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Field study of the distribution and behavior of Oligocottus maculosus Girard : a tidepool cottid of the… Green, John Marshall 1967

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A F I E L D S T U D Y O F T H E D I S T R I B U T I O N A N D B E H A V I O R O F O L I G O C O T T U S M A C U L O S U S GIRARD, A T I D E P O O L C O T T I D O F T H E N O R T H E A S T P A C I F I C O C E A N by J O H N M A R S H A L L G R E E N B.S., U n i v e r s i t y of M i c h i g a n , 1961 M.S., U n i v e r s i t y of M i a m i , 1964 A T H ESIS S U B M I T T E D IN P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y i n the Department of Zoology We acdept this t h e s i s as co n f o r m i n g to the r e q u i r e d standard The U n i v e r s i t y of B r i t i s h C olumbia November, 1967 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and Study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by h.i>s representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Corambia Vancouver 8, Canada Date jQjL^^ Co /f^ ? A B S T R A C T The study was concerned f i r s t of a l l with the d i s t r i b u t i o n p a t t e r n at low tide of Oligocottus maculosus G i r a r d and other c o t t i d f i s h e s inhabiting tidepools on the west coast of V a n c o u v e r Island, B.C. F i v e s p e c i e s (O. maculosus, G. r e m e n s i s , Clinocottus acuticeps, C. ein b r y u m and C. globiceps) have the i r c e n t e r s of d i s t r i b u t i o n i n the i n t e r t i d a l zone. Seven species (Hemilepidotus hernilepidotus, A r t e d i u s l a t e r a l i s , A. f e n e s t r a l i s , A s c e l i c h t h y s rhodorus, O. s n y d e r i , E n o p h r y s bi s o n and Leptocottus armatus) inhabit tidepools but are most abundant i n the subtidal zone. O. m a c u l o s u s is the most abundant and widely d i s t r i b u t e d tide-p o o l c o t t i d i n the i n t e r t i d a l zone. Only three other species (C. acuticeps, C. embryum and C. globiceps) r e g u l a r l y inhabit tidepools above L L H W (lowest l o w e r high water). The p r i m a r y environmental f a c t o r c o r r e l a t e d with the d i s t r i b u t i o n of O. maculosus i s exposure to wave action. In exposed t r a n s e c t s this species is r e s t r i c t e d to the upper i n t e r t i d a l zone, while in shel t e r e d t r a n s e c t s it inhabits tidepools throughout the i n t e r t i d a l zone. Observations show that O. maculosus responds to water turbulence by re t r e a t i n g to cover. It i s concluded that to inhabit a given tidcpool O. maculosus must have a minimum p e r i o d of low turbulent conditions. T h i s species has 'capitalized' on the tidcpool habitat to invade the open coast environment. The study's second c o n c e r n was to determine the fi d e l i t y of v i i i n d i v i d u a l O. m a c u l o s u s to the tidcpool in which they a r c found. O. m a c u l o s u s shows f i d e l i t y to s p e c i f i c tidepools and w i l l r e t u r n to these pools when d i s p l a c e d f r o m them. The r e s u l t s indicate that the n a v i g a t i o n a l a b i l i t y of O. maculosus i s not solely dependent upon f a m i l i a r i t y .with g e o g r a p h i c a l features of the i n t e r t i d a l zone. It is suggested that homing b e h a v i o r functions as a m echanism s t a b i l i z i n g the s p a t i a l d i s t r i b u t i o n of this species. T h i r d l y , the study was c o ncerned W i t h determining what f a c t o r s affect the f i e l d a c t i v i t y such as feeding and spawning of O. m a c u l o s u s , and a c o m p a r i s o n of its f i e l d a ctivity to that under c o n t r o l l e d conditions. In the n a t u r a l habitat its a c t i v i t y i s dependent p r i m a r i l y upon such f a c t o r s as turbulence, temperature and light. F i e l d o bservations on feeding behavior support M o r r i s 1 (I960) co n c l u s i o n , drawn f r o m p h y s i o l o g i c a l studies, that a p p r o x i m a t e l y the 16°C i s o t h e r m i s the l i m i t i n g environmental factor in the south-ward d i s t r i b u t i o n of this species. Under constant conditions O. maculosus exhibits a tida l rhythm of l o c o m o t o r a c t i v i t y . The c h a r a c t e r i s t i c s of the rhythm indicate that it i s entrained d i r e c t l y by the tide. H y d r o s t a t i c p r e s s u r e is suggested as the p o s s i b l e s y n c h r o n i z e r . The rhythm is not d i r e c t l y r e l a t e d to the f i e l d a c t i v i t y of O. maculosus. It is concluded that it r e p r e s e n t s the coupling of an avoidance or escape response to a b i o l o g i c a l clock. V l l l Such a m e c h a n i s m would function with, and be p a r t i a l l y r esponsible f o r , the homing behavior. TABLE OF CONTENTS PAGE ABSTRACT vi LIST OF TABLES ix LIST OF FIGURES xi ACKNOWLEDGMENTS xv GENERAL INTRODUCTION 1 LOCATION OF STUDY AREA 4 GENERAL ENVIRONMENTAL CONDITIONS 6 Geological Features 6 Temperature of the Sea Water 9 Salinity of the Sea Water 12 Meteorological Conditions 12 Sea State Conditions , 14 Tidal Features 1 6 ' SPECIFIC ENVIRONMENTAL FEATURES 26 Methods •; 2 6 Surveying'and levelling 26 Determination of tklcpool volumes — 27 Determination of temperature and salinity 27 Determination of oxygen and pIT 28 Determination of exposure 29 Determination of flora and fauna 31 i i P A G E Resul t s 32 T e m p e r a t u r e ; 32 Sa l i n i t y 34 C h e m i c a l features 38 G e n e r a l d i s t r i b u t i o n of benthic biota 40 L O C A L D I S T R I B U T I O N O F T I D E P O O L C O T T I D S — 52 Methods 53 Quantitative and qualitative c o l l e c t i o n s 53 P e r i o d i c trapping and poisoning 55 Res u l t s 57 G e n e r a l d i s t r i b u t i o n pattern 57 E n v i r o n m e n t a l f a c t o r s and d i s t r i b u t i o n 62 P h y s i c a l and c h e m i c a l tidepool f a c t o r s 62 E x p o s u r e 67 B i o t i c f a c t o r s 72 Size 74 Seasonal changes 76 Population fluctuations and growth 77 HIGH T I D E M O V E M E N T S AND H O M I N G BEHAVIOR.... 81 Methods 84 Observations 84 Tag g i n g 85 Taggin g experiments 89 i i i PAGE Results 91 High tide distribution and movements 91 Tagged fish 93 Duration of Residence in tidepools 96 Straying 97 High tide distribution of other species 97 Homing behavior 98 Definition of homing 98 Homing success 99 Behavior of transplants . 99 Possible influencing factors 104 Position of home pool 104 Distance from home pool , 104 Time of year 106 Captivity 108 Tagging of other species 109 ACTIVITY STUDIES 113 Methods 115 Field observations 115 Activity apparatus 115 i v P A G E R e s u l t s 121 A c t i v i t y under n a t u r a l conditions 121 T e m p e r a t u r e . . 121 S a l i n i t y ..' 1 2 4 T u r b u l e n c e 125 L i g h t 1 2 6 Inter- and i n t r a s p e c i f i c i n t e r a c t i o n s 126 A c t i v i t y under c o n t r o l l e d conditions 127 The n a t u r a l rhythm . 127 Influence of the tide 130 E n t r a i n m e n t under natural conditions 131 Constant conditions 133 T e m p e r a t u r e 133 DISCUSSION A N D C O N C L U S I O N S 134 D i s t r i b u t i o n • 134 L o c a l 134 G e o g r a p h i c a l 138 Other species 139 Movements and homing , 140 E c o l o g i c a l s i g n i f i c a n c e 144 P A G E T i d a l Rhythm ,'. 146 Number of o s c i l l a t o r s 148 E c o l o g i c a l s i g n i f i c a n c e 150 S U M M A R Y 152 L I T E R A T U R E C I T E D 156 L I S T O F T A B L E S T A B L E P A G E I S u r f a c e seawater t e m p e r a t u r e and sa l in i ty data c o l l e c t e d at a station at the m o u t h of San J u a n Inlet and at a station a p p r o x i m a t e l y 4 k i l o m e t e r s o f f - s h o r e { F r o m A n o n . , 1955). 11 II M a x i m u m sur face t e m p e r a t u r e s r e c o r d e d in a s e r i e s of t idepools on A u g u s t 15, 1966 in r e l a t i o n to the t ime of f looding of each p o o l . T h e sea , s u r f a c e t e m p e r a t u r e was 10.66 C. 33 III E f f e c t of r a i n on the sa l in i ty of t idepools subject to l i t t l e sur face run off. P o o l s e m e r g e d for l e s s than eight h o u r s . 39 IV E f f e c t of r a i n on the sa l in i ty of t idepools subject to s u r f a c e r u n off. P o o l s e m e r g e d for l e s s than eight h o u r s . 39 V C a t e g o r i e s into w h i c h cott ids s p e c i e s , taken at B o t a n i c a l B e a c h , a r e p l a c e d with r e s p e c t to t h e i r o c c u r r e n c e in t idepoo l s . 58 V I S u m m a r y of cot t id spec i e s taken in 67 p o i s o n c o l l e c t i o n s m a d e at B o t a n i c a l B e a c h f r o m 1965 to 1967. N u m b e r i n f a r left of each row is the total n u m b e r of c o l l e c t i o n s in wh ich that spec ies was taken. 59 VII S u m m a r y of cot t id s p e c i e s taken in 56 c o l l e c t i o n s m a d e between P a c h e n a P o i n t , B . C . , and Cape St. E l i a s , A l a s k a , f r o m 1965 to 1967. N u m b e r in far left of e a c h row is the total n u m b e r of c o l l e c t i o n s in which that spec ies was taken. 60 VIII Cot t ids taken f r o m a v e r t i c a i s e r i e s of t idepools n e a r P a c h e n a P o i n t , B . C . , d u r i n g Ju ly 1966. 61 IX S u m m a r y of nine e x p e r i m e n t s i n v o l v i n g h o m e poo l r e l e a s e s of O. m a c u l o s u s . R e c o v e r i e s within the f i r s t two weeks of tagging a r e not i n c l u d e d . 94 X T A B L E P A G E X Summary of 2 1 experiments involving transplant releases of O. maculosus. 1 0 0 / 1 XI Summary of 20 transplant experiments of O. maculosus showing the homing success of different size groups. 102 XII Summary of four experiments involving home pool releases of C. globiceps. 110 XIII Summary of nine experiments involving transplant releases of C. globiceps. I l l XIV Summary of nine transplant experiments of C. globiceps shov/ing the homing success of different size groups. 112 LIST OF FIGURES FIGURE PAGE 1 Chart of southwestern Vancouver Islai.d, B.C. showing location of study site. 5 2 Aerial photograph of the study site. 8 3 Aerial photograph of the intertidal zone at the study site. 8 4 Mean monthly temperatures of the surface water at Botanical Beach and Amphitrite Point. 10 • 5. Mean monthly salinities of the surface water at Botanical Beach and Amphitrite Point. 10 6 Mean maximum, mean minimum and mean monthly air temperatures at Botanical Beach and mean monthly air temperatures at Pachena Point. 13 7 Total monthly precipitation at Port Renfrew and at Pachena Point. 15 8 Sea state observations at Botanical Beach. 17 9 Sea state observations at Swiftsure Bank. 18 10 Computer plotted tide curve for Port Renfrew. 19 11 Computer plotted tide curve for Port Renfrew. 20 12 Variations in tidal day periods and tidal semi-daily periods at Port Renfrew. 22 13 Tide factors at Port Renfrew. 23 14 Submergence and emergence curves for the 24 intertidal zone at Port Renfrew. 15 Percent of the year that various heights in the intertidal zone rit Port Renfrew are covered by the sea. 25 P h o t o g r a p h of a s u r f s e n s o r bolted to the s u b s t r a t u m . C o m p a r a t i v e temperature charts f r o m two ti d e p o o l s of d i f f e r e n t depths. Continuous temperature r e c o r d s f r o m a single t i d e p o o l . Continuous temperature r e c o r d s f r o m a single t i d e p o o l . D o m i n a n t features of the d i s t r i b u t i o n of the i n t e r t i d a l f l o r a and fauna at B o t a n i c a l Beach. P h o t o g r a p h of the upper and lower i n t e r t i d a l zone at B o t a n i c a l Beach. P h o t o g r a p h of the upper and lower i n t e r t i d a l zone at B o t a n i c a l Beach. P h o t o g r a p h of an exposed v e r t i c a l t r a n s e c t at B o t a n i c a l Beach. P h o t o g r a p h of a l o w e r i n t e r t i d a l m oderately s h e l t e r e d tidepool. P h o t o g r a p h of a lower i n t e r t i d a l exposed tidepool. P h o t o g r a p h of an upper i n t e r t i d a l tidepool of i n t e r m e d i a t e exposure. P h o t o g r a p h of an exposed tidepool near the m i d tide l e v e l . P h o t o g r a p h of an upper i n t e r t i d a l exposed tidepool. P h o t o g r a p h of the i n t e r t i o r of an upper i n t e r t i d a l exposed ti d e p o o l showing a minnow trap at its bottom. x i i i F I G U R E P A G E 30 Photograph of the i n t e r i o r of an i n t e r m e d i a t e l y exposed tvdepool at the m i d tide l e v e l . 50 31 Photograph of a mode r a t e l y sheltered, upper i n t e r t i d a l tidepool, 50 32 Photograph of a s e r i e s of tidepools in the upper i n t e r t i d a l zone. • 51 33 Photograph of an upper i n t e r t i d a l tidepool in a slate formation. 51 34 Number of O. maculosus and C. globiceps taken i n p o i son c o l l e c t i o n s f r o m a single tidepool poisoned at different times of the year. 66 35 D i s t r i b u t i o n of O. maculosus as a function of exposure and tide height. 68 36 Density of O. maculosus p e r l i t r e of tidepool volume as a function of tide height. 69 37 D i s t r i b u t i o n of globiceps as a function of exposure and tide height. 70 38 D i s t r i b u t i o n of C. embryum as a function of exposure and tide height. 71 39 Length frequency d i s t r i b u t i o n s of O. maculosus f r o m tidepools of di f f e r e n t tide heights. 75 40 Seas o n a l population fluctuations in O. maculosus and C\ globiceps. .78 41 Length frequency d i s t r i b u t i o n s of populations of O. m a c u l o s u s trapped at different times of the year"! 80 42 Photograph of a gillnet site. 86 43 P e r c e n t of a tidepool population of O. maculosus out of the pool at the time of high tide during di f f e r e n t months. 92 x i v F I G U R E S P A G E 44 Homing s u c c e s s of O. maculosus as a function of the distance r e l e a s e d f r o m the home pool. 10 5 45 Homing suc c e s s of O. maculosus as a function of the time of the year. 107 46 A c t i v i t y apparatus. 11.7 47 P e r c e n t of the total O. maculosus population of a tidepool in the shallow parts of the pool in r e l a t i o n to the temperature of the pool water. 123 48 R e c o r d of the act i v i t y of O. maculosus under conditions of constant temperature and n a t u r a l light. 128 49 R e c o r d of the ac t i v i t y of O. maculosus under conditions of constant temperature and constant darkness. A s u r f sensor r e c o r d is a l s o shown. 129 A C K N O W L E D G M E N T S I am indebted to the various persons who a s s i s t e d me during this study. P a r t i c u l a r l y , I should l i k e to thank Dr. N o r m a n J. W i l i m o v s k y fo r h i s advice, a s s i s t a n c e in the f i e l d , review of the m a n u s c r i p t , and fi n a n c i a l support. I am grateful to D r s . B. Bary, H. D. F i s h e r and N. R. L i l e y f o r t h e i r advice during t h e study and f o r t h e i r comments on the manu-sc r i p t . F o r bis suggestions c o n c e r n i n g the manuscript, I am a l s o grateful to Mr. H. Verwey. I should l i k e to thank Mr. R. W i t s c h i , V i c t o r i a , B.C., f o r his kind c o-operation, without which the study could not have been c a r r i e d out. Dr. L. D. D r u e h l a s s i s t e d me on numerous and memorable oc c a s i o n s in the f i e l d . M r s . John M. G r e e n a s s i s t e d rne in many ways. G E N E R A L I N T R O D U C T I O N Much d e s c r i p t i v e and exp e r i m e n t a l work has been published during recent years concerning the i n t e r t i d a l and subtidal d i s t r i b u -tion of plants, p r i m a r i l y algae, and inv e r t e b r a t e animals. R e l a t i v e l y l i t t l e work of a s i m i l a r nature, however, has been published on the fishes of these shore zones. Whereas w o r k e r s i n the fiel d s of ma r i n e phycology and marine i n v e r t e b r a t e ecology a r e at the stage where they are d i r e c t i n g attention towards the dynamic aspects of i n t e r t i d a l b i o l o g i c a l phenomena, in v e s t i g a t o r s i n t e r e s t e d in the l i t t o r a l f i s h fauna a r e s t i l l l a c k i n g adequate d e s c r i p t i o n s of these phenomena. A p o s s i b l e r e a s o n for the l i m i t e d attention given to the ecology and behavior of l i t t o r a l fishes is the d i f f i c u l t y encountered when tr y i n g to study them. Unlike plants and many i n t e r t i d a l i n v e r t e b r a t e s , f i s h e s a r e t y p i c a l l y v e r y mobile once they complete e m b r y o l o g i c a l development. A l s o , except for a r e l a t i v e l y few species which can pass through periods of tidal emergence under moist but non-submerged conditions, most l i t t o r a l f ishes must r e m a i n submerged throughout the tidal c y c l e . T h e r e f o r e , diving apparatus is usually r e q u i r e d if observations and measurements of environmental p a r a m e t e r s are to be made. A s i d e f r o m the telemetry d i f f i c u l t i e s involved, such 3tudi.es can be hazardous at best, even when working in r e l a t i v e l y s h e l t e r e d areas. A p h y s i c a l feature of the shore which tends to concentrate and isol a t e i n t e r t i d a l fishes is the tidepool. Tidepools along the P a c i f i c C oast of North A m e r i c a usually contain, wher they a r e i s o l a t e d at low tide, a v a r i e d and often abundant assemblage of f i s h e s . A l o n g the west coast of Vancouver Island, B r i t i s h Columbui, about 26 species of f i s h a r e commonly found in tidepools. The f a m i l y Cottidae accounts for the m a j o r i t y of species (about 14) and i n d i v i d u a l s . The r e m a i n i n g species a r e p r i m a r i l y b l e n n i o i d f i s h e s of the f a m i l i e s Stichaeidae and Pholidae. Because these f i s h e s a r e r e a d i l y a c c e s s i b l e when the pools a r e i s o l a t e d , and because tidepool p a r a m e t e r s can be monitored r e l a t i v e l y e a s i l y , the tidepool i s an i d e a l unit to focus attention upon in o r d e r to i n c r e a s e our fundamental under standing of the ecology and behavior of i i t t o r a l f i s h e s . Despite t h e i r r e l a t i v e a c c e s s i b i l i t y , the tidepool fishes of the nor t h e a s t e r n P a c i f i c have r e c e i v e d v e r y l i t t l e attention except for their s y s t e m a t i c s . The present investigation of the tidepool fishes of the west coast of Vancouver Island, B r i t i s h Columbia, was undertaken in hopes that at least p a r t i a l answers to the following questions could be obtained: What is the l o c a l d i s t r i b u t i o n pattern of the tidepool f i s h fauna and how stable is this pattern? How are s p e c i f i c environmental f a c t o r s c o r r e l a t e d with this pattern? What is the r e l a t i o n s h i p between i n d i v i d u a l f i s h and the tidepool in which they are found? What a r c some of the behavioral mechanisms which lead to the observed distribu-tion pattern and in what way can they be considered as being adaptive? It became apparent early in the study that it would not be feasible to work with the entire tidepool fish fauna. Consequently, the cottid fishes were selected for study because of their relative abundance in species and numbers, their apparent greater dependence upon the tidepool environment than the blennioid fishes and because their taxonomy has been well established (Bolin, 1944). Similarly, Oligocottus maculosus Girard received more intensive study than any of the other cottids because of its presence and abundance in relatively high, readily accessible tidepools. The thesis consists of three major sections: Part I describes the local low tide distribution of_0. mac ulos us, the associated tidepool cottids and seasonal population fluctuations in the former species. Part II describes the high tide movements and homing behavior of O.  maculosus. Part III describes aspects of the activity of O. maculosus under natural and controlled conditions. A final discussion relates the various aspects of the study. 4 I.. L O C A T I O N O F S T U D Y A R E A The i n t e r t i d a l a r e a selected f or the present i n v e s t i g a t i o n is lo c a t e d on the southwest coast of Vancouver Island, B r i t i s h Columbia. It i s a p p r o x i m a t e l y 5 k m southwest of the logging community of P o r t Renfrew and 400 m southeast of the entrance to San Juan Inlet, i n latitude 4 8°32'N and longitude 124°27'W (Fig. 1). The site is loca t e d on the S t r a i t of Juan de F u c a , but is an open coast with a w e s t e r l y and n o r t h w e s t e r l y exposure to the P a c i f i c Ocean. The r e g i o n was selected, f i r s t l y , because the shore i s i d e a l l y suited both g e o l o g i c a l l y and b i o l o g i c a l l y f o r the study of tidepool o r g a n i s m s , and, secondly, because i t i s undisturbed yet r e l a t i v e l y a c c e s s i b l e . It was p o s s i b l e to construct r e s e a r c h and l i v i n g quarters at the site . T h i s made it feasible and convenient to c a r r y out in s i t u e xperiments and observations throughout the year. It i s of h i s t o r i c a l i n t e r e s t that the location of the r e s e a r c h l a b o r a t o r y was 75 m west of the old site of the Minnesota Seaside Station. T h i s station was operated as a summer m a r i n e and t e r r e s t r i a l b i o l o g i c a l l a b o r a t o r y by the U n i v e r s i t y of Minnesota f r o m 1900 to 1909. In re c o g n i t i o n of its e a r l y use as a b i o l o g i c a l r e s e a r c h site the shore r e g i o n i s now c a l l e d B o t a n i c a l Beach. Despite this e a r l y r e c o g n i t i o n of the uniqueness of the site for the marine i n v e s t i g a -tions, the present study, and others a s s o c i a t e d with i t , r e p r e s e n t the F i g . 1. C h a r t showing the southwestern coast of Vancouver Island, B.C., the mouth of the S t r a i t of Juan de F u c a and the no r t h e r n part of the Olympic P e n i n s u l a , Washington. The study site i s located at B o t a n i c a l Beach. 