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Comparative ecology of two sympatric tidepool fishes, Oligocottus maculosus (Girard) and Oligocottus… Nakamura, Royden 1970

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THE COMPARATIVE ECOLOGY OF TWO SYMPATRIC TIDEPOOL FISHES, OLIGOCOTTUS MACULOSUS (GIRARD) AND OLIGOCOTTUS SNYDERI (GREELEY) by ROYDEN NAKAMURA B..A.., U n i v e r s i t y o f H a w a i i , 1961 M.S., U n i v e r s i t y o f H a w a i i , 1965 A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t o f 'the r e q u i r e m e n t s f o r the degree o f D o c t o r of P h i l o s o p h y i n the Department o f Z o o l o g y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d . THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1970 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r equ i r emen t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d tha t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l owed w i thou t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Co lumbia Vancouver 8, Canada Date 1 1 ABSTRACT i There are about twelve species of c o t t l d fishes which . inhabit tidepools at Port Renfrew, Vancouver Island, B r i t i s h Columbia. Two of the more abundant species, Ollgocottus  maculosus (Girard) and Oliffocottus snyderl (Greeley), display v e r t i c a l l y zoned microdistrlbutions. Ollgocottus maculosus i s very abundant i n the upper tidepools while 0. snyderl occurs only In lower tidepools. A comparative study of the ecology of these species was made to assess the role of en-vironmental parameters i n determining t h e i r m icrodistrlbutions. Environmental parameters considered were depth, substrate and cover, food, i n t e r s p e c i f i c interactions, s a l i n i t y and tempera-ture. The relationships between the f i e l d data, behavioral and physiological laboratory experiments were used to assess the role of the various factors. The r e s u l t s indicate that the influence of the en-vironmental factors considered varied with species. The t i d e -pool d i s t r i b u t i o n of 0. maculosus i s influenced but not wholly determined by i t s high tide depth preferences. The high tide depth preferences of 0. snyderl i s not r e l a t e d to i t s tidepool d i s t r i b u t i o n . The i n t e r s p e c i f i c interactions between the two f i s h appear to a f f e c t the depth d i s t r i b u t i o n of 0. maculosus while that of 0. snyderl i s not affected.' Substrate-cover a f f i n i t i e s of 0. maculosus do not l i m i t the occurrence of t h i s species to tidepools or tidepool areas of a s p e c i f i c type, whereas O l l g o c o t t u s snyderi i s r i g i d l y bound to pools w i t h dense macrophytlc cover. This f a c t o r , however, does not account f o r the absence of 0. snyderi from upper t l d e p o o l s w i t h dense v e g e t a l cover. I n t e r s p e c i f i c i n t e r a c t i o n s between the two f i s h do not appear to g r o s s l y i n -fluence t h e i r r e s p e c t i v e m i c r o h a b i t a t preferences. The p o s s i b i l i t y of i n t e r s p e c i f i c competition f o r food appears remote as both species, though feeding on the same ba s i c items, d i s p l a y no s i g n of " i n t e r a c t i v e segregation" or "separation of food s p e c t r a " as evidenced i n competitive s i t u -a t i o n s among some other species of f i s h e s . However, 0. macu-losus does consume a g r e a t e r v a r i e t y of food. F i e l d observa-t i o n s i n d i c a t e the common occurrence of major food items i r -r e s p e c t i v e of season or v e r t i c a l l o c a t i o n of the t i d e p o o l s . For both O l l g o c o t t u s maculosus and 0» s n y d e r i , r e s i s t -ance to low s a l i n i t i e s of the magnitude encountered l n t i d e -pools i s s u b s t a n t i a l enough to a l l o w e i t h e r species to s u r v i v e most hyposaline c o n d i t i o n s found w i t h i n the i n t e r t l d a l zone. However, the occurrence of 0. maculosus beyond the upper bound-ary of the i n t e r t l d a l may be l i m i t e d by hyposaline extremes. O l l g o c o t t u s snyderi g e n e r a l l y shows a l e s s e r r e s i s t a n c e to low s a l i n i t i e s than does 0. maculosus. The t i d e p o o l d i s t r i b u t i o n of 0. maculosus i s not l i m -i t e d by t i d e p o o l temperatures as t h i s species d i s p l a y s a r e l a -t i v e ' r e s i s t a n c e and t o l e r a n c e to temperature extremes at l e a s t as great as those o c c u r r i n g l n the highest t i d e p o o l s . O l l g o -c o t t u s s n y d e r i . however, i s unable to t o l e r a t e and/or r e s i s t i v extreme temperatures o c c u r r i n g i n upper t i d e p o o l s and i s there-f o r e l i m i t e d to lower pools. I t appears t h a t the t i d e p o o l d i s t r i b u t i o n of 0. macu-losus i s not dominated by any s i n g l e f a c t o r w i t h the p o s s i b l e exception of turbulence (open,, exposed areas) and population d e n s i t y . Thus i t i s a v e r s a t i l e species, b e h a v i o r a l l y as w e l l as p h y s i o l o g i c a l l y , and i s able to e x p l o i t v i r t u a l l y a l l t i d e -pools i n the l n t e r t l d a l zone. The t i d e p o o l d i s t r i b u t i o n of 0. snyderi i s a f f e c t e d by subs t r a t e and cover as w e l l as tem-perature. Of these, temperature appears to be the l i m i t i n g f a c t o r w i t h i n the i n t e r t i d a l zone si n c e 0. s n y d e r l cannot s u r v i v e i n upper t i d e p o o l s which are c h a r a c t e r i z e d by more extreme and unstable temperatures. Table of'..Contents Abstract . -L i s t of Tables L i s t of Figures Acknowledgement Introduction . I. Depth s e l e c t i o n and the e f f e c t of I n t e r s p e c i f i c i n t e r a c t i o n s on depth d i s t r i b u t i o n . I I . The e f f e c t of i n t e r s p e c i f i c i n t e r a c t i o n s on depth d i s t r i b u t i o n I I I . Substrate and cover IV. The e f f e c t of i n t e r s p e c i f i c i n t e r a c t i o n on substrate-cover preferences V. S a l i n i t y VI. Habitat temperature, temperature tolerance and resistance A. The e f f e c t of high temperature on Ollgocottus maculosus and Ollgocottus  snyderi . ' B. The e f f e c t of rapid temperature changes on Ollgocottus maculosus and Ollgocottus snyderi C. The e f f e c t of low temperature on Ollgocottus maculosus and Ollgocottus  snyderi D. The e f f e c t of warm temperatures on the depth d i s t r i b u t i o n of Ollgocottus  snyderi VII. Food ' Discussion Summary Li t e r a t u r e Cited L i s t o f T a b l e s The v e r t i c a l d i s t r i b u t i o n o f O l l g o c o t t u s  maculosus and O l l g o c o t t u s s n y d e r i c o l l e c t e d i n t i d e p o o l s a t Pachena P o i n t , B r i t i s h C o l u m b i a C h i square v a l u e s f o r i n d i v i d u a l depth p r e f e r e n c e s o f O l l g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r i C h i square v a l u e s f o r depth p r e f e r e n c e s o f O l l g o c o t t u s maculosus and O l l g o c o t t u s  s n y d e r i t e s t e d t o g e t h e r C h i square v a l u e s f o r i n d i v i d u a l s u b s t r a t e -c o v e r p r e f e r e n c e s o f O l l g o c o t t u s  maculosus and O l l g o c o t t u s s n y d e r i C h i square v a l u e s f o r s u b s t r a t e - c o v e r p r e f e r e n c e s o f O l l g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r i when t e s t e d s e p a r a t e l y and t o g e t h e r S u r f a c e and s u b s u r f a c e s a l i n i t i e s o f t i d e p o o l s a t P o r t Renfrew R e s i s t a n c e o f O l l g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r i t o low s a l i n i t y The mean t e m p e r a t u r e s , h i g h e s t maximum and l o w e s t minimum t e m p e r a t u r e s o f t i d e p o o l s a t P o r t Renfrew S u r v i v a l o f O l l g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r i i n t i d e p o o l e n c l o s u r e s i n upper t i d e p o o l s Temperature t o l e r a n c e s and r e s i s t a n c e o f O l l g o c o t t u s maculosus Temperature t o l e r a n c e and r e s i s t a n c e o f O l l g o c o t t u s s n y d e r i P e r c e n t m o r t a l i t y o f O l l g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r i s u b j e c t e d t o sudden t e m p e r a t u r e d e c r e a s e s Percent mortality of Ollgocottus maculosus and Ollgocottus snyderl subjected to a cold environment D i s t r i b u t i o n of Ollgocottus snyderl i n simulated tidepools before and a f t e r the a p p l i c a t i o n of high temperatures Relative percent composition of diets of Ollgocottus maculosus and Ollgocottus snyderi Percent frequency of occurrence of foods i n the stomachs of Ollgocottus maculosus and Ollgocottus snyderl L i s t o f F i g u r e s F i g u r e 1. O l l g o c o t t u s maculosus G i r a r d and 0, s n y d e r i G r e e l e y 2. A Diagram o f the Depth G r a d i e n t - T i d e Tank 3. The S i m u l a t e d H i g h T i d e Depth D i s t r i b u t i o n o f 0. maculosus and 0„ s n y d e r i a c r o s s a l l depth b l o c k s 4 . The Depth D i s t r i b u t i o n o f 0. maculosus and 0. s n y d e r i w i t h a S i m u l a t e d R i s i n g T i d e 5„ The Depth D i s t r i b u t i o n o f 0. maculosus w i t h a S i m u l a t e d R i s i n g T i d e 6 . The Depth D i s t r i b u t i o n of 0. s n y d e r i w i t h a S i m u l a t e d R i s i n g T i d e / 7 . A Comparison o f the Depth D i s t r i b u t i o n o f 0. maculosus D u r i n g S i m u l a t e d H i g h T i d e s when t e s t e d s e p a r a t e l y and t o g e t h e r w i t h 0 e s n y d e r i 8. A Comparison o f the Depth D i s t r i b u t i o n o f 0 a s n y d e r i D u r i n g S i m u l a t e d H i g h T i d e s when t e s t e d s e p a r a t e l y and t o g e t h e r w i t h 0» maculosus 9. A Comparison o f the S u b s t r a t e - C o v e r P r e f e r -ences o f 0. maculosus and 0 0 s n y d e r i ( P o o l e d Data) 10. A Comparison o f the S u b s t r a t e - C o v e r P r e f e r -ences o f 0. maculosus when t e s t e d s e p a r a t e l y and t o g e t h e r w i t h 0, s n y d e r i 11. A Comparison o f the S u b s t r a t e - C o v e r P r e f e r -ences o f 0. s n y d e r i when t e s t e d s e p a r a t e l y and t o g e t h e r w i t h 0, maculosus 12. The S u b s u r f a c e S a l i n i t i e s o f a Low T i d e p o o l , H i g h T i d e p o o l . and the Sea Water a t P o r t Renfrew i n 1968 13. The S u r f a c e S a l i n i t i e s o f a Low T i d e p o o l and a H i g h T i d e p o o l a t P o r t Renfrew i n 1968 v i i i Page 5 9 1 4 1 7 1 9 2 1 25 2 7 32 37 39 4 6 4 8 i x F i gure 1 4 . 15. . 1 6 . 17. 1 8 . 19. 20, 21. 22, 23. 2 4 . The Mixed Semi-Diurnal Tide Cycle of Port San Juan The Duration of Emergence and Submergence of the Tidepools at Port Renfrew The Mean Temperatures, Maximum and Minimum Temperatures f o r Port Renfrew Tidepools over a Fourteen-Month P e r i o d The R e l a t i o n s h i p of the Tide Cycle to Subsurface Tidepool Temperatures from 13 May, 1968 to 21 May, 1968 The R e l a t i o n s h i p of the Tide Cycle to Subsurface Tidepool Temperatures from 7 J u l y , 1968 to 15 J u l y , 1968 The R e l a t i o n s h i p of the Tide Cycle to Subsurface Tidepool Temperatures from 2 4 J u l y , 1 9 6 8 to 1 August, 1 9 6 8 The Resistance of- 0 . maculosus and 0 . s n y d e r l to Heat Extremes at D i f f e r e n t A c c l i m a t i o n and Test Temperatures The Resistance of 0 . maculosus and 0 . s n y d e r l to Heat Extremes at D i f f e r e n t A c c l i m a t i z a t i o n and Test Temperatures The Average Resistance of 0 . maculosus and 0 . snyderl to Heat Extremes at D i f f e r e n t A c c l i m a t i o n and A c c l i m a t i z a t i o n Temperatures The R e l a t i o n s h i p of the Tide Cycle to Subsurface Tidepool Temperatures from 19 December, 1968 to 27 December, 1968 at Port Renfrew A Comparison of the D i e t s of Cohabiting 0o maculosus and 0 . snyderl Page 53 55 59-60 62 6 4 66 77 79 8 1 92 101 A c k n o w l e d g e m e n t s I w i s h to e x p r e s s m y s i n c e r e t h a n k s to D r . N o r m a n J . W i l i m o v s k y f o r h i s a d v i c e a n d s u p p o r t d u r i n g the c o u r s e o f t h i s r e s e a r c h , w h i c h w a s c o n -d u c t e d w i t h p a r t i a l s u p p o r t f r o m h i s N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a g r a n t s . T h i s s t u d y w o u l d n o t h a v e b e e n p o s s i b l e w i t h o u t h i s o u t s t a n d i n g e f -f o r t s to f u r t h e r m a r i n e r e s e a r c h a t t h i s u n i v e r s i t y . I a m a p p r e c i a t i v e o f t h e c r i t i c i s m a n d a d v i c e o f the m e m b e r s o f m y t h e s i s c o m m i t t e e , D r . P . W . H o c h a c h k a , D r . N . R . L i l e y , a n d D r . T . C a r e -f o o t . T o D r . J . D . M c P h a i l , a s p e c i a l t h a n k s f o r t h e u s e o f a l a r g e p a r t o f h i s l a b o r a t o r y s p a c e , a s w e l l a s f o r the u s e o f l a b o r a t o r y t e m p e r a t u r e m o n i -t o r i n g e q u i p m e n t a n d o t h e r m i s c e l l a n e o u s a p p a r a t u s . I a m a l s o g r a t e f u l to D r . H . R . N o r d a n f o r t he u s e o f l a b o r a t o r y r e f r i g e r a t i o n e q u i p m e n t . T o M r . E u g e n e M c C u l l o c h a n d M r . D a v i d A n d e r s o n , I w o u l d l i k e to e x p r e s s m y a p p r e c i a t i o n f o r t e c h n i c a l a d v i c e a n d a s s i s t a n c e . I a m a l s o g r a t e -f u l to M r . R o b i n A l l e n f o r a d v i c e r e g a r d i n g the s t a t i s t i c a l t r e a t m e n t o f e x p e r i -m e n t a l d a t a , a n d to M r . W i l l i a m W e b b f o r the t i d e c y c l e c o m p u t e r p r o g r a m . I w i s h to t h a n k M r . H o n g W o o K h o o f o r a s s i s t a n c e a n d m a n y i n t e r e s t -i n g d i s c u s s i o n s d u r i n g o u r n u m e r o u s f i e l d e x p e d i t i o n s a t P o r t R e n f r e w . I w o u l d a l s o l i k e to t h a n k D r . M i l t o n T o p p i n g f o r the m a n y s t i m u l a t i n g d i s c u s s i o n s r e g a r d i n g t h i s r e s e a r c h . F i n a l l y , I w i s h to t h a n k M r . M u r r a y S m i t h , M r . N o r m a n S m i t h , a n d t h e i r r e s p e c t i v e f a m i l i e s f o r t h e i r h o s p i t a l i t y a n d c o n s t a n t w i l l i n g n e s s to b e o f a s s i s t a n c e a t P o r t R e n f r e w . I n t r o d u c t i o n . The i n t e r t i d a l zone of temperate rocky shores w i t h t h e i r c h a r a c t e r i s t i c v e r t i c a l zonatlon of b i o t a have been s t u d i e d i n many d i f f e r e n t regions of the world (Doty, 1957)• This environment provides a p a r t i c u l a r l y good s i t u a t i o n f o r o b t a i n i n g a b e t t e r understanding of marine ecosystems because of t h e i r wide range of environmental c o n d i t i o n s over short d i s t a n c e s ( B o l i n , 1948). I n t i d e p o o l s , a l t e r n a t i n g periods of emergence and submergence caused by the t i d a l c y c l e r e s u l t i n f l u c t u a t i o n s and v a r i a t i o n s i n physico-chemical c o n d i t i o n s which are a l s o c o r r e l a t e d to the v e r t i c a l l e v e l of a given t i d e p o o l . Numer-ous c o r r e l a t i o n s between s p e c i f i c environmental f a c t o r s and the v e r t i c a l d i s t r i b u t i o n of the i n t e r t i d a l b i o t a of rocky shores have been made (Huntsman, 1917; A l l e e , 1922; Klugh, 1924; Southward, 1953; Doty, 1957; Widdowson, 1965; Struhsaker, 1968). Various hypotheses have been p o s t u l a t e d to e x p l a i n such v e r t i c a l zonation (Stephenson and Stephenson, 1940; Doty, 1946, 1950, 1957)o C o r r e l a t i o n s between s p e c i f i c p h y s i o l o g i c a l a t -t r i b u t e s of l i t t o r a l organisms and physico-chemical c o n d i t i o n s of the i n t e r t i d a l have a l s o been demonstrated ( G a l l , 1918; Broekhuysen, 1940; Segal, 195&; M o r r i s , i960, 1961; Read, 1963; Sandlson, 1967; Hardin, 1968). Few s t u d i e s on i n t e r s p e c i f i c r e l a t i o n s h i p s i n t h i s environment have a l s o been made ( M i t c h e l l ? 1953: Sasaki and H a t t o r i , 1969). The majority of research on t h i s environment has dealt with macrophytic algae, crustaceans, or molluscs, with l i t t l e attention being paid to the more motile forms such as the tidepool f i s h e s . Comprehensive information on the general ecology, physiology, and behavior are a v a i l a b l e f o r only* com-paratively few animals (Aciuaea spp, Balanus spp, Mytllus spp» L l t t o r l n a spp). Studies on tidepool f i s h e s (Miles, 1920; Williams, 1957, Morris, i960, 196I; Gibson, 1965, 1966) have been few. 