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The effect of tidal transport on the zooplankton population of a local inlet Thomas, Andrew Charles 1981

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THE EFFECT OF TIDAL TRANSPORT ON THE ZOOPLANKTON POPULATION OF A LOCAL INLET by ANDREW CHARLES THOMAS B.Sc.,McGill University,Montreal,1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Oceanography And Zoology) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 1982 (c) Andrew Charles Thomas, 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (.3/81) i i ABSTRACT A series of cruises was made over 14 months to determine the ef f e c t of physical transport on the zooplankton of Indian Arm, whose deep water is separated from the marine influence of the S t r a i t of Georgia by a series of shallow s i l l s . The dominant transport process during the study period was t i d a l exchange. The topographic features of the i n l e t , coupled with density s t r a t i f i c a t i o n found over the year, r e s t r i c t e d the exchange of water and plankton to a surface phenomenon. Four copepod species were sampled using horizontally towed Clarke-Bumpus nets and v e r t i c a l l y towed SCOR nets and one meter conical nets. These were analysed to determine the relati o n s h i p between d i f f e r e n t l i f e history patterns and t i d a l exchange, and the effect of thi s relationship on the populations of these species inside Indian Arm. Corycaeus anglicus is a surface water to mid depth organism found in highest numbers in Vancouver Harbour. The population density reaches a peak in the f a l l and remains high throughout the winter with transport concomittant with t h i s peak. Euchaeta japonica exhibits ontogenetic depth preferences, na u p l i i and Stage I copepodites are found mainly in deep water below 200 meters, Stages II-IV are found mainly in shallow water, and Stages V and VI (adults) are found scattered over most of the water colunm. This species reproduces throughout the year in both Indian Arm and the S t r a i t of Georgia. Euchaeta japonica was transported mainly as the Stage III copepodite and primarily during the winter months despite the fact that the species i s found in surface waters in large numbers at other times of the year, thus producing an isolated population in Indian Arm during the summer. Metridia p a c i f i c a i s a strong d i e l migrator found extensively in the upper 50 meters at night, and from 250 meters to 50 meters during the day. Transport of the species across the s i l l occurs at a l l times of the year but i s s i g n i f i c a n t l y greater at night, regardless of the phase of t i d e . Eucalanus  bunqi i s an ontogenetic migrator, overwintering in deep water (greater than 150 meters), and coming to the surface in the spring to spawn; juvenile stages are found in surface waters during the summer. The data show that this species is transported only during the summer while i t is in surface water. Consequently nauplii and younger copepodites are the dispersal stages. The data suggest that the species does not reproduce in Indian Arm and that transport of the species during the summer months can account for the entire overwintering population found in the i n l e t . An analysis of the c o r r e l a t i o n of changes in the zooplankton community with physical parameters varying over the t i d a l cycle was made. Species known to migrate d i e l l y show s i g n i f i c a n t differences in numbers between ' day and night samples. Relatively few species show differences which can be correlated to the d i r e c t i o n of t i d a l movement. The most s i g n i f i c a n t changes seen in the zooplankton community occur in association with changes in hydrographic properties. Moreover, these changes are manifested not at the species l e v e l , but at i v t h e community l e v e l a s c h a n g e s i n s u c h p a r a m e t e r s as d i v e r s i t y and d o m i n a n c e . The e f f e c t o f t r a n s p o r t on t h e z o o p l a n k t o n community i n I n d i a n Arm v a r i e s f r o m s p e c i e s t o s p e c i e s . Q u a l i t a t i v e l y , t h e e f f e c t depends upon t h e o r g a n i s m s ' l i f e c y c l e i n c l u d i n g a s u r f a c e d w e l l i n g s t a g e , a n d / o r i t s a b i l i t y t o s u r v i v e t h e s u r f a c e w ater t r a n s p o r t c o n d i t i o n s . Q u a n t i t a t i v e l y , t h e e f f e c t d e pends on t h e amount o f t i m e s p e n t i n s u r f a c e w a t e r , w h i c h v a r i e s w i t h t h e d e p t h d i s t r i b u t i o n o f t h e o r g a n i s m , d e t u r m i n e d by i t s b e h a v i o r a l c h a r a c t e r i s t i c s . The o v e r a l l e f f e c t of t i d a l e x c hange w i l l be t o d r i v e t o w a r d s e q u i l i b r i u m t h e p o p u l a t i o n o f z o o p l a n k t o n f o u n d i n I n d i a n Arm and t h e S t r a i t o f G e o r g i a . I t i s t h e b i o l o g y of t h e i n d i v i d u a l s p e c i e s w h i c h d e t e r m i n e s t h e e x t e n t o f i n t e r a c t i o n w i t h t h i s t r a n s p o r t p r o c e s s and hence t h e amount o f e xchange w h i c h t a k e s p l a c e . V TABLE OF CONTENTS ABSTRACT . i i LIST OF TABLES v i i LIST OF FIGURES v ix ACKNOWLEDGEMENTS .. .. . x i i Introduction 1 Overview 1 Physical Considerations 3 Bio l o g i c a l Considerations 5 The Study Area 8 Summary of Considerations 9 Materials and Methods 11 Hydrographic Data 11 i) F i e l d Proceedures 11 i i ) Laboratory Proceedures and Data Reduction ....... 12 Bio l o g i c a l Data 15 i) F i e l d Proceedures 15 i i ) Laboratory Proceedures and Data Reduction 17 Results and Discussion 24 Hydrographic Data 24 i) Deep water Intrusions 24 i i ) Estuarine C i r c u l a t i o n 26 i i i ) T i d a l Exchange .....28 Transport of the Study Species 32 i) Corycaeus anqlicus 32 v i i i ) Euchaeta japonica 34 i i i ) Metridia p a c i f i c a 37 iv) Eucalanus bunqi 40 Community Changes Over a T i d a l Cycle 44 Conclusions 55 References 62 Tables 70 Figures 99 LIST OF TABLES Table I : Cruise dates and numbers 70 Table I I : Sampling Depths 71 Table I I I : Animals and Taxonomic Groups Identified for the Community Analysis at IND 0 (Cruise 80/18) 73 Table IV: Animal densities per cubic meter at the sampling depths on cruise 81/33 75 Table V: S t a t i s t i c a l treatment of replicates 76 Table V I : Volume transport of water across the Indian Arm s i l l , calculated from current meter readings 77 Table V I I : Average volume transport for large and small t i d a l exchanges, calculated from the model predictions. 78 Table V I I I : Density of Corycaeus anqlicus in the study area 79 Table IX: Transport of Corycaeus anqlicus across the Indian Arm s i l l during the study period 81 Table X: Density of Euchaeta japonica in the study area. .. 82 Table X I : Euchaeta japonica seasonal transport across the Indian Arm s i l l and population in Indian Arm 84 Table XII: Percent composition of Euchaeta japonica density in p o t e n t i a l l y exchangable water, January, 1981. Deduced from Figure 10 85 Table XIII: Percent composition of Euchaeta japonica density in p o t e n t i a l l y exchangable water, October, 1980. Deduced from Figure 18 86 v i i i Table XIV: Density of Euchaeta japonica copepodite Stages I, I I, and III in the S t r a i t of Georgia and Indian Arm in October (Cruise 80/18). 87 Table XV: Density of Metridia p a c i f i c a in the study area. . 88 Table XVI: Density of Metridia p a c i f i c a over the Indian Arm s i l l 90 Table XVII: Transport of Metridia p a c i f i c a across Indian Arm s i l l 91 Table XVIII: Density of Eucalanus bungi in the study area. 92 Table XIX: Seasonal transport of Eucalanus bungi across the Indian Arm s i l l and the overwintering population in Indian Arm 94 Table XX: Presence of Eucalanus bungi young copepodite stages (I, II, and III) in the study area during July (Cruise 80/12) 95 Table XXI: U-Test results for community parameters over the t i d a l cycle at IND 0 (Cruise 80/18) - 96 Table XXII: Kruskal Wallis results for zooplankton community changes over the t i d a l cycle at IND 0 (Cruise 80/18) 97 LIST OF FIGURES Figure 1; The study area 100 Figure 2; Longitudinal depth p r o f i l e through the study area 1 02 Figure 3; Density structure in the study area during winter, 1981 104 Figure 4; Density structure in the study area during winter, 1980 106 Figure 5; Oxygen concentration in water below 150 meters at Station IND 2.0, over time 108 Figure 6; Current vectors 110 Figure 7; North-south components (along the channel) of current vectors 112 Figure 8; Total and net transport of Corycaeus anglicus across the Indian Arm s i l l during each cruise 114 Figure 9; Mean concentration of Corycaeus anglicus in the study area in October 116 Figure 10; Temperature/Salinity plot of study area water during January, 1981 (Cruise 81/1) 118 Figure 11; Depth d i s t r i b u t i o n of Metridia p a c i f i c a 120 Figure 12; Total and net transport of Eucalanus bungi across the Indian Arm s i l l during each cruise 122 Figure 13; Temperature/Salinity plot of study area water during July, 1980 (Cruise 80/12) 124 Figure 14; Temperature/Salinity plot of water at IND 2.0 ..126 X Figure 15; The t i d a l cycle at IND 0 during Cruise 80/18 (October, 1980) . . . 128 Figure 16; Temperature at each sampling depth at IND 0 over the t i d a l cycle (Cruise 80/18). 130 Figure 17; S a l i n i t y at each sampling depth at IND 0 over the t i d a l cycle (Cruise 80/18) 132 Figure 18; Temperature/Salinity plot of the study area water during October, 1980 (Cruise 80/18) 134 Figure 19; Temperature/Salinity plot of water from 0 meters at the Indian Arm s i l l over the t i d a l cycle 136 Figure 20; Temperature/Salinity plot of average T/S properties from 5, 10, and 20 meters (below the pycnocline) at the Indian Arm s i l l over the t i d a l cycle. 138 Figure 21; Density of the four most abundant copepods at IND 0 over the t i d a l cycle (Cruise 80/18) 140 Figure 22; Density of the second four most abundant copepods at IND 0 over the t i d a l cycle (Cruise 80/18). .142 Figure 23; Total zooplankton d i v e r s i t y and dominance over the t i d a l cycle at IND 0 (Cruise 80/18) 144 Figure 24; Diversity and dominance of the copepod community ' over the t i d a l cycle at IND 0 (Cruise 80/18) 146 Figure 25; Diversity and dominance of a l l other invertebrate zooplankton over the t i d a l cycle at IND 0 (Cruise 80/1 8) 1 48 Figure 26; Diversity and dominance of invertebrate zooplankton (minus larvaceans and siphonophores) over Figure 27; Kendalls c o e f f i c i e n t of concordance between time adjacent samples over the t i d a l cycle at IND 0 (Cruise ACKNOWLEDGEMENTS I w i s h t o e x p r e s s my s i n c e r e t h a n k s t o my s u p e r v i s o r , D r . A.G. L e w i s , f o r h i s f r i e n d s h i p , c a n d i d g u i d a n c e , a d v i c e , and s u p p o r t i n a l l m a t t e r s t h r o u g h o u t t h e s t u d y . By i t s n a t u r e , a s t u d y i n b i o l o g i c a l o c e a n o g r a p h y n e c e s s i t a t e s an u n d e r s t a n d i n g o f p r i n c i p l e s o u t s i d e t h e i m m e d i a t e f i e l d . I w i s h t o t h a n k D r s . R.W. B u r l i n g , W.J. Emery, a n d S. Pond f o r t h e i r p a t i e n t e x p l a n a t i o n s o f p h y s i c a l p r o c e s s e s t o a b i o l o g i s t , a n d e s p e c i a l l y D r . P.B. C r e a n f o r h i s h e l p w i t h t h e t i d a l m o d e l . My t h a n k s a r e a l s o g i v e n t o D r s . C.J. K r e b s , W.E. N e i l l , a nd J . P a r s l o w f o r t h e i r h e l p w i t h t h e s t a t i s t i c s . I w o u l d l i k e t o t h a n k Mr. A. Ramnarine f o r h i s a d v i c e and. c h e e r f u l a s s i s t a n c e a t s e a , and my f e l l o w g r a d u a t e s t u d e n t s who gav e w i l l i n g l y o f t h e i r t i m e t o h e l p w i t h t h e f i e l d work. The c o - o p e r a t i o n a n d a s s i s t a n c e e x t e n d e d t o me by t h e o f f i c e r s a nd crew o f C.S.S. V e c t o r and.C.S.S. R i c h a r d s o n were a p p r e c i a t e d , a s was t h e a c a d e m i c and t e c h n i c a l a d v i c e g i v e n me by numerous c o l l e a g u e s i n t h e D e p a r t m e n t . o f O c e a n o g r a p h y . I w i s h t o t h a n k t h e D e p a r t m e n t o f Z o o l o g y f o r p r o v i d i n g me w i t h . T e a c h i n g A s s i s t a n t s h i p s , my s u p e r v i s o r f o r h i s f i n a n c i a l a s s i s t a n c e and C h e v r o n Canada f o r a s c h o l a r s h i p i n t h e f i n a l s t a g e s o f my s t u d y . F i n a l l y , I owe a s p e c i a l t h a n k y o u t o t h o s e t r u e f r i e n d s , whose u n d e r s t a n d i n g a n d e n c o u r a g e m e n t saw me t h r o u g h t h e s e y e a r s . 1 INTRODUCTION Overview The spacial d i s t r i b u t i o n of a planktonic organism i s , by d e f i n i t i o n , controlled by the movements of the water in which i t occurs. Superimposed on th i s are the physical, chemical, and b i o l o g i c a l properties of the water within which the organism must be able to survive. Given the continuity of favorable water properties, the potential exists for organisms separated v e r t i c a l l y but at the same geographic location to be transported in d i f f e r e n t directions by v e r t i c a l l y discrete bodies of water moving in d i f f e r e n t d i r e c t i o n s . In coastal waters, transport of organisms by such physical processes as t i d a l currents and estuarine c i r c u l a t i o n i s well known (e.g. Redfield, 1941; Barlow, 1955; Tyler and Seliger, 1978) and i t has been suggested (Stromgren, 1975) that variations in such transport a f f e c t the zooplankton communities of fjords. S i m i l a r l y , i t has been shown that physical, chemical, and b i o l o g i c a l properties of the water encountered by the organisms as they are transported are important (e.g. Evans, 1973; Bary and Regan, 1976). N e r i t i c plankton, however, have an additional l i m i t a t i o n placed upon their d i s t r i b u t i o n by the topographic features of the coastline with which they are associated. This l i m i t a t i o n i s manifested primarily through the influence of these topographic features on the physical 2 processes involved in transport (e.g. Trinast, 1975; Alldredge and Hamner, 1980). The general purpose of t h i s study i s to examine the effect of physical transport on the zooplankton community of a l o c a l i n l e t . The hypothesis to be tested i s that the presence or absence of transport, and changes in i t s rate, are responsible for the quantitative and q u a l i t a t i v e nature of zooplankton populations in an i n l e t . S p e c i f i c questions that the study set out to answer were: 1) Can the transport of zooplankton be quantitatively measured across an i n l e t mouth? 2) Is the transport affected by d i f f e r e n t behavior patterns? 3) What effect does transport have on the i n l e t populat ions? 4) Do d i f f e r e n t transport processes have di f f e r e n t e f fects on the actual transport of zooplankton? 5) What numerical changes take place in the zooplankton population being transported across the i n l e t mouth over the t i d a l cycle? 