125*40'W 12515' 124'50' 124*25' 12fOO' 6 first time since 1909 that intensive investigations have been conducted there. II. GENERAL ENVIRONMENTAL CONDITIONS .Geological Features The geological feature dominating Botanical Beach is a Tertiary sandstone and conglomerate formation. This formation is apparently a remnant of a once extensive coastal plain of Oligocene or early Miocene sedimentary rocks which, according to Holland (1964), probably existed all along the southwest coast of Vancouver Island. Where the formation extends into the intertidal zone benches exist which are several hundred feet long and extend out a similar distance from the high water mark. Local variations in the texture and hardness of the formation have resulted in very irregular surfaces and a large number of tidepools of various shapes and sizes. •i The following description from the 1906 Annual Announcement of the Minnesota Seaside Station (Anon. , 1906) is a rather picturesque but factual account of these pools: At mid and low tides a great sandstone shelf is uncovered in which boulders have ground innumerable cistern-like pot-holes varying in size from mere teacups to great wells, twenty feet across, and thirty or more in depth. These act as natural aquaria and serve to segregate the plants and animal populations, to the very great convenience and instruction of students and collectors. Nothing like this natural formation is known to exist in connection with other seaside stations. ... A great advantage is gained by the extraordinary accessibility of the rich marine flora and fauna. Where the Tertiary formation has been completely eroded, harder rocks of the Vancouver Group (cf. Hull, 1906 and Clapp, 1917) are exposed. Relatively few tidepools. occur in these slate and shale formations, and where they do occur they are usually long, relatively shallow pools which follow the lines of stratification (Fig. 33). A further description of the physiography of the tidepools in the vicinity of the study site is given by Henkel (1906). The aerial photographs in Figs. 2 and 3, taken during a low water spring tide, show the physical features of the intertidal zone in the vicinity of the field laboratory. In many places the intertidal rock formations end abruptly and drop vertically into ten to twenty feet of water at extreme low tide. In adjacent locations the intertidal zone has an even slope of approximately 20 degrees which continues in the subtidal. The sandstone benches are mostly free of unconsolidated material but immediately in front of the field laboratory a stretch of the shore approximately 30 m wide is littered with glacially deposited boulders and cobbles. In this same area coarse sand and gravel occur above the 9' tide level. 8 Fig. 2. Aerial view of the study site during a low water spring tide. Nearly the entire rock formation shown is Tertiary sand-stone. The shore facing to the left of the photograph is exposed to Pacific swells. The research facility is located in about the middle of this shore. Fig. 3. Aerial view of the intertidal zone in front of the research facility (note the position of the tree shadows in Fig. 2). Boulders can be seen littering the intertidal /.one in the left side of the photograph. This shore faces westerly with open exposure to Pacific s w e l l s . 9 T e m p e r a t u r e of the Sea Water A l m o s t weekly temperature and s a l i n i t y readings for the s u r f a c e sea water at B o t a n i c a l Beach were made f r o m November 1965 to M a r c h 1967. A n inductive s almometer (Model RS52, I n d u s t r i a l Instruments Inc. , New Jersey) was used for these m easurements. The mean monthly temperature of the surface water for 1966 is shown, in F i g . .4. Two features a r e c h a r a c t e r i s t i c . The average t e m p e r a t u r e is r e l a t i v e l y low and the amplitude of v a r i a t i o n is c o m p a r a t i v e l y s m a l l . The highest temperature (11. 8°C) o c c u r r e d during August and the lowest (6. 7°C) during F e b r u a r y . The most southern station on the west coast of Vancouver Island where daily r e c o r d s of surface sea water temperature a r e kept, i s •Amphitrite P o i n t (see F i g . 1). F o r c o m p a r i s o n the average mean monthly, s u r f a c e sea-water temperatures at A m p h i t r i t e Point f o r the p e r i o d 1935 to 1964 ( H o l l i s t e r , 1966) also a r e shown in F i g . 4. Sea water temperature data c o l l e c t e d at stations off the mouth of San Juan Inlet by'the P a c i f i c Oceanographic Group f r o m October 1951 to October 1952 (Anon., 1955) indicate that there is l i t t l e t e mperature v a r i a t i o n between the off-shore and on-shore surface sea water in the v i c i n i t y of the study site (Table 1). 10 i 1 — r ~ — i 1 i r i r — i — ~ i d F M A M J J A S O N D Months F i g . 4. M e a n m o n t h l y t e m p e r a t u r e of the surface water at B o t a n i c a l B e a c h ( o — o ) f or 1966, and the average m e a n month ly t e m p e r a t u r e of the s u r f a c e water at A m p h i t r i t e P o i n t (o"-o) , B . C . , f o r the p e r i o d 1935-1964 ( H o l l i s t e r , 1966). 3 2 -0 N ° 0s- 3 1 -1 >» 4— 3 0 -CZ o 2 9 ~ CO 28 -i 1 r M J J Months F i g . 5. M e a n m o n t h l y sa l in i ty of the sur face water at B o t a n i c a l B e a c h ( o — o ) for 1966, and the average m e a n m o n t h l y s a l i n i t y of the sur face water at A m p h i t r i t e P o i n t ( o " « o ) , B . C . , . f o r the p e r i o d 1935-1964 ( H o l l i s t e r , 1966). 11 . T A B L E I Surface sea water temperature and sal i n i t y data c o l l e c t e d at a station near the mouth of San Juan Inlet and at a station a p p r o x i -mately 4 k m o f f - s h o r e (Anon., 1955). T e m p e r a t u r e S a l i n i C / oo n e a r - s h o r e off-shore n e a r - s h o r e off-shore October 6, 1951 11. 17 11.31 29. 54 31. 10 November 5, 1951 8. 85 10. 65 31. 55 31. 95 March.6, 1952 7. 20 7. 80 31. 00 31. 30 A p r i l 25, 1952 7. 85 ' 8. 33 31.79 31. 91 June 3, 1952 9. 19 9. 38 31.52 31. 57 August 13, 1952 9. 35 9. 78 32.09 31. 83 September 23, 195 2 10.25 10. 31 31. 56 31. 44 12 S a l i n i t y of the Sea Water The mean monthly sa l i n i t y of the siirface water at B o t a n i c a l B e a c h for 1966 is shown in F i g . 5. T h e r e was a seasonal v a r i a t i o n in the s a l i n i t y of the shovo water of approximately 3.0% o. The highest s a l i n i t y (32.35% 0) o c c u r r e d during the c o m p a r a t i v e l y dry summer months and the. lowest s a l i n i t y (28.35%») o c c u r r e d during the wet winter months. T h i s seasonal v a r i a t i o n is t y p i c a l of the west coast of Vancouver Island as shown in F i g . 5 by the average (1935-1964) mean monthly s a l i n i t y at A m p h i t r i t e P o i n t ( H o l l i s t c r , 1966). A s with the temperature of the shore water, there appears to be l i t t l e v a r i a t i o n between the s a l i n i t y of the on-shore and off-shore surface sea-water in the v i c i n i t y of the study site (Table I). M e t e o r o l o g i c a l Conditions R e c o r d s of maximum and m i n i m u m a i r temperatures at B o t a n i c a l Beach were kept f r o m October 1965 to January 1967. The mean monthly maximum and m i n i m u m a i r temperatures are shown in F i g . 6. The da i l y range in temperature is s m a l l , the s u mmer being c o o l and the winter mil d . D u r i n g December 1965 and January and F e b r u a r y 1966 m inimum temperatures of below f r e e z i n g were r e c o r d e d on only eleven days. The lowest temperature was -2.2°C. T e m p e r a t u r e s above 18°C were r e c o r d e d on only five days during the summer of 1966. The highest temperature was 22.2°C. ~i 1 1 1 1 1 — i r — i — i 1 r J F M A M J J A S O N D Months Mean monthly air temperatures at Botanical Beach for 1966 (o—o mean maximum, L — a mean, minimum, o — o mean) and average mean monthly air temperatures at Pachena Point (c-o) B . C . , for the period 1931-1960 (Anon., 1965). 14 No continuous records of rainfall were kept at Botanical Beach, but such records are kept at Port Renfrew by British Columbia Forest Products Ltd. , who kindly made them available to me. These records for 1965 are. presented in Fig. 7. Daily rainfall data are collected at Peichena Point (Fig. 1) and for comparison the averiige monthly, rainfall at this station for 1931-1960 is also shown in Fig. 7. Annual precipitation all along the west coast of Vancouver Island is high, usually over 85 in. (216 cm) and is characterized by marked seasonality. During the spring and summer the' prevailing flow of air from the northwesterly direction is cool, relatively dry and stable. In the fall and winter the high pressure center over the North Pacific weakens and moves south to be replaced by a low pressure center. The prevailing flow of moist winter air is from the southwest on the west coast of Vancouver Island, often easterly in the Strait of Juan de Fuca. Dense fog is characteristic of the summer months and during July, August and September 1966 it was on shore for at least half the day on an average of ten days per month. Sea State Conditions Sea state data were recorded on a semi-daily basis from November 1965 to December 1966 at ail times that the study site 15 J F M A M J J A S . O N D Months F i g . 7. T o t a l monthly p r e c i p i t a t i o n at P o r t Renfrew ( ) for 1965, and average monthly p r e c i p i t a t i o n at Pciche-na Po i n t , B.C. ( ) for the p e r i o d 1931-1960 (Anon., 1965). was occupied. All observations were made from the shore. The height of the swell was measured with a stadia rod graduated in tenths of feet using the horizon as a reference level. These data are presented in Fig. 8 as the percent of the total number of observations made each month that had sea swells of 0-lft. , 2-3 ft. , and greater than 6 ft. It is apparent that the sea is considerably rougher in the winter and early spring than in the summer and early fall. These observations correspond with sea state data recorded on a semi-daily basis during 1956 by the light ships Swiftsure and Relief (Anon. , 1958) at Swiftsure Bank (Fig. 1) off the mouth of Juan de Fuca Strait (Fig. 9). Tidal Features At Botanical Beach the tides are of the mixed semi-diurnal type. There is about equal inequality in both the high and low water. Consecutive high tides and consecutive low tides are comparatively equal only during the new moon periods. These features of the tides are evident in the 14-day cycles shown in Figs. 10 and 11. The two tides of each tidal day depart from a 12. 4 hour periodicity by as much as 2. 6 hours. The time interval between the lower low water and the higher high water is almost always longer than the time interval between the higher low water and lower high LI J F M A M J J A S O N D Months °° Fig. 9. Percent of total observations of sea state at Swiftsure Bank for 1956 with swells of 2: 6 ft. (o), 2-3 ft. (•), and 0-1 ft. ( A ) f (Anon., 1958). Computer plotted curve of th* *• -October 8 to October 2-> l g " ^ a t Renfrew f o r t h e D - - s t a r t e r ^ s ^ e s ^ - ~ P « . . » £ b ^ T F i g . 11. Computer plotted c u r v e of the tide at P o r t Renfrew f o r the p e r i o d D e c e m b e r 19, 1966 to J a n u a r y 2, 1967. F i r s t q u a r t e r moon is r e p r e s e n t e d by © and f u l l moon i s r e p r e s e n t e d by O. 21 water. The tidal day departs f r o m a 24. 8-hour p e r i o d i c i t y usually by l e s s than 20 minutes and never by more than a p p r o x i m a t e l y 48 minutes. The v a r i a t i o n s in tidal p e riods and t i d a l day periods for June and July, 1966 a r e shown in F i g . 12. The amplitude of extreme tides i s a p p r o x i m a t e l y 12.0 feet. A s u m m a r y of a l l the tida l features at P o r t Renfrew i s presented in F i g . 13. C u r v e s showing the duration of maximum single e m e r gences and submergences as a function of height i n the i n t e r -t i d a l zone for the p e r i o d M a y 1 to June 14, 1966 were p r e p a r e d f r o m six-minute t i d a l p r e d i c t i o n s for P o r t Renfrew ( F i g . 14). It i s apparent that there a r e definite steps in these curves which a r e r e l a t e d to p a r t i c u l a r t i d a l f a c t o r s . F i g . 15 shows the p e r c e n t of the year that v a r i o u s heights in the i n t e r t i d a l zone a r e covered. Seasonally there is a change in the time of day at which extreme high and low tides occur. F r o m m i d September to m i d M a r c h the lowest low tides occur in the late afternoon and evening while the highest high tides occur near m i d day. F r o m mid M a r c h to m i d September the lowest low tides occur during the e a r l y m o r n i n g and the highest high tides occur near midnight. F i g . 12. D i a g r a m showing the r e l a t i v e l y s m a l l changes in the lengths of the da i l y tidal p e r iods, i.e., High High Water to Low High Water and Low High Water to Low High Water (upper part of the diagram) as compared with the r e l a t i v e l y l a r g e changes in the lengths of the s e m i - d a i l y tidal p e r i o d s , i.e., High High Water to Low High Water (lower p a r t of the diagram). T i m e s of the high tide are f r o m six minute tidal p r e d i c t i o n s for P o r t Renfrew (Canadian H y d r o g r a p h i c O f f i c e , Ottawa). LH - LH 25 HH-HH 24 June 15 July I 1966 July 15 23 12 -- HHHVV 10 - - MHHW a> i 4— 8 - - HLHW - MLHW - LHHW igh HHLW - - MTL - LLHW <u 6 -xz - MHLW Tide 4 -2 -0 -HLLW -LHLVV -LLLVV -- MLLW May I -June 14 1966 F i g . 13. T i d a l f a c t o r s at P o r t Renfrew for the p e r i o d M ay 1 to June 14, 1966. HHL/W equals Highe3t H i g h e r Low Water, MHHW'equals Mean Hi g h e r High Water, etc. F r o m six minute tidal p r e d i c t i o n s for P o r t Renfrew (Canadian H y d r o g r a p h i c O f f i c e , Ottawa). - H H H W 2 j 0 80 220 Hours F i g , 1 4 . M a x i m u m du r a t i o n of single submergence (o c) and e m e r g e n c e (c——o) - f o r v a r i o u s heights i n the i n t e r t i d a l zone at P o r t R e n f r e w f o r the p e r i o d M a y 1 to June 14, 1966. F r o m six minute t i d a l p r e d i c t i o n s f o r P o r t R enfrew (Canadian H y d r o g r a p h i c O f f i c e , Ottawa). 25 F i g . 15. P e r c e n t of the y e a r that v a r i o u s heigh.ts in the i n t e r t i d a l zone at P o r t Renfrew are c o v e r e d by the sea, F r o m 15 minute p r e d i c t i o n s of the tide at P o r i Renfrew for 1966. III. S P E C I F I C E N V I R O N M E N T A L F E A T U R E S Methods Surveying and Levelling The intertidal zone at the study site was extensively sur-veyed and levelled during the summer of 1965. Additional surveying and levelling was completed in the spring and summer of 1966. A K&E Paragon transit, Zeiss Self-Levelling level, steel 100 ft. measuring tape and a stadia rod graduated in tenths of a foot were used in these operations. Fifteen permanent bench marks were established on the shore. They were located from near the lowest water spring tides to above highest water spring tides. As no previously established bench mark was present at this site the heights of the bench marks relative to mean tide level were determined from six minute tidal predictions for Port Renfrew obtained from the Canadian Hydrograph Office, Ottawa. Over a period of several months in the summer of 1966 the times of submergence and emergence of one of the more sheltered bench marks were recorded on days when sea swells were less than one foot. The average of the heights determined in this way was taken as being the height of the bench mark relative to the mean tide level at Port Renfrew. 27 During the initial and subsequent levelling and surveying operations a large number of tidepools were given identifying numbers and the vertical height of each relative to one of the bench marks was determined. These data were recorded along with notes describing the general physical features, maximum depth and surface dimensions of each tidepool. Maps were also prepared showing the horizontal relationships of many of these tidepools. Determination of Tidepool Volumes The volumes of 50 tidepools which had been surveyed and levelled were determined by fluorescene dilution. A known amount of concentrated fluorescene solution weis injected into a tidepool with a 50 ml syringe. The pool was then thoroughly mixed with, a wooden oar after which a 100 ml sample was taken. The samples were kept in tightly sealed glass jars until they were analyzed. All samples were analyzed within one week after they were taken with a Model 111 Fluorometer, Turner Associates, Palo Alto, California. Values obtained with the dilution technique were found to be within 3% of values obtained by manually emptying pools and directly measuring the volume of the water removed. Determination of Temperature and Salinity The same inductive salinometer that was used to measure the temperature and salinity of the shore water was used to monitor 28 temperature and s;-. Unity changes i n tidepools. Often, however, when only temperature observations were being made a glass m e r c u r y thermometer was used. A s u b m e r s i b l e Ry^n 15-day r e c o r d i n g thermometer, Ryan R e c o r d i n g T h e r m o m e t e r Company, Seattle, Washington, was used during the summer and f a l l of 1966 to monitor on a n e a r l y continuous b a s i s the temperature fluctuations in a single tidepool. Another Ryan r e c o r d i n g thermometer, an 8-day model, was used s e v e r a l times i n conjunction with the above model to compare the temperature c h a r a c t e r i s t i c s of tidepools at different l e v e l s and tidepools of dif f e r e n t depths. E a c h of these thermometers was secured with w i r e to Hie bottom of the tidepool in which it was placed. D e t e r m i n a t i o n of Oxygen and pH Water samples to be analyzed for d i s s o l v e d oxygen were obtained by siphoning water d i r e c t l y f r o m tidepools into B O D (b i o l o g i c a l oxygen demand) bottles. The modified W i n k l e r method of oxygen a n a l y s i s was used (Str i c k l a n d and P a r s o n s , I960). Hydrogen ion determinations were rruide with a Beckman Mo d e l N-2 pH meter, Scienti f i c Instruments D i v i s i o n , F u l l e r t o n , C a l i f o r n i a . Exposure of Tidepools The degree of exposure of tidepools was determined with a device referred to by Green and Druchl (in preparation) as a surf sensor. The sensor consists of two 13cm long, 0.6cm diameter brass rods mounted horizontally 3. 8 cm above a 1. 3 cm thick, 7.6cm x 12.7cm plexiglass plate (Fig. 16). When in operation, a sensor is attached to the substratum at a known vertical height in the intertidal zone by a 1/2 in. bolt through the center of its base. The bolt is screwed into an anchored 1/2 in. diameter Philip shield. The rods are connected by rubber insulated telephone drop-line to a Rustrak Model 91, six volt recorder situated above high water. The gap separating the free ends of the rods is adjusted so that the recorder circuit is completed causing a maximum deflection of the chart stylus when the rods are submerged by the surf or the flooding tide. Conversely, with each emergence of the rods the stylus falls to zero. By running two or more sensors in conjunction with one another, the relative exposure of different pools or locations in the intertidal zone was determined by comparing the actual time at which a sensor became submerged or emerged with the predicted time of submergence or emergence for that vertical height. The predicted submergence and emergence times were based on six minute tidal Surf sensor bolted to the substratum iit the 7 ft. tide level. Wires leading to the recorder are at the top of the photograph. Note the abundance of Littorina, Balanus and Acmaea. 31 predictions for Port Renfrew provided by the Canadian Hydrographic Office, Ottawa. Surf sensor data were used to place pools into one of four exposure categories: sheltered, moderately sheltered, moderately exposed, or exposed. With a 3 ft. on-shore swell, actual flooding of pools in these classes preceded the predicted time of flooding by approximately 1/2, 1-1/2, 2-1/2, and 3-1/2 hours respectively. Determination of Flora and Fauna Observations were made throughout the year to assess the dominant flora and fauna of tidepools at different heights and with different exposures. Such observations were generally made at low tide from above the surface of the pool, but in some cases a face mask was used in particularly deep or well-shaded pools. On the basis of all the tidepools observed, organisms were classified as being abundant, common, rare or absent. The vertical distributions of the dominant exposed benthic algae and invertebrates were determined in the same way as the vertical heights of the tidepools. Results Physical and Chemical Features of the Tidepool Environment In common with organisms living in the subtidal region, tide-pool inhabitants are not exposed to periodic intervals of desiccation,, In many other respects, however, tidepool environmental factors vary considerably more than do the same factors below the intertidal zone. The rhythmical changes which occur in the physical and chemical properties of tidepools have previously been investigated by a number of workers, notably Klugh (1924), Johnson and Skutch (1928), Gersbacher and Dennison (1930), Humphrey and Macy (1930), Stephenson, Zoond and Fyre (1934), Pyefinch (1943) and Naylor and Sinns (1958). 1. Temperature Temperature is one of the most obvious and important environmental parameters which shows large fluctuations in tidepools. The temperature range encountered in a particular pool depends primarily upon the degree of isolation of the pool from the sea (Table II). This factor is in turn determined by the vertical position of the pool, its exposure and the sea state. Therefore, just as the maximum length of single emergences is critical in determining the amount of desiccation of the open rock habitat, it is also of direct T A B L E II M a x i m u m surface temperatures r e c o r d e d in a s e r i e s of tidepools on August 15, 1966 in r e l a t i o n to the time of flooding of each pool. The sea sur f a c e temperature was 10. 66 C. Tide Height M a x i m u m Surface F l o o d i n g T i d e p o o l of P o o l T e m p e r a t u r e T i m e Number (feet) ( C) ( P D L S T ) 2005 4.0 11.72 1100 15 5.0 11.96 1200 932 8.5 14.60 1300 102 9.0 17.08 1330 103 8. 