t r i b u t i o n s exhibit no s i m i l a r i t y between populations, and show no evidence of the normal age d i s t r i b u t i o n . Dayton e t . a l . (1984) have reported a weakly bimodal age d i s t r i b u t i o n for a population Laminaria s e t c h e l l i i i n C a l i f o r n i a i n which the f i r s t and fourth year classes are most abundant. The data of Kain (1971; 1963) and of Dayton e t . a l . (1984) are consistent with data obtained i n t h i s study for Laminaria s e t c h e l l i i i n B r i t i s h Columbia; Rain's data support the argument proposed above concerning saltatory recruitment i n Laminaria. Absence of the normal age d i s t r i b u t i o n among the populations studied does not necessarily imply that the populations are declining i n size. I f the number of embryosporophytes produced within a population each year i s s u f f i c i e n t to e n t i r e l y replace that same population (and estimates of meiospore production indicate that t h i s i s p l a u s i b l e ) , then the population may experience no decrease i n size. One can postulate that the number of embryosporophytes i n i t i a t e d f a r exceeds the number of r e c r u i t s surviving to begin the second year. I f t h i s i s true, then the populations studied may best be described by a Deevey Type I I I survivorship curve. Williams (1975) has discussed the ramifications of a very high rate of gamete production coupled with a very low rate of o f f s p r i n g s u r v i v a l . Williams' discussion makes the important point that such systems may not, i n f a c t , behave according to Markovian dynamics. Markovian dynamics demand, s t r i c t l y , that the sum of the elements of each column i n the appropriate Leslie-type matrix equals one, and further assume that the state of the system (population) at time T+l i s predictable from the observed state at time T+0. If a system proves to be non-Markovian i n behavior, then conventional matrix formulations are not applicable. An important consequence of non-Markovian behavior to the dynamics of Laminaria s e t c h e l l i i i n p a r t i c u l a r , and to the kelp l i f e h istory i n general, i s that i f population size at time T+l i s not determined by the l i f e h i s t o r y parameters observable at time T+0, then the population dynamics may be the r e s u l t of stochastic processes which cannot be estimated according to e x i s t i n g models. - 74 - 2 0 25 AUG 81 2 0 2 6 SEPT 81 20 2 0 29 OCT 81 _ • c H DEC 81 ~ 20 11 FE B 82 c o CL 20 20 20 20 20 18 MAR 82 II JUNE 82 07 J U LY 82 02 SEPT 82 2 8 U 20 26 mm b a s e d i a m e t e r Figure 5.1. S i z e c l a s s d i s t r i b u t i o n by ba s a l d i a m e t e r f o r ten repeated samples a t W i z a r d Rock. - 75 - Figure 5.2. Age c l a s s d i s t r i b u t i o n a t W i z a r d Rock, 18 Nov. 1982. - 76 - F i g u r e 5.3. Age c l a s s d i s t r i b u t i o n among each of two p o o l e d samples from W i z a r d Rock. Above: November, December, 19 81, and J a n u a r y , March, 19 82; below: A p r i l , June, J u l y , Septem- b e r , 1982. - 77 - 20 20 20 20 c CD £ 20 CD Q_ 20 20 20 2 5 A U G 81 26 S E P T 81 290CT 81 11 DEC 81 18 M A R 82 20 A P R 82 25 JULY 82 1 I- 15 S E P T 82 20 - 10 NOV 82 I I I I—T 2 8 K 20 26 mm base d i amete r F i g u r e 5.4. S i z e c l a s s d i s t r i b u t i o n by b a s a l d i a m e t e r f o r n i n e r e p e a t e d samples a t E x e c u t i o n Bay. - 78 - c 20 u a> CL — 1 — 1 1 — | — i , , , 2 A 6 8 10 12 U age F i g u r e 5.5. Age c l a s s d i s t r i b u t i o n a t E x e c u t i o n Bay, 10 Nov. 1982. 