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The analysis of zooplankton population fluctuations in the strait of Georgia, with emphasis on the relationships… Gardner, Grant Allan 1976

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THE ANALYSIS OF ZOOPLANKTON POPULATION FLUCTUATIONS IN THE STRAIT OF GEORGIA, WITH EMPHASIS ON THE RELATIONSHIPS BETWEEN CALANUS PLUMCHRUS MARUKAWA AND CALANUS MARSHALLAE FROST by GRANT ALLAN GARDNER B.Sc, U n i v e r s i t y of Guelph, 1970 M.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY xn THE FACULTY OF GRADUATE STUDIES Department of Zoology and I n s t i t u t e of Oceanography We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1976 Grant Allan Gardner, 1976 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s for an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d tha t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Zoology The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1WS Date October 5, 1976 i ABSTRACT In 1971, changes were observed i n the over w i n t e r i n g p o p u l a t i o n s i z e s of Calanus plumchrus Marukawa, Galanus marshallae F r o s t and C a l a -nus p a c i f i c u s c a l i f o r n i c u s Brodsky i n the S t r a i t of Georgia, B r i t i s h Columbia. Calanus plumchrus and C. p a c i f i c u s were l e s s common than i n previous years, while C. marshallae was more common. Based on s c a t t e r e d data taken s i n c e the t u r n of the century, these changes appeared t o be abnormal. Because Calanus plumchrus c o n s t i t u t e d a s i g n i f i c a n t propor-t i o n of the biomass of the zooplankton community, i t was p o s s i b l e t h a t the observed f l u c t u a t i o n s were i n d i c a t i v e of changes i n the s t r u c t u r e of the zooplankton community w i t h i n the S t r a i t . Thus a unique opportunity was presented t o study a zooplankton community and I t s r e l a t i o n s h i p to environmental parameters. M u l t i p l e c o r r e l a t i o n a n a l y s i s , c l u s t e r a n a l y s i s , m u l t i p l e r e g r e s s i o n a n a l y s i s , f a c t o r a n a l y s i s and p r i n c i p a l components a n a l y s i s were used t o analyse zooplankton concentrations and hydrographic d a t a taken i n over-w i n t e r i n g p e r i o d s from I969 to 197^ - A d d i t i o n a l hydrographic data were used t o examine r e l a t i o n s h i p s between p h y s i c a l and b i o l o g i c a l d a t a three and s i x months out of phase. The m u l t i v a r i a t e techniques allowed an e f f i -c i e n t a n a l y s i s of the r e l a t i o n s h i p s w i t h i n and between the b i o l o g i c a l and p h y s i c a l d a ta banks. More than one m u l t i v a r i a t e method was used as each method g i v e s a s l i g h t l y d i f f e r e n t viewpoint on the data. A combination of methods thus produces a more complete p i c t u r e of the system being ana-l y s e d , while p o i n t s of overlap between the techniques a c t as i n t e r n a l checks on the consistency of the a n a l y s i s . The a n a l y s i s i n d i c a t e s a recent s h i f t i n the hydrographic regime i i of the S t r a i t of Georgia. The s h i f t is most obvious i n the s a l i n i t y , but can a l s o be seen i n the temperature, and i n both cases i s s t r o n g e s t i n S t r a i t of Georgia deep water. I t i n v o l v e s s u b t l e changes i n s a l i n i t y and temperature s t r u c t u r e . These changes axe of u n c e r t a i n b i o l o g i c a l s i g -n i f i c a n c e but i n d i c a t e f l u c t u a t i o n s i n the process of deep water formation. Deep water i s formed i n the Southern Passages by the mixing of incoming S t r a i t of Juan de Fuca intermediate and deep water w i t h o u t f l o w i n g near surface f r e s h e r water. Changes i n e i t h e r of these components, or i n the degree of mixing, may produce some changes i n the q u a l i t y of the deep water, which i n t r u d e s i n t o the S t r a i t of Georgia i n l a t e summer. These changes i n q u a l i t y appear t o a f f e c t the zooplankton community. I n d i v i d u a l zooplankton species are s t r o n g l y i n f l u e n c e d by tempera-t u r e and s t a b i l i t y c h a r a c t e r i s t i c s or r e l a t e d f a c t o r s . Temperature and s t a b i l i t y d u r i n g the f a l l i n t r u s i o n are p a r t i c u l a r l y important t o the overwintering zooplankton community three months l a t e r . The same two f a c t o r s i n s p r i n g a l s o a f f e c t zooplankton i n the f o l l o w i n g w i n t e r . The concentrations of Calanus plumchrus and C. marshallae have s i g n i f i c a n t (p^O.05) l i n e a r r e g r e s s i o n s with concurrent temperature at 350 m. The re g r e s s i o n l i n e s have opposite slopes and i n t e r s e c t i n the re g i o n of nor-mal ambient temperature a t 350 m. This r e s u l t suggests t h a t deep water temperature, or a temperature associated, f a c t o r , s t r o n g l y a f f e c t s the r e -l a t i v e f l u c t u a t i o n s i n the numbers of both species. P r i n c i p a l components and f a c t o r a n a l y s i s of the hydrographic data both suggest t h a t the most important f a c t o r i n the s t r u c t u r e of the water column i s i t s s u b d i v i s i o n i n t o near surface, intermediate and deep water. However, i n both temperature and s a l i n i t y components a p o r t i o n of the i i i v a riance i s a s s o c i a t e d w i t h a temporal trend w i t h i n the deep water. P r i n c i p a l components of the zooplankton s i m i l a r l y a s s o c i a t e 15% of the zooplankton variance w i t h a temporal trend. No species i s s t r o n g l y weighted on these components, and the a s s o c i a t i o n appears t o be a f u n c t i o n of the whole community, r a t h e r than of i n d i v i d u a l s p e c i e s . As an adjunct t o t h i s i n v e s t i g a t i o n , e c o l o g i c a l s e p a r a t i o n between Calanus plumchrus and C. marshallae was i n v e s t i g a t e d . Both species have s i m i l a r d i s t r i b u t i o n s and l i f e h i s t o r i e s . Feeding competition between them i s minimized by a separation i n t h e i r a b i l i t y t o f i l t e r s m a l l p a r t i -c l e s from the water. Calanus plumchrus can feed r e a d i l y on p a r t i c l e s above 3>5 ym i n diameter, while C. marshallae can not e f f i c i e n t l y f i l t e r p a r t i c l e s below about 10.5 ym i n diameter. Thus, Calanus plumchrus can e x p l o i t a p o t e n t i a l l y r i c h food source with no competition from Calanus  marshallae. This advantage may maintain Calanus plumchrus w i t h i n the S t r a i t of Georgia d e s p i t e the d e t r i m e n t a l e f f e c t of a s h i f t i n deep water temperature or r e l a t e d f a c t o r s . I t a l s o suggests t h a t , given a more "normal" p h y s i c a l c l i m a t e , Calanus plumchrus could r e v e r t t o i t s t r a d i -t i o n a l dominance. I f Calanus plumchrus continues t o drop, or remains a t suppressed l e v e l s , the economically important f i s h species t h a t u t i l i z e i t as food w i l l have t o s h i f t prey species, probably t o Calanus marshallae. Feeding on C. marshallae w i l l i n v o l v e a gre a t e r energy expenditure to obtain the same r a t i o n , and may be d e t r i m e n t a l to some pre d a t o r s . i v TABLE OF CONTENTS ABSTRACT i LIST OF FIGURES v i i LIST OF TABLES v i i i ACKNOWLEDGEMENTS x GENERAL INTRODUCTION 1 THE STUDY AREA 11 DESCRIPTION AND ANALYSIS OF STRAIT OF GEORGIA ZOOPLANKTON I n t r o d u c t i o n 1? Sample C o l l e c t i o n and A n a l y s i s I n t r o d u c t i o n 19 Procedure 19 E v a l u a t i o n of sampling gear 222 S t a t i s t i c a l Methodology I n t r o d u c t i o n 24-Data treatment ' 26 S t a t i s t i c a l procedures 28 Ev a l u a t i o n of technigues 31 R e s u l t s Hydrographic regime d u r i n g the study p e r i o d 39 R e s u l t s of sample s o r t i n g 4-6 D i v e r s i t y and m u l t i p l e c o r r e l a t i o n 53 C l u s t e r a n a l y s i s 53 Canonical c o r r e l a t i o n 58 Regression a n a l y s i s 59 F a c t o r a n a l y s i s 63 V P r i n c i p a l components a n a l y s i s * 65 D i s c u s s i o n Data manipulation 74-D i v e r s i t y and m u l t i p l e c o r r e l a t i o n a n a l y s i s 75 C l u s t e r a n a l y s i s 77 Canonical c o r r e l a t i o n a n a l y s i s 79 Regression a n a l y s i s 83 F a c t o r and p r i n c i p a l components a n a l y s i s 88 ASPECTS OF THE ECOLOGY OF THE APPARENTLY CO-OCCURRING SPECIES CALANUS PLUMCHRUS MARUKAWA AND CALANUS MARSHALLAE FROST In t r o d u c t i o n 96 D i s t r i b u t i o n 98 Feeding I n t r o d u c t i o n 99 Procedure 99 Rearing and Breeding I n t r o d u c t i o n 101 Procedure 101 v C a l o r i m e t r y I n t r o d u c t i o n 102 Procedure 104-Re s u l t s D i s t r i b u t i o n 105 Feeding 105 Rearing and breeding 110 vi Galorimetry 112 Discussion 113 SUMMARY 125 REFERENCES' 129 APPENDIX A 144 v i i LIST OF FIGURES F i g u r e 1: D i s t r i b u t i o n of major c u r r e n t s i n the oceanic r e g i o n adjacent t o the study area 12 F i g u r e 2: The study area and i t s major d i v i s i o n s 13 F i g u r e 3^a-e): Temperature i s o p l e t h s f o r f i v e consecutive years at Geo 174-8 4-0 F i g u r e 4-(a-e): S a l i n i t y isopTeths f o r f i v e consecutive years at Geo 174-8 4-1 F i g u r e 5: F l u c t u a t i o n s i n s a l i n i t y at s e l e c t e d depths i n s u ccessive Decembers at Geo 174-8 4-3 F i g u r e 6: Summary of the c o r r e l a t i o n c o e f f i c i e n t s between the zooplankton species i n the b a s i c dataamatrix 54-F i g u r e 7: C l u s t e r i n g of the p a r t i t i o n e d months 55 F i g u r e 8: C l u s t e r i n g of species, p a r t i t i o n e d raw d a t a 57 F i g u r e 9: Regression of Calanus plumchrus and C. marshallae against temperature at 350 m 64 F i g u r e 10: V e r t i c a l d i s t r i b u t i o n of Calanus plumchrus and C. marshallae d u r i n g overwintering 106 F i g u r e 11: Second m a x i l l a e of Calanus plumchrus and Calanus  marshallae. Major d i s t i n c t f i l t e r i n g zones are shown i n o u t l i n e 107 F i g u r e 12: F i l t e r i n g e f f i c i e n c y curves f o r Calanus plumchrus and Calanus marshallae 109 v i i i LIST OF TABLES Table I : D i v e r s i t y i n d i c e s and t h e i r methods of c a l c u l a t i o n 29 Table I I : L i s t of a l l species or groups sorted 4-7 Table I I I : P r o p o r t i o n ^ each species i n each of the regions of the water column found at Geo 1748 4-9 Table IV: The concentrations (no./m ) of the three Calanus species d u r i n g the study p e r i o d 51 Table V: E f f e c t of transforming the raw data on two species and two months chosen at random from the data matr i x 52 Table V I : The numbers of s i g n i f i c a n t p o s i t i v e and negative c o r r e l a t i o n c o e f f i c i e n t s i n the species c o r r e l a t i o n m a t r i x 53 Table V I I : Grouping of species by v e r t i c a l d i s t r i b u t i o n p a t t e r n 58 Table V I I I : Summary of the s i g n i f i c a n t c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t s 60 Table IX: Summary of a l l r e g r e s s i o n equations s i g n i f i c a n t at F = 0.10 6 1 , 6 2 prob Table X: I n i t i a l f a c t o r i n g of zooplankton data 66 Table X I : Secondary f a c t o r i n g of species a s s o c i a t e d w i t h the f i r s t f a c t o r of Table X 67 Table X I I : P r i n c i p a l components of (the hydrographic data 68 Table X I I I : Rank order of standardized cases on each p r i n c i p a l component 70 Table XIV: P r i n c i p a l components a n a l y s i s of the p a r t i t i o n e d zooplankton data 72 Table XV: F i l t r a t i o n zone a n a l y s i s of the second m a x i l l a e of Calanus plumchrus and C. marshallae 105 Table XVI: Development times and growth r a t e s of Calanus plumchrus at 8 C I l l Table XVII: O v e r a l l growth r a t e s f o r Calanus plumchrus reared i n the l a b o r a t o r y , expressed as per cent change i n weight per day I l l i x Table XVIII: Average c a l o r i f i c value per unit dry weight and per i n d i v i d u a l 109 X ACKNOWLEDGEMENTS I t i s a pleasure t o acknowledge the a s s i s t a n c e and guidance which Dr. A.G. Lewis has provided d u r i n g my tenure at the U n i v e r s i t y of B r i t i s h Columbia. Drs. R.E. Foreman, G.C. Hughes, C.J. Krebs, T.R. Parsons and S. Pond a l s o gave v a l u a b l e a s s i s t a n c e both i n my research and i n the p r e p a r a t i o n of t h i s t h e s i s . They have read the manuscript c r i t i c a l l y , and any e r r o r s t h a t remain are wholly my own. I wish to extend my thanks to a l l of the members of the I n s t i t u t e of Oceanography f o r p r o v i d i n g the s t i m u l a t i n g atmosphere t h a t makes i n t e r d i s c i p l i n a r y research both i n t e r e s t i n g and e x c i t i n g , and i n p a r t i c u l a r t o A. Ramnarine and M.P. Storm who helped t o smooth out many of the t e c h n i c a l problems t h a t might otherwise have made the c o l -l e c t i o n of data much more d i f f i c u l t and c e r t a i n l y l e s s i n t e r e s t i n g . The gathering of samples from over a f i v e year p e r i o d of n e c e s s i t y i n v o l v e s the a s s i s t a n c e and co-operation of a great many people. Among these people, s p e c i a l thanks go t o Dr. M.S. Evans and Mr. D.P. Stone, who c o l l e c t e d many of the samples. The o f f i c e r s and crew of the Cana-d i a n Hydrographic S e r v i c e ships Vector and P a r i z e a u , and of the Canadian Navy ship Laymore, were a l s o outstanding i n t h e i r co-operation and h e l p -f u l n e s s . In p a r t i c u l a r , a l l of the o f f i c e r s and crew who have served on the C.S.S. Vectorahave acted w i t h cheerfulness and w i l l i n g n e s s under a l l c o n d i t i o n s of weather and sea s t a t e t o make the c o l l e c t i o n of samples not j u s t p o s s i b l e , but pleasant and e x c i t i n g . Much of my research was funded by NRC A-206?, a grant to Dr. A.G. Lewis. P e r s o n a l funding was a l s o obtained from the N a t i o n a l Research C o u n c i l of Canada, v i a an NRC s c h o l a r s h i p i n 1970/71, and from the Department of Zoology, UBC, v i a a s e r i e s of Teaching A s s i s t a n t s h i p s . The g r e a t e s t thanks of a l l must go t o my wi f e , Beverley, who persevered through those years when the end seemed out of s i g h t . Without her continued support, encouragement and good s p i r i t s , the d i f f i c u l t i e s i n v o l v e d i n preparing f o r the Ph .D. degree would have been magnified t e n f o l d . 1 GENERAL INTRODUCTION In 1971> a change was noted In the l o c a l p o p u l a t i o n l e v e l s of three congeneric species of p l a n k t o n i c marine copepod. One of these species, Calanus plumchrus, i s a major source of food f o r h e r r i n g , salmon and other p l a n k t i v o r e s (Campbell 1933; Lebrasseur e t a l . I969), and i n the sp r i n g can reach numbers s u f f i c i e n t t o create a monomyctic s i t u a t i o n i n c e r t a i n areas of the S t r a i t of Georgia (Parsons, LeBrasseur e t a l . I969). In November 19711 the abundance of t h i s s pecies was observed t o be about an order of magnitude l e s s than i t s abundance i n December I969 and December 1970 ( F u l t o n , pers. comm.; Gardner 1972). Simultaneously, the p o p u l a t i o n of Calanus p a c i f i c u s appeared t o have decreased while the popul a t i o n of C. marshallae appeared t o have increased. Other data (e.g. Stephens et a l . 19&9) e s t a b l i s h t h a t the overwintering l e v e l s of C. plumchrus were s t a b l e f o r at l e a s t the f i v e years preceding the de-c l i n e . S i m i l a r data do not e x i s t f o r the other two Calanus species, as they were not considered separate species i n the S t r a i t of Georgia u n t i l I969 (Woodhouse 1971) • Observations on C. plumchrus were sporadic p r i o r t o 1965. The data t h a t do e x i s t (e.g. Campbell 1933i 193 -^) consider C. plumchrus t o be the dominant l o c a l zooplankton species, and the overwintering l e v e l s of the species appear t o have been c o n s i s t e n t l y higher than those obser-ved In f a l l 1971• Th i s s t r o n g l y suggests t h a t the low numbers i n 1971 c o n s t i t u t e an "abnormal" e c o l o g i c a l event i n t h a t they do not r e f l e c t the behaviour of the po p u l a t i o n over the l a s t h a l f - c e n t u r y . F u l t o n (1973; p e r s . comm;) suggests t h a t the i n f e c t i o n of C. plumchrus by the p a r a s i t i c yeast Metschnikowia sp. may have i n i t i a t e d or c o n t r i b u t e d t o 2 the decline, but the significance of the yeast in the Strait of Georgia has yet to be established. The presence of the yeast, however, in addition to 1the concurrent population fluctuations of Calanus marshallae and C. pacificus, further suggests that the decline of Calanus plumchrus is not an isolated event and that a change in the relative importance of the three species might be occurring. Copepods constitute the predominant class within the marine zoo-plankton (Raymont 1963; Tait I968). Consequently, changes in the popula-tion levels of, and ..in the interactions between, copepod species can have a pronounced effect on the structure of the zooplankton community as a whole, and by extrapolation can affect the structure of the marine food chain. The analysis and description of such population changes w i l l have both local and general significance. Locally, the importance of the Strait of Georgia zooplankton as food for migrating and developing s a l -monids and other commercially important fishes suggests that changes in the structure of the zooplankton community may have economic as well as ecological repercussions. In a more general sense, the analysis of factors affecting fluctuations within zooplankton communities w i l l be important to our understanding of the dynamics of such communities both in estuaries and in the open ocean. Seasonal and annual fluctuationss in species and communities have been investigated previously from many different viewpoints, but our understanding of such fluctuations i s s t i l l far from complete. Never-theless, certain conclusions can be drawn which apply to population,:s ftLugiisAiations in general. Fluctuations in the population level of a species are not unusual 3 on a seasonal time scale, and are intuitively more acceptable than stable population levels or populations that follow a smooth, sigmoid curve (Slobodkin 1954-)• Furthermore, the fluctuations should be more pronounced in a more widely varying environment. The complexity of food webs and the constancy of the environment in tropical areas w i l l tend to dampen oscillations; however, the relative simplicity of food webs and the pronounced seasonality of the environment in temperate and polar climates w i l l reinforce oscillations (Dunbar i960). Heinrich (1962b), for example, has described different types of seasonal cycle in the zooplankton of Arctic and north temperate waters. The cycles which he describes are a l l characterized by at least one peak in abundance during the year. The variation within such cycles is associated with the pronounced seasonality of the phytoplankton (Raymont 1963; Parsons and Takahashi 1973), which in turn w i l l be gov-erned by the seasonality of the physical environment. In n e r i t i c habi-tats, geographic, t i d a l and runoff considerations also become important factors and may complicate the analysis of seasonal fluctuations (Par-sons and Takahashi 1973)• Oscillations in the population levels of single species over multi-year periods are also well known. Although most of the species studied have been t e r r e s t r i a l (e.g. Arctic fox and lemmings: Elton 194-2; wolf: Cole 1951; tent caterpillars: Wellington 1957, I960; locusts: Waloff I966, cited by Odum 1971), such fluctuations have also been noted in aquatic organisms (e.g. Sears and Clarke 194-0; Slobodkin 195^; Dunbar i960). In :one of the most extensive studies of the population fluctu-ations in a marine plankton community, Sears and Clarke (194-0) monitored 4 l a r g e amplitude f l u c t u a t i o n s i n the zooplankton species on the continen-t a l s h e l f i n the Gape God area. The area monitored was h y d r o g r a p h i c a l l y r e l a t i v e l y s t a b l e from year t o year, and there was no apparent env i r o n -mental c o n t r o l over the observed f l u c t u a t i o n s i n p o p u l a t i o n s i z e s . The Sears and Clar k e a n a l y s i s i s l a r g e l y d e s c r i p t i v e ; they appear t o have "b been i n v e s t i g a t i n g a system c h a r a c t e r i z e d by l a r g e year to year f l u c t u a -t i o n s i n numbers of many of i t s species. Although Sears and Cl a r k e f e l t t h a t these f l u c t u a t i o n s were of b a s i c importance, they were unable t o e s t a b l i s h a cause f o r them. In these and s i m i l a r s t u d i e s , there has been a tendancy t o approach the problem on a species l e v e l . Although i t i s p r o f i t a b l e t o examine such f l u c t u a t i o n s from an a u t e c o l o g i c a l viewpoint, t h e i r p o s s i b l e rami-f i c a t i o n s suggest using an approach t h a t w i l l y i e l d more information on popu l a t i o n and community processes. There have u n f o r t u n a t e l y been few attempts to d i s c u s s such f l u c t u a t i o n s i n terms of t h e i r e f f e c t on the K zooplankton, phytoplankton or p e l a g i c communities. C l a r k e (195^) emphasized t h a t attempts t o d i s c o v e r the causes and e f f e c t s of f l u c t u a t i o n s i n communities of organisms have not been very s u c c e s s f u l . M u l t i y e a r changes i n p o p u l a t i o n l e v e l s , and t h e i r e f f e c t on community s t r u c t u r e i n a l a r g e , moderately s t r a t i f i e d estuary such as the S t r a i t of Georgia, have not been s t u d i e d . To a t t a c k t h i s problem, and t o i n v e s t i g a t e r e l a t i o n s h i p s w i t h i n a community, f i r s t r e q u i r e s c l a r i f i c a t i o n of the concept of "community" as i t a p p l i e s t o marine ecosystems. M i l l s (1969) reviewed the community concept i n marine zooplankton and i n other animal assemblages. He found t h a t the term "community" had 5 been used in many different ways, and that i t was impossible to decide which view was most meaningful or whether there were other views that were more meaningful. Despite this ambiguity, Mills proposed that the term be retained, rather than replaced with a series of new terms, and suggested defining a community as "...a group of organisms occurring in a particular environment, and separable, by means of ecological survey, from other groups." Traditionally, studies of communities, lik e studies of population fluctuations, have been based more frequently on te r r e s t r i a l than aquatic ecosystems because of the relative accessibility of suitable study areas and our greater familiarity with "dry land" (e.g. Grombie 1947; Elton 19^6; Elton and Miller 195 * 0• Terrestrial organisms are often d i s t r i -buted in an approximately two-dimensional space, and are more readily obtained and maintained in the laboratory than are most marine organisms. Furthermore, historical records of species occurrences are l i k e l y more complete than for marine species, and borders between neighbouring habi-tats are often more readily defined. In the marine environment, the st study of communities i s more d i f f i c u l t . When the communities are s t i l l confined to a nearly two-dimensional space, as in intertidal and benthic organisms, their study may be approached in much the same manner as i s used for the study of ter r e s t r i a l organisms (e.g. Odum and Smalley 1959; Vinogradova 1959; Gonnell 196la, b; Thorson I966). When the organisms are planktonic, their analysis becomes very complicated. Mills' definition assumes that the environment of a community can be expressed by an array of suitable parameters. In te r r e s t r i a l commu-nities, these parameters can be components of the substratum type, 6 micro-climate, vegetation type w i t h i n the range or s i m i l a r complex v a r i a b l e s . I n t e r t i d a l communities are often d e f i n e d p a r t i a l l y i n terms of substratum type and t i d a l regime. D e f i n i n g the environment of a pl a n k t o n i c community, which i s arrayed i n a three-dimensional space and bordered by c l o s e l y s i m i l a r environments, i s l e s s s t r a i g h t f o r w a r d . The development of methods by which the marine environment could be "compartmentalized" i n a manner s u i t a b l e f o r community a n a l y s i s began with the e a r l i e s t extensive e c o l o g i c a l i n v e s t i g a t i o n s of marine zooplank-ton. I n i t i a l l y , t h i s work i n v o l v e d the i n v e s t i g a t i o n of a s s o c i a t i o n s between d i s c r e t e assemblages of species and i d e n t i f i a b l e bodies of water. R u s s e l l ' s work i n the B r i t i s h I s l e s (1935, 1936a, b; 1939) pro-vided the b a s i s f o r thist&ype of work, and Bary (1959. 1963a, b, c; 1964) f u r t h e r developed the technique of using species-water body r e l a t i o n s h i p s t o i n v e s t i g a t e species' a s s o c i a t i o n s and d i s t r i b u t i o n p a t t e r n s . Bary a p p l i e d t h i s technique over a l a r g e geographic area, and d e l i n e a t e d three d i s t i n c t types of water and a s s o c i a t e d groups of zooplankton i n the waters of the A t l a n t i c Ocean north and east of B r i t a i n . The f a c t o r s r e s p o n s i b l e f o r maintaining a species-water mass a s s o c i -a t i o n are s t i l l unknown. Wilson (1951) demonstrated d i f f e r e n c e s between water bodies by showing t h a t water from the E n g l i s h Channel and water from the C e l t i c Sea had s i g n i f i c a n t l y d i f f e r e n t e f f e c t s on the r e a r i n g of a q u a t i c i n v e r t e b r a t e s . F u r t h e r experiments (Wilson and Armstrong 1958, I96I) showed t h a t the p r o p e r t i e s r e s p o n s i b l e v a r i e d temporally i n the same l o c a l i t y , as w e l l as v a r y i n g g e o g r a p h i c a l l y , but the p r o p e r t i e s i n v o l v e d could not be i s o l a t e d . Bary (1964) has a l s o p o s t u l a t e d the existence of such p r o p e r t i e s or groups of p r o p e r t i e s , but could not 7 c o r r e l a t e them with any known chemical or p h y s i c a l parameters of the water body. Despite the i n a b i l i t y t o determine the f a c t o r s r e s p o n s i b l e f o r v a r i a t i o n s i n water q u a l i t y , the species-water body approach i s s t i l l v a l i d and has been widely used In the P a c i f i c - notably by B i e r i ( 1 9 5 9 ) , LeBrasseur ( 1 9 5 9 ) , Aron ( 1 9 6 2 ) and Fager and McGowan ( 1 9 6 3 ) . The d e v e l -opment of techniques f o r examining the d i s t r i b u t i o n of organisms with respect t o water bodies has given the b i o l o g i c a l oceanographer the a b i l i t y t o d i f f e r e n t i a t e e c o l o g i c a l l y unique areas of the environment and t o i d e n t i f y species groups a s s o c i a t e d w i t h such areas. U n t i l the f a c t o r s operating to make these areas d i s t i n c t are known, however, the study of marine zooplankton communities w i l l be hampered. Nevertheless, the i n v e s t i g a t i o n of species i n t e r r e l a t i o n s h i p s and community dynamics, both from p r a c t i c a l and t h e o r e t i c a l viewpoints, has proceeded r a p i d l y i n recent years (e.g. H e i n r i c h 1 9 6 2 a , b; Anraku and Omori 1 9 6 2 ; M u l l i n 1 9 6 3 , I 9 6 8 ; Brooks and Dodson I 9 6 5 ; J e f f r i e s I 9 6 7 ; Geynrikh I 9 6 8 ; Ikeda 1 9 7 0 ; Hodgkin and R i p p i n g a l e 1 9 7 1 ; S a i l a and P a r r i s h 1 9 7 2 ; Fager 1 9 7 3 ) . The i n v e s t i g a t i o n of the zooplankton community of the S t r a i t of Georgia has not proceeded at the same r a t e as the study of zooplankton communities i n other areas. L o c a l l y , most of the previous work i s e i t h e r temporally r e s t r i c t e d and d e a l s with the ecology of only a few species (e.g. Campbell 1 9 3 3 , 193^; Pandyan 1 9 7 1 ; Woodhouse 1 9 7 1 ; Lewis et a l . 1971, . 1 9 7 2 ; Gardner 1 9 7 2 ; Evans 1 9 7 3 ; F u l t o n 1973) or t r e a t s many species, p r i m a r i l y i n a taxonomic context (e.g. Campbell 1 9 2 9 a , b, 1 9 3 0 ; F u l t o n 1 9 6 8 , 1 9 7 2 ) . The only "comprehensive" plankton survey of the S t r a i t of Georgia 8 i s t h a t of Legare (1957)• Unfortunately, Legare's data are from two sampling p e r i o d s only, and h i s techniques are open t o question. H i s deepest net ha u l was from 250 m, c o m p l e t e l y . c u t t i n g o f f the overwin-t e r i n g p o p u l a t i o n of Calanus plumchrus (e.g. Gardner 1972) and perhaps of other species as w e l l . The net th a t he used was very small ( c a , 0.2 m mouth area) and was equipped with a mesh s i z e and type (25xxx b o l t i n g c l o t h ) t h a t would r e s u l t i n cl o g g i n g and r e j e c t i o n of water, y i e l d i n g a biased sample (e.g. Tranter and F r a s e r 1968). In a d d i t i o n , with the exception of surface temperature, Legare d i d not monitor any. hydrographic parameters. Since Legare&s survey, the P a c i f i c B i o l o g i c a l S t a t i o n i n Nanaimo has c o l l e c t e d a considerable amount of p h y s i c a l and b i o l o g i c a l data i n the S t r a i t of Georgia (e.g. Stephens et a l . I969), but the data have not been f u l l y analysed and are presented only as raw data w i t h l i t t l e i n t e r p r e t a t i o n . Parsons, LeBrasseur and Barraclough (1970) have syn-t h e s i z e d many of these data i n t o a review of production l e v e l s i n the S t r a i t of Georgia, but d i s c u s s s e l e c t e d species only. The p r o d u c t i v i t y of the S t r a i t of Georgia was examined i n more d e t a i l i n a s e r i e s of papers d e a l i n g with primary production (Parsons, Stephens and LeBras-seur 1969)1 secondary production (Parsons, LeBrasseur et a l . I969) and f i s h g r a z i n g (LeBrasseur et a l . I969). The p e r i o d examined, however, was r e s t r i c t e d t o the s p r i n g of 1967 > o n i y near surface waters i n the F r a s e r R i v e r plume were sampled. Consequently, no examination of the zooplankton community i n terms of temporal v a r i a t i o n and i n terms of b a s i c hydrographic parameters has been c a r r i e d out i n the S t r a i t of Georgia. 