5 24.00 1500 97 10.0 24.16 1500 34 importance r e l a t i n g to the temperature v a r i a b i l i t y of the tidepool habitat. It i s usual, however, that two tidepools equally i s o l a t e d f r o m the sea w i l l have di f f e r e n t temperature c h a r a c t e r i s t i c s because of d i f f e r e n c e s in f a c t o r s such as depth and degree of shading. T h i s is evident in F i g . 17 i n which simultaneous 6-day continuous r e c o r d s of the bottom temperatures of two pools at the 9 ft. tide l e v e l with the same exposure but with different depths are shown. Shading may be due either to plants or other cover within the pool or to obstructions above the pool. T e m p e r a t u r e s at the same depth in shaded and non-shadcd portions of a single pool have d i f f e r e d by as much as 3°C when the s u r f a c e of the pool r e a c h e d its maximum temperature. Continuous r e c o r d s of the bottom temperature of a 30 c m deep, • m o d e r a t e l y s h e l t e r e d tidepool at the 9 ft. l e v e l were obtained for much of the summer and e a r l y f a l l of 19t>6 (Fig. 18 and 19). These r e c o r d s show the effect of both the daily tidal cycle and the lunar fo r t n i g h t l y t i d a l c y c l e on the te'mperiiture fluctuations of the pool. 2. S a l i n i t y The s a l i n i t y of tidepools can d i f f e r f r o m the s a l i n i t y of the sea either as a r e s u l t of evaporation or of the inflow of water of higher or lower s a l i n i t y . E vaporation was found to be i n s i g n i f i c a n t I °c J u l y 9 Jr 12. 1 7 . C o m p a r i s o n of the bottom t e m p e r a t u r e s of two tidepools with the same exposure and v e r t i c a l height, but with d i f f e r e n t depths. The upper c h a r t was in a pool with a depth of 36cm and the lo w e r c h a r t was in a pool with a depth of 94cm. <_r. I Q J Z I j I ^ Z l E i _ C 3 j I l j , . . V - - ^ ^ ^ 1 ^ ^ ; A _ ^ A ; ; V :• 'y- -v y y y • '~ ^ g \ y y ^ ^ ^ ^ ^ y \ ^y^ X_LJ__J 30 July \ -\ \ • V \-.\"\ \ .V.--.-.\- VA-vA \ July y y : rr-Vr~\ F i g . U Records from a recording thermometer in a 36cm deep tidepool at the 9 ft. tide level covering parts of June, July and August, 1966. The variations caused by the daily and fortnightly tidal cycles can be seen. L E D 'iILiJ._C f [A . H ' ' f • / •• / ^}-~-:P'P::r:f::: <H'/V ii 'fi fi f i h i ) ' i /" /"/ / t /•/'" f 1 A u g u i t " « L - - - - : — • 3 1 S t p r . m b e r » ; I • / .-C-—- K-S t p t t m b o r 13 5 « p t » m b * r so O c t o b e r F i g . 19. R e c o r d s f r o m a r e c o r d i n g t h e r m o m e t e r i n a 36cm deep tidepool at the 9 ft. tide l e v e l c o v e r i n g p a r t s of August, September and October, 1966. The n e a r l y flat r e c o r d f r o m September 14 to 18 was c a u s e d by a s t o r m . in raising the salinity of tidepools unless the pools were isolated from the sea for weeks at a time. In tidepools completely isolated through-out sunny summer days maximum daily increases in salinity of less than 0 . 4%o\vere recorded. Precipitation can significantly alter the salinity characteristics of tidepools. Table III shows the extent to which the surface salinity of pools is lowered even when there is little or no surface drainage into them. Table IV shows the surface and bottom salinities of pools which have extensive run off entering them. It is evident from both tables that in the absence of active mixing,pools can become strongly stratified with respect to salinity. Because of the heavy rains and subsequent run off which occur, particularly during the winter, some pools and surge channels even at the lowest tide levels may have very low salinities at low tide. Salinities of less than 4. 0%ewere frequently recorded at the 2 ft. level in several surge channels which, at high tide, had salinities of over 2 8 . 0 % i 3. Chemical Features Oxygen and pH were not extensively investigated at the study site but sufficient data were collected to substantiate the findings of Klugh (1924), Pyefinch (1943) and Stephenson, Zoond and Fyre (1934). These workers investigated diurnal and tidal changes in dissolved oxygen and hydrogen ion concentration of the tidepool environment 39 TABLE III Effect of rain on the salinity of tidepools subject to little surface run off. Pools emerged for less than eight hours. Depth of Pool 0. 2m 0. 5 m 1. lm 0. 7 m 1. 5m Surface Temperature °C 8. 28 8. 20 8. 00 9. 84 9. 56 Salinity %. 8. 64 6. 60 27. 24 26. 04 9.40 Bottom Temperature °c 8. 40 8. 36 8. 08 8. 92 9. 36 Salinity %o 29. 20 30. 52 31. 28 29. 56 28. 12 TABLE IV Effect of rain on the salinity of tidepools subject to surface rim off. Pools emerged for less than eight hours. Deoth of Pool 0. 3m 0. 3m 0. 3m 0. 3m Surface T e mpe rat ur e °C 8. 96 6. 24 7. 92 8. 60 Salinity %, 3. 16 16. 56 5. 88 3. 24 Bottom Temperature °c 8.32 7. 81 8. 86 8. 60 Salinity 27. 80 29. 08 29. 68 28. 24 40 and concluded that the range of variation of these factors is primarily dependent upon the density of the flora. In tidepools in which the ratio of plants to animals is large, dissolved oxygen and pH variations are greater than in pools in which this ratio is small. Most of the tidepools above the 3 ft. tide level have sparse algal floras, but some tidepools at all tide levels have dense growths of eel grass (Phvllospadix scouleri). Thus, at all levels in the intertidal zone there are pools at any one time with different dissolved oxygen and pH characteristics. In an attempt to determine whether dissolved oxygen might be a limiting factor in certain tidepools, oxygen determinations were made in several high tidepools which contained large growths of Phvllospadix. Determinations were made during the phase of the monthly tide cycle when the pools were isolated for maximum periods of darkness. The lowest concentrations obtained approximated 15% saturation. General Features of the Benthic Biota Very little information has been published concerning the vertical distribution of the intertidal benthic flora and fauna of the west coast of Vancouver Island. The most comprehensive study relating to the site at Botanical Beach is the investigation by Rigg and Miller (1949) in the vicinity of Neah Bay, Washington (see Fig. 1). / Widdov/son (1965) investigated the vertical and horizontal distributions of a number of intertidal algae and invertebrates along the southwest coast between Port Renfrew and Victoria. Green and Druehl (in preparation) determined the vertical distributions of dominant benthic organisms in three vertical transects at Botanical Beach. These authors were able to relate differences between transects to quantita-tively evaluated differences in the exposure of the transects to surf. The benthic biota at Botanical Beach is that of an open coastal environment. This is typified by the presence of Postelsia palmaeforrniis, a kelp which is restricted to rocky shores with exposure to heavy surf (Smith, 1944). Few qualitative differences were found during the summer of 1966 between the intertidal flora and fauna at Botanical Beach and at such fully exposed shore sites as Pachena Point on the west coast of Vancouver Island and the west coast of Cape Flattery on the northwestern tip of the Olympic Peninsula, Washington. The transition from open coast to sheltered coast along the southwest coast of Vancouver Island between Port Renfrew and Victoria is exemplified by the shoreward boundaries of open coastal forms and the seaward boundaries of sheltered forms (Widdowson, 1965). The more conspicuous biotic features of the intertidal zone at the study site are shown in Fig. 20. The division of the shore into the upper intertidal zone and the lower intertidal zone is Other Invertebrates Acmaea digitalis A • scutum A. 'pelta Littorina sitehana Cribrina xanthogrammica Balanu.'i glandula B. carlo sus Heraigrapsus nudus Searlesia dira Mopalia mucosa Crepidula adunca Leptasterias aequalis Petrolisthes eriomerus Strongylocentrotus ] purpuratus & franciscanuS Pugettia gracilis I Calliostoma costatura I \j Balanophylla elegans i Sndoc^ad^ia Thais emarginata. T orina scutalata ...ytxlus californianus Mitella polymerus Katherina tunicata j-r. Laminaria setchellii v ^ P leurophycus Costaria Lessoniopsis Hedophyllum Egregia na nana Fig. 20. Dominant features of the distribution of the intertidal benthic flora and fauna at Botanical Beach. arbitrary but useful. The lower iitertidal zone is characterized by a cover of kelp which has its upper .'imit at about the 6 ft. tide level. This height corresponds with several tide factors as can be seen in Fig. 1 1 . Hedophyllum dominates the lever intertidal zone except in very exposed transects where it is largely replaced by Alaria nana and Lessoniopsis (Fig. 2 3 ) . The upper intertidal zone, on the other hand, is mostly devoid o f algal cover (Figs. 21 and 2 2 ) . .Only in very exposed transects, where Postelsia occurs (Fig. 2 3 ) , and in sheltered transects where Fucus occurs, is algal cover present. The upper intertidal zone is characterized primarily by three invertebrate genera: Acmaea, Littorina and Balanus (Fig. 2 0 ) . Several species of sub tidal algae such as Laminaria setchellii,  L i . ephemera, Pterygophora californica and Pleurophycus have upper levels at about the 1 ft. to 2 ft. tide levels. Because of the essentially subtidal character of the flora and fauna at these levels, they are considered as part of the subtidal zone. It is not justified, as Lewis ( 1 9 6 4 ) points out, to extend the intertidal zone to the limits o f the extreme low tides. The benthic biota surrounding a particular tidepool depends upon the location of the pool. Tidepools in the upper and lower intertidal zone typically contain little algal cover aside from that F i g . 2 1 . M o d e r a t e l y exposed to m o d e r a t e l y sheltered t r a n s e c t showing upper and lower parts of the i n t e r t i d a l zone. The band of kelp is p r i m a r i l y Hcdophyllum. It m a r k s the upper l i m i t of the lower part of the i n t e r t i d a l zone F i g . 2 2 . The lower part of the i n t e r t i d a l zone is c h a r a c t e r i z e d by a dense cover of kelp. The upper part of the i n t e r t i d a l zone has little or no alga l cover. T r a n s e c t in F i g . 2 1 is i n the center of the photograph beyond the sandstone shelf. 45 - -* F i g . 23. E x p o s e d transect. The band of Hedophyllum is rep l a c e d by A l a r i a and L e s s o n i o p s i s , and P o s t c l s i a o c c u r s in the upper i n t e r t i d a l zone. The highest point in the tra n s e c t is at the 9 ft. tide l e v e l . Water is at about the 2 ft. tide l e v e l . afforded by calcareous genera such as Corallina, Calliarthron and Bossea (Figs. 25 and 27-31). A tidepool at any location may, however, contain large growths of eli grass (Phyllospadix scouleri) (Figs. 24, 26 and 30-32). It is only in some lower intertidal, moderately sheltered to sheltered tidepools (Fig. 24) that relatively dense algal cover occurs. Despite the fact that Hedophyllum is dominant throughout much of the lower intertidal zone, it is present only in the shallowest parts of tidepools, if present at all (Figs. 25 and 27). In contrast to pools above approximately the 2 ft. to 3 ft. tide levels, lower pools often " contain extensive algal cover afforded by such predominantly subtidal algae as Laminaria, Cos tar ia and Pleurophycus and a variety of bladed and filamentous reds and greens. The upper limits of subtidal and lower intertidal invertebrates are generally pushed upwards by tidepools. Thus, such species as Mytilus californianus, Katherina tunicata, Calliostoma costatum, Acmaea mitra, Strongylocentrotus purpuratus and Anthopleura  xanthogrammica occur at conspicuously higher tide levels in pools than they do in the open rock habitat. Conversely, many of the upper intertidal invertebrates such as Acmaea digitalis, Thais emarginata, Balanus and Littorina do not regularly inhabit the deeper tidepools of the upper intertidal zone. 47 Fig. 24. A moderately sheltered tidepool at the 3.5 ft. tide level. Hedophyllum and Egregia are abundant outside of the pool. Odonthalia, Iredaea and Phyllospadix are abundant in the pool. Fig. 25. An exposed tidepool at the 4 ft. tide-level. Hedophyllum surrounds the pool but is not as abundant as in Fig. 24. There is little vegetation in the pool aside from calcareous algae. Mytilus is abundant at levels just above the pool. 48 F i g . 26. A m o d e r a t e l y e x p o s e d t i d e p o o l at the 6 ft. tide l e v e l . H e d o p h y l l u m i s abundant at tide l e v e l s below the pool but not above i t . The dominant vegetation i n the p o o l i s P h y l l o s p a d i x . F i g . 27. A n e x p o s e d t i d e p o o l at the 5 f t . tide l e v e l . Some H e d o p h y l l u m i s around the p o o l and in i t s s h a l l o w e s t pc'irts. M y t i l w s i s abundant i n and above the poo l . C l u m p s of M i l e l l a a l s o a r e attached above the poo l . F i g . 28. A n exposed tidepool at the 8 ft. tide l e v e l . The surface of the pool c o r r e s p o n d s with the upper l i m i t of M y t i l u s in this location. Clumps of Mite 11a can be seen with the M y t i l u s below the pool, and around the edge of the pool. C o r a l l i n e algae are the only conspicuous vegetation in the pool. F i g . 2 9 . An exposed tidepool at the 8 ft. tide l e v e l with a wire minnow trap at its bottom. Co r a i l ina and M y t i l u s are conspicuous in the pool. Note the loose rock at the bottom and the absence of c r u s t o s e algae around it. Fig. 30. A moderately sheltered tidepool at the 7.5 ft. tide level. Corallina, Phvllospadix, Mytilus and Anthopleura are conspicuous in the pool. Fig. 31. A moderately sheltered tidepool at the 8.5 ft. tide level. Corallina and Phyllospadix grow in the deeper parts of pool while Odonthalia and Spongornorpha grow in its shallower parts. 51 F i g . 32. T i d e p o o l s of intermediate exposure at the 9.5 ft. tide l e v e l . Note the absence of m a c r o s c o p i c vegetation outside the pools. F i g . 33. A t i d e p o o l at the 10 ft. tide level showing the general p h y s i c a l features of pools in the shale and slate f o r mations. P h y l l o s p a d i x is conspicuous in the pool. L O C A L D I S T R I B U T I O N O F T I D E P O O L C O T T I D S The objective of this part of the present study was to define some of the f a c t o r s in the environment of tidepool cottids along the west coast of Vancouver Island, B. C. , and to relate c e r t a i n f a c t o r s to the l o c a l d i s t r i b u t i o n and abundance of these f i s h . P a r t i c u l a r emphasis has been given to Oli^ocottus maculosus, the most abundant and widely d i s t r i b u t e d of the i n t e r t i d a l cottids in this a r e a . In the past v a r i o u s w o r k e r s have noted that species of n o r t h -e a s t e r n P a c i f i c cottids inhabit, and may be r e s t r i c t e d to, the tidepool habitat (Greeley 1899, B o l i n l 9 4 4 , Clemens and Wilby 1961, and M a c P h e e and Clemens 1963). G r e e l e y (1899) also r e p o r t e d that some tidepool cottids occur only in tidepools with a p a r t i c u l a r f l o r a , and that some species occupy pools at definite heights in the i n t e r t i d a l zone. The only recent contributions to knowledge of the l o c a l d i s t r i b u -tion of n o r t h e a s t e r n P a c i f i c tidepool cottids are the studies by M o r r i s (I960, 1962). These studies eirc p r i m a r i l y concerned with temperature and s a l i n i t y as possible factors d e t e r m i n i n g the geographical d i s t r i b u t i o n of s e v e r a l species, but he also comments ( M o r r i s , 1962) upon the local, d i s t r i b u t i o n along the Oregon coast of O. maculosus, O. snydcyi, Clinocottus globiceps and. Leptocottus armatus. His data indicate that the; 16" C i s o t h e r m is the l i m i t i n g factor in the southward 53 distribution of O. maculosus and C. globiceps (Morris, 1960). He also suggests that a low Q is responsible for the ability of O. maculos us to inhabit high tidepools (Morris, 1962). Methods Quantitative and Qualitative Collections The distribution of species at low tide is based primarily upon poison collections made in tidepools and at subtidal stations. Chem Fish Collector, a rotenone-base chemical manufactured by Chemical Insecticides Corporation, Metuchcn, New Jersey, was used as a fish toxicant. It was found to be better suited for making quantitative and qualitative collections of the tidepool fish fauna than a variety of other fish toxicants and anesthetics such as cresol, quinaldine, chloral hydrate, 2-phenoxyethanol, and tricaine 'me thane sulfonate. The typical reaction of northeastern Pacific tidepool fish to Chem Fish Collector is an initial period of activity during which they leave the seclusion of rocks and crevices, followed by a short period of immobility that -proceeds death. The initial activity usually takes them to the surface or edge of the tidepool where they can be easily captured with a hand net or forceps. The response to other toxicants and anesthetics is not as general. Many species become immobilized before they leave 'he seclusion of rocks and crevices. This makes it difficult or impos.-.ible to recover them. Gibson (1965a) has reported that he was able to make quantitative collections of British tidepool fishes with quinaldine. The tidepool fishes with which he worked either respond differently to quinaldine than the fishes investigated in the present study, or the tidepools in which he made his collection were much better suited for being thoroughly searched. Cresol is an effective fish toxicant and causes a response similar to Chem Fish Collector. It is a more corosive chemical, however, and is much more injurious to the invertebrate fauna than rotenone. Other rotenone-base fish toxicants have the same general effect upon the fish fauna as Chem Fish Collector. But because of its greater potency, and composition, Chem Fish Collector is effective, unlike the others, at concentrations that do not alter the clarity of the water. It is therefore possible to make a thorough search of the pool following the application of the toxicant. Precise quantities to add to pools were not determined. If the fish did not respond to the initial dosage within ten to fifteen minutes, more was added. It was never necessary to add a quantity of toxicant which interfered with the clarity of the water. After the toxicant was mixed into the tidepool, small dip nets and forceps were used to retrieve the fish and transfer them to 10% formalin. 55 From May 1964 to May 1967, 87 tidepool or subtidal collections were made, mostly in the vicinity of Botanical Beach; 20 were made between Pachena Point and Triangle Island, which is located just off the northwestern tip of Vancouver Island. During the summer of 1965, 36 collections were made between Prince Rupert, B.C., and Cape St. Ellas, Alaska. Periodic Trapping ajnd Poisoning of Tidepools Two series of tidepools with a combined volume of approxi-mately 3, 800 litres were trapped with wire minnow traps (Fig. 29) bimonthly or monthly from December 1965 to September 1967. The purpose of the trapping was to assess changes in the fish populations of the pools and to obtain data on growth for the species present. The pools were moderately sheltered to moderately exposed and were situated between the 8. 5 ft. and 9. 2 ft. tide levels. The traps were baited with broken pieces of Mytilus C a l i f o r n i a nus. The usual trapping period was four hours. On some occasions, however, high surf necessitated an early removal of the traps from the pools. Trapping was usually confined to the daylight hours. When trapping was necessary at night, the tidepools were artificially illuminated during the trapping period. The trapping of several pools just previous to poisoning them revealed that a very high proportion of the total number of 56 O. maculosus and C. globiceps over 55mm in length were taken in the traps. For example, in one pool 14 O. maculosus and 2 C.  globiceps were taken after two hours of trapping. Subsequent poisoning took one additional O. maculosus. In another pool two hours of trapping took 5 O. maculosus and 7 globiceps, while subsequent poisoning took 2 additional C. globiceps. One tidepool at the 9. 4 ft. tide level was poisoned on a monthly basis or as close to a monthly basis as surf and weather conditions permitted. The pool had a maximum depth of 36cm and a volume of 42 litres. The purpose of the monthly poisoning was to obtain growth data for the fish present and to determine any seasonal differences in the degree of repopulation, or in the species which repopulated the pool. AH measurements of live fish were made to the nearest mm. No anesthetic was used and the fish were released immediately after being measured into the pool from which they had been taken. Preserved fish were measured with dial calipers to the nearest tenth of a mm. All measurements represent total length. .' Results Genera.I Distribution Patteriis On the basis of poison collections 16 species of littoral cottids common to the west coast of Vancouver Island can be placed into one of three categories: (1) those primarily restricted to tide-pools, (2) those primarily restricted to the sub tidal zone, and (3) those which occur both in tidepools and subtidally. The species placed in each of. these categories are listed in Table V under the respective headings : primary tidepool cottids , s ubtidal cottids , and secondary tidepool cottids. Table VI summarizes all the collections made at Botanical Beach and the number in which the various cottid species were taken. Table VII summarizes the collections made between Botanical Beach and Cape St. Elias, Alaska. The most obvious feature of the local distribution of the tidepool cottids is that at any given site the species characteristic of one tide level are different from those at other tide levels. In this respect the tidepool cottids exhibit vertical zonation just as does the intertidal benthic flora and fauna. The details of this zonation LIS it occurs at Pachena Point is shown in Table VIII. Like the vertical distribution of species of benthic plants and invertebrates, 'the occurrence, abundance and vertical ranges of the TABLE V Categories into which cottid species, taken at Botanical Beach, are placed with respect to their occurrence in tideoools. Primary Tidepool Cottids Subtidal Cottids Secondary Tidepool Cottid: Oligocottus maculosus O. remensis Clinocottus globiceps C. embryum C. acuticeps Jordania zonope Hemilepidotus spinosus Blepsias cirrhosus Artedius harringtoni Hemilepidotus hetnilepidotus Artedius lateralis A. fenestralis Ascelichthys rhodorus Oligocottus snyderi Enophrys bison Leptocottus armatus T A B L E VI S u m m a r y of co t t i d s p e c i e s taken in 67 p o i s o n c o l l e c t i o n s made at B o t a n i c a l B e a c h f r o m 1965 to 1967. T h e n u m e r a l in f a r l e f t of each row i s the total number of c o l l e c t i o n s i n which that s p e c i e s was taken. Other numbers show the number of c o l l e c t i o n s i n which any two species were taken together. CO 3 a c u t i c e p s Clinocottus acuticep s Oligocottus maculosus Clinocottus globiceps Clinocottus embryum Oligocottus snyderi Artedius lateralis Hemilepidotus hemilepidot Hem il ep id otu s spinosus Ascelichthys rhodorus CO CO -H 0 2 O c 0 0 to u 'r-i 5 Artedius f ene stralis Artedius harringtoni Jordania zonope Enophry s bison « CO 5 1 0 rt 0 ? Is Blepsias cirrhosus 9 8 9 O. m a c u l o s u s 32 27 7 10 8 .4 5 4 i 1 C. globiceps 48 21 7 3 5 1 5 1 1 2 C. embryum 30 4 4 1 4 3 1 O. s n y d e r i -alis 9 12 7 9 5 1 1 1 1 A. late 3 12 5 6 5 • 1 1 H. hemi l e p i d o t u s 12 7 4 2 2 1 1 H. spinosus orus 1 1 1 A. rhod 1 1 3 3 1 1 O. r e m e n s i s / 0 1 1 X 1 1 A. f e n e s t r a l i s 4 1 1 A. h a r r i n g t o n i ! 