'Chase motile groups of animals play important r o l e s i n the ecosystem as secondary consumers. Port Renfrew ( B r i t i s h Columbia, Canada) was selected as the research s i t e because of the great abundance and d i v e r -s i t y of tidepools. In addition, some information on the geology, oceanography and biology of the area was a v a i l a b l e (Henkel, 1901s Widdowson, 1965; Green, 1967). Another im-portant advantage was i t s i s o l a t i o n from dense human habita-t i o n and comparative i n a c c e s s i b i l i t y . Within the rocky i n t e r t i d a l zone of Port Renfrew, located on the west coast of Vancouver Island (48° 32' north •latitude, 124° 27' west longitude), there are perhaps twelve species of c o t t l d f i s h e s , which may be classed as i n t e r t i d a l (Green, 1967). These fishes exhibit v e r t i c a l l y s t r a t i f i e d m i c r o d i s t r l b u t i o n s . Two of the more abundant species are Ollgocottus maculosus (Glrard) and 0. snyderl (Greeley). These have s i m i l a r body configurations and maximum si z e and can be distinguished only by the number of rows of c i r r i on the l a t e r a l body surfaces, c e r t a i n color variants, and gen-e r a l pigmentation patterns (Figure 1). . Both are bottom dwelling carnivores that are usually sedentary on the bottom or sides of tidepools. Ollgocottus snyderi tends to be more reclusive than 0. maculosus and i s generally found i n closer association with cover such as eel grass (Phyllospadix schouleri), corraline algae or other macrophytic algae. Their reproductive habits are similar, with spawning occurring during the late winter, spring and early summer. Individual males generally pair off with single females during the spawning process (Atkinson, 1939y Morris, 1956) and adhesive pigmented eggs are l a i d in clumps under rocks or in. crevices. In both ssecies, the newly-hatched larvae are pelagic for the duration of their larval existenoe. Tide-pools are repopulated by post-larvae of 0. maculosus throughout the summer and f a l l , the exact time depending on ivhen they hatched (Atkinson, 1939). "What are believed to be returning post-larval 0. aiyderi have been observed and collected in shallow mid-level pools at Port Renfrew during the early f a l l . Post-larval 0. maculosus have been oollected i n . shallow algae-filled upper level ( >7»0') tidepools during the same period. Upon entering the tidepools, the translucent post-larvae of "both species begin to take on the pigmentation characteristic of their respective species. " The vast majority of .the 0. maculosus population i s found in the higher level tidepools (Table 1). This i s especially true in the more exposed regions such as Pachena Point (Vancouver Island). In the : t less exposed areas of ^Port Renfrew, this species tends. to be ubiquitous within the intertidal zone and- occurs comonlyoinrthe lower l e v e l tidepools O l l g o c o t t u s maculosus G i r a r d and O l l g o c o t t u s s n y d e r l G r e e l e y ( f r o m Clemens and. W l l b y , 1946) • T a b l e 1 . The v e r t i c a l d i s t r i b u t i o n o f O l i g o c o t t u s maculosus and O l l g o c o t t u s s n y d e r l c o l l e c t e d i n t i d e p o o l s a t Pachena P o i n t , B r i t i s h Columbia. ( D a t a from Green (MS.) 1 9 6 7 ) T i d e H e i g h t 0. maculosus 0. s n y d e r i ( f e e t ) 1 0 2 0 7 0 7 3 0 6 3 1 4 . 5 0 10 3 o 5 0 52 . 2 0 7 T o t a l 2 1 3 70 O l l g o c o t t u s s n y d e r l i s r e s t r i c t e d t o the m i d d l e and l o w e r t i d e p o o l s o n l y ( 7 . 5 ' l e v e l ) . One b a s i c q u e s t i o n w h i c h a r i s e s i s , what a r e the r o l e s o f the p h y s i c o - c h e m i c a l parameters and i n t e r s p e c i f i c i n t e r a c t i o n s i n m a i n t a i n i n g t h e s e d i s t r i b u t i o n p a t t e r n s ? I n a t t e m p t i n g t o answer t h i s q u e s t i o n , the f o l l o w -i n g e n v i r o n m e n t a l parameters were c o n s i d e r e d : 1 . Depth 2 . S u b s t r a t e - C o v e r 3 . S a l i n i t y 4 . Temperature -5« I n t e r s p e c i f i c I n t e r a c t i o n s 6 . Food and F e e d i n g B e h a v i o r . 7 I. Depth Selection and the e f f e c t of I n t e r s p e c i f i c interactions on depth d i s t r i b u t i o n . The breadth of the I n t e r t i d a l zone i s governed by the magnitude of the t i d a l range c h a r a c t e r i s t i c of a given region and by shore topography. The t i d a l range at Port Renfrew i s approximately 12.4 feet (Widdowson, 1965) and r e s u l t s i n a substantial depth gradient across the i n t e r t i d a l surface during periods of high t i d e s . Since the m l c r o d i s t r l b u t i o n patterns of the two spe-cies are based e n t i r e l y on c o l l e c t i o n s made only at low tide, and since r e l a t i v e l y l i t t l e i s known of the high tide d i s -t r i b u t i o n s of 0 . maculosus and 0 . snyderi, i t i s conceivable that the tide pools i n which the two species are found are selected by the f i s h during the high tide purely on the basis of depth. A bottom-dwelling f i s h caught i n a low-level t i d e -pool may prefer deeper water during the high tide and i t s occurrence i n that pool simply r e f l e c t s a depth preference rather than a preference f o r a s p e c i f i c c h a r a c t e r i s t i c of the pool. In order to examine this p o s s i b i l i t y , experiments i n a depth gradient tank were conducted. Materials and Methods A large wooden tank (8" x 8' x 1') containing a seven foot depth gradient i n the form of a series of steps was b u i l t (see figure 2 ) . Each step was one foot high. Plexiglass viewing ports were i n s t a l l e d at frequent l e v e l s and every other step was modified to form a pool, A Diagram o f the Depth G r a d i e n t - T i d e Tank showing the Arrangement o f G r a d i e n t L e v e l s and Depth B l o c k s . 10 The tank was designed to accommodate a simulated s e m i d i u r n a l t i d e c y c l e which was generated through two sub-mersible e l e c t r i c water pumps and a system of l a r g e r e s e r v o i r tanks. One pump was used to f l u s h sea water out of l a r g e r e s e r v o i r s and i n t o the observation tank while the other pump was used to pump the sea water out of the observation tank and back i n t o the r e s e r v o i r s . Since the f l u s h i n g r a t e of the two pumps was f i x e d , the water depth was determined by the amount of time the r e s p e c t i v e pumps were i n op e r a t i o n . The o p e r a t i o n a l times of the pumps were c a l c u l a t e d and set on two automatic e l e c t r i c a l time switches. I n t h i s manner i t was p o s s i b l e to simulate a t i d e c y c l e of any magnitude under seven. During periods of "high t i d e " when a depth gradient was present, thermal s t r a t i f i c a t i o n was prevented by constant a e r a t i o n o r i g i n a t i n g a t each h o r i z o n t a l l e v e l i n the tank. Temperatures i n the " t i d e p o o l s " during "low t i d e " were i n f l u e n c e d to a great extent by the ambient a i r tem-perature as c o o l i n g apparatus was used only i n the l a r g e r e s e r v o i r tanks. During warm weather i t was impossible to c o n s i s t e n t l y m aintain temperatures ( < 12.0°C) i n the " t i d e -pools." However, most experiments i n the depth g r a d i e n t -t i d e tank were conducted during the c o o l e r months of the year (December-February) and only the data from one s e r i e s of experiments were e l i m i n a t e d because of high a i r tempera-t u r e s . I n i t i a l experiments i n the tank were conducted to determine i n d i v i d u a l depth preference of the two sp e c i e s . The depth d i s t r i b u t i o n p a t t e r n s d u r i n g p e r i o d s o f t i d e change were a l s o o b t a i n e d . A l l f i s h u s e d i n t h e s e e x p e r i m e n t s were c a p t u r e d a t the r e s e a r c h s i t e and k e p t f o r a t l e a s t two weeks i n h o l d i n g t a n k s i n the l a b o r a t o r y . The w a t e r l e v e l s o f the h o l d i n g t a n k s were k e p t between 6 and 8 i n c h e s j t e m p e r a t u r e l e v e l s were m a i n t a i n e d between 7.0 and 11.0°C. T h i s range o f t e m p e r a t u r e s was w i t h i n t h a t f o u n d i n t h e f i e l d a t t h e time t h e f i s h were c a p t u r e d . Care was t a k e n t o m i n i m i z e the p o s s i b i l i t y o f c o n d i t i o n i n g the f i s h t o n o i s e o r o t h e r d i s -t r a c t i o n s p r i o r t o b e i n g f e d . T e s t Proced.ures 1 . D u r i n g the e x p e r i m e n t s the t i d e tank was c o n s t a n t l y i l l u m i n a t e d . 2. The t o t a l l e n g t h o f the f i s h used ranged from 5«4 t o 8,7 cm. t o t a l l e n g t h (0. s n y d e r i ) and 6.0 t o 8.0 cm. (0. m a c u l o s u s ) . 3. P r i o r t o each e x p e r i m e n t , the tank was c o m p l e t e l y emptied e x c e p t f o r the l o w e r t h r e e " t i d e p o o l s . " 4. E q u a l numbers o f 0. maculosus o r 0. s n y d e r l were p l a c e d i n each o f the t h r e e " t i d e p o o l s , " (3-4 f i s h p er p o o l ) 5. A p p r o x i m a t e l y t w e l v e hours a f t e r the f i s h were i n -t r o d u c e d i n t o the t e s t tank, the w a t e r l e v e l was g r a d u a l l y r a i s e d t o an o p e r a t i o n a l h e i g h t o f 5'6" a t a r a t e o f about one f o o t per hour, 6. T h i s " h i g h t i d e " l e v e l (5'6") was m a i n t a i n e d f o r a p e r i o d o f f o u r t o s i x h o u r s . 12. 7. Following each "high t i d e " (5'6"), the water l e v e l was gradually lowered at a rate of about one foot per hour u n t i l the depth or l e v e l of the water was only 1»0". 8 0 This "low ti d e " l e v e l was maintained f o r a period of four to six hours a f t e r which time the cycle was repeated* 9» Positions and v e r t i c a l l e v e l s of each f i s h were re-corded every 30 minutes over a complete "tide cycle,," 10. During each half-hourly recording, general behavioral observations were made. 11. Each group of f i s h was ca r r i e d through at l e a s t three complete " t i d a l " cycles. 12. Nine (9) f i s h were used i n each experiment. 13« Frequency d i s t r i b u t i o n s were analyzed by chi square analysis. ( It should be borne i n mind here that a complete separation of dependent and independent data was not possible due to d i f f i c u l t i e s i n tracing the exact movements of in d i v i d u a l f i s h i n the experi-mental tank.) Results The r e s u l t s of these experiments show that during the simulated high tide, the depth d i s t r i b u t i o n of 0. maculosus i s greater towards the shallower waters of the test tank (see Figure 3s Table 2). These differences In frequency of oc-currence of f i s h i n the four depth blocks are shown to be highly s i g n i f i c a n t by chi square analysis (P = less than 0.005). The Simulated High Tide Depth D i s t r i b u t i of Oligocottus maculosus and 0, snyderi i n the Depth Gradient-Tide Tank. Oligocottus maculosus C obs 167 Oligocottus snyderi £ obs 203 50 4 0 3 0 2 0 10 0 • A B C D (4'6"-5'6") (3'-<4'6") (|'6"-<3') (0-<l'6") D e p t h B l o c k 15 Table 2. Chi Square values of A l l o p a t r i c Depth Preference Experiments f o r O l i g o c o t t u s maculosus and O l i g o c o t t u s s n y d e r i . O l l g o c o t t u s maculosus %• O l i g o c o t t u s snyderi % Depth A 2 1,2 52 25,6 5?6"-4,6" Depth B 5 Blocks C 76 3.0 45.2 39 63 19.2 31.0 4°6"-3'0" 3'0"-l'6" D 84 50.2 49 24,1 l'6"-0 ,0" T o t a l 167 99.9 203 99.9 A vs, B vs, C vs. D Chi Sq. = 149.3 •5.7 d/f = 3 3 P = 0.001 0.100 0. macu-los u s vs, 0. snyderl Chi Sq, 79.3 d/f 3 P 0,001 The depth d i s t r i b u t i o n f o r 0. s n y d e r l i s uniform through the shallow and deep waters of the gr a d i e n t (Figure 3, Table 2) , Chi square a n a l y s i s of the d i s t r i b u t i o n of 0, snyderl i n d i c a t e s no s i g n i f i c a n t d i f f e r e n c e s between the four depth bl o c k s i n the t e s t tank. (P = 0.050) (Table 2). F i g u r e 4 0 The Depth D i s t r i b u t i o n of O l l g o c o t t u s maculosus and 0 n s n y d e r l with a Simulated R i s i n g T i d e , \ X 0 . maculosus 1 O 0 . snyderi 1 ® S.F.C. wa te r level Time (minutes) The Depth D i s t r i b u t i o n of Ollgocottus  maculosus with a Simulated Rising Tide, % fish in upper foot layer of S.FC. Vert ical height level (feet) The Depth D i s t r i b u t i o n of Oligocottus  snyderi with a Simulated Rising Tide. 22 D i s t r i b u t i o n a l r e c o r d s and g e n e r a l b e h a v i o r a l o b s e r v a -t i o n s o f 0 . maculosus made d u r i n g p e r i o d s o f c h a n g i n g w a t e r depth i n d i c a t e h i g h f r e q u e n c i e s o f o c c u r r e n c e ( > 50%) and much l o c o m o t o r movement i n the upper one f o o t l a y e r o f the t o t a l w a t e r mass r e g a r d l e s s o f de p t h . ( F i g u r e s 1, 2 ) . F o r 0 . s n y d e r l . however, the c h a n g i n g t i d e l e v e l does n ot appear t o a f f e c t i t s depth d i s t r i b u t i o n (< 50% f r e q u e n c y o f o c c u r -r e n c e i n the upper one f o o t l a y e r o f the t o t a l w a t e r mass), and a l t h o u g h no q u a n t i t a t i v e d a t a a r e a v a i l a b l e , g e n e r a l b e h a v i o r a l o b s e r v a t i o n s r e v e a l e d some i n c r e a s e i n l o c o m o t o r a c t i v i t y . I I . The e f f e c t o f i n t e r s p e c i f i c i n t e r a c t i o n s on depth d i s t r i b u t i o n . I n o r d e r t o det e r m i n e p o s s i b l e i n t e r s p e c i f i c e f f e c t s on t h e i r depth d i s t r i b u t i o n , e x p e r i m e n t s were, conducted when 0 . maculosus and 0 . s n y d e r l o c c u r r e d t o g e t h e r i n a depth g r a d i e n t . M a t e r i a l s and Methods The p r o c e d u r e s f o r t h i s e x p e r i m e n t a r e b a s i c a l l y t he same as t h o s e f o r p r e v i o u s e x p e r i m e n t s on depth p r e f e r e n c e s . I n t h i s e x periment b o t h s p e c i e s were t e s t e d s i m u l t a n e o u s l y i n the depth g r a d i e n t - t i d e tank, u s i n g e q u a l numbers (9) o f each s p e c i e s . Each s p e c i e s used i n t h e s e e x p e r i m e n t s was main-t a i n e d i n s e p a r a t e h o l d i n g t a n k s . They ranged i n t o t a l l e n g t h from 4 .9 cm. t o 9.5 cm. f o r 0 . s n y d e r l and 6.0 cm. t o 7.3 cm. f o r 0 . maculosus. 23 R e s u l t s The depth d i s t r i b u t i o n of 0. maculosus t e s t e d together with 0. snyderi during periods of sus t a i n e d "high t i d e " was uniform across the four depth blocks (Figure 7). Chi square a n a l y s i s shows that there was no s i g n i f i c a n t d i f f e r e n c e s be-tween the frequencies of the r e s p e c t i v e depth blocks (P > 0.100). (Table 3 ) . Comparison of t h i s d i s t r i b u t i o n to that obtained i n experiments where the d i s t r i b u t i o n of t h i s spe-c i e s was t e s t e d alone and was h e a v i l y skewed to the shallower water i n d i c a t e s s i g n i f i c a n t d i f f e r e n c e s (P < 0.001). (Table 3, F i g u r e 7). For Oo snyderl t e s t e d together w i t h 0. maculosus„ the frequencies of occurrence during periods of sustained "high t i d e " were uniform across the depth blocks (Figure 8 ) . Chi square a n a l y s i s I n d i c a t e s t h a t these frequency values are not s i g n i f i c a n t (P > 0.100). Comparison of t h i s d i s -t r i b u t i o n to that obtained when t h i s species was t e s t e d I n -d i c a t e s no s i g n i f i c a n t d i f f e r e n c e s (P 0.100). (Table 3). No i n t e r s p e c i f i c aggressive behavior was observed •for both s p e c i e s . A Comparison of the Depth D i s t r i b u t i o n of Oligocottus maculosus During Simu-lated High Tides when tested alone and. together with Oo snyderi. 60 S e p a r a t e < obs 167 Together £ obs 165 50 40 30 20 A B D ( 4 ' 6 " - 5 ' 6 " ) ( 3 ' - < 4 ' 6 " ) ( | ' 6 " - < 3 ' ) ( 0 - < l ' 6 B ) D e p t h B l o c k A Comparison o f the Depth D i s t r i b u t i o n o f O l l g o c o t t u s s n y d e r l D u r i n g Simu-l a t e d H i g h T i d e s when t e s t e d s e p a r -a t e l y and t o g e t h e r w i t h Oo maculosus„ 6 0 50 4 0 S e p a r a t e K obs 203 T o g e t h e r £ obs 135 30 o c CT 20 n (4'6"-5'6") B (3- <4'6") c (l'6"-<3') D (0-<l'6") Depth Block 28 Table 3 . Chi Square values of Depth Preference Experiments f o r O l l g o c o t t u s maculosus and O l l g o c o t t u s  snyderl» Oo snyderi 0. maculosus D i s t r i b u t i o n D i s t r i b u t i o n Separate Together Separate Together Depth A 52 4 7 2 38 5%6n-b*6 Depth B 3 9 2 0 5 37 4 « 6 " - 3 ' 0 Blocks C 6 3 32 7 6 3 5 3 ° 0 " - l » 6 D 4 9 3 6 84 5 5 l ' 6 " - 0 ' T o t a l 2 0 3 1 3 5 1 6 7 1 6 5 Together vs. . Separate 7 7 o 6 Chi Sq. 5 . 0 2 7 d/f 3 3 P = 0 . 1 0 0 0 . 0 0 1 29 I I I . S u b s t r a t e and Cover G r e e l e y (1901) and Green (1962) have r e p o r t e d on the ralcrohabltats o f 0 . maculosus and 0 . s n y d e r i based on f i e l d o b s e r v a t i o n s . S i n c e the o b s e r v e d m i c r o d i s t r i b u t i o n p a t t e r n s c o u l d s i m p l y be a r e f l e c t i o n o f s u b s t r a t e - c o v e r d i f f e r e n c e s i n t i d e p o o l s a t d i f f e r e n t v e r t i c a l l e v e l s , q u a n t i t a t i v e e s t i m a t i o n s o f the s u b s t r a t e - c o v e r p r e f e r e n c e s o f t h e two s p e c i e s was d e s i r e d . An e x p e r i m e n t a l f o r m a t s i m i l a r t o t h a t u s e d by Hoese (1966) was adopted. M a t e r i a l s and Methods I n t h e s e e x p e r i m e n t s c o n d u c t e d i n t w e n t y - g a l l o n a q u a r -i a , t he f i s h were p r e s e n t e d a l t e r n a t i v e c h o i c e s o f s u b s t r a t e and c o v e r i n w h i c h t h e bottoms were e q u a l l y d i v i d e d i n t o t h r e e zones, each r e p r e s e n t i n g a d i f f e r e n t m i c r o h a b l t a t . The t h r e e m i c r o h a b l t a t s were e e l g r a s s ( P h y l l o s p a d l x s c h o u l e r i ) w i t h sand bottom, r o c k s w i t h sand bottom, and. sand bottom w i t h no c o v e r . The r e l a t i v e p o s i t i o n s o f the t h r e e zones were changed i n each o f the t h r e e t e s t a q u a r i a . T e s t P r o c e d u r e 1. F i s h were c a p t u r e d a t the s t u d y s i t e about t w e n t y - f o u r hours p r i o r t o the ex p e r i m e n t s and k e p t i n ou t d o o r h o l d i n g t a n k s . 