9 I t i s important to understand and be able to d e s c r i b e the r e l a t i o n -s h i p s between zooplankton species w i t h i n a community, and the i n t e r a c t i o n between species or species groups and the p h y s i c a l environment. F u r t h e r -more, i t i s e s s e n t i a l t o assess the impact of the apparent s h i f t i n the numbers of the three Calanus species i n the S t r a i t of Georgia on the zooplankton community as a whole. To examine these aspects of the ecology of the l o c a l zooplankton, I have s o r t e d and counted a s e r i e s of v e r t i c a l and h o r i z o n t a l tows from an oceanographic s t a t i o n i n the S t r a i t of Georgia. The data have been analysed by a v a r i e t y of s t a t i s t i c a l techniques designed t o y i e l d the maximum amount of informa t i o n on the s t r u c t u r e of the zooplankton community and on the i n t e r a c t i o n s of the community and i t s component members with the hydrographic regime i n the S t r a i t . W i t hin the context of t h i s study, I have looked a t the e c o l o g i c a l separation of Calanus plumchrus and C. marshallae. The co-occurrence of congeneric species i s e c o l o g i c a l l y i n t e r e s t i n g and not w e l l under-stood. Hence, s p e c i f i c .information regarding the r e l a t i o n s h i p s between the three species of Calanus commonly found i n the S t r a i t of Georgia i s important i n i t s e l f . Furthermore, the dominance of Calanus i n the zoo-plankton biomass (Parsons, LeBrasseur e t a l . 1969; Gardner 1972) sug-gests t h a t c l a r i f y i n g the r e l a t i o n s h i p between species of Calanus i s important t o an understanding of the zooplankton community as a whole. Woodhouse (1971) has e s t a b l i s h e d t h a t Calanus marshallae and C. p a c i f i c u s are i n f a c t a l l o p a t r i c species; however, the simultaneous d i s t r i b u t i o n s of C. marshallae and C. plumchrus have not been f u l l y e s t a b l i s h e d . The importance of Calanus plumchrus as a source of food f o r young 10 salmon i n the S t r a i t of Georgia (Campbell 1933; Lebrasseur et a l . I969) suggests t h a t i n t e r a c t i o n s between C. plumchrus and C. marshallae could a f f e c t the general ecology and economic importance of the S t r a i t , as w e l l as the s t r u c t u r e of the zooplankton community. Because of the p o s s i b l e importance of t h i s i n t e r a c t i o n , I have examined the degree of overlap between the two species w i t h respect t o s e l e c t e d aspects of d i s t r i b u t i o n , f e e d i n g and breeding. In a d d i t i o n , I have examined the r e l a t i v e food value of G. plumchrus and C. marshallae i n order t o e s t i -mate the e f f e c t on p l a n k t i v o r e s of a s h i f t i n the r e l a t i v e numbers of the two sp e c i e s . These r e s u l t s , i n conjunction w i t h the a n a l y s i s of p o p u l a t i o n f l u c t u a t i o n s i n the other members of the zooplankton, w i l l be used t o de s c r i b e the extent and causes of f l u c t u a t i o n s i n the zooplankton com-munity s i n c e 1969- A unique opportunity f o r t h i s typeoof i n v e s t i g a t i o n has been generated by the s h i f t i n the p o p u l a t i o n l e v e l s of the three Calanus s p e c i e s . The r e s u l t s of t h i s i n v e s t i g a t i o n w i l l not only be of value l o c a l l y , but should help t o c l a r i f y some of the general p r i n c i p l e s of zooplankton community ecology. 11 THE STUDY AREA The S t r a i t of Georgia i s a semi-enclosed body of water open a t both ends to the i n f l u e n c e of the North P a c i f i c Ocean ( F i g . 1) . The ocean-ography of b'oth the S t r a i t of Georgia and the adjacent s u b a r c t i c P a c i f i c has been d e s c r i b e d (e.g. Doe 1955; P i c k a r d 1956; T u l l y and Dodimead 1957; Waldichuk 1957; Dodimead et a l . 1963; Dodimead and P i c k a r d I967). The most conspicuous c h a r a c t e r i s t i c of the S t r a i t i s the es t u a r i n e c i r c u l a -t i o n r e s u l t i n g from i n t e r a c t i o n s between incoming oceanic water and out-going f r e s h e r water which o r i g i n a t e s i n the drainage basins surrounding the S t r a i t . At l e a s t $0% of the f r e s h water e n t e r i n g the S t r a i t comes from the basins drained by the F r a s e r and Squamish R i v e r s (Herlinveaux and Giovando I969). The i n s i d e passage, which connects the northern end of the S t r a i t of Georgia with the P a c i f i c , i s c h a r a c t e r i z e d by con-s t r i c t e d and winding waterways. The c o n s t r i c t i o n s s u f f i c i e n t l y hinder the t r a n s f e r of water t h a t the c o n t r i b u t i o n of the northern passages t o thelcomposition of the water i n the S t r a i t of Georgia i s small compared to the c o n t r i b u t i o n of the S t r a i t of Juan de Fuca (Waldichuk 1957; Herlinveaux and Giovando I969) • Tbethes:s'o.uth^,stheeGulfiiE&landseahd San ^uahhArch'ipelago separate the main body of the S t r a i t from d i r e c t access t o the S t r a i t of Juan de Fuca and hence the open ocean. Both Waldichuk (1957) and T u l l y and Dodimead (1957) separated the S t r a i t of Georgia i n t o the Southern Approaches, the Northern Approaches and the C e n t r a l S t r a i t ( F i g . 2 ) . The mechanisms by which water i n the C e n t r a l S t r a i t i s formed have been discussed at some length, p a r t i c u l a r l y by Waldichuk. Surface water ( i . e . water above the p r i n c i p a l p y c n o c l i n e ) tends to be v a r i a b l e , l a r g e l y due t o t i d a l a c t i o n and the v a r i a b l e 12a Figure 1: D i s t r i b u t i o n of major currents i n the oceanic region adjacent to the study area. Currents marked with an a s t e r i s k are seasonal; subsurface currents are indicated by a dashed l i n e . (Based on Dodimead et a l . I963) WEST LONGITUDE 13a Figure 2: The study area and i t s major d i v i s i o n s . 14 e f f e c t of f r e s h water r u n o f f . S t r a i t of Georgia intermediate and deep waters are f a r l e s s v a r i a b l e , and o r i g i n a t e i n the Southern Approaches as a combination of incoming Juan de Fuca intermediate and deep water and outflowing surface water. The Southern Passages are c h a r a c t e r i s t i s c a l l y w e l l mixed throughout the water column d u r i n g most of the year (Gardner 1972; Evans 1973). The composition of the water e n t e r i n g the Southern Approaches from the S t r a i t of Juan de Fuca w i l l vary wit h v a r y i n g offshore oceanographic c o n d i t i o n s . The major e a s t e r l y current at t h i s l a t i t u d e i s the West Wind D r i f t ( F i g . 1). This current diverges as i t approaches the coast. One branch moves n o r t h e r l y towards the G u l f of Alaska and the other moves so u t h e r l y as the C a l i f o r n i a Current. A small p o r t i o n of the water, however, i n t r u d e s i n t o the c o a s t a l waters o f f Vancouver I s l a n d (Dodimead et a l . I963).and may r e s u l t i n the movement of near surface water from the C e n t r a l S u b a r c t i c Domain i n t o Juan de Fuca. In a d d i t i o n , the pre-v a i l i n g summer winds i n the eastern North P a c i f i c are from the northwest and blow roughly p a r a l l e l t o the rcoast. A net offshore movement of surface water r e s u l t s due t o JFEkman t r a n s p o r t (e.g. Sverdrup et a l . 1942), and upwelling can occur from May through September i n c o a s t a l waters. The upwelled water o r i g i n a t e s on the c o n t i n e n t a l s h e l f at depths of 200-300 m (Doe 1955) and r e a d i l y i n t r u d e s i n t o Juan de Fuca. Water from t h i s depth does not normally approach the coast (Dodimead et a l . I963) and upwelling i s necessary t o introduce i t in£o inshore waters. Water of southern o r i g i n can a l s o reach the S t r a i t of Juan de Fuca. A deep countercurrent ( c a . 200 m) adjacent t o the coast b r i n g s water from 15 the eastern boundary r e g i o n of the s u b t r o p i c s t o the west coast of B r i t i s h Columbia (Dodimead et a l . 1963)- The extent of t h i s " C a l i f o r -n i a Undercurrent Domain" v a r i e s s e a s o n a l l y and annually and thus has a f l u c t u a t i n g e f f e c t on the S t r a i t of Juan de Fuca. During the upwelling season, the northward f l o w occurs only at depths of 200 m or g r e a t e r (Sverdrup and Fleming 1941). When upwelling ceases, a surface counter-current, the Davidson Current, develops as w e l l , r e s u l t i n g i n n o r t h e r l y f l o w along the coast at a l l depths (Sverdrup et a l . 1942). In these c o n d i t i o n s , water o r i g i n a t i n g i n the Columbia R i v e r system can r e a d i l y be c a r r i e d north and i n t o Juan de Fuca. At other times of the year, there i s s t i l l a d i s t i n c t northward f l o w near the sea bed between the mouth of the Columbia R i v e r and the S t r a i t of Juan de Fuca (Barnes et a l . 1972). Whatever the o r i g i n s of the water e n t e r i n g Juan de Fuca, the complex i n t e r a c t i o n between oceanic water and f r e s h water i n the Southern Ap-proaches r e s u l t s i n a f i n e l y balanced system. Increased r u n o f f , which •would have a d i l u t i n g e f f e c t , occurs at times of increased input of higher s a l i n i t y oceanic water and v i c e - v e r s a . Hence, the s a l i n i t y of the S t r a i t of Georgia bottom water does not vary g r e a t l y from year t o year, although other chemical c h a r a c t e r i s t i c s of the water may vary more markedly due to d i f f e r e n c e s i n the makeup of the incoming oceanic water and of the f r e s h water r u n o f f . Water moves i n t o the S t r a i t a t i n t e r -mediate depths f o r much of the year,(Herlinveaux and Giovando I969), but i n the l a t e summer and f a l l the i n t r u d i n g water i s s u f f i c i e n t l y dense t o r e p l a c e the deep water i n the S t r a i t of Georgia (Waldichuk 1957; Gardner 1972). 16 Once in the Strait of Georgia, the intruding water mixes slowly with the water i t displaced. The bottom topography of the Central Strait i s relatively smooth, and other than the boundaries of the main basin there are few structural barriers to lateral mixing processes. The result i s a large deep water mass in the Central Strait overlain by a much more variable but relatively thin surface layer. There are no currently documented physical or chemical processes within the Central Strait that might lead to large-scale permanent horizontal heterogeneity of-the zooplankton community found there. 17 DESCRIPTION AND. ANALYSIS OF STRAIT OF GEORGIA ZOOPLANKTON I n t r o d u c t i o n There axe many d i f f i c u l t i e s i n adequately sampling p o p u l a t i o n s d i s -persed i n a three-dimensional medium. Zooplankton tend t o be d i s t r i b u t e d i n patches r a t h e r than continuously (Cushing I96I). Since the s i z e and shape of the patches probably v a r i e s , r e p l i c a t e net hauls taken i n the same area can be q u i t e d i f f e r e n t (Barnes 194-9; Barnes and M a r s h a l l 1951; Hopkins I963; Wiebe and Holland 1968; Wiebe 1970) . The c h a r a c t e r i s t i c s of zooplankton patfaheseareapoorly understood. Wiebe's data (^^O^^ug -gest t h a t they are approximately c i r c u l a r with a r a d i u s of about f i f t y meters, and are d i s t r i b u t e d randomly. Denman and P i a t t (1975)1 on the other hand, f e e l t h a t phytoplankton patches a r i s i n g from p h y s i c a l t r a n s -p o r t processes range from about f i f t y meters - t o s e v e r a l k i l o m e t e r s i n s i z e . U n t i l our understanding of the mechanisms and c h a r a c t e r i s t i c s of plankton patchiness i s more d e t a i l e d , p a t c hiness w i l l remain a source of e r r o r t h a t can n e i t h e r be f u l l y evaluated or compensated f o r . I n c o r r e c t choice of sampling gear can a l s o l e a d t o e r r o r . V a r i a -t i o n i n sampling e f f i c i e n c y of d i f f e r e n t zooplankton sampling devices i s l a r g e , and yet there are no u n i v e r s a l l y accepted standard designs f o r such n e t s . The f a c t o r s which must be considered i n d e s i g n i n g an adequate net have, however, been i n v e s t i g a t e d (e.g. Tranter and F r a s e r I968; N a t i o n a l Academy of Science I969) • The two most important v a r i a b l e s are net s i z e and mesh s i z e . Wiebe and Holland (1968) suggest t h a t on a t h e o r e t i c a l b a s i s l a r g e r nets sample more e f f i c i e n t l y and w i t h l e s s e r r o r than smaller n e t s . Very l a r g e nets, however, can be awkward and d i f f i -c u l t to handle at sea, and a balance must be achieved between catching 18 e f f i c i e n c y and handling c h a r a c t e r i s t i c s . The choice of optimum mesh s i z e also requires a compromise. The mesh aperture should be small enough to capture a l l of the organisms to be sampled. However, as the mesh aperture decreases, the r i s k of cl o g -ging of the meshes and subsequent r e j e c t i o n of water increases. These two f a c t o r s must a l s o be balanced when designing equipment f o r sampling zooplankton. 19 Sample Collection and Analysis Introduction The zooplankton analyses presented here are based on samples taken at Geo 1748, a station approximately. 14.-.-5 km •-east of Nanaimo, . Brit i s h Columbia (-Fig. 2). Geo 1748,. .with a bottom depth of .420 m,.- i s in one..of the deepest parts of the ..Strait of .Georgia. Based on previous records (Stephens et a l . 1969; Gardner 1972; Evans 1973). i f is reasona-ble to consider the zooplankton found at this station as typical of open water Strait of Georgia zooplankton. The station was monitored by the Institute of Oceanography, University of British Columbia, on an a l -most continuous monthly basis from October 1969 to December 1974, and thus samples from a five year period were available. Procedure Two types of sample were collected; s t r a t i f i e d tows taken at twelve depths (10, 30, 50, 75, 100, 150, 200, 250, 300, 350, 375, 390 m) with modified Clarke-Bumpus opening/closing samplers (Paquette and Fro-lander 1957), and vertical hauls taken from 390 m to the surface with a conical net having a seventy centimeter mouth diameter. The st r a t i f i e d tows were discontinued after June 197*+> but the vertical hauls were available for the entire sampling period. Concurrent hydrographic data were collected in each month from stan-dard depths (0, 10, 20, 30, 50, 75, 100, 150, 200, 250, 300, 350, 375, 390 m). Hydrographic data could not be taken with the December 1972 biological data because of time restrictions!;; however, hydrographic data from November 1972 were used as the best approximation of the 20 missing December data. Temperature i n situ'was measured using r e v e r -s i n g thermometers, and a water sample was taken from each depth f o r s a l i n i t y d etermination. Surface data were taken from a bucket sample using a standard s a l i n i t y sample b o t t l e and an ordinary thermometer graduated i n 0.1 G° increments. Density values, expressed as sigma-t, were then c a l c u l a t e d f o r each depth according to standard nomographs prepared by the U.S. Navy Hydrographic O f f i c e (H.O. Misc. 1504-7, Nos. 3-8). Each v e r t i c a l h a u l sample was placed i n a s i x t e e n ounce g l a s s j a r and immediately preserved by the a d d i t i o n of s u f f i c i e n t n e u t r a l b u f f e r e d f o r m a l i n to make up an approximate 5% ( v o l / v o l ) s o l u t i o n (e.g. Steedman 1976). The Glarke-Bumpus samples were t r e a t e d s i m i l a r l y (see Gardner 1972; Evans 1973)' I n an a l y s i n g the b i o l o g i c a l m a t e r i a l , emphasis was placed on v e r t i c a l h a u l samples taken i n e a r l y winter (October t o Decem-ber) . During these months, l e s s short-term f l u c t u a t i o n occurs i n the zooplankton p o p u l a t i o n than a t any other time of the year, and the p o s s i b i l i t y of the masking of year t o year v a r i a t i o n by seasonal v a r i a -t i o n i s minimized. In the l a b o r a t o r y , each v e r t i c a l h a u l sample was pl a c e d i n a so r -t i n g t r a y , and a l l l a r g e organisms ;(?eirg. Euphausiids, l a r g e Tomopteris, l a r g e amphipods,...) were removed. The remaining m a t e r i a l was placed i n a plankton s p l i t t e r and s p l i t i n t o two equal p o r t i o n s , one of which was d i s c a r d e d . Any conspicuous species t h a t were present i n s m a l l enough numbers to be completely removed were sorted from the remaining h a l f . This h a l f was f u r t h e r s p l i t using a modified Folsom Plankton S p l i t t e r (Gardner 1972), and the subsampling/sorting process was 21 continued u n t i l s o r t i n g was complete. With few exceptions, only a d u l t and immediately p r e - a d u l t stages were s o r t e d . F l u c t u a t i o n s i n the s i z e of successive generations of a species w i l l be r e l a t e d t o the number of s e x u a l l y mature i n d i v i d u a l s produced w i t h i n each generation. As the a d u l t i s often a s h o r t - l i v e d stage, estimates of the breeding p o p u l a t i o n t h a t are based on the num-ber of i n d i v i d u a l s i n the stage immediately preceding the ad u l t w i l l be more p r e c i s e than estimates based s o l e l y on the number of a d u l t s cap-tu r e d . When i d e n t i f i c a t i o n was p.ossible, young stages of major species were a l s o s o r t e d , Some species were combined i n t o groups f o r conven-ience; however, i t has been shown (Williamson 19^1; Bainbridge and Fo r s y t h 1972) t h a t the mixture of species d a t a with group d a t a should not d e t r a c t from the data a n a l y s i s . In other species, e s p e c i a l l y i n non-copepod groups, i t was d i f f i c u l t to d i f f e r e n t i a t e l a t e r l i f e h i s t o r y stages. In these cases, a l l stages t h a t were not obviously j u v e n i l e were sorted and counted as a u n i t . The Glarke-Bumpus samples were sorted t o e s t a b l i s h the v e r t i c a l d i s t r i b u t i o n of Calanus plumchrus and Calanus marshallae, and t o obta i n the depth d i s t r i b u t i o n of each species sorted i n the v e r t i c a l h a u l s . Two months, November and January 1973, were chosen a t random and sorted f o r the two Calanus species only. November and December 1971 were chosen f o r complete s o r t i n g . In the l a t t e r case, s e l e c t i n g two contiguous months reduces e r r o r due to annual f l u c t u a t i o n . In a d d i t i o n , i n Novem-ber 1971 the h o r i z o n t a l tows were taken between 1700 and 1800hr, e a r l i e r than i n any other winter month. In December, the :tows were 'taken-'between midnight and 0200hr. November 1971 was s e l e c t e d i n t e n t i o n a l l y t o get as 22 c l o s e as p o s s i b l e t o the pre-migration v e r t i c a l d i s t r i b u t i o n of species w i t h a d i e l m i g r a t i o n p a t t e r n . When averaged with the December data, a mean p o s i t i o n f o r each species w i t h i n the water column was generated. For v e r t i c a l l y m i g r a t i n g species t h i s meant t h a t the average p o s i t i o n c a l c u l a t e d included s p e c i f i c d a ta from both the n i g h t d i s t r i b u t i o n and the l a t e afternoon d i s t r i b u t i o n , j u s t a f t e r sunset. E v a l u a t i o n of sampling gear The mesh aperture of both types of net was 350 ym. This i s l a r g e r than the 200 urn aperture s i z e recommended by UNESCO f o r c a p t u r i n g smaller mesozooplankton (Tranter and F r a s e r 1968), but corresponds c l o s e l y t o the 333 urn aperture recommended by the N a t i o n a l Academy of Sciences (I969) as the sma l l e s t mesh r e t a i n i n g i t s f i l t e r i n g e f f i c i e n c y f o r the d u r a t i o n of a f i f t e e n minute tow. Both nets capture a wide s i z e -spectrum of zooplankton, i n c l u d i n g l a r g e numbers of the e a r l y copepodite stages of n u m e r i c a l l y important copepod species (e.g. Gardner 1972; Evans 1973)• N e i t h e r design of net i s i d e a l . Perhaps the major o b j e c t i o n t o the use of the Clarke-Bumpus sampler i s t h a t i t s small s i z e , and the mechani-c a l c l u t t e r i n and around the mouth, f a c i l i t a t e avoidance of the sampler by the more mobile species. Such avoidance may r e s u l t i n a biased sam-p l e , with the degree of b i a s f l u c t u a t i n g with both <ttowing speed and mesh s i z e (Regan I963). These problems p r i m a r i l y a f f e c t the est i m a t i o n of zooplankton p o p u l a t i o n s i z e s . The Clarke-Bumpus sampler i s , however, one o f the best samplers a v a i l a b l e f o r e s t i m a t i n g the v e r t i c a l d i s t r i -b u t i o n of a species, as i t i s one of the few plankton samplers t h a t 23 allows the t a k i n g of d i s c r e t e ' s t r a t i f i e d h auls (McHardy 1961). The seventy centimeter net used i n the c o l l e c t i o n of the v e r t i c a l hauls approximates the p r e f e r r e d s p e c i f i c a t i o n s o u t l i n e d by Tranter and F r a s e r (I968). I t s major weakness appears t o be a s e n s i t i v i t y t o the patchiness i n plankton d i s t r i b u t i o n s . The Glarke-Bumpus sampler, s i n c e i t i s towed h o r i z o n t a l l y f o r about 0.5 km, tends to average out the e f f e c t s of s m a l l - s c a l e patches ( G i l f i l l a n I967). The v e r t i c a l h a u l u s u a l l y has a much s h o r t e r path l e n g t h and may or may not t r a n s e c t a patch. F o r my samples, I assume t h a t the v e r t i c a l haul givessan accu-r a t e estimate of the r e l a t i v e p r o p o r t i o n s of the v a r i o u s species t h a t i t captures. T h i s assumption i s supported by the r e l a t i v e l y long path length of the v e r t i c a l tow (390 m), and by the f a c t t h a t the deep water i n the area i s h o r i z o n t a l l y w e l l mixed. G i l f i l l a n (I967) a l s o suggests t h a t the seventy centimeter net g i v e s a r e p r e s e n t a t i v e sample of the zooplankton, although he recommends a higher towing speed than i s nor-mally f e a s i b l e . 24 S t a t i s t i c a l Methodology I n t r o d u c t i o n The raw d a t a c o n s i s t e d of a time s e r i e s of concentration values f o r each of a number of species. A n a l y s i n g any such f a m i l y of continuous v a r i a b l e s as a u n i t , r a t h e r than i n d i v i d u a l l y , r e q u i r e s the use of some form of m u l t i v a r i a t e a n a l y s i s . In e c o l o g i c a l research, m u l t i v a r i a t e techniques have been a p p l i e d p r i m a r i l y i n two separate areas: numerical taxonomy (e.g. Sokal and Michener 1958; Rohlf and Sokal 1962; Sokal and Sneath I963; Wallace and Bader I967), and the a n a l y s i s of community s t r u c t u r e i n p l a n t s and r e l a t i v e l y sedentary animals (e.g. Goodall 1954; Cassie and Michael I968; L i e and K e l l y 1970; Dayyet a l . 1971; Lindstrom 1974). T y p i c a l l y , the data f o r community analyses are obtained from a t r a n s e c t along which there i s some gradation i n an environmental para-meter. The data are often taken from a s e r i e s of quadrats of standard s i z e placed a t random along the t r a n s e c t l i n e . Each quadrat i s exhaus-t i v e l y counted to produce concentration values f o r each of the species found i n i t , and the r e s u l t s are combined t o form a matri x of species data. Each species i s thus represented by a s e r i e s of concentration values corresponding to i t s concentration i n successive quadrats (e.g. Lindstrom 197^) • The data i n my p r o j e c t d i f f e r from t h i s form only i n tha t the concentration values are arrayed along a temporal r a t h e r than a s p a t i a l a x i s . This d i f f e r e n c e w i l l not a f f e c t the use of m u l t i v a r i a t e a n a l y s i s , and may s i m p l i f y the i n t e r p r e t a t i o n of some of the techniques used, s i n c e the a x i s along which the data are arrayed i s more r e g u l a r . Previous m u l t i v a r i a t e analyses of zooplankton data have tended t o 25 be r e s t r i c t e d i n both scope and number. Williamson (1961, I963) analysed plankton records i n the North Sea by both p r i n c i p a l components and mul-t i p l e c o r r e l a t i o n analyses. His data consisted of average abundance values f o r twenty-three species over ten years, and were r e s t r i c t e d to June, J u l y and part of August, during the herring season. The analyses showed a s i g n i f i c a n t r e l a t i o n s h i p between the zooplankton and the herring which Williamson attempted to i n t e r p r e t on a b i o l o g i c a l b a s i s . Angel and Fasham (1973» 197*+) have made extensive use of f a c t o r analysis and p r i n -c i p a l components analysis to examine the data from the SOND Cruise of I965, i n an e f f o r t to separate species groups by v e r t i c a l d i s t r i b u t i o n pattern and water mass r e l a t i o n s h i p s . The SOND data consisted of one d day s e r i e s and one night s e r i e s of v e r t i c a l hauls covering 19 depth ranges, and a s i m i l a r set of hor i z o n t a l tows taken with an Isaacs-Kidd Midwater Trawl. In analysing the v e r t i c a l haul data, Angel and Fasham were dealing with a maximum of 38 samples and i n cases where only night or day data were considered, with a maximum of 19 samples. More recently, Angel and Fasham (1975) and Fasham and Angel (1975) have used f a c t o r analysis and c l u s t e r analysis to examine the d i s t r i b u -t i o n and water mass r e l a t i o n s h i p s of planktonic ostracods i n the north-east A t l a n t i c Ocean. They examined data from s i x stations, each of which was sampled at 16 depth horizons once during the day and once d>-r during the night. The stations were analysed independently, making the e f f e c t i v e data base f o r each a n a l y s i s a set of 32 samples. Lo c a l l y , Marlowe and M i l l e r (1975) have used nested f a c t o r analysis to examine the zooplankton community at ocean weather st a t i o n "Papa" i n the subarctic P a c i f i c . They c o l l e c t e d t h e i r data i n a very r e s t r i c t e d 26 time p e r i o d , however, and analysed b i o l o g i c a l data only. T h e i r data base c o n s i s t e d of 36 samples (two day s t a t i o n s and two n i g h t s t a t i o n s sampled at nine depths each). These and s i m i l a r analyses g e n e r a l l y consider only one or two m u l t i v a r i a t e techniques. In a d d i t i o n , w i t h the exception of Williamson (1961, I963) they are a l l of a geographic r a t h e r than a temporal nature. For my analyses, i n f o r m a t i o n has been obtained w i t h s i x d i f f e r e n t s t a -t i s t i c a l techniques: m u l t i p l e c o r r e l a t i o n , c l u s t e r a n a l y s i s , p r i n c i p a l components a n a l y s i s , c a n o n i c a l c o r r e l a t i o n , f a c t o r a n a l y s i s and m u l t i p l e r e g r e s s i o n . D i v e r s i t y i n d i c e s have a l s o been c a l c u l a t e d f o r a l l of the d a t a . These techniques w i l l be evaluated i n a l a t e r s e c t i o n . Data treatment S a l i n i t y and temperature values were chosen from f i v e depths: 10, 50, 200, 300,and 350 m. S t a b i l i t y values expressed as ^ d e p t h y ^ were c a l c u l a t e d over f i v e depth ranges: 0-10, 10-50, 50-200, 200-300 and 300-350 m. Using more than these f i v e s u b d i v i s i o n s of each para-meter i s expensive and complicated. As w i l l be shown i n the r e s u l t s s e c t i o n , the s u b d i v i s i o n s chosen adequately represent the f u l l range of the three hydrographic parameters. The scope of the b i o l o g i c a l d a t a was such t h a t i t was necessary t o reduce the data b l o c k t o a more manageable s i z e . Data were o r i g i n a l l y recorded as the number of organisms of each species per cubic meter, e i t h e r i n t e g r a t e d over the whole water column ( v e r t i c a l net haul) or f o r a s p e c i f i c depth range ( h o r i z o n t a l tow). This o r i g i n a l data i n c l u -ded concentration values f o r many species which were present i n very 27 low numbers. Because of the v a r i a b i l i t y inherent i n zooplankton sampling, concentrations of l e s s than about 0.05 per cubic meter are d i f f i c u l t t o d i s c r i m i n a t e . In such cases, the apparent absence of the species from a sample i s v i r t u a l l y meaningless. I t may be present i n a concentration only s l i g h t l y below normal, but low enough t o be in d e t e c -t a b l e . Thus the v a r i a t i o n induced by the sampling gear masks the n a t u r a l v a r i a t i o n i n the popu l a t i o n s i z e s of uncommon species. Other species i n the o r i g i n a l data b l o c k were present i n app r e c i a b l e numbers, but ap-peared i n only a few samples, adding e x c e s s i v e l y t o the v a r i a b i l i t y of the d a t a . To reduce data v a r i a b i l i t y from the above sources, species which were present i n concentrations of l e s s than 0.05 per cubic meter and/or i n l e s s than 50$ of the samples were dropped from the a n a l y s i s . These c r i t e r i a are s i m i l a r t o those of Marlowe and M i l l e r (1975) who el i m i n a t e d species present i n l e s s than three samples and/or i n concen-t r a t i o n s l e s s than 0.05 per cubic meter. A f t e r the b a s i c data matrix was constructed, data from the two sets of h o r i z o n t a l tows were used t o c a l c u l a t e the average p r o p o r t i o n of the pop u l a t i o n of each species i n each of the three types of water r e c o g n i -zable a t Geo 17*4-8. These water types are: near surface (0-75 m), intermediate (75-200 m) and deep (200-390 m) (Gardner 1972). The t o t a l c oncentration of a species as c a l c u l a t e d from each v e r t i c a l haul was s p l i t i n t o three components based on the c a l c u l a t e d p r o p o r t i o n s . S S i m i l a r l y . , s p l i t t i n g ^ a l l l s p e c i e s y i e l d e d a p a r t i t i o n e d d a ta m a t r i x con-s i s t i n g of the concentration of each species i n each of the three regions of the water column over the time p e r i o d f o r which data were a v a i l a b l e . Some of the s t a t i s t i c a l methods used (e.g. c o r r e l a t i o n and re g r e s s i o n ) 28 contain the i m p l i c i t assumption t h a t the data being analysed are nor-mally d i s t r i b u t e d . D e v i a t i o n s from n o r m a l i t y may be c o r r e c t e d f o r by a p p l y i n g a n o r m a l i z i n g f u n c t i o n t o the data block p r i o r to the analyses (e.g. Barnes 1952; Williamson 1963; Gassie and Michael I968). My b a s i c data matrix was transformed using the f u n c t i o n : x' = l n ( x + 0.01). Logarithmic transformations have been used p r e v i o u s l y with s i m i l a r d a t a (e.g. Williamson I963: x 1 = l o g ( x ) ; Hughes et a l . 