6) Are these changes associated with measurable variables such as t i d a l d i r e c t i o n , daylight, or hydrographic parameters? Inherent in such a study i s an understanding of two interacting systems: the physical oceanographic processes which are responsible for water movements at the i n l e t mouth, and the 3 zooplanktonic b i o l o g i c a l processes occurring in the water i t s e l f . Physical Considerations Geologically, a fj o r d is a submerged g l a c i a l valley forming a deep, narrow, steep sided i n l e t . The s i l l frequently found at the mouth i s normally a terminal moraine, which i s also a result of g l a c i a t i o n and forms a r e l a t i v e l y shallow barrier separating the deep water of the fjord from coastal water. S i l l s are known to markedly influence physical transport processes (Skreslet, 1973; Gade, 1976) and have the o v e r a l l effect of r e s t r i c t i n g the exchange between the fj o r d and adjacent coastal water. This effect i s seen most dramatically as an i s o l a t i o n of the fj o r d deep water (Anderson and Devol, 1973; Siebert et al,l979; Heggie and B u r r e l l , 1981) . The physical mechanisms responsible for the transport of water into or out of a fj o r d can be divided into those of a ba r o c l i n i c nature, driven by horizontal density gradients, and those of a barotropic nature, driven by a horizontal pressure gradient. Estuarine c i r c u l a t i o n i s a semi permanent density current driven by runnoff entering the i n l e t , and primarily a f f e c t s surface c i r c u l a t i o n . The seaward flowing surface layer is driven by a down i n l e t sloping free surface. V e r t i c a l entrainment of saline water from below, into t h i s outflowing layer, results in an up i n l e t compensatory flow in the 4 subsurface layers (see Dyer, 1973). The magnitudes of up i n l e t subsurface flow and down i n l e t surface flow are dependent on the volume of fresh water input, and both are p o t e n t i a l l y capable of transporting zooplankton. Replacement of fjo r d deep water can occur i f coastal water above s i l l depth i s of greater density than the resident water of the f j o r d (Anderson and Devol, 1973; Lafond and Pickard, 1975). The process i s set up by v e r t i c a l d i f f u s i v e mechanisms within the f j o r d which gradually reduce the density of the resident i n l e t deep water (Muench and Heggie, 1978). The intrusion of dense coastal water into the deep basin of a fj o r d is an intermittent process dependent upon the rate of density decrease in the fj o r d deep water and the seasonal changes in the density of water at s i l l depth outside the f j o r d . An intrusion is most l i k e l y to occur at a time when the offshore surface density is at a maximum. The timing of this maximum and thus of the intrusion w i l l vary depending upon l o c a l coastal oceanographic processes and runnoff patterns (see Gade, 1976). Over a shallow s i l l there i s a l i m i t a t i o n imposed upon the magnitude of a baroclinic flow by the irregular boundaries of the channel. Superimposed on any existent b a r o c l i n i c flows are transport mechanisms of a barotropic nature driven by a pressure gradient such as those due to tides, l o c a l wind f i e l d s , and atmospheric pressure changes. No boundary related l i m i t a t i o n exists on these flows such that frequently, they can completely override semipermanent or intermittent b a r o c l i n i c flows. In such a case the ba r o c l i n i c flow w i l l serve only to diminish or 5 augment the barotropic flow depending on their r e l a t i v e directions (Gade and Edwards, 1980). In most sha l l o w - s i l l e d fjords therefore, the dominant short term transport process w i l l be that of t i d a l exchange. Estuarine c i r c u l a t i o n w i l l be evident only as a ; net flow varying seasonally with fresh water input and superimposed on the t i d a l flow. Density driven intrusive flows might be strong enough to override the t i d a l flow for short periods of time depending on the density gradient established across the s i l l (Skreslet and Loeng, 1977). While the magnitude of such intrusions i s often big enough to replace large volumes of fj o r d water in a short period of time (Cannon and Ebbesmeyer, 1978), they are of a seasonal nature and often episodic, with many years passing between each renewal (Gade, 1973). B i o l o g i c a l Considerations Although the width of the mouth of a f j o r d w i l l obviously have a quantitative effect on plankton exchange i t w i l l have l i t t l e q u a l i t a t i v e e f f e c t . This i s because the horizontal distance over which zooplankton species d i s t r i b u t i o n s change are usually orders of magnitude larger than the width of i n l e t mouths. S i l l depth, however, w i l l not only have a quantitative e f f e c t , but also a q u a l i t a t i v e e f f e c t on plankton exchange. V e r t i c a l gradients in both water properties and zooplankton d i s t r i b u t i o n s are of the same scale as s i l l depths and often 6 much s m a l l e r , e s p e c i a l l y i n c o a s t a l r e g i o n s . T h e r e a r e two n e c e s s a r y p r e r e q u i s i t e s f o r t h e t r a n s p o r t o f o r g a n i s m s i n t o o r o u t o f an i n l e t . F i r s t , a p h y s i c a l mechanism must be p r e s e n t whereby water i s a c t i v e l y b e i n g e x c h a n g e d a c r o s s t h e i n l e t mouth. O b v i o u s l y t h i s water must be n e a r o r above s i l l d e p t h f o r s u c h a f l o w t o be p o s s i b l e . S e cond, t h e o r g a n i s m must be p r e s e n t i n t h e moving w a t e r . B o t h o f t h e s e p r e r e q u i s i t e s a r e v a r i a b l e and a number o f p o t e n t i a l p o s s i b i l i t i e s c a n be p r o p o s e d . 1) G i v e n a c o n s t a n t t r a n s p o r t mechanism, t h e number of o r g a n i s m s e x c h a n g e d w i l l v a r y a s e a c h s p e c i e s r e a c h e s i t s maximum p o p u l a t i o n d e n s i t y i n t h e w ater above s i l l d e p t h a t d i f f e r e n t t i m e s o f t h e y e a r . The q u a n t i t a t i v e n a t u r e o f t h e z o o p l a n k t o n t r a n s p o r t w i l l t h u s v a r y w i t h s e a s o n a l c y c l e s i n p o p u l a t i o n abundance. 2) In c o n t r a s t , i f t h e p o p u l a t i o n o f an o r g a n i s m r e m a i n s s e a s o n a l l y u n i f o r m , v a r i a t i o n s i n t r a n s p o r t c a n o n l y o c c u r w i t h c h a n g e s i n t h e m a g n i t u d e o f t h e p h y s i c a l f l o w . 3) I f a t r a n s p o r t mechanism o c c u r s on a s e a s o n a l or e p i s o d i c b a s i s , s u c h a s a d e n s i t y d r i v e n i n t r u s i o n , o n l y t h o s e a n i m a l s p r e s e n t above s i l l d e p t h d u r i n g t h e e v e n t w i l l be p o t e n t i a l l y t r a n s p o r t a b l e . Thus, an a n i m a l w h i c h m i g r a t e s v e r t i c a l l y , e i t h e r on a d i e l b a s i s o r o n t o g e n e t i c a l l y , w i l l be p o t e n t i a l l y 7 transportable only at that time, or developmental stage, when i t i s in water above s i l l depth. B i o l o g i c a l variables which must be integrated with the physical variables thus include species s p e c i f i c behavioral and reproductive c h a r a c t e r i s t i c s . The species chosen for transport analysis were copepods having d i f f e r e n t depth d i s t r i b u t i o n s and l i f e history patterns. Corycaeus anglicus Lubbock i s primarily a surface dwelling species which reproduces in the f a l l . Cameron (1957) suggests that this i s an inshore species which breeds in i n l e t s . Eucalanus bungi (Johnson) migrates ontogenetically, overwintering in deep water (greater than 150 meters) and r i s i n g to the surface in the spring to spawn. The younger stages develop in near surface water before migrating to deep water in the f a l l (Sekiguchi, 1975). This species i s a very common member of the North P a c i f i c plankton community (Vinogradov, 1968). Euchaeta japonica Marukawa reproduces throughout the year (Evans, 1973). While Fulton (1968) and Stone (1979) report the adults of t h i s species to be a deep l i v i n g organism, d i f f e r e n t l i f e history stages show s p e c i f i c depth preferences (Lewis and Ramnarine, unpublished data). Nauplii and C-I copepodite stages inhabit deep water (over 200 meters), stages C-II to C-IV inhabit near surface water, while C-V and adult stages are found scattered from the surface to deep water. Metridia p a c i f i c a Brodskii i s found in large numbers in surface water during the day but migrates d i e l l y to below 50 meters at night. This 8 species breeds in the spring and f a l l , reaching a population peak in the summer (Stone, 1977). The Study Area The area chosen for study was Indian Arm, a shallow s i l l e d f j o r d connected to the S t r a i t of Georgia through Burrard Inlet (Figure 1). Exchange with the S t r a i t of Georgia i s limited by the shallow s i l l s at F i r s t Narrows, Second Narrows, and at the entrance to Indian Arm i t s e l f (Figure 2). The physical oceanography of the Indian Arm - Burrard Inlet system has been studied in some d e t a i l by Gilmartin (1962), Tabata (1975), and Davidson (1979). Pickard (1961) categorizes B r i t i s h Columbia i n l e t s according to their fresh water input, stating that the d i s t r i b u t i o n of hydrographic properties in a given' i n l e t i s largely explained by the nature and volume of i t s fresh water input. Indian Arm is c l a s s i f i e d as a medium runnoff i n l e t with l i t t l e or no contribution from g l a c i e r s . Generally, tides are of a semi-diurnal nature and hydrographic properties and c i r c u l a t i o n follow a regular annual cycle of changes. Major intrusions of deep water are responsible for occasional deviations from t h i s seasonal cycle (Pickard, 1975). Such intrusions take place during the winter on an episodic basis, and are capable of replacing a major portion of the volume of Indian Arm in one month (Davidson, 1979). General patterns of zooplankton d i s t r i b u t i o n in the S t r a i t 9 of Georgia area, including Indian Arm, have been studied (Legare, 1957; Gardner, 1977; Mackus et a l , 1980, etc.) and patterns of production and seasonal cycles i d e n t i f i e d (Parsons et a l , 1970). The area follows a boreal seasonal cycle, most zooplankton species reaching a population maximum in the summer after the spring phytoplankton bloom. Primary production in the Burrard Inlet - Indian Arm system has been studied by Gilmartin (1964) , and more recently by Stockner and C l i f f (1979) who consider n i t r a t e l i m i t a t i o n and grazing to be the p r i n c i p a l factors c o n t r o l l i n g primary production. Zooplankton studies include those of Shan (1962) on copepods and McHardy and Bary (1965) on ostracods. Shan relates the d i s t r i b u t i o n of four species of copepods to water properties while Woodhouse (1971) and Evans (1971) discuss the d i s t r i b u t i o n a l ecology of a few select species. Although hypotheses were put forth by these authors, no previous attempt has been made to study mechanisms responsible for the d i s t r i b u t i o n of Indian Arm zooplankton. Summary of Considerations In general, the q u a l i t a t i v e and quantitative nature of the plankton community in a f j o r d i s a function of 1) b i o l o g i c a l and chemical properties of the water within the i n l e t , 2) the planktonic community outside the i n l e t , and 3) the degree of exchange between the two. This degree of exchange i s a function of f j o r d topography, and i t s i n t e r r e l a t i o n with the barotropic and b a r o c l i n i c currents present in the area. Seasonal cycles and species s p e c i f i c behavioral patterns w i l l determine the effect 1 0 o f t h i s i n t e r r e l a t i o n on p l a n k t o n e x c h a n g e between I n d i a n Arm and t h e S t r a i t o f G e o r g i a . 11 MATERIALS AND METHODS Hydrographic Data i) F i e l d Proceedures A series of seven cruises was made over the period January 1980 to November 1981 (see Table I ) . Ship time for these cruises was provided by the Canadian Hydrographic Service on the Canadian Survey Ships Richardson and Vector. The cruises between February 1980 and March 1981 served as the data c o l l e c t i n g series for both b i o l o g i c a l and hydrographic parameters. The January 1980 cruise was an equipment testing exercise from which no b i o l o g i c a l data resulted while, during the November 1981 cruise, replicate zooplankton tows were made for s t a t i s t i c a l application (no hydrographic data being taken). Figure 1 shows the positions of the six stations occupied during each cruise. They form a transect from the deep water of the S t r a i t of Georgia (stations GEO 1748 and FRA 1) through Burrard Inlet and across the shallow s i l l s (stations VAN 24 and IND 0) into the deep water of Indian Arm (stations IND 1.5 and IND 2.0). The exact location of each station i s given in the Department of Oceanography U.B.C. Data Reports 1980 and 1981. (Station GEO 1748 was not occupied during the Feb. 1980 cruise.) Hydrographic samples at each station were taken from the 12 surface to close to the bottom. Sp e c i f i c sample depths and the water depth at each station are shown in Table I I . Station IND 0, on the s i l l at the entrance to Indian Arm, was occupied on each cruise for a period of 25 hours (approximately an entire t i d a l c y c l e ) . Samples from this station were taken at each of four depths every 3 hours over the t i d a l cycle to provide information on the temporal v a r i a b i l i t y of the hydrographic and b i o l o g i c a l parameters. A l l hydrographic samples were collected with National Institute of Oceanography bottles mounted with Yashino Keike reversing thermometers. Temperature and oxygen were measured at sea, temperature with an accuracy of +/- 0.02 degrees C , and dissolved oxygen content by Winkler t i t r a t i o n with the reagent modifications discussed by C a r r i t t and Carpenter (1966), having an accuracy of +/- 0.05 ml/1. Surface temperature and s a l i n i t y values were collected from bucket samples, the bucket thermometer graduated in tenths of a degree C. , At station IND 0, with the vessel at anchor, a Marine Advisors current meter with deck readout (velocity and direction) was deployed over the stern. Readings were taken at 5 and 20 meters depth as often as conveniently possible but never less than 45 minutes apart. i i) Laboratory Proceedures and Data Reduction S a l i n i t y was measured using an Auto-lab inductively coupled 1 3 s a l i n o m e t e r w i t h a r e p o r t e d a c c u r a c y o f +/- 0.003 p p t . i n t h e s a l i n i t y r a n g e above 28 p p t . and +/- 0.02 p p t . below t h i s v a l u e . D e n s i t y ( e x p r e s s e d a s sigma T) was t h e n c a l c u l a t e d u s i n g Knudsen's f o r m u l a and a p p l y i n g c o r r e c t e d t e m p e r a t u r e and s a l i n i t y v a l u e s . F i n a l c a l c u l a t i o n of a l l h y d r o g r a p h i c p a r a m e t e r s was c a r r i e d o u t u s i n g a Department of O c e a n o g r a p h y p r o g r a m on a PDP 12 c o m p u t e r . A l l c u r r e n t meter r e a d i n g s were f i r s t c h a n g e d from k n o t s t o m e t e r s p e r s e c o n d . The m a g n i t u d e and d i r e c t i o n o f e a c h r e a d i n g was t h e n p l o t t e d a s a f u n c t i o n o f t i m e . As t h e c h a n n e l a t Ind 0 i s r e l a t i v e l y n arrow, w i t h a n o r t h - s o u t h a x i s , i t was f e l t t h a t any c r o s s c h a n n e l component t o t h e f l o w would be due t o e d d i e s and t u r b u l e n c e i n d u c e d by t h e h i g h l y i r r e g u l a r c h a n n e l b o u n d a r i e s . T h e s e components would be moving a l o n g t h e c h a n n e l a x i s i n c o r p o r a t e d i n t o t h e mean f l o w and as s u c h s h o u l d a v e r a g e t o z e r o o v e r t i m e . The c r o s s c h a n n e l components t o t h e f l o w measured by t h e c u r r e n t m e t e r s were t h u s i g n o r e d . A s u b s e q u e n t p l o t was t r a c e d showing o n l y t h e a l o n g c h a n n e l , n o r t h - s o u t h , component of f l o w as a f u n c t i o n o f t i m e o v e r t h e s a m p l i n g p e r i o d of a t i d a l c y c l e . The n o r t h - s o u t h components of f l o w were t h e n a v e r a g e d o v e r e a c h ebb o r f l o o d e v e n t t o a r r i v e a t a mean f l o w a t e a c h of t h e d e p t h s sampled f o r e a c h t i d a l p hase o b s e r v e d . S i n c e e a c h c u r r e n t meter d e p t h r e p r e s e n t e d an a p p r o x i m a t e l y e q u a l p o r t i o n o f t h e t o t a l c r o s s s e c t i o n a l a r e a o f t h e c h a n n e l a t IND 0, t h e two mean f l o w s were a v e r a g e d t o o b t a i n a s i n g l e mean f l o w f i g u r e f o r t h a t p h a s e o f t h e t i d e . T h i s mean f l o w was m u l t i p l i e d by t h e c r o s s 1 4 sectional area of the channel at Ind 0 to obtain the average volume transport, and then by the duration of the ebb or flood event to ar r i v e at an estimate of the volume of water transported during that p a r t i c u l a r t i d a l phase. This procedure was followed for each phase during which b i o l o g i c a l samples were taken and for each cruise. The ramifications of boundary f r i c t i o n on thi s c a l c u l a t i o n are discussed in the next section. A second estimate of volume transport was obtained using a numerical model which predicts t i d a l elevation and average t i d a l currents across each of a series of transects running through Burrard Inlet and into Indian Arm. The model was written in 1972 by Dr. P.B. Crean of the Department of Oceanography U.B.C. and the Federal Department of Fish e r i e s and Oceans and was further updated in 1977 by M. Foreman. The model was set up to predict the t i d a l current at section S7, immediately adjacent to the sampling station Ind 0 (see Figure 1). The output gave a prediction of the average current across t h i s section every! hour over the entire study period. The hourly current values corresponding to those times during which the station was occupied were then averaged in sequence to obtain an average current v e l o c i t y for each hour. The v e l o c i t i e s for each t i d a l phase were then summed and multiplied by the cross sectional area of section S7 to obtain the second estimate of volume, transport for each phase of the t i d a l cycle during which data was c o l l e c t e d . Other t i d a l parameters such as times and elevations were taken from Canadian Tide and Current Tables Vol 5, 1980 and 15 1981, published by the Canadian Hydrographic Service. Corrections were made to the predictions using Vancouver Harbour, as a reference port and applying the differences published for Deep Cove as a secondary port. (Deep Cove i s the closest secondary port to the t i d a l station IND 0, see Figure 1). . B i o