2 J. zonope 1 E . b i s on 1 L. a r m a t u s B. c i r r h o s u s 1 1 TABLE VII Summary of cottid species taken in 56 collections made between Pachena Point, B.C. and Cape St. Elias, Alaska, from 1965 to 1967. The numeral in far left of each row is the total number of collections in which that species was taken. Other numerals show the number of collections in which any two species were taken together. C. acuticeps U O. maculosus C. globiceps to i -tl c O --3 o u ^ C O 3 1 C. embryum o u ° 1 CO O 1 1 15 O. snyde ri A. lateralis o r u rt o & c P S 5 O 1 1 22 co O 1 5 3 rt 10 H. hemilepidotus H. soinosus cn +J O T3 • f-i a , CD CU 20 0 a, A. rhodorus cn 10 O. remensis U) •»-> o u o CO •r4 I—I O A. fenestralis A. harringtoni C 0 4-1 CO. « ! .2 •? 4-1 R CD cn 03 O w 10 J. zonope E. bison L. a r m a t u s B. cirrhosus T A B L E VIII Cottids taken f r o m a v e r t i c a l s e r i e s of tidepools near Pachena Point, B. C , during July 1966. T i d e Height F e e t Dominant benthic O r g a n i s m Oligoc ottus maculosus Clirioc ottus globiceps Clinoc ottus embryum Oligoc ottus snyderi Artedius lateralis Kemilepidotus hemilepidotus ! Artedius fene stralis Ascelichthy s rhodorus 10 C o r a l l i n a 207 43 7 M i t e l l a & M y t i l u s 3 14 3 6 M i t e l l a & M y t i l u s 3 24 23 1 4.5 Hedophyllum 10 3 1 3.5 Hedophyllum 1 52 8 8 5 2 L a r n i n a r i a 1 7 1 3 primary tidepool cottids vary from one vertical transect to another. For example, in some transects, as is shown in Table VIII, O.  maculosus occurs only in the upper intertidal zone. Ln other transects it occurs from, the upper intertidal zone to the lowest tide levels. C1 inoco11us embryurn, on the other hand, is rarely abundant at tide levels other than those shown in Table VIII and in many transects it is absent. In some transects C. globiceps extends throughout the intertidal zone, whereas in others it is restricted to the upper intertidal zone or absent altogether. In transects where it occurs C. acuticeps is restricted to the upper intertidal zone, whereas O. remensis has been collected only in the lower intertidal zone. The secondary tidepool cottids all have their lower limits in the subtidal zone and all of them have upper limits in the lower intertidal zone. Artedius lateralis, O. snyderi and Ascelichthys rhodorus have occasionally been observed in tidepools in the upper intertidal zone but they do not regularly inhabit this part of the intertidal zone at the study site. These species do, however, regularly occur higher in the lower intertidal zone than other secondary tidepool cottids. Envi ronmcntal Factors and Pistributions Physical and Chemical Tidepool Factors It has been shown that the physical and chemical conditions in tidepools vary considerably depending upon such factors as the depth of the pool, its f l o r a and fauna, weather conditions, and the extent to wlucli the pool is .Isolated f r o m the sea. The latte r factor determines the effects that, the other f a c t o r s have and it' i n turn depends p r i m a r i l y upon -he height of the pool, and s e c o n d a r i l y upon the pool's exposure and the sea state. P o o l s below L L H W ( F i g . 11) w i l l flood twice in each lunar day. P o o l s above this height w i l l flood no more than once per lunar day during the neap p e r i o d of the monthly tidal c y c l e . P o o l s located above L H H W ( F i g . 11) w i l l be i s o l a t e d for at least two consecutive t i d a l days each lunar month. These r e l a t i o n s h i p s between v e r t i c a l height, length of emergence and t i d a l f a c t o r s a r e i l l u s t r a t e d in F i g . 12. The upper l i m i t s of most of the tidepool cottids are situated below L L H W . T h r e e of the four species (O. maculosus, C. globiceps,  C. embryum and C. acuticeps) which r e g u l a r l y inhabit pools above this l e v e l a l s o inhabit pools above LHHW. Only C. embryum inhabits pools above L L H W but does not occur above LHHW. T h i s means that a l l the tidepool. cottids except O. maculosus, C. globiceps and C. ac uticeps have upper distributions c o r r e l a t e d with daily, ti d a l l y -related, changes in environmental .conditions. A l l the secondary tidepool cottids have upper l i m i t s c o r r e l a t e d with s e m i - d a i l y , t i d a l l y - r e l a t e d , changes in environmental conditions. 6 4 Because of the effects and possibly interactive effects of factors other than the vertical position of a tidepool, it is very difficult to determine what single factor, if any, in a pool is limiting the vertical distribution of a species. Tidepools of the same shape and size unfortunately do not occur in neat vertical transects. In this respect the tidepool environment is more difficult to evaluate than the open rock environment. If temperature were limiting the upper distribution of a species, thuit species would be expected to be found higher in the intertidal zone in deep shaded pools than in shallow open pools. It ha.s not been possible, on the basis of poison collections and trap catches, to correlate vertical distributions with depth or other physiographic characteristics of tidepools for any of the cottids which do not occur above LLMW. It might also be expected that seasonally, vertical distributions would change in response to more favorable temperatures in tidepools above LLHW. But again such shifts have not been observed in the cottids which occur only below this tide level. The fact that seasonal changes in distribution patterns in these cottids do not occur even in transects where heavy run off at low tide causes the salinity to be much lower than that of the sea, indicates the ineffectiveness of salinity as a factor affecting the local distributions of these species. 65 For all three of.the species which inhabit tidepools above LHHW seasonal shifts in distributions with respect to specific pools do occur (see below). In several of these cases the changes in distribu-tion appear to be related to seasonal changes in temperature character-istics of the pools. Fig. 34 shows the number of O. maculosus and C.  globiceps taken in a shallow pool at the 9. 5 ft. tide level during 1966 and 1967. It is obvious that the pool is a more favorable habitat during the fall than during the summer despite the fact that it receives heavy run off during the former period. Although these data suggest that high temperatures can restrict the distributions ofjO. maculosus and C. globiceps, temperature can not be used to explain the horizontal distributions of these species. In sheltered and moderately sheltered transects C. globiceps does not occur in pools which have less extreme temperature fluctuations than those in higher moderately exposed and exposed pools where the species does occur. This is also true for the distribution of C. embryum. O. maculosus inhabits tidepools throughout the intertidal zone in sheltered and moderately sheltered transects, but has a high lower vertical distribution in exposed transects. Clearly the horizontal differences in the vertical distribution of O. maculosus can not be related to tidal fluctuations in physical and chemical factors within tidepools. 400 300 -1 o c-Fig. 34. Total number of O. maculosus (o--.o) and. C. globiceps (o — o) taken in poison collections in the same tidepool poisoned at different times of the year. The tidepool was located at the 9.5 ft. - tide level, had a maximum depth of 36cm and a volume of 42 litres. 67 E x p o s u r e The v e r t i c a l d i s t r i b u t i o n of O. maculosus at B o t a n i c a l B e a c h is c o r r e l a t e d with the degree to which the i n t e r t i d a l zone is exposed to surf. Where there is no protection f r o m open sea swells, this s p e c i e s o c c u r s only in tidepools in the upper i n t e r t i d a l zone. In s h e l t e r e d t r a n s e c t s , however, it o c c u r s in tidepools and surge channels to as low as the extreme lowest tides. It has never been ta.ken in a c o m pletely subtidal c o l l e c t i o n . The r e l a t i o n s h i p between exposure and the percent of the total c o t t i d fauna r e p r e s e n t e d by O. maculosus, as determined on the b a s i s of surf sensor data and poison c o l l e c t i o n s , is shown in F i g . 35. F i g . 36 shows that the density of O. maculosus per l i t r e of tidepool volume is a l s o c o r r e l a t e d with exposure. It is apparent f r o m the f o r m e r f i g u r e that the factor(s) which l i m i t s the lower v e r t i c a l range of the species does not exclude it f r o m the lowest tide l e v e l s in either s h e l t e r e d or m oderately sheltered transects. The v e r t i c a l distributions of the other two abundant p r i m a r y tidepool cottids at B o t a n i c a l Beach are also c o r r e l a t e d with exposure. F i g . 37 shows that the r e l a t i o n s h i p between the v e r t i c a l range of C. globiceps and exposure is n e a r l y the r e c i p r o c a l of .that of O.  maculosus. , The v e r t i c a l range of C. embryum (F i g . 38) tends to be r e l a t e d to exposure in the same way as that of C. globiceps but this Fig. 35. Percent of the total cottid fauna of tidepools represented by O. maculosus as a function of exposure and tide height. Exposure categories arc (E) exposed, (ME) moderately exposed, (MS) moderately sheltered, and (S) sheltered. See text for explanation of exposure scale. Collections were made during July and August 1966. 0. maculosus as percent of total cottids 89 10 9 ~ A A 8 -O O O SZ o> CD XZ <D "5 6 -5 " 4 -A O O 2 " I -0 — .037 1 .37 Number / litre 3.7 F i g . 36. Density of O. maculosus over 55mrn in total length per l i t r e of tidepool volume as a function of tide height in exposed ( A ) and moderately exposed (O) tidepools. C o l l e c t i o n s were made during J u l y 1966. F i g . 37. P e r c e n t of the total cottid fauna of tidepools r e p r e s e n t e d by C. globiceps as a function of exposure and tide height. E x p o s u r e c a t e g o r i e s a r c (E) exposed, (ME) moderately exposed, (MS) m o d e r a t e l y sheltered, and (S) s h e l t e r e d . See text for explanation of exposure s c a l e . C o l l e c t i o n s were made during July and August 1966. F i g . 38. P e r c e n t of the total cottid fauna of tidepools r e p r e s e n t e d by C . embryum cis a function of exposure and tide height. E x p o s u r e cat e g o r i e s a r e (E) exposed, (ME) moderately exposed, (MS) m o d e r a t e l y sheltered, and (S) sheltered. See text f o r explanation of exposure scale. C o l l e c t i o n s were made during July and August 1 9 6 6 . species is completely absent from sheltered and moderately sheltered tidepools. Because of the relatively few collections which contained O. remensis and C. acuticeps it is difficult to determine the relationship between the distributions of these species and exposure. At the study site, however, O. remensis has only been taken in moderately exposed to moderately sheltered tidepools in the lower intertidal zone. C. acuticeps, on the other hand, has-only been taken in moderately sheltered to sheltered tidepools in the upper intertidal zone. The upper limits of the vertical distribution of the secondary tidepool cottids do not appear to be as markedly correlated with exposure as are those of the primary tidepool cottids. Poison collections do indicate though that most of these species are more abundant and tend to have slightly higher vertical distributions in areas with intermediate exposures. Biotic. Factors The conspicuous vertical and horizontal variations in the benthic fauna and flora have been referred to in an earlier section of the paper. Since these variations are correlated with tidal factors in the same way as are the distribution's of those tidepool cottids which only occur "below LHHW, the distribution of these cottids is 7 3 a l s o c o r r e l a t e d with the benthic biota. Only JD . s n y d e r i , however, has a s u f f i c i e n t l y discontinuous distribution below the upper l i m i t s of its v e r t i c a l range that a s p e c i f i c biotic factor can be c o r r e l a t e d with its d i s t r i b u t i o n . T h i s species has r a r e l y been c o l l e c t e d at the study site, or at other c o l l e c t i n g s i t e s , where e e l g r a s s was not abundant. The l o c a l d i s t r i b u t i o n of O. maculosus is not c o r r e l a t e d with conspicuous b i o t i c features of the environment. Its o c c u r r e n c e at the lowest and highest tide l e v e l s in moderately s h e l t e r e d and s h e l t e r e d t r a n s e c t s and in tidepools above the 3 ft. to 6 ft. tide l e v e l s in m o d e r a t e l y exposed to exposed transects means that it inhabits pools with the widest p o s s i b l e range of biotic features. It inhabits tidepools with a l l other tidepool cottids. Often the only cottids i n lower i n t e r t i d a l , moderately exposed to exposed pools where it does not occur a r e C. embryurn, and C. globiceps. Yet it commonly inhabits higher pools in which both C. embryum and C. globiceps have higher densities. One can suggest that biotic f a c t o r s may be important in r e l a t i o n to the distr i b u t i o n s of embryum and C. globiceps. Both species do not inha'oit pools in transects where p h y s i c a l and c h e m i c a l e n v i r o n m e n t a l conditions are l e s s v a r i a b l e than conditions in pools inhabited:by these species in other transects. T h e r e is no b a s i s , 74 however, to suggest what factor(s) may be important. Size The verticiil range inhabited by O. maculosus depends upon the size of the fish. 0-year fish (£ 55mm) do not occur as low in any vertical transect as do older fish. Even in sheltered transects few 0-year fish inhabit tidepools below the upper intertidal zone. Larger fish inhabit pools as high as. those inhabited by juveniles provided that the pools are deep enough. These features of the distribution of O. maculosus are shown in Fig. 39. Specimens less than 45mm in length often inhabit tidepools less than 10cm deep, and specimens smaller tihan 15mm in length can be taken in shallow depressions no more than several cm deep. Fish larger than 55mm do not usually inhabit tidepools less than 10cm deep. For most other tidepool cottids 0-year fish tend to be more abundant near the upper limit of the species' vertical distribution. But only for jC. globiceps do 0-year fish inhabit! pools not generally inhabited by larger fish of the species. The disparity between the distributions in the upper intertidal zone in sheltered and moderately sheltered transects of Cj_ globiceps and C . e m b r y u m (Figs. 37 and 38) is due largely to the occurrence of juvenile C . globiceps in sheltered I- r e q u e n c y CM o • • o ri r- CO CT-! o H n O »--/ f f • J 0 O r> kCi w a << o *< ft' I I1 » J a o 3 M .5 v- -1 o ri w o o >-I o a. o • Ii o n P. r t G cn to Q' •1 fi. 0. '0 o o rr to o o O a n c: »~* o cn M O rj o D n CO — 4 -:x I 3 3 o 0) o o CD o 5 A O i 0) N Tide height 76 to moderately, s h e l t e r e d upper i n t e r t i d a l pools. Juvenile globiceps a l s o tend to move t~> lower pools at a s m a l l e r si z e than do juvenile Q.  maculosus. Seasonal Changes T h e r e do not appear to be si g n i f i c a n t seasonal shifts in the upper or lower v e r t i c a l l i m i t s of Q. maculosus. T h e r e are, however, se a s o n a l l y r e l a t e d changes in the o c c u r r e n c e of this species in p a r t i -c u l a r tidepools. In some moderately s h e l t e r e d to exposed pools in the upper i n t e r t i d a l zone few, if any, O. maculosus occur except during the summer months. A p p a r e n t l y these pools become uninhabitable during the winter months because of surf-induced a b r a s i v e action of cobbles and boulders which l i t t e r their bottoms. Such pools a r c t y p i c a l l y devoid of any biota during the winter months except for p o s s i b l y a belt of c o r a l l i n e algae around their upper edge. Other tidepools at the study site become completely f i l l e d with sand or g r a v e l during the summer and therefore fis h are absent during this period. With the off-shore movement of sand which o c c u r s during the f a l l and wi titer, these pools become populated with juvenile O^ mac ulosus . T e m p e r a t u r e has been mentioned above as p o s s i b l y having a seasonal, effect in some pools. A s t o r m during January 1967 dislodged two boulders f r o m a tidepool at the 8 ft:, tide l e v e l which was being trapped on a monthly 77 b a s i s . E a c h boulder weighed about 10kg and they were the only c o v e r in the pool. Whereas trap catches previous to the s t o r m in d i c a t e d a population of about 20 O. maculosus, no f i s h were caught or o b s e r v e d in the pool after the storm. S i m i l a r declines i n other tidepool populations of O. maculosus following: the d i s r u p t i o n of the pools by s torms have been observed. None of the other p r i m a r y or secondary tidepool cottids appear to have di s t r i b u t i o n s patterns which v a r y seasonally. Only C. globiceps and C. acuticeps, because of their o c c u r r e n c e in the upper i n t e r t i d a l zone, are usually affected.by the conditions mentioned above. Population F l u c t u a t i o n s and Growth Over the two y e a r s that populations of _0. maculosus in s e v e r a l s e r i e s of tidepools were monitored by p e r i o d i c trapping, s i g n i f i c a n t seasonal fluctuations in these populations occured. The r e s u l t s of the monthly trapping of two s e r i e s of tidepools is shown in F i g . 40. It is evident f r o m this graph that the population declined s h a r p l y during the winter and e a r l y s p r i n g and built up again over the summer and e a r l y f a l l . Length frequency a n a l y s i s of the trap catches shows that the build up resulted f r o m the r e c r u i t m e n t of 1-year and 0-year c l a s s fis h rather than a re - invasion of the pools by l a r g e r fish. 4 0 0 i 1 1 i 1 r — — ! 1 1 1 i 1 r~—i 1 1 1 1 r A M J J A . S O N D J F M A M J J A S O i 9 6 6 1967 M o n t h s F i g . 40. T o t a l numbers of O. m a c u l o s u s over 55mm i n total length (©•••o) and c o C. globiceps over 60mm in total length ( o — - o ) t r a p p e d i n t%vo s e r i e s of tidepools at d i f f e r e n t t i m e s of the year. This decrease in the population of O. maculosus during the winter and spring occurs throughout the vertical and horizontal range of the species at the study site. Thus, by February and March many pools at the lower vertical range of the species have few, if any, O. maculosus in them, In this way the lower limits of the species do tend to be pushed upwards over the winter, but it does not appear to be due to active emigration of fish from the pools. The only other tidepool cottid for which similar data are available is C, globiceps (Fig. 40). This species also shows a population decline during the winter and early spring. The growth of O. maculosus will be treated in detail in a later paper. However, in connection with the seasonal aspects of the distribution and population fluctuations of this species, it is useful to include data regarding seasonal aspects of growth. Fig. 41 shows monthly length frequencies of O. maculosus from poison and trap collections. It is apparent that the species grows little if at all during the winter months, and that growth was most rapid during late spring and summer. •80 21 May I9G6 , , , ,*-> ;in r,i. * , , 2 9 June 1966 . vr 22 July 1966 19 August 1966 i i i T i 1 1 r- i 1 6 Sep tember 1966 ^ A A V . 26 S •ptember 1966 November 1966 23 November 1966 0 10 2 0 30 4 0 50 6 0 70 8 0 9 0 100 Total length - mm 3 0 20 10 0 2 0 10 0 2 0 10 0 20 10 O 20 10 0 2 0 10 0 30 2 0 10 O 20 10 0 9 December 1966 8 Jonuary I9G7 25 January 1967 2 4 February 1967 22 March 1967 19 Ap r i l 1967 18 May I9C7 12 June 1967 ^ i ; _ _ I i l r ^ i v r _ ^ _ 1 — i i r 0 10 20 30 4 0 10 6 0 70 8 0 90 100 Total length - 'mm F i g . 41. Length frequency diagrams of G. maculosus captured with wire minnow traps from the same ser ies of tide -pools at different times of the year . 