1972, Gassie and Michael I968: x 1 = In(x + 1.0)). The e f f e c t i v e n e s s of the transforma-t i o n was evaluated by examining skewness and k u r t o s i s , before and a f t e r treatment, of two species and two months chosen at random from the data bank. For some analyses, i t was an advantage to f u r t h e r reduce e i t h e r the intrasample v a r i a b i l i t y of the zooplankton data or the number of species being considered. In these cases, species which had b a r e l y met the c r i t e r i a f o r being included i n the b a s i c zooplankton matrix were a l s o e l i m i n a t e d . The data manipulation y i e l d e d e i g h t matrices: the matrix of each hydrographic v a r i a b l e versus month, the b a s i c zooplankton species con-c e n t r a t i o n versus month matrix, the p a r t i t i o n e d and/or transformed ver-s i o n s of the b a s i c m a t r i x and the transformed and p a r t i t i o n e d core species m a t r i x . S t a t i s t i c a l procedures Unless otherwise noted, the s t a t i s t i c a l analyses were performed v i a l i b r a r y programmes a v a i l a b l e on the IBM 370/168 system maintained by the Computing Centre of the U n i v e r s i t y of B r i t i s h Columbia. The reference 29 name f o r each UBG programme i s given i n the t e x t when the programme i s f i r s t mentioned. I n i t i a l l y , v a r i o u s standard measures of d i v e r s i t y (Table I) were c a l c u l a t e d from the raw data p r i o r t o r e d u c t i o n of the Table I : D i v e r s i t y i n d i c e s and t h e i r methods of c a l c u l a t i o n . ( v a r i o u s sources; summarized i n Parsons and Takahashi 1973) H = I T l o « 2 n ^ n ^ L . - n . ! H ' = - | i ^ ° S 2 H * -H' H R (redundancy) = „, m a * . E (evenness) = max min max where: H i s the value whxch H would have xf a l l species were max x • -i -U present i n equal numbers H'.' ' i s the value which H would have i f only one species mm , were present n. i s the number of species ' i ' i n the sample p?" i s the p r o p o r t i o n of species ' i ' i n the sample N i s the t o t a l number of organisms i n the sample H i s d e f i n e d analogously t o H 1 max max i n i t i a l species l i s t . An i n i t i a l m u l t i p l e c o r r e l a t i o n (UBC *C0RN) was then c a r r i e d out on the transformed b a s i c zooplankton species data. The i n t e n t of these i n i t i a l manipulations was t o get a p r e l i m i n a r y ' estimate of the degree and types of i n t e r a c t i o n s o c c u r r i n g between the species, and t o look f o r i n d i c a t i o n s of a change i n d i v e r s i t y , a b a s i c community parameter. For the c o r r e l a t i o n a n a l y s i s , and f o r a l l other s t a t i s t i c a l programmes, the 1Q% p r o b a b i l i t y l e v e l i s used as the c r i -t e r i o n f o r r e j e c t i o n of the n u l l hypothesis (H ). 30 The remaining analyses were s e l e c t e d t o i n v e s t i g a t e i n more d e t a i l the r e l a t i o n s h i p s between groups of zooplankton species and the r e l a -t i o n s h i p of these groups t o hydrographic parameters. The p a r t i t i o n e d data matrix was c l u s t e r e d using a c l u s t e r a n a l y s i s programme prepared by Mr. E r i c Minch f o r Dr. R.E. Foreman, Department of Botany, UBC. Both c l u s t e r i n g of species and c l u s t e r i n g of samples were c a r r i e d out. To examine r e l a t i o n s h i p s between the hydrographic data and the b i o l o g i c a l data, c a n o n i c a l c o r r e l a t i o n s were c a l c u l a t e d t ( w i t h UBC BMD 06M) with the b i o l o g i c a l and p h y s i c a l d a ta b l o c k s i n phase and three and s i x months out of phase. Hydrographic data f o r these comparisons were obtained e i t h e r from I n s t i t u t e of Oceanography data r e p o r t s (1970-1975)', or from o r i g i n a l data. For the c a n o n i c a l c o r r e l a t i o n s , the species were grouped according t o t h e i r p o s i t i o n i n the water column. Calanus plum-chrus and C_. marshallae were run as s i n g l e species 'groups' i n a d d i t i o n t o being run w i t h i n t h e i r own groupings. Chi-square s i g n i f i c a n c e values f o r the c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d by hand from the Lambda s t a t i s t i c using B a r t l e t t ' s t e s t (Cooley and Lohnes 1971)• Each species i n the core data species m a t r i x was regressed (using UBC *STRP) against each hydrographic v a r i a b l e i n the same phase r e l a -t i o n s h i p s as f o r the c a n o n i c a l c o r r e l a t i o n s . Because of the h i g h degree of i n t e r s p e c i f i c c o r r e l a t i o n among the amphipods, S c i n a b o r e a l i s was added t o the core species matrix f o r t h i s a n a l y s i s . The s u b d i v i s i o n s of each hydrographic v a r i a b l e were t r e a t e d as a s e r i e s of f i v e inde-pendent v a r i a b l e s a g a i n s t which the dependent v a r i a b l e , ln(0.01 + number of species 'A' per m ), was regressed. Only those independent v a r i a b l e s which were s i g n i f i c a n t were included i n the f i n a l r e g r e s s i o n equation. 31 Significance was defined as having F ^ '< 0.10, where F i s the ratio of the mean square due to regression to the deviations mean square, and F\prob i s the probability of having an equivalent or higher value of F. To examine redundancy and natural grouping within the zooplankton species, a factor analysis (UBG *FAN) of the partitioned, transformed data was carried out. The largest grouping generated in this analysis was refactored as a separate unityto increase the definition of the factors. Principal components analysis (UBG BMD 01M) of both the winter hydrographic data and the core species biological data were carried out to gain further information on the degree of redundancy in the data, and on the most influential components of the community. Evaluation of techniques The use of sophisticated multivariate techniques for the ordi-nation and analysis of community data has expanded greatly in the past twenty-five years, largely due to the increased efficiency and availabi-l i t y of d i g i t a l computers. The ab i l i t y to handle complex sets of data has generated a large number of conflicting methods, many of which have been argued against as often as they have been supported (e.g. Beals 1973; Whittaker 1973; Lindstrom 197*+) • Many techniques are available, however,that can shed considerable light on underlying ecological struc-ture i f the results are carefully evaluated and the methodological aseu---sumptions are consistent with the data collection and data base i t s e l f . The techniques used in analysing my data overlap to a certain extent. Such overlap is not necessarily redundant, as i t w i l l provide points of 32 contact between the techniques t h a t w i l l be h e l p f u l i n e v a l u a t i n g t h e i r e f f i c i e n c y . The d i v e r s i t y a n a l y s i s i s the l e a s t overlapping of the set of analyses. Conceptually, d i v e r s i t y can be considered t o be r e l a t e d t o the u n c e r t a i n t y i n v o l v e d i n p r e d i c t i n g which species an animal would be confronted with i n i t s next random encounter with another animal ( L l o y d et a l . I968). I f d i v e r s i t y measurements are made on the same community a,t d i f f e r e n t times, observed d i f f e r e n c e s i n d i v e r s i t y w i l l be due t o d i f f e r e n c e s i n the r e l a t i v e numbers of species as w e l l as i n the t o t a l number of i n d i v i d u a l s . By comparing the d i f f e r e n c e i n d i v e r s i t y between the beginning and end of a time p e r i o d with f l u c t u a t i o n s d u r i n g the time p e r i o d , i t should be p o s s i b l e t o t e s t f o r the presence of temporal trends i n the d i v e r s i t y of the system. Hummon (1974), f o r example, has success-f u l l y used a s i m i l a r i t y index of h i s own design ( S u r ) t o i n v e s t i g a t e n temporal and s p a t i a l r e l a t i o n s h i p s among i n t e r t i d a l marine g a s t r o t r i c h s . He examined data from a one year p e r i o d only, however, and the temporal b i a s i n h i s r e s u l t s r e l a t e s more t o annual c y c l i n g than t o long term f l u c t u a t i o n . The other analyses which I have used are more c l o s e l y i n t e r r e l a t e d . ! Three of the techniques ( c o r r e l a t i o n , c a n o n i c a l a n a l y s i s and r e g r e s s i o n ) y i e l d a p r o b a b i l i t y l e v e l , 'p 1, which can be used t o accept or r e j e c t a n u l l hypothesis. S i g n i f i c a n c e l e v e l s f o r 'p' are p r i m a r i l y a f u n c t i o n of convenience, w i t h the 1% and % l e v e l s most often used (Snedecor and Cochran I967) . I have d i v i d e d t e s t s which show p^< 0.10 i n t o three ranges of s i g n i f i c a n c e : 0.015 p, 0.01* p^: 0.05, 0.05-< p '< 0.10. Choosing p '< 0.05 would be more reasonable on a s t a t i s t i c a l b a s i s ; 33 however, since the number of samples i s s m a l l , there i s a higher proba-b i l i t y of committing a t y p e - I I e r r o r ( i . e . a ccepting H q when i t i s a c t u a l l y f a l s e ) . I f p '< 0.05 were the s o l e c r i t e r i o n f o r s i g n i f i c a n c e , and a l l s t a t i s t i c a l l y i n s i g n i f i c a n t c o r r e l a t i o n s or r e g r e s s i o n s were d i s -carded, a r e l a t i o n s h i p f o r which p = 0.075 would be ignored. Such a r e l a t i o n s h i p , however, might have a sound b i o l o g i c a l b a s i s which would a i d i n the i n t e r p r e t a t i o n of the a n a l y s i s . Hence, p o t e n t i a l l y v a l u a b l e in f o r m a t i o n might be l o s t by c u r t a i l i n g the a n a l y s i s of b o r d e r l i n e cases s i g n i f i c a n t at l e v e l s of 'p' between 0.05 and 0.10. The use of a s l i g h t -l y higher s i g n i f i c a n c e l e v e l minimizes t h i s p o s s i b i l i t y . S u b d i v i d i n g the s i g n i f i c a n t r e l a t i o n s h i p s according t o the degree of s i g n i f i c a n c e i s o l a t e s r e l a t i o n s h i p s w h i c h d h a v e t s t a t i s t i c a l e s i g n i f i c a r i c e s f r o m those w i t h debatable s t a t i s t i c a l s i g n i f i c a n c e but which s t i l l might be h e l p f u l i n understanding the processes being evaluated. The f i r s t of the i n t e r r e l a t e d analyses i s m u l t i p l e c o r r e l a t i o n a n a l y s i s . M u l t i p l e c o r r e l a t i o n a n a l y s i s i n d i c a t e s the degree and types of i n t e r a c t i o n o c c u r r i n g between d i f f e r e n t species. I t i s perhaps the technique which i s l e a s t s u s c e p t i b l e t o d i s t o r t i o n and most r e a d i l y i n t e r -p r e t e d ; however, i t may a l s o y i e l d the l e a s t i n f o r m a t i o n . C l u s t e r ana'A l y s i s w i l l f u r t h e r r e f i n e the d a ta a n a l y s i s by c o n s t r u c t i n g aggregations of s i m i l a r l y v a r y i n g s p e c i e s . The species composition of these c l u s t e r s can then be examined, and a b i o l o g i c a l or p h y s i c a l b a s i s f o r t h e i r occur-rence p o s t u l a t e d . Groups of s i m i l a r species may have s i m i l a r responses t o environ-mental f a c t o r s . The demonstrated r e l a t i o n s h i p between such groups and environmental c h a r a c t e r i s t i c s (e.g. Bary 1963a, b, c, 1964; Fager and 34 McGowan 1963) i n d i c a t e s t h a t environmental parameters often c o n t r o l zoo-* plankton abundance. Canonical c o r r e l a t i o n i s a s t a t i s t i c a l method f o r comparing i n t e r c o r r e l a t i o n s between two co n c e p t u a l l y d i f f e r e n t domains measured w i t h i n a s i n g l e system (Cooley and Lohnes 1971) • Although i t was; developed f o r t y years ago by H o t e l l i n g (1935, 1936), c a n o n i c a l cor-r e l a t i o n has not been widely used i n the a n a l y s i s of zooplankton data. The major o b j e c t i o n t o t h i s method i s th a t the c o r r e l a t i o n c o e f f i c i e n t generated i s only a measure of the overlap between two mathematically d e r i v e d c a n o n i c a l v a r i a t e s which are not n e c e s s a r i l y important compo-nents of t h e i r r e s p e c t i v e data s e t s (Cooley and Lohnes 1971)• The d e r i v a t i o n of a "redundancy index" by Stewart and Love (1968) has pro-vided a means of e s t i m a t i n g the a c t u a l degree of overlap between the twon domains as represented i n the f i r s t and subsequent p a i r s of c a n o n i c a l v a r i a t e s . There i s considerable a p r i o r i support f o r the assumption t h a t con-d i t i o n s d u r i n g the s p r i n g bloom and the l e s s prominent f a l l bloom, w i t h i t s a s s o c i a t e d i n t r u s i o n of oceanic water, may be important f a c t o r s i n r e g u l a t i n g the s i z e of overwintering p o p u l a t i o n s of zooplankton species. By s e l e c t i n g b l o c k s of hydrographic and b i o l o g i c a l data t h a t are tempo:-?a-r a l l y separated, and c a l c u l a t i n g the c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t and the redundancy between c a n o n i c a l f a c t o r s ofdthese b l o c k s , the pos-s i b l e e f f e c t of the hydrographic regime a t one time of the year on the b i o l o g i c a l regime a t a l a t e r date may be explored. The f u n c t i o n a l r e l a t i o n s h i p between i n d i v i d u a l species and hydro-graphic parameters i s a l s o of i n t e r e s t and can be i n v e s t i g a t e d by mul-t i p l e r e g r e s s i o n a n a l y s i s . Although my data do not adhere s t r i c t l y t o 35 the assumptions underlying the c l a s s i c a l l i n e a r r e g r e s s i o n model, d e v i -a t i o n s from the model are s m a l l , and the i n t e n t of the a n a l y s i s i s not so much r i g o r o u s as i t i s h e u r i s t i c . L i n e a r r e g r e s s i o n i s most often used i n the e v a l u a t i o n of experimental data, when the independent va-r i a b l e can be measured without e r r o r (e.g. drug dosages, exposure times, . . . ) . I am e s s e n t i a l l y comparing the v a r i a t i o n i n hydrographic parame-t e r s a t a s e r i e s of s p e c i f i c depths with p o p u l a t i o n s that are found over a depth range. The hydrographic parameters represent the hydrographic regime over a depth range, however, and are an index of the general con-d i t i o n s t o which a species i s exposed. The e r r o r i n v o l v e d In the measure-ment of such parameters i s s u f f i c i e n t l y small t h a t i t w i l l be considered n e g l i g i b l e i n terms of the b i o l o g i c a l e f f e c t s i n which I am i n t e r e s t e d . F or example, temperature measurements can be made w i t h an e r r o r of about + 0.02 G°, a s m a l l e r r o r compared t o the range of temperatures l i k e l y t o be found over the d u r a t i o n of sampling at any one depth at Geo 17*4-8. Such ranges should be on the order of 0.50 G° or l a r g e r . Trends w i t h i n a block of s i m i l a r measurements become d i f f i c u l t t o d e s c r i b e as the amount of data c o l l e c t e d increases (Grieg-Smith 1971)• I t i s impossible, however, t o c o l l e c t only those data which w i l l be meaningful! F a c t o r a n a l y s i s can reduce complex data blocks t o a r e l a t i v e -l y few important f a c t o r s . The degree t o which data can be reduced i s an index of the redundancy of the measurements. The f a c t o r s generated can o f t e n , but not always, be i n t e r p r e t e d i n b i o l o g i c a l terms. F a c t o r a n a l y s i s i s a c t u a l l y a general term f o r a v a r i e t y of pro-cedures (Cooley and Lohnes 1971)• The b a s i c technique was o r i g i n a l l y "developed by p s y c h o l o g i s t s as a t o o l f o r measuring the underlying t r a i t s 36 i n a b l o c k of c h a r a c t e r data (Anderson I963)• A few f a c t o r a n a l y t i c a l methods have been s u c c e s s f u l l y used i n the a n a l y s i s of zooplankton data (e.g. Angel and Fasham 1973, i9?4-, 1975; Williamson 1961, 1963). One of these i s p r i n c i p a l components a n a l y s i s (PGA). P r i n c i p a l components a n a l y s i s i s complementary t o c l u s t e r a n a l y s i s . L i k e other f a c t o r i n g methods, PGA e x t r a c t s f a c t o r s from an aggregate of s i m i l a r i t y data. In PGA, the f i r s t f a c t o r e x t r a c t e d i s the f a c t o r ac-counting f o r most of the covariance among the v a r i a b l e s . The next f a c t o r i s orthogonal t o the f i r s t , and hence uncorrelated w i t h i t . I t i s the next highest c o n t r i b u t o r t o the covariance. A succession of f a c -t o r s can be e x t r a c t e d - the number being determined by the e c o l o g i c a l meaningfulness of the f a c t o r s and by the balance between the degree of complexity encountered and the degree of completeness cfesiiedd(Wflliams-son 1961, I963; O r l o c i 1973). The advantage of PGA i s t h a t i t i s a s t a t i s t i c a l method of d e s c r i b i n g i n t e r r e l a t i o n s h i p s i n terms of a s m a l l number of f a c t o r s (Rohlf and Sokal I962). The problem with t h i s method, i s t h a t even the "important" f a c t o r s may have no b i o l o g i c a l meaning (Goodall 1954). Normally, however, the a r i t h m e t i c a l f a c t o r s can be a s s o c i a t e d with known b i o l o g i c a l parameters (e.g. Williamson I963; Gassie and Michael I968). Both p r i n c i p a l components and c l u s t e r a n a l y s i s have been c r i t i c i z e d as being too s u s c e p t i b l e t o d i s t o r t i o n a n d i i n general too complicated t o g i v e meaningful r e s u l t s (Beals 1973; O r l o c i 1973; Whittaker and Gauch 1973)• P a r t of the d i s t o r t i o n i s caused by the fundamental c l a s h be-tween the l i n e a r i t y of the models and the n o n - l i n e a r i t y of the ecosystem. This d i s t o r t i o n should be reduced i n my data, as they are arrayed along a. 37 a temporal a x i s , r a t h e r than along a complex gr a d i e n t , and the objec-t i v e of the a n a l y s i s i s t o i n v e s t i g a t e p a t t e r n s of v a r i a t i o n within- a community r a t h e r than environmental c o r r e l a t e s with communities (e.g. A l l e n I968). Furthermore, Beals (1973) suggests t h a t methods such as PGA are more meaningful when a p p l i e d t o a narrow range of the environ-ment , where the communities i n question approach homogeneity. Hughes et a l . (1972) a l s o found t h a t PGA was more s e n s i t i v e t o heterogeneity than was c l u s t e r a n a l y s i s . R e s t r i c t i n g the a n a l y s i s of my d a ta t o a s i n g l e community under c l o s e l y s i m i l a r environmental c o n d i t i o n s i n t r o -duces a degree of homogeneity which should enhance the e f f e c t i v e n e s s of p r i n c i p a l components a n a l y s i s . The other advantage of PGA i s t h a t the a n a l y s i s generates the rank order of each standardized case on each component, f a c i l i t a t i n g the a s s o c i a t i o n of components with d e f i n e d seg-ments of the data, and making the a s s o c i a t i o n of b i o l o g i c a l meaning wi t h the components l e s s hazardous. B a s i c f a c t o r a n a l y s i s of the type c a r r i e d out by the UBG l i b r a r y programme *BAN gives s i m i l a r r e s u l t s t o p r i n c i p a l components a n a l y s i s , and has been used more e x t e n s i v e l y i n plankton r e s e a r c h . The programme as a v a i l a b l e i s more f l e x i b l e than PGA, and has the advantage t h a t species may be r e a d i l y grouped according to t h e i r r e l a t i o n s h i p w i t h each a x i s . The f a c t o r s produced may be r o t a t e d to f i n d an o r i e n t a t i o n which might be more r e a d i l y i n t e r p r e t e d i n terms of the b i o l o g y of the system. Varimax r o t a t i o n , which I have used, r o t a t e s the axes i n order t o "clean up" the f a c t o r s t r u c t u r e by s i m p l i f y i n g the columns of the f a c t o r matrix (Cooley and Lohnes 1971) • I t i s perhaps the most acceptable of the p o s s i b l e r o t a t i o n s (Glass and Taylor I966) . Because of i t s f l e x i b i l i t y , 38 t h i s method of f a c t o r a n a l y s i s was used t o examine r e l a t i o n s h i p s w i t h i n the zooplankton b a s i c data block, while PCA was used t o f a c t o r the hydrographic data and a l s o the zooplankton core species data. 39 Results Hydrographic regime during the study period A visual inspection of the temperature and salinity data indi -cates that the general features of the distribution of hydrographic parameters comform with previously published descriptions of the hydro-graphy of the Strait of Georgia (Tully and Dodimead 1957; Waldichuk 1957; Gardner 1972; Evans 1973). The annual fluctuation of hydrographic properties i s typified by the fluctuation in 1971/72 (Figs. 3c, 4c). In spring, the upper part of the water column i s strongly s t r a t i f i e d as a result of the warming of surface water by insolation and lowering of surface s a l i n i t i e s due to runoff. The near surface density gradient i s a maximum at this time, exceeding 1.00 (sigma-t units per meter increase in depth) in June. Waters deeper than 200 m are cool (less than 8.5 C) and have almost no temperature gradient. The salinity i s less than ° . 31 °/oo,,anddthe deep water salinity gradient i s weak. In late summer, the intrusion of warm, high salinity deep water formed by mixing processes in the Southern Approaches is the most s t r i -king feature of the hydrographic regime. Salinity in the deep water has increased to 31-15 °/oo, and a l l temperatures are close to 9-0 G. Des-pite the change in temperature and salinity distributions in spring and f a l l , stratification in water deeper than 50 m is s t i l l very weak. Near surface st a b i l i t y i s relatively high in August, but decreases consider-ably by September due largely to atmospheric cooling. By November, further intrusions originating in the Southern Ap-proaches have entered the deep basin of the Strait of Georgia and i n -creased the salinity and temperature of the near bottom water at Geo 1748. 40 a F i g u r e 3(a-e): Temperature i s o p l e t h s , i n G, at Geo 1748 between I969 and 1974. Dotted l i n e s (...) i n d i c a t e i n t e r p o l a t i o n s over missing data p o i n t s . Dashed l i n e s ( ) i n d i c a t e the 9-0 G i s o p l e t h . Sampling depths are i n d i c a t e d w i t h a small dot. 40b TIME (month) 40c 4-ia Figure 4(a-e): Salinity isopleths, in °/ 0 0, for five con-secutive years at Geo 1748. Dotted lines (.vdi<?<)/fc§ndicate interpolations over missing data points. Dashed lines ( ) in-dicate the 31 °/ 0 0 isopleth. Sampling depths are indicated with a small dot. TIMEfrttnths) 41c 42 The g r e a t e s t change, however, i s i n the upward extent of high s a l i n i t y water. Water of g r e a t e r than 31 °/ 0 0 has reached 250 m i n November, compared with 300 m i n September, and a l l depths between 50 and 390 m show increased s a l i n i t y . S a l i n i t i e s and temperatures from deeper than 50 m are g e n e r a l l y higher i n ' w i n t e r than at any other time of the year. S t a b i l i t y i s s t i l l low i n deep and intermediate waters, but has a l s o dropped i n near surface water. The d e n s i t y gradient i n December i s I s l e s s than OiOlnjihroughoutmthe water column, and thus b a r r i e r s to ver-t i c a l movement are minimized. Although the above d e s c r i p t i o n i s based on events i n 1971/72, i t i s r e p r e s e n t a t i v e of the average annual c y c l e of hydrographic proper-t i e s . To put t h i s p a r t i c u l a r year i n t o p e r s p e c t i v e , i t must be compared to the other years f o r whichddata are a v a i l a b l e . In t h i s way, changes i n hydrographic s t r u c t u r e t h a t r e l a t e t o long-term trends can be i s o l a t e d . The annual d i s t r i b u t i o n s of temperature and s a l i n i t y have been p l o t -ted f o r each year of the survey ( F i g s . 3, 4 ) . The time p e r i o d from A p r A p r i l through A p r i l of the f o l l o w i n g year was used i n order t o bracket the f a l l i n t r u s i o n , which extends past the end of the calendar year. With one exception, there has been a gradual increase i n the s a l i n i t y of the i n t r u d i n g water mass throughout the study p e r i o d . T h i s f e a t u r e i s more r e a d i l y seen by examining s a l i n i t y a t s e l e c t e d depths d u r i n g suc-c e s s i v e Decembers ( F i g . 5)- P i c k a r d (1975), examining the same pheno-menon over a s h o r t e r time p e r i o d , f e l t t h a t i t i n d i c a t e d a trend i n the S t r a i t of Georgia toward higher s a l i n i t i e s i n deep water, but t h a t such changes were q u i t e s m a l l . The changes i n s a l i n i t y are more apparent when data from 1974- are 4 3 * F i g u r e 5: F l u c t u a t i o n s i n s a l i n i t y a t s e l e c t e d depths i n successive Decembers at Geo 1748. (Data f o r 1972 are from November) 43b 29.60 • V U 1 1 L _L I L '68 '69 7 0 V I 7 2 7 3 74 Y E A R 1 44 added t o P i c k a r d ' s d a t a . In 1973/4, s a l i n i t i e s exceeded 31.25 ° / 0 0 at depths gr e a t e r than 300 m. This higher than normal s a l i n i t y was apparent a t only one depth i n the preceding year (390 m i n November), and was not present i n any other year, with one exception. The exception was I970/7I, when the annual c y c l e i n deep water was very s i m i l a r t o the cy c l e i n 1973/74. Without the data from 1970/71, i t would be tempting t o p o s t u l a t e a long-term trend i n the deep water hydrographic regime i n the S t r a i t of Georgia. With t h i s data, however, i t i s l e s s probable th a t the trend i s s i g n i f i c a n t . S i m i l a r trends i n the temperature v a r i a t i o n over the study p e r i o d can a l s o be described; however, the trends are more tenuous. Tempera-tures above 9-0 G at depths gr e a t e r than 50 m are l e s s common i n the l a t t e r h a l f of the sampling p e r i o d than i n the f i r s t h a l f . Temperatures below 9-0 G p r e v a i l e d i n most of the water column f o r two successive years (1971/72, 1972/73), but i n the l a s t year f o r which data are a v a i l -able (1973/7*+) the 9-0 G isotherm once more reached the deepest depths sampled. The absolute changes are s m a l l . Deep water temperatures of greate r than 9-5 0 or l e s s than 8 .75 0 were r a r e l y noted. Combining both temperature and s a l i n i t y data, i t appears t h a t there has been a s l i g h t s h i f t i n the hydrographic regime of the S t r a i t of Georgia w i t h i n the study p e r i o d . T h i s s h i f t i s due p r i m a r i l y t o i n -creases i n the s a l i n i t y of water i n t r u d i n g from the Southern Approaches. The temperature regime a l s o appears t o have s h i f t e d , towards c o o l e r deep water, but the v a r i a t i o n s i n v o l v e d are l e s s i n d i c a t i v e of a trend than are the v a r i a t i o n s •in, s a l i n i t y . 5 These changes i n the hydrography may be r e l a t e d t o a long-term 45 a l t e r a t i o n of the general hydrographic character of the S t r a i t . A l t e r -n a t i v e l y , i n view of the d e v i a t i o n i n the 1970/71 d i s t r i b u t i o n of s a l i -n i t y and the general v a r i a b i l i t y i n the temperature f i e l d , the changes may be p a r t of a normal c y c l i c f l u c t u a t i o n w i t h a p e r i o d of gr e a t e r than f i v e years. The r o l e of these hydrographic changes on the zooplankton i s d i f -f i c u l t t o assess without f u r t h e r a n a l y s i s . The absolute values of the changes i n temperature and s a l i n i t y are small compared t o t t h e range i n the same parameters w i t h i n the water column. However, the changing hydro-graphy r e f l e c t s v a r i a t i o n i n the formation of the water masses of the S t r a i t of Georgia. The changes observed i n deep water, f o r example, w i l l be r e l a t e d to the p h y s i c a l mixing processes i n the Southern Ap-proaches. I n c r e a s i n g s a l i n i t y of i n t r u d i n g deep water can r e s u l t from increased s a l i n i t y of incoming Juan de Fuca deep water, or from v a r i a -t i o n s i n the degree of mixing between the Juan de Fuca water and out-going f r e s h e r water. In the former case, the i n f l u x of water of higher than normal s a l i n i t y from Juan de Fuca might r e f l e c t more i n t e n s i v e upwelling o f f s h o r e and l e s s d i l u t i o n of the upwelled water. In the l a t t e r case, p r o p e r t i e s of the mixing water masses other than s a l i n i t y (e.g. organic carbon content, t r a c e metal content, p a r t i c u l a t e content, ...) w i l l a l s o vary due t o v a r i a t i o n s i n the degree of mixing. In e i t h e r case, the composition of the i n t r u d i n g water w i l l be changing, and these changes may be a f f e c t i n g the zooplankton community. Temperatures w i l l a l s o be a f f e c t e d by f l u c t u a t i o n s i n the forma-t i o n of water d e s t i n e d t o move i n t o the S t r a i t of Georgia. In a d d i t i o n , near surface water i n the S t r a i t w i l l be s e n s i t i v e t o atmospheric 46 f l u c t u a t i o n s . The changes i n the temperature and s a l i n i t y f i e l d s are thus i n d i c a t i v e of changes i n other, l e s s r e a d i l y d e f i n e d , water q u a l i t y parameters i n the S t r a i t of Georgia. Whether or not these changes are ass o c i a t e d with and perhaps r e s p o n s i b l e f o r concomitant changes w i t h i n the zooplankton community i s a question which I hope t o answer i n the f o l l o w i n g a n a l y s i s . R e s u l t s of sample s o r t i n g A t o t a l of 22 v e r t i c a l hauls covering the p e r i o d from October I969 to December 1974 were s o r t e d . Eleven of these samples were t r u e "winter data" and are included, i n the analyses reported here;, the others were s p r i n g and summer data used t o e s t a b l i s h the extent of v a r i a t i o n d u r i n g the s p r i n g phytoplankton bloom and i n e a r l y summer. Over 75 d i f f e r e n t groups (Ta,ble I I ) were i d e n t i f i e d i n the course^of s o r t i n g the samples. Most of these were s i n g l e s p e c i e s , but some were groups of a few s i m i l a r species that could not be r e a d i l y d i f f e r e n t i a t e d , w h i l e others were subsets of the same'species. These groups represent almost one m i l l i o n i n d i v i d u a l organisms sorted and recorded i n the i n i t i a l sample a n a l y s i s . The i n f l u e n c e of the s u b a r c t i c P a c i f i c on the S t r a i t of Georgia suggests t h a t species found ihethe S t r a i t should be predominately c o l d water or ubiquitous s p e c i e s . LeBrasseur and Kennedy (1972) v e r i f y t h a t the species composition of the S t r a i t of Georgia i s almost i d e n t i c a l t o th a t found at ocean weather s t a t i o n "Papa", w i t h i n the s u b a r c t i c water mass, and i n my study those species of the 75 i d e n t i f i e d f o r which ade-quate d i s t r i b u t i o n records e x i s t are n e a r l y a l l c o l d water or widespread Table I I : L i s t of a l l species or groups sorted. AMPHIPODA COPEPODA CTENOPHORA Caliiopus sp. **Cyphocaris challengerl **Euprimno abyssalis E, macropa Hyperia sp. Orchomenella sp. **Parathemisto pacifica **Scina borealis S t i l i p e s sp. CHAETOGNATHA **Sagitta elegans COELENTERATA Medusae **Aeglna sp. **Aequorea sp. Aglantha sp. Hyboecdon sp. Phialidium sp. Proboscidactyla sp. Rathkea.sp. .