20 c CD u CD °- 20 — i — i — i — i — i — r — i — , — , — 2 4 6 8 10 12 14 16 F i g u r e 5.6. Age c l a s s d i s t r i b u t i o n among each of two pooled samples from E x e c u t i o n Bay. Above: November, 1981, and January, March, 1982; below: May, J u l y , Septemeber, and October, 1982. - 80 - CHAPTER 6 GENERAL DISCUSSION A synthetic discussion of r e s u l t s gained from i n v e s t i g a t i o n of congeneric species suffers from problems of s i m p l i f i c a t i o n inherent i n comparison of d i s s i m i l a r taxa. However, the hypothesis formulated for the purposes of t h i s study allowed the testing of three predictions put f o r t h i n Chapter 1. These w i l l be addressed i n turn. 1. Estimated fecundity (as meiospore production) was not d i f f e r e n t o o between the two species (L. ephemera: 1.49 X 10 (Cable Beach) and 2.90 X 10 (Execution Bay); L. s e t c h e l l i i : 1.91 X 10 8 (Wizard Rock) and 1.80 X 10 8 (Execution Bay)). This r e s u l t i s contrary to the p r e d i c t i o n of increased fecundity i n the semelparous sporophyte. I t should be noted, however, that sporic contribution to o v e r a l l f i t n e s s may be very d i f f e r e n t between the two species, even i n the absence of s t a t i s t i c a l differences i n fecundity. As Fisher (1931) has discussed, o f f s p r i n g produced early i n the parents' l i f e t i m e may be more valuable (e.g. make a greater contribution to population rate of increase) than the same number of o f f s p r i n g produced l a t e r i n the parents' l i f e t i m e . On t h i s basis, one might predict a greater ' r ' for Laminaria g ephemera (producing 10 spores at an age of 6 to 8 weeks) than for Laminaria g s e t c h e l l i i (producing 10 spores at 2 or more years of age). 2. Developmental time to maturity was observed to be shorter for the semelparous than for the iteroparous sporophyte, as predicted. Individuals of Laminaria ephemera were estimated to become reproductive at an age of 6 to 8 weeks. Conversely, Laminaria s e t c h e l l i i did not become reproductive at l e s s than 1 year of age, and seldom before the second or even t h i r d year. Delayed - 81 - maturity i n the iteroparous sporophyte possibly r e s u l t s from p a r t i t i o n i n g of available resources between the al t e r n a t i v e processes of reproduction and of stipe growth and maintenance. 3. There i s no evidence i n these data that annual reproductive e f f o r t (as the mean r a t i o of sorus surface area to vegetative surface area) i s greater for the semelparous than for the iteroparous sporophyte. The r a t i o of sorus surface area to vegetative surface area i n Laminaria ephemera varied from 13% to 19% (Cable Beach) and from 14% to 32% (Execution Bay); in Laminaria s e t c h e l l i i . t h i s r a t i o v a r i e d from 1% to 18% (Wizard Rock) and from 2% to 32% (Execution Bay). Between species, the maximum mean values (L. ephemera: 32%; L. s e t c h e l l i i : 30%) are nearly i d e n t i c a l , and therefore do not support the expectation of increased reproductive e f f o r t i n the semelparous species. Between-species differences i n maximum in d i v i d u a l reproductive e f f o r t are smaller (L. ephemera. Execution Bay: 92%; L. s e t c h e l l i i , Execution Bay: 84%) than are i n t r a s p e c i f i c differences i n reproductive e f f o r t (L. s e t c h e l l i i , Wizard Rock: 44%; L. s e t c h e l l i i . Execution Bay: 84%). These data indicate that reproductive e f f o r t i s variable both within and between populations of a single species, and such v a r i a b i l i t y may preclude any comparisons of reproductive e f f o r t between species. The p r e d i c t i o n of increased reproductive e f f o r t with age among populations of the iteroparous species was not supported by these data. This r e s u l t may be at t r i b u t a b l e to the observed high v a r i a b i l i t y i n in d i v i d u a l reproductive e f f o r t , which may obscure o v e r a l l trends within populations. A l t e r n a t i v e l y , the discrete method of sampling used i n th i s study may have precluded i d e n t i f i c a t i o n of age-specific trends i n reproductive e f f o r t among in d i v i d u a l s . - 82 - For a stable population i n which b i r t h rate equals death rate, any i n d i v i d u a l must replace i t s e l f once during i t s l i f e t i m e . The high sporic fecundities exhibited by Laminaria ephemera are s u