2 . The t o t a l l e n g t h s o f the f i s h used were 5 -0 t o 8 . 2 cm. f o r P. s n y d e r l and 5«1 t o 8 . 1 cm. f o r 0 . maculosus. 3. S i x t o t e n i n d i v i d u a l s o f e i t h e r 0. maculosus o r 0. s n y d e r l were d i s t r i b u t e d among the t h r e e m i c r o -h a b i t a t s i n each o f the t h r e e t e s t a q u a r i a , 4. Ten c o n s e c u t i v e c o u n t s (one minute a p a r t ) o f the num-b e r o f i n d i v i d u a l s i n the r e s p e c t i v e m i c r o h a b l t a t s were made eve r y s i x t y m i n u t e s i n each o f the t h r e e t e s t a q u a r i a , 5. G e n e r a l b e h a v i o r a l o b s e r v a t i o n s were a l s o made d u r i n g t h e h o u r l y c o u n t s , 6. The d u r a t i o n o f each e x p e r i m e n t , e x c l u s i v e o f a t w e l v e hour w a i t i n g p e r i o d , ranged from t e n t o f i f t e e n h o u r s . 7. The f r e q u e n c y d i s t r i b u t i o n s were compared by c h i square a n a l y s i s , (However, i t s h o u l d be borne i n mind t h a t a complete s e p a r a t i o n o f dependent and indepe n d e n t d a t a was n o t p o s s i b l e due t o d i f f i c u l t i e s i n t r a c i n g the e x a c t movements o f i n d i v i d u a l s , ) R e s u l t s The f r e q u e n c i e s o f o c c u r r e n c e o f 0, maculosus were h i g h e s t i n t h e r o c k - s a n d zone, m o d e r a t e l y h i g h i n the e e l g r a s s - s a n d zone, and l o w e s t i n the s a n d - o n l y zone. ( F i g u r e 9 ) • C h i square a n a l y s e s i n d i c a t e t h a t t h e s e d i f f e r e n c e s a r e s i g n i f i c a n t (P = <0.0C1) ( T a b l e 4 ) . The d i s t r i b u t i o n o f 0, s n y d e r i was g r e a t e s t towards the e e l g r a s s - s a n d zone w i t h o n l y moderate t o few i n d i v i d u a l s i n t he r o c k - s a n d zone and v e r y few i n d i v i d u a l s i n the sand-o n l y zone ( F i g u r e 9 ) , C h i s q u a r e - a n a l y s e s i n d i c a t e t h a t t h e s e d i f f e r e n c e s a r e s i g n i f i c a n t (P =<0.001) ( T a b l e 4 ) . A Comparison o f the S u b s t r a t e - C o v e r P r e f e r e n c e s o f O l i g o c o t t u s maculosus and Oo s n y d e r l i n Three S i m u l a t e d M i c r o h a b l t a t s . ( P o o l e d Data) 8 0 0. maculosus 60 4 0 2 0 0. snyderi Grass Sand Rock Sand Sand only Table 4. D i s t r i b u t i o n of 0. maculosus and 0. snyderl i n three Substrate-Cover Zones. Numbers of Observations E e l Grass Rock Chi Species n Sand Bottom % Sand Bottom % Sand Bottom % T o t a l Square P 0. maculosus 10 438 31.2 746 53.1 220 15.7 1404 296.6 0.001 0. maculosus 7 212 30.8 397 57.7 79 11.4 688 222.4 0.001 T o t a l - 650 3 1 . 1 1143 54.6 299 14.2 2092 479.1 0.001 0. s n y d e r l 8 603 59.5 333 3 2 . 9 77 7.6 1013 409.8 0.001 0. snyderi 7 662 77.6 89 10.4 103 12.1 854 650.0 0.001 0. snyderl 6 607 77.3 142 18.1 36 4.6 785 704.9 0.001 T o t a l I872 70.6 546 21.3 216 8.1 2652 1724.7 0.001 0 . maculosus (Pooled) vs 0 . s n y d e r l (Pooled) 746.1 0.001 V_0 34 Comparison and a n a l y s i s o f t h e d i s t r i b u t i o n p a t t e r n o f 0. maculosus t o t h a t o f 0,, s n y d e r l i n d i c a t e s i g n i f i c a n t d i f f e r e n c e s (P =<!0.001). ( F i g u r e 9, T a b l e 4). IV. The e f f e c t o f i n t e r s p e c i f i c i n t e r a c t i o n s on s u b s t r a t e - c o v e r p r e f e r e n c e s . The o b j e c t i v e o f the e x p e r i m e n t s d e s c r i b e d below was t o d e t e r m i n e the pr e s e n c e o r absence o f i n t e r s p e c i f i c i n t e r -a c t i v e e f f e c t s on t h e m l c r o h a b i t a t c h o i c e s Of the two s p e c i e s when b o t h o c c u r r e d t o g e t h e r . The f o l l o w i n g e x p e r i m e n t s were co n d u c t e d . M a t e r i a l s and Methods The p r o c e d u r e s f o r t h e s e e x p e r i m e n t s were b a s i c a l l y t h e same as d e s c r i b e d f o r the s t u d y o f i n d i v i d u a l s u b s t r a t e and c o v e r p r e f e r e n c e s . E q u a l numbers o f 0. maculosus and 0. s n y d e r i were s i m u l t a n e o u s l y i n t r o d u c e d i n t o t e s t a q u a r i a c o n t a i n i n g t h e t h r e e s i m u l a t e d m i c r o h a b l t a t s ( e e l g r a s s - s a n d , r o c k - s a n d , and s a n d ) . As i n the p r e v i o u s s u b s t r a t e - c o v e r e x p e r i m e n t s , the f i s h were put i n t o the t e s t a q u a r i a t w e l v e hours p r i o r t o the s t a r t o f each e x p e r i m e n t i n o r d e r t o m i n i -mize the e f f e c t s o f shock from h a n d l i n g and sudden e n v i r o n -m e n t a l change. These e x p e r i m e n t s g e n e r a l l y l a s t e d from t e n t o f i f t e e n h o u r s . The f r e q u e n c i e s o f o c c u r r e n c e o f b o t h s p e c i e s i n the t h r e e m i c r o h a b l t a t s were r e c o r d e d and t h e r e s u l t i n g f r e q u e n c y d i s t r i b u t i o n s compared t o thos e o b t a i n e d when t h e two s p e c i e s were t e s t e d s e p a r a t e l y . The f i s h u sed i n the s e e x p e r i m e n t s ranged i n t o t a l l e n g t h from 5°0 t o 8,2 cm, t o t a l l e n g t h (0, s n y d e r i ) and 5«1 t o 8,0 cm, t o t a l l e n g t h (0. m a c u l o s u s ) . R e s u l t s F o r O l i g o c o t t u s maculosus, t h e o r d e r o f p r e f e r e n c e f o r the t h r e e m i c r o h a b l t a t s remained the same as t h a t i n the e a r l i e r s e p a r a t e - s p e c i e s e x p e r i m e n t s . Thus the h i g h e s t f r e -q u e n c i e s were noted f o r t h e r o c k - s a n d zone, f o l l o w e d by the e e l g r a s s - s a n d zone, w i t h the l o w e s t v a l u e s f o r t h e sand-o n l y z o n e . ( F i g u r e 10). However, c h i square a n a l y s e s o f the I n d i v i d u a l and combined s p e c i e s d i s t r i b u t i o n s i n d i c a t e s i g -n i f i c a n t d i f f e r e n c e s i n number o c c u p y i n g each m i c r o h a b i t a t (P = 0.010) ( T a b l e 5) , S i m i l a r l y , the o r d e r o f p r e f e r e n c e s f o r O l i g o c o t t u s  s n y d e r l t e s t e d t o g e t h e r w i t h 0. maculosus remained the same as t h a t i n the i n d i v i d u a l e x p e r i m e n t s , w i t h t h e h i g h e s t f r e -q u e n c i e s o c c u r r i n g i n the e e l g r a s s - s a n d zone, f o l l o w e d by the r o c k - s a n d and s a n d - o n l y zones r e s p e c t i v e l y ( F i g u r e 11). However, a g a i n , t h e f r e q u e n c i e s o b t a i n e d i n the s i n g l e spe-c i e s e x p e r i m e n t s were found t o be s i g n i f i c a n t l y d i f f e r e n t from t h o s e o b t a i n e d i n the combined s p e c i e s e x p e r i m e n t s (P = 0.001) ( T a b l e 5). D u r i n g the c o u r s e o f a l l t h e s e e x p e r i m e n t s , no i n t e r s p e c i f i c o r i n t r a s p e c i f 1 c a g g r e s s i v e b e h a v i o r was obs e r v e d . A Comparison o f the S u b s t r a t e - C o v e r P r e f e r e n c e s o f O l l g o c o t t u s maculosus i n Three S i m u l a t e d M i c r o h a b l t a t s when t e s t e d s e p a r a t e l y and t o g e t h e r w i t h Oo snyderl» • Separate 2 T o g e t h e r Expt "9 Expt "5 Expt *6 Expt ' 7 n Grass Sand Rock Sand Sand Only Grass Sand Rock Sand Sand Only Unequal *s test animals between both experiments A Comparison o f t h e S u b s t r a t e - C o v e r P r e f e r e n c e s o f O l l g o c o t t u s s n y d e r l i n Three S i m u l a t e d M i c r o h a b l t a t s when T e s t e d S e p a r a t e l y and Together w i t h 0. maculosuso Expt 4 Expt 8 H|S e p a r a t e Together Expt 3 Expt -1 ML Grass Sand Rock Sand Sand Only Expt I Expt 6 Grass Sand R o c k Sand Sand Only 40 T a b l e 5. D i s t r i b u t i o n o f 0, maculosus and 0. s n y d e r i I n t h r e e S u b s t r a t e - C o v e r Zones when t e s t e d s e p a r a t e l y and together., 0. maculosus E x p ' t a l , E e l G r a s s Rock C h i C o n d i t i o n s n Sand Sand Sand T o t a l Square • P S e p a r a t e 7 212 397 79 '688 29.453 0.001 Together 7 242 341 25 .608 S e p a r a t e 10 438 746 220 1404 T o g e t h e r 8 162 653 209 1024 Together 6 33 552 33 588 - -0. s n y d e r l E x p ' t a l . E e l G r a s s Rock C h i C o n d i t i o n s n Sand Sand Sand T o t a l Square P S e p a r a t e 8 603 333 77 1013 675 23.555 0.001 T o g e t h e r 8 326 31 1032 S e p a r a t e 7 662 89 103 854 53.207 0.001 T o g e t h e r 7 650 226 93 969 S e p a r a t e 6 607 142 36 . 785 45.170 0.001 Together 6 373 152 74 599 V. S a l i n i t y The s a l i n i t i e s of t i d e p o o l s during periods of t h e i r i s o l a t i o n from the sea may vary due to evaporation, p r e c i p i -t a t i o n and/or t e r r e s t i a l runoffo The e f f e c t of evaporation appears to be minimal at Port Renfrew. Green (196?) r e p o r t s high t i d e p o o l s . i s o l a t e d "throughout the summer days," that the maximum d a l l y s a l i n i t y Increases due to evaporation were l e s s than 0.4$. The c l i m a t i c c o n d i t i o n s a t Port Renfrew are such that t i d e p o o l s a l i n i t i e s are o f t e n a f f e c t e d by heavy r a i n -f a l l and t e r r e s t i a l r u n o f f , e s p e c i a l l y during the w i n t e r and sp r i n g . A c t i v e mixing does not u s u a l l y occur i n most pools during t h e i r I s o l a t i o n at low t i d e and the f r e s h and s a l i n e waters s t r a t i f y to form h a l o c l i n e s (Doty, 1957; Green, 1967). Data documenting bottom s a l i n i t y regimes of s t r a t i -f i e d t i d e p o o l s were obtained over a four t e e n month p e r i o d at Port Renfrew. S a l i n i t y samples i n the open ocean were a l s o c o l l e c t e d c l o s e to shore during the same pe r i o d . Most t i d e -pool s a l i n i t y samples were taken from three pools which were a l s o being monitored f o r temperature. Both surface and subsurface (approximately sixer more inches below surface) samples were taken from these pools which were l o c a t e d at the 6.0, 9°5 and 10.5 f o o t l e v e l s r e -s p e c t i v e l y . These f i e l d data which were c o l l e c t e d from January, I968 to February, 1969, are summarized on Table 6. I n g e n e r a l , the bottom s a l i n i t i e s of a l l the pools are very 42 s i m i l a r ( F i g u r e 12). S u r f a c e s a l i n i t i e s were low d u r i n g the r a i n y months, e s p e c i a l l y a f t e r a p e r i o d o f heavy r a i n f a l l ( F i g u r e 13)o There a r e some p o o l s i n t h e paths o f r u n o f f c h a n n e l s , i n w h i c h m i x i n g o f s a l i n e and f r e s h w a t e r commonly oc c u r s o Under t h e s e c i r c u m s t a n c e s , s a l i n i t i e s l e s s t h a n 4.0 °/oo have been r e c o r d e d (Green, 1967)0 Bottom d w e l l i n g s p e c i e s such as 0. maculosus and Oo s n y d e r i a r e n o t l i k e l y t o be a f f e c t e d by the low s a l i n i t y w a t e r i n t h e upper l a y e r s o f the p o o l . N e v e r t h e l e s s , the f o r m e r s p e c i e s i s o f t e n f o u n d i n v e r y s h a l l o w h y p o s a l i n e p o o l s o r i n t h e upper l a y e r s o f the h a l o c l i n e . C o m p a rative e x p e r i m e n t s on t h e s e n s i t i v i t y o f 0. maculosus and 0. s n y d e r i t o low s a l i n i t i e s were c o n d u c t e d t o d e t e r m i n e t o what e x t e n t low s a l i n i t y m ight c o n t r i b u t e t o t h e i r r e s p e c t i v e d i s t r i b u -t i o n s . The i n t e r s p e c i f i c d i f f e r e n c e s i n s e n s i t i v i t y t o low s a l i n i t y were measured by the r e s i s t a n c e o f each s p e c i e s t o t h i s f a c t o r . R e s i s t a n c e t o low s a l i n i t y was e x p r e s s e d i n terms of the average time the s p e c i e s s u r v i v e d a g i v e n s a l -i n i t y l e v e l . M a t e r i a l s , Methods and T e s t P r o c e d u r e s 1. Groups o f O l i g o c o t t u s maculosus and 0. s n y d e r i were c a p t u r e d a t the s t u d y s i t e , t r a n s p o r t e d t o the l a b -o r a t o r y and k e p t i n h o l d i n g t a n k s f o r p e r i o d s o f two t o f o u r weeks. 2. A l l f i s h were a c c l i m a t e d t o 30.5 °/oo a t 9.0 t o 11.0°C. 3. A l l groups o f f i s h were exposed t o a t l e a s t n i n e hours o f l i g h t p e r day. 4 3 4 0 F i s h were f e d every o t h e r day w i t h p r e p a r e d d r i e d f o o d s o r f r o z e n chopped shrimp. 5 . T e s t p r o c e d u r e : a„ T e s t s a l i n i t i e s o f 2.0 and ? e 5 % o w e r e o b t a i n e d by t h e d i l u t i o n o f s ea w a t e r from t h e Vancouver P u b l i c Aquarium w i t h d i s t i l l e d w a t e r . b. Four t o s i x 0. maculosus and/or 0. s n y d e r i were p l a c e d i n about f i v e t o s i x g a l l o n s o f c o n s t a n t l y a e r a t e d s e a wa t e r a t the t e s t s a l i n i t y a t ap-p r o x i m a t e a c c l i m a t i o n t e m p e r a t u r e (10 . 5°C), c. The t o t a l l e n g t h ranges o f the f i s h u sed i n t h e s e e x p e r i m e n t s were 7 . 3 5 cm. t o 5 » 3 8 cm. f o r 0.  maculosus and 8 . 7 8 cm. t o 5 « 3 0 cm. f o r 0. s n y d e r i . d. A f t e r t h e f i s h were put i n t o the r e s p e c t i v e t e s t s a l i n i t i e s , p e r i o d i c o b s e r v a t i o n s were made f o r m o r t a l i t i e s and g e n e r a l b e h a v i o r . e. The c r i t e r i a f o r de a t h were the l a c k o f r e s p i r a -t o r y movements and absence o f r e s p o n s e t o p r o b i n g . R e s u l t s The r e s u l t s o f t h e s e e x p e r i m e n t s a r e summarized i n T a b l e 7» I n general,, 0. maculosus shows a g r e a t e r r e s i s t a n c e t o low s a l i n i t y t han 0. snyderi» I n the e x p e r i m e n t s a t 2.0 °>6o» a l l Oo s n y d e r i were f o u n d dead w i t h i n 24 h o u r s . O l i g o c o t t u s maculosus exposed t o the same s a l i n i t y s u r v i v e d from 88 t o 102 h o u r s . A t a s a l i n i t y o f 7*5 °/6o, 0. maculosus s u r v i v e d as l o n g as 192 h o u r s , when the ex p e r i m e n t was t e r m i n a t e d , w h i l e 44 75% o f 0„ s n y d e r i d i e d w i t h i n the f i r s t 9 6 h o u r s . A l l Oo maculosus and the s i n g l e 0 . s n y d e r l w h i c h s u r v i v e d the 8 day p e r i o d a t 7 » 5 °/oo s a l i n i t y were b l o a t e d and i n a c t i v e . F o r most o f t h e t i m e , a l l f i s h appeared s t r e s s e d , a l t h o u g h r e s p i r a t o r y movements and r e s p o n s e s t o p r o b i n g n e v e r d i s a p -peared. Upon r e t u r n t o normal s e a w a t e r ( 3 0 . 5 °/oo) the t e s t a n i m a l s s u r v i v e d f o r s e v e r a l weeks, e x c e p t f o r the s i n g l e 0 . s n y d e r i , w h i c h d i e d w i t h i n one and a h a l f weeks. T a b l e 6. S a l i n i t y o f T i d e p o o l s a t P o r t Renfrew (°/oo) P o o l A n n u a l H e i g h t Mean Maximum Minimum SFG B 0 T SFC B 0 T SFC BOT 6 . 0 ° 2 3 . 9 3 0 . 7 31.4 (Apr.68) 3 1 o 5 (Jul.68) 14.2 29 . 3 (Jan 868) (Feb!68) 9 . 5 ' 2 9 . 7 3 0 . 7 31.4 (Apr,68) 3 1 . 7 (Jul.68) 2 3 . 2 29.4 (Jan.68) (Feb.68) 1 0 . 5 ' 2 2 . 0 3 0 . 7 3 0 . 9 (Dec.68) 31.4 (Jul.68) 4 . 1 28.4 (Oct.68) (Jan.68) On-shore Seawater 3 0 . 9 31.6 (Apr.68) 3 0 . 0 (Feb.68) The S u b s u r f a c e S a l i n i t i e s o f a Low T i d e p o o l ( 6 . 0 ' l e v e l ) , a H i g h T i d e -p o o l ( 9 . 5 ° l e v e l ) , and the S a l i n i t i e s o f the On-shore Sea Water a t P o r t Renfrew i n 1 9 6 8 . High tide pool On-shore sea water The S u r f a c e S a l i n i t i e s o f a Low T i d e p o o l (6*0 8 l e v e l ) and a H i g h T i d e p o o l (9.5 s l e v e l ) a t P o r t Renfrew i n 1968. High tide pool I Q G Q T a b l e 7« The R e s i s t a n c e o f Q 0 maculosus and 0. s n y d e r l t o Low S a l l n l t i e s e S p e c i e s S a l i n i t y (°/oo) L D 5 0 X R e s i s t (Min.) (Minutes) C e s s a t i o n Resp. Mvmts.; P o s i t i v e Probe Response (Minutes) Time t o 100$ M o r t a l i t y ( M i n u t e s ) T o t a l M o r t a l i t 0. s n y d e r l . 2.0 0. maculosus 2.0 1040 : 5955 5838.8 240 1440+ 1040 6165 100^ 100% 0. s n y d e r l 0. maculosus 7.5 7.5 75^ 0% 50 V I . H a b i t a t t e m p e r a t u r e , temperature t o l e r a n c e and r e s i s t a n c e . Temperature regimes o f h i g h l e v e l t i d e p o o l s a r e more extreme and u n s t a b l e t h a n those o f l o w e r l e v e l p o o l s ( K l u g h , 1924; Hewett, 1937; Doty, 1957, 1965). The d i f f e r i n g d i s t r i -b u t i o n s o f 0. maculosus and 0. s n y d e r l a r e c o n c e i v a b l e r e -f l e c t i o n s o f the d i f f e r e n c e s i n the t h e r m a l regimes o f the r e s p e c t i v e m i c r o h a b i t a t s . I f so, one c o u l d e x p e c t , a p r i o r i , 0. maculosus t o be more t o l e r a n t o f tem p e r a t u r e extremes and f l u c t u a t i o n s t h a n 0. s n y d e r i . I n o r d e r t o examine t h e e f f e c t o f m i c r o h a b i t a t tem-p e r a t u r e on l o c a l d i s t r i b u t i o n o f the two s p e c i e s , i t was n e c e s s a r y t o e s t a b l i s h the r e l a t i o n s h i p o f the t i d a l c y c l e t o 1)' the t e m p e r a t u r e c h a r a c t e r i s t i c s o f the t i d e p o o l s and to 2) the p h y s i o l o g i c a l and b e h a v i o r a l r e s p o n s e s o f the f i s h t o t e m p e r a t u r e . M a t e r i a l s and Methods The 1968 t i d e h e i g h t s f o r P o r t Renfrew were c a l c u -l a t e d from p u b l i s h e d d a t a (U.S. Department o f Commerce, 1968 T i d e T a b l e s f o r West Coast N o r t h and South A m e r i c a , i n c l u d i n g the H a w a i i a n I s l a n d s ) . An e s t i m a t i o n o f the degree o f exposure a t d i f f e r e n t l e v e l s a t the r e s e a r c h s i t e was o b t a i n e d from the d a t a o f Green (1967) which was based on a s e r i e s o f 6-minute t i d a l h e i g h t p r e d i c t i o n s f o r 1966. 