**Species A (unidentified) Siphonophora Chelophes appendlculata (?) Dimophyes arctica Lensia baryi **Muggia atlantica **Nanomia bijuga N. cara Species B (unidentified) Acartia c l a u s l i **A. longiremus Aetidlus armatus A. pacificus Bradyldius saanichi Calanus cristatus **C.. marshallae (Frost 1974) **C. pacificus (Woodhouse 1971) **C. plumchrus (Marukawa 1921; Campbell 1934) **Candacia columblae Centropages abdominalis **Chiridlus g r a c i l i s Corycaeus anglicus Epilabidocera amphitrites •"••Eucalanus bungii bungii Gaetanus intermedius **Gaidlus columbiae G. pungens Heterorhabdus tanner! **Metridia okhotensis **M. pacifica Microcalanus pigmaeus pusillus Oithona helgolandicus * * 0 . spinirostris Oncaea borealis **Pareuchaeta elongata (Campbell 1934': as Euchaeta japonlca; see Appendix A) **Pseudocalanus minutus  S caphocalanus brevicornis  Scolecithricella minor S. subdentata  Spinocalanus brevicaudatus  Tharybis fultoni Tortanus discaudatus Beroe cucumis  Pleurobrachia pileus EUPHAUSIIDAE **Euphausia pacifica  Nematoscelis d i f f i c l l i s  Thysanoessa longipes T. spin i f era POLYCHAETA Rhynchonerella angelini . Tomopteris renata **T. septentrionalis unidentified l a r v a l forms PTEROPODA **Clione limacina MISCELLANEOUS **Limacina sp. **Oikopleura sp. Decapod larvae and adults f i s h larvae parasitic copepods **Ostracods (unsorted) larv a l squid and octopus unidentified cumaceans unidentified mysids NB: Unless another reference i s given above, the species were identified from zooplankton keys prepared by John Fulton (1968, 1972, 1973). The identification of some of the species was checked with Fulton s original source. For further information, see Appendix A. • **These 29 species (or groups) were retained after i n i t i a l examination of the data. As two species were subdivided due to the presence of appreciable numbers of juvenile stages in the samples, data were generated for 32 species/groups. 48 species (e.g. Eucalanus b u n g i i b u n g i i : Davis 1949, Mori 1964; Calanus  marshallae: F r o s t 1974; Oithona s p i n i r o s t r i s : Mori 1964; A c a r t i a l o n g i -remus: Davis 1949, Mori 1964; Oncaea h o r e a l i s (= c o n i f e r a ? ) : Davis 1949; Euphausia p a c i f i c a : Ponomareva 1963; Tomopteris s e p t e n t r i o n a l i s : Dales 1957, Tebble 1962; Cyphocaris c h a l l e n g e r i : Bowman and McLain 1967; S a g i t t a  jgl'igans: B i e r i 1959) • In a d d i t i o n , some species are endemic to the S t r a i t of Georgia and neighbouring waters (e.g. Gai d i u s columbiae Park 1967; B r a d y i d i u s s a a n i c h i Park I966). There are only two d e f i n i t e exceptions to the c o l d water r u l e . Calanus p a c i f i c u s ( v a r . c a l i f o r n i c u s Brodsky 1962) i s a wa r m - t r a n s i t i o n a l water species found from 23°N l a t i t u d e t o 52°N l a t i t u d e along the westtcoast of North America. This species i s probably maintained i n the S t r a i t , of Georgia by the northward f l o w i n g Da-vidson Current and C a l i f o r n i a Countercurrent (Woodhouse 1971)• A e t i d i u s  armatus, a minor species i n the S t r a i t , has been described as a t r o p i c a l and s u b t r o p i c a l species (.Davis l-949, ;tMori 1964), and may be maintained i n the S t r a i t of Georgia i n the same way as Calanus p a c i f i c u s . The i n i t i a l species l i s t was reduced t o the 29 species marked i n Table I I . The m a j o r i t y of the species e l i m i n a t e d were r a r e species ap-pearing i n only a small p r o p o r t i o n of the samples. Others were present i n concentrations too small to be r e l i a b l e . The 29 species r e t a i n e d (=32 s u b d i v i s i o n s ) , along with t h e i r corresponding concentration values over the p e r i o d of the study, c o n s t i t u t e d the " b a s i c data matrix". T h i s matrix was then!"further reduced. The r e s u l t i n g "core species matrix" was composed of 20 s u b d i v i s i o n s : 14 t r u e species, 1 group.and 2 subdivided species (see Table I I I ) . None of the species e l i m i n a t e d t o form the core species l i s t were important elements of the biomass, nor d i d the varia n c e Table I I I : Proportion of each species in each of the regions of the water column found at Geo 1748. Acronyms are included to f a c i l i t a t e later reference to the species in figures. REGION SPECIES ACRONYM Near Surface (0-75 m) Intermediate (75-200. m) Deep (200-350 m) **Cyphocaris challengeri CYPHOC 0.14 0.17 0.69 **Euprimno abyssalis EUPRIM 0.56 0.28 0.16 **Parathemisto pacifica PMISTO 0.27 0.51 0.22 Scina borealis SCINA 0.03 0.17 0.81 **Sagitta elegans SAGELE 0.23 0.10 0.67 Aegina sp. AEGINA 0.57 0.43 Aequorea sp. - AEQUOR 0.30 0.70 **Medusa sp. A MEDSPA 0.07 0.35 0.58 Muggia atlantica MUGGIA 0.29 0.54 0.17 **Nanomia bijuga • NANOM 0.32 0.18 0.50 Acartia longiremus ACARLO 0.95 0.05 **Calanus marshallae CMARSH 0.07 0.93 **C. pacificus CPACI 0.01 0.16 0.83 **C. plumchrus CPLUM 1.00 Gandacia columbiae CANDAC 0.13 0.10 0.77 **Chiridius g r a c i l i s CHIRID 0.27 0.42 0.31 **Eucalanus bungii bungii EUCAL 0.01 0.02 0.97 Gaidius columbiae GAIDCO 0.16 0.46 0.38 Metridia okhotensis METOK 0.03 0.97 **M. pacifica (* CIV) MPAC1 0.02 0.04 0.94 (< CIV) MP AC 2 0.21 0.40 0-39 Oithona spinirostris OSPIN 0.10 0.57 0.33 **Pseudocalanus minutus PSEUDO 0.02 O.98 **Pareuchaeta elongata (< CIV) PARI 0.44 0.15 . 0.41 (* CIV) PAR2 0.27 0.41 0.32 (total) . PARTOT 0.35 0.24 0.40 **Euphausia pacifica EUPAC 0.71 0.02 0.28 **Tomopteris septentrionalis TOMSEP 0.10 0.45 0.45 Clione limacina CLLIM 0.19 0.50 0.31 Limacina helicina LIMAC 0.06 0.39 0.55 Oikopleura sp. OIKOP 0.46 0.13 0.41 **Ostraccds OSTRAC 0.20 0.31 0.49 Species marked with a double asterisk (**) are "core species" 50 i n t h i n t h e i r concentrations i n d i c a t e the presence of l a r g e annual f l u c t u a -t i o n s i n t h e i r numbers. Data from the 24 Clarke-Bumpus samples t h a t were completely sorted were ..used t o estimate the p r o p o r t i o n of each species i n each hydrographi-c a l l y d e fined r e g i o n of the water column (Table I I I ) . These propor-t i o n s are c o n s i s t e n t with the a v a i l a b l e data on the v e r t i c a l d i s t r i b u -t i o n s of the species sorted (e.g. F u l t o n I968; Gardner 1972; Evans 1973)• : The' p r o p o r t i o n s were'-then:.used^to: c a l c u l a t e -the a c t u a l number per.-cubic meter-of each species' i n each region of the water column. I f the concentration values f o r the three Calanus species are i s o l a -ted from the b a s i c data m a t r i x (Table I V ) , the extent of the f l u c t u a t i o n s t h a t they underwent d u r i n g the sampling p e r i o d can be examined. The f l u c t u a t i o n s are not as extensive as they i n i t i a l l y appeared t o be i n f a l l 1971• November 1971 was an unusually poor month f o r Calanus plum-chrus , accentuating the apparent d i f f e r e n c e between 1971 and 1970. How-ever, p r i o r t o November 1971 the c o n c e n t r a t i o n of Calanus plumchrus was, w i t h one exception, always gre a t e r than t h a t of C. marshallae, while d u r i n g and a f t e r November 1971 C. marshallae was c o n s i s t e n t l y more nu-merous than C. plumchrus. The concentration of Calanus p a c i f i c u s was comparable t o t h a t of C. marshallae i n I969, but i n a l l other samples was c o n s i s t e n t l y lower. The raw zooplankton data showed s i g n i f i c a n t skewness and k u r t o s i s . ' Transforming the data e l i m i n a t e d the skewness and k u r t o s i s (Table V) and the transformed data could then be used as input f o r s t a t i s t i c s pro-grammes s e n s i t i v e t o the n o r m a l i t y of the data. 51 Table IV: The conc e n t r a t i o n s (no./m ) of the three Calanus species d u r i n g the study p e r i o d . Mean values represent the mean f o r one year based on the over w i n t e r i n g samples. SPECIES plumchrus 0, aG:rsmarshallae C_. p a c i f i c u s By month Mean Byymonthh Mean By month Mean Oct 69 72.20 48.93 23.07 31.25 18.30 22.51 Nov 69 25-61 29.70 21.77 Dec 69 48.96 40.97 27.^5 Nov 70 47.34 46.30 9.39 7-34 3.84 2.96 Dec, • 70 45.38 5.29 2.08 Nov 71 5.08 22.08 27.63 38.29 1.81 1.73 Dec 71 39-08 48.94 1.66 Dec 72 12.49 (12.49) 60.38 (60.38) 4.56 (4.56) Nov 73 27.21 22.86 39.81 41.99 0.88 0.70 Dec 73 18.50 44.06 0.52 Dec 74 11.40 (11.40) 22.55 (22.55) 4.51 (4.51) Table V: E f f e c t of transforming the raw data on skewness and kurtosis of two species (Calanus pl"*chrus (CPLUM) and Parathemisto p a c i f i c a (PMISTO)) and two months (October 1969 and December 1972; chosen at random from the data matrix. Tests f o r skewness and kurtosis are from Geary (1936). RAW DATA TRAN SFORMED DATA SKEWNESS COEFFICIENT: /b. (m2) 3 372 i r ( x . - x ) 3 n i •iz(x.-x)2 n I 1^1 -Z(x.-x)3 n x -E ( x . - x ) 2 n I PMISTO 0.20 0.08 0.86 0.81 -0.06 0.09 CPLUM 377 3300 0.45 0.61 -0.28 0.59 OCT 69 477 25300 2.43** 4.64 -3.45 0.35 DEC 72 A 31 16800 1.88** 5.46 -6.31 0.49 RAW DATA TRANSFORMED DATA v4(x,-x)2 7n~~ / £ ( x f x ) : KURTOSIS COEFFICIENT: PMISTO 1.29 1.49 0.87 2.56 2.98 0.86 . CPLUM 55.75 64.39 0.87 2.00 2.59 0.77 a - OCT 69 67.17 109.17 0.62** 8.98 10.77 0.83 / n E ^ - x ) 2 DEC 72 67.78 99.55 0.68** 9.14 11.21 0.82 1 - 3 where: m, = — 2 ( x - x ) j n l ^ ( x . - x )2 n 1 ** implies a s i g n i f i c a n t c o e f f i c i e n t (p'<0.01). Significance levels for both tests f o r the range of sample size s tested are found i n Geary (1936). n = 11 for the species data, n = 25 for the October data and n = 23 for the December data A l l summations are summed over the range of i = 1,2,3 n 53 D i v e r s i t y and m u l t i p l e c o r r e l a t i o n A l l of the d i v e r s i t y i n d i c e s were s t a b l e , and none showed any trend over the p e r i o d examined. The m u l t i p l e c o r r e l a t i o n of the b a s i c d a t a block y i e l d e d 75 c o r r e l a t i o n s s i g n i f i c a n t at p '< 0.10. There i s no i n t u i t i v e p a t t e r n t o the d i s t r i b u t i o n of c o r r e l a t i o n s ( F i g . 6). F i f t e e n per cent of the c o r r e l a t i o n c o e f f i c i e n t s a r e s s i g n i f i c a n t (p '< 0.10; Table V I ) . Table VI: The numbers of s i g n i f i c a n t p o s i t i v e and negative c o r r e l a t i o n c o e f f i c i e n t s i n the species c o r r e l a t i o n matrix (maximum pos-s i b l e number of c o r r e l a t i o n s i s 4-96) . Sign of ' r ' ( c o r r e l a t i o n c o e f f i c i e n t ) S i g n i f i c a n c e 0.01 ^ p 0.01 < p '< 0.05 0.05 < p '< 0.10 T o t a l s + - t o t a l 9 3 12 133 8 21 20 12 42 52 23 75 C l u s t e r a n a l y s i s C l u s t e r i n g of the p a r t i t i o n e d data withmmonths as v a r i a b l e s y i e l d s three c l u s t e r s d i s t i n c t at the 0.50 l e v e l on a i s i m l l a r i t y s c a l e ranging from 0.0 t o 1 .'0 ( F i g . 7)- Each c l u s t e r c o n s i s t s of a l l of the d a t a from one of the three regions of the water column found at the s t a t i o n . The only exception i s the i n c l u s i o n of intermediate water 54 a Figure 6 : Summary of the correlation coefficients between the zooplankton species in the basic data matrix. Only correlations significant at pf<0.10 are shown, and only the sign of the coefficient i s given. Acronyms are as in Table III. 54b E U C A L l G A I D C O l M E T O K I M P A C 1 P S E U D O W P A R T O T I E U P A C I T O M S E P I C L L I M l L I M A C I O I K O P OSTRACEI 55 a Figure 7: C l u s t e r i n g of the p a r t i t i o n e d months. (A = near surface, B = intermediate, C = deep water) o z > 70 O m o O C T 6 9 C D E C 6 9 C N O V 7 3 C D E C 7 3 C D E C 7 4 C D E C 7 1 C D E C 7 2 C D E C 7 0 C N O V 7 1 C N O V 6 9 C " N O V 7 0 C -O C T 6 9 A -O C T 6 9 B -D E C 6 9 A -N O V 7 0 A -D E C 7 C A " N O V 7 1 A " D E C 7 1 A " D E C 7 2 A " N O V 6 9 A -N O V 7 3 A " D E C 7 3 A -D E C 7 4 A -D E C 6 9 3 -P E C 7 3 B r N O V 7 3 B " D E C 7 4 B " D E C T I B -D E C 7 2 B " D E C 7 0 B -N O V 7 1 B -N O V 6 9 B -N O V 7 0 B ~ S I M I L A R I T Y p O p O CD 03 ^ O) 56 data from October 1Q6Q within the near surface water cluster. There are no major subdivisions in any of the three clusters; however, in both deep and intermediate water clusters there i s a tendency for November?)dataatoG be grouped separately from December data, and for data taken in the l a t -ter part of the sampling period to be grouped separately from earlier data. Two major clusters of species were produced at a similarity level of 0.12 (Fig. 8). The f i r s t cluster contains 12 of the 32 species. (N.B. Not a l l of the elements of the data matrices are true species, but are referred to as such for the sake of convenience). Six of these twelve species are the only true deep water species identified. They f a l l into a single cluster separable at.the 0.50 level. The other six do not f a l l into any distinct cluster, and include species with differing depth distributions. The second major species cluster does not contain--any-large; wa-. ter type associated groups.. The only two species always found shallower than 200 m do not f a l l into any cluster at the 0.30 level. The only two species found in both near surface and deep water, but uncommon at i n -termediate depths, are similarly unclustered. The remaining species f a l l into a number of small clusters that appear not to be related to the region in which the species i s found, but rather to the region in which i t i s rarest. For example, in the cluster composed of Nanomia  bijuga, Pareuchaeta elongata ( 5 C I V and total), Cyphocaris challenger! and Sagitta elegans, which i s clustered at the O.65 level, a l l of the species but Gyp'ohallengeri have a concentration minimum in intermediate water, even though they have a measurable concentration in a l l three 57 a Figure 8: C l u s t e r i n g of species, p a r t i t i o n e d raw data. Acronyms as i n Table I I I . S I M I L A R I T Y O AEOUOR C L L I M OSPIN C P A C I SCINA C A N D A C M E TOK E U C A L C P L U M P S E U D O MPACI C MARSH A C A R L O AEGINA TJ m EU PAC o OIKOP m in C H I R I D MPAC2 LI MAC ME DSP A E U PRIM MUGGIA PMISTO PAR2 NANOM PARI PAR TOT C Y P H O C S A G E L E OSTRAC G A I D C O TOM SEP o o 0) o Ol 58 types of water. Cyphocaris c h a l l e n g e r i has a concentration minimum i n near surface water, but the concentration i n intermediate water i s almost i d e n t i c a l w i t h the minimum. S i m i l a r l y , the 0stracod/Gaidius columbiae/  Tomopteris s e p t e n t r i o n a l i s c l u s t e r , formed at the same s i m i l a r i t y l e v e l , shows a concentration minimum i n near surface water. Canonical c o r r e l a t i o n Grouping core species by p a t t e r n of depth d i s t r i b u t i o n , and running Calanus plumchrus and G. marshallae as s i n g l e species, y i e l d e d s i x groups (Table V I l ) . The s i g n i f i c a n t c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t s Table V I I : Grouping of species by v e r t i c a l d i s t r i b u t i o n p a t t e r n . Group C h a r a c t e r i s t i c s Species  1 Minimum concentration at i n t e r - Euphausia p a c i f i c a mediate depths, some v e r t i c a l Nanomia bi.juga migration Pareuchaeta elongata (<CIV and t o t a l ) S a g i t t a elegans Minimum concentration i n deep water, Euprimno a b y s s a l i s but g r e a t e r than 10% of the popula- Parathemisto p a c i f i c a t i o n i n each region of the water column Minimum concentration nearv.surface, most species w i t h a mid-depth maxi-mum; at l e a s t 10% of the p o p u l a t i o n i n each r e g i o n of the water column A l l s pecies w i t h a maximum concentra-t i o n i n deep water, and a n e g l i g i b l e c o ncentration ( l e s s than 10% of the t o t a l ) i n near surface water Tomopteris s e p t e n t r i o n a l i s  M e t r i d i a p a c i f i c a (<GIV) C h i r i d i u s g r a c i l i s Ostracods a) Calanus plumchrus  Pseudocalanus minutus  M e t r i d i a p a c i f i c a (SCIV) Calanus marshallae  Calanus p a c i f i c u s b) Calanus plumchrus c) G. marshallae  59 (R c's) between b l o c k s of zooplankton and b l o c k s of hydrographic data are, with only three exceptions, a l l g r e a t e r than 0.95- No s p e c i f i c trends appeared i n the c a n o n i c a l c o r r e l a t i o n s , much as wi t h the m u l t i -p l e c o r r e l a t i o n r e s u l t s , and the o v e r a l l p i c t u r e i s s t i l l very complex. For example, the f i r s t c a n o n i c a l f a c t o r f o r water column s t a b i l i t y i n August and September has s i g n i f i c a n t r e l a t i o n s h i p s w i t h a l l but two groups, and can account f o r over 95% of the v a r i a t i o n i n Calanus  plumchrus. The Euphausia pacifica/Nanomia b i j u g a group can be r e l a t e d to almost a l l of the f a c t o r s checked, while Calanus marshallae shows s i g n i f i c a n t r e l a t i o n s h i p s w i t h temperature only. The deep water group i s most s t r o n g l y r e l a t e d t o s t a b i l i t y i n June/July, but i s a l s o r e l a t e d to s t a b i l i t y i n phase and three months out of phase, as w e l l as t o other f a c t o r s . Despite t h i s inherent complexity, there appears t o be a d e f i -n i t e r e l a t i o n s h i p between the hydrographic parameters, p a r t i c u l a r l y temperature and s a l i n i t y , and the zooplankton data. The r e s u l t s are summarized i n Table VIII. Regression a n a l y s i s The r e g r e s s i o n a n a l y s i s (Table IX) supports the r e l a t i o n s h i p of zooplankton with s t a b i l i t y and temperature.that was i n i t i a l l y i n d i -cated by the c a n o n i c a l a n a l y s i s . Only 6 of the 3*+ s i g n i f i c a n t (p^O.10) r e g r e s s i o n equations i n v o l v e s a l i n i t y . Although temperature i s one of the f a c t o r s t h a t determines s t a b i l i t y , t h i s a s s o c i a t i o n does not appear to be r e s p o n s i b l e f o r the f a c t that each parameter generates a s i m i l a r number of s i g n i f i c a n t r e g r e s s i o n equations. The m a j o r i t y (60$l) of the temperature r e g r e s s i o n s i n v o l v e temperatures from 200 m or deeper, while 60 Table V I I I : Summary of the s i g n i f i c a n t c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t s . Data i n Phase Group St Data Three Months Out of Phase  T S S t Data S i x Months Out of Phase  T S St 1 R c P %s2 0.9978 -0.05 23.0 — 0.9985 — - 0.05 26.0 0.9978 0.10 21.2 0.9970 0.10 24.0 0.9946 0,05-26.6 2 R c P O.976O 0.05 11.4 3 R c p %s2 • — 0,9937 0.01 — 30.4 0.9995 0.05 51.7 4a R c P %S2 0.9999 -0.01 26.4 — 0.9991 — 0.05 — 22.7 0.9958 0.10 25.1 0.9950 0.10 13.0 4b R c P fs2 0.8764 -0.05 76.8 j_ 0.9918 0.005 98.4 4c R c fcS2 0.8916 -0.10 79.5 0-.-9383 0.10 88.0 0.9921 0.10 7.8 0.9971 0.9607 b.01 0.05 12.31 8 0 . § P J 0.9980 0.05 13.3 0.9979 0.05 15.4 0.9984 0.05 27.7 0.9974 0.05 33.6 0 *9881 0.005 97.6 0.9907 0.9738 0.05 0.10 30 9 • X V39.9 where1: R i s the c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t c 2 f<£ i s the per cent of the variance i n the zooplankton accounted f o r by the hydrographic f a c t o r 'p' i s the Chi-square p r o b a b i l i t y t h a t R c i s not s i g n i f i c a n t T = temperature, S = s a l i n i t y , St = = s t a b i l i t y A double s et of values i m p l i e s t h a t both the f i r s t and second p a i r s of c a n o n i c a l f a c t o r s were s i g n i f i c a n t l y c o r r e l a t e d 61 Table IX: Summary of a l l r e g r e s s i o n equations s i g n i f i c a n t at = 0.10. IN PHASE REGRESSIONS Temperature: GYPHOG SAGELE. GMARSH GPLUM EUGAL S a l i n i t y : GPAGI EUGA1 OSTRAG = -1.02(T 350 S t a b i l i t y : ) +10.03 OSTRAG = 1.37(T 3 0 0) -2.99(T 11.21 ) + 30.25 350 2 . 7 2(T 3 5 Q) - 21.27 -0.4-3(T 1 0) + 4.4? - 7 - 0 2(S 3 5 0) + 220.24 3 . 6 9 ( S 3 5 Q ) - 114.23 - 0 . 2 9(S 1 0) + 11.40 MPAG1 = 1 . 3 ' . 7 6(St 1 0_ 5 0) + 2.82 1 . 9 9 ( S t Q _ 1 0 ) + 4.13 THREE MONTHS OUT OF PHASE Temperature: GYPHOG EUPRIM PMISTO S a l i n i t y : GMARSH - 0 . 9 6(T 5 Q) + 9.^4 -2 . 8 8(T 5 Q) +24.29 S t a b i l i t y : GYPHOG NANOM - 3 . 1 9(T 5 Q) + 3 . 1 5 ( T 3 0 Q ) 0.57(S 1 Q) +18.99 GMARSH CHIRTD EUGAL PARTOT 0.96(St Q_ 1 0) + 0.63 1 . 2 9(st 0_ 1 0) + l 5 . o 3 ( s t 1 0 _ 5 0 ) - 2 7 6 . 6 9(St 5 0_ 2 0 0) 3 1 . 0 7(St 1 Q_ 5 0) + 1.65 - 4 6 . 3 4(St 1 0_ 5 Q) + 2.09 - 1 . 8 l(St 0_ 1 0) + 1.44 0 .95(St 0_ 1 Q) 26.86(St 1 0_ 5 0) : ^ 6 - i ? ( s t 5 0 _ 2 0 0 ) +8b9.4:2(st2_300) + 1.26 TOMSEP = -0.66(St 0_ 1 0) - 2488.64(St 2_ 3 0 0) SAGELE = + 3.77 - 0 . 6 l ( S V l 0 ) + 2.25 8 1 3 . 5 3(St 2_ 3 0 Q) CONTINUED ON FOLLOWING PAGE... 62 Table IX (Cont'd): SIX MONTHS OUT OF PHASE Temperature: S t a b i l i t y : CYPHoc = -0 .66(T 5 Q) + 6.17 PMISTO = 3 5 - 7 7(St 1 0_ 5 0) - 4 8 1 . 4 ( S t 5 0 _ 2 0 Q ) SCLNA = -8. 4 8 ( T 3 0 Q ) + 69-99 SAGELE = - 0 . 8 1 ( S t Q _ 1 0 ) + 1.44 CMARSH = -0 .93(T 5 Q) - 4 . 91(T 3 0 0) TOMSEP = - 2 . 1 7(St Q_ 1 0) + 1-56 +52.05 OSTRAG 4= - 1 . 4 0 ( S t 0 _ 1 0 ) + 3-81 MPAG1 = - 2 . 0 3(T 3 0 Q) + 0 . 59(T 3 5 0)PART0T = - 1 3 4-3D(^ 5 Q_ 2 Q Q) + 2-22 + 16.40 PARTOT = 2 .34(T 3 0 Q) + 8.00(T 3 5 0) S a l i n i t y : EUCAL = 4 . 7 5(S 2 Q 0) - 144.54 SAGELE = - 7 . 9 8(S 3 0 Q) + 8.00 ( S 3 5 Q ) NB: A l l equations are of the form: l n ( y + 0.01) = ax^ + bXg + c x 3 + dx^ + ex^ + K where: y i s the concentration of the species (no./m3) a,b,c,d,e are the c o e f f i c i e n t s of the independent v a r i a b l e s x^,x^,x„,x^,x,, are the s u b d i v i s i o n s of the independent v a r i a b l e 'x' K i s a constant A l l temperatures are i n °C at the s u b s c r i p t e d depth A l l s a l i n i t i e s are i n °/ Q O at the s u b s c r i p t e d depth A l l s t a b i l i t i e s are i n u n i t s of afa^+uS"^ over the sub-s c r i p t e d depth range \ i? J In t h i s and other t a b l e s , the depth ranges 200-300 m and 300-350 m are concatenated t o 2-300 m and 3~350 m r e s p e c t i v e l y f o r convenience. 63 the m a j o r i t y (68%) of the s t a b i l i t y r e g r e s s i o n s i n v o l v e the top 50 m of the water column. A l s o , only two species show simultaneous s i g n i f i c a n t r e g r e s s i o n s on temperature and s t a b i l i t y . The m a j o r i t y of the s i g n i f i c a n t r e g r e s s i o n equations i n v o l v e only a constant and one independent v a r i a b l e of the f i v e t e s t e d simultaneously. S t a b i l i t y three months out of phase produced the highest number of s i g n i -f i c a n t r e g r e s s i o n s , f o l l o w e d by temperature s i x months out of phase, and then by temperature i n phase. One p a r t i c u l a r l y i n t e r e s t i n g aspect of the r e g r e s s i o n a n a l y s i s i s the r e l a t i o n s h i p between Calanus plumchrus and C. marshallae. The r e -g r e s s i o n of the two species against temperature at 350 m, a depth at which there i s considerable overlap between the two po p u l a t i o n s (see F i g . 10), y i e l d s r e g r e s s i o n l i n e s of opposite slope which i n t e r s e c t i n the r e g i o n of normal ambient temperature ( F i g . 9)• F a c t o r a n a l y s i s The i n i t i a l f a c t o r a n a l y s i s of the p a r t i t i o n e d , transformed zooplankton data produced e i g h t f a c t o r s which together could y i e l d 90% of the variance i n . t h e data matrix. A f t e r varimax r o t a t i o n , these f a c -t o r s could account f o r v i r t u a l l y 100% of the va r i a n c e i n the matrix. A l l of the species with high p o s i t i v e l o a d i n g s on the f i r s t f a c t o r are deep water species t h a t are almost absent from near surface water. The three species w i t h the highest negative l o a d i n g s on t h i s f a c t o r are sur-f a c e and surface to mid-depth species with few r e p r e s e n t a t i v e s i n deep water. The second f a c t o r i s a s s o c i a t e d w i t h species which have a mid-depth minimum and undergo some degree of v e r t i c a l m i g r a t i o n . F a c t o r 64a F i g u r e 9: Regression of Calanus plumchrus and 0. marshallae against temperature at 350 m. Equations of the form: l n ( y + 0.01) = mx + b. 64b ''8.6 87 88 8.9 9.0 9*1 92 93 9.4 95 96" T E M P E R A T U R E (°C) 65 number three i s a s s o c i a t e d p r i m a r i l y with species which are most h i g h l y concentrated i n deep water but have app r e c i a b l e numbers at mid-depths and s m a l l numbers near the su r f a c e . F a c t o r f o u r i s a s s o c i a t e d with those species which have a mid-depth maximum. The other f a c t o r s are l e s s e a s i l y a s s o c i a t e d with s p e c i f i c groups of species; however, these f i r s t f o u r f a c -t o r s can account f o r 73% of the variance i n the zooplankton matrix. The only l a r g e species group produced i n the i n i t i a l f a c t o r analy-s i s was the group of 13 species a s s o c i a t e d with the f i r s t f a c t o r . To exa-mine the s t r u c t u r e of t h i s grouping i n more d e t a i l , i t was t r e a t e d as a separate group of species and r e - f a c t o r e d i n the same manner as the o r i g i -n a l d a t a block. The seven f a c t o r s produced y i e l d e d 100% of the vari a n c e i n the zooplankton. A f t e r r o t a t i o n , they s t i l l reproduced a l l of the varia n c e i n the zooplankton data, but t h e i r i n d i v i d u a l c o n t r i b u t i o n s t o the variance were more e q u i t a b l e . The f i r s t f a c t o r was as s o c i a t e d w i t h species whose concentration was highest i n deep water and tapered o f f t o -wards the surface. The second f a c t o r was a s s o c i a t e d w i t h two of the shallow species, which had hig h negative l o a d i n g s , and one deep water sp e c i e s . The other f a c t o r s were aMoassoeiated with s i n g l e s p e c i e s . The r e s u l t s of the f a c t o r i n g are shown i n Tables X and X I . P r i n c i p a l components a n a l y s i s The r e s u l t s of the p r i n c i p a l components a n a l y s i s of the hydro-graphic data are given i n Table X I I . S u f f i c i e n t eigenvalues were e x t r a c t e d i n each case t o y i e l d at l e a s t 95% of the variance of the data matrix. The remaining variance was l o s t i n t r u n c a t i n g the number of eigenvalues under c o n s i d e r a t i o n . Truncated eigenvalues i n d i v i d u a l l y accounted f o r an Table Xt I n i t i a l f a c t o r i n g of zooplankton data VARIMAX FACTOR LOADINGS Species Acronym: Factor: 1 2 3 4 5 6 7 8 CPLUM 0.97 0.08 0.01 0.08 0.08 -0.10 0.01 O.05 PSEUDO 0.9? 0.0? -0.03 -0.13 0.04 -0.14 . 0.01 -0.06 MPAC1 0.97 -0.04 0.12 0.04 0.13 0.04 0.11 -0.02 EUCAL 0.94 -0.08 0.20 0.11 -0.16 0.02 -0.11 -0.10 METOK 0.8? . 0.10 0.14 -0.25 0.24 0.08 -0.01 -0.02 CMARSH 0.79 O.58 -0.03 -0.12 O.07 -0.08 -0.01 -0.02 SCINA 0.78 0.22 -O.52 -0.15 -0.04 0.15 0.05 -0.05 OTHOC 0.65 -0.17 -0.24 0.19 -0.09 " 0.35 0.26 -0.49 CP AC I 0.61 0.35 -0.25 -0.06 0.29 -0.25 0.05 0.21 CANDAC 0.52 -0.39 -0.12 0.26 0.48 0.06 0.03 0.06 ACARLO -0.69 -0.43 -0.05 -O.34 0.29 0.33 . -0.02 0.16 HUGGIA -0.73 0.05 -0.39 -0.41 -0.22 0.11 0.00 -0.27 AEG IN A -0.81 0.00 0.01 -0.05 0.26 0.1? 0.0? -0.03 OIKOP ** ****** -0.14 * * X - * * XXX -0.68 0.22 . -0.15 0.05 -0.24 -0.25 0.10 PARTOT -0.45 -0.70 -0.29 0.00 -0.03 O.36 0.02 -0.15 EUPAC -0.11 -0.75 -0.03 0.18 0.07 -0.08 -0.05 -0.2? PARI -0.25 . -0.75 -0.35 0.16 -0.15 -0.06 0.18 -0.11 SAGELE 0.40 -0.86 0.04 -0.53 0.05 0.13 0.02 0.11 0.12 MEDSPA 0.18 0.00 0.23 0.44 -0.26 -0.13 0.22 OSTRAC 0.02 -0.31 -0.61 -0.47. 0.34 -0.18 -0.01 . 0.11 PMISTO -0.48 9.06 -0.82 -0.04 -0.13 0.25 -0.06 -0.0? LIMAC 0.10 -0.04 -0.95 -0.21 ******** 0.05 -0.15 -0.16 0.03 GAIDCO -0.26 0.48 -0.10 -0.65 -0.14 -0.12 0.42 0.13 TOMSEP 0.18 0.23 0.02 -0.79 0.32 0.03 -0.14 0.29 OSPIN 0.00 0.01 -0.27 -0.88 ******** 0.05 -0.11 -0.37 -0.09 HPAC2 -0.10 -0.08 -0.03 -0.25 0.90 * ¥. -y.-x -0.02 -0.13 -0.03 PAR2 -0.10 0.16 O.I? 0.05 -0.0? 0.92 0.06 0.08 EUPRTM . -0.5'+ -0.15 -0.42 0.20 0.08 0.60 -0.09 -0.26 AEQUOR O.38 0.23 -0.04 -0.16 0.39 -0.23 -0.57 0.03 CLLIM -0.19 -0.24 -0.43 -0.10 0.20 0.11 -0.30 0.55 ******** CHIRID -0.29 -0.24 -0.43 -0.10 0.20 .0.11 -0.30 0.55 NAN 014 -0.10 0.58 0.00 0.12 0.0? 0.00 0.14 -O.78 **#-M~X-**-* % of zooplankton variance accounted f o r by each factor: 3^.0 16.0 13.0 10.0 7.0 7.0 6.0 6.0 67 Table XI: Secondary factoring of species associated with the f i r s t factor of Table X. Species Acronym: VARIMAX FACTOR LOADINGS Factor: 1 2 3 4 .5 6 7 CPAGI 0.91. 