f f i c i e n t to allow for a successful rate of replacement, and a l t e r n a t i v e mechanisms of population increase ( i . e . enhanced gametophyte longevity or fecundity) need not be invoked i n order to account for the observed population processes. Laminaria s e t c h e l l i i , however, exhibits an annual sporic fecundity of the same magnitude as as L. ephemera, but maintains an annual sporophyte replacement rate much smaller than that of L. ephemera. This suggests the existence of species- s p e c i f i c differences i n the contribution of the gametophyte to observed population processes. Such differences may be effected by a l t e r a t i o n of gametophyte l i f e h istory c h a r a c t e r i s t i c s . The problem of a l t e r a t i o n of gametophyte l i f e h istory c h a r a c t e r i s t i c s must be approached i n t u i t i v e l y . Inherent i n a l l non-vegetative reproductive events i s the r i s k of o f f s p r i n g mortality, or lack of success; the magnitude of r i s k i s v a r i a b l e between reproductive events. Reproduction—associated r i s k i n a single zygote-to-zygote cycle increases as the product of the r i s k terms associated with each phase of the cycle. For those complex l i f e h i s t o r i e s maintaining only a single reproductive episode per zygote-to-zygote cycle ( i . e . d i p l o n t i c organisms), the relevant r i s k term i s simply that of the observed reproductive episode. However, for complex l i f e h i s t o r i e s with more than one reproductive episode per zygote-to-zygote cycle, reproduction- associated r i s k may be s i g n i f i c a n t l y increased. In order for complex-life-history populations to remain stable or to increase i n size, the enhanced r i s k associated with complexity must be compensated for or exceeded by an increase i n fecundity. For complex l i f e - 83 - h i s t o r i e s , o v e r a l l (zygote-to-zygote) fecundity increases as the product of the i n d i v i d u a l fecundities of between-stage reproductive events. I t i s a t t r a c t i v e to predict mean fecundities of greater than one for a l l stages i n the complex l i f e h i s t o r y : t h i s would a f f o r d the greatest potential for compensation of mortality accruing to reproduction-associated r i s k . A l t e r n a t i v e l y , i f reproduction-associated r i s k accrues to more than one phase, but fecundity i s greater than one i n only a single phase, then fecundity within that single phase must increase m u l t i p l i c a t i v e l y over a comparable value for the non-complex condition. Data presented above do not bear d i r e c t l y on the problem of gametophyte l i f e h i s t o r y c h a r a c t e r i s t i c s , and no estimates are available for processes of gametophyte survivorship and fecundity i n the f i e l d . 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BASIC Microcomputer Models i n Biology. Addison Wesley Publ. Co., Reading, Mass. 354 pp. Stearns, S.C. 1976. L i f e h i s t o r y t a c t i c s : a review of the ideas. Quart. Rev. B i o l . 51: 3-47. Stearns, S.C, and R.E. Crandall. 1981. Quanitative predictions of delayed maturity. Evolution 35: 455-463. Taylor, H.M. , R.S. Gourley, C E . Lawrence, and R.S. Kaplan. 1974. Natural s e l e c t i o n of l i f e - h i s t o r y a t t r i b u t e s : an a n a l y t i c a l approach. Theor. Popn. B i o l . 5: 104-122. Tinkle, D.W. 1969. The concept of reproductive e f f o r t and i t s r e l a t i o n to the evolution of l i f e h i s t o r i e s of l i z a r d s . Amer. Nat. 103: 501-516. Usher, M.B. 1969. A matrix model for forest management. Biometrics 25: 309-315. Walker, D.C 1980. Sorus abci s s i o n from laminae of Nereocvstis luetkeana (Mert.) Postels and Ruprecht. Ph.D. Thesis, University of B r i t i s h Columbia. Williams, G.C. 1966. Natural selection, the costs of reproduction, and a refinement of Lack's p r i n c i p l e . Amer. Nat. 100: 687-690. Williams, G.C. 1975. Sex and Evolution. Princeton University Press, Princeton, N.J. 201 pp. - 