51 S u b s u r f a c e t i d e p o o l ; t e m p e r a t u r e s were m o n i t o r e d I n t h r e e p o o l s o f s i m i l a r s i z e a t d i f f e r e n t l e v e l s (6.0, 9.5. 10.5 f o o t l e v e l s ) o v e r a f o u r t e e n month p e r i o d . S e l f -c o n t a i n e d s u b m e r s i b l e t h e r m o m e t e r - r e c o r d e r u n i t s (Ryan I n -d u s t r i e s , S e a t t l e , Washington) were b o l t e d t o the bottoms o f t i d e p o o l s on s t a i n l e s s s t e e l b r a c k e t s . The r e c o r d i n g element o f each u n i t p l o t t e d temperatures c o n t i n u o u s l y f o r e i g h t - d a y p e r i o d s . The a p p a r a t u s had a range o f 0.0 t o 30.0°C w i t h an a c c u r a c y o f 9Q%, R e c o r d e r c h a r t s were u s u a l l y changed e v e r y two weeks, thus i n s u r i n g s e v e r a l days o f c o n t i n u o u s t e m p e r a t u r e r e c o r d s f o r each month. Mean t e m p e r a t u r e s f o r each r e c o r d i n g period, ( e i g h t days) were c a l c u l a t e d a t s i x - h o u r l y i n t e r v a l s (0000, 0600, 1200, 1800 hours) f o r each day o f a r e c o r d i n g p e r i o d . Thus f o r a f u l l e i g h t - d a y r e c o r d i n g p e r i o d the mean tempera-t u r e r e p r e s e n t s a t o t a l o f t h i r t y - t w o t e m p e r a t u r e measure-ments. A n n u a l mean t e m p e r a t u r e s were a l s o c a l c u l a t e d from t h e s e d a t a . F i e l d D a t a An example o f the mixed s e m i d i u r n a l t i d e c y c l e c h a r -a c t e r i s t i c o f the r e s e a r c h a r e a i s shown on F i g u r e 14. Dur a -t i o n o f p e r i o d s o f exposure o f p o o l s t o a t m o s p h e r i c c o n d i t i o n s a t d i f f e r e n t h e i g h t l e v e l s a r e shown on F i g u r e 15 (Green, 1967). A c r i t i c a l l e v e l o c c u r s a t P o r t Renfrew a t about 7.5 f e e t . F o r t i d e p o o l l e v e l s between 1.5 and 6.5 f e e t above mean low wa t e r , the maximum d u r a t i o n o f a s i n g l e emergence I s about t e n h o u r s . A t l e v e l s above 6.5 f e e t , the maximum F i g u r e 14. The M i x e d S e m l - D l u r n a l T i d e C y c l e o f P o r t San Juan (From Green, 1 9 6 7 ) . F i g u r e 15, The D u r a t i o n o f Emergence and Sub-mergence o f t h e T i d e p o o l s o f P o r t Renfrew (From Green, I967). Tide height - feet _ o — ro 01 t?i CD -o CD CD o — ro 56 d u r a t i o n o f emergence g r e a t l y i n c r e a s e s from about twenty hours a t t h e 7.5 f o o t l e v e l , t o about 35° hours a t the 11.0 f o o t l e v e l . The mean t e m p e r a t u r e s , h i g h e s t maximum and l o w e s t minimum t e m p e r a t u r e s o f t h e t i d e p o o l s a t the 6.0, 9.5 and 10.5 f o o t l e v e l s from December, 1967 t o J a n u a r y , I969 a r e shown on Ta.ble 8 and F i g u r e 16. On F i g u r e s 17, 18, and 19 the n a t u r a l t h e r m a l regimes o f t i d e p o o l s from the d i f f e r e n t h e i g h t l e v e l s on a day t o day b a s i s a r e p r e s e n t e d . These c l e a r l y show the t e m p e r a t u r e d i f f e r e n c e s a s s o c i a t e d w i t h the t i d e c y c l e and v e r t i c a l p o s i t i o n o f the t i d e p o o l s . The sudden te m p e r a t u r e changes c h a r a c t e r i s t i c o f h i g h e r p o o l s a r e c l e a r l y e v i d e n t . Summary o f F i e l d D a t a 1. The P o r t Renfrew i n t e r t i d a l zone i s governed by a mixed s e m i - d i u r n a l t i d e c y c l e , the magnitude o f wh i c h i s about 12.4 f e e t . 2. The maximum d u r a t i o n o f emergence o f P o r t Renfrew t i d e p o o l s below the 6.5 f o o t l e v e l r anges from 0. t o 10 hours w h i l e t h a t o f p o o l s between 6.5 and .11.0 f o o t l e v e l s range from 20 t o 330 h o u r s . 3. The mean t e m p e r a t u r e s o f h i g h l e v e l t i d e p o o l s a r e g r e a t e r than t h o s e o f l o w e r l e v e l t i d e p o o l s d u r i n g the warmer months o f the y e a r . 4. The mean te m p e r a t u r e s o f h i g h e r l e v e l t i d e p o o l s a r e o f t e n l e s s t h a n those o f l o w e r l e v e l t i d e p o o l s d u r -i n g the c o l d w i n t e r months. 5. The temperature extremes of low l e v e l tidepools never exceed, or go below, those of higher l e v e l poolso 6. The upper l e v e l tidepools have highly variable ex-treme temperature regimes while those of lower l e v e l pools tend to be stable. 7. Sudden, and often large, temperature changes occur i n tidepools with the onset of inundations caused by r i s i n g tide l e v e l s . 8. Sudden temperature changes i n tidepools are d i r e c t l y r e l a t e d to the t i d a l phase and the v e r t i c a l p o s i t i o n of the tidepools, t h e i r period of exposure to at-mospheric conditions, and the time of the year. Table 8. Mean Temperatures of Tidepools at Port Renfrew (°C) Tide Highest Lowest Pool Annual 8-day 8-day Highest Lowest Height Mean Mean Mean Maximum Minimum 6.0° 9.7* 12.9 .6.8 18.2 5.1 (Jul.68) (Jan-Peb.68) (Jul.68) (Feb.68) 9.5' 10.7 16.2 5.9 23.5 0.5 (Jul.68) (Dec.67) (Jul.68) (Dec.67) 10.5' 12.7** 18.0 8.4 22.8 6.9 (Jul.68) (Dec.68) (Jul.68) (Dec.68) * = No data late August - October **= Data from July - December only The Mean Temperatures, Maximum and Minimum Temperatures f o r A l l R e c o r d i n g 'Periods Over a F o u r t e e n Month P e r i o d (1967-68) i n T i d e p o o l s a t P o r t Renfrew. H i g h T i d e p o o l = 10.5' l e v e l ( @ ) H i g h T i d e p o o l =' 9.5° l e v e l ( © ) Low T i d e p o o l = 6.0° l e v e l ( x ) I 3 - V I - 6 3 5 - V I - 6 8 - 2 0 - V - 6 8 1 2 - V - 6 8 7 - V - 6 8 2 9 - I V - 6 8 2 2 - I V - 6 3 - I 4 - I V - 6 3 27-111-68 • 18-111-63 5-111-68 25-11 - 6 8 20-11 - 6 8 12- 11-68 5-11 -68' 2 8 I 6 8 21 I 6 8 13- 1 - 6 8 2 4-XII-67 I 6-XII-67 O o i n o » o Pi in in jarima i I < I 0) ro OJ i < T 01 0) I < cn 0) 03 I < Cn CO i < 01 CO r o — ' — . r o CD | r o i 01 t ! CO 1 cr> 1 < >< 1 X X J T" CO 01 01 01 01 cn CO CO • CO. 01 CO CO © © High X Low pools pools The R e l a t i o n s h i p o f the T i d e C y c l e t o S u b s u r f a c e T i d e p o o l Temperatures from 13 May, 1968 t o 21 May, 1968 a t P o r t Renfrew. H i g h T i d e p o o l = 9.5" l e v e l Low T i d e p o o l = 6,08 l e v e l Tide pool . Temperature °C 2 5 2 0 1 5 1 0 5 Noon Tide height (Feet ) 0 + 133 137 138 ay (Julian date) 139 Low tide pool High tide pool The R e l a t i o n s h i p o f the T i d e C y c l e t o S u b s u r f a c e T i d e p o o l Temperatures from 7 J u l y , 1968 t o 15 J u l y , 1968 a t P o r t Renfrew., H i g h T i d e p o o l = 9<>5' l e v e l Low T i d e p o o l =6.0" l e v e l Day ( Julian date ) Low tide pool High ride poo) The R e l a t i o n s h i p o f the T i d e C y c l e t o S u b s u r f a c e T i d e p o o l Temperatures from 2k J u l y , 1968 t o 1 August, 1968 a t P o r t Renfrew. Hig h T i d e p o o l = 10.5° l e v e l ( ) H i g h T i d e p o o l = 9.5' l e v e l ( Low T i d e p o o l = 6.0V l e v e l ( ) Tide pool Temperature C° Tide height ( F e e t ) 206 207 208 209 Day ( Julian date ) Low tide poo! High tide pool High tide pool A. The E f f e c t o f H i g h Temperature on O l l g o c o t t u s maculosus and 0. s n y d e r l * C o m p a rative e x a m i n a t i o n . o f the response o f t h e two s p e c i e s t o t e m p e r a t u r e was a c c o m p l i s h e d i n both l a b o r a t o r y and f i e l d e x p e r i m e n t s . F i e l d Temperature T o l e r a n c e E x p e r i m e n t s M a t e r i a l s and Methods I n t h e s e e x p e r i m e n t s , s m a l l groups o f 0, maculosus and 0. s n y d e r i were e n c l o s e d i n t i d e p o o l s o r i n w i r e en-c l o s u r e s w h i c h were p l a c e d i n t i d e p o o l s a t d i f f e r e n t v e r t i -c a l h e i g h t l e v e l s f o r p e r i o d s up t o t h r e e weeks. Ob s e r v a -t i o n s were made on t h e c o m p a r a t i v e s u r v i v a l o f the two 6 s p e c i e s . A s e r i e s o f f i v e (5) t i d e p o o l s a t v a r i o u s h e i g h t l e v e l s (6.0, 8.5» 9°5» 10,5 and 12.0 f e e t ) were u s e d i n t h e s e e x p e r i m e n t s . Four p o o l s c o n t a i n e d t e m p e r a t u r e r e c o r d i n g u n i t s . Three o f t h e s e (6.0, 9.5 and 10.5 f o o t l e v e l s ) were t h e same p o o l s u s e d t o m o n i t o r t i d e p o o l t e m p e r a t u r e s . The r e m a i n i n g p o o l was l o c a t e d a d j a c e n t t o a p o o l which con t a i n e d t e m p e r a t u r e r e c o r d i n g a p p a r a t u s . Two o f the f i v e t e s t p o o l s were c o v e r e d w i t h heavy gauge s t e e l w i r e mesh c o v e r s which were b o l t e d down a l o n g the edges o f the t i d e p o o l s . T e s t P r o c e d u r e s 1. O l l g o c o t t u s maculosus and 0. s n y d e r l were c a p t u r e d a t the r e s e a r c h s i t e a t m i d - l e v e l t i d e p o o l s . 2. E q u a l numbers o f each s p e c i e s were i n t r o d u c e d t o the t e s t t i d e p o o l s a t v a r i o u s h e i g h t l e v e l s . 3« Sample numbers i n the e x p e r i m e n t s v a r i e d a c c o r d i n g t o the s i z e o f the c o v e r e d p o o l s and/or the number o f a v a i l a b l e t e s t a n i m a l s . N v a r i e d from 4 t o 10 o f each s p e c i e s . 4. The t o t a l l e n g t h o f the f i s h used i n the s e e x p e r i -ments ranged from 5«3 cm. t o 8.6 cm. f o r 0. macu-l o s u s and from 4.2 cm. t o 9.2 cm. f o r 0. s n y d e r i . 5. The time the f i s h were f i r s t e n c l o s e d i n the p o o l s o r minnow t r a p s was n o t e d on t h e te m p e r a t u r e r e -c o r d e r c h a r t s and marked the b e g i n n i n g o f each e x p e r i m e n t . 6. P e r i o d i c checks on the m o r t a l i t i e s and t e m p e r a t u r e i n the v a r i o u s e x p e r i m e n t s were made. 7. Each experiment was continued f o r a t l e a s t one semi-l u n a r c y c l e (up t o t h r e e weeks) o r u n t i l a l l i n d i -v i d u a l s o f one o r the o t h e r s p e c i e s were dead. R e s u l t s 0. maculosus g e n e r a l l y showed h i g h e r s u r v i v a l t h a n 0. s n y d e r i i n the h i g h e r t i d e p o o l s ( T a b l e 9 ). These r e s u l t s , c o u p l e d w i t h the l a r g e d i f f e r e n c e i n t h e r m a l regimes o f h i g h and low t i d e p o o l s , l e n d s u p p o r t t o the s u g g e s t i o n t h a t tem-p e r a t u r e i s a c a u s a l f a c t o r I n d e t e r m i n i n g the d i s t r i b u t i o n . T a b l e 9. P e r c e n t a g e S u r v i v a l of O l l g o c o t t u s maculosus and Oo s n y d e r l I n t i d e p o o l e n c l o s u r e s i n upper t i d e p o o l s (Summer 1 9 6 8 ) H i g h P o o l 1 0 o 5 e l e v e l H i g h P o o l 1 0 . 5 ' l e v e l E x p t . 0. maculosus 0. s n y d e r l E x p t o 0. maculosus 0. s n y d e r l # 1 1 0 0 ^ 75% #2 1 0 C $ 0.0% # 3 66% 0.0% # 4 66% 0.0% L a b o r a t o r y Temperature T o l e r a n c e E x p e r i m e n t s M a t e r i a l s , Methods and T e s t P r o c e d u r e s l o Groups o f O l l g o c o t t u s maculosus and 0. s n y d e r i were c a p t u r e d a t the s t u d y s i t e , t r a n s p o r t e d t o the l a b o r a t o r y and e x c e p t f o r t e m p e r a t u r e , m a i n t a i n e d under s i m i l a r c o n d i t i o n s , 2 0 The t o t a l lengths o f the f i s h u s ed i n t h e s e e x p e r i -ments were 2 . 5 5 cm. to 7.68 cm. f o r 0 , maculosus and 4 , 0 0 cm, t o 8 . 4 8 cm. f o r 0. s n y d e r l . 3. Most o f the f i s h used i n t h e s e e x p e r i m e n t s were caught i n the l a t e s p r i n g and. summer and were main-t a i n e d a t t e m p e r a t u r e s o f 1 0 . 0 , 1 4 . 0 , 1 7 , 0 and 19»0°C f o r a minimum of t h r e e weeks b e f o r e e x p e r i m e n t s were conducted. The f i s h were m a i n t a i n e d a t s a l i n i t i e s r a n g i n g from 29.5 t o 31.5 % o . A l i m i t e d number o f f i s h o f b o t h s p e c i e s was caught d u r i n g t h e f a l l and w i n t e r and were u s e d w i t h i n a few days o f c a p t u r e . D u r i n g t h e s h o r t t i m e between c a p t u r e and e x p e r i m e n t a t i o n , t h e s e f i s h were k e p t a t 8.0 and 10.0°C (30.5 °/oo), s i m i l a r t o f i e l d c o n -d i t i o n s a t t h e time o f c a p t u r e . A n o t h e r group caught i n t h e f a l l and w i n t e r was a c -c l i m a t e d t o 5.0°C a t 30.5 °/oo s a l i n i t y . F i s h a c c l i m a t e d d u r i n g t h e summer were p r o v i d e d about t w e l v e t o f o u r t e e n h o u r s o f l i g h t p e r day. W i n t e r a c c l i m a t e d f i s h were p r o v i d e d w i t h about < n i n e h o u r s p e r day. A l l f i s h were f e d e v e r y o t h e r day w i t h f r o z e n b r i n e s h r i m p . O c c a s i o n a l l y l i v e b r i n e s h r i m p o r f r e s h chopped prawns were s u b s t i t u t e d . The d a t a from t h e e x p e r i m e n t s o u t l i n e d below a r e p r e s e n t e d i n two ways: a. Temperature " t o l e r a n c e , " w h i c h r e f e r s t o t h e a b i l i t y o f a group o f f i s h t o s u r v i v e t w e l v e h o u r s o f exposure t o a g i v e n t e s t t e m p e r a t u r e . " T o l e r a n c e " i s e x p r e s s e d i n terms o f t h e l e n g t h o f time r e q u i r e d f o r 50# o f a t e s t g r o u p t o d i e ( L D < n ) . b. Temperature " r e s i s t a n c e / ' w h i c h r e f e r s t o the average time a group o f f i s h i s a b l e t o s u r v i v e a g i v e n t e s t t e m p e r a t u r e . 10e T e s t P r o c e d u r e a. Ten g a l l o n t e s t j a r s h a l f f i l l e d w i t h s e a w a t e r ( a p p r o x i m a t e l y 30.5 °/oo). b. The w a t e r was a e r a t e d and cooled, t o the a c c l i m a -t i o n t e m p e r a t u r e o f the f i s h t o be t e s t e d . c. A f t e r a c c l i m a t i o n t e m p e r a t u r e was a t t a i n e d i n t h e t e s t jars„ s i x t o t e n i n d i v i d u a l s o f each s p e c i e s were i n t r o d u c e d . d. A f t e r a p e r i o d o f s i x t y t o n i n e t y m i n u t e s , t h e t e m p e r a t u r e p f the w a t e r was g r a d u a l l y r a i s e d t o t h e d e s i r e d , t e s t l e v e l . e. Temperature o f the w a t e r was m o n i t o r e d by an a u t o m a t i c t w e n t y - f o u r c h a n n e l c o n t i n u o u s tem-p e r a t u r e r e c o r d e r ( H o n e y w e l l Co., Vancouver, B.C. ) 0 Occasional s p o t checks, were made w i t h a s t a n d a r d s u b m e r s i b l e thermometer (-10 t o 110 degrees C ) . f 0 The time o f death was r e c o r d e d f o r each i n d i -— v i d u a l whenever p o s s i b l e . When the a c t u a l time o f d e a t h was not o b s e r v e d , the time was t a k e n t o be h a l f w a y between the l a s t two o b s e r v a t i o n s . go The c r i t e r i a f o r death were the absence o f r e -s p i r a t o r y movements and l a c k o f r e s p o n s e t o p r o b i n g . R e s u l t s The r e s u l t s o f t h e s e e x p e r i m e n t s a re summarized on Ta b l e s 10, 11 and F i g u r e s 20, 21, 22. O l l g o c o t t u s maculosus and Oo s n y d e r i a c c l i m a t e d i n t h e summer t o 10.0°C and the n s u b j e c t e d t o 30.0°C show v e r y d i f f e r e n t p h y s i o l o g i c a l r e -sponses. O l l g o c o t t u s s n y d e r i a t t h i s l e v e l o f a c c l i m a t i o n cannot t o l e r a t e 30»0°C. O l l g o c o t t u s maculosus i n the same two e x p e r i m e n t s r e s i s t e d the t e s t t e m p e r a t u r e f o r an average o f .19.8 and 27.8 minutes r e s p e c t i v e l y . LD^Q v a l u e s f o r t h e s e f i s h were 1 4 . 0 and 19 . 0 minutes r e s p e c t i v e l y . No L D ^ v a l u e s c o u l d be a s s e s s e d f o r 0. s n y d e r i a t 30.0°C s i n c e a l l f i s h d i e d b e f o r e the t e s t t e m p e r a t u r e was a t t a i n e d . Groups o f f i s h a c c l i m a t e d a t l 4 . 0°C and t e s t e d a t 28.0°C had the f o l l o w i n g average r e s i s t a n c e t i m e s : 53*5 minutes (0. s n y d e r i ) and 8 1 0 . 0 minutes (0. maculosus). The LD^Q v a l u e s f o r t h e s e e x p e r i m e n t s were 4 6 min u t e s f o r 0. s n y d e r i and 610 minutes f o r 0. maculosus. O t h e r groups a c c l i m a t e d a t 1 4 . 0 ° C and t e s t e d a t 25.0°C had average r e s i s t a n c e times o f 1268.8 (0. s n y d e r i ) and 3901.7 minutes (0. maculosus) w i t h LD^Q v a l u e s o f 1485 minutes and 3^40 m i n u t e s , r e s p e c t i v e l y . A t a t e s t t e m p e r a t u r e o f 25«0°C, f i s h t e s t e d a l m o s t i m m e d i a t e l y a f t e r b e i n g t r a n s p o r t e d t o the l a b o r a t o r y from the r e s e a r c h s i t e ( f i e l d t e m p e r a t u r e a p p r o x i m a t e l y 10.0°C) had average r e s i s t a n c e t i m e s o f 4 2 8 . 