0.09 0.00 -0.25 -0.05 0.C9 - ' 0.01 SCINA 0.73 0.32 -0.46 0.20 -0.18 0.14 -0.14 CMARSH 0.73 0.44 -0.15 -0.19 0.03 0.23 -0.16 CPLUM 0.59 0.44 -0.26 -0.39 -0.29 0.21 -0.34 PSEUDO 0.57 0.48 -0.28 -0.21 -0.25 O.30 -O.36 MPAC1 0.49 ******** 0.35 ******** -0.33 -0.42 -0.34 0.31 -0.35 EUCAL 0.25 0.52 -0.38 . -O.38 -0.22 0.31 -0.47 ACARLO -0.33 -0.75 0.24 0.51 -0.14 -0.01 -0.05 AEGINA -0.26 -O.90 ******** 0.15 ******** 0.12 0.22 -0.17 0.16 CYPHOC 0.15 0.19- -0.94 ******** -0.09 ******** -0.20 0.11 -0.08 MUGGIA -0.23 -0.32 0.02 0.79 0.41 -0.18 0.13 CANDAC ******** ******** -0.93 ******** . -0.22 0.07 0.08 -0.21 -0.18 0.10 ******** O.69 ******** -0.07 METOK 0.55 0.23 -0.22 -0.23 -0.14 % of zooplankton variance accounted for by each factor: . 27.1 21.3 13-3 12.2 7.6 5.6 Table X I I : P r i n c i p a l components of the hydrographic data. VARIABLE EIGEN-VALUES % OF TOTAL VARIANCE CUMULATIVE % VARIANCE SUB-DIVISIONS EIGENVECTORS Temperature 2.64 53 53 T 1.34 27 80 T 50 0.85 18 98 T 200 T 300 T 350 S a l i n i t y 3.80 76 76 S 10 0.97 19 94 s 5 0 0.16 4 98 S 200 S 300 S 350 S t a b i l i t y 1.96 39 39 s t o -1.73 35 74 s t i o . 0.93 18 92 s t 5 0 1 2 3 0.04 -0.71 -0.58 0.15 -0.69 0.55 0.53 0.05 0.47 0.60 0.05 -0.22 0.58 0.13 -0.31 0.22 97 St St 200-300 300-350 0.26 -0.87 -0.20 0.48 -0.26 0.37 0.48 0.22 0.65 0.48 0.29 -0.44 0.49 0.21 -0.46 0.50 -0.31 -O.56 -0.13 0.68 -0.071. -0.12 0.11 •0.49 0.11 0.70 0.32 0.02 0.66 -0.43 0.62 0.23 O.67 -0.03 -0.70 69 i n s i g n i f i c a n t amount of the variance i n the parameter. The f i r s t three of f i v e p r i n c i p a l components of temperature generate 98% of the va r i a n c e . The f i r s t component has high negative l o a d i n g s on deep water data and n e g l i g i b l e l o a d i n g s on near surface water. The second component has high negative l o a d i n g s on near surface water and n e g l i g i b l e l o a d i n g s on deep water temperatures F a c t o r three has a high negative l o a d i n g on T^Q, and high p o s i t i v e l o a d i n g s on T^Q and Tgoo* S a l i n i t y a l s o has three major components. The f i r s t component r e -l a t e s most s t r o n g l y t o deep and intermediate water. The second component has a s i n g l e high negative l o a d i n g on the shallowest depth and the t h i r d component has a s i n g l e high p o s i t i v e l o a d i n g on intermediate water with two l e s s e r negative l o a d i n g s on deep water. S t a b i l i t y components show l e s s redundancy. A l l f i v e are r e q u i r e d to y i e l d lOQ&oof the vari a n c e i n the s t a b i l i t y m a t r i x . The f i r s t f o u r , however, y i e l d <J]% of the vari a n c e . The f i r s t t h r ee can be a s s o c i a t e d w i t h near surface, deep and intermediate water r e s p e c t i v e l y . The f o u r t h has a high p o s i t i v e l o a d i n g on StgQQ -^ QQ> a h i g h negative l o a d i n g on S t300-350" The r e s o l u t i o n of the p r i n c i p a l components of each of temperature, s a l i n i t y and s t a b i l i t y i n t o three depth r e l a t e d groupings i s r e l a t e d t o the d i v i s i o n of the water column a t Geo 1748 i n t o three d i s t i n c t r e g i o n s . Thus the major o r i e n t a t i o n of the p r i n c i p a l components i s r e l a t e d to the p h y s i c a l s t r u c t u r e of the water column. The rank ordering of the stan-dardized cases on hydrographic data components (Table X I I I ) suggests i n a d d i t i o n the presence of a temporal b i a s i n the components. T h i s i s par-t i c u l a r l y t r u e of the f i r s t component of temperature. L a t e r months have 7 0 Table XIIIi Rank order of standardized cases on each principal component. HYDRODATA COMPONENTS Temperature S a l i n i t y S t a b i l i t y jSt 2 n d 3 r d jSt 2nd 3 r d l 3 t 2nd 3 r d kth 8 5 6 2 2 6 4 8 7 4 7 11 10 1 11 10 6 7 2 5 11 7 4 3 9 4 7 6 6 2 6 10 7 7 4 2 5 9 4 8 10 3 3 6 10 7 9 3 9 10 1 9 9 8 5 3 10 1 1 7 9 8 5 5 7 8 8 2 5 1 3 2 11 9 1 11 3 11 3 9 2 4 2 4 3 1 11 4 11 6 5 1 8 10 8 9 1 5 8 3 4 6 1 11 6 5 2 10 10 11 ZOOPLANKTON COMPONENTS ^st 2 n d 3 r d kth 5 t h 6 t h 7 t h 3c lb 7a 3a ?b 6b 8c 10c 10b 7b 3b 7c 6c 8a 9c l i b 7c 3c 7a 6a 8b 7c 3b 3a 10a 4b 3b 11c l c 5b 8b 4a 3b 3c l i b 8c 9b 10a 10b 8b 3a 10a 11c 2b 8c 10c 4a 9b l l a 5c 8b 10b 9a 4c l i b 10c 2c 7b 10c 5a 3a 7b 2a 4c 4b l l a 4b 3c 4b 3a 3b 6b l i b l l a 8a 2b 2c 6c l a 11c 4c 8c 9a 10b 10b lc 9a ?a 5b 9c 2b 9b 10a 9b 9c 2b l l a 3b 7b 10c 9c 9b lb 11c 3c lb l l a 5a la 2c 10b 4a 8b 3a 6a 5c 6b ?c 4a l i b 5a 5b l i e l c 7a 4b 5b 11c 5c 5b 5c 8b 4c 2b 2a 6b l i b 2a 4a 5a 4b 9a 6c 7c 5a 2c 5b 6b 3c l a 7b l a 2a 5c 3a 5c lb lb 6c 4c l a 10a 2c l c lc 6a 10c ?a 9a 9c 3a 6a l i b 10a 6a 7a 8a 3b 8a 9b 8c l c l a 8c 3c 2a l l a lb 7c l l a 7a 4a 6c 10b 8a 6c 8a 7c 4b 6b 11c la 7b 5a 4a 4c 8b 9c lc lb 4a 6a 2a 8c 9a 5b 9a 2a 4c 2b 2c 10c 5a 9c 6a 6c 2c 2b 10a 5c 9b Month Codeoi 1 - Oct 69 4 - Nov 70 7 - Doc 71 10 » Dec 73 Depth Codesi a - 0-75 m 2 - Nov 69 5 - Dec ?0 8 - Dec 72 11 - Dec 74 b - 75-200 m 3 - Dec 69 6 - Nov 71 9 - Hov ?3 c - 200-390 m NBi If no dopth code Is given, the month code rofers to the whole water column 71 high rankings on t h i s component, while e a r l y months have low rankings. In a d d i t i o n , temperatures a t depths g r e a t e r than 200 m have the highest l o a d i n g s on the f i r s t temperature component, suggesting t h a t the tempor-a l b i a s i s a f u n c t i o n of deep water r a t h e r than of near surface water. A temporal b i a s a l s o shows up i n the s a l i n i t y data, although t o a l e s -ser extent, but the case rankings of the s t a b i l i t y components are not s e q u e n t i a l . The f i r s t seven eigenvectors of the zooplankton core species matrix y i e l d 94% of the vari a n c e of the matrix (Table XIV). Of the seven, only three account i n d i v i d u a l l y f o r more than 10% of the variance, the l a r g e s t accounting f o r J & f o . In many re s p e c t s , t h e r e s u l t s are s i m i l a r t o those seen i n the f a c t o r a n a l y s i s (Tables X, X i ) . The f i r s t three components generated appear t o have species a s s o c i a t i o n s s i m i l a r to the a s s o c i a t i o n s w i t h the f i r s t three f a c t o r s generated, although the absolute values of the c o e f f i c i e n t s of the eigenvectors are g e n e r a l l y lower i n the p r i n c i p a l components a n a l y s i s . The f i r s t three f a c t o r s account f o r over 60% of the zooplankton variance i n both analyses. The species/eigenvector a s s o c i a t i o n s of the two analyses d i v e r g e a f t e r the t h i r d f a c t o r i s e x t r a c t e d . T h i s divergence may be due i n p a r t to the re d u c t i o n of the species matrix to twenty core species i n the p r i n -c i p a l components a n a l y s i s . The f o u r t h p r i n c i p a l component has high nega-t i v e l o a d i n g s on the three amphipod species (Cyphocaris c h a l l e n g e r i , Euprimno a b y s s a l i s and Parathemisto p a c i f i c a ) and on j u v e n i l e Pareuchaeta  elongata (PAR2). The highest p o s i t i v e l o a d i n g i s 0.25, w i t h Euphausia  p a c i f i c a . Component number f i v e has high negative c o e f f i c i e n t s w i t h species t h a t have a near surface minimum and a mid-depth maximum, but 72 Table XIV: P r i n c i p a l components a n a l y s i s of the p a r t i t i o n e d zooplankton data. Eigenvalues Per cent of t o t a l v a riance Cumulative per cent of variance. 7.21 36 36 3.80 19 55 2.99 15 70 1.70 9 79 1.24 6 85-1.01 5 90 0.89 4 94 S p e c i e s — — : 1 2 3 4 5 6 7 EUPAC -0.14 -0.37 -0.07 00003 -0.11 0.03 -0.30 T0MSEP 0.12 0.24 -0.27 0.27 -0.49 0.02 0.21 SAGELE 0.03 -0.41 -0.17 0.13 -0.21 -0.31 0.10 CYPH0C 0.13 -O.36 0.09 -0.42 -0.01 0.12 -0.01 EUPRIM -0.27 -0.06 0.01 -0.45 -0.01 0.15 -0.09 PMIST0 -0.23 0.06 -0.16 -0.46 0.28 -0.01 0.14 MEBSPA 00006 0.00 -0.37 -0.05 -0.33 0.03 -0.65 NAN0M -0.13 -0.39 0.08 0.08 -0.02 0.48 -0.08 CHIRID -0/16 0.11 -O.36 -0.04 -0.13 -0.49 -0.32 CMARSH ' 0.35 0.09 -0.02 -0.19 0.06 0.13 -0.02 CPLUM 0.34 -0.15 -0.07 -0.10 -0.01 -0.10 -0.06 EUCAL 0.31 -0.23 0.10 -0.06 -0.07 -0.16 -0.09 MPAC1 0.33 -0.22 -0.04 -0.07 -0.09 -0.03 0.02 MP AG 2 -0.02 0.05 -0.37 0.07 -0.35 0.52 -0.12 PSEUD0 0.34 -0.15 -0.08 -0.08 -0.03 -0.01 0.02 PARI -0022 -0.34 -0.13 0.02 0.20 -0.17 0.29 PAR2 -0.07 0.08 0.23 -0.45 -0.50 -0.13 -0.21 GPACI 0.27 0.07 -0.27 -0.15 0.21 0.05 0.17 OSTRAC -0.04 -0.06 -0.52 -0.09 CO. 00 0.08 0.33 PARTOT -0.30 -0.25 -0.09 -0.13 -0.18 0.10 0.11 73 t h i s r e l a t i o n s h i p i s not c o n s i s t e n t , as some species showing t h i s p a t t e r n have n e g l i g i b l e c o e f f i c i e n t s . The remaining eigenvectors can not r e a d i l y be a s s o c i a t e d w i t h any d e f i n i t e species group,.' The rank o r d e r i n g of cases on p r i n c i p a l components (Table X l l l ) r e -i t e r a t e s the d i v i s i o n of the water column i n t o three r e g i o n s . A l l of the deep water cases have high rankings on the f i r s t component, while the near surface cases have the lowest rankings. For component two, i n t e r -mediate water has the highest rankings, w i t h a trend i n the remaining rankings f o r November and December data t o be ranked i n separate b l o c k s , with November cases ranked lowest. The ranks of the standardized cases on component three are temporally arrayed. December 196-9, a l l depths, ranks highest on the f o u r t h component. December 1971, a l l depths, has the three highest rankings on component f i v e , w h i l e the f i n a l three months sampled monopolize the lowest ranks. Components s i x and seven are s i m i -l a r l y a s s o c i a t e d w i t h s p e c i f i c months: November 1971 and December 1972 r e s p e c t i v e l y . 74 D i s c u s s i o n Data manipulation Over 75 groups or species of zooplankton were i d e n t i f i e d i n the samples; however, many are o n l y • p e r i p h e r a l members of the zooplankton communi-ty.,,Liii:-.that.. t h e i r : c o n t r i b u t i o n t o the community biomass i s very s m a l l , a, and s e v e r a l are present i n small numberssldifficultttoa.assessaacc.urately with a v a i l a b l e sampling methods. The e l i m i n a t i o n of such species i n order to reduce background noise i n data a n a l y s i s i s accepted p r a c t i c e . Angel and Fasham (1973) chose only 50 of 212 i d e n t i f i e d copepod species, 8 of 84 i d e n t i f i e d amphipod species and 13 of 16 i d e n t i f i e d chaetognath species f o r f a c t o r a n a l y s i s of d i f f e r e n t segments of the SOND C r u i s e zooa, plankton data. The e l i m i n a t e d species were not considered to be present i n s u f f i c i e n t l n u m b e r s f o r " u s e f u l a n a l y s i s " . S i m i l a r l y , Cassie and Michael (1968) found only 12 species i n s u f f i c i e n t abundance f o r numeri-c a l a n a l y s i s , and reduced t h i s number t o 8 species f o r c a n o n i c a l c o r r e l a -t i o n a n a l y s i s w i t h sediment p r o p e r t i e s a t 21 s t a t i o n s . Grieg-Smith (1971) has discussed the r a t i o n a l e behind the elimina--; t i o n of s e l e c t e d data p r i o r t o a n a l y s i s . He suggests t h a t often a l a r g e p r o p o r t i o n of the data i s e s s e n t i a l l y background n o i s e . Even though .this n o i s e may contain meaningful i n f o r m a t i o n , i t might s t i l l be d e s i r -able t o e l i m i n a t e i t f o r p r a c t i c a l reasons. The degree to which a com-p l e x data bank can s a f e l y be reduced can only be a r r i v e d at e m p i r i c a l l y , but there i s an i n d i c a t i o n t h a t 10-20% of the o r i g i n a l data may be s u f f i -c i e n t i n some cases (e.g. Ashton 1964, c i t e d i n Grieg-Smith 1971; A u s t i n and Grieg-Smith I968). Although I e l i m i n a t e d s e v e r a l species, many other apparently minor 75 zooplankton species were r e t a i n e d f o r a n a l y s i s . Species present i n low but meaningful numbers may s t i l l be good i n d i c a t o r s of s u b t l e f l u c t u a -t i o n s w i t h i n the community. F o r example, Lewis and Ramnarine ( l Q 6 ° ) and Lewis et a l . (1971, 1972) have shown th a t the e a r l y developmental stages of Euchaeta japonica ( = Pareuchaeta elongata i n my a n a l y s i s ) a a r e s e n s i -t i v e t o i n t e r a c t i o n s of t r a c e metals w i t h types of d i s s o l v e d organic substances i n sea .water. F i e l d p o pulations of P. elongata may r e a c t t o changes i n these agents sooner than such d i f f e r e n c e s can r e a d i l y be measured. Other species probably r e a c t s i m i l a r l y t o t r a c e metal/organic i n t e r a c t i o n s and t o other f a c t o r s which i n f l u e n c e "water q u a l i t y " . Reac-t i o n s of i s o l a t e d species can thus be important as they might i n d i c a t e a change t h a t w i l l e v e n t u a l l y a f f e c t the whole community. I t i s consequently b e t t e r t o e r r on the si d e of r e t a i n i n g more species than necessary than on that of d i s r e g a r d i n g p o s s i b l y important s p e c i e s . The species which were disregarded at t h i s i n i t i a l stage of the data manipulation were present i n such low numbers as to be of l i t t l e value f o r s t a t i s t i c a l comparison with other species or with p h y s i c a l parameters. As a r e s u l t , the community as described i n t h i s t h e s i s can be considered t o c o n s i s t of a block of 29 groups f o r which r e l i a b l e data could be obtained. This l i s t can be f u r t h e r reduced t o the core species l i s t i f i t i s d e s i r e d t o examine e i t h e r trends known t o be common t o the whole community or trends w i t h i n major species. D i v e r s i t y and m u l t i p l e c o r r e l a t i o n a n a l y s i s I t i s p r e f e r a b l e t o r e t a i n the maximum number of species i n the i n i t i a l stages of a n a l y s i s i f the i n t e n t of the i n i t i a l methods i s to 76 obtain an overview of the community. D i v e r s i t y i s such an a n a l y t i c a l method. I t i s s e n s i t i v e t o both the number of species and the number of i n d i v i d u a l s , and consequently the best estimate of d i v e r s i t y w i l l be based not on a reduced data block, but on a b l o c k of as many species as p o s s i b l e . On t h i s b a s i s , the d i v e r s i t y of the overwintering zooplankton community of the S t r a i t of Georgia was almost constant w i t h i n the sampling p e r i o d . Since d i v e r s i t y i s not a species s p e c i f i c measurement, an ap-parent constancy i n d i v e r s i t y does not imply a l a c k of change i n e i t h e r the species composition of the t o t a l p o p u l a t i o n of the community. I t does suggest, however, t h a t any changes which have occurred have tended t o o f f s e t each other, with no trend towards more or fewer s p e c i e s , or towards higher or lower a c t u a l numbers. The c o r r e l a t i o n matrix a l s o suggests a r e l a t i v e l y s t a b l e community, and supports the i m p l i c i t assumption t h a t the zooplankton assemblage with which I am d e a l i n g may be c a l l e d a community. The predominance of p o s i -t i v e c o r r e l a t i o n c o e f f i c i e n t s suggests a f a i r l y c l o s e l y k n i t group of organisms, but there are few s t r i k i n g r e l a t i o n s h i p s w i t h i n the matrix. The most obvious f e a t u r e i s the closeness of the r e l a t i o n s h i p s among the amphipod s p e c i e s . Each species i s p o s i t i v e l y c o r r e l a t e d w i t h the others, and thus t h e i r p o p u l a t i o n * , f l u c t u a t i o n s may be r e g u l a t e d by f a c t o r s which a f f e c t c h a r a c t e r i s t i c s common to a l l members of the group. There i s no immediate i n d i c a t i o n of what these f a c t o r s might be; however, feeding h a b i t s are u n l i k e l y to be d i r e c t l y i n v o l v e d . Euprimno a b y s s a l i s . i s equipped f o r r a p t o r i a l f e e d i n g while the other species are equipped f o r f i l t e r f e e d i n g . S i m i l a r l y , the v e r t i c a l d i s t r i b u t i o n p a t t e r n s of the s p e c i e s are d i f f e r e n t . 77 Aside from e s t a b l i s h i n g the i n t e r c o r r e l a t i o n between amphipod spe c i e s , the c o r r e l a t i o n a n a l y s i s does not gi v e much i n s i g h t i n t o the s t r u c t u r e of the zooplankton community. I t would be more u s e f u l t o com-pare the c o r r e l a t i o n s t r u c t u r e of the community over d i f f e r e n t time p e r i o d s . This would r e q u i r e a c q u i s i t i o n of enough data t o generate a s e r i e s of c o r r e l a t i o n matrices,- each r e p r e s e n t i n g the i n t e r c o r r e l a t i o n s of the species over a f o u r or f i v e year p e r i o d . I f these two-dimensional matrices were arranged along a temporal!'.axis, they would form a three-dimensional ma t r i x amenable t o m u l t i v a r i a t e a n a l y s i s . The number and degree of s i g n i f i c a n t c o r r e l a t i o n s should change as the species con-verged towards or diverged from a more d i v e r s e community. I t might be p o s s i b l e t o d i s c o v e r trends i n the c o r r e l a t i o n s t r u c t u r e t h a t would be i n d i c a t i v e of s u b t l e s h i f t s i n the community s t r u c t u r e . The c u r r e n t l y a v a i l a b l e data are not s u f f i c i e n t t o f u r t h e r explore t h i s p o s s i b i l i t y . C l u s t e r a n a l y s i s C l u s t e r a n a l y s i s generates the f i r s t concrete p i c t u r e of the s t r u c t u r e of the zooplankton community. The c l u s t e r s w i t h i n which the p a r t i t i o n e d months f a l l are s t r o n g l y a s s o c i a t e d with the p a r t i t i o n i n g . The c l o s e s t a s s o c i a t i o n s are w i t h i n r e g i o n s of thexwater column. For example, near surface samples are c l u s t e r e d together r a t h e r than samples from the whole water column taken i n the same month. Although t h i s pat-t e r n of a s s o c i a t i o n suggests t h a t s p a t i a l separation i s more important i n determining r e l a t i o n s h i p s than i s temporal se p a r a t i o n , i t i s l a r g e l y the r e s u l t of the a r t i f i c i a l p a r t i t i o n i n g of the water column. R e l a t i o n s h i p s w i t h i n each of the three groups are more l i k e l y t o r e f l e c t the presence 78 of temporal trends i n the zooplankton and t o be unaffected by the p a r t i -t i o n i n g . The segregation of the deep water samples i s apparently based on the f a c t t h a t they are temporally separated. There i s a group w i t h i n the deep water c l u s t e r , and separable a t a s i m i l a r i t y l e v e l of O.63, t h a t contains a l l of the samples taken a f t e r November 1971• October and December I969 form a second d i s c r e t e group at t h i s l e v e l , while the r e -mainder of the samples form a t h i r d group. Although the temporal groupings of the intermediate water data are l e s s d i s t i n c t , the l a s t three intermediate water samples taken d u r i n g the survey are grouped, as are s i x of the f i r s t e i g h t samples. In near sur-f a c e water there i s a l s o evidence of temporal separation w i t h i n the data. November and December 1971 are c l u s t e r e d with December 1972. In a d d i t i o n , December 1973 and 1974 are grouped with November 1973; however, November I969 i s a l s o c l u s t e r e d w i t h t h i s group. The general i n d i c a t i o n from these groupings i s t h a t recent deep water samples are separable from e a r l i e r samples, and t h a t t o a l e s s e r extent intermediate and near surface samples may be s i m i l a r l y separable. There i s a l s o an i n d i c a t i o n t h a t grouping of s i m i l a r months occurs f o r intermediate and deep water samples. Intermediate depth samples from November 1969, 1970 and 1971 are grouped, as are the corresponding three samples i n deep water. This grouping probably r e f l e c t s a r e a l s i t u a t i o n , as November and December represent s l i g h t l y d i f f e r e n t p o i n t s i n the annual c y c l e of the community. The f a c t t h a t t h i s shows up i n the c l u s t e r i n g process supports the a b i l i t y of c l u s t e r a n a l y s i s t o d i s -c r i m i n a t e a s s o c i a t i o n s w i t h i n a data s e t . C l u s t e r i n g of species a i s o produces groups t h a t are d i s t r i b u t i o n 79 o r i e n t e d r a t h e r than time o r i e n t e d . The deep water species form a par-t i c u l a r l y d i s t i n c t group. Species which have unusual v e r t i c a l d i s t r i b u -t i o n p a t t e r n s (e.g. A c a r t i a longiremus, which i s the only d i s t i n c t near surface species, and Aegina sp., the only other species absent from deep water) do not f i t i n with any c l u s t e r . Species c l u s t e r s are a l s o p a r t l y r e l a t e d t o the p a r t i t i o n i n g of the data; however, s i n c e the p a r t i t i o n i n g r e f l e c t s the a c t u a l v e r t i c a l d i s t r i b u t i o n p a t t e r n s of the species, the c l u s t e r i n g i s as i n d i c a t i v e of the s t r e n g t h of the d i s t r i b u t i o n a l a s s o c i a -t i o n s as i t i s of the p a r t i t i o n i n g method. C l u s t e r a n a l y s i s suggests that the community i s h i g h l y s t r u c t u r e d . The s p a t i a l arrangement of the species i s apparently more important than are temporal changes i n community s t r u c t u r e , and t h e r e has been no tempor-a l s h i f t of s u f f i c i e n t i n t e n s i t y t o d i s r u p t the b a s i c p a t t e r n of the community. Canonical c o r r e l a t i o n a n a l y s i s C l u s t e r a n a l y s i s i n d i c a t e s the importance t o the community of the v e r t i c a l d i s t r i b u t i o n of species w i t h i n the water column. The e f f e c t of the hydrographic regime on species grouped by t h i s c r i t e r i o n can be c l a r i f i e d by c a n o n i c a l c o r r e l a t i o n a n a l y s i s . The importance of tempera^, t u r e and s t a b i l i t y f a c t o r s i n t h i s a n a l y s i s i s i n t r i g u i n g . Only 5 of 24 s i g n i f i c a n t c a n o n i c a l a c o r r e l a t i o n s are w i t h s a l i n i t y , and none of the s a l i n i t y f a c t o r s can account f o r greater than 34% of the corresponding zooplankton v a r i a n c e . Temperature, however, appears t o be p a r t i c u l a r l y important. The most obvious temperature e f f e c t i s on Calanus marshallae. I t appears that the overwintering p o p u l a t i o n of t h i s species i s a s s o c i a t e d 80 w i t h or a f f e c t e d by temperature v a r i a t i o n a t a l l times of the year, w i t h at l e a s t 79% of the zooplankton variance expressed i n the appropriate temperature f a c t o r . Group 1 (Euphausia p a c i f i c a , Nanomia b i j u g a , Pareu-chaeta elongata ( t o t a l and mature), and S a g i t t a elegans) i s a l s o a f f e c t e d by temperature throughout the year and by s a l i n i t y and s t a b i l i t y a t cer-t a i n times as w e l l ; however, the amount of zooplankton variance t h a t i s expressed i n the appropriate hydrographic f a c t o r i s low, never exceeding 27%. The phase r e l a t i o n s h i p s between zooplankton and hydrographic para-meters u n d e r l i n e the r o l e of the hydrographic regime i n determining the s i z e of the o v e r w i n t e r M g populations of many zooplankton s p e c i e s . The importance of hydrographic c o n d i t i o n s i n t h i s respect i s not unusual, but hydrographic c o n d i t i o n s three months previous appear t o be as impor-t a n t as, or perhaps more important than, hydrographic c o n d i t i o n s i n the preceding May and June, d u r i n g a time of high p r o d u c t i v i t y (Stephens et a l . 1969). Two hydrographic events are evident i n August and September t h a t might a f f e c t o verwintering populations of zooplankton. There i s a de-crease i n the d e n s i t y gradient i n near surface waters. The breakdown of the d e n s i t y s t r a t i f i c a t i o n r e s u l t s from the c o o l i n g of near surface water due t o atmospheric c o o l i n g , from the i n c r e a s e i n surface s a l i n i t i e s caused by reduced f r e s h water r u n o f f , and from wind induced mixing pro-cesses. As a r e s u l t , n u t r i e n t s again become a v a i l a b l e f o r a u t o t r o p h i c uptake and a secondary phytoplankton bloom may develop.iiin the f a l l ( T u l l y and Dodimead 1957)• The extent of t h i s secondary bloom w i l l be a f u n c t i o n of the t i m i n g of the appearance of s u f f i c i e n t mixing to renew the n u t r i e n t s 81 i n the euphotic zone. I f the d e n s i t y gradient breaks down l a t e r than usual, n u t r i e n t s may not become a v a i l a b l e u n t i l the daylength has de-creased s u f f i c i e n t l y t o s e r i o u s l y hamper a u t o t r o p h i c production. Such :a decrease i n primary production would have a d e t r i m e n t a l e f f e c t on h e r b i -vorous species which must accumulate reserves of body l i p i d s t o maintain themselves over the winter. Conversely, an e a r l y r e t u r n i t o v e r t i c a l homogeneity could r e s u l t i n a l a r g e f a l l bloom t h a t would be b e n e f i c i a l to many species. The second hydrographic event o c c u r r i n g i n August/September i s the annual i n t r u s i o n of warm, high s a l i n i t y deep water i n t o the S t r a i t of Georgia. The c h a r a c t e r i s t i c s of the i n t r u d i n g water are d e r i v e d from both incoming Juan de Fuca intermediate water and f r e s h water r u n o f f t h a t are mixed together i n the Southern Approaches (Waldichuk 1957') • I n my data, t h i s i n t r u s i o n i s normally apparent i n August i n deep water, and i s always apparent i n September i n water below 200-300 m. By November/ December, the extent of the deep water mass has increased due t o f u r t h e r i n t r u s i o n s and t o mixing processes. The occurrence of the i n t r u s i o n suggests t h a t "water q u a l i t y " para-meters i n the S t r a i t of Georgia are changing. Data from Lewis • . . (1976) i n d i c a t e high n i t r a t e i n Juan de Fuca deep water, which makes up p a r t of the i n t r u d i n g water mass. Increases i n t h i s n u t r i e n t are of im-portance to f u t u r e phytoplankton pr o d u c t i o n . Lewis et a l . (I97i) have shown an increase i n the l a b o r a t o r y s u r v i v a l of the prefeeding stages of Pareuchaeta elongata i n sea water c o l l e c t e d d u r i n g the f a l l i n t r u s i o n . They suggest t h a t organic substances found i n the i n t r u d i n g water could be a f f e c t i n g the s u i t a b i l i t y of deep water f o r the s u r v i v a l of prefeeding 82 stages of P . elongata. Evans (1973), however, f e l t t h a t changes i n the s u r v i v a l of young stages of P. elongata were l e s s important than morta-l i t y of l a t e r l i f e ' - h i s t o r y stages, and th a t s u b t l e changes i n water q u a l i t y would not generate changes i n the po p u l a t i o n s i z e of the s p e c i e s . Evansi hypothesis does not reduce the s u i t a b i l i t y of young n a u p l i a r stages of the organism t o l a b o r a t o r y t e s t i n g f o r changes i n water q u a l i t y . Such changes may have s u b t l e e f f e c t s on other species or on the community as a whole. R e l a t i o n s h i p s between the hydrographic regime and zooplankton s i x months l a t e r appear t o a f f e c t a l l groups with the exception:of the "group" c o n s i s t i n g of Calanus plumchrus only (Group 4b). Since s p r i n g i s the op-timum r e p r o d u c t i v e p e r i o d f o r most zooplankton, the relationshipbbetween the hydrographic regime i n s p r i n g and overwintering zooplankton concentra-t i o n s i s probably connected t o re p r o d u c t i v e success. Calanus plumchrus i s known t o breed w e l l before the s p r i n g phytoplankton bloom (Gardner 1972). T h i s t i m i n g apparently a l l o w s i t t o graze the bloom more e f f i -c i e n t l y . The development r a t e of the younger stages appears t o be f l e x i -b l e and co-ordinated with the a v a i l a b i l i t y of phytoplankton('(Gardner 1972) . The a b i l i t y t o time development to c o i n c i d e w i t h increased primary produc-t i o n might make the younger developmental stages l e s s s u s c e p t i b l e t o vari-^ a t i o n i n the phytoplankton. The e a r l y developmentaof the p o p u l a t i o n might a l s o make i t l e s s s u s c e p t i b l e t o hydrographic v a r i a t i o n i n May and June. V a r i a t i o n s i n other species probably r e s u l t from a gre a t e r s e n s i t i v i t y to the e f f e c t s of the hydrographic regime on primary p r o d u c t i v i t y , which i n t u r n w i l l a f f e c t reproduction and s u r v i v a l of the next generation. In phase data a l s o suggest, t h a t both temperature and s t a b i l i t y 83: v a r i a t i o n s c o n t r i b u t e t o f l u c t u a t i o n s i n zooplankton species. Since there are no l a r g e - s c a l e hydrographic events d u r i n g the overwintering p e r i o d , i t i s d i f f i c u l t t o analyse the importance of s t a b i l i t y , or of any other hydrographic f a c t o r s , without l o o k i n g at more s p e c i f i c hydro-graphic/zooplanktonic r e l a t i o n s h i p s . Regression a n a l y s i s Regression s u p p l i e s some of the d e f i n i t i o n l a c k i n g i n the c a n o n i c a l a n a l y s i s at the expense of a l o s s of g e n e r a l i t y . The r e s u l t s support the conclusions based on the c a n o n i c a l c o r r e l a t i o n c o e f f i c i e n t s . In a d d i t i o n , the r e l a t i o n s h i p between hydrographic parameters at s p e c i f i c depths and s i n g l e zooplankton species can now be estimated. The l a r g e s t number of s i g n i f i c a n t r e l a t i o n s h i p s occurs w i t h s t a b i l i t y t hree months out of phase. Canonical a n a l y s i s f i r s t suggested the impor-tance of the hydrographic regime i n the l a t e summer, and r e g r e s s i o n ana-l y s i s now shows t h a t the s t a b i l i t y s t r u c t u r e of the water column i n l a t August and September i s important t o over 50% of the core species. Alsoso most a l l of the s t a b i l i t y v a r i a b l e s i n v o l v e d i n these r e l a t i o n s h i p s are near surface parameters. The d e n s i t y g r a d i e n t i n water deeper than 200 m i s extremely small ( c a . 