l o g i c a l Data i) F i e l d Proceedures B i o l o g i c a l samples were taken using Clark-Bumpu's nets (Clark and Bumpus, 1950) to obtain v e r t i c a l l y discrete samples and either a SCOR net or a conical meter net to obtain v e r t i c a l hauls. Stations occupied were the same as those used to c o l l e c t hydrographic data so that each station had a concurrent set of hydrographic and b i o l o g i c a l samples. The depths sampled are shown in Table II. At station IND 0, samples were taken at three depths every three hours, simultaneously with the hydrographic samples. These samples were used to resolve the temporal changes in the plankton concentration over the t i d a l cycle. Each Clark-Bumpus net used had a mouth aperture of 12 cm. and was f i t t e d with a net of Number Two mesh (mesh size:350 microns). Each net incorporated the modifications recommended by Paquette and Frolander. (1957) and contained a c a l i b r a t e d flow 16 meter which allowed samples to be quantitative (see McHardy, 1961). At stations with a water depth greater than 60 meters two Clark-Bumpus tows were made, each with 3 or 4 nets attached to the wire. The f i r s t tow sampled the 3 to 4 shallower depths, the second the remaining deeper depths. A l l tows were 15 minutes in duration and made with the speed of the towing vessel adjusted to maintain a wire angle of approximately 30 degrees. Depending on sea conditions, vessel speed was usually about 1.5 knots. At station IND 0 a small fiberglass 150 H.P. inboard/outboard runnabout f i t t e d with a derrick and a gas powered winch was used in making the Clark-Bumpus tows. The larger research vessel was anchored on station to complete the hydrographic work and the v e r t i c a l plankton hauls. This small boat was unavailable for the February 1980 cruise and the larger research vessel was used to make the tows. During this cruise one tow was made every six hours res u l t i n g in a single depth series from each t i d a l phase. V e r t i c a l hauls were taken using either a SCOR net (mesh size : 303 microns) or a Meter net (mesh size 330 microns), from as close to the bottom as possible (see Table II) to the surface. A constant hauling speed of 0.5 meters/second was maintained. At stations deeper than 60 meters, a second haul was made from 50 meters to the surface in an attempt to separate the surface plankton from deeper plankton. The main purpose of the v e r t i c a l hauls was to provide an integrated sample of the entire water column. Immediately after sampling, each net was washed down with 17 sea water.. The sample was then transferee! into either 4 or 8 ounce l a b e l l e d glass jars and preserved in a calcium carbonate buffered formalin solution of approximately 5% formal in:seawater . The purpose of the November 1981 cruise was to take rep l i c a t e zooplankton tows in order to establish s t a t i s t i c a l confidence l i m i t s applicable to copepod densities calculated from previous cruises. A series of six replicate Clark-Bumpus tows were made, each with three nets on the wire. A l l tows were made with the vessel starting at the same location (IND 2.0) and moving in the same di r e c t i o n along a . fixed; course. Each tow lasted 15 minutes and a l l were made during the same t i d a l phase (a small ebb) to minimize the v a r i a b i l i t y in the samples caused by t i d a l e f f e c t s (see Sameoto, 1975). The sampling depths chosen (see Table IV) were designed to increase the probability of consistently catching each of the copepod study species at at least one depth..In addition, four replicate v e r t i c a l hauls were made at station IND 0 using the SCOR net. A l l hauls were of id e n t i c a l length, used a constant hauling speed and were made during the same t i d a l phase. Samples from a l l the b i o l o g i c a l replicates were treated and preserved in the usual manner. i i) Laboratory Proceedures and Data Reduct ion Zooplankton were sorted and counted using a Wild M5 dissecting microscope. A l l samples were completely examined for 18 the relevant species and no s p l i t t i n g of hauls was attempted. The laboratory procedures therefore contributed no sampling error or bias to the data beyond any counting errors.> The taxonomic l e v e l to which the zooplankton were sorted varied with each taxonomic group (see Table I I I ) . For the analysis of changes in the whole zooplankton community over the t i d a l cycle at IND 0 i t was f e l t that i d e n t i f i c a t i o n to species would be important only for taxonomic groups which contained numerous l o c a l species. This procedure w i l l not greatly af f e c t the v a l i d i t y of the parameters used to describe changes in the zooplankton community over the t i d a l cycle as each was used only to compare samples treated in a similar fashion. Some bias w i l l be introduced by the lumping of taxa. However, th i s effect w i l l be minimized due to the few specimens found in each group, and. also the limited number of species actually lumped together. (Where the number of species included in a group is known, i t i s given in the table.) Copepods more mature than the f i r s t copepodite stage were i d e n t i f i e d to species but not sorted by age or sex. Medusae, ostracods, amphipods and cladocerans were i d e n t i f i e d to genus while groups with low taxonomic d i v e r s i t y or very few individuals were ' i d e n t i f i e d only as s p e c i f i c a l l y as was needed to delineate separate groups (see Table I I I ) . No satisfactory key exists for i d e n t i f y i n g naupliar stages and they were c l a s s i f i e d as a separate group. Copepods used in the transport study were sorted to species and those exhibiting a known ontogenetic depth preference, Euchaeta japonica (Evans, 1973; 19 Lewis and Ramnarine, unpublished data) and Eucalanus bungi (Krause and Lewis, 1979), were sexed and aged to the f i r s t copepodite stage. Copepods were sorted using Brodskii (1950) and Fulton (1968) as keys. Other groups of zooplankton were sorted using Fulton (1968). Serious doubt regarding the correct taxonomic name for two of the study species remains in the published and unpublished l i t e r a t u r e . Evans (1973) states that Euchaeta  japonica should c o r r e c t l y be c a l l e d Pareuchaeta elongata . Thorpe (1980) claims to have found s i g n i f i c a n t differences in. the Metr i d i a specimens found in Indian Arm and those found in the North P a c i f i c which have been described as Metridia pac i f ica by. Brodskii ••( 1950-)-. As. the taxonomic status of these species is. s t i l l unresolved, and such work i s beyond the scope of t h i s , ecological study, the names used correspond to those found in the keys most commonly used f o r . B r i t i s h Columbia zooplankton. Following i d e n t i f i c a t i o n and counting, the data were transformed into density values using the volume of water f i l t e r e d by each net as measured by the calibrated flow meter associated with that net. A l l zooplankton densities are expressed in number per cubic meter of water and a l l transport calculations were done using these values. The sampling depths chosen for Cruise 81/33, to establish confidence l i m i t s , resulted in a data table,which could be used to calculate s t a t i s t i c a l parameters for a l l of the copepod study spec ies. Eucalanus bungi was consistantly caught by the 200m net while Euchaeta japonica and Metridia pac i f i c a were both 20 consistantly caught at 100m. Corycaeus anglicus was caught at a l l three depths but most consistantly at 100m and 20m (see Table IV). The s t a t i s t i c a l procedure to establish confidence l i m i t s was that recommended by Cassie (1962), using a logl0(x+1) transformation as in Stone (1977) to log normalize the plankton d i s t r i b u t i o n (see Cassie, 1968). The transformed replicate data were used to calculate a log standard deviation for each species (see Table V). This log standard deviation was then applied to s i m i l a r l y transformed data- from previous cruises and, using the t value associated with the.original five degrees of freedom established from the 6 replicate tows, was used to establish 95% confidence l i m i t s for each density value. These transformed confidence l i m i t s were then changed to their o r i g i n a l form of animals per cubic meter. Mathematically expressed, the procedure followed was: 95% LIMITS = (log r +/- log sd t) antilog - 1 where r is the number of animals per cubic meter of a particular species, log sd i s the logarithmic standard deviation of the species as estimated from the r e p l i c a t e s , and t i s the t value associated with 5 degrees of freedom. The c o e f f i c i e n t of variation (CV) is a measure of plankton patchiness and can be used to compare the r e l a t i v e v a r i a b i l i t y of r e p l i c a t e s . It i s useful when one can assume a log normal d i s t r i b u t i o n of animals which, for plankton, i s acceptable in most cases. CV is calculated by expressing the sample standard deviation as a percentage of the sample mean. Cassie (1962) 21 states that the c o e f f i c i e n t for plankton usually has a value between 22 and 44% and that much higher values are not rare. The CV values calculated for Euchaeta japonica and Metridia p a c i f i c a at 100m are both within t h i s range and the values for Eucalanus  bungi at 200m and Corycaeus anglicus at 100m and 20m are only s l i g h t l y larger, (see Table V) . Higher values of CV are due to low mean values of plankton counts. In these cases the assumption of a log normal d i s t r i b u t i o n becomes less tenable and the d i s t r i b u t i o n actually approaches, a Poisson d i s t r i b u t i o n . As the mean, of replicate counts gets smaller the log normal d i s t r i b u t i o n results in a less s a t i s f a c t o r y representation of the data (Cassie, 1962). Low densities of copepods in the samples are thus the: probable cause of the high values of CV seen in Table V. The logarithmic c o e f f i c i e n t of variation (CV) is also useful in comparing the va r i a b i 1 i t y of . replicates as the. v a r i a b i l i t y within samples- resulting from an interaction of. bi o l o g i c a l and physical processes i s more l i k e l y . to be mu l t i p l i c a t i v e . than additive (Cassie, 1968). CV values calculated for the study species (see Table V) are a l l within the range found by Stone .(1977) for similar coastal zooplankton samples. A r t i f i c i a l l y low values are generated by very low mean values in the re p l i c a t e s . The log (x+1) transformation, which w i l l have l i t t l e e f fect on larger values, w i l l overcorrect smaller, values.. This may be closer to the Poisson d i s t r i b u t i o n discussed above than to the log normal d i s t r i b u t i o n . 22 S t a t i s t i c a l procedures used in analysing the data, were ca r r i e d out on the University of B r i t i s h Columbia MTS system and programs found in the Institute of Animal Resource Ecology Data Center. Population parameters used in analysing zooplankton d i f ferences over the t i d a l cycle were calculated, using Zoology 403 s t a t i s t i c a l programs written by Dr. C.J. Krebs of the Department of Zoology at the University of B r i t i s h Columbia. The cal c u l a t i o n of animals transported across the s i l l during a t i d a l event involved averaging depth s p e c i f i c samples to a r r i v e .at mean animal densities for each sampling time. The cross sectional area of the channel at IND 0 is approximately 30,445 meters 2. At each sampling time, each of the three nets used .was assumed to have obtained a zooplankton sample representative of that portion of the water column to which i t was closest. The 5 meter net represents the depth in t e r v a l 0-7.5 meters, the 10 meter net from 7.5-15 meters, and the 20 meter, net from 15-bottom. From the depth p r o f i l e published on Chart 3434 of the Canadian Hydrographic Service i t was calculated that the cross sectional area enclosed by each of these depth intervals i s approximately equal (+/- 4%). The animal densities from each net could thus be averaged to obtain the mean animal, density for each.sampling time across the IND 0 cross section. As the sampling in t e r v a l was every three, hours and the duration of a t i d a l event was about six hours, there were often two and sometimes three such mean animal density, values calculated for each t i d a l phase. The f i n a l animal density which can be multiplied by the volume transport figures was obtained by averaging a l l d e n s i t y values taken during a t i d a l phase. 24 RESULTS AND DISCUSSION Hydrographic Data i) Deep water Intrusions The shallow s i l l present at the entrance to Indian Arm r e s t r i c t s the exchange of water with the S t r a i t of Georgia and thus the horizontal continuity of water properties : across the study area. For . a deep water intrusion to occur, water above s i l l depth (approximately 20 meters) in the S t r a i t of Georgia must be more dense than resident f j o r d deep water. In the S t r a i t of Georgia, surface water.density reaches a maximum in winter due to the reduced flow of the Fraser River (Waldichuck, 1957). An Indian Arm deep water intrusion i s therefore primarily a winter phenomenon. Figure 3 shows the density structure with depth along a longitudinal axis through the study area in January, 1981. Water of s u f f i c i e n t density to replace Indian Arm bottom water is present above s i l l depth at stations GEO 1748 and .FRA .1. At F i r s t Narrows however, v e r t i c a l mixing . is such that surface densities are severely reduced by the outflowing brackish water from Vancouver Harbour. Further mixing at Second Narrows and the Indian Arm s i l l reduced the density of water passing Station IND 0 to a value equivalent to that at approximately 40 meters in Indian Arm. The density of water at the actual entrance to 25 Indian Arm was thus dynamically incapable of penetrating below about 40 meters and bottom water in Indian Arm remained undisturbed. A similar density structure was present during the winter of 1980 (see Figure 4). A very d i s t i n c t indicator of bottom water replacement i s the oxygen concentration in deep water (Davidson, 1979). Due to b i o l o g i c a l and chemical oxygen•, demand, r e l a t i v e l y stagnant water in the f j o r d basin w i l l have a low oxygen concentration, the amount depending on d i f f u s i o n within the f j o r d and primarily, on the length of time since the la s t renewal.. Intruding V. water, orig i n a t i n g in the upper water column of the S t r a i t of Georgia w i l l have:a much higher concentration. Figure 5 shows the. effect of this intruding oxygenated water on the oxygen concentration at Station IND 2.0 from 150 meters to the bottom from-August 1970 to A p r i l 1981. (Data was obtained from the Department of Oceanography University of B r i t i s h Columbia, Data Reports 1970 -1981). The negative slope- following an intrusion r e f l e c t s the balance between b i o l o g i c a l respiration, chemical oxygen demand and d i f f u s i o n . Immediately obvious is the' lack of any apparent oxygen increase during the study period, January 1980 - A p r i l 1981. The resident deep water of Indian Arm remained undisturbed: by any major physical event and the oxygen concentration steadily decreased r e f l e c t i n g the net oxygen demand. During the study period, no major deep water intrusion took place and transport of deep water zooplankton across the . s i l l , such as .that reported by Stone (1977), was not possible. Water exchange between Indian Arm and the S t r a i t of Georgia was due to 26 t i d a l action and estuarine c i r c u l a t i o n and the potential existed for the exchange of shallow dwelling organisms only. i i ) Estuarine C i r c u l a t i o n The pattern of estuarine c i r c u l a t i o n in Indian Arm has two d i s t i n c t features. F i r s t , there i s a bimodal seasonal cycle with a mid summer maximum due to snow melt in the mountainous drainage basin and a second maximum in the late f a l l - e a r l y winter months (October, November, December), in response to a l o c a l peak in p r e c i p i t a t i o n (Davidson, 1979). Second, the c i r c u l a t i o n i s complicated by intense v e r t i c a l mixing at the s i l l s . This decreases the density of water moving into the i n l e t in deeper layers by mixing brackish outward moving surface water down into .the incoming water. S i m i l a r l y , : there i s ; an increase in density of near surface water by v e r t i c a l mixing with the inward moving dense water in the d e e p e r l a y e r s . An example of this phenomenon can be seen in Figures.3 and 4. This strong v e r t i c a l mixing at the s i l l s greatly reduces the transport potential of this mechanism. Large quantities of the outward moving surface layer are returned into the i n l e t by being mixed down into the lower layer (Gade, 1976). Organisms in the upper, layer are thus p a r t i a l l y returned to the i n l e t . Likewise, organisms in the denser water outside which might otherwise have been transported into the i n l e t , .are mixed up into the seaward flowing surface water. This trapping of water and i t s associated properties within a f j o r d by.mixing over a s i l l i s a well known phenomenon (e.g. Gade, 1976). 