90 - APPENDIX 1 STIPE RING FORMATION IN LAMINARIA SETCHELLII INTRODUCTION V i s i b l e concentric rings at the base of some kelp stipes have been used by various authors (Novaczek, 1981; Kain, 1971, 1963: Parke, 1948) to determine minimum age of the i n d i v i d u a l . C o r r e l a t i o n a l evidence has been invoked to show that these rings are annual. Kain (1963) and Novaczek (1971) r e l a t e r i n g formation i n Laminaria hyperborea and i n Ecklonia radiata to seasonal periods of fast and slow growth, coupled with observation of periods of annual hapteron i n i t i a t i o n . Direct observation of stipe r i n g formation has not been reported i n the l i t e r a t u r e . The r e s u l t s of a 12 month .in s i t u tagging study are given below. These r e s u l t s constitute direct evidence that r i n g formation i n Laminaria s e t c h e l l i i i s annual. MATERIALS AND METHODS One hundred i n d i v i d u a l s of Laminaria s e t c h e l l i i at Wizard Rock were tagged and numbered on 27 October 1981 for the purpose of repeated observation. Tags were securely fastened by nylon cable t i e s positioned at the base of each st i p e . Subsequent observations showed that most tags did not remain i n place, but moved f r e e l y up and down the stipe with water motion. A l l tagged i n d i v i d u a l s were harvested from Wizard Rock on 19 November 1982. Plants were returned to the laboratory, where l o n g i t u d i n a l - and cross- - 91 - sections of some stipes were made. RESULTS AND DISCUSSION In only 17% of the surviving tagged plants did the cable t i e remain i n place at the stipe base for an entire year. These ten plants had developed l o c a l i z e d 'saddles' from constraint of l a t e r a l growth i n the region of the cable t i e . In every case, the increase i n g i r t h of surrounding tissues corresponded, i n lo n g i t u d i n a l section, to one c o r t i c a l growth ring (Figure A . l ) . The observed g i r d l i n g phenomenon can be explained according to growth patterns reported for perennial species of Laminaria. Increase i n stipe g i r t h r e s u l t s from meristodermal c e l l d i v i s i o n s , and subsequent production of a secondary cortex i n t e r i o r to the meristoderm. A r t i f i c i a l constraint of l a t e r a l expansion may allow the occurrence of l i m i t e d c e l l d i v i s i o n s , but precludes increase i n cross-sectional area of the stipe. The meristoderm would therefore remain i n t a c t , but would undergo no development of secondary cortex and no increase i n stipe g i r t h i n the g i r d l e d region. Seasonal harvesting and sectioning of kelp stipes from two s i t e s (re: Materials and Methods, Chapter 4) indicated that meristodermal d i v i s i o n rates are greatest i n the months of March and A p r i l ; t h i s corresponded to a time of observable stipe 'peeling', and to i n i t i a t i o n of new rings. Cross-sections of stipes made during these months showed a d i s t i n c t , dense outer tissue layer, succeeded by a narrow, i n c i p i e n t layer of loosely-arranged secondary cortex. It i s apparent, then, that Laminaria s e t c h e l l i i stipe rings are produced annually, and that new rings are i n i t i a t e d synchronously within a population. - 92 - Generally, r i n g widths become successively narrower with increasing age or with increasing stipe diameter; accuracy of observation consequently decreases with increasing number of rings. V i s i b l e rings are therefore an i n d i c a t i o n of minimum age, i n years, i n discrete time, and r e s u l t i n g data should be interpreted accordingly. - 93 - A t r an s i t i on zone 1mm F i g u r e A . l . L o n g i t u d i n a l c r o s s - s e c t i o n o f s t i p e b a s e , s h o w i n g g i r d l e d r e g i o n and i n c r e a s e i n g i r t h o f a d j a c e n t t i s s u e s . (Drawn f r o m a p h o t o g r a p h ) . - 94 - APPENDIX 2 GAMETOPHYTE CULTURE OF LAMINARIA EPHEMERA AND L. SETCHELLII MATERIALS AND METHODS More than 60 r e