0.002), and i s c l o s e r t o being a constant than a v a r i a b l e . Consequently, r e l a t i o n s h i p s between the s i z e of overwintering populations and the d e n s i t y s t r a t i f i c a t i o n of deep water are not s t a t i s -t i c a l l y r e a l i s t i c , and r e l a t i o n s h i p s between near surface s t a b i l i t y and zooplankton concentrations are more l i k e l y t o beimeaningful. Many of the species which are r e l a t e d t o near surface s t a b i l i t y are species found i n deep and intermediate water. I t i s i n i t i a l l y d i f f i c u l t 84 t o see the importance t o a deep water species of s t a b i l i t y i n near sur-f a c e water. The frequent occurrence of such a r e l a t i o n s h i p , however,• suggests t h a t i t i s b i o l o g i c a l l y important. The connection, i f r e a l , must be r a t h e r i n d i r e c t . Some p o s s i b i l i t i e s are discussed i n the f o l -lowing paragraphs. The r o l e of d e n s i t y s t r a t i f i c a t i o n i n the f a l l phytoplankton bloom probablybcontributes to the r e l a t i o n s h i p , and was considered i n d i s c u s -s i n g the c a n o n i c a l c o r r e l a t i o n b f t s e v e r a l zooplankton groups with the s t a b i l i t y of the whole water columnsin l a t e summer. A weakly s t r a t i f i e d water column would be more r e a d i l y broken down by mixing processes. In i n t e r p r e t i n g the c a n o n i c a l c o r r e l a t i o n i t was hypothesized t h a t e a r l y mixing would l e a d to e a r l y n u t r i e n t regeneration and a s u b s t a n t i a l f a l l bloom of phytoplankton. I f t h i s hypothesis were t r u e , then the slope of the r e l a t i o n s h i p between a zooplankton species and near surface s t a b i l i t y would be negative. High s t a b i l i t y would imply reduced phytoplankton, which i n t u r n would imply reduced overwintering populations of zooplank-ton. I n f a c t , f i v e of the eigh t r e g r e s s i o n equations do have negative slopes, supporting my hypothesis. Three s p e c i e s , however, i n c l u d i n g Calanus marshallae, have p o s i t i v e slopes with near surface s t a b i l i t y . These exceptions suggest thatoother f a c t o r s are inv o l v e d i n the r e l a t i o n -ship between zooplankton and the s t a b i l i t y s t r u c t u r e of the water column. The e f f e c t of water column s t r a t i f i c a t i o n on phytoplankton a f f e c t s overwintering zooplankton populations i n d i r e c t l y , s i n c e the phytoplankton are more a v a i l a b l e i n e a r l y f a l l . A mechanism can be p o s t u l a t e d by which near surface s t a b i l i t y i n August and September can more d i r e c t l y a f f e c t the overwintering p o p u l a t i o n s of deep water s p e c i e s . 85 Near surface s t a b i l i t y i n d i r e c t l y i n d i c a t e s the degree of mixing between f r e s h water r u n o f f and incoming deep water. I n s o l a t i o n pro-cesses i n near surface water a l s o a f f e c t the s t a b i l i t y s t r u c t u r e , but are not connected with r u n o f f . The r e l a t i v e importance of temperature and s a l i n i t y to d e n s i t y g r a d i e n t s can be estimated from my data by c a l c u l a -t i n g the c o r r e l a t i o n between s t a b i l i t y and the two hydrographic parameters s e p a r a t e l y . This c o r r e l a t i o n shows th a t near surface s t a b i l i t y i s more h i g h l y c o r r e l a t e d w i t h the corresponding s a l i n i t y g r a d i e n t ( r = O.98, p^O.Ol) than with the temperature gradient ( r = O.76, p<;0.0l). Hence the s t a b i l i t y i s a good approximation of the s a l i n i t y g r a d i e n t i n near surface water. High s t a b i l i t y i n near surface water i m p l i e s high r u n o f f . Increased r u n o f f i m p l i e s t h a t more f r e s h water i s a v a i l a b l e f o r mixing and bottom water formation. Hence the c o n t r i b u t i o n of near surface water t o the deep water mass w i l l be g r e a t e r . Conversely, i n a year w i t h l e s s than average: r u n o f f and a lower d e n s i t y gradient i n near surface water, l e s s f r e s h water w i l l be a v a i l a b l e f o r mixing and the c o n t r i b u t i o n of surface water t o the deep water mass w i l l be decreased. This i s a tenuous sug-gest i o n at best, and i s d i f f i c u l t ! , i f not impossible, t o q u a n t i f y . How-ever, the time l a g i n v o l v e d i n t h i s case Is three months. The formation of bottom water i n the S t r a i t of Georgia predates the i n t r u s i o n a t Geo 1748 by about two t o three months (Lewis et a l . 1971; Evans 1973; Gardner unpub.). This t i m i n g suggests t h a t near s u r f a c e events i n J u l y and August d i r e c t l y i n f l u e n c e the composition of bottom water at Geo 1748 i n November and December, and supports the r e l a t i o n s h i p between near surface events i n l a t e summer and overwintering deep water zooplankton species. T h i s 86 more d i r e c t r e l a t i o n s h i p , a c t i n g i n conjunction w i t h the e f f e c t of s t a b i -l i t y on phytoplankton, can account f o r much of the r o l e of the hydrogra-p h i c regime i n August and September on the overwintering zooplankton. Temperature r e l a t i o n s h i p s three months out of phase are a l s o of i n t e r e s t . A l l three of the amphipod species i n the core species l i s t a re i n v e r s e l y r e l a t e d t o temperature a t 50 m. The high degree of i n t e r c o r -r e l a t i o n i n these species was shown p r e v i o u s l y i n the c o r r e l a t i o n analy-s i s . I t appears t h a t near surface temperatures i n l a t e summer are r e l a -ted t o t h i s i n t e r c o r r e l a t i o n ? but i t i s d i f f i c u l t to see how t h i s might have come about. The maximum concentrations of the three amphipod species are i n d i f f e r e n t regions of the water column d u r i n g overwintering, so the connection may be very i n d i r e c t , and will-meed f u r t h e r study before i t can be r e s o l v e d . Regressions with hydrographic data i n phase and s i x months, out of phase each generate a s i m i l a r number of s i g n i f i c a n t r e g r e s s i o n equations, but no s i n g l e parameter has a m a j o r i t y of the r e g r e s s i o n s i n the way t h a t s t a b i l i t y data dominated the r e l a t i o n s h i p s of zooplankton with hydrographic data three months out of phase. There are few obvious r e l a t i o n s h i p s . The hydrographic regime i n s p r i n g a f f e c t s the ultimate-s i z e of overwintering populations of zooplankton, but the mechanisms are d i f f i c u l t t o unravel because of the complexity of events i n the i n t e r -vening time p e r i o d . The success of breeding may be i n v o l v e d , p a r t i c u l a r l y i n those species w i t h annual l i f e c y c l e s . The i n t e n s i t y of the s p r i n g bloom w i l l a l s o be i n v o l v e d as i t w i l l determine the a v a i l a b i l i t y .of food f o r the herbivores d i r e c t l y and the ca r n i v o r e s i n d i r e c t l y . In phase r e g r e s s i o n s are c h a r a c t e r i z e d by r e l a t i o n s h i p s between deep 87 water temperature and deep water s p e c i e s . S a l i n i t y and s t a b i l i t y r e l a V t i o n s h i p s are reduced and a f f e c t only a few s p e c i e s . The r e g r e s s i o n s of Calanus plumchrus and C. marshallae against temperature are p a r t i c u l a r l y important. The i n v e r s e nature of the r e l a t i o n s h i p s suggests temperature, or a temperature r e l a t e d f a c t o r , as the d r i v i n g f o r c e behind the f l u c t u -a t i o n s of the two species-. I t i s p o s s i b l e t h a t the f a c t o r s generating the f l u c t u a t i o n s a f f e c t only one of the two s p e c i e s , and t h a t the other species increases or d e c l i n e s a c c o r d i n g l y y The egg production of Calanus species i s on the order of 200-300 eggs d u r i n g the breeding season (Mar-s h a l l and Orr 1955b), s u f f i c i e n t f o r C ...-marshallae t o increase i n number s o l e l y due t o the f a v o r a b l e c o n d i t i o n s generated by a d e c l i n e i n Calanus  plumchrus, and t o a l l o w such an i n c r e a s e t o occur without a n o t i c e a b l e time l a g . Conversely, a change i n a f a c t o r l i m i t i n g only the p o p u l a t i o n d e n s i t y of C. marshallae might a l l o w C. marshallae t o increase i n numbers t o the detriment of C. plumchrus. E i t h e r of these p o s s i b i l i t i e s could create an a r t i f i c i a l r e g r e s s i o n between the second species and tempera-t u r e , but would not m a t e r i a l l y a l t e r the f a c t t h a t temperature or a tem-perature r e l a t e d f a c t o r was r e s p o n s i b l e f o r the f l u c t u a t i o n s i n number. The f a c t t h a t a temporal trend common to the whole zooplankton community e x i s t s , as w i l l be d i s c u s s e d l a t e r , s t r o n g l y supports the hypothesis t h a t the f a c t o r s r e s p o n s i b l e f o r f l u c t u a t i o n s i n number are a c t i n g on the community as a u n i t , r a t h e r than on i n d i v i d u a l s p e c ies. In the case of Calanus plumchrus and Calanus marshallae, a suffi-:V. c i e n t l y abnormal temperature might s h i f t the e q u i l i b r i u m between the species s u f f i c i e n t l y t h a t one species could r e p l a c e the other. Informa-t i o n t o be discussed i n the l a b o r a t o r y r e s u l t s suggests t h a t the 88 replacement of C. marshallae by G. plumchrus i s more l i k e l y t o occur than the replacement of G. plumchrus by G. marshallae. F a c t o r and p r i n c i p a l components a n a l y s i s F a c t o r a n a l y s i s and p r i n c i p a l components a n a l y s i s both i n d i -cate the degree t o which the o r i g i n a l d a t a could conceivably have been reduced i f the i n t e r a c t i o n s of i n d i v i d u a l species had not been c o n s i -dered as important as the i n t e r a c t i o n s of groups of species. The f a c t o r a n a l y s i s i n d i c a t e s a considerable amount of redundancy i n the zooplankton data. The f i r s t 8 f a c t o r s y i e l d almost a l l of the variance i n a zooplankton matrix of 32 groups. F u l l y h a l f of the t o t a l v a r i a n c e i s contained In two f a c t o r s which can be roughly estimated by as few as f o u r key species. The composition of the f a c t o r s supports e a r l i e r conclusions based on r e g r e s s i o n and c a n o n i c a l a n a l y s i s . The f i r s t f o u r f a c t o r s are d i s t r i b u t i o n o r i e n t e d . The a s s o c i a t i o n of deep water species with the f i r s t f a c t o r , which yieldss34% of the zooplankton v a r i a n c e , i n -d i c a t e s the dominance of deep water species i n the. community. Species w i t h deep water maxima dominate the t h i r d f a c t o r as w e l l , and c o n t r i b u t e h e a v i l y t o the second. The f o u r t h f a c t o r , however, i s a s s o c i a t e d only w i t h species having maximum concentrations at. intermediate depths. There i s no f a c t o r s p e c i f i c a l l y r e l a t e d t o species found p r i m a r i l y i n near sur-f a c e or both near surface and intermediate water. These species aree a s s o c i a t e d with the f i r s t f a c t o r , on which they have high negative l o a d i n g s . R e - f a c t o r i n g the 13 species a s s o c i a t e d w i t h the f i r s t f a c t o r confirms t h a t i t i s p r i m a r i l y a s s o c i a t e d w i t h deep water species, but i n d i c a t e s 89 t h a t the near surface species should not be disregarded as they can account f o r approximately Jk% of the v a r i a n c e a s s o c i a t e d with the f a c t o r . F u r t h e r d i v i s i o n s w i t h i n t h i s group of 13 species appear t o be a s s o c i a t e d w i t h s p e c i f i c d i s t r i b u t i o n p a t t e r n s . The second f a c t o r i n g does not y i e l d much new information on the community s t r u c t u r e , but suggests which species could best be used t o represent the f i r s t major f a c t o r of the whole species matrix. Using inf o r m a t i o n generated by the f a c t o r a n a l y s i s , and the v e r t i c a l d i s t r i b u -t i o n p a t t e r n s i n d i c a t e d by other analyses, a small group of species can be s e l e c t e d which are r e p r e s e n t a t i v e of the general community. Such a group might cont a i n Calanus plumchrus, Pseudocalanus minutus, A c a r t i a  longiremus, S a g i t t a elegans, Euphausia p a c i f i c a , Limacina sp. and Oithona  s p i n i r o s t r i s . These seven species, which are a l l V r e a d i l y i d e n t i f i e d , are the major r e p r e s e n t a t i v e s i n f a c t o r s accountingffor 75% of the variance i n the zooplankton community. Use of these species only would not e l i m i n a t e s o r t i n g samples completely, but could a c t as a p r e l i m i n a r y check. I f data from t h i s b l ock of species i n d i c a t e d g r e a t e r than usual v a r i a t i o n i n the overwintering zooplankton, or changes i n the r e l a t i o n s h i p s between major species, then i t might be a d v i s a b l e t o s o r t and count samples more tho-roughly. Otherwise, the amount of work i n v o l v e d i n monitoring the zoo-plankton community could be g r e a t l y decreased. In many cases, zooplankton monitoring programmes are not species s p e c i f i c , and y i e l d data such as "wet weight biomass of t o t a l zooplank-ton", " t o t a l copepods", "zooplankton displacement volume" or s i m i l a r measures of abundance (e.g. Stephens et a l . I969). When i n d i v i d u a l species are monitored, the species arecoften chosen s u b j e c t i v e l y r a t h e r than 90 o b j e c t i v e l y . There can be considerable merit t o these approaches, depen-d i n g on the purposes f o r which the data are c o l l e c t e d ; however, i t i s dangerous t o lump species haphazardly. F a c t o r a n a l y s i s provides an ob-j e c t i v e c r i t e r i o n f o r s e l e c t i n g key species when- i t i s n e i t h e r l o g i s t i c c a l l y nor economically f e a s i b l e t o monitor a l l species. Other c r i t e r i a , such as the economic importance of c e r t a i n species, or the c o n t r i b u t i o n of a species to the community biomass, could a l s o be considered, but i f the o b j e c t i v e i s t o monitor the community r a t h e r than p a r t i c u l a r s p ecies, i t i s e s s e n t i a l t h a t the species chosen be r e p r e s e n t a t i v e of t h a t commu-n i t y . These suggestions are p r i m a r i l y designed f o r the monitoring of year t o year v a r i a t i o n w i t h i n the zooplankton,. l2They.tcouldiberadapt,edDtOiT.an°; examinatiohoof seasonal v a r i a t i o n , but i t would probably be more d i f f i c u l t t o s e l e c t species which adequately represent the community throughout the year. I t would a l s o be b e t t e r t o monitor a l a r g e r number of species i n a seasonal survey i f species s p e c i f i c d a t a were r e q u i r e d , as might be the case i n a study of species succession, or i n a b a s e l i n e study. S i m i l a r d a ta r e d u c t i o n methods can be a p p l i e d t o the monitoring of hydrographic v a r i a b l e s , but the gain i s not as appreciable as the number of hydrographic .variables i s normally already reduced due t o the l o g i s t i c s of data c o l l e c t i o n and the p r e l i m i n a r y s e l e c t i o n of represen-t a t i v e depths. As a r e s u l t , p r i n c i p a l components a n a l y s i s of my data i n -d i c a t e s t h a t there i s l e s s redundancy i n the m a t r i x of hydrographic data than there was i n the zooplankton d a t a . The data are very s t r o n g l y r e l a t e d t o the water column s t r u c t u r e at Geo 17^8. This r e l a t i o n s h i p i s not unexpected, as the d i v i s i o n of the water column at t h i s s t a t i o n 91 i n t o three separate bodies of water i s w e l l known (e.g. Gardner 1972). However, water masses are more normally designated by i n s p e c t i o n of a s e r i e s of t e m p e r a t u r e / s a l i n i t y curves from the area under i n v e s t i g a t i o n . P r i n c i p a l components a n a l y s i s can be used e i t h e r as a check on a r b i t r a r y d e s i g n a t i o n of regions w i t h i n the water column or as a method f o r de-f i n i n g such regions from c o l l e c t e d data. The method could a l s o be used i n the d e s c r i p t i o n ^ of: water masses i n the open ocean. The d i f f i c u l t y x with using p r i n c i p a l components a n a l y s i s i n t h i s manner i s t h a t both regions of the water column and t r u e water masses are d e f i n e d on the b a s i s of two u s u a l l y independent v a r i a b l e s , n e i t h e r of which i s n e c e s s a r i l y s u f f i c i e n t i n i t s e l f . Taking the p r i n c i p a l components of temperature and s a l i n i t y s e p a r a t e l y and comparing the r e s u l t s would be one p o s s i b l e way t o determine the s t r u c t u r e of the whole block of hydrographic data. A l t e r n a t i v e l y , the frequency d i s t r i b u t i o n of a s e r i e s of two-dimensional squares (temperature x s a l i n i t y ) could be determined (e.g. Montgomery 1955. Hansen 1973) and analysed by p r i n c i p a l components methods. In most cases, t h i s treatment would probably be as tedious and time consuming as t r a d i t i o n a l methods. However, i n an area where waters from many d i f f e r e n t sources are i n t e r a c t i n g and c o n s t a n t l y s h i f t i n g , and a complex mass of data i s r e a d i l y accumulated and not so r e a d i l y d e c i -phered, s t a t i s t i c a l techniques of t h i s type would be more e f f i c i e n t i n d e f i n i n g and keeping t r a c k of water s t r u c t u r e . The o b j e c t i v i t y of p r i n -c i p a l components a n a l y s i s as compared w i t h t r a d i t i o n a l techniques, en-hances the appeal of s t a t i s t i c a l approaches to t e m p e r a t u r e / s a l i n i t y analy-s i s . As advanced computer technology makes such analyses more r e a d i l y a v a i l a b l e and l e s s cumbersome, they w i l l probably become more widely 92 accepted and used. They have the a d d i t i o n a l advantage of being more t r a c t a b l e t o modelling or t o numerical manipulation than t r a d i t i o n a l approaches. Wang and Walsh (1976), f o r example, have r e c e n t l y used p r i n c i p a l components a n a l y s i s ( e m p i r i c a l orthogonal f u n c t i o n a n a l y s i s i n t h e i r terminology) t o examine the h o r i z o n t a l and s p a t i a l temporal v a r i a t i o n s of an upwelling ecosystem. T h e i r data included values f o r su r f a c e tem-perature, c h l o r o p h y l l f l o u r e s c e n c e and n u t r i e n t d i s t r i b u t i o n s as w e l l as d e n s i t y and n u t r i e n t d i s t r i b u t i o n s w i t h i n the water column. They separated n u t r i e n t uptake processes from the dominant conservative pro-cesses, and were able t o d i s c u s s the l a r g e - s c a l e c h a r a c t e r i s t i c s of the upwelling ecosystem i n a meaningfullway. Wang and Walsh were concerned more with i s o l a t i n g i n f o r m a t i o n concerning the b i o l o g i c a l processes than with studying the p h y s i c a l processes. However, they suggest t h a t p r i n -c i p a l components a n a l y s i s i s a powerful t o o l f o r o b j e c t i v e l y a n a l y s i n g s e t s of oceanographic data. S t a b i l i t y data can be used i n a d d i t i o n t o temperature and s a l i n i t y d a t a t o check the boundaries of regions of the water column a t Geo 17^8. D e s p i t e the r e l a t i v e l a c k of s t a b i l i t y s t r u c t u r e below 200 m, the second s t a b i l i t y eigenvector, on which deep water s t a b i l i t y values have high l o a d i n g s , accounts f o r 35% of the va r i a n c e i n the ma t r i x of s t a b i l i t y d a ta. Such a high l o a d i n g i n d i c a t e s t h a t deep water d e n s i t y s t r u c t u r e should not be ignored d e s p i t e the almost n e g l i g i b l e d e n s i t y g r a d i e n t . The p r i n c i p a l components aloheado not g i v e much i n s i g h t i n t o tern-.-p o r a l trends i n the hydrographic regime. I f a s e r i e s of data s e t s , each covering s e v e r a l years', could be assembled, then changes i n i n t e r n a l 93 s t r u c t u r e might be manifested as changes i n the component s t r u c t u r e w i t h time. As w i t h c o r r e l a t i o n matrices, the c u r r e n t l y used data are not s u f f i c i e n t i n scope f o r t h i s type of a n a l y s i s . P r i n c i p a l components a n a l y s i s , however, generates inform a t i o n concerning the rank ordering of standardized cases on the d e r i v e d p r i n c i p a l components, and e s s e n t i a l l y i n d i c a t e s , i n order, the r e l a t i v e c o n t r i b u t i o n of each case t o each com-ponent . This i n f o r m a t i o n confirms the presence of a d e f i n i t e temporalt trend i n the hydrographic data monitored d u r i n g the study p e r i o d . The rankings on the f i r s t p r i n c i p a l component of temperature sepa-r a t e temperature data taken between October I969 and December 1970 from temperature data taken between November 1971 and December 197^ - This component represents 53% of the variance i n temperature, and i s a s s o c i a t e d more c l o s e l y w i t h temperatures from below 50 m. The h i g h ranking of data from the second h a l f of the sampling p e r i o d , a f t e r December 1970, on the f i r s t component of the temperature matrix, suggests t h a t most of the v a r i a t i o n i n the temperature data has occurred s i n c e the s t a r t of the f l u c t u a t i o n s i n Calanus plumchrus and C. marshallae, and was p r i m a r i l y a s s o c i a t e d with water below 50 m. The rankings on the f i r s t s a l i n i t y component, which accounts f o r 76% of the variance i n the s a l i n i t y matrix, separate I969 data from 1973 and I974 data, and suggest t h a t much of the s a l i n i t y v ariance i s a s s o c i a t e d with the f i r s t p a r t of the sampling p e r i o d . T h i s component i s a l s o more c l o s e l y a s s o c i a t e d with deep water than w i t h near surface water. S t a b i l i t y f a c t o r s are not as s t r o n g l y temporal i n t h e i r o r i e n t a t i o n . However, the rankings on s a l i n i t y / a r e the i n v e r s e of those on temperature. The highest rankings on the f i r s t temperature component go t o the most 94 recent months, while the highest rankings on the f i r s t s a l i n i t y component go t o the e a r l i e s t months. Since temperature and s a l i n i t y both i n f l u e n c e d e n s i t y , consistency i n the rankings on s t a b i l i t y components can not be expected. The p r i n c i p a l components a n a l y s i s of hydrographic data showed the presence of a year t o year trend i n the temperature and s a l i n i t y v a lues. P r i n c i p a l components a n a l y s i s of the zooplankton data adds t o the evidence f o r a temporal s h i f t . The p r i n c i p a l components of the core zooplankton species are l e s s s t r i k i n g than the f a c t o r s generated by the f a c t o r a n a l y s i s . S i m i l a r r e l a t i o n s h i p s between species groups and f a c t o r s are apparent, but there are nothigh f a c t o r l o a d i n g s , probably due t o r e s t r i c t i n g the analy-s i s t o core species and thus reducing the var i a n c e i n the matrix being f a c t o r e d . From the standpoint of temporal change, however, the i n t e r e s t t i n g and important p a r t of the p r i n c i p a l components a n a l y s i s of the zoo-plankton i s the ra n k i n g of the standardized cases on the components. The temporal s h i f t i s not as apparent i n the zooplankton m a t r i x as i t was i n the hydrographic d a t a . The f i r s t component, which accounts f o r 36% of the zooplankton variance, i s d i s t r i b u t i o n a l . I t r e i t e r a t e s the importance of deep water species groups w i t h i n the zooplankton community. The second component supports the f i r s t a a n d i n d i c a t e s t h a t 19% of the zoo-plankton variance i s a s s o c i a t e d w i t h intermediate depth samples which have no temporal a s s o c i a t i o n . The t h i r d component, however, has no obvious depth or species a s s o c i a t i o n s , yet accounts f o r 15% of the zooplankton va r i a n c e . I t i s s t r o n g l y temporally o r i e n t e d . The f i r s t 15 ranks go t o data from between December 1971 and December 1974. The lowest 12 ranks go t o data from between October I969 and December 1970. November and 95 December 1971. the months i n which the s h i f t i n Calanus plumchrus and C. marshallae was f i r s t noted, havebintermediate rankings. The temporally as s o c i a t e d zooplankton variance obviously o r i g i n a t e d at the same time as the i n i t i a l s h i f t i n the two Calanus species, and has been present s i n c e t h a t time. N e i t h e r Calanus nor any other species has a high l o a d i n g on the t h i r d ' f a c t o r ; however. JvThe temp or a l t trend i s a s s o c i a t e d more with the community i n general than with any p a r t i c u l a r s p e c ies. The t e m p o r a l i t y which i s evident i n the f a c t o r s of the two primary hydrographic parameters i s a mathematical expression of the changes i n S t r a i t of Georgia deep water which are represented i n F i g u r e s '3, 4 and •5. These f i g u r e s i n d i c a t e d a s h i f t i n deep water s a l i n i t y and a l e s s well—-' d e f i n e d s h i f t i n deep water temperature. The s t a t i s t i c a l analyses sug-gest temperature or temperature a s s o c i a t e d phenomena t o be the parame-t e r s ) which a f f e c t ( s ) the b i o l o g i c a l system the most, and a l l o w the changes i n hydrography to be more c l e a r l y d e f i n e d than i s p o s s i b l e from the raw data. 96 ASPECTS OF THE ECOLOGY OF THE APPARENTLY CO-OCCURRING SPECIES CALANUS PLUMCHRUS MARUKAWA AND C. MARSHALLAE FROST I n t r o d u c t i o n The apparent co-occurrence of congeneric species r a i s e s the p o s s i -b i l i t y t h a t competition may be o c c u r r i n g between them. According t o the c l a s s i c a l f o r m u l a t i o n of the competitive e x c l u s i o n p r i n c i p l e (Hardin i960) one of the species should, given s u f f i c i e n t time f o r an e q u i l i -brium t o be reached, r e p l a c e the other. This replacement w i l l not occur i f there are f a c t o r s which w i l l act t o separate the niches of the s i m i l a r ' s p e c i e s . There i s considerable controversy over the degree of importance which the competitive e x c l u s i o n p r i n c i p l e might have i n the " r e a l world". D i f f i c u l t i e s i n d e f i n i n g a nic h e f o r any one species, i n e v a l u a t i n g l i m i -t i n g resources, and i n e v a l u a t i n g the s t a b i l i t y of populations a l l con-t r i b u t e t o t h i s controversy. Hutchinson (I96I) suggests t h a t although the p r i n c i p l e may not be a p p l i c a b l e t o the plankton, the types of competition described i n the theory could s t i l l be present. The assumption underlying the c l a s s i c a l concept of competition i s t h a t there i s a common resource t h a t i s l i m i -t i n g . Congeneric species are more l i k e l y to co-occur i f the resources they e x p l o i t are p a r t i t i o n e d i n such a way as t o minimize the overlap between the areas which they u t i l i z e . Calanus marshallae and C_. plumchrus appear t o co-occur i n the S t r a i t of Georgia, and the f l u c t u a t i o n s which have been observed i n the numbers of the two species suggest the p o s s i b i l i t y t h a t the changes i n t h e i r p o p u l a t i o n s i z e s are l i n k e d and th a t G. marshallae may have increased i n numbers to the detriment of C. plumchrus (pers. obs.). The two species are m o r p h o l o g i c a l l y s i m i l a r , d i f f e r i n g p r i m a r i l y i n s i z e . They are both 97 l a r g e compared t o most other c a l a n o i d copepods. The prosome l e n g t h of the f i f t h copepodite stage of Calanus plumchrus i s 3.90+0.15 mm, while t h a t of C. marshallae i s 2.74+0.11 mm (mean + one standard d e v i a t i o n : Gardner, unpub.). Both species are herbivorous and they have s i m i l a r l i f e c y c l e s . The s i m i l a r i t y betweenithese two species suggests t h a t unless there are d i f f e r e n c e s between them which a l l o w them t o e x p l o i t non-overlapping niches, they may be i n competition. E c o l o g i c a l separation of outwardly s i m i l a r species may be due t o d i f f e r e n c e s i n d i s t r i b u t i o n , feeding or l i f e h i s t o r y . These parameters w i l l be examined to determine ifj/t'hey-c o n t r i B u t e t t o n i c h e t s e p a r a t i o n between the two copepod s p e c i e s . In a d d i -t i o n , the food value of the species w i l l be examined t o gain some a p p r e c i -a t i o n f o r the e f f e c t t h a t the change i n numbers i n the two species might have on higher t r o p h i c l e v e l s . 98 D i s t r i b u t i o n Representative Clarke-Bumpus tows were s o r t e d as p r e v i o u s l y d e s c r i b e d (pp. 20, 21) to e s t a b l i s h the v e r t i c a l d i s t r i b u t i o n of the two s p e c i e s . T h e i r d i s t r i b u t i o n s were known t o overlap h o r i z o n t a l l y i n the S t r a i t of Georgia from previous surveys,(Woodhouse 1971; Gardner 1972). 