27 A second ramification of t h i s v e r t i c a l mixing and i t s reduction of the incoming water density is the maintenance of the estuarine c i r c u l a t i o n as a system associated: with the upper water column. Water which was p o t e n t i a l l y capable of penetrating into deep water and involving a large part of the water column in the c i r c u l a t i o n , is now , maintained in the upper, layers. Estuarine c i r c u l a t i o n in Indian Arm i s thus r e s t r i c t e d to the upper water column. A crude estimation of the magnitude of the transport, by estuarine c i r c u l a t i o n in Indian Arm can be obtained as follows:. Total volume of freshwater entering Indian Arm = 41 cu. m/sec. . (Davidson, 1979) = 1.29 x 109 cu. m/year = R S a l i n i t y Of upper layer at IND 0 (averaged over a l l . cruises) = 21.1ppt=S . S a l i n i t y of lower layer at IND 0 (averaged over a l l c r u i s e s ) = 26.0ppt =S' Assuming a constant volume of Indian Arm and conservation of s a l t in the i n l e t , using: Knudsen's equations (from Saelen, 1967), the volume of water, V , entering the i n l e t i s ; V = R S/S'-S = 5. 55 x 1 0 9 cu. m/year The volume of Indian Arm (D. Dunbar, Pers. Comm.) is approximately 2.25 x 109 cu. meters. Estuarine;circulation i s . p o t e n t i a l l y capable of replacing the t o t a l volume of the i n l e t 28 about twice per year. The volume of water brought into the i n l e t by flood tides (see next section) is approximately 4.2 x TO 1 0 cu. m/year. Averaged over a year, estuarine c i r c u l a t i o n i s responsible for about 13% of the water entering Indian Arm. The estuarine c i r c u l a t i o n makes up a small part of the t o t a l transport at the s i l l . At times of maximum fresh water input the percentage brought into, the i n l e t via t h i s mechanism would increase. The s i g n i f i c a n t . f e a t u r e of t h i s mechanism i s i t s effect on the surface layers of water- in Indian Arm. Although the flow i s superimposed on the dominant t i d a l ., exchange, estuarine c i r c u l a t i o n establishes, a net seaward movement, in the upper layer of the water column. . Over many t i d a l , cycles t h i s net-movement would be an e f f e c t i v e mechanism for the transport of zooplankton species l i v i n g in the near surface water of the i n l e t . . . . i i i ) T i d a l Exchange During the study period, tides were the dominant transport mechanism at the Indian . Arm s i l l . The volume of water transported during a t i d a l phase was estimated both by current meter and by t i d a l model. The current meter deployed at Indian 0 during each cruise met with .varying success. The meter f a i l e d , to work s a t i s f a c t o r i l y during Cruise 80/2 and the d i r e c t i o n a l indicator f a i l e d to operate during Cruise 80/12 resulting in no current meter estimate of volume transport over these cruises. An 29 example of the current meter- data c o l l e c t e d i s shown in Figure 6 (from Cruise 81/6). Figure 7 shows the data generated by ignoring the cross channel components of flow. In. Figure 6 the flow at both 20 meters and 5 meters i s shown to be predominantly:' north-south or along the channel; cross channel components, however, are evident. The north-south component of flow was always in the di r e c t i o n of t i d a l flow at 5 meters. At 20 meters the flow is both smaller in magnitude and more varied in i t s response to t i d a l d i r e c t i o n . The general trend, however, i s for the flow at both depths to be in the- same di r e c t i o n as the t i d a l flow. Table. VI shows the calculated volumes of water transported across the s i l l during each of the t i d a l phases over which currents were measured. In. a l l cases the calculated volume of ,. water transported across the s i l l was in the same . d i r e c t i o n as.... t i d a l flow, which i s to be expected. The residual, or net flow, at the end of a complete t i d a l cycle should be close to zero excluding the freshwater outflow (about 13% of t i d a l flow, see previous section). For the current meter data the net transport (summed over the t i d a l cycle) is the same order of magnitude as the transport during an entire t i d a l phase, and is of ten larger (see Table VI). Moreover, the calculated net flow i s often up i n l e t , p recisely opposite to the predicted down i n l e t net flow caused by the freshwater. These: are indicators of the error involved in the c a l c u l a t i o n of volume transport with the sampling techniques used. There are a number of possible explanations for these errors. Calculation of the Reynolds Number at Ind 0 showed that the flow would be f u l l y 30 turbulent at any current ve l o c i t y above approximately 0.01 meters/second. This indicates that the flow i s turbulent at any time other than slack water. For a f u l l y turbulent flow in a channel there i s a cross channel current shear such that the flow, i s at a maximum near the surface.in the center of the channel and f a l l s to a minimum near the boundaries due to f r i c t i o n a l e f f e c t s . This effect i s greatly i n t e n s i f i e d in a channel of such highly irregular boundaries as those found on the Indian Arm s i l l . The current meter at 5 meters in the center of the channel therefore measured a maximum flow, and the.20 meter current readings r e f l e c t a decrease in flow of unknown magnitude presumably due to bottom f r i c t i o n . The current meter readings give no. estimate of the reduced current v e l o c i t i e s near the l a t e r a l boundaries. Multiplying by the cross section of the channel therefore results in an overestimation of volume transport. In addition/ because readings were taken on the order of once every half hour, small eddies induced in the highly turbulent •flow resulted in cross channel components which were treated as major components to the flow in the channel during the ca l c u l a t i o n s . Sampling at a much higher frequency might have eliminated these cross channel components of eddies by averaging. The sampling frequency did not enable, these high frequency events to be averaged out of the main flow. Other errors which could not be avoided with the sampling gear available were induced by movements of the ship while at anchor. Although these were minimized as much as possible by eliminating readings taken during large ship movements, smaller or slower 31 movements were not always detectable, especially at night. For the above reasons, volume transport values obtained from current meter readings were not used in the c a l c u l a t i o n of zooplankton transport. The current meter values were used only for comparison and as an indicator of the general v a l i d i t y of volume transport calculated from the t i d a l model predictions of v e l o c i t y . Table VI and Table - VII show the volume,transport calculated from the two series of data. Upon summation over the single complete t i d a l cycles associated with the cruise times, i t was found that volume transport calculated from the t i d a l model also yielded very large net flows. Unlike the current meter data, however, the t i d a l model was able, to provide transport values for tides immediately prior to and immediately.after the sampled tide; Assuming that the t o t a l volume of Indian Arm was not in flux, and that the net flow should be small, (equal to the freshwater outflow), the volumes of water transported over t i d a l phases of similar v e r t i c a l i change, regardless of d i r e c t i o n , could be averaged. The result was an average volume transport associated with any large or small t i d a l change which was applicable to the zooplankton data from the cruise to which the volumes correspond (see Table VII). It was f e l t that these average values would y i e l d a more r e l i a b l e estimate of longer term transport trends. The a p p l i c a b i l i t y of model derived data to the real environment must always be questioned. Any model is obviously a s i m p l i f i c a t i o n and the t i d a l model i s no exception. V e l o c i t i e s predicted are those due to t i d a l action only and no account of 32 freshwater outflow or other physical transport mechanism is taken. The model i s based on the volumes of water needed to meet t i d a l height requirements across transects through the i n l e t . Volume transport across the Ind 0 cross section i s therefore based on the volume of water which must pass th i s plane.to account for empirically predicted t i d a l heights in Indian Arm. Unlike the current . meter derived v e l o c i t y data, the model v e l o c i t i e s are derived from a volume consideration and are therefore averaged over the entire cross section. It is at the s i l l that the model w i l l be the least accurate (Dr. S. Pond,: Pers. Comm.), although this inaccuracy i s primarily in the time scale of predictions rather than i t s magnitude. It was f e l t that the model would y i e l d s u f f i c i e n t l y r e l i a b l e data to enable ca l c u l a t i o n of general trends over the study period. The inaccuracy in the times of predicted flows would be r e l a t i v e l y unimportant as the precise timing of individual t i d a l events w i l l not aff e c t estimates of t i d a l volume transport over long periods of time which was the objective of. the study. Transport of the Study Spec ies i_) Corycaeus anqlicus The density of C. anglicus at each depth sampled over the fi v e cruises in the study area i s shown in Table VIII. A number of general trends are immediately, obvious. The spec ies i s never found in great numbers in the S t r a i t of Georgia and is most numerous in Vancouver Harbour (Station VAN 24) and at IND 0. 33 While i t is more numerous in Indian Arm than in the S t r a i t of Georgia, in general i t seems not to be present in large numbers in deep water areas. C. anglicus i s found over most of the water column at the deeper stations but is most numerous at the^ surface and mid depths. Maximum population densities were recorded.at the time of the f a l l cruise (October), in agreement with Legare (1957) Seasonal trends in the magnitude of C. anglicus transport across the Indian .Arm s i l l are concommitant with, the f a l l , population peak (see Figure 8). Due to i t s presence throughout, the year in near surface water one would expect transport over the s i l l on a continuous basis. Figure 8 supports t h i s . A.crude estimate of the t o t a l transport- of C.. anglicus between each cruise can be . obtained by, assuming.that values calculated for each cruise can be applied'to a l l the t i d a l cycles occurring in the time i n t e r v a l . Values for adjacent cruises were applied to half the t i d a l cycles to estimate the transport.between cruises. Table IX shows that the transport of C. anglicus between cruises approximates (within an order of magnitude) the population of the species in Indian Arm calculated at the time of the second cruise. . The t o t a l population of a species in an area should be. a function of transport .(imigration and emigration), mortality and n a t a l i t y within the area. The transport values- show that the t o t a l population in Indian Arm can be accounted for.by exchange over the s i l l . Moreover, population variations such as the decrease between January 1981 (cruise 81/1) and March 1981 34 (cruise 81/6) are accounted for by transportation out of the i n l e t as seen during the January cruise. Figure 9 shows the average concentration of C. anqlicus in the upper 50 meters during i t s breeding season in October. The large population at VAN 24 i s an obvious feature and suggests a prefered breeding s i t e and a major source of this species. Although no counts of juveniles or egg clusters were made for t h i s species and no conclusive evidence can be presented regarding the a b i l i t y of C. anqlicus to reproduce in Indian Arm, the transport data suggest that mortality and n a t a l i t y play a minor role in determining the population density of t h i s .species: in Indian Arm. It is thus suggested that the i n l e t population is primarily a result of transport across the s i l l from Vancouver Harbour. i i) Euchaeta japonica • The depth d i s t r i b u t i o n of E. japonica during the five cruises at each .station'is. shown in Table X. The species i s present in the S t r a i t of Georgia and in Indian Arm at a l l times of the year but is absent from Vancouver Harbour and the Indian Arm s i l l from March u n t i l January. Exchange of t h i s species across the s i l l was therefore observed only during the winter months. The species i s found in large numbers above s i l l depth in the S t r a i t of Georgia and in Indian Arm in October. T i d a l exchange of water and plankton are known to occur at t h i s time, yet the population in Indian . Arm appears to be unaffected. Transport was observed during Cruises 80/2 and.81/1 only and 35 c a l c u l a t i o n of the exchange of E. japonica during the winter months was carried out using figures derived from only these two cruises. Transport was assumed to commence sometime between the October cruise and the January cruise and was assumed to have terminated sometime after February as i t was not observed in March. The numbers of E. japonica exchanged over the winter period of November, December, and January are given in Table XI. Transport of E. japonica seems to have l i t t l e c o r r elation with the density of the species in Indian Arm as shown in the same table. A net transport into the i n l e t i s calculated for the winter months yet available measurements of post winter (or transport) conditions (Cruises 80/12 and 81/6) show a decrease in the population. Cruise 80/18, an : example of pre winter conditions, shows a , larger population in Indian Arm than both "during and after the period of exchange. This implies that transport has a r e l a t i v e l y small effect on the population and that other factors such as mortality and n a t a l i t y are the dominant factors c o n t r o l l i n g population density of the species in Indian Arm. Table XII shows that E. japonica is present in water transported across the s i l l primarily as a Stage III copepodite. The table shows that the high density of Stage I l l ' s at the s i l l i s not simply a result of higher concentrations of this stage in p o t e n t i a l l y exchangeable water. Figure 10 shows that s i l l water exchanged over the t i d a l cycle during the January 1981 cruise was most similar in temperature and s a l i n i t y properties (and, presumably in other b i o l o g i c a l l y important properties as well, 36 e.g. Bary, 1963) to water from the upper 10 meters of Vancouver Harbour and water from the upper 30 meters of Indian Arm.. The percentage of Stage III E. japonica in thi s water i s considerably less than that found in t i d a l l y exchanged water above the s i l l . It is interesting to note, however, that in the S t r a i t of Georgia, water which is above s i l l depth, or hydrographically similar to that which i s , (see Figure 10), has a similar percent composition of Stage III copepodites to water found. over the s i l l . The high percentage of Stage III copepodites in the S t r a i t of Georgia i s not the reason for winter transport per se. Potentially exchangable , water in October (Cruise 80/18, see Figure 18) shows a similar high percentage of this stage (see.Table XIII) and. similar densities to those found- in January yet transport does not occur.. Reasons for the lack of transport during the summer can only be- speculated upon as the data obtained during this study do not explain the anomaly. A-breeding population of E. japonica exists in both the S t r a i t of Georgia and Indian Arm at this time. The presence of juvenile stages (copepodite Stages I,II,and III) is- evidence of this (see Table XIV). In spite of 1) observed exchange of water between the twoareas, 2) evidence of the exchange: of other species, and 3) the presence of E. japonica in pot e n t i a l l y exchangeable water, the populations are isolat e d for much of the year. It is possible that summer exchange occurs via naupliar stages which were- not i d e n t i f i e d or counted. E. japonica spends approximately 20 days (Evans,. 1971) as a nauplius larva, which i s enough time for i t to be 37 transported from the S t r a i t of Georgia into Indian Arm or vice versa. The complete absence of Stage I and II copepodites from both Vancouver Harbour and Ind 0, however, reduces the li k e l i h o o d of such an occurrence. Furthermore, Evans (1971), states that the naupliar stages are seldom observed above 100 meters in the study area. Their exchange across the 20 meter s i l l s thus appears unlikely. A possible explanation for the lack of summer transport i s the presence of b i o l o g i c a l l y inadequate conditions in the waters of Vancouver Harbour and the Indian Arm s i l l . i i i ) Met r i d i a pac i f ica The density of M. p a c i f i c a in the study area at each station on each cruise, is shown, in Table XV.. The species i s common at every depth sampled and i s found throughout the year. Transport across the s i l l at IND 0 was observed on each cruise.