p l i c a t e gametophyte cultures each of Laminaria ephemera and Laminaria s e t c h e l l i i were established during the period May through July, 1981. A l l cultures were i n i t i a t e d as follows: f e r t i l e fronds were c o l l e c t e d and immediately returned to the laboratory, where they were maintained i n flowing sea water for a maximum of 24 hours before use. Fronds or portions of fronds were s u r f a c e - s t e r i l i z e d (0.1% Betadine solution i n s t e r i l e sea water), and p a r t i a l l y dessicated. Soral tissues were then reimmersed i n s t e r i l e sea water at 10°C; a f t e r zoospore release, 1 ml of spore suspension was pipetted into each 60 X 15 mm p e t r i dish already containing 15 mis Provasoli's enriched sea water (PES). A l l dishes were sealed with Parafilm to avoid s a l i n i t y increase by evaporation. Dishes were stacked 5 deep and placed i n Percival incubators at 5, 10, and 15°C, under long-day (16L:8D) conditions, at 2 irradiance of about 100jUE/cm / s e c , cool white fluorescent l i g h t . Medium was replaced at approximate bi-weekly i n t e r v a l s . Germanium dioxide was added to cultures at a concentration of 5 mg/l (Lewin, 1966). Each frond selected for culture i n i t i a t i o n was used to e s t a b l i s h 5 r e p l i c a t e cultures. No two fronds were from the same parent sporophyte. The products of 12 or more parental genotypes were therefore represented among the cultures of each species. A l l study s i t e s (Laminaria ephemera: Cable Beach and Execution Bay; Laminaria s e t c h e l l i i : Wizard Rock and Execution Bay) were represented. Results were pooled w i t h i n species. - 95 - Observations are presented i n Table A . l . Results are q u a l i t a t i v e , and no s t a t i s t i c a l inferences are made. For each combination of treatment, character, and time, a '+' i s recorded i f that character was present i n at least some cultures; a '-' indicates that no cultures exhibited that character. RESULTS Laminaria ephemera germinated and grew vegetatively at 5, 10, and 15°C. Gametophytes were s t r i c t l y isomorphic, and t h e i r morphology was more sim i l a r to females of other species of Laminaria than to males of other species. Oogonium development was observed only a f t e r the ninth week at 10 and 15°C. No sexuality was observed at 5°C. Antheridia were never i d e n t i f i e d among the cultures, but were presumed to be present i n cultures which produced sporophytes. There was sparse development of sporophytes at 10 and 15°C. Some sporophytes were i s o l a t e d from the dishes and removed to bubble culture, or to greenhouse culture, where they attained o v e r a l l lengths of 15 to 25 cm. Gentle grinding of vegetatively-growing gametophytes a f t e r the second month often i n i t i a t e d production of oogonia. Laminaria s e t c h e l l i i germinated and grew vegetatively at 5, 10, and 15°C. Gametophytes were heteromorphic. At 10 and 15°C, oogonia and antheridia were observed among some cultures by the end of the second week, and among most cultures by the fourth week. Dense production of sporophytes was observed within sexual cultures. Ten and 15°C treatments were terminated after 4 weeks. Cultures held at 5°C were maintained for 4 months; these grew vegetatively, but produced neither oogonia nor antheridia. T°C WEEKS LAMINARIA EPHEMERA 1-2 3-4 5-8 9-12 13-16 LAMINARIA SETCHELLII 1-2 3-4 5-8 9-12 13-16 05°C GERMINATION VEGETATIVE GROWTH OOGONIA ANTHERIDIA SPOROPHYTES + + i i i + I I I + I I I + I I I + + i i i 10°C GERMINATION VEGETATIVE GROWTH OOGONIA ANTHERIDIA SPOROPHYTES + + + + + + + + - - - + + + + + TERMINATED + + TERMINATED + + TERMINATED + TERMINATED 15°C GERMINATION VEGETATIVE GROWTH OOGONIA ANTHERIDIA SPOROPHYTES + + + + + + - - - + + - - - + + + + + TERMINATED + + TERMINATED + + TERMINATED + + TERMINATED Table A . l . Results of gametophyte c u l t u r e experiments. See t e x t f o r e x p l a n a t i o n of symbols.

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