99 Feeding I n t r o d u c t i o n Feeding experiments w i t h Calanus plumchrus (Pandyan 1971; Gard-ner unpub.) i n d i c a t e t h a t the f i f t h copepodite stage (CV) feeds f o r only a s h o r t t t i m e before i t apparently ceases f e e d i n g and migrates i n t o deep water. Very young CV's and e a r l i e r copepodites are d i f f i c u l t t o obt a i n and are present f o r only a short time each year. In a d d i t i o n , f e e d i n g experiments w i t h copepods are extremely prone t o e r r o r and v a r i a t i o n . For these reasons, I have concentrated on measurements of the mechanical f e e d i n g a b i l i t y of Calanus plumchrus and C. marshallae• The process of f i l t r a t i o n i n copepods has been w e l l d escribed (Mar-s h a l l and Orr 1955b; Gauld 1964; M a r s h a l l 1973). The main f i l t e r i n g appendages are the second m a x i l l a e . These p a i r e d appendages form a " f i l t e r i n g basket" through which water i s passed. The a b i l i t y of the organism t o feed on p a r t i c l e s of a given s i z e range w i l l depend upon the smal l e s t openings i n the meshes of the f i l t e r i n g apparatus. The s i z e of these openings w i l l be a d i r e c t f u n c t i o n of the d i s t a n c e between i n d i -v i d u a l s e t u l e s on the setae of the second m a x i l l a . T h i s spacing i s termed the i n t e r - s e t u l e d i s t a n c e (ISD). Procedure The The second m a x i l l a e of s e v e r a l specimens-sof the f i f t h copepo-d i t e of Calanus plumchrus and G. marshallae were removed by mic r o - d i s s e c -t i o n and mounted on g l a s s s l i d e s i n CMC-S, a non-resinous s t a i n i n g moun-t a n t . The m a x i l l a e were examined and d i v i d e d i n t o zones w i t h i n which the ISD's were approximately uniform. The o u t l i n e of each m a x i l l a was 100 drawn to scale using a camera lucida mounted on a Wild M-20 compound microscope equipped with phase contrast. The relative area of each zone was measured from the drawings using a polar planimeter. Ten ISD's were used to calculate the mean ISD for each zone of each of twelve different maxillae. The f i l t e r i n g efficiency for particles of a given size was then calculated according to Nival and Nival's (1973) equation (Eqn 1). D, -x. k J n I . 2s. F ^ E P . I T * e 3 (Eqn 1) 1 j = l ^ 2 S j ( 2 T T ) 2 where: i s the f i l t e r i n g efficiency for particles of diameter D^ p . i s the proportion of the total f i l t e r i n g surface belonging 1 to the j zone X = x - 2s^ (two standard deviations below the mean ISD of zone l) i = x + 2s (two standard deviations above the mean ISD of zone 1) s i s the standard deviation of the ISD of zone ' j ' x. i s the mean ISD of zone ' j ' J Efficiencies calculated for Acartia c l a u s i i using this equation have shown a good f i t with the results of short term grazing experi-ments, and appear to be a good estimate of basic f i l t e r i n g a b i l i t y (Nival and Nival 1976). The results for Calanus plumchrus and C. marshallae were plotted as f i l t e r i n g a b i l i t y versus particle diameter, yielding a curve of theoretical mechanical feeding a b i l i t y . 101 Rearing and Breeding I n t r o d u c t i o n D i f f i c u l t i e s are often encountered i n s u c c e s s f u l l y maintaining p o p u l a t i o n s of zooplankton i n the l a b o r a t o r y (Kinne 1970). Although some success has been obtained w i t h c e r t a i n species (e.g. Z i l l i o u x and Wilson I966; H e i n l e 1969; Lewis and Ramnarine 1969; Borgmann 1973a, b ) , good l a b o r a t o r y data on zooplankton p o p u l a t i o n s are scarce. The evalua-t i o n of e c o l o g i c a l r e l a t i o n s h i p s between species, however, can be aided by l a b o r a t o r y d e r i v e d estimates of p h y s i o l o g i c a l r a t e s . The growth r a t e of a species may be important i n a l l o w i n g t h a t species t o e f f i c i e n t l y e x p l o i t i t s environment. Estimates of the growth r a t e may be r e a d i l y obtained i n the l a b o r a t o r y i f the species can be reared through one com-p l e t e l i f e c y c l e . Procedure Ovigerous females of each species were kept i n 150 ml t e s t tubes of f i l t e r e d sea water (Geo 1748, 350 m) i n an incubator a t 8 G. This temperature approximates ambient sea water temperatures i n the en-vironment. A f t e r egg l a y i n g , the a d u l t s were removed and the growth of the young stages observed. Water was changed a t f o u r t o f i v e day i n t e r -v a l s and the developing n a u p l i i were fed by the a d d i t i o n of phytoplankton. One s e r i e s (A) r e c e i v e d a mixture of I s o c h r y s i s sp. and D u n a l i e l l a sp. The other s e r i e s (B) re c e i v e d only I s o c h r y s i s sp. f o r the f i r s t two weeks, and then was f e d on the same regime as s e r i e s A. 102 Galorimetry I n t r o d u c t i o n The importance of copepods i n the food chain depends to a great extent on t h e i r l i p i d content, which has been e x t e n s i v e l y analysed (e.g. F i s h e r 1962; L i t t l e p a g e 1964; L i n f o r d 1965; Ackman et a l . 1970; Lee et a l . 1971, 1972, 1974; Wissing et a l . 1973). The l i p i d content of cope-pods consists.;.largely of wax e s t e r s (Nevenzel 1970; Lee et a l . 1971) and i n many species, the t o t a l l i p i d content shows an annual c y c l e , ( F i s h e r 1962; Gomita et a l . 1966). The s i z e d i f f e r e n c e between Calanus plumchrus and C. marshallae sug-gests t h a t t h e i r food value (expressed as a f u n c t i o n of l i p i d content) i s d i f f e r e n t . A p l a n k t i v o r e would need to graze a l a r g e r number of Calanus  marshallae than G_. plumchrus t o obtain an e q u i v a l e n t r a t i o n . This type of response has been demonstrated f o r j u v e n i l e salmon feeding on three s i z e ranges of prey (pink salmon: Parsons and LeBrasseur 1970; chum s a l -mon: LeBrasseur I969) • These salmon species showed both a preference f o r prey i n the s i z e range 2.5-4.5 mm i n t o t a l l e n g t h and an avoidance of s m a l l e r prey. The p r e f e r r e d length range u n f o r t u n a t e l y i n c l u d e s both C. plumchrus and C. marshallae; however, the general p a t t e r n of these r e s u l t s supports my contention t h a t a s h i f t t o a prey species of s m a l l e r average s i z e may be d e t r i m e n t a l . LeBrasseur (I969) d i d not f i n d any d i f f e r e n c e i n food value between the d i f f e r e n t s i z e ranges of prey. However, he judged food value on the b a s i s of observed growth i n f i s h which were f e d on three s i z e ranges of food i n a h i g h l y a r t i f i c i a l s i t u a t i o n . In the f i e l d , the major e f f e c t of a s h i f t i n prey s i z e might be t o increase the amount of energy expended 103 In g r a z i n g , and t o increase the g r a z i n g time necessary t o obtain an ade-quate r a t i o n . I n c r e a s i n g these f a c t o r s could conceivably push a preda-t o r y species c l o s e r t o a s i t u a t i o n i n which f u l l time g r a z i n g was not enough t o meet the metabolic demands of maintenance and normal growth. The s i z e d i f f e r e n c e s between the l a t e r copepodite stages of the two species might a l s o n e c e s s i t a t e a s h i f t i n the f e e d i n g s t r a t e g y of preda-t o r s . Leong and O'Gonnell (i960) show t h a t the northern anchovy f i l t e r feeds on s m a l l c p a r t i c l e s but uses a b i t i n g a t t a c k on l a r g e p a r t i c l e s . O'Connell (1972) f u r t h e r suggests t h a t f i l t e r f e e d i n g alone may not be s u f f i c i e n t to provide the f i s h with i t s r e q u i r e d r a t i o n , and t h a t l a r g e r prey are a necessary p a r t of the d i e t . In e i t h e r case, a l a r g e - s c a l e s h i f t i n the p o p u l a t i o n s i z e s of G_. plumchrus and G. marshallae may a f f e c t the s u r v i v a l of a predator which i s f o r c e d t o s h i f t to the sm a l l e r copepod as a food source. As a f i r s t approach to the problem of es t i m a t i n g p o s s i b l e e f f e c t s o f such a s h i f t , the c a l o r i f i c content of specimens of the two species was determined. Measurements of c a l o r i f i c value are more s u i t a b l e than measurements of l i p i d weight. Methods f o r e s t i m a t i n g t o t a l l i p i d s by e x t r a c t i o n rt-.qu r e q u i r e l a r g e r numbers of animals than c a l o r i m e t r y and are a l s o more subject t o e r r o r due to the d i f f i c u l t i e s of e x t r a c t i n g t o t a l l i p i d s ( L i n -f o r d 1965). R e s u l t s obtained by the c a l o r i m e t r y method are expressed as " c a l o r i e s l i b e r a t e d per mg f r e e z e - d r i e d weight". The resi d u e a f t e r burning i s n e g l i g i b l e (e.g. Wissing et a l . 1973)» and hence the r e s u l t s approximate u n i t s of " c a l o r i e s l i b e r a t e d per mg ash-free d r y weight". Carbon con-te n t may be expressed i n terms of c a l o r i f i c value ( r = O.98) by a simple 1C4 l i n e a r r e l a t i o n s h i p (Eon 2: P i a t t et a l . 1969). f a c i l i t a t i n g comparison with values reported i n the l i t e r a t u r e . cal/mg dry wt = 1351 + 106(%C) - Zl.Z(% ash) (Eqn 2) Procedure Samples of copepodites of both species were obtained i n the f i e l d and returned a l i v e t o the l a b o r a t o r y i n isotherms. In the l a b o r a -t o r y , specimens of each species were s e l e c t e d a t random, placed b r i e f l y on a p i e c e of b l o t t i n g paper t o remove excess water, and immediately f r o -zen. The f r o z e n samples were l a t e r f r e e z e - d r i e d f o r twenty-four hours and t h e i r c a l o r i f i c values determined using a P h i l l i p s o n Microbomb Calo-r i m e t e r (Comita and S c h i n d l e r I963)• Due t o the minimum weight r e q u i r e d f o r a n a l y s i s , approximately f i v e Calanus plumchrus or ten C. marshallae had t o be combined f o r each sample. This y i e l d e d samples of comparable weight (ca. 3-5 mg)• 105 Results Distribution Data from horizontal tows indicates that there i s almost 100% vertical overlap in the populations of the two species when they are overwintering (Fig. 10). During hatching and development of the next generation, the young stages of both species overlap in near surface water. Very young stages ( <Gopepodite III) can not be readily told apart; however, there i s no bimodal structure to the vertical distribution of young Galanus that might suggest vertical separation of the populations at this time (Gardner 1972). Feeding The second maxillae of Galanus plumchrus can be divided into three zones (Fig. 11; Table XV). Zone 1 takes up most of the f i l t e r i n g surface Table XV: Fi l t r a t i o n zone analysis of the second maxillae of Galanus  plumchrus and G. marshallae. Area i s expressed as per cent of total f i l t e r i n g area + one standard deviation. Zone G. plumchrus C. marshallae % of total area Mean ISD (um) % of. total area Mean ISD (ym) 1 2 3 4 . 74.2 + 4.7 2.4 + 0.4 20.8 + 4.7 4.2 + 0 . 9 5.0(approx.) 9-3 ± 2.3 68.9 + 6.4 5-3 ± 0.8 13-0 + 5.0 3.9 + 0.5 3.0 (approx.) 11.4 + 1.3 >- 15.0 •+ 5.2 12.4 + 1.1 Total 2 area (mm ) 0.450 + 0.103 0.107 + 0.019 106a Figure 10: V e r t i c a l d i s t r i b u t i o n of Calanus plumchrus and C. marshallae during overwintering. NOV 7 3 J A N ' 7 3 (0200) (1800) 10?a F i g u r e 11: Second m a x i l l a e of Calanus plumchrus and C. marshallae. Major d i s t i n c t f i l t e r i n g zones are shown i n o u t l i n e . The one " i n d i s t i n c t " zone f o r each species i s not shown (see t e x t f o r d e s c r i p t i o n ) . 107b OJ C 108 and has the smallest mesh size. Zone 2 consists of a f a i r l y distinct leading edge composed of the three or four d i s t a l setae. Zone t ^ r i s not sharply defined. It consists of a small number of heavy, strong setae found evenly dispersed along the maxilla. These setae have a very coarse mesh size and are so oriented that they cut across several of the setae of Zones 1 and 2. The effective area of f i l t r a t i o n of these setae could not be measured accurately, but was estimated to be 5% of the total effective f i l t e r i n g area. Calanus marshallae has four zones on the f i l t e r i n g surface; however, the distinction between the two finest zones and the two coarsest zones is minimal, and they intergrade more completely than the zones of Calanus  plumchrus. Zone 2, the withstheesmallest LSD's, covers only the proximal edge of the f i l t e r i n g surface. Zone h constitutes the d i s t a l edge,of t l . and zone 1, as in C. plumchrus, i s the largest zone and constitutes the central area of the f i l t e r i n g surface. Zone 3 i s analogous to zone 3 of Calanus plumchrus, and i s estimated to take up Jfo of the f i l t e r i n g sur~a face. When the curves of f i l t e r i n g efficiency are calculated and plotted (Fig. 12), i t i s obvious that Calanus plumchrus, despite having the larger body size, i s better equipped for f i l t e r i n g smalllparticles than i s G. marshallae. The curve for C. marshallae shows a plateau at 70% efficiency. This plateau i s caused by the separation between the regions of fine and coarse mesh. The actual f i l t e r i n g areas for the maxillae of the two species (Table XV) show that Calanus plumchrus has about four times the f i l t e r i n g area of C. marshallae• 109a Figure 12: F i l t e r i n g e f f i c i e n c y curveslfor.gCalanus  plumchrus and Galanus marshallae. 109b Diameter (pm) 110 Rearing and breeding Galanus marshallae could not be bred in the laboratory. Wood-house (1971) was also unsuccessful in breeding G. marshallae, although he did obtain f e r t i l i z a t i o n in one isolated instance. Galanus marshallae females returned to the laboratory from the f i e l d neither produced nor layed eggs, even though they could be kept in a controlled environment chamber for long periods of time without their condition noticeably de-teriorating . The l i f e history of Galanus plumchrus i s such that ovigerous females are readily available in January and February (Gardner 1972). Galanus  plumchrus females brought to the laboratory in an ovigerous condition shed their eggs and the eggs developed. Development through the third copepodite stage (CIIl) was common, but development to the f i f t h copepodite (CV) was unusual. Using development times obtained in the laboratory rT (Table XVl),aand inserting them into Winberg's (1956) equation (Eqn 3), rates were calculated for growth between successive stages (NB: naupliar stages were grouped) and for overall growth from both egg and f i r s t cope-podite to GV (Tables XVI, XVIl). where: %AW i s the per cent increment in wet weight per day W^  and Wg are the weights of the stages of the organism at the beginning and end of the growth interval t i s the time in days to go. ifrom stage 1 to stage 2 I l l Table XVI: Development times and growth r a t e s of Calanus plumchrus a t 8 C. Wet weights are der i v e d from measurements of f i e l d samples taken c o n c u r r e n t l y w i t h the l a b o r a t o r y s e r i e s . Times are based on 25 specimens f o r the young stages, and on 10 specimens f o r the o l d e s t stages ( o l d e r than the second copepodite). S e r i e s Stage Mean time Development time Mean wet %AW/day to f i r s t between successive weight appearance stages (days) (mg) (days) A Egg 7.0 0.003* CI 60.8 53-8 0.15 9-5 C I I 73.8 13.0 0.28 4.9 c m 78.4 4.6 0.52 14.4 CIV 87.8 9.4 1-39 11.0 CV 110.0 22.2 3.02 2-5 B Egg 10.0 0.003* CI 53-2 43.2 0.15 6-9, C I I 55-6 2.4 0.28 29.8 G U I 59-3 3-7 0.52 18.2 CIV 68.3 9.0 1.39 11.5 GV 86.5 18.2 3.02 3.0 *Data d e r i v e d from F u l t o n (1973) Table XVII: O v e r a l l growth r a t e s f o r Calanus plumchrus reared i n the la b o r a t o r y , expressed as % change i n weight per day. S e r i e s CI t o CV Egg t o CV A 6.3 6.9 B 9.4 9.4 112 C a l o r i m e t r y Seasonal v a r i a t i o n i n c a l o r i f i c values of e i t h e r species could not be detected. The average c a l o r i f i c values (Table XVIIl)^show t h a t there i s l i t t l e d i f f e r e n c e i n food value (expressed i n calories/mg) be-tween the two species; however, the d i f f e r e n c e i n r e l a t i v e s i z e of Calanus  plumchrus and Calanus marshallae r e s u l t s i n a l a r g e d i f f e r e n c e i n c a l o r i -f i c value per i n d i v i d u a l . Table X V I I I : Average c a l o r i f i c value per u n i t dry weight and per i n d i v i d u a l (+ one standard d e v i a t i o n ) . Cal/mg f r e e z e - d r i e d wt Calories/copepod (approx.) C. plumchrus 5.92 + 0.70 3.08 C. marshallae 6.16 + 0.-6-1-- • 1.23 113 D i s c u s s i o n The f i e l d data i n d i c a t e t h a t Galanus plumchrus and G_. marshallae have the same o v e r w i n t e r i n g ' d i s t r i b u t i o n p a t t e r n a t Geo 17^8. There i s no evidence f o r p h y s i c a l separation of the two species at t h i s or any other time of the year f o r which data are a v a i l a b l e . F r o s t (1974) d e s c r i b e s Galanus marshallae as o c c u r r i n g north of 40° north l a t i t u d e i n c o a s t a l a, and near shore waters of the eastern North P a c i f i c and B e r i n g Sea. Gala-nus plumchrus i s more widely d i s t r i b u t e d i n the North P a c i f i c (Geynrikh I968), but i s apparently found i n a l l of the areas from which Galanus  marshallae has been reported. I t i s probable t h a t the two species co-e x i s t throughout the range of Galanus. marshallae, although there i s l i t t l e d ata on the simultaneous d i s t r i b u t i o n of each species. Given the f a c t t t h a t they c o - e x i s t , we can i n v e s t i g a t e e c o l o g i c a l f a c t o r s which act t o reduce the p o s s i b i l i t y of competition between them. The major e c o l o g i c a l d i f f e r e n c e between the species i s i n t h e i r a b i l i t y t o f i l t e r p a r t i c l e s out of the surrounding water. A n a l y s i s of the primary f i l t e r i n g appendage, the second m a x i l l a , shows s i m i l a r i t i e s i n general s t r u c t u r e between the two species, but d i f f e r e n c e s i n f i n e s t r u c t u r e which a f f e c t the e f f i c i e n c y w i t h which small p a r t i c l e s can be removed from the water. Calanus plumchrus can t h e o r e t i c a l l y e x p l o i t the s i z e range of p a r t i c l e s of diameter 3 -7 ym almost without competition from G. marshallae, and maintains an advantage i n f i l t e r i n g a b i l i t y f o r p a r t i -c l e s between 7 and 12'>ym i n diameter. P a r t i c l e s of l e s s than 12 ym i n diameter have not been very w e l l s t u d i e d . They c o n s t i t u t e the lower range of the nanoplankton (2-20 um i n diameter: Parsons and Takahashi 1973)> and there are i n d i c a t i o n s t h a t 114 they make up a l a r g e p o r t i o n of the p a r t i c u l a t e organic biomass i n the marine ecosystem. Parsons (1972) concludes t h a t i n March and A p r i l the p r i n c i p a l primary producers i n the s u b a r c t i c P a c i f i c Ocean are nanoplank-ton i n the range 8-16 pm i n diameter. He a l s o shows secondary peaks of abundance f o r p a r t i c l e s of 4 pm i n diameter. Anderson (1965'). found t h a t a 5 pm f i l t e r r e t a i n e d as l i t t l e as 42% of the organic p a r t i c u l a t e s i n water c o l l e c t e d o f f the Oregon and Washington coasts, w h i le M c A l l i s t e r et a l . (I960) found t h a t i n summer, 75% of the c h l o r o p h y l l 'a' at ocean weather s t a t i o n "Papa" w i l l pass through a 10 ym f i l t e r . K i t chen et a l . (I975)f a l s o working o f f the Oregon coast, measured the numbers of par-t i c u l a t e s i n v a r i o u s s i z e c l a s s e s i n the range from 8-105 ym i n diameter. They of t e n found the peak biomass t o be at the lower l i m i t of t h e i r s i z e range, but d i d not l o o k at the biomass d i s t r i b u t i o n of p a r t i c l e s of diameter l e s s than 8 pm. L o c a l l y , Pandyan (1971) examined the volume of p a r t i c u l a t e matter a v a i l a b l e a t v a r i o u s depths i n v a r i o u s seasons i n Howe Sound, a body of water which opens d i r e c t l y i n t o the S t r a i t of Georgia. She found t h a t p a r t i c l e s i n near bottom water were g e n e r a l l y between 3-6 and 14.5 pm 5 7 i n diameter, and t h a t the t o t a l volume ranged from 10 t o 10 cubic pm per ml. De s p i t e evidence of the importance of s m a l l p a r t i c l e s t o the t o t a l biomass, they are not r e g u l a r l y included i n b i o l o g i c a l surveys and l i t t l -i s known about the types of p a r t i c l e which c o n t r i b u t e t o the s m a l l e r nanoplankton. K i t c h e n et a l . (.1^ 975) found a high c o r r e l a t i o n between p a r t i c u l a t e organic carbon and c h l o r o p h y l l ' a 1 , suggesting t h a t much of the p a r t i c u l a t e organic biomass i s phy t o p l a n k t o n i c . In a d d i t i o n , S e k i and 115 and Kennedy (1969) r e p o r t t h a t the l e v e l of marine b a c t e r i a and other he.terotrophs i n the S t r a i t of Georgia i s g e n e r a l l y s u f f i c i e n t f o r main-tenance of the zooplankton and i s consequently an important component of the organic p a r t i c u l a t e biomass. However, the only comprehensive examina-t i o n of the composition of the l o c a l phytoplankton which included very small p a r t i c l e s i s the work by Buchanan (1966) i n Indian Arm, a f j o r d type i n l e t near Vancouver. Unfortunately, Buchanan was not d i r e c t l y concerned w i t h the d i s t r i -b u t ion of d i f f e r e n t s i z e classes,,and r e p o r t s the s i z e s of species only as an adjunct t o t h e i r d e s c r i p t i o n and only f o r c e r t a i n s p e c ies. Buchanan found t h a t a l l of the predominant p l a n k t o n i c heterotrophs i n Indian Arm were i n the nanoplankton s i z e range (defined by Buchanan as 5-60 ym i n diameter, c f . Parsons and Takahashi 1973) °r sm a l l e r . He encountered 336 species, of which he considered 88 to be of major e c o l o g i c a l impor-tance. In many groups, the major species were l e s s than 10 ym i n d i a -meter. F o r example, i n the Ghrysophyceae, which Buchanan considered im-portant and connected with n u t r i e n t regeneration, at l e a s t 6 of the 15 species were under 10 ym i n diameter. S i m i l a r l y , a t l e a s t 50% of the major Haptophyceae were species under 6 un, and both major Ghlorophyceae were under 5 ym. These data g e n e r a l l y support the hypothesis t h a t very small ( i . e . l e s s than 12 um i n diameter) p a r t i c l e s are an important com-ponent of the l i v i n g organic p a r t i c u l a t e biomass of the S t r a i t of Georgia. The n o n - l i v i n g f r a c t i o n of the p a r t i c u l a t e matter must a l s o be con-si d e r e d as a n u t r i e n t source. N o n - l i v i n g organic p a r t i c u l a t e m a t e r i a l i s present i n l e v e l s much higher than the l e v e l of l i v i n g p a r t i c u l a t e s ( R i l e y 1970), but has been stud i e d l e s s . I t s n u t r i t i v e value has not 116 been e s t a b l i s h e d , but probably v a r i e s depending on i t s source and degree of degradation, and on the e f f i c i e n c y of the organism u t i l i z i n g i t . I n -g e s t i o n of small organic p a r t i c u l a t e s has been demonstrated f o r a number of copepod species. Corner et al.9(1.974) found t h a t overwintering C a l a -nus h e l g o l a n d i c u s could not o b t a i n s u f f i c i e n t n u t r i t i o n from n a t u r a l l e v l e v e l s of suspended matter i n sea water. However, the species could feed e f f i c i e n t l y on dead barnacle n a u p l i i . S i m i l a r l y , Paffenh '6f errand S t r i c k -land (1970) showed t h a t while C. h e l g o l a n d i c u s d i d not feed on " n a t u r a l d e t r i t u s " (e.g. unstructured m a t e r i a l such as organic aggregates), i t c could feed r e a d i l y on dead diatoms and would a l s o i n g e s t p o l y s t y r e n e b a l l s . Furthermore, P o u l e t (1976) has e s t a b l i s h e d t h a t n o n - l i v i n g organic p a r t i c u l a t e s are a b a s i c food f o r Pseudocalanus minutus. In s p i t e of the a v a i l a b i l i t y of small organic p a r t i c u l a t e s , i t i s commonly assumed t h a t copepods w i l l s e l e c t i v e l y feed on l a r g e p a r t i c l e s when they are a v a i l a b l e (e.g. M u l l i n 1963; Richman and Rogers 1969; Har-grave and Geen 1970). Most experiments on s i z e s e l e c t i v i t y are l a b o r a t o r y o r i e n t e d and i n v o l v e exposing the organism to concentrations of food much higher than are found i n the environment. P e t i p a (1965, c i t e d by M a r s h a l l 1973) suggests t h a t when feeding a c t i v e l y i n the sea, a copepod i s more l i k e l y to feed i n d i s c r i m i n a t e l y . M a r s h a l l (1973)1 i n an extensive review of the l i t e r a t u r e concerning feeding i n copepods, concludes t h a t although marine copepods often s e l e c t f o r l a r g e r c e l l s i z e s when gr a z i n g , t h e i r preferences are not f i x e d but can change t o take advantage of a v a i l a b l e food. Thus the approximation of the f i l t e r i n g net t o a "leaky s i e v e " (Boyd 1976) i s perhaps the most r e a l i s t i c approach t o take. The presence of a l a r g e biomass of p a r t i c l e s of diameter l e s s than 117 12 ym i n the S t r a i t of Georgia, and the a b i l i t y of C. plumchrus t o f i l t e r p a r t i c l e s as small as 2.0 ym i n diameter, suggests t h a t Galanus plumchrus can not vonly graze on a p o r t i o n of the p a r t i c u l a t e biomass u n a v a i l a b l e to G. marshallae, hut t h a t i t can obtain a l a r g e p r o p o r t i o n of i t s r a t i o n from s m a l l organic p a r t i c u l a t e s . Galanus plumchrus w i l l a l s o be able t o i n g e s t s m all i n o r g a n i c p a r t i -14 c u l a t e s . Vyshkvartseva and Gutel'makher (1971) allowed G - l a b e l l e d bac-t e r i a to adsorb onto c l a y p a r t i c l e s up to 18 ym i n diameter, and then allowed Galanus g l a c i a l i s (= C. marshallae?, see appendix A) t o graze the mixture. Galanus g l a c i a l i s was able t o i n g e s t the p a r t i c l e s and assimi?-l a t e the organic matter. The r i v e r s d r a i n i n g i n t o the S t r a i t of Georgia are a r i c h source of i n o r g a n i c p a r t i c u l a t e s . S e k i et a l . (I969) examined the c o n t r i b u t i o n to the S t r a i t of Georgia of p a r t i c u l a t e m a t e r i a l c a r r i e d by the Nanaimo R i v e r . They found t h a t i n l a t e winter, more than 90% of the p a r t i c u l a t e matter i n both the r i v e r and the estuary c o n s i s t e d of p a r t i c l e s of l e s s than 4 ym i n diameter. Most of t h i s m a t e r i a l was i n o r -ganic and capable of adsorbing organic m a t e r i a l . This type of sedimen-t a r y m a t e r i a l could be grazed by Galanus plumchrus but not be C. marshallae. Thus, Galanus plumchrus i s equipped t o f i l t e r a wider and more d i -verse spectrum of p a r t i c u l a t e matter than i s Galanus marshallae. Because of the a b i l i t y of Galanus plumchrus to handle p a r t i c l e s as small as 2.0 ym, i t might a l s o be able t o feed on more d i f f u s e suspended m a t e r i a l such as d e t r i t u s . D e t r i t a l m a t e r i a l was u n a v a i l a b l e t o Galanus helgo-l a n d i c u s (Corner et a l . 19?4); however, the s m a l l e s t i n t e r - s e t u l e d i s -tance of G. helgolandicus i s reported t o be 5 ym (Vyshkvartseva and Gutel'makher 1971)• This would make i t l e s s e f f i c i e n t than Calanus 118 plumchrus i n the handling of d i f f u s e m a t e r i a l . Such m a t e r i a l might be important i n maintaining the metabolism of Calanus plumchrus d u r i n g overwintering, but there i s no data at the moment to s u b s t a n t i a t e t h i s hypothesis. In addition..to a s u p e r i o r a b i l i t y i n the handling of small p a r t i c l e s , Calanus plumchrus i s a l s o equipped t o f i l t e r more wateryper u n i t weight than i s G. marshallae• The f i l t e r i n g s u rface of the second m a x i l l a of C. plumchrus has an area of approximately 0.4-5 mm . The t o t a l e f f e c t i v e f i l t e r i n g surface can be estimated by the t o t a l f i l t e r i n g surface of the two second m a x i l l a e . Based on the second m a x i l l a e , Calanus plumchrus 2 has an e f f e c t i v e f i l t e r i n g area of approximately 0.90 mm , and C. mar-2 s h a l l a e has an e f f e c t i v e f i l t e r i n g area of approximately 0.21 mm , or 2J% of the area a v a i l a b l e t o C. plumchrus. However, Calanus plumchrus (CV) has a mean wet weight of 3-0 mg as compared with 1.2 mg f o r C. mar-s h a l l a e (CV) (Gardner unpub.). Suppose we d e f i n e a rough mechanical e f f i c i e n c y f a c t o r (F ) as the r a t i o between e f f e c t i v e f i l t e r i n g surface and mean wet weight. T h i s y i e l d s a f i g u r e r e p r e s e n t i n g the area of f i l t e f i h g r s u r f a c e f p e r u n i t of body weight. For the f i f t h copepodite of Calanusnplumchrus, the F^ i s 0.3, while f o r the same stage of C. marshallae i t i s 0.2. Furthermore, si n c e C. plumchrus i s l a r g e r than G. marshallae, i t should have a lower metabolic r a t e , and hence have a lower energy requirement per u n i t body weight (e.g. Hoar I966; Ikeda 1970). This hypothesis i s not s t r i c t l y a p p l i c a b l e s i n c e r e s p i r a t i o n i n copepods can vary s e a s o n a l l y and r e g i o n -a l l y as w e l l as with s i z e . F or two c l o s e l y r e l a t e d species from the same region, however, the r e l a t i o n s h i p between weight and metabolism should be 119 approximately l i n e a r (Gonover 1959)• Using a d i f f e r e n t approach, Parsons and S e k i (1970) reached a s i m i l a r c o n c l u s i o n . They used data from v a r i -ous sources t o show t h a t the l a r g e r the copepod, the smaller the t o t a l phytoplankton p o p u l a t i o n necessary t o support growth. A l l of the above f a c t o r s suggest t h a t Galanus plumchrus can not only f i l t e r a v a i l a b l e food resources more e f f i c i e n t l y , but cantobtain an ade-quate r a t i o n more readily, than C. marshallae even under c o n d i t i o n s where both species can trap the a v a i l a b l e p a r t i c l e s with 100% e f f i c i e n c y . In d e s c r i b i n g the f e e d i n g c a p a b i l i t i e s of Galanus plumchrus and C. marshallae 1, I have disregarded three important v a r i a b l e s : the r a t e at which water is•passed over the mouth p a r t s , the a s s i m i l a t i o n e f f i c i e n c y of the copepods and the seasonal f l u c t u a t i o n s i n the m e t a b o l i c c r a t e of t the copepods. The e f f e c t s of these v a r i a b l e s should not adversely a f f e c t my conclusions, however. I have suggested t h a t metabolic r a t e and s i z e are approximately l i n e a r l y r e l a t e d . There could s t i l l be seasonal f l u c t u a t i o n s i n meta-bol i s m t h a t would a f f e c t the r e l a t i o n s h i p between the.two s p e c i e s . Measurements of the metabolic r a t e of Galanus plumchrus were not repro-d u c i b l e due t o l i m i t a t i o n s i n equipment. I t has been suggested, however, t h a t C. plumchrus overwinters i n a s t a t e s i m i l a r to diapause (Gardner 1972). The copepod has been sta t e d t o reduce or cease feeding d u r i n g t h i s p e r i o d (Pandyan 1971), but i n l i g h t of i t s a b i l i t y to graze p a r t i c l e s of a s i z e often disregarded i n feeding experiments, i t i s p o s s i b l e t h a t some feeding s t i l l goes on. Galanus plumchrus can s u r v i v e f o r l o n g p e r i o d s i n f i l t e r e d (0.45 um) sea water (Gardner 1972); however, b a c t e r i a growing i n the sea water a f t e r f i l t r a t i o n could become a v a i l a b l e t o G. 120 plumchrus by aggregating i n t o p a r t i c l e s l a r g e enough t o be f i l t e r e d from the water. Thus i t i s impossible t o s t a t e t h a t f e e d i n g ceases completely d u r i n g overwintering, although i t i s undoubtedly very.much reduced from feeding d u r i n g other times of the year. S i m i l a r s t u d i e s have not been c a r r i e d out on Galanus marshallae i n the S t r a i t of Georgia; however, Borgmann (1973b) measured oxygen consump-t i o n of Galanus g l a c i a l i s (= marshallae) c o l l e c t e d from August t o Novem-ber 1972 i n l o c a l waters. He d i d not note any change i n the r e s p i r a t i o n r a t e of C. g l a c i a l i s over t h i s time p e r i o d , and the r e s p i r a t o r y r a t e s which he obtained correspond very w e l l w i t h the r a t e obtained by Ikeda (1970) f o r Galanus g l a c i a l i s (= marshallae?') captured between June and August i n the B e r i n g Sea. Borgmann (pers. comm.) u n s u c c e s s f u l l y attemp-ted s i m i l a r measurements on Galanus plumchrus captured i n the e a r l y f a l l . These data support the assumption t h a t the overwintering metabolism of Galanus marshallae w i l l not l i k e l y drop below t h a t of C. plumchrus. Thus energy b e n e f i t s obtained by Galanus plumchrus due t o i t s a b i l i t y t o graze more e f f i c i e n t l y w i l l not be l o s t i n the maintenance of a higher metabolic r a t e . The e f f i c i e n c y w i t h which food i s a s s i m i l a t e d has a l s o not been e s t a b l i s h e d f o r e i t h e r Galanus plumchrus or G. marshallae. However, there i s no b a s i s f o r assuming t h a t a s s i m i l a t i o n i n e i t h e r of these two species i s s i g n i f i c a n t l y higher than i n the other. A s s i m i l a t i o n e f f i -c i e n c i e s i n copepods i n general appear t o be high, but are v a r i a b l e w i t h i n s p e cies. Corner et a l . (1967), f o r example, r e p o r t a gross feeding e f f i c i e n c y i n a d u l t Galanus finmarchicus of 34%, while M a r s h a l l and Orr (1955a) suggest an a s s i m i l a t i o n e f f i c i e n c y of 90% f o r the same species. 