5 minutes (0. s n y d e r i ) and 5362.2 minutes (0. m a c u l o s u s ) . LD^Q v a l u e s from t h e s e e x p e r i m e n t s were 2 8 0 and 5127 m i n u t e s , r e s p e c t i v e l y . 7 3 A n o t h e r group o f 0. maculosus t e s t e d a t 2 6 . 5°C i m m e d i a t e l y upon r e t u r n from the f i e l d ( t e m p e r a t u r e a p p r o x i m a t e l y 1 0 . 0°C) had an average r e s i s t a n c e o f 980 minutes and an LD^Q v a l u e o f 9 7 2 o 5 m i n u t e s . The average r e s i s t a n c e t i m e s o f 0 . maculosus and 0 . s n y d e r i a c c l i m a t e d a t 1 7 . 0°C and t e s t e d a t 28 . 0°C were 2 6 0 . 4 and 9 1 . 2 m i n u t e s , r e s p e c t i v e l y . The LD^Q v a l u e s were 9 4 ( 0 . s n y d e r i ) and 240 ( 0 . maculosus) m i n u t e s , r e s p e c t i v e l y . I n two e x p e r i m e n t s u s i n g o n l y t h r e e i n d i v i d u a l s o f b o t h s p e c i e s a t 1 9 . 0°C a c c l i m a t i o n t e m p e r a t u r e and 3 0 . 0°C t e s t t e m p e r a t u r e , a l l 0. s n y d e r l d i e d a l m o s t s i m u l t a n e o u s l y a f t e r about f i v e m i n u t es o f exposure t o the t e s t t e m p e r a t u r e w h i l e 0 . maculosus s u r v i v e d an average o f 4 1 . 3 m i n u t e s . S i x 0. maculosus caught i n the w i n t e r ( f i e l d tempera-t u r e 8.0 t o 9»0°G) and t e s t e d I m mediately a t 25.0°C had an average r e s i s t a n c e t ime o f 1 8 1 6 . 7 minutes w i t h an LD^Q v a l u e o f 2 2 8 0 m i n u t e s . A g r a p h i c a l r e p r e s e n t a t i o n o f a l l t h e e x p e r i m e n t s a t the d i f f e r e n t a c c l i m a t i o n ( f i s h a d j u s t e d t o c o n t r o l l e d l a b o r a t o r y e n v i r o n m e n t ) , a c c l i m a t i z a t i o n ( f i s h a d j u s t e d t o environmental c o n d i t i o n s i n the f i e l d ) , and t e s t t e m p e r a t u r e s c o n s i s t e n t l y show the g r e a t e r t o l e r a n c e and r e s i s t a n c e o f 0 . maculosus t o h i g h t e m p e r a t u r e extremes ( F i g u r e s 2 0 , 2 1 ) . Curves o f average r e s i s t a n c e times a t t e s t t e m p e r a t u r e s o f 2 5.0, 28.0 and 30.0°C a t d i f f e r e n t l e v e l s o f a c c l i m a t i z a t i o n and a c c l i m a t i o n s u p p o r t t h i s v i e w ( F i g u r e 2 2 ) . 74 In comparing the L D ^ Q data, the most important d i f -ference between the two species appears to be at acclimation and acclimatization l e v e l s below l4°C. Below t h i s point, 0, snyderi cannot survive exposure for twelve hours to 25»0°C while 0. maculosus can. (The sign i f i c a n c e of t h i s becomes apparent when considering the fact that twelve hours ( 720 minutes) approximates the maxi-mum duration of a single emergence of a tidepool at about the 7.5* l e v e l and that 25.0°C temperatures have been ob-served i n some upper pools at Port Renfrew,,) Table 10, Temperature Tolerance and Resistance of Ollgocottus maculosus. Acclimation Test Tolerance Temperature Temp. LDeO X" Resist Date °C Minures Minutes n 13-XII-68 8-9* 25.0 2280 1816.7 6 28-VLTJ.-68 10* 25; 0 5127 5362.2 6 16-VIII-68 14 25.0 3640 3901.7 6 9-IX-68 10* 26.5 972.5 980.0 5 16-VIII-68 14 28.0 610 810.0 6 15-VIII-68 14 28.0 337 -- 6 29-VIII-68 17 28.0 240** 260.4 5 28-V-68 10 30.0 14 19.8 6 28-V-68 10. 30.0 19 27.8 6 27-V-68 19 30.0 41.3 3 * = Acclimatization temperature ** = 60^ mortality point 75 T a b l e 11. Temperature T o l e r a n c e and R e s i s t a n c e o f O l i g o c o t t u s s n y d e r i . Date A c c l i m a t i o n Temperature °c T e s t Temp. °C T o l e r a n c e LD50 M i n u t e s X R e s i s t M i n u t e s n 9-IX-68 10.0* 25.0 280 428.5 6 23-VIII-68 14.0 25.0 1485 1268.8 6 23-VIII-68 14.0 28.0 46 53.5 6 28-VIII- 68 17.0 28.0 94 91.2 6 28-V-68 10.0 .30.0 0 0 6 27-V-68 19.0 30.0 5 3 * = A c c l i m a t i z a t i o n t e m p e r a t u r e * * = 100^ m o r t a l i t y p o i n t The R e s i s t a n c e o f O l l g o c o t t u s  maculosus and 0» s n y d e r i t o Heat Extremes a t D i f f e r e n t A c c l i m a t i o n and T e s t Temperatures. (IB) 10* C Acclimation temperature 30*C Test temperature ( fish died before test temp attained 25* -<30* ) 2 3 4 5 6 7 B 9 10 2 3 4 5 6 7 fl 8 100 Log res is tance time (minutes) I 4 * C Acclimation temperature 27.0* C - 2 8 . 0 ' T e s t femperature (mortalities occurred between 27 .0* - 27.8*C ) 2 3 4 5 .3 7 B » 10 3 4 5 6 7 6 9 10 2 3 4 3 « 7 0 9 K 2 3 4 9 * 7 8 9 0 , 0 0 0 Log resistance time (minutes) The R e s i s t a n c e o f O l l g o c o t t u s  maculosus and 0. s n y d e r i t o Heat Extremes a t D i f f e r e n t A c c l i m a t i z a t i o n and T e s t Temperatures., (2A) IO°C A c c l i m i t i z a t i o n t e m p e r a t u r e 2 5 . 0 ° T e s t t e m p e r a t u r e 100. 90 eo-70-60 = 50-O "°" ^ 30-$S 20-10-0 • — 10 A' A 2 3 4 5 6 7 6 9 100 2 3 4 5 6 7 6 9 1000 2 3 4 5 6 7 8 9 10,000 Log resistance t ime (minutes) (2B) IO°C Acclimitization temperature 26.5° Test temperature 8°C Acclimitization temperature 25.0°C Test temperature 100-90-8 0 : 70-60-50-0~5 2o - i IOi 0-1 3 4 5 6 7 B 9 I 0 0 2 3 4 5 6 7 8 9 1 0 0 0 2 3 4 5 6 7 8 9 10.000 Log resistance t ime (minutes) • 0 maculosus A Q snyderi The Average R e s i s t a n c e o f O l l g o c o t t u s  maculosus and 0. s n y d e r i t o Heat Extremes a t D i f f e r e n t A c c l i m a t i o n and A c c l i m a t i z a t i o n Temperatures„ T e m p e r a t u r e r e s i s t a n c e c u r v e s o f 0. m a c u l o s u s a n d 0. s n y d e r i 1000 9 B 7 6-5-4 3" C a> E cu o d. o 10 cu a> cn o i _ > o 100 9 8 7 6 5-4-3-10 9 8 7 6' 5 4" 3-2-Test Temperature 2 8 - 3 0 ° C Test.Temperature 2 5 ° C 1/' rl0,000 • I.OOO -100 •5 5° 10° 20° 5° 10° 6 ° 20 -10 Acclimation Temperature °C © - — 0 . maculosus (Spring-Summer) A — 0 . snyderi (Spring-Summer) O,Acc l imi t iza t ion temperature ( Dec, Sept. 1968 respectively) 82 B. The E f f e c t o f R a p i d Temperature Changes on O l l g o c o t t u s maculosus and 0 . s n y d e r i S i n c e the upper p o o l s a t t a i n g r e a t e r t e m p e r a t u r e ex-tremes r e l a t i v e t o the te m p e r a t u r e o f the sea, the e x t e n t o f r a p i d t e m p e r a t u r e changes caused "by t h e r i s i n g t i d e s a r e much more d r a s t i c t h a n t h o s e of l o w e r l e v e l p o o l s . Thus i t was p o s s i b l e t h a t the r e s t r i c t i o n o f 0 . s n y d e r i t o l o w e r l e v e l t i d e p o o l s was d i r e c t l y r e l a t e d t o an i n a b i l i t y t o w i t h s t a n d sudden t e m p e r a t u r e changes. I n i t i a l l y , two p i l o t e x p e r i m e n t s were c o n d u c t e d i n the f i e l d . One c o n s i s t e d o f moving s m a l l numbers o f O l l g o -c o t t u s maculosus and 0. s n y d e r i d i r e c t l y from 11 .5°C wat e r i n t o a s h a l l o w t i d e p o o l a t 2 3 » 5°C A f t e r a two-hour p e r i o d , the f i s h were s u b j e c t e d t o a sudden t e m p e r a t u r e d e c r e a s e ( t o 13 .5°C) by the a d d i t i o n o f f r e s h c o l d s e a w a t e r . Ob-s e r v a t i o n s on the r e a c t i o n s and s u r v i v a l o f the two s p e c i e s were made. I n a n o t h e r p r e l i m i n a r y f i e l d t e s t , t he f i s h were t r a n s -f e r r e d t o s m a l l s h a l l o w t i d e p o o l s a t a temp e r a t u r e o f about 1 3 . 5°C. The f i s h were k e p t i n the p o o l s over a t h r e e t o f o u r -hour p e r i o d as the water temperature was g r a d u a l l y i n c r e a s e d t o 2 2 . 0°C. A f t e r about two hpurs, the temp e r a t u r e was dropped sud-d e n l y t o 1 0 . 5°C i n one o f the p o o l s by a d d i n g l a r g e volumes o f f r e s h s e a w a t e r . T h i s p r o c e d u r e was r e p e a t e d over two co n s e c u -t i v e low wa t e r p e r i o d s . F or b o t h f i e l d e x p e r i m e n t s , c o n t r o l a n i m a l s were sub-j e c t e d t o s i m i l a r h i g h t e m p e r a t u r e s f o r comparable l e n g t h s 8 3 o f time b u t were not s u b j e c t e d t o the sudden drop i n tempera-t u r e o I n s t e a d , h i g h t e m p e r a t u r e s were allowed t o g r a d u a l l y d e c r e a s e t o comparable l o w e r t e m p e r a t u r e s ( 1 3 » 5°C) as i n the e x p e r i m e n t a l g r o u p s . More r i g i d l y c o n t r o l l e d e x p e r i m e n t s f o l l o w i n g t h e same form a t as the f i e l d e x p e r i m e n t s were c o n d u c t e d i n the l a b o r a t o r y . The methods and t e s t p r o c e d u r e s f o r t h e s e a r e o u t l i n e d below. M a t e r i a l s . Methods, and T e s t P r o c e d u r e s ( L a b o r a t o r y E x p e r i m e n t s ) 1 „ O l l g o c o t t u s maculosus and 0 . s n y d e r i from the r e -s e a r c h s i t e were e i t h e r h e l d l n l a b o r a t o r y h o l d i n g t a n k s f o r a t l e a s t two weeks a t 1 0 . 0°C ( 3 0 . 5 °/oo s a l i n i t y ) b e f o r e c o n d u c t i n g e x p e r i m e n t s , o r u s e d Immediately a t the f i e l d l a b o r a t o r y upon c a p t u r e . ( F i e l d t e m p e r a t u r e a p p r o x i m a t e l y 1 0 . 0°C) 2 . E q u a l numbers o f e i t h e r o r b o t h s p e c i e s were p l a c e d i n two t e s t a q u a r i a c o n t a i n i n g f i v e t o seven g a l l o n s o f c o n s t a n t l y a e r a t e d s e a water a t about 1 1 . 0°C. 3 . The tem p e r a t u r e o f the w a t e r was g r a d u a l l y r a i s e d t o 2 2 . 5 ° t o 2 3 . 5°C o v e r a p e r i o d o f t h r e e t o f o u r hours w i t h 2 0 - w a t t e l e c t r i c a l aquarium h e a t e r s , 4 . The 2 2 . 5 ° t o 2 3 . 5°C t e m p e r a t u r e l e v e l s were main-t a i n e d from f o u r t o s i x h o u r s . 5 . A t the end o f t h e f o u r t o s i x hours a t 2 2 . 5 ° t o 2 3 » 5°C, t h e f i s h were s u b j e c t e d t o sudden tempera-t u r e d e c r e a s e s down t o 1 1 . 0°C by e i t h e r a d d i n g c o l d s e a w a t e r t o the t a n k s o r by p h y s i c a l t r a n s f e r o f the f i s h t o t a n k s c o n t a i n i n g c o l d s e a wa t e r (io.5°c). 6 . C o n t r o l f i s h were s u b j e c t e d t o a l l o f the above w i t h t h e e x c e p t i o n o f t h e sudden t e m p e r a t u r e de-c r e a s e s ( # 5 ). I n l i e u o f t h i s r a p i d t e m p e r a t u r e change, the water t e m p e r a t u r e o f the c o n t r o l groups was a l l o w e d t o g r a d u a l l y c o o l down t o 1 1 . 0°C o v e r a t h r e e t o f o u r hour p e r i o d . 7o The s i z e ranges o f the f i s h u s e d i n t h e s e e x p e r i -ments were 5«0 cm. t o 8 . 1 cm. t o t a l l e n g t h ( 0 . macu-l o s u s ) and 5 ° 2 cm. to 8.? cm. t o t a l l e n g t h ( 0 .  s n y d e r i ) . R e s u l t s The r e s u l t s o f the p i l o t e x p e r i m e n t s i n the f i e l d a r e shown on T a b l e 1 2 . F o r experiment Number 1 , i n whi c h the f i s h were t r a n s f e r r e d d i r e c t l y from 1 1 . 5°C t o 2 3 . 5°C and k e p t I n the warm water f o r about two hours b e f o r e b e i n g s u b j e c t e d t o a sudden 1 0 , 0°C te m p e r a t u r e d e c r e a s e , m o r t a l -i t i e s were o b s e r v e d among b o t h s p e c i e s . T o t a l m o r t a l i t i e s o f 0 . s n y d e r i i n the t e s t group o c c u r r e d w i t h i n t w e n t y - f o u r hours a f t e r t h e sudden temperature d e c r e a s e . Only one 0 . maculosus ( o u t o f t h r e e ) i n the t e s t group d i e d , and t h i s m o r t a l i t y a l s o o c c u r r e d w i t h i n t w e n t y - f o u r hours a f t e r t h e sudden temperature d e c r e a s e . M o r t a l i t i e s among the two con-t r o l groups o f t h i s p i l o t experiment o c c u r r e d more t h a n t w e n t y - f o u r hours a f t e r the time a t w h i c h the maximum 8 5 t e m p e r a t u r e (23.5°C) was a l l o w e d t o g r a d u a l l y d e c r e a s e t o f i e l d t e m p e r a t u r e ( 1 1 . 5°C). A l l e x p e r i m e n t a l 0 . s n y d e r i d i e d ( t h r e e ) , w h i l e one o f t h r e e c o n t r o l 0. maculosus d i e d . T a b l e 12 . P e r c e n t M o r t a l i t y o f F i s h S u b j e c t e d t o Sudden Temperature Decrease and C o n t r o l s . E x p e r i m e n t a l C o n t r o l Oo. . O^. Oo. 0. Exper i m e n t No. maculosus s n y d e r i maculosus s n y d e r i n F i e l d 1 33.3 100.0 33.3 100.0 3*4 F i e l d 2 0.0 0.0 0.0 0.0 3X4 L a b o r a t o r y 3 — 0.0 - - 33.3 3 X 2 L a b o r a t o r y 4 0.0 0.0 0.0 0.0 6x4 The second f i e l d e x p e r i m e n t , i n whi c h the te m p e r a t u r e o f t h e p o o l c o n t a i n i n g t h e e x p e r i m e n t a l f i s h was a l l o w e d t o g r a d u a l l y i n c r e a s e from 13.5 t o 2 2 . 0 ° C and m a i n t a i n e d a t t h i s l e v e l f o r about two hours b e f o r e s u d d e n l y d r o p p i n g t h e tem-p e r a t u r e t o about 11.0°C, r e s u l t e d i n no m o r t a l i t i e s among the c o n t r o l and e x p e r i m e n t a l groups o f b o t h s p e c i e s a f t e r t w e n t y - f o u r h o u r s . I n b o t h f i e l d e x p e r i m e n t s , 0 . s n y d e r i c o n s i s t e n t l y appeared s t r e s s e d d u r i n g p e r i o d s o f h i g h e r t e m p e r a t u r e s (above 18 . 0°C). These s t r e s s r e a c t i o n s were c h a r a c t e r i z e d by r a p i d r e s p i r a t o r y movements, l i t t l e o r no pause between sequences o f r e s p i r a t o r y movements, and absence o f escape 8.6 b e h a v i o r when d i s t u r b e d . O l i g o c o t t u s maculosus d i d n o t d i s p l a y t h e s e symptoms o f s t r e s s u n t i l extreme t e m p e r a t u r e s were r e a c h e d ( a t l e a s t 20.0°C). The r e s u l t s o f the l a b o r a t o r y e x p e r i m e n t s p r o v i d e d more c o n s i s t e n t r e s u l t s . As shown i n T a b l e 12, no e x p e r i -m e n t a l m o r t a l i t i e s were o b s e r v e d i n ex p e r i m e n t Number 3 u s i n g o n l y 0. s n y d e r i . I n t h i s e x p e r i m e n t , t e m p e r a t u r e s were r a i s e d g r a d u a l l y from 11.0°C t o 22.5 - 23.5°C b e f o r e the sudden change i n tem p e r a t u r e was a p p l i e d . W i t h i n an hour a f t e r t he a p p l i c a t i o n o f sudden te m p e r a t u r e change, t h e s e e x p e r i m e n t a l group f i s h d i s p l a y e d f e e d i n g b e h a v i o r i n resp o n s e t o o c c a s i o n a l movement o f d e t r l t a l m a t e r i a l t h r o u g h the w a t e r . Of the c o n t r o l f i s h i n ex p e r i m e n t Number 3» one 0. s n y d e r i d i e d , presumably from the e f f e c t s o f the extended time a t h i g h t e m p e r a t u r e extremes d u r i n g the i n i t i a l s t a g e s o f the g r a d u a l c o o l i n g p r o c e s s (22,5°C t o about 15.0°C). D u r i n g t h e p e r i o d s o f r i s i n g (15<>0 t o 22.5°C) and s u s t a i n e d t e m p e r a t u r e (22.5 - 23»5°C), D°th e x p e r i m e n t a l and c o n t r o l groups d i s p l a y e d p r o g r e s s i v e l y I n c r e a s e d r e a c t i o n s t o tem-p e r a t u r e s t r e s s . The s i g n s o f s t r e s s a r e as d e s c r i b e d above w i t h the a d d i t i o n o f f l a r e d o p e r c u l a and s p r e a d f i n s , and o c c a s i o n a l e r r a t i c d a r t i n g movements. C o n t r o l a n i m a l s con-t i n u e d t o d i s p l a y symptoms of s t r e s s d u r i n g the f i r s t few hours o f t h e p e r i o d o f g r a d u a l l y d e c r e a s i n g t e m p e r a t u r e s ( i e . aquarium h e a t e r s o f f ) u n t i l t e m p e r a t u r e s approached the 13.0 - 11.0°C l e v e l . In experiment Number 4, both species were tested simultaneously within twelve hours of capture at the r e -search s i t e ( f i e l d temperature 10.5°C). A greater number of animals were avail a b l e f o r t h i s experiment. (Six con t r o l J 0. maculosus and s i x control 0. snyderi; s i x experimental 0. maculosus and six experimental 0. snyderi). No mortal-i t i e s among the control and experimental animals of both species were observed f o r an eight-hour period following the time at which the sudden temperature decrease was applied to the experimental group. Among the experimental f i s h , no i signs of d i s t r e s s were observed during the eight-hour obser-vation period. Signs of stress were observed among the con-t r o l groups of both species f o r at l e a s t three hours a f t e r the point at which the temperature was allowed to gradually cool. These signs d i d not cease u n t i l a temperature of 1 4 . 8 ° C was reached. Stress reactions were observed among a l l groups dur-ing the periods of r i s i n g (15.0 to 22.5+ ° C ) and sustained (22.5 - 23.5 ° C ) temperatures. Experiment Number 4 was f u r -ther characterized by much locomotor a c t i v i t y by both spe-cies during periods of stress. In a l l "temperature shock" experiments i n which both species were tested simultaneously, 0 . snyderi i n v a r i a b l y appeared to become stressed e a r l i e r and to a much greater extent than d i d 0 . maculosus. 