> M. pac i f ica i s known to exhibit a strong d i e ! migration (Stone, 1977) and evidence of th i s i s shown in Figure 11. Station FRA 1 was sampled during daylight on Cruise 80/12 and at night on Cruise 81/1. The daytime sample shows the majority of animals at mid depth, centered-around 100 meters/ while at night the population was concentrated near the surface; At Station IND 0, evidence of the d i e l migration was seen over a single cruise. Table XVI shows the densities of M. paci f ica at each depth over the t i d a l cycle during the day and during the night in October (Cruise 80/18). Results of a t-test to determine differences between day and night densities, show that the concentration of 38 M. p a c i f i c a was s i g n i f i c a n t l y higher at night regardless of the. di r e c t i o n of t i d a l movement. However, a similar test for a l l data from Cruises 80/12 and 81/6 found no s i g n i f i c a n t . d i f f e r e n c e between the two sets of samples. Cruise 81/6 data from only 20 meters, however, shows a highly s i g n i f i c a n t . increase at night (Table XVI). Transport of M. pac i f ica across the s i l l during each cruise is shown in Table XVII. While transport occurs throughout the year, the d i r e c t i o n of net transport seems to have l i t t l e c o r r e l a t i o n with season and shows no clear trends over the study period. The t o t a l number of animals estimated to have been transported between each cruise was calculated by averaging values from adjacent cruises over the number of t i d a l cycles which took place.in the time in t e r v a l between the cruises. There was l i t t l e c o r r elation between transport and the t o t a l : population of M. pac i f ica in Indian Arm at the time of. the second cruise. The population seemed to remain r e l a t i v e l y constant (within confidence l i m i t s ) over the f i r s t four cruises yet transport over th i s time period varied both in magnitude and d i r e c t i o n . The population decrease between Cruise 81/1 and 81/6 is supported by the d i r e c t i o n of net transport at this time, but only accounts for approximately 15% of the change. These data indicate that transport has a minor . e f f e c t on the .. population densities of the species in Indian Arm and that factors, such as seasonal breeding cycles and mortality probably play a more dominant role. The lack of c o r r e l a t i o n between net transport and seasonal breeding cycles could also be an a r t i f a c t of the 39 s a m p l i n g p r o c e d u r e . The s p e c i e s o c c u r s i n h i g h d e n s i t i e s i n t h e upper p o r t i o n o f t h e water column and i t i s n o t u n r e a s o n a b l e t o assume t h a t t h e d i s t r i b u t i o n i s p a t c h y . The a d v e c t i o n of p a t c h e s of t h i s s p e c i e s a c r o s s t h e s i l l by t i d a l c u r r e n t s would p r o d u c e v a r i a b i l i t y i n t h e d e n s i t y o f t h e s p e c i e s w h i c h c o u l d have been m i s s e d by t h e s a m p l i n g i n t e r v a l u s e d . The c o e f f i c i e n t o f v a r i a t i o n (CV).,. c a l c u l a t e d . f o r M. pac i f i c a ( s e e T a b l e . V ) , however, does not i n d i c a t e h i g h d e g r e e s o f p a t c h i n e s s . (Samples from w h i c h t h e CV c a l c u l a t i o n were made were a l l t a k e n from t h e same l o c a t i o n o v e r a s h o r t p e r i o d o f t i m e . ) Where d e p t h p e r m i t s , t h e d i e l m i g r a t i o n o f M. pac i f l e a w i l l t a k e t h e a n i m a l below s i l l d e p t h and o u t o f p o t e n t i a l l y e x c h a n g e a b l e . w a t e r . In s h a l l o w e r water,, s u c h as o v e r t h e s i l l , t h e a n i m a l may. m i g r a t e t o a p o s i t i o n . v e r y n e a r . t h e s e d i m e n t -w a t e r ' i n t e r f a c e , d e p t h s w h i c h c o u l d n ot be sampled w i t h t h e equipment a v a i l a b l e . The d i e l m i g r a t i o n o f z o o p l a n k t o n i s t h o u g h t , t o be made i n r e s p o n s e t o c h a n g e s ( o r r a t e s of change) i n l i g h t i n t e n s i t y s u c h t h a t d a y l i g h t c a u s e s a downward m i g r a t i o n t o a d e p t h of s u i t a b l y l o w . l i g h t . In s h a l l o w water t h i s d e p t h may be u n a t t a i n a b l e but a v e r y c l o s e a s s o c i a t i o n w i t h th e s e d i m e n t - w a t e r i n t e r f a c e o r even an im m e r s i o n i n t o t h e s e d i m e n t ( L e w i s , P e r s . Comm.), mi g h t p r o d u c e t h e n e c e s s a r y l i g h t c o n d i t i o n s . : I f s u c h i s t h e c a s e , a n i m a l s c a r r i e d i n t o s h a l l o w water by t i d a l c u r r e n t s w i l l have a g r e a t l y r e d u c e d o r n e g l i g i b l e t r a n s p o r t d u r i n g t h e day by c u r r e n t s i n t h e water c o l u m n above them. A t n i g h t , a s t h e y move away from t h e s e d i m e n t - w a t e r i n t e r f a c e , t h e y a g a i n become s u s c e p t i b l e not o n l y 40 to the current in the water column but also the sampling equipment. Transport of M. p a c i f i c a i s , affected in a quantitative manner by the d i e l migration such.that exchange of the.species occurs mainly at night. The e f f e c t of .this migration may at f i r s t appear to have an effect on d i s t r i b u t i o n , however, because the migration occurs throughout the year and the species i s in p o t e n t i a l l y exchangeable water each time i t nears the surface, there w i l l be no effect on the o v e r a l l exchange. The long term effect of t h i s situation is to allow continual exchange of the populations in the S t r a i t of Georgia and in Indian Arm. This, suggests that they can be considered a single population, exposed to d i f f e r e n t environmental factors depending upon, their location. iv) Eucalanus bungi E. bungi was the least abundant of the copepods chosen for study. Its density at each station over the study period at each depth i s shown in Table XVIII. Immediatly obvious i s the ontogenetic v e r t i c a l migration exhibited by t h i s species in the S t r a i t of Georgia. The overwintering population i s seen to occupy deep water (below 1 50 • meters ).• During, the.summer they are scattered over much of the water column and present in near, surface water in large numbers. By f a l l (Cruise 80/18), they are again scarce in the upper water column and found mainly in deep 41 water. A further c h a r a c t e r i s t i c to be noted from this table i s the complete absence of t h i s species from the upper 100 meters of Indian Arm. This i s in accordance with the.distribution seen by Krause and Lewis (1979). Figure 12 shows that the ontogenetic migration has severe ramifications on the exchange of E. bungi between Indian Arm and the S t r a i t of Georgia. From the data, transport over the s i l l appears to occur only during the summer when the species i s present in surface water in the S t r a i t of Georgia. This species is not present in the p o t e n t i a l l y exchangeable water of Indian Arm (Figure 13, Table XVIII). The data indicate that specimens found in Vancouver Harbour and at IND 0 had their o r i g i n in the S t r a i t of Georgia and that . transport is primarily u n i d i r e c t i o n a l . . . An estimate of the t o t a l seasonal transport of E. bungi across the s i l l i s shown in Table XIX. Transport values calculated from the data, c o l l e c t e d during Cruise 80/12 were multiplied by the t o t a l number of t i d a l cycles in which E. bungi occupies near surface (potentially exchangeable) water , in the S t r a i t of Georgia. Krause . and Lewis (1979), found that peak populations in these waters occurred in June and July, dropping sharply in August. Transport was estimated to have occurred over a two and a half month period and Table XIX shows that such a period of transport can account for the entire overwintering population, in Indian Arm. The transport data suggests that n a t a l i t y within the i n l e t has l i t t l e influence on the population and that the dominant process governing population density i s 42 exchange across the s i l l . This suggestion is supported by the d i s t r i b u t i o n of younger copepodite stages (Stages. I, II, and III; Table XX) during the breeding season (Cruise 80/12). While the presence of these stages in near surface water of the S t r a i t of Georgia indicates a reproducing population they are never observed in Indian Arm. Lack of a breeding population in Indian Arm i s supported by similar data from Krause and Lewis (1979). E. bungi appears to be transported across the s i l l p rimarily as younger copepodite stages, in spite of the fact that these stages are never seen in Indian Arm (see also Krause and Lewis, 1979). Data from IND 0 (Table XX) show that the transported organisms are a l l younger than Stage IV and that, similar to Euchaeta japonica , the primary dispersive stages of E. bungi seem to be the young copepodites. The data suggest that there i s no breeding population of E. bungi in Indian Arm and that animals observed in the i n l e t are solely a result of summer transport. The fate of these animals the following spring when they migrate into surface water to spawn is unknown. No data on the horizontal or v e r t i c a l d i s t r i b u t i o n of E. bungi in the v i c i n i t y of Indian Arm at the time of the onset of the upward migration is available. However, two possibi1 i t i e s exist,. f i r s t , that the organisms might migrate into near surface water as they do in the S t r a i t of Georgia, but be c a r r i e d out of the i n l e t by the seaward flowing upper layer. The magnitude of this flow would be at i t s seasonal peak as a resu l t of spring run o f f . Such a situation would remove a l l E. bungi from Indian Arm except those which f a i l e d to migrate; no 43 juvenile stages would be observed, and no animals would be found in near surface water following the migration. A similar s i t u a t i o n has been observed in Knight Inlet (Stone, 1979) where surface dwelling plankton are completely advected from the headwaters of the i n l e t under conditions of high run o f f . Second, E. bungi might f a i l to migrate into surface water in Indian Arm and be unable to complete i t s l i f e cycle. Vinogradov (1968) states that migration of t h i s species might be triggered by variations in water temperature. Such seasonal changes would have to occur at depths below • 200 meters to a f f e c t the overwintering population. In open ocean situations, such deep seasonal changes are small or nonexistant. Penner (1978) suggests that a more plausible trigger to the spring migration, is the increase in sinking d e t r i t a l material caused by the onset of the spring phytoplankton bloom. Figure 14 shows that changes in the temperature of Indian Arm bottom water are quite small and have no seasonal pattern but show a continuous warming trend over the entire study period. Seasonal temperature changes do occur in the deep water of the S t r a i t of Georgia (Pickard, 1975) although Penner (1978) found that the upward migration of E. bungi had started before any such change had occurred. In Indian Arm the timing of the bloom varies but i s a dominant feature of the seasonal cycle of primary production (Gilmartin, 1964) and could provide the necessary cue. The timing of the upward-migration in r e l a t i o n to the onset of the spring phytoplankton bloom has not been studied in s u f f i c i e n t d e t a i l to allow deductions regarding i t s cause. However, any appreciable 44 advection of phytoplankton d e t r i t u s out of the i n l e t by estuarine c i r c u l a t i o n could reduce the stimulatory e f f e c t . Zooplankton Community Changes at IND 0 Over a Tidal Cycle Data analysis on the four copepod species chozen for the transport study, centered on seasonal trends, the interaction of depth d i s t r i b u t i o n and l i f e history patterns with transport processes, and the e f f e c t s of transport on the population in Indian Arm. Corequisite to t h i s was an analysis of changes and patterns in the zooplankton community and hydrographic properties which were manifested over the much shorter time period of a single t i d a l cycle. Unlike a rive r fed estuary, the. s i l l provides a location which, over a t i d a l cycle w i l l be subjected to marine influence on both flood and ebb tides. As water is exchanged across the s i l l by t i d a l currents one might expect the zooplankton community and hydrographic properties to change depending upon the source of the water and the degree of mixing i t has undergone. Both, of these, variables can be investigated using temperature and s a l i n i t y c h a r a c t e r i s t i c s as conservative tracers. Figure 15 shows the t i d a l cycle and the sampling times of Cruise 80/18 (sample numbering i s in a code related to Cruise 80/18 and has no meaning apart from the samples being consecutive). The semidiurnal nature of the tide is obvious. Large fluctuations in both temperature and s a l i n i t y take place in the surface water (see Figures 16 and 17) due to the strong influence of l o c a l p r e c i p i t a t i o n , runnoff, and other weather 45 p a t t e r n s . Such f l u c t u a t i o n s d e c r e a s e s h a r p l y w i t h d e p t h . F i g u r e 18 shows t h e t e m p e r a t u r e and s a l i n i t y c h a r a c t e r i s t i c s o f water a t e a c h s t a t i o n i n . t h e s t u d y a r e a a t t h e t i m e o f t h e c r u i s e . A l t h o u g h t h e c o l d e s t t e m p e r a t u r e s a r e f o u n d i n I n d i a n Arm deep w a t e r , s t r a t i f i c a t i o n i s s u c h t h a t n e a r s u r f a c e w ater ( p o t e n t i a l l y e x c h a n g a b l e a c r o s s t h e s i l l ) i s c o n s i d e r a b l y warmer, and water r e s i d e n t i n V a n c o u v e r Harbour, i s b o t h c o o l e r and more s a l i n e . Water f o u n d o v e r t h e s i l l d u r i n g a t i d a l c y c l e w i l l , be . a m i x t u r e o f t h e s e l a t t e r two t y p e s of w a t e r , i t s c h a r a c t e r i s t i c s d e p e n d e n t upon t h e r e l a t i v e amounts of e a c h p r e s e n t a t any g i v e n t i m e . S u r f a c e water a t hour 14 (sample 14) shows t h e l a r g e s t c hange i n b o t h t e m p e r a t u r e and s a l i n i t y ( s e e F i g u r e s 16 and 17). I t s c o r r e l a t i o n w i t h t h e t i d a l c y c l e and t h e r e a s o n i t s h o u l d be so d i f f e r e n t from a d j a c e n t samples i s d i f f i c u l t t o e x p l a i n . F i g u r e 19 shows t h e t i m e p r o g r e s s i v e T/S p l o t f o r water a t 0 m e t e r s . Two c h a r a c t e r i s t i c s b e a r n o t i n g ; t h e e x t e n t of t h e d i f f e r e n c e o f t h e water from sample 14 and t h e s i m i l a r i t y of t h e water from s a m p l e s 16, 17, and 18, a l l o f w h i c h were t a k e n d u r i n g t h e same f l o o d t i d e . T h i s s i m i l a r i t y i s p r o b a b l y due t o i n t e n s e v e r t i c a l m i x i n g o f t h e water as i t moves t h r o u g h Second Narrows and o v e r t h e I n d i a n Arm s i l l c r e a t i n g a more homogeneous body o f w a t e r . The z o o p l a n k t o n community a t t h e s i l l i s more l i k e l y t o be i n f l u e n c e d by changes i n t h e c h a r a c t e r i s t i c s of w a t e r below 5 m e t e r s w h i c h a c c o u n t s f o r a p p r o x i m a t e l y 90% of t h e w a t e r column. Changes i n t h e h y d r o g r a p h i c p r o p e r t i e s o f t h i s water, t a k e p l a c e 46 over the t i d a l cycle. Furthermore, these changes can be correlated with the di r e c t i o n of t i d a l movement and the source of the water. Figure 20 shows the time progressive T/S plot from each sample time averaged over the deeper part of the water column (5, 10 and 20 meters). Correlations between c h a r a c t e r i s t i c s of the deeper water and the t i d a l cycle are more obvious. The coldest and most saline water occurs towards the end of, and immediately a f t e r , a large flood tide (samples 11, 18 and 19), l a b e l l e d Type A. Figure 18 confirms that this i s to be expected from water originating in Vancouver Harbour. Samples 12 and 13, l a b e l l e d Type B, appear to be very similar to each other and although warmer and fresher than the previous group, are s t i l l more saline than other water sampled over the t i d a l cycle. Samples 12 and 13 probably r e f l e c t a s l i g h t mixing of Indian Arm water with the water brought into the s i l l v i c i n i t y during the large flood previously discussed. Water from samples 14, 15, 16, and 17, lab e l l e d Type C, are the least saline water found over the t i d a l cycle and occur during and immediately after a large ebb. Figure 18 confirms that water advected out of Indian Arm w i l l have these c h a r a c t e r i s t i c s . The