121 In a d d i t i o n , Gonover (1966a, b) c a l c u l a t e d the a s s i m i l a t i o n e f f i c i e n c i e s f o r Calanus hyperboreus and obtained values of 55% t o 80%, dependent on the degree of s a t i a t i o n . F i l t r a t i o n r a t e s are a l s o unrecorded f o r e i t h e r species. However, Calanus plumchrus i s mechanically more e f f i c i e n t a t o b t a i n i n g n u t r i t i o n , and should be able t o f i l t e r water at a lower r a t e w h i l e s t i l l o b t a i n i n g the same r a t i o n per u n i t body weight. Thus, energy expenditure on f i l -t r a t i o n w i l l be l e s s and net metabolic requirements l e s s . The general i n t e r p r e t a t i o n of the r e s u l t s and d i s c u s s i o n of the feed i n g a b i l i t i e s of Calanus plumchrus and C. marshallae i s t h a t G. plum-chrus has both mechanical and p h y s i o l o g i c a l advantages over Calanus mar-s h a l l a e . I t appears from- the r e g r e s s i o n a n a l y s i s d i s cussed p r e v i o u s l y t h a t f l u c t u a t i o n s i n Calanus plumchrus and G. marshallae are as s o c i a t e d w i t h year t o year f l u c t u a t i o n s i n the deep water temperature regime of the S t r a i t of Georgia e i t h e r d i r e c t l y or through temperature r e l a t e d f a c -t o r s . C u r r e n t l y , a trend towards lower deep water temperatures has r e s u l -ted i n a s h i f t i n favour of Calanus marshallae and a d e c l i n e i n Calanus  plumchrus. Over a long p e r i o d of time, however, i f the temperature r e -turns t o more normal l e v e l s the e c o l o g i c a l advantages of G. plumchrus should help t o r e - e s t a b l i s h i t i n i t s t r a d i t i o n a l concentrations i n the S t r a i t . I f the temperature remains low f o r some time, C. plumchrus w i l l be a t a disadvantage but should be able t o maintain i t s p o p u l a t i o n because of i t s a b i l i t y t o e x p l o i t p o r t i o n s of the food spectrum u n a v a i l a b l e to C. marshallae. In c o n d i t i o n s which favoured Calanus plumchrus more than usual (e.g. abnormally warm deep water), G. marshallae would be put at a disadvantage. 122 I t i s l e s s l i k e l y t h a t C_. marshallae could recover as w e l l from adverse c o n d i t i o n s , as i t i s l e s s capable than C_. plumchrus at e x p l o i t i n g the food resources of i t s environment, p a r t i c u l a r l y i f competition f o r food develops between C. plumchrus and C_. marshallae. The d i f f i c u l t i e s en-countered i n r e a r i n g C. marshallae i n the l a b o r a t o r y may be i n d i c a t i v e of a lower t o l e r a n c e than G_. plumchrus t o some unknown water q u a l i t y parame-t e r . T h i s apparently lower t o l e r a n c e supports the hypothesis t h a t G. marshallae i s l e s s able to "cope wit h " adverse c o n d i t i o n s , but does not i n d i c a t e what .the adverse c o n d i t i o n s might be. The above arguments suggest t h a t , under more "normal" c o n d i t i o n s , Galanus plumchrus could permanently r e p l a c e Galanus marshallae. As such a replacement has not occurred i n the past, environmental c o n d i t i o n s f a -vouring G. marshallae probably occur at s u f f i c i e n t i n t e r v a l s to maintain the species i n the S t r a i t of Georgia. Occasional i n t r u s i o n s of c o l d e r water than usual wouEid probably have t h i s r e s u l t . The current f l u c t u a -t i o n s i n the two species might then be the r e s u l t of a more intense, more r e g u l a r c o l d water i n t r u s i o n over a p e r i o d of some years, as discussed above. The growth r a t e s obtained f o r Galanus plumchrus i n the l a b o r a t o r y agree w e l l with other published r a t e s d e s p i t e low o v e r a l l s u r v i v a l r a t e s . They are probably r e p r e s e n t a t i v e of the p a t t e r n of growth i n the f i e l d . F u l t o n (1973) obtained growth r a t e s f o r Galanus plumchrus of 10.6%AW/day from egg t o GV, but does not d i s c u s s s p e c i f i c r a t e s from stage t o stage. Parsons, LeBrasseur et a l . (I969) d e r i v e an o v e r a l l growth r a t e from n a u p l i i t o GV of 6.6%/day, with values from 3-5 t o 14% f o r d i f f e r e n t seg-ments of the l i f e c y c l e . T h e i r highest value was obtained f o r growth 123 between the n a u p l i a r stages (an average value) and the GI. Growth from GI t o G U I was reduced (3-5%/day), but p i c k e d up again between the G U I and CV; (8.7%/day). These values suggest t h a t the g r e a t e s t growth occurs through the n a u p l i i and CI, while my f i g u r e s suggest t h a t maximum growth r a t e occurs through the intermediate stages ( C I I t o CIV). Parsons' data were taken on c r u i s e s separated by two week pe r i o d s , and h i s estimates f o r the time of f i r s t appearance of each stage are consequently only ac-curate w i t h i n s e v e r a l days. The e r r o r introduced by these i n a c c u r a c i e s would be gr e a t e s t f o r the short term events c h a r a c t e r i z i n g r a p i d growth. The averaging of data f o r the n a u p l i a r stages w i l l a l s o l e a d to d i f f e r -ences i n the growth r a t e estimates f o r e a r l y stages. These f a c t o r s , p l u s the minor d i f f e r e n c e s i n the wet weight estimates f o r the i n d i v i d u a l stages,, can account f o r most of the d i f f e r e n c e s between Parsons' growth r a t e estimates and my own. Because of the frequency with which I was able t o sample growing c u l t u r e s of C. plumchrus, my estimates- of growth r a t e probably b e t t e r r e f l e c t the a c t u a l p a t t e r n of growth than other p u b l i s h e d r a t e s . The p p a t t e r n suggested i s one of very r a p i d growth through the intermediate copepodite stages. This p a t t e r n can a l s o be seen i n the f i e l d , where many d i f f e r e n t copepodite stages can appear w i t h i n a short time p e r i o d . This r a p i d growth enables Calanus plumchrus to b e t t e r e x p l o i t the a v a i l a -b l e phytoplankton, and may be another example of i t s f i t n e s s to s u r v i v e i n the S t r a i t of Georgia. I f , i n s p i t e of i t s apparent advantages, Calanus plumchrus i s unable to maintain h i g h p o p u l a t i o n numbers i n the S t r a i t of Georgia and i s r e -placed by C. marshallae, the e c o l o g i c a l i m p l i c a t i o n s are cons i d e r a b l e . 124 Predators on Galanus plumchrus would need to e x p l o i t a l t e r n a t i v e sources of food more h e a v i l y . This would most l i k e l y meanviincreased predation on G_. marshallae. The d i f f e r e n c e i n energy content and s i z e of the two species i s such t h a t a predator would have t o remove more than twice the number of G. marshallae t o obtain an equivalent r a t i o n . The increase i n searching time which t h i s i m p l i e s would be d e t r i m e n t a l t o the predator. 125 SUMMARY Between 1969 and 1974, the composition of the S t r a i t of Georgia zooplankton community s h i f t e d s u b t l y i n response t o changes i n the cha-r a c t e r i s t i c s of the environment. By using a s e r i e s of m u l t i v a r i a t e a n a l y t i c a l techniques t o examine zooplanktonic and hydrographic data, i t i t shown t h a t the change i n the zooplankton i s temporally d i r e c t e d w i t h i n the p e r i o d of the study, r a t h e r than f l u c t u a t i n g about an equi-l i b r i u m c o n d i t i o n . Changes i n the zooplankton can b e l i n k e d t o s i m i l a r temporal changes i n the. hydrographic regime. C l u s t e r a n a l y s i s groups deep andeintermediate water i n a rough tem-p o r a l sequence on the b a s i s of b i o l o g i c a l data. P r i n c i p a l components and f a c t o r analyses d e s c r i b e a p o s s i b l e p h y s i c a l b a s i s f o r the observed tem-p o r a l d i f f e r e n c e s i n the hydrography. Although the changes i n the phy-s i c a l environment are c h a r a c t e r i z e d by changes i n temperature and s a l i n -i t y , they r e f l e c t changes i n other, unmeasured, parameters t h a t have had a more d i r e c t i n f l u e n c e on the zooplankton. Canonical c o r r e l a t i o n and r e g r e s s i o n i n d i c a t e the importance of the hydrographic regime t o the zooplankton community, while p r i n c i p a l components a n a l y s i s of the zoo-plankton i n d i c a t e s t h a t 15% of the zooplankton v a r i a n c e i s a s s o c i a t e d w i t h a temporal s h i f t . Taken together, these analyses i n d i c a t e t h a t the changes which have occurred i n the p h y s i c a l and b i o l o g i c a l s e c t o r s of the environment are r e l a t e d , and f u r t h e r i n d i c a t e the presence of a s u b t l e temporal trend i n the zooplankton community of the S t r a i t of Georgia. Although 15% of the zooplankton v a r i a n c e i s a s s o c i a t e d w i t h a tem-p o r a l trend, the zooplankton community i s b a s i c a l l y s t a b l e and has a 126 s t r u c t u r e based on the v e r t i c a l d i s t r i b u t i o n of i t s component s p e c i e s . The most obvious u n i t w i t h i n the community i s a group of deep water s p e c i e s . Other species groupings a l s o tend t o be a s s o c i a t e d with de-f i n a b l e p a t t e r n s of v e r t i c a l d i s t r i b u t i o n . A l l of the groups, however, in t e r g r a d e s u f f i c i e n t l y t h a t they can not r e a d i l y be subdivided i n t o independent communities. There i s considerable redundancy i n the zooplankton data which can be reduced by c a r e f u l s e l e c t i o n of species f o r complete monitoring. Fac-t o r a n a l y s i s provides an o b j e c t i v e means of s e l e c t i n g key species f o r continued monitoring. Seven species (Calanus plumchrus, Pseudocalanus  minutus, A c a r t i a longiremus, S a g i t t a elegans, Euphausia p a c i f i c a , Lima-c i n a sp. and Pithona s p i n i r o s t r i s ) are recommended f o r d e t a i l e d observa-t i o n i n the S t r a i t of Georgia. These species a c c u r a t e l y represent the general zooplankton community and can be r e a d i l y monitored on a long term b a s i s . The overwintering s i z e of the zooplankton community i n the S t r a i t of Georgia i s s t r o n g l y l i n k e d with hydrographic events i n the f a l l . Changes i n the composition of incoming oceanic water, i n the composition of o utflowing f r e s h e r water and i n the mechanics of mixing between these two types of water a l l a c t t o a l t e r the composition of the deep water which i n t r u d e s i n t o the S t r a i t of Georgia i n l a t e summer and f a l l . These v a r i a t i o n s i n deep water have important e f f e c t s on the overwintering popu-l a t i o n s i z e s of deep water species, and consequently on the makeup of the zooplankton community t h a t i s present i n the S t r a i t of Georgia when the s p r i n g zooplankton bloom commences. Hydrographic events i n s p r i n g and f a l l l a l s o d i r e c t l y a f f e c t the a v a i l a b i l i t y of food by r e g u l a t i n g ,_>hyto 12? phytoplankton growth. Hence they i n d i r e c t l y a f f e c t zooplankton growth i n a d d i t i o n t o the d i r e c t i n f l u e n c e d e s c r i b e d above. I t i s t h i s f l u c t u a t i o n i n deep water p r o p e r t i e s that has generated much of the s h i f t i n the zooplankton community. The most important aspect of t h i s r e l a t i o n s h i p i s the e f f e c t of the environmental changes observed i n deep water temperature s t r u c t u r e on the overwintering p o p u l a t i o n s of Galanus plumchrus and Galanus marshallae. F l u c t u a t i o n s i n the numbers of ifehese species are p a r t i c u l a r l y c r i t i c a l because of the economic importance of Calanus plumchrus. The trend of the observed changes has been towards decreased overwintering numbers of Calanus plumchrus and increased num-bers of C. marshallae• Other data suggest t h a t these changes are abnor-mal and may represent a permanent s h i f t ; however, there are not s u f f i c i e n t d a t a t o confirm or deny t h i s p o s s i b i l i t y . The two species of Calanus are s u f f i c i e n t l y s i m i l a r i n d i s t r i b u t i o n and l i f e h i s t o r y that an i n v e s t i g a t i o n of the r e l a t i o n s h i p s between them i s both e c o l o g i c a l l y i n t e r e s t i n g and necessary t o f u r t h e r d e f i n e the charac t e r of the f l u c t u a t i o n s observed i n t h e i r numbers. E c o l o g i c a l separation of the species i s based l a r g e l y on the a b i l i t y of Calanus  plumchrus t o feed on p a r t i c l e s down t o about 2.5 ym i n diameter, while C. marshallae can feed .only p o o r l y on p a r t i c l e s below about 8.0 ym. In the S t r a i t of Georgia, the concentration of a v a i l a b l e food p a r t i -c l e s with diameters between 2.0 and 8.0 ym i s considerable. T h i s gives plumchrus an e c o l o g i c a l advantage over C. marshallae which has been at l e a s t t e m p o r a r i l y o f f s e t by hydrographic changes i n favour of G. marshal-l a e . The advantage i s f u r t h e r enhanced by the p a t t e r n of growth i n C_. plumchrus. The e a r l y l i f e h i s t o r y stages develop s l o w l y , and may be 128 a b l e t o adjust to v a r i a t i o n s i n the t i m i n g of the s p r i n g phytoplankton bloom. Intermediate stages are c h a r a c t e r i z e d by f a s t growth which may a l l o w more e f f i c i e n t u t i l i z a t i o n of the phytoplankton when they are a a v a i l a b l e . I t i s l i k e l y t h a t the two species w i l l r e t u r n t o t h e i r h i s t o r i c a l c oncentrations i f the 'hydrographic regime r e t u r n s t o i t s pre-1969 com-p o s i t i o n . This may a l s o be-true of the general zooplankton community, but w i l l only pe provable by continued monitoring of both the zooplank-ton and hydrography of the S t r a i t of Georgia. I f no f u r t h e r change occurs, the p l a n k t i v o r e p o p u l a t i o n of the S t r a i t of Georgia may s u f f e r . 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LeBrasseur. 1970. The a v a i l a b i l i t y of food to d i f -f e r e n t t r o p h i c l e v e l s i n the marine food chain. Pages 325-3^3 i n S t e e l e , J.H. (ed.), Marine Food Chains. O l i v e r and Boyd, Edinburgh Parsons, T.R., R.J. LeBrasseur and W.E. Barraclough. 1970. L e v e l s of pro-d u c t i o n i n the p e l a g i c environment of the S t r a i t of Georgia, B r i t i s h Columbia: a review. J.Fish.Res.Bd.Can. 27:1251-1264 Parsons, T.R., R.J. LeBrasseur, J.D. F u l t o n and O.D. Kennedy. 1969. Pro-d u c t i o n s t u d i e s i n the S t r a i t of Georgia.. P a r t I I . Secondary pro-d u c t i o n under the F r a s e r R i v e r Plume, February t o May, 1967-J.exp.mar.Biol.Ecol. 3:39~50 Parsons, T.R. and H. S e k i . 1970. Importance and general i m p l i c a t i o n s of organic matter i n aquatic environments. Pages 1-28 i n Hood, D.W. (ed.), Organic matter i n n a t u r a l waters• I n s t . M a r . S c i . , U n i v e r s i t y of Alaska, Occas. P u b l . No. 1. 625pp Parsons, Parsons, T.R., K. Stephens and R.J. LeBrasseur. 1969- Production s t u d i e s i n the S t r a i t of Georgia. P a r t I . Primary production under the F r a -ser R i v e r Plume, February t o May, I967. J.exp.mar.Biol.Ecol. 3:27-38 Parsons, T.R. and Masuyuki Takahashi. 1973- B i o l o g i c a l oceanographic  processes. Pergamon Press, N.Y. I86pp P e t i p a , T.S. 1965- The food s e l e c t i v i t y of Calanus h e l g o l a n d i c u s . Pages 100-110 i n I n v e s t i g a t i o n of the plankton of the B l a c k Sea and the  Sea of Azov" Akad.Sci.Ukr.S.S.R. (M.A.F.F. t r a n s l . N.S. 72; o r i g i n a l not seen, c i t e d by M a r s h a l l 1973) P i c k a r d , G.L. 1956. Surface and bottom c u r r e n t s i n the S t r a i t of Georgia. J.Fish.Res.Bd.Can. 13:581-590 . 1975- Annual and longer term v a r i a t i o n s ©f deepwater p r o p e r t i e s i n the c o a s t a l waters of southern B r i t i s h Columbia. J.Fish.Res.Bd.Can. 32:1561-1587 P i a t t , Trevor, V.M. Brown and B. I r w i n . 1969- C a l o r i c and carbon equiva-l e n t s of zooplankton biomass. J.Fish.Res.Bd.Can. 26:2345-2349 140 Ponomareva, L.A1.!, 1963 . Euphausiids of the North P a c i f i c . T h e i r d i s t r i b u -t i o n and ecology. Akademiya Nauk S.S.S.R., I n s t i t u t Okeanologyii. T r a n s l a t e d from the Russian by the I s r a e l Program f o r S c i e n t i f i c T r a n s l a t i o n s , Jerusalem, 1966. P o u l e t , S.A. 1976. Feeding of Pseudocalanus minutus on l i v i n g and non-l i v i n g p a r t i c l e s . M a r . B i o l . 34:117-125 Raymont, J.E.G. • Plankton and p r o d u c t i v i t y i n the oceans. Pergamon Press L t d . , Lond., N.Y., Toronto. 660pp Regan, Lance. 1963- F i e l d t r i a l s w i t h the Clarke-Bumpus plankton sampler. Ms. Rept. No. 16, I n s t i t u t e of Oceanography, U n i v e r s i t y of B r i t i s h Columbia. Richman, S. and J.N. Rogers. 1969- Feeding of Calanus helgolandicus on synchronously growing populations of the marine diatom Ditylum  b r i g h t w e l l i i . Limnol.Oceanogr. 14:701-709 R i l e y , G.A. 1970. P a r t i c u l a t e organic matter i n seawater. Adv.Mar.Biol. 8:1-118 Rohlf, F . J . and R.R. So k a l . 1962. The d e s c r i p t i o n of taxonomic r e l a t i o n -ships by f a c t o r a n a l y s i s . S y s t . Z o o l . 11:1-16 R u s s e l l , F.S. 1935• On the value of c e r t a i n p l a n k t o n i c animals as i n d i c a -t o r s of water movements i n the E n g l i s h Channel and North Sea. J.mar. biol.Assoc.U.K. 29:309-332 . 1936a. A review of some aspects of plankton research. Rapp. P-V.Reun.Cons.int.Explor.Mer 95:3-31 .19'1936b. Observations on the d i s t r i b u t i o n of plankton animal i n d i c a t o r s made on C o l . E.T. P e e l j s yacht "St. George!! i n the mouth of the E n g l i s h Channel. J.mar.biol.Assoc.U.K. 20:507-552 . 1939- Hydrographical and b i o l o g i c a l c o n d i t i o n s i n the North Sea as i n d i c a t e d by plankton organisms. J.Cons.Cons.int.Explor.Mer 14:171-192 S a i l a , S.G. and J.D. P a r r i s h . 1972. E x p l o i t a t i o n e f f e c t s upon i n t e r s p e c i -f i c r e l a t i o n s h i p s i n marine ecosystems. F i s h . B u l l . 70:383-393 Sears, Mary and G.L. C l a r k e . 1940. Annual f l u c t u a t i o n s i n the abundance of marine zooplankton. B i o l . B u l l . 79:321-328 S e k i , H. and O.D. Kennedy. I969. Marine b a c t e r i a and other heterotrophs as food f o r zooplankton i n the S t r a i t of Georgia d u r i n g the winter. J.Fish.Res.Bd.Can. 26:3165-3173 S e k i , H., K.V. Stephens and T.R. Parsons. I969• The c o n t r i b u t i o n of a l l o c h -thonous b a c t e r i a and organic m a t e r i a l s from a small r i v e r i n t o a semi-enclosed area. Arch.Hydrobiol. 66:37-^7 141 Slobodkin, L.B. 1954. P o p u l a t i o n dynamics i n Daphnia obtusa Kunz. Ecol.Monogr. 24:69-88 Snedecor, G.W. and W.G. Cochran. 196?. S t a t i s t i c a l methods. The Iowa St St a t e U n i v e r s i t y P r e s s , Ames, Iowa. 593PP S o k a l , R.R. and G.D. Michener. 1958. A s t a t i s t i c a l method f o r e v a l u a t i n g systematic r e l a t i o n s h i p s . U.Kan.Sci.Bull. 38:1409=1438 S o k a l , R.R. and P.H.A. Sneath. 1963- P r i n c i p l e s of numerical taxonomy. W.H. Freeman and Co., San F r a n c i s c o and Lond. 359PP Steedman, H.F. 1976. General and a p p l i e d d a ta on formaldehyde f i x a t i o n and p r e s e r v a t i o n of marine zooplankton. Pages 103-154 i n Steedman, H.F. (ed.), Zooplankton f i x a t i o n and preservation,. Monographs on oceanographic methodology 4, the UNESCO Press, P a r i s . 350pp Stephens, K., J.D.FFulton and O.D. Kennedy. I969. Summary of b i o l o g i c a l oceanographic observations i n the S t r a i t of Georgia, I965-I968. Fish.Res.Bd.Can., Tech. Rept. No. 110 Stewart, D.K. and W.A. Love. I968. A general c a n o n i c a l c o r r e l a t i o n index. P s y c h o l . B u l l . 70:160-163 Sverdrup, H.U. and R.H. Fleming. 1941. The waters o f f the coast of southern C a l i f o r n i a , March to J u l y , 1937. B u l l . S c r i p p s Inst.Oceanogr. 4:261-378 Sverdrup, H.U., M.W. Johnson and R.H. Fleming. 1942. The oceans. P r e n t i c e -H a l l , Inc., Englewood C l i f f s , N.J. 1087pp T a i t , R.V. I968. Elements of marine ecology. Butterworths, Lond. 272pp Tebble, N. 1962. The d i s t r i b u t i o n of p e l a g i c polychaetes across the North P a c i f i c Ocean. ;B.uIl'.Brit ;Mus. (Nat .Hist. )ZSo<hlog-j'373-492 Thorson, Gunnar. 1966. Some f a c t o r s i n f l u e n c i n g the recruitment and e s t a -blishment of marine benthic communities. Neth.J.Sea Res. 3:267-293 Tranter, D.E. and J.H. F r a s e r (eds.). 1968. Zooplankton sampling. UNESCO Monographs on oceanographic methodology, No. 2, UNESCO, P a r i s . T u l l y , J.P. and A.J. Dodimead. 1957- P r o p e r t i e s of the water i n the S t r a i t of Georgia, B r i t i s h Columbia, and i n f l u e n c i n g f a c t o r s . J.Fish.Res. Bd.Can. 14:241-319 Vinogradova, N.G. 1959. The zoogeograpnical d i s t r i b u t i o n of the deep water bottom fauna i n the abys s a l zone of the ocean. Deep-Sea Res. 5:205-208 V.yshkvartseva, N.V. and B.L. Gutel'makher. 1971. Trapping a b i l i t y of the f i l t e r i n g apparatus of some Calanidae. H y d r o b i o l . J . 7:58-63 Waldichuk, M i c h a e l . 1957- P h y s i c a l oceanography of the S t r a i t of Georgia, B r i t i s h Columbia. J.Fish.Res.Bd.Can. 14:321-486 142 Wallace, J.VT. and R.S. Bader. I 9 6 7. F a c t o r a n a l y s i s of morphometric t r a i t s i n the house mouse. S y s t . Z o o l . 16:144-152 Waloff, Z. 1966. The upsurges and r e c e s s i o n s of the desert l o c u s t : an h i s t o r i c a l survey. Antilocust.Mem. No. 8 , Lond. O r i g i n a l not seen, c i t e d by Odum ( 1971) Wang, Dong-Ping and J . J . Walsh. 1 9 7 6 . O b j e c t i v e a n a l y s i s of the upwelling system o f f Baja, C a l i f o r n i a . J.Mar.Res. 34:43-60 Wellington, W.G. 1 9 5 7 . I n d i v i d u a l d i f f e r e n c e s as a f a c t o r i n p o p u l a t i o n dynamics: the development of a problem. Can.J.Zool. 35:293^323 . i 9 6 0 . Q u a l i t a t i v e changes i n n a t u r a l p o p u l a t i o n s d u r i n g changes i n abundance. Can.J.Zool. 3 8 : 2 8 9 - 3 1 4 Whittaker, R.H. and H.G. Gauch, J r . 1973- E v a l u a t i o n of o r d i n a t i o n t e c h n i -ques. Ghpt. 11 i n Whittaker, R.H. (ed.), Ordination and c l a s s i f i c a -t i o n of communities. Dr. W. Junk b-v, P u b l i s h e r s , The Hague. 737PP Wiebe, P.H. 1 9 7 0 . S m a l l - s c a l e s p a t i a l d i s t r i b u t i o n i n oceanic zooplankton. Limnol.Oceanogr. 15:205-217 and W.R. H o l l a n d . 1 9 6 8 . Plankton p a t c h i n e s s : e f f e c t s on repeated net tows. Limnol.Oceanogr. 13:315-321 Williamson, M.H. I 9 6 I . An e c o l o g i c a l survey of a S c o t t i s h h e r r i n g f i s h e r y . P a r t IV: Changes i n the plankton d u r i n g the p e r i o d 1 9 4 9 - 1 9 5 9 -B u l l . M a r . E c o l . 5:207-229 . 1 9 6 3 . The r e l a t i o n of plankton t o some parameters of the her-r i n g p o p u l a t i o n of the north-western North Sea. Rapp.P-V.Reun.Cons. int.Explor.Mer 1 5 4 : 1 7 9 - 1 8 5 Wilson, D.P. 1 9 5 1 . A b i o l o g i c a l d i f f e r e n c e between n a t u r a l sea waters. J . Max. b i o l . Assoc. U-^ K. 30:1-19 and F.A.J. Armstrong. 1 9 5 8 . B i o l o g i c a l d i f f e r e n c e s between sea waters: experiments i n 1954 and 1 9 5 5 . J.mar.biol.Assoc.U.K. 37:331-348 Wilson, D.P. and F.A.J. Armstrong. 1961. B i o l o g i c a l d i f f e r e n c e s between sea waters: experiments i n i 9 6 0 . J.mar.biol.Assoc.U.K. 41:663-681 Winberg, G.G. 1 9 5 6 . Rate of metabolism and food requirements of f i s h e s . Nauchyne Trudy Balurusskovo Gosudaruennovo U n i v e r s i t a t a imeni V.L. Lenina, Minsk. 253pp (Fish.Res.Bd.Can., T r a n s l . Ser. No. 194) Wissing, T.R., R.M. MacDonald, Mohamed A. Ibrahim and Leo Berner. 1973-C a l o r i f i c values of marine animals from the G u l f of Mexico. Gont r i b . i n Mar.Sci. 17:1-9 143 Woodhouse, CD. 1971. A study of the e c o l o g i c a l r e l a t i o n s h i p s and taxono-mic s t a t u s of two species of the genus Calanus (Crustacea:Copepoda). Ph.D. Thesis, I n s t i t u t e of Oceanography and Department of Zoology, U n i v e r s i t y of B r i t i s h Columbia. Z i l l i o u x , E.J. and D.F. Wilson. I966. C u l t u r e of a p l a n k t o n i c c a l a n p i d copepod through m u l t i p l e generations. Science 151:996-998 144 APPENDIX A The proper i d e n t i f i c a t i o n of marine zooplankton i s a d i f f i c u l t and time-consuming process. P u b l i s h e d d e s c r i p t i o n s commonly d i s c u s s only one stage i n d e t a i l (e.g. Davis 1949; Mori 1964; Brodsky 1967; Ful t o n 1968, 19?2, 1973) and many species are p o o r l y d e s c r i b e d and d i f f i c u l t to i d e n -t i f y a c c u r a t e l y . The amount of work i n v o l v e d i n s a t i s f a c t o r i l y i d e n t i -f y i n g a l l of the species encountered i n my research would have been pro-h i b i t i v e . For my purposes, i t was s u f f i c i e n t t h a t each species be i d e n t i -f i e d as best as p o s s i b l e using r e a d i l y a c c e s s i b l e d e s c r i p t i o n s . In most cases, and e s p e c i a l l y w i t h the copepods, t h i s r e s u l t e d i n i d e n t i f i c a t i o n t o the species l e v e l . This is-mot to suggest t h a t the i d e n t i f i c a t i o n s are absolute; however, they represent the best i d e n t i f i c a t i o n p o s s i b l e without attempting d e t a i l e d d e s c r i p t i o n s t h a t are best l e f t to q u a l i f i e d s y s t e m a t i s t s . The systematics of Pareuchaeta elongata are a case i n p o i n t . T h i s species has been s t u d i e d and r e f e r r e d t o i n the S t r a i t of Georgia under two names: Euchaeta japonica Marukawa (e.g. Campbell 1934; Lewis and Ram-n a r i n e 1969; Lewis et a l . 1971, 1972) and Pareuchaeta elongata E s t e r l e y (Evans 1973)• The type specimens are l o s t , t h e o o r i g i n a l d e s c r i p t i o n s are vague and even the v a l i d i t y of the genus Pareuchaeta has been c h a l l e n -ged . I have used the name Pareuchata elongata on the b a s i s of arguments advanced by Evans (1973)» but the controversy i s not yet r e s o l v e d . The nomenclature of Calanus species i s another example of confusion and u n c e r t a i n t y . Calanus plumchrus was r e f e r r e d to as C. tonsus f o r much of t h i s century (e.g. Campbell 1933, 1934; see Gardner 1972 f o r a more complete aceo.unt^.ionWoodhouse (1971) was the f i r s t t o d e s c r i b e Calanus 145 g l a c i a l i s and G. p a c i f i c u s as separate species i n t h i s area. P r e v i o u s l y they had been considered a s i n g l e species and often r e f e r r e d t o as Calanus  finmarc h i c u s . Calanus g l a c i a l i s i n the North P a c i f i c has s i n c e been rede-f i n e d by F r o s t (1974) as a new species, Calanus marshallae, which i s r&u r e a d i l y d i s t i n g u i s h e d from t r u e C. g l a c i a l i s ( F r o s t , pers. comm.). These examples are of species t h a t are among the most stud i e d species i n the S t r a i t of Georgia. Many of the other species have never been c l o s e l y examined. Although progress i s being made, i t w i l l r e q u i r e a major e f f o r t to b r i n g the systematics of the l o c a l zooplankton t o the p o i n t where i n -d i v i d u a l species can be„confidently i d e n t i f i e d i n a l l t h e i r l i f e h i s t o r y stages. U n t i l t h i s goal i s reached, most species i d e n t i f i c a t i o n s must be q u a l i f i e d and not regarded as absolute. 

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