81 HIGH TIDE MOVEMENTS AND HOMING BEHAVIOR Basic to the understanding of the ecology and behavior of any mobile species of animal is a knowledge of the movements of indivi-duals of the species. It is important to know the area covered by the individual in its normal activities of feeding and reproduction, whether or not special migrations for reproduction or other purposes occur, and if the individual tends to stay, in a particular area for a considerable period of time. Previous studies on fishes have shown that a large numb of marine and freshwater species have restricted movements, and that many species during reproductive and non-reproductive periods will .return to a formerly occupied site, if they are displaced to another location (see review by Gerking, 1959). Certain tidepool fishes have been investigated in regard to their movements and apparent homing behavior. Beebe (1934) and Aronson (1951) found that Bathygobius soporator returned, after being released in other tidepools, to the pools in which they had been captured. Williams (1957) concluded from returns of marked specimens of Clinocottus ana lis and Girella nigricans, which were released into the same pools in which they were captured, that both species homed to particular pools. On the basis of one experiment in which 10 of 35 specimens were still in the same pool 10 days after being marked, Gerbacher and Denison (1930) suggested that Oligocottus macules us shows fidelity to individual pools. Observa-tions by Hubbs (1921) indicated that Amphigo.no pter us a u r or a also occupied the same tidepool on successive low tides. More recently Gibson (1967b)investigatcd the range of movements of two British tidepool species-, Blennius pholis and Acanthocottus bubalis (-Enophrys bubalis). He concluded that both species move over limited areas and that at least the former species moves over a "home range" which includes several tidepools. In all the above studies it was assumed that the species undo investigation leaves the tidepool at high tide to make an on-shore feeding migration and subsequently retreats to the tidepool as the tide ebbs. Such movements away from the pool are crucial to the homing hypothesis in studies which do not involve displacement, of specimens to other pools. Even so, the evidence concerning high tide movements has been primarily circumstantial. Only Williams (1957) attempted to directly observe the movements at high tide of the species he investigated. He concluded that tihe assumption that fish did-not remain in the pool for the interval between consecutive low tides was undoubtedly true for Girc 1 la nigricans. The data were not so obvious for Clinocottus analis, even though at one shore location he observed an apparent complete upward shift in the vertic distribution of this species during the flooding. He observed tagged specimens of C. ana lis only about 1? . times, and although each of these fish was "at a considerable distance from the pool in which it was last observed" it is not mentioned if all these fish were ever seen in the home pool again. Gibson (1967b) made no direct observations on the movements at high tide of either of the species studied. But he concluded that Blennius pholis probably leaves the tidcpool in that it feeds to some extent on barnacles, which are not common in pools, and the fact that the species has a tidal rhythm of activity in which its locomotory activity is enhanced for 4 hours around high tide. The first stage of this phase of the study was to make direct observations on the movements at high tide of O. maculosus at a variety of shore sites with respect to exposure to surf, and during different seasons of the year. The second purpose was to determine, through tagging experiments, the relationship of individual fish to particular tidepools. Attempts were also made to determine some of the factors which affect the tendency and ability of O. maculosus to return to specific pools after being displaced from thorn. Observations and homing experiments were also made on other tidepool cottids in the study area. Methods High Tide Distribution The high tide distribution of i O . maculosus was determined primarily by direct observations of tagged (see below) and untagged specimens. As a result of surf conditions, most of the observations had to be made from beneath the water surface. At times of calm seas, and in sheltered locations, however, it was possible to make observations on the distribution and movement of the species from above the sea surface. Under these conditions observations were made either from a vantage point, such as, a rock or ledge, above the water or while standing in the water. During most of the underwater observations a face mask and a snorkel were used, but SCUBA equipment was used on some occasions. Because of the roughness of the sea, particularly during the winter months, it was sometimes necessary to confine the observations to the more sheltered sites. Even during the winter months, however, there were periods of calm sea conditions which permitted observations to be made at the most exposed parts of the study site. Notes concerning the distance and area covered by tagged specimens and the general distribution of tidcpool populations were recorded on an underwater writing pad. In one moderately sheltered area monthly observations were made to determine the number of . 2 CX_ maculosus at high tide in an area of approximately Sm surrounding a single tidepool. This pool was also trapped on a monthly basis and it was therefore possible to calculate the number of fish in the area surrounding the tidepool as a percent of toted population of the pool. Monofilament gillnets of 1/2 in. mesh, knot to knot, placed at various depths and sites in the intertidal zone were also used to assess distributions at high tide. Each net was mounted on two, 6 lem long, 13mm diameter, steel rods (Fig. 42). The rods.were threaded at the bottom end so they could be screwed into 1/2 in. Philip shields anchored in the substratum. Three shields were placed 2m equidistant from one another at each gillnet site. Thus, all 3 sides of a triangle could be closed off with netting. The net was loosely hung between the rods and weighted so its bottom lay along the contour of the shore. Nets were examined for fish either just before or just after the ebbing tide exposed them. T a g g i n g The principal type of tag used consisted of one or two colored embroidery beads attached to the fish's dorsal musculature midway between the anterior and posterior dorsal fins. The beads were attached with 3 lb. test monofilament nylon line inserted through the 86 F i g . 42. G i l l n e t site showing the three equidistant supporting rods anchored in the substratum. R e s e a r c h facility-i s i n the background. musculature with a #11 stainless steel sewing needle. Previous to the actual tagging operation tags consisting of a 10cm piece of line with a single bead securely ticci to one end and a single loop in the line just below the bead were prepared. During the tagging operation the free end of the line was pushed through the fish's dorsal musculature about 3mm below the mid-dorsal surface and then through the loop below the bead. The loop was tightened and two knots in the free end were cinched tightly against it. When two beads were used, the procedure was the same except that the second bead was placed on the line just after it was passed through the fish. Two other methods of marking fish were also used. Fin clipping was done extensively in conjunction with bead tags so that the individual fish could be identified. It was usually restricted to one or both pelvic fins, but in some instances anterior and posterior portions of the anal and dorsal fins were clipped. Tags consisting of colored silk thread were used in a few experiments when the movement of marked fish was being observed from underwater. The thread was inserted in the same way and position as the bead tags and then knotted above the median dorsal surface. The free ends were cut so they were about the same length as the fish. The ends were then coated with vaseline so they would float. 88 Fish were caught for tagging with baited minnow traps or with small dip nets. No tines the tic was used during the marking of any fish, and each fish was sexee1 and measured after being tagged. Two conditions were used to evaluate the effects of tagging on survival. Over a period of 18 months 25 bead-tagged O. maculosus (55mm to 70mm) were held in aquaria with 20 non-tagged O. maculosus (55mm to 70mm) for a minimum period of 6 months each. The water in the aquaria was not circulated or filtered and it was renewed only every week or 10 days. Daily temperature fluctuations in the aquaria corres-ponded to those which occur in tidepools in the upper intertidal zone. There were no mortalities of either control or tagged fish. In order to more accurately simulate natural conditions, 10 bead-tagged O. maculosus (60mm to 70mm) and 8 non-tagged O.  macidosus (63mm to 71mm) were held in an 80 litre covered tidepool at the 9 ft. tide level. These fish were held in the pool from November 10, 1965 to June 9, 1966. One tagged and one non-tagged fish died between the 12th and 22nd of February, 1966, as a result of being caught under the screen cover. Another tagged fish lost its tag between the 25th and 30th of jMarch, but was in healthy condition with the wound completely closed when the experiment was terminated. All 8 of the remaining tagged fish were in good physical condition at the termination of the experiment. The flesh surrounding the tags of all these fish, however, was to varying degrees worn away and the tags of several fish were about to be lost. The latter observations indicated that tag loss could occur in the pool, environment in a matter of months and perhaps weeks. The fact that there were no mere hazards on which the tags could become snagged in the covered pool than in the aquaria, suggests that tag loss was probably due to the abrasive action of turbulent water. If this is true, one should expect to observe, as was the case, fewer tags lost during the summer than winter. Tag loss does not result in increased mortality. Bead tags wer forcefully removed from 10 C\_ maculosus one week after they had been attached. Five of these fish were held in an aquarium and five were held in the covered pool. At the end of 4 weeks'no deaths had occured and the wounds of all the fish were healing. Types o_f Tagging Experiments Two types of tagging experiments were conducted: those involving transplant releases and those involving home pool releases. In the former experiments fish from one tidepool were tagged and subsequently released at a location other than the pool in which they were captured. Usually they were relased into another pool, but some were released directly into the sea. In the latter experiments tagged 90 fish were released into the same pool in which they were captured. Data on the flooding history of the pools and suri conditions were recorded. The primary means of obtaining recovery data were by extensive and intensive trapping of pools with minnow traps and from nocturnal observations of pools. The latter method proved to be an extremely effective and quick way of obtaining recovery data. Because tidepool cottids leave their hiding places at night and position themselves in the open, they can be easily observed and captured with a small hand net. In this way a large number of pools can be examined in a relatively short time. Tagging studies were initially undertaken to determine the fidelity of individual fish to particular pools, and to what extent trans-planted fish will return to a pool. Later, further studies were carried out to try and answer several questions about the observed homing instinct: how is homing affected by such factors as the season of the year, the distance to which specimens are transplanted from the home pool and the length of time fish are held in captivity? Results High Tide Distribut'on and Movements Observations on the distribution of _CX maculosus during high tides were concerned piJmarily with determining whether this species moves out of and away from the tidepools in which it is found at low tide. On the basis of diving observations and gillnet catches, it was found that the characteristics of the high tide distribution of this species depends upon both space and time factors at the study site. Horizontally along the shore there is a difference between the high tide distribution of fish inhabiting tidepools in exposed transects as opposed to those inhabiting tidepools in sheltered transects. In the exposed habitat O. maculosus does not regularly leave the tidepool whereas in the sheltered habitat it does. Seasonally there is a change in the high tide distribution of fish inhabiting tidepools of intermediate exposure. Fig. 43 shows the seasonal change in the average number of O. maculosus, as a percent, of the total tidepool population, observed at high tide on a flat surrounding a moderately sheltered tidepool. It is apparent that the only time at which a significant percent of the pool population was out of the pool was during July, August and September. 92 F i g . 43. P e r c e n t of the total tidepool population of O. maculosus out of.the tidepool at high tide dinting different months of the year. The value for each month represents the average f or at least six high tides. 93 In transects vhere the high tide distribution encompasses a larger area than the lo.v tide distribution, the species does not exhibit a.complete upward shift :n its vertical distribution. There are always fish which remain in the tidepool or at the same tide height as the pool regardless of how low in the intertidal zone it is located. The only specimens which tend to show a more or less complete tidal shift in their vertical distribution are 0-year fish in some sheltered and moderately sheltered areas. If there are no physical impediments to following the flooding tide to its highest levels, these fish migrate shoreward as their pools are flooded and then move off-shore again as the tide ebbs. This on-shore, off-shore migration can be seen particularly well at the study site in an area where a large sheltered tidepool at the 7 ft. tide level has only sand and gravel shoreward of it-Tagged fish According to the above observations, at least in certain tidepools and during certain months of the year, the same individuals of O. maculos us will be in particular tidepools on successive days and for successive weeks. Data from 117 O. maculosus that were tagged and subsequently released into the tidepools from which they were taken, show that this is so (Table IX). 94 TABLE IX Summary of nine experiments involving home pool releases of O. maculosus. Recoveries within the first two weeks of tagging are not included. Numbe r Percent Percent recovered resident re sident Number Num.be r in home of of Date tagged recovered pool recovered tat fed 9s ds ?s cfs ?s cfs 22-X-65 9 22 13 6 18 12 6 18 12 100 . 82 23-X-65 •4 7 3 4 6 2 4 6 2 100 86 22-VI-66 3 4 1 3 . 4 1 2 3 1 75 75 18-VII-66 22 44 22 21 42 21 21 42 21 100 96 8-IX-66 3 7 4 3 7 4 3 7 4 100 100 8-IX-66 2 . 4 2 1 3 2 0 2 2 50 50 9-X-66 3 5 2 3 5 2 2 4 2 80 80 10-X-66 0 5 5 0 5 5 0 5 5 100 100 25-XI-66 12 19 7 10 13 3 iO 13 3 100 68 Totals 58 117 59 51 103 52 48 100 52 94 100 97 83 88 86 95 A s i d e f r o m obtaining data by extensive and intensive trapping of tidepools, and night observations at low tide, high tide observations were a l s o made on pools in which tagged fis h were r e l e a s e d . A t times when sea conditions permitted, broken pieces offre s h My t i l us were . p l a c e d at the bottoms of tidepools at or near the time of high tide. T h i s r e s u l t s in a convergence of the O. maculosus and other cottids in the pool to the My t i l us. In this manner it is possible to b r i n g a l l the tagged f i s h in the pool into view. The number of o b s e r v e d tags can then be c o m pared with the number of tagged f i s h r e l e a s e d into the pool. Observations of this type c o n f i r m e d that: in exposed pools throughout the year, and in tidepools of intermediate exposure during most of the year, n e a r l y a l l the O. maculosus r e m a i n e d in the pool the entire time that it \ V CL S flooded. Observations of tagged f i s h in tidepool areas of intermediate exposure a l s o p r o v i d e d i n f o r m a t i o n on the distance away f r o m the home pool that O. maculosus w i l l t r a v e l during the season of the year when e x c u r s i o n s f r o m the pool a r e made. V e r y m a r k e d d i f f e r e n c e s between i n d i v i d u a l f i s h were observed. S e v e r a l tagged specimens which were observed at least three times a week for over a month were never seefi more than 1 to 2m f r o m the edge of their pool. The ' Z p a r t i c u l a r pool i s located on a flat shelf with an area of over.250m . D u r i n g observations on these f i s h , other tagged f i s h f r o m pools on. the 9 6 same shelf but 3 to 5m away would frequently move into the vicinity of this tidepool. But even on this shelf where movement or vision was not restricted in any way, no tagged fish was ever seen more than 10m from its home pool and later observed again in its home pool. • Duration of Residence in Specific Tidepools The length of time that individual fish spend in a single tidepool cannot be calculated from decreases in tag returns with time because tag loss is such a significant factor. It is also likely that tagged fish are more susceptible to predation, at least in certain pool areas, than non-tagged fish. Duration of residence in specific tidepools was determined on the basis of data from fish which retained their tags for long periods, or remained identifiable as a result of clipped fins or other morphological characteristics which enabled positive identification. These data indicate that for the majority of O. maculosus over 55mm in length, inhabiting pools of intermediate exposure and exposed tidepools, the pool in which it was found was its permanent home pool. Forty O. maculosus have been observed in the same pool for over 6 months, and 10 have been followed in the same pool for more than a year. \ 97 Straying Some O. maculosus have been observed over a period of time in two or more pools. Table IX shows that 3 fish that were released into the pooh in which they were trapped were never taken again in that poolbut were taken in another pool. Also, 10 fish which were still in the home pool at. least two weeks after being tagged were, later observed in other pools. All of these fish are referred to as strays. Nine strays were observed in the second pool for at least one month before they disappeared and two of them were in the second pool for at least four months. Only 2 strays were observed in more than two pools. One of these was in the second pool for no more than a week, but was in the third pool for at least three months. High Tide Distribution of Other Species No cottid species other than 0._ maculosus were ever caught in gillnets situated in the upper intertidal zone. Two non-cottids, Hexagrammos ste 1.1eri and Scbastodcs melanops, were frequently caught in gillnets in the upper intertidal zone. During diving-observations these species have been observed at tide levels above 8 ft. Both species appear to follow the flooding tide on-shore, remain in the intertidal zone throughout the high tide and then retreat to lower levels as the tide ebbs. 9S Observations at high tide did not show that any of the secondary tidepool cottids have a tidal on-shore migration which carries them into the upper intertidal zone. Artedius lateralis and O. snvderi were frequently seen during the summer months feeding on open shelves between and away from tidepools, but usually they were never more than 5 to 7m from a pool. Two blennoid species, Phytichthys chirus and Pholis ornata were frequently seen feeding in eel grass beds 15 or more metres from the tidepools. Homing Behavior Definition Williams (1957) in his study of homing behavior of rocky shore fishes defined horning as the presence of the same fish in the same pool on two successive observations of the fish during two different low tides. Homing should indicate that a species has navigational abilities rather than just fidelity to a particular geographical site. Consequently, on the basis of what has been stated about the high tide distribution of (X maculosus, the above definition of homing is clearly inadequate for this species. Homing must be defined in O. maculosus, and in other species with similar high tide distributions, in terms of the return of individual fish to tidepools from which they have been displaced. Homing experiments therefore consisted of tagging fish from specific pools and releasing them at sites other than the pool in 99 which they were carght. Only the i n i t i a l r e c a p t u r e of such a f i s h in the pool in which it w;.s o r i g i n a l l y caught was c o n s i d e r e d as an instance of homing. Homing s u c c e s s T r a n s p l a n t experiments were rum in the same general a r e a of the study site as the home pool r e l e a s e experiments and in many experiments the same pools were used. Twenty-one transplant e xperiments i n v o l v i n g 149 O. maculosus are s u m m a r i z e d in Table X. It i s apparent f r o m the re s u l t s of most of the i n d i v i d u a l experiments and c e r t a i n l y f r o m the grand totals, that this s p e cies p o s s e s s e s strong homing behavior. It i s a l s o apparent that O. maculosus has the a b i l i t y to re t u r n to the home pool after being d i s p l a c e d over r e l a t i v e l y long distances. The data show that there is no difference in the homing behavior between males and females. A l s o over the range that was investigated, homing behavior is apparently not dependent upon age (Table XI). B e h a v i o r of transplants Often it was not possible due to unfavorable tide or surf conditions, to thoroughly s e a r c h the home pool on the low tides i m m e d i a t e l y following the r e l e a s e of transplanted f i s h . Because of this it could not always be established in what time span s u c c e s s f u l 100 T A B L E X S u m mary of 21 experiments involving transplant r e l e a s e s of O. macules us. Number r e - P e r c e n t P e r c e n t Number Number c o v e r e d in homed of homed of Date tagged r e c o v e r e d home pool r e c o v e r e d tagged 9 s o's 9s c*s 9s c/s 22-X-65 6 12 6 5 11 6 5 10 5 91 83 22-1-66 9 11 7 6 7 1 5 6 1 86 55 20-11-66 3 6 3 3 6 3 3 6 3 1.00 100 2-III-66 2 5 3 1 3 2 1 3 2 100 60 30-IV-66 0 7 7 0 7 7 0 7 7 100 100 2-V-66 7 16 9 5 11 6 5 11 6 100 69 10-VT-66 4 6 2 4 6 2 3 5 2 83 83 16-VI-66 3 7 4 3 7 4 2 5 3 71 71 16-VI-66 3 9 6 1 7 6 1 6 4 71 56 22-VI-66 0 2 2 0 1 1 0 1 1 100 50 24-VIII-66 5 9 4 5 8 3 5 8 3 100 89 2-IX-66 2 3 1 2 3 1 1 2 1 67 67 2-IX-66 3 3 0 1 1 0 1 1 0 100 33 25-IX-66 7 8 1 5 6 1 3 3 0 50 38 27-IX-66 3 .4 1 .? . 