88 C. The E f f e c t o f Low Temperature on 0. maculosus and 0. s n y d e r l . F i e l d d a t a i n d i c a t e d t h a t w i n t e r t e m p e r a t u r e s o f upper t i d e p o o l s were g e n e r a l l y much l e s s t h a n t h o s e o f l o w e r t i d e p o o l s ( F i g u r e 23). Bottom t e m p e r a t u r e s o f l o w e r t i d e -p o o l s t e n d e d t o be s t a b l e and a p p r o x i m a t e d t h a t o f the on-shore seawater (8.0 - 10o0°C) o I n upper p o o l s , bottom tem-p e r a t u r e s i n t h e o r d e r o f 2.0°C have been r e c o r d e d , w h i l e t e m p e r a t u r e s as low as 0.5°C have been i n f r e q u e n t l y o b s e r v e d . T h i n l a y e r s o f i c e c o v e r i n g t i d e p o o l s were o b s e r v e d on s e v -e r a l o c c a s i o n s d u r i n g t h e w i n t e r o f 1968. I f t e m p e r a t u r e d i f f e r e n c e s a r e i m p o r t a n t i n c o n t r o l -l i n g the d i s t r i b u t i o n o f the s p e c i e s , one would e x p e c t c o r -r e s p o n d i n g d i f f e r e n c e s between th e two s p e c i e s i n r e s i s t a n c e t o low t e m p e r a t u r e s . E x p e r i m e n t s were co n d u c t e d t o d e t e r m i n e the i m p o r t a n c e o f low t e m p e r a t u r e s on the d i s t r i b u t i o n o f the two s p e c i e s . Groups o f f i s h c a p t u r e d a t t h e r e s e a r c h s i t e i n the w i n t e r were a c c l i m a t e d t o 5«0° and 16.J5°C f o r a p e r i o d o f t h r e e weeks a t a 30.5 °/oo s a l i n i t y . Only a s m a l l number o f f i s h were a v a i l a b l e f o r t e s t i n g as 0. s n y d e r i d i d n o t g e n e r a l l y s u r v i v e w e l l a t t h e s e p a r t i c u l a r a c c l i m a t i o n tem-p e r a t u r e s . A t 5»0°C a c c l i m a t i o n t e m p e r a t u r e , 0. s n y d e r i c e a s e d f e e d i n g a f t e r a few days and became q u i e s c e n t . O l i g o c o t t u s maculosus a t the same a c c l i m a t i o n t e m p e r a t u r e c o n t i n u e d t o f e e d though a t g r e a t l y r e d u c e d r a t e s . I t a l s o became i n a c t i v e d u r i n g c o l d t e m p e r a t u r e a c c l i m a t i o n . W i n t e r - c a u g h t O l i g o c o t t u s s n y d e r i h e l d a t l6.5°C g e n e r a l l y became p r o g r e s s i v e l y weaker d u r i n g t h e p e r i o d o f a c c l i m a t i o n . However, t h o s e s u r v i v i n g the a c c l i m a t i o n p e r -i o d a p peared t o be i n good p h y s i c a l c o n d i t i o n . O l i g o c o t t u s  maculosus had l i t t l e t r o u b l e a c c l i m a t i n g t o l6.5°C. I n c o n d u c t i n g t h e s e e x p e r i m e n t s , t e c h n i c a l d i f f i -c u l t i e s w i t h t h e r e f r i g e r a t i o n u n i t made i t i m p o s s i b l e t o m a i n t a i n a s t e a d y t e m p e r a t u r e l e v e l . Thus e x p e r i m e n t a l t e m p e r a t u r e s f l u c t u a t e d o v e r a p e r i o d o f s e v e r a l days (-1.5 t o 5»0°C). N e v e r t h e l e s s , some i n f o r m a t i o n on t h e r e l a t i v e c a p a c i t i e s o f t h e two s p e c i e s t o r e s i s t c o l d was o b t a i n e d . T e s t P r o c e d u r e 1. O l l g o c o t t u s maculosus and 0. s n y d e r i were p l a c e d i n p l a s t i c p a i l s (about two and a h a l f g a l l o n s ) - c o n -t a i n i n g s e a w a t e r a t the p a r t i c u l a r a c c l i m a t i o n t o w h i c h the f i s h were t o be h e l d , eg, 5«0 and l6.5°C. 2. The sea water was c o n s t a n t l y a e r a t e d and the s a l i n i t y l e v e l a d j u s t e d t o 30.5 °/oo. 3. The f i s h were p l a c e d I n a r e f r i g e r a t o r s e t a t 2.0°G. 4-. P e r i o d i c checks were made on m o r t a l i t i e s , tempera-t u r e s and g e n e r a l b e h a v i o r . 5. The time a t which a f i s h no l o n g e r responded t o p r o b i n g and showed no s i g n s o f r e s p i r a t o r y movements was n o t e d as the time o f d e a t h . 6.o The e x p e r i m e n t s were c o n t i n u e d u n t i l a l l specimens o f b o t h s p e c i e s had d i e d . 7 . The t o t a l l e n g t h o f the f i s h u s e d I n t h e s e e x p e r i -ments were 4 . 3 5 cm. t o 6.04 cm. f o r 0 . maculosus and 4 . 6 0 cm. t o 7 * 3 5 cm. f o r 0 . s n y d e r i . R e s u l t s The r e s u l t s w h i c h a r e summarized on T a b l e 13 show t h a t Oo maculosus can cope w i t h low t e m p e r a t u r e extremes whereas 0 e s n y d e r i c a n n o t . The d i f f i c u l t y e x p e r i e n c e d by Oo s n y d e r i i n a c c l i m a t i n g t o 5<>0oC over a t h r e e week p e r i o d s u p p o r t s t h i s c o n c l u s i o n . I n t h e s e e x p e r i m e n t s , m o r t a l -i t i e s d i d n o t o c c u r u n t i l a t l e a s t t w e n t y - f o u r hours exposure t o the t e s t t e m p e r a t u r e 0 T a b l e 1 3 . P e r c e n t M o r t a l i t y o f 0 . maculosus and 0 e s n y d e r i S u b j e c t e d t o a V a r y i n g C o l d Environment ( 5 . 0°C t o - 1 . 5°C). A c c l i m a t i o n Temperature 0 . maculosus 0 . s n y d e r i n 5o0°C 1 6 . 5°C 0 . 0 0 . 0 1 0 0 o 0 1 0 0 . 0 4,4 ^.3 The R e l a t i o n s h i p o f the T i d e C y c l e t o S u b s u r f a c e T i d e p o o l Temperatures from 19 December, 1968 t o 27 December, 1968 a t P o r t Renfrew. H i g h T i d e p o o l = 9.5" l e v e l Low T i d e p o o l =6.0° l e v e l N o o n N N N N I T i d e p o o l T e m p e r a t u r e T i d e h e i g h t ( F e e t ) D a y ( J u l i a n d a t e ) Low tide pool High tide pool D. The E f f e c t o f Warm'Temperatures'on the Depth D i s t r i b u t i o n o f O l l g o c o t t u s s n y d e r i . The e x p e r i m e n t s on t e m p e r a t u r e t o l e r a n c e and r e s i s t -ance u n e q u i v o c a l l y demonstrated t h e g r e a t d i f f e r e n c e s i n r e s p o n s e t o t e m p e r a t u r e extremes between O l l g o c o t t u s macu-l o s u s and 0. s n y d e r l . S i n c e t h e s e f i s h a r e m o t i l e , an a t t e m p t was made t o examine t h e i r a b i l i t y t o b e h a v i o r a l l y t h e r m o r e g u l a t e , u s i n g the depth g r a d i e n t - t i d e tank (see S e c t i o n I) w i t h a p p r o -p r i a t e m o d i f i c a t i o n s . U n f o r t u n a t e l y , • o n l y one s e r i e s o f e x p e r i m e n t s u s i n g 0. s n y d e r i c o u l d be pe r f o r m e d . The c o m p l e t e d e x p e r i m e n t c o n s i s t e d o f o b s e r v i n g and comparing the d i s t r i b u t i o n p a t t e r n s o f 0. s n y d e r i among t h r e e s i m u l a t e d t i d e p o o l s a t d i f f e r e n t v e r t i c a l h e i g h t l e v -e l s b e f o r e and a f t e r t h e a p p l i c a t i o n o f h i g h t e m p e r a t u r e (23.5°G) t o the uppermost " t i d e p o o l . " M a t e r i a l s . Methods and. T e s t P r o c e d u r e s .1. The d e p t h g r a d i e n t - t i d e t a n k was m o d i f i e d , by a d d i n g 20-watt aquarium h e a t e r s f i t t e d w i t h s t y r o f o a m f l o a t s t o the two upper s i m u l a t e d t i d e p o o l s . 2.. The r e s p e c t i v e aquarium h e a t e r s were a t t a c h e d t o a v e r t i c a l g u i d e l i n e w h i c h p r e v e n t e d h o r i z o n t a l move-ment b u t p e r m i t t e d v e r t i c a l movement i n t h e w a t e r column i m m e d i a t e l y above t h e " t i d e p o o l " d u r i n g t h e r i s i n g and d r o p p i n g " t i d e s . " 3 . Temperature probes were p l a c e d a t a l l l e v e l s i n the tan k and t e m p e r a t u r e s were c o n s t a n t l y m o n i t o r e d on a m u l t i - c h a n n e l recorder,, 4. N i n e f i s h were d i s t r i b u t e d i n e q u a l numbers ( t h r e e ) i n each o f the t h r e e " t i d e p o o l s " p r i o r t o the s t a r t o f the experiment,, 5o A f t e r a w a i t i n g p e r i o d o f about t w e l v e h o u r s , a s i m -u l a t e d s e m i - d i u r n a l t i d e c y c l e was I n i t i a t e d , The t i d a l range was from 1 B 0 " t o 5° 6 " . 6c F o r a p e r i o d o f f o u r days, the numbers o f f i s h i n each o f the p o o l s a t the end o f each "low t i d e " was r e c o r d e d . 7 . D u r i n g t h i s f o u r - d a y p e r i o d ' t e m p e r a t u r e d i f f e r e n c e s were m i n i m i z e d by c o o l weather. Temperatures ranged from 1 1 . 5 t o 1 3 . 5 ° C . 8. A f t e r t h i s p e r i o d o f m i n i m a l t e m p e r a t u r e d i f f e r e n c e s , the h e a t e r i n the uppermost " t i d e p o o l " was t u r n e d on d u r i n g the p e r i o d s o f " l o w t i d e s . " 9 . The numbers o f f i s h l n the t h r e e p o o l s a t "low t i d e " were r e c o r d e d d u r i n g the p e r i o d s o f h i g h t e m p e r a t u r e s l n the upper p o o l . 1 0 . The t e m p e r a t u r e i n the h i g h e s t p o o l d u r i n g p e r i o d s o f emergence was g r a d u a l l y r a i s e d from about 1 3 . 0°C to 23»5°C o v e r a f o u r - h o u r p e r i o d w h i l e t h e tempera-t u r e s i n t h e two l o w e r p o o l s remained more o r l e s s c o n s t a n t a t about 1 3 . 0°C. 95 11. The h i g h t e m p e r a t u r e o f the uppermost p o o l was main-t a i n e d f o r f o u r t o s i x hours a f t e r w h i c h time t h e . p o o l was i n u n d a t e d by the r i s i n g " t i d e . " 12. The numbers o f f i s h i n the r e s p e c t i v e " t i d e p o o l s " a t "low t i d e " were r e c o r d e d o v e r a f o u r - d a y p e r i o d a f t e r a t h r e e - d a y l e a r n i n g p e r i o d . 13. The depth g r a d i e n t - t i d e tank was k e p t c o n s t a n t l y i l -l u m i n a t e d and t h e w a t e r c o n s t a n t l y a e r a t e d d u r i n g t h e c o u r s e o f t h e ex p e r i m e n t . 14. The s i z e range o f t h e f i s h used i n t h i s e x p e r i m e n t was 4,9 cm. t o 9»5 cm. t o t a l l e n g t h . R e s u l t s The d i s t r i b u t i o n o f 0. s n y d e r i i n the t h r e e s i m u l a t e d t i d e p o o l s b e f o r e the a p p l i c a t i o n o f h i g h t e m p e r a t u r e t o the uppermost p o o l was b i m o d a l w i t h the g r e a t e s t number o f oc-c u r r e n c e s o b s e r v e d i n the l o w e s t and h i g h e s t p o o l s , w i t h the l e a s t number o b s e r v e d i n the m l d l e v e l p o o l . The r a t i o o f the f r e q u e n c i e s o f the n i n e f i s h was 11:3:19« I n terms o f a h i g h v s . low l e v e l p o o l , t h e d i s t r i b u t i o n i s s i m i l a r t o the depth d i s t r i b u t i o n o f 0. s n y d e r i o b t a i n e d i n e a r l i e r e x p e r i m e n t s i n whi c h the depth d i s t r i b u t i o n was found t o be the same f o r s h a l l o w v s . deep r e g i o n s o f the de p t h g r a d i e n t -t i d e tank d u r i n g " h i g h t i d e . " S i n c e q u a n t i t a t i v e d a t a on l e a r n i n g ( c o n d i t i o n i n g , e x t i n c t i o n , e t c . ) by c o t t i d f i s h e s i s v i r t u a l l y n o n - e x i s t e n t and s i n c e t h e r e i s a h i g h degree o f v a r i a t i o n i n d a t a o f t h i s k i n d f o r o t h e r s p e c i e s ( B u l l , 1957)t the p e r i o d a l l o t t e d f o r t he f i s h t o a s s o c i a t e h i g h t e m p e r a t u r e s w i t h the upp e r -most " t i d e p o o l " was a r b i t r a r i l y s e t a t t h r e e days w h i c h r e -p r e s e n t s a t o t a l o f t h r e e h i g h t e m p e r a t u r e a p p l i c a t i o n s ( i e . t h r e e " l o w t i d e " p e r i o d s ) . T h i s time p e r i o d was p a r t i a l l y de-c i d e d on the b a s i s o f o b s e r v a t i o n s by t h i s w r i t e r and Boyd (1969» p e r s o n a l communication) on the f e e d i n g b e h a v i o r o f the two s p e c i e s o f O l i g o c o t t u s i n w h i c h i t was found t h a t b o t h s p e c i e s c o u l d be r a p i d l y c o n d i t i o n e d t o w a t e r s u r f a c e d i s t u r b a n c e s p r i o r t o f e e d i n g . The r e s u l t i n g p o s t - l e a r n i n g p e r i o d f r e q u e n c i e s among the t h r e e s i m u l a t e d t i d e p o o l s were v e r y low f o r the uppermost and m i d l e v e l p o o l s and v e r y h i g h f o r the lowermost p o o l . The r a t i o o f t h e f r e q u e n c i e s o f the h i g h , mid and low p o o l s was 8:7:^3 compared t o the 11:319 r a t i o o b t a i n e d b e f o r e ex-treme t e m p e r a t u r e s were a p p l i e d t o the uppermost " t i d e p o o l . " C h i square a n a l y s e s o f the two r a t i o s i n d i c a t e s i g n i f i c a n t d i f f e r e n c e s a t the 0.001 p r o b a b i l i t y l e v e l (see T a b l e I k ) , These d a t a i n d i c a t e t h a t 0. s n y d e r i has the a b i l i t y t o t h e r m o r e g u l a t e b e h a v i o r a l l y and t o a v o i d t e m p e r a t u r e r e -gimes w h i c h may cause p h y s i o l o g i c a l s t r e s s ( L e . upper l e v e l t i d e p o o l s ) . The f a c t t h a t 23«5°C te m p e r a t u r e s caused s t r e s s on t h i s s p e c i e s was f u r t h e r documented by o b s e r v a t i o n s o f acu t e l o s s o f e q u i l i b r i u m by two f i s h t r a p p e d i n the upper-most p o o l under h i g h t emperature c o n d i t i o n s (23»5°C) from f o u r t o s i x h o u r s . One o f th e s e i n d i v i d u a l s d i e d s e v e r a l days l a t e r i n the t e s t tank. A l l o t h e r f i s h appeared t o be i n f a i r t o good c o n d i t i o n a f t e r the ex p e r i m e n t and s u r v i v e d 97 f o r s e v e r a l weeks I n h o l d i n g t a n k s a t 11.5°C. No e x p e r i m e n t s were c o n d u c t e d w i t h 0. maculosus. T a b l e 14. . •'. D i s t r i b u t i o n o f 0. s n y d e r l i n S i m u l a t e d T i d e p o o l s B e f o r e and A f t e r the A p p l i c a t i o n o f Heat. 5 f e e t 3 f e e t 1 f o o t " H i g h t i d e p o o l " " M i d l e v e l p o o l " "Low t i d e p o o l " B e f o r e a p p l i c a t i o n o f h e a t • •. i :. (11.5-13.5°C) 11 3 19 A f t e r a p p l i c a t i o n o f h e a t . •• (23.5°c) 8 •? 43 H Q = 11:3:19 = 8:7:43 ( X 2 ) P = 0.001 V I I . Food I n an e a r l i e r s t u d y (Nakamura, u n p u b l i s h e d d a t a ) , the f o o d o f 0. maculosus and 0. s n y d e r i c o l l e c t e d from t i d e p o o l s a t v a r i o u s t i m e s o f the y e a r was examined t o d e t e r m i n e whether " i n t e r a c t i v e s e g r e g a t i o n " ( N i l s s o n , 1955. 1958, I960, 1965) o r " s e p a r a t i o n o f f o o d s p e c t r a " ( N i k o l s k i l , 1963) between two c l o s e l y r e l a t e d s p e c i e s o c c u r r e d as a r e s u l t o f i n t e r -s p e c i f i c c o m p e t i t i o n f o r f o o d . The d a t a from t h i s s t u d y were a n a l y s e d i n terms o f r e l a t i v e p e r c e n t a g e c o m p o s i t i o n * o f t o t a l d i e t and p e r c e n t a g e f r e q u e n c y * * o f o c c u r r e n c e o f s p e c i f i c f o o d organisms i n stomachs c o n t a i n i n g f o o d . B o t h s p e c i e s g e n e r a l l y f e e d upon the same f o o d , the major Items b e i n g amphipods, Iso p o d s , copepods, c h l r o n o m i d l a r v a e and a n n e l i d s ( F i g u r e 24, T a b l e s 15, 16), O t h e r f o o d s such as o s t r a c o d s , decapods, c a p r e l l i d s and m o l l u s c s were o f minor i m p o r t a n c e f o r b o t h s p e c i e s as they c o m p r i s e d o n l y a v e r y s m a l l p a r t o f the t o t a l d i e t s and were i n f r e q u e n t l y found i n stomach samples. Q u a l i t a t i v e l y , t h e o n l y d i f f e r -ence i n t h e d i e t s o f the two s p e c i e s was t h a t t i n y f i s h were e a t e n o n l y by 0. maculosus. Q u a n t i t a t i v e d i f f e r e n c e s were most a p p a r e n t i n t h e consumption o f copepods and c h l r o n o m i d l a r v a . These organisms * P e r c e n t C o m p o s i t i o n = P e r c e n t a g e o f the v a r i o u s i t e m s mak-i n g up t h e t o t a l d i e t . ** P e r c e n t Frequency o f O c c u r r e n c e = P e r c e n t a g e o f t o t a l number o f stom-achs c o n t a i n i n g a p a r t i c u l a r f o o d i t e m . were p r e y e d upon t o a g r e a t e r e x t e n t by 0. maculosus„ L a r g e d i f f e r e n c e s l n the consumption o f amphipods and n e r e i d worms, w h i c h were c o n s i d e r e d t h e two most i m p o r t a n t f o o d organisms, f o r e i t h e r s p e c i e s , were not o b s e r v e d . A Comparison o f the D i e t s o f C o h a b i t i n g O l l g o c o t t u s maculosus and 0. s n y d e r i . Top = % R e l a t i v e C o m p o s i t i o n o f T o t a l D i e t . Bottom = % Frequency o f O c c u r -r e n c e o f Organisms i n Stomachs C o n t a i n -i n g Food. AMPHIPODA ISOPODA C O P E P O D A ANNELIDA INSECTA DECAPODA OSTRACODA C A P R E L L A MOLLUSCA PISCES 100 % 1 0 0 % 0. maculosus Q snyderi AMPHIPODA ISOPODA COPEPODA ANNEL IDA INSECTA DECAPODA O S T R A C O D A C A P R E L L A MOLLUSCA P I SCES 1 0 0 % 1 0 0 % T a b l e 15. R e l a t i v e P e r c e n t C o m p o s i t i o n o f D i e t s o f 0. maculosus and 0. s n y d e r i (upper f i g u r e = 0 a maculosus, l o w e r f i g u r e = 0. s n y d e r i ) Date P o o l n Amphlpoda I s o p o d a Copepoda A n n e l i d s I n s e c t a C a p r e l l a O s t r a c o d a Decapoda M o l l u s c a P i s c e s 3 Feb C 16 59o5 ,4.1 14 . 9 2.7 12.2 0.0 2.7 1.4 2.7 0 .0 67 1 5 7 d 14.3 0.0 28.6 0.0 0.0 0 .0 0 .0 0 . 0 0 .0 15 Mar D 17 6 0 . 3 12.3 1.4 15.1 4 . 1 0.0 0 .0 6.8 0 . 0 0 .0 67 4 36 .4 9.1 9.1 18 . 2 0.0 0 .0 9.1 18 . 2 . 0 . 0 0 .0 15 Mar B 17 34.3 1 2 0 4 36.2 10.5 1.9 0.0 1.0 1.9 0 . 0 0 . 0 67 1 85.7 0 .0 0.0 0.0 14 . 3 0.0 0.0 0 . 0 0 . 0 0 .0 17 May B 21 5 .6 2 ,4 8 6 . 6 1.2 3 .0 0.0 0.2 0.2 0 . 6 0.2 66 3 l 4 . 1 74.6 7.0 0 .0 1.4 0.0 0.0 0 . 0 0 .0 0 .0 5 June A 16 24 . 4 1.3 63.8 1.8 6.3 0.0 1.3 0 . 3 0 .3 0.7 66 21 57.5 18.3 9.2 7.8 3.3 0.2 0.7 0.7 2.6 0 .0 1 Oct B 29 12 0 6 2,0 77 0 5 2.5 2.3 0.0 0.0 2 .5 0 .0 0.7 66 8 62.5 12.5 2 8 . 1 12.5 0.0 12.5 0.0 0 .0 0 .0 0 . 0 12 Dec A 4 82 . 5 10.7 1.9 1.9 0 .0 1.9 0.0 0 .9 0 . 0 0 .0 66 69 78.1 5.1 1.7 14 . 6 0 . 0 0.2 0.0 0 .4 0 . 