eight most abundant copepod species were plotted against the t i d a l cycle and analysed using a Spearman Rank Correlation C o e f f i c i e n t for changes in the density which could be correlated with t i d a l height. Figure 21 shows the four most abundant copepods and the t i d a l cycle. Oithona helgolandica was the only species which showed a s i g n i f i c a n t c o r r e l a t i o n , greater densities being found at times of high water. Figure 22 shows 47 the second four most abundant copepods, two of which showed a s i g n i f i c a n t c o r r e l a t i o n . Corycaeus anglicus was found to be in greater densities at times of high water, and Calanus pacificus at times of low water. Two indices of d i v e r s i t y were calculated, Simpson's (Simpson, 1949) which i s sensitive to changes in common species, and the Shannon-Weiner (logs taken to base 2; Patten,1962) which is sensitive to changes in rarer species. These indices and percent dominance (McNaughton, 1967) were calculated for the community as a whole, for copepods only, for a l l other invertebrates, and for a l l other invertebrates minus larvaceans and siphonophores (which make up 85% of the numbers of other invertebrates). These data were plotted against the t i d a l cycle and analysed using Spearman Rank Correlation: Coefficient for changes which seemed to be in phase with t i d a l height (see Figures 23, 24, 25, and 26). The inverse relationship ^etween percent dominance of copepods and t i d a l height was s t a t i s t i c a l l y s i g n i f i c a n t , increasing on an ebb tide and decreasing with the flood ( Figure 24). Simpsons index of d i v e r s i t y for copepods was p o s i t i v e l y correlated with t i d a l height and both this and the Shannon-Weiner index showed d i s t i n c t minima reached at times of low tid e , most notably for Simpson's index (more common.species). These c h a r a c t e r i s t i c s could be due to a fjo r d copepod community, dominated by only a few copepod species, which is moved towards the s i l l during the ebb t i d e . The d i v e r s i t y and dominance of other invertebrates ( Figure 48 25) does not show a consistent relationship to t i d a l height and no s i g n i f i c a n t c o r r e l a t i o n was found. Maximum d i v e r s i t y for both indices i s reached during the large ebb tide and minimum d i v e r s i t y occurs at the end of the major flood t i d e . These data points are due largely to changes in the densities of larvaceans and siphonophores. When these two very dominant groups are removed (Figure 26), these maxima disappear. The remainder of the invertebrates did not show s i g n i f i c a n t c orrelation with t i d a l height. Diversity and dominance for the t o t a l zooplankton community ( Figure 23) probably strongly r e f l e c t the overwhelming influence of the large numbers of larvaceans and siphonophores. An analysis of variance using a randomized complete block design for one rep l i c a t e was calculated for the t o t a l density at each sampling time. The results show a s i g n i f i c a n t difference (p =0.05) in the numbers of copepods caught at each sampling time, indicating that s i g n i f i c a n t changes in copepod densities do occur: over the t i d a l cycle. The question then to be asked i s do these changes occur in r e l a t i o n to any i d e n t i f i a b l e physical parameter? Three dif f e r e n t parameter relationships were s t a t i s t i c a l l y tested to answer this question: 1) The community might show a variation in rela t i o n to the di r e c t i o n of t i d a l flow which could not be resolved from the graphs previously analysed. 2) If the population has a s i g n i f i c a n t number of 49 diurnal v e r t i c a l migrators, the community might show variations between samples taken at night and during the day. 3) Based on hydrographic data, the water moving over the s i l l could be grouped into three categories based on similar temperature and s a l i n i t y c h a r a c t e r i s t i c s (see Figure 20). The zooplankton community might vary between these water types. Samples were divided into those taken, on an ebb tide (Numbers 11, 14, 15, and 19) and those taken during a flood tide (Numbers 12,13,16, 17, and 18, see Figure 15) and a U-test used to test a number of d i f f e r e n t parameters and species densities for s i g n i f i c a n t differences between the two. There i s a s i g n i f i c a n t increase (p = 0.05) in the numbers of siphonophores during ebb tides, suggesting a larger population of these animals in Indian Arm than in Vancouver Harbour. Both the Simpson's and Shannon-Wiener index indicate a higher d i v e r s i t y of other invertebrates during ebb tides (p = 0.05). This could be due to a more diverse community of invertebrates in Indian Arm than in the shallower region of Vancouver Harbour. The reason for parameters having a c o r r e l a t i o n with t i d a l height yet showing no difference between ebb and flood t i d a l phases might be the s t r i c t d i v i s i o n of samples between ebb and flood based on sampling time. Hydrographically, i t i s d i f f i c u l t to decide in which tide a sample taken within an hour of slack water should be placed. Evidence . of this . can be seen more 50 c l e a r l y in Figure 20 showing the changes in the hydrographic properties. A comparison with Figure 15 shows that water c h a r a c t e r i s t i c s do not fluctuate s t r i c t l y in unison with t i d a l d i r e c t i o n . Samples were then divided into those taken during the day (Numbers 11, 12, 13, 18, and 19) and those taken at night (Numbers 14, 15, 16, and 17). A U-test was run on a number of d i f f e r e n t species densities and other community parameters to test for s i g n i f i c a n t differences between the groups, results of which are shown in Table XXI. Two of the tested parameters showed s i g n i f i c a n t differences. ,Corycaeus anglicus had higher densities during the day, a trend which i s opposite to that expected i f there was a d i e l migration. The data were thus not interpreted as evidence of migration. Euphausiids, however, are known to be strong d i e l migrators (Bary, 1967) and we see s i g n i f i c a n t l y higher densities at night than during the day (p = 0.5). Two factors might contribute to this increase: 1) Euphausiids in Indian Arm which during the day have migrated into deeper water and are therefore unexchangable, might move into near surface water at night and be carried over the s i l l by either t i d a l currents or the seaward flowing surface component of the estuarine c i r c u l a t i o n . 2) Euphausiids which might permanently inhabit the shallow areas in the v i c i n i t y of the s i l l might migrate to depths in such close proximity 51 to the sediment-water interface so as to be unavailable to the sampling equipment used. During the night, their upward movement would increase their c a t c h a b i l i t y . It i s interesting to compare these v e r t i c a l haul data to those derived from the Clarke-Bumpus nets used in the transport study. A s i g n i f i c a n t difference ( t - t e s t , p =0.05) was found in the density of Metridia p a c i f i c a (a known d i e l migrator), between day and night samples using Clarke-Bumpus nets (see Table XVI), yet the v e r t i c a l hauls f a i l e d to show thi s for samples taken at the same location at the same time (see Table XXI). This discrepancy could be due to the previously discussed patchy nature of the d i s t r i b u t i o n of this species, and the f a i l u r e of a single v e r t i c a l haul to adequately sample the community. The Clarke-Bumpus nets, which integrate over a larger horizontal distance, might quantitatively sample a patchy species more e f f e c t i v e l y . The f i n a l hypothesis to be tested was that there were di f f e r e n t community parameters or groups of zooplankton carried over the s i l l that were associated with the hydrographically discernable water types characterized by temperature and s a l i n i t y shown in Figure 20. Such an association has been noted in the open ocean in space (e.g. Bary, 1963) but in the l i t e r a t u r e few examples exist of variations over time at a single station. A notable exception i s Stone (1977), who documented water type and copepod associations on a seasonal basis in Knight Inlet. Data presented by . Stromgren (1975), 52 i n d i c a t e that copepod d i v e r s i t y c o u l d be a f u n c t i o n of the c i r c u l a t i o n of the f j o r d , s p e c i f i c a l l y of the t r a n s p o r t i n the upper p a r t of the water colunm. The water c h a r a c t e r i s t i c s were d i v i d e d i n t o the three groups d i s c u s s e d e a r l i e r (see F i g u r e 20); type A composed of samples 18, 19 and 11, type B of samples 12 and 13, and type C of samples 14, 15, 16, and 17. The only s t i p u l a t i o n imposed on these groupings was that samples w i t h i n them should be c h r o n o l o g i c a l l y c o n s e c u t i v e , a l o g i c a l r e s t r i c t i o n when l o o k i n g f o r trends or p a t t e r n s w i t h i n a continuum. Sample 11 can be c o n s i d e r e d as o c c u r r i n g both before sample 12, and a f t e r sample 19-as the t i d e at t h i s p o i n t had completed an e n t i r e c y c l e . The r e l a t i o n s h i p of the above hydrographic groupings to the copepod data was t e s t e d by c a l c u l a t i n g K e n d a l l ' s c o e f f i c i e n t of concordance of copepod d e n s i t i e s f o r p a i r s of c o n s e c u t i v e samples over the t i d a l c y c l e , ( F i g u r e 27). The three highest l e v e l s of concordance each support the groupings made based on hydrographic data. S i m i l a r l y , samples at the beginning or end of any group show a higher concordance with the adjacent sample w i t h i n t h e i r group than with the adjacent sample o u t s i d e t h e i r group in each case. T h i s i s most obvious between samples 17 and 18. The d e c i s i o n to p l a c e samples 11 and 19 i n the same group i s s t r o n g l y supported by the concordance data. A K r u s k a l - W a l l i s one way a n a l y s i s of v a r i a n c e was used to t e s t f o r d i f f e r e n c e s between the three water types i n a number of community parameters, the r e s u l t s of which are presented i n Table XXII. There were s i g n i f i c a n t d i f f e r e n c e s i n the Shannon-53 Weiner and Simpson's d i v e r s i t y index for copepods. The community in water type A, at the end of the major flood tide, had a higher d i v e r s i t y than that of the other water types found at d i f f e r e n t times over the s i l l . This pattern i s opposite to that found by Stromgren (1975) in two Norwegian fjords where an increased exposure to coastal water led to a decreased d i v e r s i t y . A possible explanation for this discrepancy might be differences in fresh water influence. The Norwegian data , were obtained at a time of low run o f f , but in Indian Arm, the fresh water input of October might be expected to result in a higher d i v e r s i t y of marine plankton in water ori g i n a t i n g in coastal regions due to the increasing estuarine conditions encountered towards the head of the i n l e t . The only tested copepod which showed a s i g n i f i c a n t change in density associated with the water types was C. anglicus which was found to be in higher numbers in water type A. This supports the data presented in the transport chapter on this species which indicated a Vancouver Harbour o r i g i n of th i s species..No significance could be found in the association of changes in other parameters with water type. The most d i s t i n c t changes in the copepod community are manifested over the t i d a l cycle not in re l a t i o n to the dir e c t i o n of t i d a l flow d i r e c t l y , but rather in relation to hydrographically discernable bodies of water advected over the s i l l by t i d a l currents. This suggests that turbulence and mixing induced by the boundary conditions of the harbour system are such that water properties become temporally dissociated from t i d a l d i r e c t i o n . The source of the water, however, can be traced 54 t h r o u g h h y d r o g r a p h i c p r o p e r t i e s . Water a s s o c i a t e d w i t h t h e end of a l a r g e f l o o d t i d e was shown t o be t h e most u n i q u e i n t e r m s of community p a r a m e t e r s . W o o l d r i d g e and Erasmus (1980) have shown t h a t c e r t a i n z o o p l a n k t o n s p e c i e s u t i l i z e t h e t i d a l c u r r e n t s v i a b e h a v i o r a l p a t t e r n s t o m a i n t a i n t h e m s e l v e s w i t h i n an e s t u a r y . I f s u c h were t h e c a s e a t t h e f j o r d mouth, one would e x p e c t t o see s i g n i f i c a n t c h a n g e s i n s p e c i e s d e n s i t i e s i n r e l a t i o n t o t i d a l d i r e c t i o n , w h i c h t h e d a t a d i d n o t show. The i m p o r t a n c e o f m a i n t a i n i n g p o s i t i o n w i t h i n a f j o r d m i g h t n o t be so c r i t i c a l t o t h e s u r v i v a l o f a z o o p l a n k t o n as i t i s i n an e s t u a r y where water c o n d i t i o n s a r e d r a s t i c a l l y d i f f e r e n t f r o m c o a s t a l w a t e r . Community c h a n g e s a s s o c i a t e d w i t h t h e t y p e s o f water were more p r e v a l e n t i n c o p e p o d s t h a n o t h e r i n v e r t e b r a t e s . M o r e o v e r , t h e s e c h a n g e s were f o u n d a t t h e community l e v e l r a t h e r t h a n a t t h e s p e c i e s l e v e l . The r e a s o n f o r t h i s c o u l d be due t o t h e i n f l u e n c e o f r a r e r s p e c i e s of c o p e p o d s on t h e d i v e r s i t y i n d i c i e s . The c h a n g e s o c c u r r i n g i n t h e d e n s i t y o f t h e s e s p e c i e s o v e r t h e t i d a l c y c l e c o u l d not be d i s t i n g u i s h e d w i t h t h e t e c h n i q u e s u s e d i n t h i s s t u d y . More numerous s p e c i e s d i d not show c h a n g e s o v e r t h e t i d a l c y c l e . An e x c e p t i o n t o t h i s g e n e r a l i t y was f o u n d f o r C. a n g l i c u s w h i c h had a s o u r c e i n c l o s e p r o x i m i t y t o one s i d e of t h e s i l l . D u r i n g t h e summer, a s i m i l a r r e s p o n s e m i g h t be e x p e c t e d f o r E. b u n g i as i t a l s o has a s o u r c e on o n l y one s i d e of t h e s i l l . 55 CONCLUSIONS The e f f e c t o f p h y s i c a l t r a n s p o r t on t h e z o o p l a n k t o n community o f I n d i a n Arm was i n v e s t i g a t e d t h r o u g h . a d e t a i l e d s t u d y o f a s e r i e s o f key c o p e p o d s p e c i e s . The d a t a i n d i c a t e d t h a t a g e n e r a l s t a t e m e n t on t h e e f f e c t of p h y s i c a l t r a n s p o r t , e n c o m p a s s i n g t h e whole z o o p l a n k t o n community, was not p o s s i b l e due t o t h e u n i q u e n a t u r e of e a c h s p e c i e s . S p e c i e s s p e c i f i c d i f f e r e n c e s , o c c u r r i n g p r i m a r i l y as a r e s u l t o f d i f f e r e n t b e h a v i o r a l p a t t e r n s , r e s u l t e d i n d i f f e r i n g t r a n s p o r t c h a r a c t e r i s t i c s among t h e s t u d y s p e c i e s . The d a t a showed t h a t a q u a n t i t a t i v e e s t i m a t e o f z o o p l a n k t o n t r a n s p o r t : a c r o s s t h e i n l e t mouth was p o s s i b l e . The a c c u r a c y o f t h e e s t i m a t e depended upon t h e r e s o l u t i o n o f s p a t i a l and t e m p o r a l c h a n g e s i n t h e z o o p l a n k t o n community as. i t c r o s s e d t h e s i l l , and on t h e a c c u r a c y of t h e volume t r a n s p o r t c a l c u l a t i o n . The v a r i a b i l i t y of t h e d a t a r e v e a l e d d i s t i n c t l i m i t a t i o n s i n t h e a b i l i t y of t h e t e c h n i q u e t o r e s o l v e s m a l l e r c h a n g e s . T h i s v a r i a b i l i t y seemed g r e a t e s t f o r more abundant s p e c i e s s u c h a s M e t r i d i a p a c i f i c a . The r e a s o n s f o r t h i s were p r o b a b l y due t o t h e p a t c h y n a t u r e of t h e s p e c i e s d i s t r i b u t i o n . In s u c h a c a s e , e s t i m a t e s o f t r a n s p o r t o v e r s h o r t p e r i o d s o f t i m e s u c h a s a s i n g l e t i d a l c y c l e were l e a s t r e l i a b l e . E x t r a p o l a t e d o v e r a s e a s o n , , however, g e n e r a l t r e n d s c o u l d be shown. F o r l e s s a b undant s p e c i e s , s u c h as E u c a l a n u s b u n g i , t h e r e s u l t s were l e s s v a r i a b l e and t r a n s p o r t e s t i m a t e s o v e r a s i n g l e t i d a l c y c l e seemed more r e l i a b l e . T h e s e d a t a c o u l d a l s o be e x t r a p o l a t e d o v e r 56 an e n t i r e s e a s o n and showed c l o s e c o r r e l a t i o n w i t h o b s e r v e d p o p u l a t i o n t r e n d s i n I n d i a n Arm. B e c a u s e o f t h e t i m e i n t e r v a l b e t w e e n them, t h e c r u i s e s y i e l d e d d a t a w h i c h c o u l d o n l y be u s e d t o d e s c r i b e g e n e r a l s e a s o n a l t r e n d s i n t h e t r a n s p o r t o f t h e s p e c