2 0 2 2 0 100 50 -27-IX-66 2 5 3 2 2 0 1 1 0 50 20 l-XI -66 2 4 2 2 4 2 2 4 2 100 100 101 TABLE X (continued) Number re- Percent Percent Number Number covered in homed of homed of Date tagged recovered home pool recovered tagged ? s ds ?s ds $s ds 9-XI-66 3 5 2 3 4 1 3 3 0 75 60 9-XT-66 0 5 5 0 4 4 0 4 4 100 80 9-XI-66 2 5 3 2 2 0 2 2 0 100 40 9-XI-66 5 10 5 4 7 3 4 . 7 3 100 70 Totals 71 142 71 56 109 53 49 96 47 88 89 88 69 66 68 T A B L E XI Summary of 20 transplant experiments of O. homing success of different size groups. maculo-s us showing the Size groups (mm) Numbe tagged Number recovered Numbe r recovered in home pool Percent homed of tagged 50-54 5 5 4 80 55-59 9 6 6 67 60-64 22 16 15 68 65-69 28 25 22 79 70-74 27 22 19 70 75-79 17 13 11 65 80-84 19 16 16 84 85-90 5 4 3 60 • 103 homing was accomplished. However, in a l l nine of such instances when it was p o s s i b l e to make observations, a l l the f i s h which s u c c e s s f u l l y homed were in the home pool by the second low tide. T h e s e ob s e r v a t i o n s , along with incomplete observations f r o m other experiments, suggest that most s u c c e s s f u l homing i s a c c o m p l i s h e d within the f i r s t one or two high tides following r e l e a s e . F r e q u e n t l y i t was pos s i b l e to thoroughly s e a r c h and observe the pool i n which the transplants were r e l e a s e d . In three instances the l a t t e r pool was poisoned during the f i r s t low tide f o l lowing the r e l e a s e of tra n s p l a n t e d f i s h . These observations showed that even if t r a n s p l a n t e d f i s h w ere not s u c c e s s f u l at ret u r n i n g to the home pool, they did not r e m a i n i n the pool into which they were transplanted. Only four of over 100 transplanted f i s h f o r which such observations w ere made were s t i l l i n the transplant pool following the f i r s t high tide. Two of these f i s h r e m a i n e d in the transplant pools f o r about two weeks and then returned to their r e s p e c t i v e home pools. A t h i r d f i s h r e m a i n ed in the transplant pool for about four weeks and then it a l s o r e t u r n e d to its home pool. The fourth fis h was taken with poison in the transplant pool on the f i r s t low tide following its r e l e a s e . T h i s immediate movement away f r o m the transplant pool was shown not to be r e l a t e d to the density of Ch_ maculosus or other cottids in the transplant pool. Neither the r e m o v a l by poisoning of the entire 104 fish fauna or the removal by trapping of most cf the cottid fauna several days prior to transplanting fish into a pool resulted in the transplanted fish remaining a longer time in that pool. Reciprocal transplants in which the same number of tagged fish were, interchanged between two pools also did not modify this behavior. Possible Influencing Factors Position of pools The transplant experiments in Table X involved transplanting fish to pools which had a variety of spatial relationships to the home pools. In some experiments the two pools were at about the same tide level while in other experiments the two pools encompassed nearly the entire vertical distribution of O. maculosus. In still other experiments the two pools were both vertically and horizontally separated from each other. Comparisons of the results of individual experiments indicate that the vertical and horizontal positions of the pool relative to one another do not influence homing success. Distance from home pool The transplant experiments summarized in Table X involved the transplanting of fish by as much as 102m from, their home pool. The relationship between homing success and distance for these experiments is shown in Fig, 44. Even the greatest distance over which fish were Distance - feet 120 160 200 J J L 260 T 45 60 Distance - m r i s . Homing success of transplanted O. maculosus as a function of the distance away from the home pool that they were released. o transplanted was within the homing ability of the species. The fish in experiments involvirg distances of over 50m do tend to have a lower homing success than fish released at a shorter distance from the home pool, but this may reflect the effects of complexities and irregularities of the substratum rather than the effects of distance alone. The experiment in which high homing success was obtained over a distance of 102m involved the return of fish across a relatively level and non-dissected portion of the shore. The fact; that O. maculosus will move considerable distances in search of the home pool is indicated by three transplant experiments which are not included in Table X. In each of two experiments, 20 O. maculosus were tagged and transplanted to a pool in the area of the study site where the homing studies were being conducted from a large pool approximately 240m away. In the third experiment 10 O. maculosus were similarly treated. Extensive trapping and night observations of pools within 60 to 90m of the pools in which these fish were released indicated that all transplanted fish moved completely out of the study area. Unfortunately, it was not possible to determine if any of these fish successfully homed. Time of year Homing success as a function of the time of year is shown in Fig. 45. It is important to note that during all seasons of the year ! 0 0 9 0 -8 0 -S 7 0 -o o o 6 0 -5 0 -"I 4 0 o x 3 0 2 0 -10 O o o o o o o o ~! 1 1 1 1 1 1 1 1 1 1——r J F M . A M J J A S 0 N D M o n t h s . 4 5 . H o m i n g s u c c e s s of t r a n s p l a n t e d O. m a c u l o s u s as a function of the month of the y e a r d u r i n g which the t r a n s p l a n t s were made. 108 O. maculosus exhibits homing behavior. The fact that all these experiments were conducted in intermediately exposed to exposed parts of the study site means that homing occurs at those times of the year when the fish are seldom, if ever, normally out of the home pool., Captivity Nearly all the transplanted fish were held in captivity over at • least one tide cycle before being released. In five experiments transplanted fish were held in aquaria over three tide cycles. Homing success in these five experiments was no lower than the average success of all the other experiments. Ln one instance a tagged fish which was being held in a covered pool escaped after being in the pool for six months. This fish was subsequently trapped in the pool from which it was originally taken. It remained in this pool for at least two months before disappearing. The movement of fish out of an unfamiliar pool on the first tide that floods the pool appears to occur regardless of how long the fish have been held in captivity. In one of the two experiments described above in which 20 O. maculosus were transplanted from a pool 2 0 0 m from the study area., the fish were held for two weeks before being released. Still they left the transplant pool, on the 109 first tide that flooded it. Similar results were obtained in another experiment involving six tagged fish from a single pool which had been held for six months in an aquarium with six tagged fish from another part of the study area. At the end of six months all 12 fish were released into the home pool of the first six. Intensive trapping a week later showed that, all six of the original fish from that pool were still in the pool, but that none of the other six fish were. Tagging of Other Species The only tidepool cottid besides O. maculosus that was frequently tagged was globiceps. Tables XII and XIII show the results of home pool and transplant releases. Like O. maculosus this species shows fidelity to specific tidepools and will home to these pools when displaced from them. Table XIII shows that, unlike the former species, there was a greater tendency for transplanted male C. globiceps to disappear than transplanted females. Table XIV also indicates that the smallest size groups that were tagged show a stronger tendency to home to specific pools than larger size groups. A total of 7 CL._ embryum (4 males and 3 females) were fin clipped and returned to the pools in which they were taken. After a period of one month, five of these fish (3 males and 2 females) were taken in the same pools into which they had been released. T A B L E XII Summary of four experiments involving home pool releases of C. globiceps. Numbe r tagged Number recovered Numbe r recovered in home pool Percent resident of recove red Percent resident of tagged Males 11 11 9 82 82 Females 28 25 25 100 89 Males Females 39 36 34 94 87 T A B L E XIII Summary of nine experiments involving transplant releases of C. globiceps. Numbe r tagged Number recovered Number recovered in home pool Percent homed of recovered Percent homed of tagged Males 28 17 16 94 57 Females 19 15 14 93 74 Males 47 3d 30 94 64 Female s T A B L E XIV Summary of nine trai. splant experiments of C. globiceps showing the homing success of different size groups. Numbe r Size groups (mm) Numbe r tagged Number recovered recovered in home pool Percent homed of tagged 50-54 11 9 9 82 55-59 - 6 6 5 83 60-64 3 2 2 67 65-69 3 2 2 67 70-74 4 3 2 50 75-79 4 3 3 75 80-84 5 3 3 60 85-90 1 0 0 0 113 ACTIVITY STUDIES Rhythmic locomotor activity which persists under 'constant' conditions has been investigated in a wide variety of organisms (see Sollberger, 1965). Such rhythmic activity has been found to be in phase with solan- and lunar (tidal) cycles. The only studies of activity rhythms under 'constant' conditions in intertidal fish, however, are the investigations by Gibson (1965b, 1967b)on inter-tidal fish of the British Isles. He found that Blennius pholis and Acanthocottus bubalis (=Enophrys bubalis) exhibit rhythmic locomotor activity when held under 'constant' conditions. Both species show enhanced locomotor activity for several hours around high tide and this behavior persists in the laboratory for severed clays. The only other tidal rhythms which have been reported in fishes are tidal rhythms of oxygen consumption. Gompcl (1938) described such a rhythm in Pleuronectes platessa and Schwartz and Robinson (1963) suggested that a similar rhythm is present in Opsanus tau. Despite the current emphasis on rhythm research, very few studies have been concerned with the ecological aspects of rhythmic locomotor activity which persists under 'constant' conditions. It is generally accepted tla t a behavior pattern which retains its periodicity in the absence of obvious time cues, i. e. , the sun and the moon, is 114 adaptive. But i t cannot be a s s u m e d that the e n v i r o n m e n t a l factor(s) with which the r h y t h m i s s y n c h r o n i z e d i s (are) d i r e c t l y r e l a t e d to the rhythm's adaptive functions ( C l o u d s l e y - T h o m p s o n 1961). A l s o i t cannot be assumed, as Gibson (1967b) did, that the rhythm has s p e c i a l s i g n i f i c a n c e d u r i n g the n o r m a l daily existence of the organism. The purpose of this aspect of the p r e s e n t study was to investigate the a c t i v i t y of O. maculosus under both n a t u r a l and c o n t r o l l e d conditions. It was hoped that i f this s p ecies showed r h y t h m i c l o c o m o t o r a c t i v i t y under 'constant' conditions, i t would be p o s s i b l e to r e l a t e this a c t i v i t y to its f i e l d b ehavior. B y this approach it was thought that i n f o r m a t i o n r e l a t i n g to the adaptive function(s) of the r h y t h m might be brought to light. Methods Field Observations Li order to make observations on the behavior and to assess the activity of tidepool fishes under natural conditions, field observations covering all months of the year were conducted from October 1965 to March 1967. Observations were made from both above and below the surface of the water, at all times of the day and night and at all phases of the daily and monthly tidal cycle. For the purpose of making low tide observations from above the surface of tidepools, several pools were selected which permitted the observer to sit almost directly above the pool with an unobstructed view of its interior. Low tide observations made from below the surface of a pool were made with a face mask and snorkel, the observer lying prone either in or beside the pool. Snorkeling equipment was used during most of the observations made on submerged pools. On a few occasions SCUBA gear was used. Observations were made to attempt to determine the influence of temperature, light, salinity, surf, and inter- and intraspecific associations on the behavior of _0. maculosus. Activity Apparatus In the past, a variety of methods have been used to monitor fish activity under laboratory conditions. Following Bohun and Vinn (1966) such techniques can be broadly grouped as consisting of: direct observations; the measurement of a physiological parameter, such as oxygen consumption; the direct attachment of the fish to a recorder; the use of a mechanical device between the fish and recorder; or, the use of electronic sensor devices. In the present study activity apparatus was designed of a mechanical type similar to that used by Harder and Hemple (1954) to monitor diurnal locomotor rhythms in pleuronectids and later by Kruuk (1963) in a behavioral study of Solea vulgaris. More recently the same technique was used by Gibson (1965b, 1967a) in his studies of tidal rhythms of locomotor activity in blennioid and cottid fish of the British Isles. The functioning of the apparatus depends upon the mechanical disturbance of a false aquarium bottom as the fish rises from the bottom to swim or change its position. This disturbance is then relayed by mechanical or electrical means to a recording device. Most littoral fishes are well suited for this type Cf apparatus because of their negative buoyancy and demersal habit. Because of this and its relative simplicity which makes its use in the field feasible, this technique was used in the activity chambers designed for this study. The activity chambers (20cm x 20cm x 25cm) were constructed of 0. 6cm plexiglass (Fig. 46). Holes of 0. 6cm diameter located in the sides of the chamber permitted circulation of water through the F i g . 46. A c t i v i t y apparatus: a. r e c o r d e r ; b. p l e x i g l a s s wall; c. counter-weight; d, c l a m p used as p o s i t i v e t e r m i n a l ; e. slide weight f o r s e n s i t i v i t y adjustment; i . balance arm; g. f a l s e bottom. 118 chamber. The false bottom of 0. 6cm galvanized wire screen was attached to a balance arm by a 1.0cm diameter stainless steel rod. The balance arm was counter-weighted at the opposite end, and a slide weight enabled sensitive adjustment of the system for various sized fish. The recording system consisted of a two-channel Rustrak model 91 recorder powered from a 6 volt wet cell. The apparatus was constructed so that any vertical movement of the false bottom activated the recorder circuit and resulted in a mark on the chart paper. Chart speeds of 1 in. per 30 min. and 1 in. per 10 min. were used. All experiments were run at the study site and all fish, except those which had been held for particular reasons, were placed in chambers within 5 to 10 minutes after they were taken from the natural environment. Most of the fish were caught with a small hand net, both at night and during the day. Some were captured by baited and non-baited minnow traps. Specimens were transferred from the pools to the chambers in plastic buckets containing pool water. The chambers were rinsed and filled with fresh seawater before each fish was introduced. Temperature v/as maintained as nearly constant as possible by insulating the chambers and water bath. A Ryan continuous recording thermometer in the water bath 119 showed a maximum temperature fluctuation during a run of usually less than 1. 5°C. The temperature of the water bath was usually kept within a degree or two of the shore water (7° to 11°C), but runs were made at temperatures from 4° to 17°C. Chambers were operated under three light regimes: natural light, continuous and complete darkness, and continuous light. No quantitative or qualitative analysis of the continuously light condition was attempted. A 60 watt bulb was kept burning 2m above the chamber which was covered by a 3mm sheet of green fibreglass. No attempt was made to shut out natural light other than to shade the chambers from direct sunlight. When runs were made under natural light conditions the chambers were shielded from the light except for the green fibreglass cover. The chambers were always shaded from direct sun or moonlight. Continuous complete darkness was provided by placing the chambers and water bath in a light proof 3800 litre wooden stave tank. Specimens were taken from pools of different heights and exposures. Usually specimens were placed in the chambers at approximately low tide, but some were placed in the chambers immediately following high tide and others at various intervals between successive high tides. Data were recorded concerning flooding history of the pools from which fish were taken. 120 In many cases a surf sensor located at the pool from which the fish was taken, or at a. known height in the intertidal zone, was connected to the same recorder as the activity chamber. In this way it was possible to directly compare the flooding of the pool, or a known vertical height, and the time of high tide with the activity of the fish. When a surf sensor was not used, tidal periods and heights were determined from six minute tidal predictions for Port Renfrew. Some specimens were run in a chamber for four or five days, but most specimens were in the chamber for 48 hours or less. None of the specimens were fed during a run, and each was sexed and measured on its removal from the chamber. Because the activity studies were conducted at the study site, the specimens were minimally disturbed as a result of handling. Also, due to the isolation of the site there were no periodic disturbances or background noise associated with the experimental facilities. Results Activity Under Natural Conditions To determine the effects of some environmental factors on the activity of O . maculosus under natural conditions, observations were conducted on a series of tidepools at the 8. 5 ft. tide level which consisted of deep central pools surrounded by shallow water 5 to 10cm in depth (Fig. 31). Under favorable conditions O. maculosus moves outof the deeper parts of these pools to feed in the beds of Odonthalia and Spongomorpha. which grow in their shallow parts. During unfavorable conditions the fish retreat to or remain in the deeper water where they seek the seclusion of rocks and other cover. Throughout 1966 and parts of 1965 and 1967 observations were made to try and determine what factors cause the fish to be in the deeper parts of the pools. T e mp eraturo Temperature was one of the factors that was frequently monitored on a continuous or periodic basis during low tide in the shallow parts of the pools. At the same time that temperature was being monitored observations were made at periodic intervals to determine what percent of the total pool population of O. maculosus were in the shallow part of the pool. 122 F i g . 47 shows that at temperatures above a p p r o x i m a t e l y 15°C the f i s h either r e t r e a t to or r e m a i n in the deeper water. Because the time of day at which this temperature is reached v a r i e s c o n s i d e r a b l y f r o m day to day, depending on the state of the sea and the weather as •well as the ti d a l c y c l e , it can be shown that there a r e no d a i l y or t i d a l r h y t h m i c r e s p o n s e s involved. Some of the observation pools were situated in such a manner that it was p o s s i b l e to siphon water into them f r o m a higher pool. The pool that was siphoned f r o m was deep enough so that water near its bottom never r e a c h e d a temperature much above, that of the sur f a c e sea water. Thus, by siphoning f r o m different depths it was po s s i b l e to add water of the same temperature or a lower temperature to the obs e r v a t i o n pools. If the water i n the shallow parts of a pool i s cooled after it has w a r m e d to a temperature above 15-17°C the f i s h i m m e d i a t e l y move out into the cooled part of the pool. T h i s is the same r e a c t i o n that o c c u r s when the tide f i r s t floods one or part of one of these pools. Ii , on the other hand, water of the same temperature is added to the pool, the f i s h become active for s e v e r a l minutes and make b r i e f e x c u r s i o n s out of the deeper water, but they then move back to the deeper parts of the pool. 123 Fig. 47. Percent of the total tidepool population of O. maculosus (--«•) in the shallow parts of a tidepool in relation to the temperature (——) in that part of the pool. The effects of rain and flooding on the temperature are shown. 124 Li the absence of tidal flooding the fish will move into the shallow parts of the pool again if convective cooling lowers the temperature oi these parts of the pool below the temperature of the deeper water. In the winter months temperatures of less than 5°C appear also to keep the fish from moving out into the shallow parts of the pool. Salinity Variations in salinity, at least over a wide range, do not apparently affect the natural activity of O. maculosus. Following periods of heavy rainfall it was not uncommon for the shallow parts of the observation pools to have salinities as low as 10.00%a Under these conditions the fish move into the shallow parts of the pools and feed as long as the temperature is not too high. In other tidepools in which the bottom salinities were as low as 3 . 