4 0 . 0 P o o l s Combined 117 2 3 . 6 3.5 61.4 4 . 3 4 . 3 0.1 0.7 1.0 0 . 4 0.4 107 70.0 11.8 3 .6 12.2 0.6 0.5 0.2 0 .6 0 . 6 0 . 0 H O T a b l e 16. P e r c e n t Frequency o f O c c u r r e n c e o f Foods i n the Stomachs o f Oo maculosus and 0. s n y d e r i (upper f i g u r e = 0 9 maculosus, l o w e r f i g u r e = 0. s n y d e r i Date P o o l n Amphipoda I s o p o d a Copepoda A n n e l i d s I n s e c t a C a p r e l l a O s t r a c o d a Decapoda M o l l u s c a P i s c e s 3 Feb C 1 6 5 7 . 1 5 7 . 1 1 4 . 3 1 4 . 3 1 4 . 3 0 . 0 1 4 . 3 7 . 1 1 4 . 3 0 . 0 67 1 1 0 0 . 0 1 0 0 . 0 0 . 0 1 0 0 o 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 15 Mar D 17 7 6 . 4 4 1 . 2 5 . 9 5 2 . 9 1 1 . 8 0 . 0 0 . 0 2 4 , 4 .0.0 0 . 0 67 4 5 0 . 0 2 5 . 0 2 5 . 0 5 0 . 0 0 . 0 0 . 0 2 5 . 0 5 0 . 0 0 . 0 0 . 0 15 Mar B 17 7 0 . 9 4 7 . 1 3 5 . 0 4 7 . 1 1 1 . 8 0 . 0 5 . 9 1 1 . 8 0 . 0 0 . 0 67 1 1 0 0 . 0 0 . 0 0 . 0 0 . 0 1 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 17 May B 2 1 65.O 4 5 . 0 7 5 . 0 2 5 . 0 4 0 . 0 0 . 0 5 . 0 5 . 0 1 0 . 0 5 . 0 6 6 3 1 0 0 . 0 1 0 0 . 0 3 3 . 0 0 . 0 3 3 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 5 June A 1 6 9 3 . 8 3 1 . 3 7 5 . 0 4 3 . 8 81.3 0 . 0 2 5 , 0 1 2 . 5 12 0 5 2 5 . 0 6 6 2 1 9 0 . 4 4 7 . 6 1 9 . 0 5 7 . 1 1 9 . 0 0 . 0 4 . 8 4 . 8 1 9 . 0 0 . 0 1 Oct B 29 < 6 5 . 5 2 4 . 1 2 7 . 6 2 0 . 7 6 . 9 0 . 0 0 . 0 2 0 . 7 \ 0 . 0 6 . 9 6 6 8 8 7 . 5 2 5 . 0 3 7 . 5 3 7 . 5 0 . 0 1 2 . 5 0 . 0 0 . 0 0 . 0 0 . 0 12 Dec A 4 1 0 0 o 0 5 0 . 0 5 0 . 0 5 0 . 0 0 . 0 2 5 . 0 0 . 0 2 5 . 0 0 . 0 0 . 0 66 6 9 9 1 . 3 3 1 - 9 1 4 . 5 8 1 . 5 0 . 0 1 . 4 0 . 0 4 . 3 4 . 3 0 . 0 P o o l s 1 5 . 4 3 . 4 6 . 0 Combined 117 7 1 . 8 3 1 . 6 3 9 . 3 3 3 . 3 2 5 . 6 1 . 7 6 . 8 1 0 7 8 9 o 6 3 6 . 4 1 7 . 8 6 9 . 2 6 . 5 1 . 9 1 . 9 5 . 6 2 . 8 0 . 0 h c 104 D i s c u s s i o n The r e l a t i v e i m p o r t a n c e o f the v a r i o u s e n v i r o n m e n t a l f a c t o r s a f f e c t i n g and m a i n t a i n i n g the m i c r o d i s t r i b u t i o n s o f O l l g o c o t t u s maculosus and 0. s n y d e r i v a r y a c c o r d i n g t o the s p e c i e s . O l l g o c o t t u s maculosus . A t P o r t Renfrew d u r i n g low t i d e , 0. maculosus i s e x t r e m e l y abundant i n upper t i d e p o o l s and o c c u r s commonly i n l o w e r t i d e p o o l s . Because o f t h i s wide d i s t r i b u t i o n , one would e x p e c t t h i s s p e c i e s t o d i s p l a y a wide range o f d e p t h p r e f e r e n c e s i n the l a b o r a t o r y e x p e r i m e n t s . Such was not t h e case as 0. maculosus showed a s t r o n g p r e f e r e n c e f o r s h a l l o w d e p t h s . T h i s a p p a r e n t c o n t r a d i c t i o n may be e x p l a i n e d on the b a s i s o f the I n c r e a s e d l o c o m o t o r a c t i v i t y d u r i n g p e r i o d s o f " t i d a l change." A t such t i m e s , 0. maculosus o c c u r s m o s t l y i n the upper one f o o t r e g i o n s o f the t e s t t a n k . Under f i e l d c o n d i t i o n s , t h i s phenomenon of c o n c e n t r a t e d numbers and i n -c r e a s e d l o c o m o t o r a c t i v i t y w i t h i n t h e upper one f o o t r e g i o n s p r o v i d e s a means f o r the wide d i s t r i b u t i o n o f t h e f i s h as i n a sense t h e f i s h f o l l o w the w a t e r l e v e l . A p e r i o d i c i t y i n l o c o m o t o r a c t i v i t y a s s o c i a t e d w i t h the t i d a l c y c l e has been w e l l documented f o r 0. maculosus by Green ( l ° 6 8 ) . G i b s o n (1965, 1966) has a l s o d e m o n s t r a t e d a s i m i l a r t i d e - a s s o c i a t e d r h y t h m i c i t y i n l o c o m o t o r a c t i v i t y and homing b e h a v i o r f o r A c a n t h o c o t t u s [= Enophrys] b u b a l l s , a n o t h e r c o t t i d species,, C l l n o c o t t u s a n a l l s , an e a s t e r n P a c i f i c t i d e p o o l c o t t i d , has been s i m i l a r l y o b s e r v e d t o i n v a d e and r e t r e a t from upper l e v e l t i d e p o o l s w i t h the r i s i n g and e b b i n g t i d e s ( W i l l i a m s , 1957). Thus i t i s c o n c l u d e d t h a t t h i s i n t e r a c t i o n between s h a l l o w depth p r e f e r e n c e and i n c r e a s e d l o c o m o t o r a c t i v i t y accompanying c h a n g i n g t i d e l e v e l s c o n t r i -b u t e s t o the wide low t i d e d i s t r i b u t i o n o f 0 0 m a c u l o s u s . Under e x p e r i m e n t a l c o n d i t i o n s the d i s t r i b u t i o n o f 0. maculosus i n the presence o f 0. s n y d e r l was more u n i f o r m a c r o s s t h e d e p t h b l o c k s o f the e x p e r i m e n t a l depth g r a d i e n t and was s i g n i f i c a n t l y d i f f e r e n t from t h a t when t e s t e d a l o n e . I n no i n s t a n c e was any o v e r t a g g r e s s i v e b e h a v i o r o b s e r v e d f o r e i t h e r s p e c i e s . I t i s s p e c u l a t e d t h a t t h i s d i s t r i b u t i o n a l s h i f t may be t h e r e s u l t o f the t o t a l numbers o f i n d i v i d u a l s e x c e e d i n g some t h r e s h o l d l e v e l f o r 0. maculosus, w h i c h e l i c i t e d d i s p e r s i o n o f t h i s s p e c i e s t o low d e n s i t y r e g i o n s o f the t a n k . S i n c e f i e l d o b s e r v a t i o n s a t P o r t Renfrew i n d i c a t e t h e h i g h e s t d e n s i t i e s o f f i s h a r e i n the upper t i d e p o o l s (Green, 1968), a mechanism such as t h i s may a l s o c o n t r i b u t e t o t h e n a t u r a l s p r e a d o f 0. imaculosus t o l o w e r p o o l s . I n e x p e r i m e n t s c o n c e r n i n g s u b s t r a t e and c o v e r , 0.  maculosus shows a s t r o n g s e l e c t i o n f o r a r o c k y m i c r o e n v i r o n -ment, a moderate p r e f e r e n c e f o r a dense e e l g r a s s m i c r o -environment and a low p r e f e r e n c e f o r an open sandy m i c r o -h a b i t a t . The o r d e r o f t h e s e p r e f e r e n c e s c o i n c i d e s w i t h the f i e l d where 0. maculosus i s most abundant i n p o o l s i n which r o c k s and c r e v i c e s p r o v i d e the main s o u r c e o f p r o t e c t i v e 106 c o v e r - T h i s i s n o t a r i g i d r e q u i r e m e n t s though, s i n c e i t can l i v e i n p o o l s o f a l l t y p e s , i n c l u d i n g t h o s e w i t h dense e e l g r a s s beds and open sandy a r e a s . P o s s i b l y the v a r i e d c o l o r s and c o l o r p a t t e r n s (brown, m o t t l e d g r e y and b l a c k , g r e y - g r e e n ) o f t h i s s p e c i e s e n a b l e s i t t o be camouflaged a g a i n s t the back-grounds o f most t i d e p o o l s . I t i s w e l l known t h a t camouflage and m i m i c r y can be o f g r e a t a d a p t i v e v a l u e t o a prey as w e l l , as p r e d a t o r s p e c i e s . Thus the m i c r o d i s t r i b u t l o n o f 0. macu-l o s u s need n o t be r i g i d l y bound by i t s p a r t i c u l a r p r e f e r e n c e s f o r a r o c k y m i c r o e n v i r o n m e n t . When th e s e same s u b s t r a t e - c o v e r p r e f e r e n c e s f o r 0. maculosus were t e s t e d w i t h 0. s n y d e r i p r e s e n t , the r e s u l t s showed d i f f e r e n c e s from i t s p r e f e r e n c e s when a l o n e . However, s i n c e the o r d e r and degree o f p r e f e r e n c e s were so s i m i l a r and because no o v e r t a g g r e s s i v e b e h a v i o r was o b s e r v e d d u r i n g t h e e x p e r i m e n t s , i t may be c o n c l u d e d t h a t the c h o i c e o f m i c r o -h a b i t a t by 0. maculosus i s n o t g r e a t l y changed by the p r e s e n c e o f 0. s n y d e r i . W i t h r e s p e c t t o s a l i n i t y , i t has been e s t a b l i s h e d t h a t i n most t i d e p o o l s a t P o r t Renfrew; 1) h y p e r s a l i n e c o n d i t i o n s r e s u l t i n g from e v a p o r a t i o n r a r e l y , i f e v e r , o c c u r ; 2) hypo-s a l i n e s i t u a t i o n s w h i c h do o c c u r u s u a l l y e x i s t under s t r a t i -f i e d c o n d i t i o n s , e x c e p t where s m a l l p o o l s l i e i n the d i r e c t p a t h o f r u n o f f w a t e r ; and 3) s u b s u r f a c e s a l i n i t i e s o f t i d e -p o o l s do n o t t e n d t o v a r y e i t h e r s e a s o n a l l y o r w i t h d i f f e r -ences i n v e r t i c a l p o s i t i o n . Because 0. maculosus i s b a s i c a l l y bottom d w e l l i n g , low s a l i n i t y s h o u l d not be s i g n i f i c a n t i n 107 a f f e c t i n g I t s t i d e p o o l d i s t r i b u t i o n . T o t a l l y h y p o s a l i n e t i d e -p o o l s ( i . e . h a l o c l i n e absent) may o c c u r under s p e c i a l c o n d i -t i o n s a t P o r t Renfrew, and the p o s s i b i l i t y o f 0. maculosus e n c o u n t e r i n g v e r y low s a l i n i t i e s i s p r e s e n t . I n s m a l l s h a l l o w p o o l s i n the p a t h o f r u n o f f c h a n n e l s , s a l i n i t y l e v e l s may drop below 4.0 °/oo, though most a r e i n t h e o r d e r o f 7.5 % o . O l l g o c o t t u s maculosus can s u r v i v e h y p o s a l i n e c o n d i t i o n s (7.5 °/oo) f o r p e r i o d s as l o n g as 192 h o u r s , t h e r e f o r e hypo-s a l i n e exposure below t h i s p o i n t w h i c h i s e q u i v a l e n t t o about the 9.0 f o o t l e v e l , w ould n o t be o f such d u r a t i o n as t o be d i r e c t l y l e t h a l . F u r t h e r , the abundance o f 0. maculosus i n t i d e p o o l s above th e 9°0 f o o t l e v e l s u g g e s t s t h a t exposure t o low s a l i n i t i e s (7«5 °/oo) f o r p e r i o d s even l o n g e r t h a n 192 hours may be o f no d i r e c t consequence. O l i g o c o t t u s maculosus does n o t o c c u r i n r o c k p o o l s above the 12.4 f o o t l e v e l a t P o r t Renfrew. Such p o o l s a r e e x t r e m e l y h y p o s a l i n e (\7°5 °/oo) and remain so f o r l o n g p e r i o d s as they a r e n o t d i r e c t l y a f -f e c t e d by the t i d a l c y c l e . A " c r i t i c a l s a l i n i t y range" (5«0 t o 8.0 °/oo) w h i c h a c t s as a boundary between organisms o f f r e s h and s a l t w a t e r o r i g i n has been p o i n t e d out by K h l e b o v i c h (1968, 1969). P e a r s e and G unter (1957) s t a t e t h a t f i e l d d i s -t r i b u t i o n s t u d i e s show t h a t the numbers o f s p e c i e s o f marine organisms d e c r e a s e s as the s a l i n i t y d e c r e a s e s and t h a t the b u l k o f the p h y s i o l o g i c a l e v i d e n c e s u g g e s t s t h a t low s a l i n i t i e s a r e d e f i n i t e l y a l i m i t i n g f a c t o r . A l t h o u g h t h i s g e n e r a l i z a t i o n may be q u e s t i o n e d because o f numerous e x c e p t i o n s and because s p e c i f i c e n v i r o n m e n t a l f a c t o r s do n o t a f f e c t d i f f e r e n t s p e c i e s 108 l n the same way o r t o th e same degree, i t I s s u g g e s t e d t h a t the l i m i t a t i o n o f 0. maculosus t o o n l y t h o s e p o o l s i n f l u e n c e d by the t i d a l c y c l e i s due t o the c o n s t a n t h y p o s a l i n e c o n d i -t i o n s o f " s u p r a l i t t o r a l " p o o l s , H y p e r s a l i n e c o n d i t i o n s w h i c h o c c u r i n t h e s o u t h e r n p a r t o f i t s g e o g r a p h i c range do n o t ap-pear t o l i m i t i t s southward d i s t r i b u t i o n ( M o r r i s , i960) Temperature, an e n v i r o n m e n t a l f a c t o r i m p o r t a n t t o most p o l k i l o t h e r m i c a n i m a l s , v a r i e s g r e a t l y i n t i d e p o o l s a t P o r t Renfrew a c c o r d i n g t o t h e i r v e r t i c a l p o s i t i o n , as w e l l as s e a s o n a l l y . F r e q u e n t and r e g u l a r o c c u r r e n c e s o f l a r g e tempera-t u r e changes i n h i g h e r t i d e p o o l s have been d e m o n s t r a t e d . The c r i t i c a l t h e r m a l maxima f o r t h i s s p e c i e s a r e h i g h e r t h a n the o b s e r v e d e n v i r o n m e n t a l t e m p e r a t u r e extremes. Thus 0. maculosus i s a b l e t o s u r v i v e t h e h i g h t e m p e r a t u r e extremes n o r m a l l y en-c o u n t e r e d i n the upper t i d e p o o l s . T h i s s p e c i e s i s a l s o a b l e t o w i t h s t a n d t e m p e r a t u r e s as low as 0„5°C w h i c h were r e c o r d e d i n t h e s e same t i d e p o o l s d u r i n g the w i n t e r . A t b o t h h i g h and low e n v i r o n m e n t a l t e m p e r a t u r e extremes, 0. maculosus can s u r -v i v e l o n g enough t o a l l o w the r e t u r n o f l e s s s e v e r e tempera-t u r e s i n t i d e p o o l s by h i g h t i d e i n u n d a t i o n . B r u c e (1928) and Gray (1965) have s u g g e s t e d t h a t a b r u p t t e m p e r a t u r e changes caused by i n c o m i n g t i d e s may be more i m p o r t a n t t o i n t e r t l d a l a n i m a l s t h a n " t e m p e r a t u r e range as suc h . " The d a t a f o r 0. maculosus t e n d t o c o n t r a d i c t t h i s c o n c l u s i o n . Indeed, Lowe and Heath (1969) have s u g g e s t e d t h e e f f e c t o f such c y c l i c t e m p e r a t u r e v a r i a t i o n s may even s e r v e t o i n c r e a s e the t h e r m a l t o l e r a n c e o f f i s h . N o r r l s (1963) has shown t h a t n a t u r a l 109 t e m p e r a t u r e f l u c t u a t i o n s a f f e c t the t e m p e r a t u r e s e l e c t i o n o f G i r e l l a n i g r i c a n s , a n o t h e r f i s h i n h a b i t i n g t h e r o c k y i n t e r -t l d a l e n vironment. O l i g o c o t t u s s n y d e r i O l l g o c o t t u s s n y d e r i , u n l i k e 0. maculosus, i s r e s t r i c t e d t o t h e l o w e r t i d e p o o l s . Because o f t h i s narrow d i s t r i b u t i o n , one would e x p e c t t h i s s p e c i e s t o show a r e s t r i c t e d range o f depth p r e f e r e n c e s i n the e x p e r i m e n t a l d e p t h g r a d i e n t . How-e v e r , 0. s n y d e r i d i d n o t d i s p l a y a marked p r e f e r e n c e f o r a p a r t i c u l a r d e pth o r range o f d e p t h s . D u r i n g the p e r i o d s o f s i m u l a t e d t i d e changes, t h e r e was no c o n c e n t r a t i o n o f i n d i -v i d u a l s i n t h e s h a l l o w e r r e g i o n s and a l t h o u g h some i n c r e a s e d l o c o m o t o r a c t i v i t y was o b s e r v e d , a c t i v i t y d i d n o t a t t a i n the l e v e l s d i s p l a y e d by 0. maculosus. A c c o r d i n g t o Green ( p e r s o n a l c o m m u n i c a t i o n ) , no r h y t h m i c a c t i v i t y a s s o c i a t e d w i t h t h e t i d a l c y c l e o c c u r s i n O l l g o c o t t u s s n y d e r i . Thus i t i s c o n c l u d e d t h a t t h e h i g h t i d e d e pth p r e f e r e n c e s o f 0, s n y d e r i do n o t det e r m i n e i t s t i d e p o o l d i s t r i b u t i o n . S i n c e one c o u l d e x p e c t i t t o o c c u r l n upper t i d e p o o l s on the b a s i s o f a u n i f o r m l i t -t o r a l d e p t h d i s t r i b u t i o n d u r i n g h i g h t i d e s , t h e s e d a t a f u r t h e r s u g g e s t t h a t some o t h e r f a c t o r ( s ) i s l i m i t i n g t h i s s p e c i e s t o l o w e r t i d e p o o l s . The d i s t r i b u t i o n o f 0. s n y d e r i when t e s t e d s i m u l t a n -e o u s l y w i t h 0. maculo.sus, appeared t o be u n i f o r m a c r o s s the e x p e r i m e n t a l d e p t h g r a d i e n t and was s i m i l a r t o t h a t o b t a i n e d when i t was t e s t e d s e p a r a t e l y . Because o f t h i s and s i n c e no o v e r t a g g r e s s i v e b e h a v i o r was ob s e r v e d , t h e s e d a t a s u g g e s t 110 t h a t I n t e r s p e c i f i c a g g r e s s i o n and c o m p e t i t i o n a r e n o t i n v o l v e d i n l i m i t i n g t he d i s t r i b u t i o n o f 0. s n y d e r i . Under e x p e r i m e n t a l c o n d i t i o n s , O l l g o c o t t u s s n y d e r l d i s p l a y e d a s t r o n g p r e f e r e n c e f o r the dense e e l g r a s s m i c r o -h a b i t a t , w i t h g r e a t l y r e d u c e d p r e f e r e n c e s f o r the r o c k and sand e n v i r o n m e n t s . As i n the case o f 0. maculosus, the o r d e r o f p r e f e r e n c e c o i n c i d e s w i t h t h e f i e l d o b s e r v a t i o n s . O l l g o -c o t t u s s n y d e r l i s always found I n c l o s e a s s o c i a t i o n w i t h e e l g r a s s , c o r a l l i n e a l g a e o r o t h e r m a c r o p h y t i c a l g a l c o v e r . T h i s s p e c i e s has never been o b s e r v e d o r c o l l e c t e d i n open r o c k y o r sandy p o o l s d e v o i d o f macrophytes. Of s i g n i f i c a n c e i s t he c o n s p i c u o u s absence o f t h i s s p e c i e s from dense beds o f e e l g r a s s i n upper t i d e p o o l s ( >7.0-8.0 f o o t l e v e l s ) . I t f o l l o w s t h a t though the s u b s t r a t e c o v e r f a c t o r i s i m p o r t a n t t o the d i s t r i b u t i o n o f t h i s s p e c i e s , i t does not a c c o u n t f o r i t s r e s t r i c t i o n t o l o w e r t i d e p o o l s . The c l o s e a s s o c i a t i o n w i t h e e l g r a s s p o i n t s out the p o s s i b l e i n c r e a s e d v u l n e r a b i l -i t y o f t h i s s p e c i e s i n t i d e p o o l s d e v o i d o f m a c r o p h y t i c c o v e r . A g a i n s t a background c o l o r o f b l a c k s , browns, and w h i t e s c h a r -a c t e r i s t i c o f most t i d e p o o l s , the b r i g h t c o l o r s and c o l o r p a t t e r n s ( b r i g h t green, m o t t l e d g r e e n , red-brown, m o t t l e d p i n k ) o f 0. s n y d e r i would r e n d