i e s s t u d i e d . T h e s e s e a s o n a l t r e n d s i n d i c a t e d t h e v a r y i n g d e g r e e s t o w h i c h t r a n s p o r t a f f e c t e d t h e r e s i d e n t p o p u l a t i o n o f t h e s t u d i e d s p e c i e s i n I n d i a n Arm. The s t u d y showed t h a t t h e v a r i a b i l i t y i n t h e t r a n s p o r t o f d i f f e r e n t s p e c i e s was p r i m a r i l y a r e s u l t o f b i o l o g i c a l p r o c e s s e s w i t h i n t h e w a t e r r a t h e r t h a n c h a n g e s i n t h e m a g n i t u d e o f p h y s i c a l t r a n s p o r t . C h a n g e s i n s p e c i e s a b u n d a n c e i n p o t e n t i a l l y t r a n s p o r t a b l e w a t e r were o r d e r s o f m a g n i t u d e l a r g e r t h a n c h a n g e s i n t h e v o l u m e e x c h a n g e d a c r o s s t h e s i l l . T h i s g e n e r a l i z a t i o n i s t r u e , h o w e v e r , o n l y u n d e r t h e p h y s i c a l t r a n s p o r t r e g i m e s s t u d i e d . F o r e x a m p l e , a d e n s i t y d r i v e n i n t r u s i o n w h i c h c o u l d n o t be s t u d i e d , w o u l d r e s u l t i n v e r y l a r g e c h a n g e s i n v olume t r a n s p o r t , p o s s i b l y o f t h e same o r d e r o f m a g n i t u d e a s t h e b i o l o g i c a l c h a n g e s , a n d t h u s p r o f o u n d l y i n f l u e n c e t h e m a g n i t u d e o f z o o p l a n k t o n t r a n s p o r t . S p e c i e s s p e c i f i c b e h a v i o r p a t t e r n s seemed t o h a v e a most d r a m a t i c i n f l u e n c e on t r a n s p o r t . T h i s c o n c l u s i o n i s s i m i l a r t o t h a t r e p o r t e d by Sands a n d S v e n d s e n (1980) f o r d a t a c o l l e c t e d f r o m a N o r w e g i a n f j o r d . I n I n d i a n Arm t h i s was a r e s u l t o f t h e t r a n s p o r t m e c h anisms b e i n g a n e a r s u r f a c e phenomenon. The p h y s i c a l p r e s e n c e o f t h e s h a l l o w s i l l s , t h e i r i n d u c e d v e r t i c a l m i x i n g , a n d t h e l a c k o f a d e e p w a t e r . i n t r u s i o n p r e c l u d e d t h e e x c h a n g e o f w a t e r d e e p e r t h a n s i l l d e p t h a n d h e n c e o f t h e 57 animals a s s o c i a t e d with i t . Animals which e x h i b i t a v e r t i c a l m i g r a t i o n , such as the d i e l m i g r a t i o n of M. p a c i f i c a or the ontogenetic m i g r a t i o n of E. bungi , were t r a n s p o r t e d a c r o s s the s i l l only d u r i n g those p e r i o d s when they were present i n t h i s exchangable water. Animals which e x h i b i t an ontogenetic depth pr e f e r e n c e such as Euchaeta j a p o n i c a were t r a n s p o r t e d only at that l i f e h i s t o r y stage which occupied water above s i l l depth. Organisms whose e n t i r e l i f e h i s t o r y was spent i n p o t e n t i a l l y exchangeable water and were t o l e r a n t of the s u r f a c e water c o n d i t i o n s , such as Corycaeus a n g l i c u s , were exchanged at a l l times of the year. The magnitude of t h i s exchange was a f u n c t i o n of the seasonal d e n s i t y of the organism, and was thus c l o s e l y l i n k e d with the breeding c y c l e . One can s p e c u l a t e that a second p r e r e q u i s i t e f o r t r a n s p o r t was the a b i l i t y of the organism to s u r v i v e the p h y s i c a l and b i o l o g i c a l c o n d i t i o n s i n the exchanging water. H y d r o g r a p h i c a l l y , t h i s i n c l u d e d strong h o r i z o n t a l g r a d i e n t s i n temperature and s a l i n i t y induced by the intense v e r t i c a l mixing over the s i l l s . Organisms a l s o had to be t o l e r a n t of b i o l o g i c a l l y a c t i v e chemical elements present i n the water. T h i s i s a p o s s i b l e e x p l a n a t i o n f o r the anomalous l a c k of t r a n s p o r t d u r i n g the summer of E. j a p o n i c a . F u r t h e r m o r e , both E. j a p o n i c a and E. bungi were t r a n s p o r t e d mainly as young copepodite stages, d e s p i t e the presence of other l i f e h i s t o r y stages i n p o t e n t i a l l y t r a n s p o r t a b l e water on e i t h e r s i d e of the s i l l . T h i s c o u l d be due to an i n c r e a s e d t o l e r a n c e of these stages to near s u r f a c e water c o n d i t i o n s . 58 The e f f e c t o f t r a n s p o r t on t h e p o p u l a t i o n s i n s i d e I n d i a n Arm v a r i e d w i t h s p e c i e s a n d was d e p e n d e n t upon t h e s u r v i v a l o f t h e o r g a n i s m i n t h e i n l e t , i t s a b i l i t y t o t o l e r a t e t h e c o n d i t i o n s o f t r a n s p o r t a n d t h e m a g n i t u d e o f t h a t t r a n s p o r t . F o r o r g a n i s m s w h i c h d i d n o t r e p r o d u c e i n I n d i a n Arm, ( e . g . E. b u n g i ), t h e e n t i r e p o p u l a t i o n w i t h i n t h e i n l e t was a r e s u l t o f t r a n s p o r t a n d t h e d a t a showed t h a t t o t a l s e a s o n a l t r a n s p o r t c l o s e l y b a l a n c e d t h e t o t a l i n l e t p o p u l a t i o n . F o r a s p e c i e s w h i c h d i d r e p r o d u c e i n I n d i a n Arm, ( e . g . E. j a p o n i c a ) , t h e c o r r e l a t i o n o f t r a n s p o r t w i t h c h a n g e s i n t h e i n l e t p o p u l a t i o n was n o t s o c l o s e . N a t a l i t y w i t h i n t h e i n l e t h ad a more d o m i n a n t e f f e c t on p o p u l a t i o n t r e n d s . I n s u c h c a s e s t h e e f f e c t o f t r a n s p o r t . was m e r e l y t o u n i t e p o p u l a t i o n s g e n e t i c a l l y i n g e o g r a p h i c a l l y s e p a r a t e r e g i o n s . A l t h o u g h i t i s unknown w h e t h e r C. a n g l i c u s b r e d w i t h i n t h e i n l e t , t h e d a t a s u g g e s t e d t h a t t r a n s p o r t of t h e s p e c i e s had a d o m i n a n t e f f e c t on t h e p o p u l a t i o n i n s i d e I n d i a n Arm. V a n c o u v e r H a r b o u r seemed t o be a p r e f e r e d b r e e d i n g s i t e f o r t h e o r g a n i s m and t h e c l o s e p r o x i m i t y o f t h i s s i t e t o t h e s i l l m i g h t h a v e l e d t o t h e i n c r e a s e d t r a n s p o r t . The e f f e c t o f d i f f e r e n t t r a n s p o r t m e c h a n i s m s on t h e a c t u a l t r a n s p o r t o f z o o p l a n k t o n was d i f f i c u l t t o a s s e s s . No a n a l y s i s c o u l d be made o f t h e e f f e c t o f a d e n s i t y d r i v e n i n t r u s i o n a s no m a j o r i n t r u s i o n o f t h i s t y p e o c c u r r e d d u r i n g t h e s t u d y . The p r e d o m i n a n t t r a n s p o r t m e c h a n i s m d u r i n g t h e s t u d y p e r i o d was t i d a l e x c h a n g e . E s t u a r i n e c i r c u l a t i o n was a s m a l l component o f t h e t o t a l f l o w a c r o s s t h e s i l l a n d c o u l d n o t be a n a l y t i c a l l y s e p a r a t e d f r o m t h e t i d a l c o m p o n e n t . I n t u i t i v e l y , h o w e v e r , i t 59 seemed t h a t t h e e f f e c t o f t h i s f l o w would be m a n i f e s t e d o v e r a much l o n g e r t i m e f r a m e . E s t u a r i n e c i r c u l a t i o n w ould most s t r o n g l y a f f e c t t h o s e s p e c i e s l i v i n g i n t h e s u r f a c e w a t e r s of I n d i a n Arm as c u r r e n t s a r e s t r o n g e s t i n t h i s s h a l l o w l a y e r . A l t h o u g h t h e e f f e c t on s u b s u r f a c e o r g a n i s m s o u t s i d e t h e i n l e t w ould n o t be so p r o n o u n c e d due t o t h e s l o w e r u p i n l e t c u r r e n t v e l o c i t i e s , i t would p r o d u c e a n e t movement i n t o t h e i n l e t . E s t u a r i n e c i r c u l a t i o n t h u s e s t a b l i s h e s a n e t u p i n l e t f l o w i n t h e s u b s u r f a c e w a t e r s f o u n d o v e r t h e s i l l and a n e t e x p o r t i n t h e s u r f a c e l a y e r s of t h e i n l e t . I t c a n be h y p o t h e s i z e d t h a t t h i s w o uld have a g r e a t e r e f f e c t on V a n c o u v e r H a r b o u r z o o p l a n k t o n e n t e r i n g I n d i a n Arm t h a n t h e r e v e r s e ; o n l y t h o s e s p e c i e s i n t h e s h a l l o w , r e l a t i v e l y f r e s h s u r f a c e l a y e r s of I n d i a n Arm would be a d v e c t e d b u t , a r e g i o n s p a r s e l y p o p u l a t e d by m a r i n e z o o p l a n k t o n . ( T h i s was a l s o f o u n d i n K n i g h t I n l e t , S t o n e , 1977). Over a s i n g l e t i d a l c y c l e , d i s t i n c t c h a n g e s t o o k p l a c e i n t h e z o o p l a n k t o n community f o u n d o v e r t h e s i l l . R e l a t i v e l y few c o p e p o d s p e c i e s showed any c o r r e l a t i o n t o t i d a l h e i g h t and fewer i n d i v i d u a l s p e c i e s showed s i g n i f i c a n t c h a n g e s i n r e l a t i o n t o t i d a l d i r e c t i o n o r t i m e of d a y . Most i m p o r t a n t l y , s i g n i f i c a n t d i f f e r e n c e s i n i n d i v i d u a l s p e c i e s d e n s i t i e s d i d n o t o c c u r i n r e l a t i o n t o t i d a l d i r e c t i o n . Changes i n t h e e n t i r e c o p e p o d community o c c u r r e d i n a s s o c i a t i o n w i t h h y d r o g r a p h i c a l l y d i s c e r n a b l e t y p e s o f water a d v e c t e d o v e r t h e s i l l d u r i n g t h e t i d a l c y c l e . The c h a n g e s w h i c h d i d o c c u r seemed t o be a t t h e community l e v e l r a t h e r t h a n a t t h e s p e c i e s l e v e l . Community c h a n g e s t h u s o c c u r r e d i n r e l a t i o n t o t h e o r i g i n o f t h e w a t e r , a 60 factor which was not d i r e c t l y related to t i d a l d i r e c t i o n . The most profound difference in the copepod community was found towards the end of large flood tides. The hydrographic data suggested that the or i g i n of thi s water was Vancouver Harbour, a suggestion supported by the presence of high densities of C. anglicus found at the same time. Species which exhibit a d i e l v e r t i c a l migration were found in s i g n i f i c a n t l y higher numbers at night. Youngbleth (1980) found higher concentrations of many species of plankton in samples taken at night which he attributed to a reduced net avoidance. In t h i s study, however, only those species which have a known v e r t i c a l d i e l migration were found in greater densities at night, lending credence to the proposal that these species were transported primarily at night. Analysis of the whole zooplankton community over a t i d a l cycle pointed out limi t a t i o n s in the interpretation of the transport patterns deduced for the fo^r study species. The transport study was carr i e d out using the densities of the study species which occurred during the ebb and flood events of each cruise. S i g n i f i c a n t differences in the individual species densities were not seen in rel a t i o n to the dire c t i o n of t i d a l flow across the s i l l when the whole community was analysed. Further analysis of the zooplankton community showed, however, that very s i g n i f i c a n t changes took place in association with hydrographic properties. The differences were thus related to the o r i g i n of the water. While these hydrographic properties, indicative of the o r i g i n of this water, were temporally 61 d i s s o c i a t e d f r o m t i d a l d i r e c t i o n , i t was s t i l l t h e t i d a l f l o w w h i c h was r e s p o n s i b l e f o r t h e a d v e c t i o n o f t h e w a t e r o v e r t h e s i l l and t h e r e s u l t a n t e x c h a n g e . Thus when e x t r a p o l a t e d o v e r much l o n g e r t i m e s c a l e s i t was t h e o r i g i n o f t h e w a t e r , and i t s a s s o c i a t e d z o o p l a n k t o n , w h i c h r e s u l t e d i n t h e r e s o l u t i o n o f s e a s o n a l t r a n s p o r t p a t t e r n s . 62 REFERENCES Alldredge, A.L., and W.M. Hamner, 1980. Recurring aggregation of zooplankton by a t i d a l current. Estuarine and Coastal Marine Science 10:31-38. Anderson, J.J. and A.H. Devol, 1973. Deep water renewal in Saanich Inlet, an intermittent anoxic basin. Estuarine and Coastal Marine Science,. 1 : 1 -1 0 Barlow, J.P., 1955. Physical and b i o l o g i c a l processes determining the d i s t r i b u t i o n of zooplankton in an estuary. B i o l . B u l l . 109:211-225. Bary, B.McK., and L. Regan, 1976. Influence of water properties on a Euphausiid and a Copepod in coastal areas of B r i t i s h Columbia, Pgs. 179-191, In: Freshwater on the Sea, Eds, Skreslet et a l . Ass. Norw. Oceanog. 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Estuarine and Coastal Marine Science 10:265-288. 70 T A B L E S Table I: Cruise dates and numbers. Cruise Date 80/1 January, 1 980 80/2 February, 1980 80/12 July, 1980 80/18 October, 1980 81/1 January, 1 981 81/6 March, 1981 81/33 November, 1981 72 Table II: Sampling Depths. Station Hydrographic Data Clarke-Bumpus Tows V e r t i c a l Hauls GEO 1748 FRA 1 VAN 24 IND 0 IND 1 .5 0 5 X 10 20 X 50 X 75 100 X 150 X 200 250 X 300 350 X 375 0 5 X 1 0 20 X 30 50 X 75 100 X 1 50 X 200 X 0 5 X 10 20 X 30 50 X 0 5 X 1 0 X 20 X 0 5 X 10 20 X 30 50 X 75 100 X 375-50 50-0 200-50 50-0 50-0 20-0 175-50 50-0 73 150 1 75 IND 2.0 0 5 10 20 30 50 75 100 1 50 200 X X X XX X XX X XX 200-50 50-0 Note XX i n d i c a t e s d e p t h s a t w h i c h r e p l i c a t e s amples were t a k e n f o r s t a t i s t i c a l t r e a t m e n t . 74 Table I I I : Animals and Taxonomic Groups Identified for the Community Analysis at IND 0 (Cruise 80/18) Copepods Microcalanus pygmaeus Pseudocalanus minutus Paracalanus parvus Oithona s p i n i r o s t r i s Oithona helgolandica Oncaea b o r i a l i s Corycaeus anglicus S c o l e c i t h r i c e l l a minor Metridia p a c i f i c a Calanus pacificus Acartia longiremis Acartia c l a u s i Tortanus discaudatus Aetideus armatus Euchaeta japonica Bradyidius saanichi Other Invertebrates (where known, the number of species in each group i s given) Nauplius larvae Ostracods Conchoecia elegans Philomedes sp. 1 Paradoxostoma striungulum Siphonophores 4 Pteropods Limacina h e l i c i n a Larvaceans 2 Harpacticiod copepods Isopods Amphipods Parathemisto sp. 1 S t i l i p e s sp. 1 Medusae Phialidium sp. 1 75 Proboscidactyla sp.1 Aegina sp. 1 Aequorea sp. 1 Decopod Larvae Ctenophores 1 Cumaceans Euphausi ids 1 76 Table IV: Animal densities per cubic meter at the sampling depths on cruise 81/33. Depth Euchaeta Eucalanus Metridia Corycaeus japonica bungi p a c i f i c a anglicus 200 0.83 0.83 0.14 100 1.96 93.97 0.39 20 0.75 200 0.40 2.46 0.20 100 2.23 78.06 1.59 20 0.18 200 0.19 2.53 100 5.40 109.90 0.64 20 0.55 200 0.90 0.36 100 3.02 122.59 1.26 20 0.13 1.44 200 1.26 1.69 0.42 100 4.62 139.47 0.12 20 1.13 200 0.60 0.20 100 3.77 149.95 0.92 20 0.16 1.17 77 Table V: S t a t i s t i c a l treatment of repl i c a t e s . Species t o t a l mean S .D. : CV 95 % Confidence Limits Upper Lower At 200m E.bungi 4.18 0.7.0 0 .38 54. 57 1 .68 -0.28 M.pacifica 8.07 1 .35 1 .03 76. 64 4.00. -1 .30 C.anglicus 0.76 0.13 0 .17 131. 98 0.57 -0.31 At 100m E. japonica 21 .00 3.50 1 .35 38. 66 6.97 0.03 M.pacifica 693.93 1 1 5.66 127 .23 23. 55 185.67 45.65 C.anglicus 4.92 0.82 0 .5.5 66. 88 3.39 -0.59 At 20m C.anglicus 5.22 0.87 0 .46 53. 31 2.05 -0.31 Transformed Data At 200m E.bungi M.pac i f ica C.anglicus Derived Geometr ic Mean 0.66 1.15 0.12 log S.D. 0.10 0.20 0.06 Log 95% CV Confidence Limits Upper Lower 25.8 58.5 14.8 2.00 6.02 0.59 -0.08 -0.34 -0.22 At 100m E.japon ica M.pac i f ica C.anglicus 3.33 112.89 0.75 0.13 0.11 0.14 34.9 28.8 38.0 8.35 217.41 3.00 1 .00 58.38 -0.24 At 20m C. anglicus 0.82 0.12 31 .8 2.70 -0.11 * Note Transformation X=logl0(x+1) CV = Coefficient of Variation CV = Logarithmic Coefficient of Variation Log Confidence Limits = 95% confidence l i m i t s for a hypothetical sample containing an animal density equal to 'Mean' 78 Table VI: Volume transport of water across the Indian Arm s i l l , calculated from current meter readings. Cruise Volume Transport (Cubic Meters) 80/18 81/1 81/6 Ebb Flood Ebb Flood Ebb 1.55x107 •3.09X107 1.44x10s •1 .70x10s 4.33x107 2 . 1 5x1 0 7 7. 10X107 •1 .04x1 0 8 -2.25x107 8.35x10'' -3.06x107 3.68x107 Net Transport 1.27x10s 3. 18X107 6.72X107 *Note - denotes flow out of the i n l e t (southward) + denotes flow into the i n l e t (northward) 79 T a b l e V I I : A v e r a g e volume t r a n s p o r t f o r l a r g e and s m a l l t i d a l e x c h a n g e s , c a l c u l a t e d f r o m t h e model p r e d i c t i o n s . D a t e C r u i s e L a r g e T i d e S m a l l T i d e F e b . 1 9 8 0 8 0 / 2 7 . 5 9 X 1 0 7 4 . 9 2 X 1 0 7 J u l y 1 9 8 0 8 0 / 1 2 1 . 0 0 x 1 0 8 3 . 3 7 x 1 0 7 O c t . 1 9 8 0 8 0 / 1 8 9 . 1 3 x 1 0 7 4 . 2 7 x 1 0 7 J a n . 1 9 8 1 8 1 / 1 7 . 4 2 X 1 0 7 2 . 6 9 x 1 0 7 March 1 9 8 1 8 1 / 6 7 . 3 4 X 1 0 7 4 . 3 1 x 1 0 7 80 Table VIII: Density of Corycaeus anqlicus in the study area. Densities are in number per cubic meter. Febuary (Cruise 80/2) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2. Depth 1748 Narrows (m) 5 1 .3 0.3 0.0 0.1 .0.0 10 0.0 20 0.8 — - 0.4 0.9 0.3 0.1 50 0.0 0.0 0.1 0.4 100 0.2 0.4 0.0 1 50 0.0 0.0 0.0 175 0.2 200 1.0 0.0 250 300 350 400 - — July (Cruise 80/12) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2. Depth 1748 Narrows (m) 5 0.0 0. 