0 0 % * as a result of run off, O. maculosus was observed feeding on food material that was being washed into the pools. When food material was artificially introduced into these pools, it was eaten readily also. Turbulence The fact that O. maculosus exhibits different behavior at high tide depending upon pool exposure and season of the year lias been discussed in the section on high tide distribution and movements. Those data indicate that the behavior of this species is modified by turbulence. In areas where turbulence is usually great the species is inactive at high tide, whereas in areas where there is a minimum of turbulence the species is active at high tide. Also, at those times of the year when average conditions are most turbulent the species is inactive at high tide relative to those times of the year when average conditions are least turbulent. Over the spring and summer months fish become conditioned to the general low level of turbulence to leave the pool as soon as it begins to flood. The result is that during summer periods when storms cause turbulent conditions the fish remain out of the pools despite the turbulence. During the winter months there are days when the sea is flat calm. Observations on tidepools of intermediate exposure during these days show theit O^ macules us docs not move out of the tidepools at these times. As soon as the pool begins to flood the fish retreat to cover and remain there until shortly before the pool becomes isolated again. The response to O. maculosus to turbulence, therefore, appears to be a response conditioned to the flooding of the pool rather than a response induced by the intensity of the immediate turbulence. 126 Light In the description of the methods used in obtaining recovery data for tagged fish, it was mentioned that it is characteristic of tidepool cottids at the study site to position themselves in the open during the period of darkness while the pool is isolated. Individual O. maculosus will often position themselves in exactly the same spot in a tidepool each night the pool is isolated for weeks and even months at a time. The fact that a fish can be seen in exactly the same spot from shortly after the pool becomes isolated to just before it floods again, indicates that there is a minimum of activity during this time. In the above mentioned observation pools most of the fish remained in the deeper parts of the pools when the pools were isolated at night. Night observations at: high tide show thatJD. maculosus has a distribution similar to that during daylight high tides. At night fish in sheltered areas, and during summer fish in areas of intermediate exposure, move out of the home pool at high tide. Stomach analyses and the fact that O. maculosus appears to be primarily a sight feeder, however, indicate that little food is taken in at low light intensities. Inter - and Intraspecific Interactions During all the field observations of O. maculosus no aggressive behavior was ever ob.-served either towards other species or between 127 individuals of the species. Copulation was frequently observed and in no instance did males exhibit threat responses to the presence of other males or females. It was not uncommon to see two males attempting to copulate simultaneously with the Scime female. In such cases the two males take up positions on either side of the female. If a female is unreceptive to a male, she simply swims away. In no instance did a female ever exhibit threat: responses to a pursuing male. The introduction of food into a tidepool never leads to-threat displays between individual fish, and there is no indication of any dominance within tidcpool populations. All the fish in a pool converge on food that is placed in the pool. If the food is a broken Mytilus, they• simultaneously attempt to tear away pieces of it. Activity Under Controlled Conditions The Natural Rhythm The typical iictivity rhythm observed when freshly caught O. maculosus are placed in an activity chamber is shown in Figs. 48 and 49. These Figures show several basic features of the rhythm: (1) the activity reflects the period parameters of the concurrent natural tide cycle; (2) the mid point of the activity period corresponds to the time of the concurrent high tide; (3) the mid point of the activity period is also the time of maximum activity; and (4) the activity period 2 3 F e b 1 9 6 7 LH W tierce : 4 O 0 " zr. 4-™ -i-^ajoorji HHW Z - J 6 : 0 0-i ± = _|...._. Fig . 48. Record of the activity of a female O. maculosus (70mm) from a tidepool at the 7 ft. tide level under conditions of constant temperature (10°C) and natural light. The times of lower high water (LHW) and higher high water (HHW) are shown. IN) C O F i g . 49. R e c o r d of the a c t i v i t y of a r e m a l e O. m a c u l o s u s (65mm) f r o m a ti d e p o o l at the 3 ft. tide l e v e l under conditions of constant t e m p e r a t u r e (10 C) and constant darkness. The r e c o r d f r o m a s u r f s e n s o r l o c a t e d at the 9 ft. tide l e v e F i s a l s o shown. The times of l o w e r high water and higher high water are indicated. 1X1 vO 130 has a duration .of 2 to 3 hours. The rhythm usually r e m a i n s overt for only 24 to 48 hours. In a few specimens, however, the rhythm has r e m a i n e d overt f or 72 to 96 hours. A n a l y s i s of the a c t i v i t y of those specimens which have retai n e d o v e r t r h y t h m i c a c t i v i t y for this length of time shows that under constant conditions the a c t i v i t y p e riods lose phase with the c o n c u r r e n t tide c y c l e . Influence of the tide The fact that O. maculosus inhabits tidepools throughout the i n t e r t i d a l zone means that i t is p o s s i b l e on a given deiy to take specimens f r o m tidepools which have had v e r y different flooding h i s t o r i e s . Thus, p a i r e d experiments can be run in which one f i s h is f r o m a low pool which floods twice in each lunar day and the other f i s h is f r o m a high pool which may be flooding only once or not at a l l in each lunar day. Whereas specimens f r o m the f o r m e r tidepools always show two periods of locomotor a c t i v i t y per lunar day, specimens f r o m the latt e r tidepools may show only one or no periods of a c t i v i t y . U s u a lly if a tidepool lias not flooded during a. p a r t i c u l a r high tide (HilW or LHW) for two s u c c e s s i v e tide c y c l e s specimens f r o m that tidcpool w i l l not exhibit an a c t i v i t y p e r i o d during that high tide. Under nat u r a l conditions, t h e r e f o r e , the rhythm i s damped as r a p i d l y as it is under constant c o n t r o l l e d conditions. 1 3 1 Specimens taken from tidepools which have not been isolated from the sea. for at least four days show the same rhythmic activity typical of specimens taken from tidepools which arc isolated and flooded twice per lunar day. Entrainment under natural conditions Once a specimen no longer shows rhythmic activity under controlled conditions, it is possible to entrain a rhythm to the tide cycle by placing a specimen back into the tidepool environment. The fact that CX_ maculosus inhabits home pools means that after a specimen has been run in an activity chamber it can be released into the natural environment and then be recaptured after it has been exposed to a specified number of high tides. The following procedure was used to establish how many tide cycles a specimen must be exposed to before the overt rhythm is re-established. Six specimens were trapped from a pool and held in aquaria until they no longer showed rhythmic activity. After they had not shown rhythmic locomotor activity for two day, four of them were released into the home pool. The pool was then trapped on a daily b a s i 3 and one of the marked fish was removed from the pool each day and run in an activity chamber with a specimen which had been in the pool until that day. The two control fish which were not replaced in the tidepool were run in an activity chamber after a returned fish 132 showed overt; rhythmic, activity. In no instance did they show overt rhythmic activity. Two of these series were rim and in each case specimens which had been held in captivity did not show an overl tidal rhythm of locomotor activity until they had been re-exposed to at least two HHW tides. When specimens which exhibited no rhythmic activity were placed in tidepools which were flooded only once per lunar day, it was possible to establish a rhythm which showed only one peak per lunar day. It is possible to duplicate these situations under completely natural conditions. Specimens can be taken from pools which have not flooded for three consecutive limar days or three consecutive HHW tides, and then they can be compared with fish from the same pools rim in the activity chamber, one, two and three days after the pool has started to flood again. When this was done the same results were obtained. Fish had to be exposed to at least two flooding tides before they showed rhythmic activity. The natural light cycle Each high tide moves through, tho solar day at an average rate of about 40 min. per day. Thus HHW tides and LHW tides both occur during variously illuminated parts of the solar day (Figs. 8 and 9). Activity data from freshly caught O. maculosus do not show that there is any difference in the lengths of the activity periods which normally 133 occur during daylight periods as opposed to those v/hich occur during periods of darkness. Constant conditions Regardless of the light regime (constant light, constant darkness or natural light) under which specimens are run in an activity chamber the rhythm maintains synchronization with the concurrent tide cycle over 24 to 36 hours. Because the rhythm is damped so quickly at this point, it has not been possible to determine if photoperiod or light intensity do affect period length or the level of activity. Temperature Specimens were run in activity chambers at several tempera-tures primarily to determine if rhythmic activity would be exhibited at different temperature extremes. No rhythmic activity was observed at temperatures below 4°C or above 17°C. Between 10-13°C the rhythmic activity appears to be unaffected by temperature. 1 3 4 DISCUSSION AND CONCLUSIONS Distribution Local distribution Rasmus sen (1965) summarized the previous studies of the effects of increased exposure on the distribution of benthic intertidal organisms. In general, the presence or absence of some species and changes, usually upward shifts, in the vertical distribution of other species are associated with the degree of exposure of an intertidal transect. Several investigators have attempted with only limited success to devise relationships including such factors as wind, fetch, bottom topography, etc. , which could be used to quantify the exposure of intertidal transects, i.e. Moore (1935) and Guilcr (1950). The biological exposure scale devised by Ballantine (1961) for the compara-tive description of rocky shores was developed from the point of view that the organisms themselves are the best indicators of the exposure of a given shore. This scale is not quantitative and is unworkable at: sites far afield from the region on which it is based. It has been possible in the present study to quantify by direct measurements of submergence and emergence with an automatic recording device (Green and Druchl, in preparation) the exposure of intertidal transects and tidepools. It is concluded from data obtained from these measure-ments at Botanical Beach tluit the exposure of a given transect is the 135 only environmental factor strongly correlated with the intertidal distribution of O. maculosus. According to Rasmussen (1965) exposure is more often asso-ciated with the absence of species than with their presence. Green and Druehl (in preparation) found this to be true at Botanical Beach. In comparing the attached biota of transects of different exposure they found that more intertidal species were lost than were gained in moving from more sheltered to more exposed conditions. Ecologically there are two important aspects of exposure. These can be referred to as (1) the durational (time) aspect, and (2) the intensity aspect. With reference to the durational aspect, as exposure increases the emergence curve (Fig. 14) for a particular transect is pushed upwards, and actual or "effective" tide levels become increasingly different from theoretical tide levels. The result, as far as physical and chemical conditions arc concerned (i.e., temperature, salinity, oxygen), is less variable tidepool conditions at higher tide levels Ln exposed tidepools than in sheltered tidepools. With respect to the intensity aspect, the more exposed a vertical level is, the greater is the intensity with which breaking waves strike the substratum. Except in the case of delicate species which are obviously not able to withstand the abrasive action and stress imposed by breaking waves, it is difficult to determine if it is the duration or intensity aspect of exposure, or a combination of both, which is causally 136 related to the distribution of a particular species. The results of the present study suggest that the dominant characteristic of the inter-tidal distribution of O. maculosus can be most satisfactorily explained as an interactive effect of both aspects of exposure operating through .the behavior of the species. The explanation which the data support is that turbulence from breaking waves causes anunfavorable condition which, if persisting for more than a critical duration, prevents the species from performing necessary functions such as feeding, copulation and spawning. O. maculosus is adapted for relatively non-turbulent conditions and consequently such conditions must be of a minimum duration for O. maculosus to inhabit a specific intertidal environment. The behavioral observations show that O. maculosus reacts negatively to turbulence by retreating to cover and remaining inactive until conditions become calm again. This response is not seasonal as it is in evidence at all times of the year in those specimens inhabiting exposed tidepools. In the autumn the change from being active to inactive at high tide occurs first in those individuals inhabiting the more exposed of two otherwise similar -tidepools, showing that their change in activity is directly associated with the degree of turbulence. In the most exposed transects at the study site O. maculosus is present at all times of the year in tidepools in the upper intertidal /.one. 137 The intensity with which waves break on a particular tidepool is not, therefore, in itself the reason for the absence ot O. maculosus from lower less exposed or equally exposed tidepools. Rather, the intensity aspect of exposure is related to the distribution of O. maculosus • through its direct effect upon the level of turbulence. If turbulence has a marked negative effect upon the activity and behavior of O. maculosus, it would be expected that a decreased rate of growth and increased mortality would correspond with times of average high turbulence. At the study site both decreased, rate of growth and increased mortality do occur during the months when average conditions in the intertidal zone are most turbulent. Nakamura (pers. comm.) in a study to determine if competition for food exists between O. maculosus and O. snyderi, concluded! that such competition does not exist and that organisms comprising the food of both species are abundant and available throughout the year. A decreased amount of time for feeding due primarily to increased turbulence, and secondarily to decreased light, rather than a decreased amount of available food, would appear to be the most important factor for the seasonal growth characteristics of the species. A general decrease in the condition of individuals would contribute to increased mortality during times of continued high turbulence. 138 The above reference to a ' c r i t i c a l ' duration of calm conditions for O. maculosus to be able to inhabit a given tidepool does not i m p l y that its d i s t r i b u t i o n can be defined in t e r m s cf the t i d e - f a c t o r hypothesis d e s c r i b e d by Doty (19-16). It is not known in the case of O. maculosus • what the c h a r a c t e r i s t i c of the time f a c t o r might, be. The c r i t i c ill value could depend upon accumulated time within a c e r t a i n , c r i t i c a l , longer p e r i o d (e.g. a total of five active hours per week), or a maximum single p e r i o d within a c r i t i c a l , longer p e r i o d (e.g. at le a s t one act i v i t y p e r i o d per week with a minimum length of one hour) or some other r e l a t i o n -ship between what happens during e v e r y tidjd cycle and what happens at some longer i n t e r v a l . It seems un l i k e l y to determine the nature of the c h a r a c t e r i s t i c s of the time factor until it is p o s s i b l e to measure and evaluate turbulence in the i n t e r t i d a l environment in t e r m s re l a t i n g d i r e c t l y to the fish. G e o g r a p h i c a l d i s t r i b u t i o n The l o c a l d i s t r i b u t i o n of O. maculosus at f i r s t appearance would not seem to support M o r r i s ' c o n c l u s i o n that its southward la t i t u d i n a l d i s t r i b u t i o n is related, to the 16°C i s o t h e r m ( M o r r i s , I960). The species r e g u l a r l y inhabits tidepools which consistently have tempe r a t u r e s well above 16°C for most of the day during summer months. Some of the tidepools inhabited by this species have temperatures higher than 16°C for s e v e r a l consecutive days. 139 O b s e r v a t i o n s on the effect of temperature on the b e h a v i o r of O. macu'osus do, however, give support to M o r r i s ' c o n c l u s i o n . The i n f l e c t i o n i n the temperature - s a l i n i t y t olerance l i n e at a p p r o x i m a t e l y 16°C ( M o r r i r , I960) c o r r e s p o n d s to the temperature at which, i n the p r e s e n t study, O. m a c u l o s u s was o b s e r v e d to cease n o r m a l feeding a c t i v i t y . U n l e s s the species exhibits l a t i t u d i n a l temperature a c c l i m a t i z a t i o n , which M o r r i s (1962) indicates it does not, the d i r e c t e c o l o g i c a l s i g n i f i c a n c e of this t emperature can be seen r e a d i l y . Other species The upper v e r t i c a l l i m i t s of the l o c a l d i s t r i b u t i o n of the other tidepool cottids at B o t a n i c a l B e a c h were not found to be c o r r e l a t e d with a single e n v i r o n m e n t a l f a c t o r to the e x c l u s i o n of other f a c t o r s . Only C l i n o c ottus globiceps, C. embryum and C. acuticeps have d i s t r i b u t i o n patterns which suggest that b i o t i c f a c t o r s may be m o r e important than p h y s i c a l or c h e m i c a l f a c t o r s in d e t e r m i n i n g t h e i r d i s t r i b u t i o n in some v e r t i c a l t r a n s e c t s . Within its v e r t i c a l range the d i s t r i b u t i o n of O. s n y d e r i does appear to be r e l a t e d to the d i s t r i b u t i o n of P h y l l o s p a d i x s c h o l e r i . F u r t h e r c o n c l u s i o n s c o n c e r n i n g the l o c a l d i s t r i b u t i o n s of tidepool cottids at B o t a n i c a l B e a c h w i l l have to await m o r e f i e l d and l a b o r a t o r y studies of t h e i r physiology, behavior and ecology. What has been l e a r n e d about the d i s t r i b u t i o n of O. m aculosus should 140 caution against concluding too much f r o m l a b o r a t o r y studies which are not supported by f i e l d i nvestigations. F o r example, O. m a c u l o s u s inhabits tidepools i n which the temperature i s r e g u l a r l y well above its p h y s i o l o g i c a l optimum and c e r t a i n l y above the t e r m p e r a t u r e that i t would p r e f e r i f it could move to a lower temperature. The fact that a species inhabits only tidepools below a c e r t a i n tide l e v e l may have l i t t l e to do with the conditions i n the pools above this l e v e l other than the fact that the s p e c i e s must experience flooding once or twice p e r l u n a r day. The wide o c c u r r e n c e of t i d a l rhythms among i n t e r t i d a l o r g a n i s m s makes this an i n t r i g u i n g and p l a u s i b l e p o s s i b i l i t y . Ideally, then, p h y s i o l o g i c a l and b e h a v i o r a l e x p e r i m e n t a l situations which are being r e l a t e d to the d i s t r i b u t i o n of an i n t e r t i d a l o r g a n i s m should have t i d a l fluctuations i n c o r p o r a t e d into them. Movements and H o ming That O. m a c u l o s u s shows f i d e l i t y to s p e c i f i c tidepools and w i l l home to, o r attempt to home to these pools when they are d i s p l a c e d f r o m them, i s concluded f r o m the p r e s e n t study. It i s a l s o concluded that the high tide movements of this species are dependent upon quantitative c h a r a c t e r i s t i c s of the exposure of the home pool. The l a t t e r f a c t o r may v a r y se a s o n a l l y and when i t does there i s an accompanying change i n the high tide movements of i n d i v i d u a l s inhabiting the pool. T h i s feature of the movements at high tide of an i n t e r t i d a l 141 fish has not been described, and possibly not considered, in previous investigations of movements and homing behavior (e.g. Williams, 1957 and Gibson, 1967b). The consequence of restricted movements of a tidepool fish as the result of specific exposure characteristics of the home pool raises doubts about the validity of attributing homing behavior to a species only on the basis of the presence of the same fish in a pool on consecutive low tides, especially when the effects of exposure on the species have been evaluated. Although concluding the Clinocottus analis homes on the basis of marked fish released into their home pool, Williams (1957) showed that this species will not return to the home pool when displaced to pools a maximum of two meters away. He i attributed this to the fact that disturbance of the fish during capture and marking causes a considerable portion to abandon their home pool, and that their bottom-dwelling habits provide a limited view of the surrounding areas. How this latter statement is reconciled with the conclusion that the species homes as a result of familiarity with geographical cues outside the pool is not clear. Disturbance during capture and tagging of O. maculosus does not appear to affect homing behavior or the fidelity of an individual to the home pool. O. maculosus is also a bottom-dwelling species but will return to the home pool over con side rable di stance s, .142 In his invesHgo.ti.ons of the return to the home pool of displaced Blennius pholis and Enophrys bubalis, Gibson(1967'b) concluded that "results of the displacement experiments do not give evidence for the presence of a directed movement back to the original pool...". He further stated that: "until more evidence is available on this point, the best working hypothesis that can be put forward to explain the return of displaced fish is that, although movements may be random within the limited area of the home range, the fish are able to recognize their home'pool when they come across it by chance." The present evidence indicates that O. maculosus does exhibit directed movements back to the home pool. The mechanism by which these movements are made is not known, but certainly homing is dependent upon a precise behavior mechanism inherent in the fish. It appears also that this mechanism does not necessitate a spatial familiarity with the area covered during homing. In some areas O. maculosus exhibits regular movements away from the home pool, but even these movements arc restricted when compared with the distance over which the species will home. If individuals can recognize geographical features beyond the range of their daily movements they must have obtained this information at an age and size when they do not show strong fidelity to specific pools. 143 O. maculosus has been shown to home to and to show f i d e l i t y to sp e c i f i c pools after being held i n an unnatural environment f o r p e r i o d s as long at' six months. T h i s i n d i c a t e s that an image of the home pool i s r e t a i n e d over long p e r i o d s , and suggests that at some stage i n the development of in d i v i d u a l f i s h some s p e c i f i c c h a r a c t e r i s t i c s) of a pool is(are) i m p r i n t e d on the f i s h . U n l e s s i n f o r m a t i o n r e l a t i n g to the geo g r a p h i c a l features of the surrounding a r e a i s s i m i l a r l y 'remembered' it i s d i f f i c u l t to avoid the c o n c l u s i o n that this s p e c i e s has bicoordi n a t e navigational a b i l i t y . O r i e n t a t i o n toward the home p o o l f r o m an u n f a m i l i a r l o c a t i o n would i m p l y that the f i s h can p e r f o r m the equivalent of f i x i n g i t s p r e s e n t p o s i t i o n on a g r i d of two coo r d i n a t e s , c a l c u l a t i n g the c o u r s e to swim i n o r d e r to r e g a i n the coordinates c h a r a c t e r i s t i c of the home pool and steering the cou r s e (Hinde, 1966). Whether mac u l o s u s does orientate m o r e or l e s s d i r e c t l y toward the home pool i s not known. The transp l a n t experiments indicate that it at l e a s t orientates i n the p r o p e r d i r e c t i o n r e l a t i v e to the p o s i t i o n of the shore. Once an in d i v i d u a l i s swimming in the p r o p e r d i r e c t i o n p a r a l l e l to the shore, orientation to a s p e c i f i c depth of water or f a m i l i a r i t y with a t r a n s e c t p e r p e n d i c u l a r to the shore would then pro v i d e the cues which would enable the in d i v i d u a l to home. V a r i o u s species of l i t t o r a l c r u s t a c e a n s have been shown to p o s s e s s the a b i l i t y to orientate themselves by the sun (see P a r d i , I960). 144 In these s p e c i e s this a b i l i t y enables individuals to return to the water along a d i r e c t c o u r s e p e r p e n d i c u l a r to the shore-. Whether any such a b i l i t y e x i s t s i n O. m a c u l o s u s r e m a i n s to be learned. Hopefully, answers to some of the s p e c i f i c questions concerning orientation in this s p e c i e s w i l l r e s u l t f r o m the c u r r e n t studies; being conducted at B o t a n i c a l B e a c h by Khoo (pers. comm.). E c o l o g i c a l s i g n i f i c a n c e A c c o r d i n g to W i l l i a m s (1957) homing behavior in i n t e r t i d a l f i s h is "a m e c h a n i s m by which shallow water fi s h e s of rocky shore a r e a s avoid being le f t by the tide in unfavorable situa-iriions, such as pools that d i s a p p e a r through subsurface drainage." 'DC there i s a danger of O. macu l o s u s being le f t in unfavorable situations; at low tide, the homing i n s t i n c t would be a m e c h a n i s m of survival to the species. One is left with the question whether or not such daggers were the p r i m a r y cause f o r the development of homing and whether this is the p r i m a r y function it now s e r v e s . It would eippear, for ersamplc, that f a m i l i a r i z a t i o n with the bioti c features c h a r a c t e r i s t i c of tidepools, which retain water at low tide, v/ould prevent tilne f i s h from being stranded in a non-tidepool location., and would onet necessitate the fi s h seeking out the home pool vhen d i s p l a c e d from it. Under conditions of high turbulence, the apparently imflllexible homing behavior in O. m a c u l o s u s would seem to be a. l i a b i l i t y r.aWher than an asset. 145 The hypothesis which is suggested here is that homing behavior in O. maculosus servos much the same purpose in this species that territoriality serves in other species. Gerking (1959) states that "territoriality is a stabilising influence because it separates individuals from one another in a regular and orderly fashion in addition to making the fish intimately aware of its surroundings." Territoriality depends upon aggressive interaction among individuals in a population. As there is no aggressive interaction among individuals of O. maculosus, territoriality in the above sense does not exist in this species. It would seem, however, that in a species like O. maculosus v/hich inhabits an extremely variable and rigorous environment, a strong mechanism by which the species remains dispersed and stabilized would be of special importance and ada.pti.vene s s. In the absence of such a mechanism the species would tend to aggregate in only the most favorable habitats --the tidepool s - - within its range of distribution. Aggregated in this way the species as a whole would be more susceptible to the Unpredictability of environmental conditions typical of an exposed coast. The imprinting of visual cues of the tidepool on an individual at an age when the juvenile population is relatively well distributed throughout the range of the species, coupled with horning behavior is visualized as serving this stabilizing function in O. maculosus. 146 T i d a l Rhythm The v a r i a t i o n s in ti d a l amplitude ( F i g . 8) and tidal p e riods ( F i g . 12) at B o t a n i c a l B e a c h are not. d i r e c t l y c o r r e l a t e d with p e r i o d i -c i t i e s in l u n a r zenith and nadir. Under these conditions a b i o l o g i c a l rhythm cannot be well c o r r e l a t e d continuously with both moon and tides (Enright, 1963). The ti d a l rhythm of locomotor a c t i v i t y i n O. m a c u l o s u s not only follows the p e r i o d parameters- of the co n c u r r e n t tide a c c u r a t e l y , but a l s o responds d i r e c t l y to the flooding h i s t o r y of the pool'from which the f i s h i s taken. It i s concluded, therefore, that the rhythmic t i d a l a c t i v i t y of O. maculosus is entrained in the fi e l d by the d i r e c t influence of the tide rather than by geophysical v a r i a b l e s . It has not been p o s s i b l e in the present study to e x p e r i m e n t a l l y e s t a b l i s h what p a r a m e t e r a s s o c i a t e d with the tide operates as a sy n c h r o n i z e r . T he r e s u l t s strongly indicate though that none of the p h y s i c a l and c h e m i c a l changes, i.e. temperature eind s a l i n i t y , a s s o c i a t e d with the i n i t i a l flooding of ind i v i d u a l tidepools, function as s y n c h r o n i z e r s . Such s y n c h r o n i z e r s would be very u n r e l i a b l e as a re s u l t of the d i r e c t influence of the state of the sea and weather conditions on the time when individual, pools flood, and on the time when va r i a t i o n s in these p r o p e r t i e s occur. Specimens taken f r om high pools exhibit the same rhythmic locomotor ac t i v i t y as f i s h taken 147 from low tidepools as long as the higher pools are completely flooded during each high tido.. The rhythm is the same despite the fact that the lower pool may flood four hours before the higher pool. Also, the rhythm remains entrained in fish inhabiting low pools which are in constant contact with the sea for several consecutive days. That factors such as temperature and salinity do not operate as synchronizers is further indicated by the fact that in those situations where a pool is flooded enough to completely change its physical and chemical conditions, but not enough to bring the pool into complete contact with the sea, the rhythm is not entrained. ' Two other possible synchronizers would appear to be turbulence and hydrostatic pres sure. Enright (1965) shov/cd that the tidal rhythm of locomotor activity in the sand beach isopod, Excirolana. chiltoni, can be entrained in the laboratory by a device designed to simulate wave action on a beach. The results suggest that mechanical stimuli arising from wave action on a beach may be the normal synchronizing factor for Excirolana and perhaps other similar organisms. With respect to the tidepool habitat, turbulence would appear to be as unreliable a synchronizer as changes in factors such as temperature or salinity. Maximum turbulence is not always well correlated with the time of high tide. Also, the time at: which there is a significant change in turbulence -- the time at which the tidepool begin;; to flood--has the same limitations as a reliable synchronizer 148 as mentioned above for temperature or salinity. Hydrostatic pressure would theoretically meet the requirements of a reliable synchronizer. It reaches an average maximum value, taking into consideration variations clue to waves, at the time of high tide for any location on the Hooded portion of the intertidal zone. The problem in postulating that pressure functions as the synchronizer for the tidal rhythm of O. maculosus is to show the mechanism by which pressure cures are perceived. The swimbladder is known to function as a pressure receptor (Jones and Marshall, 1953), but O. maculosus like other cottids does not have a swimbladder or other gas-filled structure. Morris and Kittleman (1967) recently reported that two species of fish they investigated have otoliths which are piezoelectric. They suggest that this constitutes a mechanism for depth perception. If it can be demonstrated experimentally that pressure functions as the synchronizer of the tidal rhythm in O. maculosus, perhaps a similar or equally subtle pressure receptor will be involved. Number of oscillators Evidence for the existence of daily (circadtan) and tidal components in the persistant rhythmic activity of intertidal organisms has been presented by various investigators (see Palmer, 1967). 149 N e i t h e r Enright. (1963) nor Gibson (1967) found evidence of other than tidal rhythms of lo c o m o t o r a c t i v i t y in sand beach amphipods and i n t e r -t i d a l f i s h . In the present study no evidence for rhythmic a c t i v i t y other than that a s s o c i a t e d with tida l c y c l e s was found in O. maculosus. . E n r i g h t (1963) d i s c u s s e d the p o s s i b i l i t y of two separate o s c i l l a t o r s within the in d i v i d u a l being responsible f o r the tidal rhythm in Synchelidium. Apparently his c o n c l u s i o n was that the r e s u l t s did not support the concept of a t w o - o s c i l l a t o r system any more strongly than they supported a s i n g l e - o s c i l l a t o r system. Results of the present study do appear to support the concept of a t w o - o s c i l l a t o r i n t e r p r e t a t i o n of the rhythm in O. maculosus. The fact that a specimen can be entrained i n the f i e l d to exhibit a single a c t i v i t y p e r i o d each l u n a r day which is not di f f e r e n t f r o m the ac t i v i t y p e riods in f i s h which are entrained to exhibit two a c t i v i t y p e r i o d s per lun a r day, is not in agreement with what would be expected with a single - o s c i l l a t o r system. A l s o , when the rhythm is being entrained i n the f i e l d under conditions of two ti d a l floodings per day, a specimen w i l l only show one act i v i t y p e r i o d if it is removed from the pool between the fifth and sixth floodings which, again, suggests that the two o s c i l l a t i o n s are independent of one another. F r o m the point of view of synch r o n i z a t i o n and timing, the advantages of a tv/ o - o s c i l l a t o r system over a single - o s c i l l a t o r system as far as being better adapted to the v a r i a t i o n s in the lengths of the 150 tidal periods are clearly apparent. The tidal day periods (e.g. HHW-HIIW) at Botanical Beach vary by a considerably smaller time interval from day to day, and have a much smaller total variation than do the semi-daily periods (e.g. HHW - LHW) as is shown in Fig. 12. Two oscillations each with a period of approximately 25 hours would have to undergo only slight rephasing to remain in phase with the natural tide cycle. Ecological Significance The activity of O. maculosus in its natural habitat is directly dependent upon such factors as turbulence, temperature and light. The tidal rhythm of locomotor activity which this species exhibits under controlled conditions, often is not associated with the time during the day when this species is active under matural conditions. It would appear, therefore, that the rhythm represents the functioning of a biological clock which is linked to an avoidamee or escape response. Coupled with the homing behavior and an escape response to an un-familiar habitat, such a clock would be of survival value to the species. Were a fish displaced by one means or anno the r to a different tide level, or different location of the same level,, such an internal clock and associated swimming activity would eanikble the fish to home, or attempt to home, at the time of highest water.. The fact that displaced fish apparently remain in the pool into which they are transplanted at least until 1. to 2 hour:-; before the: time of high tide 151 r e g a r d l e s s of when the transplant pool floods, supports this c o n c l u s i o n . It i s c l e a r l y not v a l i d to make i n f e r e n c e s concerning the nat u r a l a c t i v i t y patterns or behavior of this species s o l e l y on the b a s i s of a ti d a l rhythm of l o c o m o t o r a c t i v i t y exhibited under constant conditions. P e r h a p s such e r r o r s in the e c o l o g i c a l i n t e r p r e t a t i o n s of rhythmic behavior are c omm only m ade. 152 S U M M A R Y 1. On the b a s i s of tidcpool c o l l e c t i o n s made on the west coast of V a n c o u v e r Island, B.C., five species of fish (Oligocottus m a culosus, O. r e m e n s i s , C l i n o c ottus acuticeps, C. embryum and C. j j l o b i c e p s ) are r e f e r r e d to as p r i m a r y tidepool cottids. T h ey have v e r t i c a l d i s t r i b u t i o n s centered in the i n t e r t i d a l zone. O. maculosus is the most abundant and widely d i s t r i b u t e d in the i n t e r t i d a l zone of these s p e c i e s . 2. Seven s p e c i e s of f i s h (Hemilepidotus hemilcpidotus, A r t e d i u s l a t e r a l i s , A. f e n e s t r a l i s , A s c e l i c h t h y s rhodorus, E n o p h r y s bison, Leptocottus armatus and O. snyderi) are r e f e r r e d to as secondary tidepool cottids. T h e y inhabit tidepools but a r c most abundant in the subtidal zone. 3. E v a l u a t i o n of enviro n m e n t a l f a c t o r s show that the d i s t r i b u t i o n of O. mac u l o s u s i s c o r r e l a t e d with exposure to wave action. In exposed t r a n s e c t s this s p e c i e s is r e s t r i c t e d to the upper i n t e r t i d a l zone, while in s h e l t e r e d t r a n s e c t s it inhabits tidepools throughout the intertidal. zone. C. embryum and C. globiceps have wider v e r t i c a l d i s t r i b u t i o n s in more exposed than in more sheltered t r a n s e c t s . C. acuticeps is r e s t r i c t e d to sh e l t e r e d tidepools in the upper i n t e r t i d a l zone, while O. r e m e n s i s inhabits .into rmediately exposed tidepools in the lower i n t e r t i d a l zone. 153 4. The upper v e r t i c a l d i s t r i b u t i o n s of the secondary tidepool cottids are not c o r r e l a t e d with a single environmental factor to the e x c l u s i o n of other factors. None of them r e g u l a r l y inhabit pools above L L H W (lowest lower high water). Within its v e r t i c a l range the d i s t r i b u t i o n of O. s n y d e r i appears to be related to the d i s t r i b u t i o n of P h v l l o s p a d i x s c h o l e r i . 5. B e h a v i o r a l observations show that O. maculosus responds to water turbulence by r e t r e a t i n g to cover. Depending upon the exposure of the tidepool, this response is always exhibited, or i s exhibited only during the turbulent p a r t s of the year. D e c r e a s e d rate of growth and i n c r e a s e d m o r t a l i t y are a s s o c i a t e d with that time of the year when • conditions in the i n t e r t i d a l zone are most turbulent. It is concluded that in o r d e r to inhabit a given tidepool, O. maculosus must have a m i n i m u m duration of low turbulent conditions. O. maculosus has 'capitalized' on the tidepool habitat to invade the open coast environment. 6. CX m aculosus shows fid e l i t y to p a r t i c u l a r tidepools and w i l l r e t u r n to these pools when dis p l a c e f r o m them. Homing succ e s s does not appear to be r e l a t e d to time of year, sex or size above 55mm, Homing o c c u r s r e g a r d l e s s of the d i r e c t i o n f r o m the home pool that f i s h are r e l e a s e d . 154 7. Individuals s u c c e s s f u l l y homed f r o m locations 102m f r o m the home pool. Observations in the tidepool a r e a where homing e x p e r i -ments were conducted show that. O. maculosus moves a maximum of 15m f r o m the home pool at high tide. T h i s indicates that; O. maculosus m a y have navi g a t i o n a l a b i l i t y not dependent solely upon f a m i l i a r i t y with p a r t i c u l a r geographical features of the i n t e r t i d a l zone. It i s suggested that homing behavior functions as a mechanism s t a b i l i z i n g the. s p a t i a l d i s t r i b u t i o n of this species. 8. C embryum and C. globiceps a l s o show fid e l i t y to p a r t i c u l a r tidepools. C. globiceps was shown to home to the tidepools in which they were captured. No tagged C. embryum were transplanted. 9. In the natural habitat a c t i v i t y such as feeding and spawning in O. ma c u l o s u s i s dependent p r i m a r i l y upon turbulence, temperature and light. In r e l a t i o n to temperature, natural feeding a c t i v i t y ceases when the water temperature r i s e s above 15-l6°C. T h i s fi e l d o b s e r v a t i o n supports M o r r i s ' (I960) conclusion, drawn f r o m his p h y s i o l o g i c a l studies, that a pproximately the 1 6°C i s o t h e r m is the l i m i t i n g e nvironmental factor in the southward d i s t r i b u t i o n of this s p e c i e s . 10. Under constant condition O. maculosus exhibits a tidal rhythm dur i n g which l o c o m o t o r ac t i v i t y i s enhanced for 2-3 hours at the time of high tide. The c h a r a c t e r i s t i c s of the rhythm indicate that it is 155 entrained directly !>y the influence of the high tide, and that the system consists of two independent oscillators. Hydrostatic pressure could be the synchronizer. 1 1. The rhythm is not directly related to the field activity of O. maculosus. It is concluded that it represents the coupling of an avoidance or escape response to an unfamiliar habitat, to a biological clock. Such a mechanism would function with, and be ptirtially responsible for, the homing behavior. 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Observations of seawater temperature and sal i n i t y of B r i t i s h Columbia c o a s t a l stations in 1964 and 1965. F i s h . Res. Bd. Can. Manus. Rep. Ser.. 226:1-133 I-Iubbs, C a r l . L. 1921. The ecology and life h i s t o r y of Amph 1 gonoptc r11a a u r o r a and other v i v i p a r o u s perches of C a l i f o r n i a . B i o l . B ull. 40 : 181 -209. H u l l , C. W. 1906. Some ge o l o g i c a l features of the M i n n e s o t a seaside station. P o s t e l s i a 2:307-347. Humphrey, R. R. and R.W. Macy. 1930. Obse rvations on some of the probable f a c t o r s c o n t r o l l i n g the size of c e r t a i n tide pool snai l s . Publ. Puget Sound B i o l . Sta. 7:205-208. Johnson, Duncan and A F. Skutch. 1928. Littoral, vegetation on a headland of M t. Dese rt Island, Maine. II. Ti d e - p o o l s and the environment and c l a s s i f i c a t i o n of s u b m e r s i b l e plant communities. E c o l o g y 9 : 307-338. Jones, J. R. H. and N. B. M a r s h a l l . 1953. 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Rasmusscn, R, A. 1965. The i n t e r t i d a l ecology of the rocky shores of the K a i k o u r a Peninsula. Ph. D. T h e s i s . Univ. Canterbury, New Zealand. 203pp. Rigg, G. B. and R. C. M i l l e r . 1949. Intertidal plant and animal. zonation in the v i c i n i t y of Neah Bay, Washington. P r o c . Calif. Acad. Sci. Ser. 4, 2 6 (10): 323-351. Schwartz, F r a n k J. and Paul T. Robinson. 1963. S u r v i v a l of exposed o y s t e r toad fish and biological, clocks. P r o g r . F i s h . Cult. 25 (3) 151-154. Smith, G.M. 1944. M a r i n e algae of .Monterey Peninsula, C a l i f o r n i a . Stanford Univ. P r e s s . 622pp. 160 Sollbcrgcr, A 196i.'- Biological rhythm research. Elsevier Publ. Co. Amsterdam, London, New York. 46 lpp. Stephenson,. 1. A, A. /.'oo.nd and J. Tyre. 1934. The liberation and utilization of oxygen by the population of rock pools. J. Exp, Biol. 11 : 162-172. Strickland, D. H. and J. R. Parsons. I960. A manual of sea water analysis (with special reference to the more common micro-nutrients and to particulate organic materials). Fish. Res. Bel. Can. Bull. 125,185pp. Widdowson, T. B, 1965. A. survey of the distribution of intertidal algae along a coast transitional, in respect to salinity and tidal factors. J. Fish. Res. Bd, Can. 22 (6): 1425-1454. Williams, G. C. 1957. Homing behaviour of California rocky shore fishe Univ. Calif. Publ. Zool. 59: 249-284. 

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