1 0.0 0.7 0.0 0.0 1 0 1 .4 20 0.4 1 .4 0.0 1 .4 0.0 0.0 50 0.0 0.8 1.2 0.6 0.0 100 0.0 0.0 o.o •• 0.0 150 0.0 0.0 0.0 0.0 1 75 0.0 200 0.0 0.0 250 0.0 300 350 0.0 400 81 October (Cruise 80/18) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 0.0 0.1 3.9 4.0 1.2 1.5 10 6.1 20 1.0 1 .4 16.6 11.5 2.6 0.7 50 0.8 0.8 25.5 2.6 0.7 100 0.2 0.3 0.2 1.0 150 0.2 1.5 0.0 1.6 175 0.1 200 1.0 0.7 250 0.0 300 350 0.4 400 ---January (Cruise 81/1) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 0.0 0.0 4.2 1.3 0.6 0.1 10 1.1 20 0.0 0.0 0.6 0.4 0.2 0.6 50 0.0 0.0 0.1 0.1 0.2 100 0.0 0.0 1.5 0.0 150 0.0 0.0 0.0 0.0 175 0.0 200 0.0 0.5 250 0.0 300 350 0.0 400 March (Cruise 81/6) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 0.0 0.0 0.8 0.3 0.5 0.2 10 0.2 20 0.0 0.1 0.6 0.2 0. 1 0.2 50 0.4 0.0 0.0 0.0 0.0 100 0.0 0.7 1.0 0.3 150 0.0 0.4 0.0 0.4 175 0.0 200 0.1 0.0 250 0.0 300 350 0.0 400 - — 82 Table IX: Transport of Corycaeus anglicus across the Indian Arm s i l l during the study period. Cruise Tidal Averaged Indian Arm Confidence Interval Cycles Transport Population Intervals Between (Second Cruise) Crui ses Upper Lower 80/2-80/12 1 32 6. 34x109 6. 32x108 7 .75x10s 0 80/12-80/18 1 08 5. 94x109 2. 72x10s 8 .74x109 3.79xl0 8 80/18-81/1 74 2. 37x108 7. 58x10s 3 .57x109 3.70x107 81/1-81/6 61 • -6. 34x108 5. 30x10s 2 .73X109 0 Note + indicates transport into the i n l e t - indicates transport out of the i n l e t 83 Table X: Density of Euchaeta japonica in the study area. Febuary (Cruise 80/2) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1 .5 IND 2.1 Depth 1748 Narrows (m) 5 0.0 0.0 0.0 1 .0 1 . 7 10 0.0 20 0.0 0.2 0.4 1 .3 1 . 2 50 0.0 0.0 2 . 1 1 . 8 100 0.8 0 .8 0. 0 150 1 .9 2 .9 2. 6 175 1 .8 200 1.0 0. 4 250 300 350 400 July (Cruise 80/12) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth 1748 Narrows (m) 5 0.0 0.0 0.0 0.0 0.0 0.3 10 0.0 20 0.0 0.0 0.0 0.0 0.0 1 .8 50 1 .2 0.6 0.0 0.7 0.0 100 2.8 2.0 0.8 1.3 1 50 13.4 0.7 2.5 2.3 175 0.0 200 1 .2 0.6 250 1.7 300 350 1.6 400 84 October (Cruise 80/18) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2 Depth(m) • Narrows 5 7.8 25.8 0. 0 0.0 0.0 0.0 10 0.0 20 2.9 3.7 0. 0 0.0 4.2 0.1 50 10.9 5.8 0. 0 8.4 5.4 100 2.6 1 .2 4.7 13.1 1 50 1 . 1 1.0 8.2 5.8 1 75 4.8 200 1 .8 1 .5 250 2.4 300 350 4.9 400 January (Cruise 81/1) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 8.6 9.5 0.2 0.8 0.0 2.2 1 0 1 .0 20 0.4 1 .0 0.6 0.9 0.2 3.5 50 2.8 0.9 0.7 1 .7 0.5 1 00 0.3 0.8 5.0 0.3 1 50 1 .4 0.9 1 .2 0.0 1 75 0.8 200 0.6 1 .0 250 • 0.4 300 350 0.0 400 March ( C r u i s e 81/6) S t a t i o n Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 4.5 4.5 0.1 0.0 0.0 0.0 10 0.0 20 1.2 1 .8 0.0 0.0 0.0 0.0 50 2.8 2.1 0.0 0.0 0.0 1 00 0.5 0.3 0.0 0.3 1 50 0.6 0.5 4.2 0.5 175 2.2 200 250 2.0 300 350 3.9 400 85 Table XI: Euchaeta japonica seasonal transport across the Indian Arm s i l l and population in Indian Arm. Feb. (80/2 Data) Transport Jan. (81/1 Data) Number per Tidal Number per Tidal Cycle Cycle 1.52x10s 7 . 5 1 X 1 0 7 Total Seasonal . Transport=3 Months =86 Tid a l Cycles (Jan. Data only) 6.46x10s 95% confidence l i m i t s - 2 . 6 1 X 1 0 7 0 1.71x10s 2.35x107 1.47x10 1 0 2.02x109 Population Feb(80/2) July(80/12) Oct(80/18) Jan(81/1) March(81/6) 3.29x10s 1.90x10? 1.19x10 1 0 2.85X109 8.78xl0 8 95% confidence l i m i t s 9.44x109 5.77X109 2.80xl0 1° 9.73X109 2.44x10s 5.18X108 2.40x108 4.55x10s 8.16x10s 2.30x10s 86 Table XII: Percent composition of Euchaeta japonica density in p o t e n t i a l l y exchangable water, January, 1981. Deduced from Figure 10. Location Copepodite Stage I II III IV v VI S i l l density 0 2.2 15 4.2 1.5 0.1 % 0 9.5 65.2 18.3 6.5 0.4 Harbour density 0 0.2 0 0 0 0 % 0 100 0 0 0 0 Indian Arm density 0 1.4 0.3 0.1 2.8 1.2 % 0 24. 1 5.1 1.7 48.3 20.7 S t r a i t density 0 0.9 10 1.9 '3.3 1.9 % 0 5 55.6 10.6 18.3 10.6 *Note 'Indian Arm' refers to the sum from both Indian Arm stations ' 'S t r a i t ' refers to the sum from both S t r a i t of Georgia stations 87 Table XIII: Percent composition of Euchaeta japonica density in p o t e n t i a l l y exchangable water, October, 1980. Deduced from Figure 18. Location Copepodite Stage I II III IV V VI Indian Arm density 0 6.3 3.8 2.2 4.5 1.3 % 0 34.8 21.0 12.1 24.9 7.2 S t r a i t density 0 9.2 12.5 9.3 19.5 6.4 % 0 16.2 2.2 16.3 34.3 11.2 * Note Values refer to the sum of both stations in each location. 88 Table XIV: Density of Euchaeta japonica copepodite Stages I, II, and III in the S t r a i t of Georgia and Indian Arm in October (Cruise 80/18). Station Sample Depth(m) GEO 1748 FRA 1 IND 1.5 IND 5 2.1 4.8 10 20 1 .6 0.3 0.1 50 8.6 4.3 5.4 4.6 100 1.8 0.8 2.9 4.1 1 50 0.9 0.4 6.3 2.2 175 4.6 200 0.3 0.8 250 1 .3 300 350 4.8 400 89 Table XV: Density of Metridia p a c i f i c a in the study area. Febuary (Cruise 80/2) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth 1748 Narrows (m) 5 65.9 9.3 10.2 49.0 18.0 1 0 17.3 20 1.4 8.3 12.9 31.1 15.7 50 1 .7 2.5 11.3 9.6 100 5.8 13.6 40.0 1 50 31.5 12.0 18.5 1 75 6.9 200 6.0 0.9 2 5 0 3 0 0 3 5 0 4 0 0 July (Cruise 80/12) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth 1748 Narrows (m) 5 0.7 0.1 0.2 9.7 1 .4 1 0 0.5 20 1 46.7 56.2 1.3 9.4 7.1 41 .2 50 4.0 9.4 0.0 10.0 0.0 1 00 23.5 297.4 58.6 70.5 1 50 67.3 26.7 24. 1 16.3 1 75 0.0 200 45.6 13.1 250 11.4 300 350 1.3 400 90 October (Cruise 80/18) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 . IND 2 Depth(m) Narrows 5 17.1 13.6 2.6 1 .4 49.7 0. 0 10 8.2 20 39.4 56.5 3.2 1 .8 14.3 0. 1 50 2.4 4.8 5.5 8.3 24. 7 1 00 15.7 4.7 29.4 61 . 1 1 50 13.0 16.5 24.9 34. 4 1 75 57.3 200 27.4 105. 5 250 22.1 300 350 53.5 400 January (Cruise 81/1) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 56.3 302.7 0.2 6.2 0.6 3.5 1 0 5.1 20 27.8 10.7 --- 1 .2 5.2 28.4 22.0 50 5.8 6.3 6.3 4.3 12.5 1 00 13.0 15.3 75.2 1 .3 1 50 • 17.5 14.7 17.2 18.4 1 75 10.0 200 11.9 95.2 250 17.9 300 350 11.5 400 March (Cruise 81/6) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2 Depth(m) Narrows 5 31 .3 1 93.4 13. 2 6.3 1 .9 4.0 10 10.0 20 77.2 20.6 15. 3 6.6 3.1 1 .7 50 13.8 9.5 12. 3 1.1. 4.8 100 23.4 10.1 22.7 4.3 1 50 56.8 9.0 3.7 0.6 1 75 8.0 200 5.7 1 .4 250 2.3 300 350 1.4 400 91 Table XVI: Density of Metridia p a c i f i c a over the Indian Arm s i l l . Cruise 80/18 Depth Density (Number per Cubic Meter) 5m 1 0m 20m 0.9 0.2 1.7 0.8 0.3 0.5 1.8 1.8 0.4 1.0 3.1 0.7 1.1 3.7 1.2 3.4 1.0 2.7 0.7 0.9 2.8 0.7 1 .4 2.1. 0.5 0.6 0.6 Day Day Day N N N Day Day Day Mean Mean Day 0.95 Night 1.86 T Test = sign • (p=0. 05) Cruise 81/6 20m 3.0 2.4 9.3 7.3 10.1 8.4 10.4 2.6 6.1 Day Day N N N N N Day Day Mean Mean Day 3.53 Night 9.10 T Test = sign. (p=0 .01 ) 92 Table XVII: Transport of Metridia p a c i f i c a across Indian Arm s i l l . Net T i d a l Average Total Population Transport Cycles Transport Population Confidense (animals) Between in Indian Arm Limits Cruises Cruise 80/2 +1.02X10 9 3 . 8 4 X 1 0 1 0 8.75x10'° 2.22X10 1 0 132 +6.45X10 1 0 Cruise 80/12 -4.20X10 7 5 . 6 4 X 1 0 1 0 1 . 0 2 X 1 0 1 1 2.65X10 1 0 108 -3.07X10 9 Cruise 80/18 -1.49X10 7 5.91x10'° 1.06x1011 2.99x10'° 74 - 1.56x1 0.9-Cruise 81/1 -2.73x10s 5.33X10 1 0 9.04X10 1 0 2.29x10'° 61 -6.19X10 9 Cruise 81/6 +7.02xl0 7 Note indicates indicates transport transport 1.12x10 1 0 into the i n l e t out of the i n l e t 2.36x10'° 4.80x10s T i d a l Volumes for each cruise in cubic meters (large tide and small tide) Cruise 80/2 Cruise 80/12 Cruise 80/18 Cruise 81/1 Cruise 81/6 7.59X107 1.00x108 9. 13X10 7 7.42X10 7 7.34X10 7 4.92x107 3.37X107 4.27x107 2.69X10 7 4 . 3 1 X 1 0 7 93 Table XVIII: Density of Eucalanus bungi in the study area. Febuary (Cruise 80/2) Station Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth 1748 Narrows (m) 5 0.0 0.0 0.0 0.0 0.0 10 0.0 20 0.0 0.0 0.0 0.0 0.0 50 0.0 0.0 0.0 0.0 100 0.0 0.0 0.0 1 50 0.2 0.0 0.0 175 0.5 200 0.0 0.0 250 300 350 400 July (Cruise 80/12) Stat ion Sample GEO FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2 Depth 1748 Narrows (m) 5 0.0 0.0 0.0 0.01 0.0 0.0 1 0 0.03 20 11.5 1 .8 0.6 0.14 0.0 0.0 50 1 .0 2.7 0.0 0.0 0.0 100 0.6 0.2 0.0 0.0 1 50 0.0 0.3 1 .5 1 .0 175 0.0 200 5.0 5.8 250 1.4 300 350 13.7 400 94 October (Cruise 80/18) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth(m) Narrows 5 0.0 0.0 0.0 0.0 0.0 0.0 10 0.0 20 0.2 0.3 0.0 0.0 0.0 0.0 50 0.0 0.0 0.0 0.1 0.0 100 0.0 0.0 0.0 0.0 150 0.2 0.0 1.0 0.8 175 6.6 200 0.1 4.5 250 0.2 300 350 6.2 400 January (Cruise 81/1) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth (m) Narrows 5 0.0 0.0 0.0 0.0 0.0 0.0 10 0.0 20 0.0 0.0 — - 0.0 0.0 0.0 0.0 50 0.0 0.0 0.0 0.0 0.0 100 0.0 0.0 0.2 0.8 150 0.0 0.0 3.5 1.2 175 3.5 200 0.0 ' 0.0 250 0.4 300 350 7.2 400 March (Cruise 81/6) Station Sample GEO 1748 FRA 1 1st VAN 24 IND 0 IND 1.5 IND 2.0 Depth (m) Narrows 5 0.0 0.0 0.0 0.0 0.0 0.0 10 0.0 20 0.0 0.0 — 0.0 0.0 0.0 0.0 50 0.0 0.0 0.1 0.0 0.0 100 0.1 0.0 0.0 0.0 150 0.0 0.1 0.6 0.2 175 0.0 200 0.6 0.4 250 2.9 300 350 0.2 400 . — • 95 Table XIX: Seasonal transport of Eucalanus bungi across the Indian Arm s i l l and the overwintering population in Indian Arm. Transport per Tid a l Total Indian Arm T i d a l Cycle Cycles Seasonal Population (from 80/12) Transport Jan(8l/1) March(8l/6) 3.85X10 6 73 2.80x10s 1 . 1 0x 109 1 .40x1 0 s Upper Confidense Limit 1.60X107 1.17x10s 2.64x10s 5.25x10s Lower Confidense Limit 0.00 0.00 3.27x10s 0.00 96 Table XX: Presence of Eucalanus bungi young copepodite stages (I, II, and III) in the study area during July (Cruise 80/12). Station < GEO 1748 FRA 1 VAN 24 IND 0 IND 1.5 IND 2. Depth 5 #/m3 0 0 0 0.01 0 0 % 0 0 0 100 0 0 10 #/m3 0.02 % 1 00 20 #/m3 3.1 1 .5 0.4 0.16 0 0 % 26.8 83.3 66.7 1 00 0 0 50 #/m3 0.2 0 0 0 0 % 20.0 0 0 0 0 100 #/m3 0 0 0 0 % 0 0 0 0 1 50 #/m3 0 0 0 0 % 0 0 0 0 200 #/m3 0 0 0 % 0 0 0 250 #/m3 0 % 0 350 #/m3 % 0 0 97 T a b l e X X I : U - T e s t r e s u l t s f o r community p a r a m e t e r s o v e r t h e t i d a l c y c l e a t IND 0 ( C r u i s e 8 0 / 1 8 ) . EBB / FLOOD DAY / NIGHT Sample 11,14,15,19/ 11,12,13,18,19/ 12,13,16,17,18 14,15,16,17 %Dominance c o p e p o d s 15 14 S.W. D i v . c o p e p o d s 16 12 Simpsons D i v . c o p e p o d s 15 T o t a l c o p e p o d s 11 %Dominance o t h e r I n v e r t . 15 12 S.W. D i v . o t h e r I n v e r t . 20* Simpsons D i v . o t h e r I n v e r t . 1 9 * M e t r i d i a pac i f i c a 10 16 P s u e d o c a l a n u s m i n u t u s 12 A c a r t i a c l a u s i 11.5 P a r a c a l a n u s p a r v u s 12 O i t h o n a h e l g o l a n d i c a 14 C o r y c a e u s a n q l i c u s 11 19* M i c r o c a l a n u s pyqmaeus 13 C a l a n u s p a c i f i c u s 15 S i p h o n o p h o r e s 20* 11 T o t a l O s t r a c o d s 13 E u p h a u s i i d s 12 20* P a r a t h e m i s t o (Amphipoda) 13.5 14.5 ** C r i t i c a l v a l u e f o r U t e s t was 18 (p=0.05) 98 Table XXII: Kruskal Wallis results for zooplankton community changes over the t i d a l cycle at IND 0 (Cruise 80/18). Parameter value %Dominance copepods 5 .8 Simpsons Div. copepods 6 .35* S.W. Div. copepods 7 .00* Total copepod densities 1 .5 %Dominance other Invert. 1 .84 Simpsons Div. other Invert. 0 .98 S.W. Div. other Invert. 3 .84 Met r i d i a . p a c i f i c a 3 .26 Pseudocalanus minutus 3 . 1 1 Paracalanus parvus 4 .00 Oithona helgolandica 4 .44 Corycaeus anglicus 6 .30* Acartia clau s i 1 .39 Microcalanus pyqmaeus 5 .40 Calanus pacificus 4 . 1 7 Euphausi ids 6 .67* Siphonophores 0 .81 Ostracods 0 .78 *Note C r i t i c a l value for Kruskal Wallis test was 6.0 (p=0.05) 99 FIGURES 1 0 0 Figure 1; The study area, showing station positions, points of reference and transect S7 used in the model volume transport prediction. 102 F i g u r e 2; L o n g i t u d i n a l depth p r o f i l e through the study area, showing the p o s i t i o n of the shallow s i l l s i n r e l a t i o n to the deeper water. ( L a t e r a l d i s t a n c e s not to s c a l e ) . STATION GE01748 FRA1 VAN 24 INDO IND 1.5 IND 2.0 1 04 F i g u r e 3; D e n s i t y s t r u c t u r e i n t h e s t u d y a r e a d u r i n g w i n t e r , 1981 ( J a n u a r y d a t a , C r u i s e 81/1) ( D e n s i t y i n Sigma T) S T A T I O N GE01748 FRA1 VAN24 INBO IND 1.5 IND 2.0 HT!M i* 1™ •—I win*— — — — — v J i a infiw i^w^— 106 Figure 4; Density structure in the study area during winter, 1980 (February data, Cruise 80/2) (Density in Sigma T) STATION 108 Figure 5; Oxygen concentration in water below 150 meters at Station IND 2.0, over time, showing the effect of a winter density driven intrusion on the oxygen concentration in Indian Arm deep water. 110 F i g u r e 6; C u r r e n t v e c t o r s d e r i v e d from t h e c u r r e n t meter d e p l o y e d a t IND 0 o v e r a t i d a l c y c l e . ( D a t a from C r u i s e 81/6, 1cm = 0.1 k n o t s ) . I l l 1 1 2 F i g u r e 7; N o r t h - s o u t h components ( a l o n g t h e c h a n n e l ) o f c u r r e n t v e c t o r s o v e r a t i d a l c y c l e a t IND 0 ( D a t a from C r u i s e 81/6, 1cm = 0.1 k n o t s ) . 113 1 14 F i g u r e 8; T o t a l and n e t t r a n s p o r t o f C o r y c a e u s a n q l i c u s a c r o s s t h e I n d i a n Arm s i l l d u r i n g e a c h c r u i s e . 1 16 Figure 9; Mean concentration of Corycaeus anqlicus in the study area in October in number per cu. meter from samples taken above 50 meters showing 95% confidense l i m i t s . 117 1 18 F i g u r e 10; T e m p e r a t u r e / S a l i n i t y p l o t o f s t u d y a r e a w a t e r d u r i n g J a n u a r y , 1981 ( C r u i s e 81/1) showing t h e T/S p r o p e r t i e s o f w a t e r e x c h a n g e d a c r o s s t h e I n d i a n Arm s i l l o v e r a t i d a l c y c l e . 1 20 F i g u r e 1 1 ; D e p t h d i s t r i b u t i o n o f M e t r i d i a p a c i f i c a a t S t a t i o n FRA 1 d u r i n g t h e day and d u r i n g t h e n i g h t . 121 HlcJ3Q 122 F i g u r e 12; T o t a l and n e t t r a n s p o r t of E u c a l a n u s b u n g i a c r o s s t h e I n d i a n Arm s i l l d u r i n g e a c h c r u i s e . 7 — 6 — Feb. July Oct. Jan. March CRUISE £ 124 Figure 13; Temperature/Salinity plot of study area water during July, 1980 (Cruise 80/12) showing the T/S properties of water exchanged across the Indian Arm s i l l over a t i d a l cycle. SALINITY (0/00) 15.0 17.0 19.0 21.0 23.0 25.0 27.0 29.0 31.0 1 26 Figure 14; Temperature/Salinity plot of water at IND 2.0 showing changes during the study period in the deep water of Indian Arm. H SALINITY (00/0) 24.0 24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28. 1 28 Figure 15; The t i d a l cycle at IND 0 during Cruise 80/18 (October, 1980) over which data for the community analysis was taken. Times and labels of samples are shown. Hour 0 was at 0800 hrs on October 28, 1980. HEIGHT (M) 0 1 2 3 4 5 6ST 1 30 Figure 16; Temperature at each sampling depth at IND 0 over the t i d a l cycle (Cruise 80/18). Hours are given as in F i g . 15. 1 32 Figure 17; S a l i n i t y at each sampling depth at IND 0 over the t i d a l cycle (Cruise 80/18). Hours are given as in F i g . 15. 134 Figure 18; Temperature/Salinity plot of the study area water during October, 1980 (Cruise 80/18) showing the T/S properties of water exchanged over the Indian Arm s i l l during a t i d a l cycle, and i t s r e l a t i o n to water in surrounding areas. 136 Figure 19; Temperature/Salinity plot of water from 0 meters at the Indian Arm s i l l over the t i d a l cycle. Sample numbers correspond to those given in Fi g . 15. I™1 138 Figure 20; Temperature/Salinity plot of average T/S properties from 5, 10, and 20 meters (below the pycnocline) at the Indian Arm s i l l over the t i d a l cycle. Sample numbers correspond to those given in Fi g . 15. i 139 TEMP. (C) 10.60 10.65 10.70 10.75 10.80 I 1 1 _ _ — — i 1 — 1 40 Figure 21; Density of the four most abundant copepods at IND 0 over the t i d a l cycle (Cruise 80/18). Hours and t i d a l height as in F i g . 15. D = Paracalanus parvus , ^ = Microcalanus pygmaeus , X = Oithona helgolandica , 0 = Pseudocalanus minutus . DENSITY (PER CU.M) 0 5 10 15 20 25 30 35 40 45 ' TtiT 1 42 Figure 22; Density of the second four most abundant copepods at IND 0 over the t i d a l cycle (Cruise 80/18). Hours and t i d a l height as in F i g . 15. X = Corycaeus anglicus , <> = Calanus pa c i f i c u s , A = Acartia c l a u s i , • = Metr i d i a pac i f ica . DENSITY (PER CU.M) 1 44 Figure 23; Total zooplankton d i v e r s i t y and dominance over the t i d a l cycle at IND 0 (Cruise 80/18). Hours and t i d a l height as in F i g . 15. 1 46 Figure 24; Dive r s i t y and dominance of the copepod community over the t i d a l cycle at IND 0 (Cruise 80/18). Hours and t i d a l height as in F i g . 15. 148 Figure 25; Diversity and dominance of a l l other invertebrate zooplankton over the t i d a l cycle at IND 0 (Cruise 80/18). Hours and t i d a l height as in F i g . 15. -6+iT 1 50 Figure 26; Diversity and dominance of invertebrate zooplankton (minus larvaceans and siphonophores) over the t i d a l cycle at IND 0 (Cruise 80/18). Hours and t i d a l height as in F i g . 15. 1 52 Figure 27; Kendalls c o e f f i c i e n t of concordance between time adjacent samples over the t i d a l cycle at IND 0 (Cruise 80/18). Hours and t i d a l height as in F i g . 15. 

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