e r i t more o b v i o u s t o p r e d a t o r s such as shore b i r d s and s m a l l mammals. The i n t e r a c t i o n o f 0. maculosus on the s u b s t r a t e -c o v e r a f f i n i t i e s o f 0. s n y d e r l was not g r e a t enough t o r e s u l t i n a s h i f t o f m i c r o h a b i t a t p r e f e r e n c e s . D u r i n g the e x p e r i m e n t s when 0. s n y d e r l and 0. maculosus were t e s t e d t o g e t h e r , no I l l o v e r t a g g r e s s i v e b e h a v i o r was o b s e r v e d on the p a r t o f e i t h e r s p e c i e s . A p p a r e n t l y the i n t e r a c t i o n between the s p e c i e s has l i t t l e b e a r i n g on the u l t i m a t e c h o i c e o f m i c r o h a b i t a t . The r e s t r i c t e d d i s t r i b u t i o n o f 0. s n y d e r i and the h i g h d e n s i t i e s o f 0. maculosus i n upper p o o l s i s n o t due t o i n t e r s p e c i f i c a g g r e s s i o n o r c o m p e t i t i o n f o r s u b s t r a t e and/or c o v e r . L i k e 0o maculosus, the tendency o f 0. s n y d e r i t o r e -main i n the l o w e r r e g i o n s o f t i d e p o o l s w i t h h a l o c l i n e s , g r e a t l y m i n i m i z e s th e exposure o f 0. s n y d e r i t o h y p o s a l i n e c o n d i t i o n s . The e x p e r i m e n t a l d a t a i n d i c a t e t h a t 0. s n y d e r i has the c a p a c i t y t o w i t h s t a n d h y p o s a l i n l t y (7.5 °/oo) f o r as l o n g as e i g h t y h o u r s , and e xcept under combined c i r c u m s t a n c e s of neap t i d e s and c o n t i n u o u s r a i n f a l l o f s e v e r a l days, t h i s p e r i o d o f time would be s u f f i c i e n t t o a l l o w s u r v i v a l between h i g h t i d e i n u n d a t i o n s i n p o o l s above the 7.0 t o 8.0 f o o t l e v -e l s . Thus i t i s b e l i e v e d t h a t h y p o s a l i n e c o n d i t i o n s do n o t l i m i t 0. s n y d e r i t o l o w e r t i d e p o o l s . The absence o f 0. s n y d e r i from h i g h e r t i d e p o o l s w i t h s u b s t a n t i a l m a c r o p h y t l c c o v e r , b u t c h a r a c t e r i z e d by tempera-t u r e extremes and f l u c t u a t i o n s , s u g g e s t s t h a t t h i s f a c t o r may l i m i t the upper d i s t r i b u t i o n a l boundary o f t h i s s p e c i e s . For f i s h l i v i n g a t about 10°C f o r t h r e e weeks, l e t h a l t e m p e r a t u r e s a f t e r t w e l v e hours of exposure, l i e a t or w i t h i n t h e l i m i t s o f the t e m p e r a t u r e extremes r e c o r d e d (23«5°C) or o b s e r v e d (25.0°C) i n the upper t i d e p o o l s (9.5, 10.5 f o o t l e v e l s ) a t P o r t Renfrew. The l e s s e r t e m p e r a t u r e r e s i s t a n c e o f t h i s spe-c i e s , as compared t o 0. maculosus, I n d i c a t e s t h a t 0. s n y d e r i 112 i s p h y s i o l o g i c a l l y i n c a p a b l e o f f u n c t i o n i n g n o r m a l l y under upper t i d e p o o l t e m p e r a t u r e r e g i m e s . I t i s c o n c l u d e d t h a t t he h i g h e r t e m p e r a t u r e s o f upper p o o l s r e s t r i c t the d i s t r i b u t i o n o f P. s n y d e r i t o l o w e r t i d e p o o l s (< 7<>0 t o 8.0 f o o t l e v e l s ) . The e f f e c t o f sudden l a r g e t emperature d e c r e a s e s as o b s e r v e d i n the f i e l d ( F i g u r e s 17, 18, 1 9 ) do n o t appear t o be d e t r i -m e n t a l t o 0. s n y d e r i , even though t h e s e changes a r e marked a t i t s upper d i s t r i b u t i o n l i m i t . I n d i c a t i o n s a r e t h a t p r o l o n g e d p e r i o d s a t h i g h t e m p e r a t u r e s a r e more h a r m f u l than r a p i d tem-p e r a t u r e changes. A l t h o u g h the e f f e c t s o f m u l t i p l e exposure t o r a p i d t e m p e r a t u r e d e c r e a s e s a r e not known, i t i s p o s s i b l e t h a t , s i m i l a r t o 0. maculosus, sudden t e m p e r a t u r e changes do no t l i m i t t h e t i d e p o o l d i s t r i b u t i o n . o f 0. s n y d e r l . The l i m i t e d l a b o r a t o r y d a t a on the e f f e c t o f tempera-t u r e on the t i d e p o o l d i s t r i b u t i o n of 0. s n y d e r l i n the e x p e r i -m e n t a l d e p t h - g r a d i e n t tank, s u p p o r t the c o n t e n t i o n t h a t h i g h t e m p e r a t u r e extremes such as those f o u n d i n upper t i d e p o o l s (23.5°C) l i m i t t he o c c u r r e n c e o f t h i s s p e c i e s t o l o w e r t i d e -p o o l s where t e m p e r a t u r e s a r e n o t extreme. D u r i n g the a p p l i c a -t i o n o f extreme t e m p e r a t u r e s (23.5°C) i n the upper p o o l o f the e x p e r i m e n t a l tank, a l l f i s h s t r a n d e d i n t h i s p o o l d i s -p l a y e d o b v i o u s s i g n s o f s t r e s s which were e x a c t l y l i k e t h o s e o b s e r v e d i n tem p e r a t u r e t o l e r a n c e e x p e r i m e n t s . Upon r a p i d c o o l i n g by simu l a t e d , h i g h t i d e I n u n d a t i o n o f the " t i d e p o o l , " s i g n s o f s t r e s s d i s a p p e a r e d . A f t e r a s e r i e s o f e n c o u n t e r s w i t h h i g h t e m p e r a t u r e s I n the upper " t i d e p o o l , " the number of i n s t a n c e s o f 0. s n y d e r i remained i n t h i s p o o l was d e c r e a s e d 113 ( T a b l e 1 4 ) . T h i s s t r o n g l y s u g g e s t s t h a t 0. s n y d e r i can l e a r n t o a v o i d h i g h t e m p e r a t u r e s and i s thus a b l e t o b e h a v i o r a l l y t h e r m o r e g u l a t e . R e g u l a r f i e l d o b s e r v a t i o n s and p e r i o d i c t i d e -p o o l c o l l e c t i o n s d i d n o t r e v e a l any s e a s o n a l m i c r o d l s t r i b u t i o n a l s h i f t s r e l a t e d t o te m p e r a t u r e v a r i a t i o n s . T h i s may be due t o s e a s o n a l a c c l i m a t i o n t o t e m p e r a t u r e . A n o t h e r p o s s i b l e e x p l a n a -t i o n i s t h a t 0. s n y d e r i may d i s p l a y homing b e h a v i o r s i m i l a r t o t h a t f o u n d i n o t h e r t i d e p o o l c o t t i d s ( C l l n o c o t t u s g l o b i c e p s , Green, 1967; C l l n o c o t t u s a n a l l s , W i l l i a m s , 1957; A c a n t h o c o t t u s [ E n o p h r y s ] b u b a l l s , G i b s o n , 1966; O l l g o c o t t u s maculosus, Green, 1967). One s m a l l t a g g i n g e xperiment (n = 6) showed one 0. s n y d e r i r e t u r n i n g t o the e x a c t p o o l from w h i c h i t was o r i -g i n a l l y c a p t u r e d a f t e r i t had been marked and r e l o c a t e d about t w e n t y - f i v e y a r d s away from i t s "home p o o l . " T h i s , however, me r e l y ^ s u g g e s t s the p o s s i b i l i t y o f homing i n t h i s s p e c i e s . Food h a b i t s and i n t e r s p e c i f i c c o m p e t i t i o n The a n a l y s e s o f the d i e t s o f O l l g o c o t t u s maculosus and 0. s n y d e r i c a p t u r e d i n the same t i d e p o o l s show t h a t b o t h s p e c i e s e a t the same b a s i c f o o d o r g a n i s m s . I n g e n e r a l , 0. maculosus appears t o have a w i d e r f o o d spectrum l n t h a t I t consumes a g r e a t e r p r o p o r t i o n o f minor f o o d i t e m s common t o the d i e t s o f b o t h s p e c i e s t h a n does 0. s n y d e r i . T h i s d i f -f e r e n c e i s a r e f l e c t i o n o f the l o w e r degree o f s p e c i f i c i t y i n m i c r o h a b i t a t r e q u i r e m e n t s of 0. maculosus and the g r e a t e r a b i l i t y of t h i s s p e c i e s t o i n v a d e a l l l e v e l s o f the i n t e r t l d a l zone. The l a r g e r q u a n t i t a t i v e d i f f e r e n c e s can a l s o be a t t r i -b u t e d t o t h e s e b e h a v i o r a l c h a r a c t e r i s t i c s o f 0. maculosus. 114 Johannes and L a r k i n ( 1 9 6 l ) s t u d y i n g c o m p e t i t i o n f o r f o o d be-tween s h i n e r s ( R i c h a r d s o n i u s b a l t e a t u s ) and r a i n b o w t r o u t (Salmo g a l r d n e r l ) o b s e r v e d d i f f e r e n c e s i n d i e t s w h i c h were t o a l a r g e degree i n f l u e n c e d by the f e e d i n g b e h a v i o r o f the r e s p e c t i v e s p e c i e s . I t has been p o s t u l a t e d by some workers ( N i l s s o n , 1955*, 1958, I960; N i k o l s k i i , I963) t h a t among f i s h , c l o s e l y r e l a t e d c o h a b i t a t l n g s p e c i e s w i t h s i m i l a r r e q u i r e m e n t s ( f o o d , space, e t c . ) f o r r e s o u r c e s w h i c h a r e i n low s u p p l y w i l l p a r t i t i o n t h e s e r e s o u r c e s among themselves i n o r d e r t o m i n i m i z e o r e l i m -i n a t e c o m p e t i t i o n . N i l s s o n (1955» 1958) o b s e r v e d t h a t two s a l m o n i d s p e c i e s i n c e r t a i n Swedish l a k e s a l t e r e d t h e i r r e -s p e c t i v e a l l o p a t r i c d i e t s and f e d on d i f f e r e n t f o o d i t e m s under c o n d i t i o n s o f sympatry and l i m i t e d f o o d . N i l s s o n c a l l e d t h i s phenomenon " i n t e r a c t i v e s e g r e g a t i o n . " N i k o l s k i i (1963) ob-s e r v e d t h e same p r o c e s s among two g o b i i d f i s h and d e s c r i b e d i t as " s e p a r a t i o n o f f o o d s p e c t r a . " Kohn (1968) o b s e r v e d s i m i l a r i n t e r s p e c i f i c f o o d r e l a t i o n s h i p s between t r o p i c a l m arine g a s t r o p o d s (Conus s p p ) . I v l e v (I96I) e s t a b l i s h e d c e r t a i n m a t h e m a t i c a l models and i n d i c e s which s e r v e d t o q u a n t i t a t i v e l y d e s c r i b e i n t e r -s p e c i f i c f o o d r e l a t i o n s h i p s . The I m p l i c a t i o n s o f such r e l a -t i o n s h i p s can be a p p r e c i a t e d by exa m i n i n g the o b s e r v a t i o n s o f F r y e r (1959) on the n u m e r o u s s p e c i e s o f the f a m i l y C l c h l i d a e i n Lake Nyasa. I n t h i s p a r t i c u l a r A f r i c a n l a k e , t h e r e a r e a l a r g e number o f s p e c i e s w h i c h have e v o l v e d w i t h a wide v a r i e t y o f b e h a v i o r a l and m o r p h o l o g i c a l a d a p t a t i o n s w h i c h 115 have enabled members of t h i s group of fishes to e f f e c t i v e l y p a r t i t i o n o f f the food resources of t h e i r environment. I t i s quite l i k e l y that the adaptive r a d i a t i o n of t h i s group of c i c h l i d s arose d i r e c t l y out of a maintenance of "separation of food spectra" or " i n t e r a c t i v e segregation." Interactive segregation with respect to other resources such as space has also been documented (Hartman, 1965). The absence of q u a l i t a t i v e differences between the diets of 0. maculosus and 0. snyderl are suggestive of an abundance of i n t e r s p e c i f i c competition f o r food i n view of t h i s concept and the accompanying observation. A series of bottom and epiphytic faunal samples taken at d i f f e r e n t times of the year (October, November, January, February, June) i n -dicate common, though often variable, occurrences of the major food items of the two species i n the tidepools of Port Renfrew. These observations support the suggestion that there i s no i n t e r s p e c i f i c competition f o r food between 0. maculosus and 0. snyderl. I t has been stated that the absence of e f f e c t i v e competition i n the presence of food abundance may enable clo s e l y related species to coexist i n s i m i l a r niches (Lack, 19^6; Hartley, 1953; Nilsson, I960; Gee and Northcote, 1963)• M i t c h e l l (1953) i n his study of food habits and possible i n t e r -s p e c i f i c competition f o r food between tidepool fishes of southern C a l i f o r n i a concluded that there i s " l i t t l e competi-tion f o r food" between the carnivorous tidepool f i s h e s . The lack of i n t e r s p e c i f i c aggressive behavior between 0. maculosus andjO. anyderi for food, space, substrate and cover under laboratory conditions add further support to these suggestions. 116 I n t e r s p e c i f i c Comparisons W i t h the p o s s i b l e e x c e p t i o n o f an a v o i d a n c e response t o h i g h d e n s i t y c o n d i t i o n s , the i n t e r t l d a l d i s t r i b u t i o n o f Oo maculosus a t P o r t Renfrew i s not g r e a t l y a f f e c t e d by the e n v i r o n m e n t a l . f a c t o r s c o n s i d e r e d i n t h i s s t u d y . S i n c e i t i s e x t r e m e l y v e r s a t i l e b e h a v l o r a l l y , as w e l l as p h y s i o l o g i c a l l y , t h i s s p e c i e s i s a b l e t o e x p l o i t v i r t u a l l y a l l t i d e p o o l s i n t h i s environment. Green (1967) has shown t h a t i n u n s h e l t e r e d a r e a s o f P o r t Renfrew, the l o w e r d i s t r i b u t i o n a l l i m i t s o f t h i s s p e c i e s may v a r y d i r e c t l y w i t h the degree o f exposure t o the open ocean and the s l o p e o f the s h o r e . The i n t e r t l d a l d i s t r i b u t i o n o f 0. s n y d e r i , i s g r e a t l y a f f e c t e d by a t l e a s t two o f t h e e n v i r o n m e n t a l f a c t o r s con-s i d e r e d i n t h i s s t u d y . These a r e s u b s t r a t e - c o v e r a f f i n i t y and t e m p e r a t u r e . Of t h e s e , temperature' i s o f p r i m a r y i m p o r t -ance s i n c e t h e r e s t r i c t e d d i s t r i b u t i o n o f 0. s n y d e r i can o n l y be e x p l a i n e d on the b a s i s o f t i d e p o o l t e m p e r a t u r e s . W i t h i n the c o n t e x t o f t h i s s t u d y , the s p e c i f i c s u b s t r a t e - c o v e r a f -f i n i t i e s o f 0. s n y d e r i s e r v e o n l y t o show c e r t a i n q u a l i t a t i v e r e q u i r e m e n t s f o r t i d e p o o l s i n h a b i t e d by t h i s s p e c i e s and do not a c c o u n t f o r i t s absence i n upper t i d e p o o l s o f a p p a r e n t s u i t a b l e s u b s t r a t e and c o v e r . Thus f o r t h i s s p e c i e s t h e p h y s i c o - c h e m i c a l environment r a t h e r t h a n the b i o t i c e f f e c t s a r e key I n d e t e r m i n i n g I t s t i d e p o o l d i s t r i b u t i o n . T h i s c o n c l u s i o n i s c o n s i s t e n t w i t h some r e c e n t i n -v e s t i g a t i o n s o f s e s s i l e i n v e r t e b r a t e forms i n wh i c h i t was found t h a t the upper d i s t r i b u t i o n a l l i m i t s o f i n t e r t l d a l 117 a n i m a l s ( i n v e r t e b r a t e s ) a r e g e n e r a l l y d e t e r m i n e d by p h y s i c o -c h e m i c a l f a c t o r s w h i l e l o w e r l i m i t s a r e d e t e r m i n e d by b i o -l o g i c a l f a c t o r s such as p r e d a t i o n and c o m p e t i t i o n ( C o n n e l l , 1961; K i t c h i n g and E b l i n g , 1969). The d i s t r i b u t i o n a l d i f f e r e n c e s i n 0. maculosus and 0. s n y d e r i i n the i n t e r t l d a l zone a r e m a i n l y due t o t i d e p o o l t e m p e r a t u r e * T h i s e n v i r o n m e n t a l f a c t o r has been one o f the most i n t e n s e l y s t u d i e d parameters o f i n t e r t l d a l ecosystems and has f r e q u e n t l y been s u g g e s t e d as the cause f o r i n t r a -and I n t e r s p e c i f i c d i s t r i b u t i o n a l d i f f e r e n c e s among th e i n t e r -t i d a l b i o t a . On a br o a d s c a l e , numerous g e o g r a p h i c a l d i s -t r i b u t i o n a l d i f f e r e n c e s have been c o r r e l a t e d t o l e t h a l tem-p e r a t u r e l e v e l s o f i n t e r t l d a l organisms ( H u t c h i n s , 1947; S c h l i e p e r , F l u g e l , and Theede, 1967; F r a e n k e l , 1968; R l t z and F o s t e r , 1968; Graham, 1970). Numerous r e l a t e d s t u d i e s on p h y s i o l o g i c a l r a c e s have a l s o been made (see V e r n b e r g , 1962; S c h n e i d e r , 1964 f o r r e v i e w o f the s u b j e c t ) . On a s m a l l e r s c a l e and f o r s p e c i f i c a r e a s , c o r r e l a t i o n s between m i c r o h a b l t a t t e m p e r a t u r e s and p h y s i o l o g i c a l t o l e r a n c e s have a l s o been shown (Broekhuysen, 1940; S a n d i s o n , 1967). H a r d i n (1968) , s t u d y i n g the l e t h a l t e m p e r a t u r e s o f two c o n g e n e r i c i n t e r t l d a l l i m p e t s (Acmaea d i g i t a l i s . A. sc a b r a ) showed d i f -f e r e n c e s d i r e c t l y r e l a t e d t o m i c r o h a b l t a t t e m p e r a t u r e s . D a v i s (1969) has demon s t r a t e d t h a t c e r t a i n l o w e r i n t e r t l d a l g a s t r o -pods have g r e a t e r r a t e s o f d e s i c c a t i o n t h a n t h o s e from h i g h e r l e v e l s . N e w e l l and Pye (1968), on the o t h e r hand, have i n d i -c a t e d t h a t t e m p e r a t u r e does n o t a f f e c t the r e s p i r a t o r y f u n c t i o n s 118 of c e r t a i n i n t e r t i d a l a l g a e . Southward (1953) i n h i s s t u d i e s on t h e I s l e o f Man, has shown t h a t t e m p e r a t u r e i s o f t e n second-a r y t o such f a c t o r s as s u b s t r a t e and exposure t o wave a c t i o n . Read (1963) d e m o n s t r a t e d s i g n i f i c a n t d i f f e r e n c e s i n t h e r m o l a -b i l i t y o f the same enzyme systems among s e v e r a l s p e c i e s of i n t e r t i d a l m o l l u s c s w h i c h were s u b s e q u e n t l y r e l a t e d t o a n e o r o b i c c o n d i t i o n s r a t h e r t h a n m i c r o h a b l t a t t e m p e r a t u r e s . A t P o r t Ren-frew, 0. maculosus i s not g r e a t l y a f f e c t e d by e n v i r o n m e n t a l t e m p e r a t u r e s w h i l e 0. s n y d e r l i s . Thus 0. maculosus, h a v i n g a wide t e m p e r a t u r e t o l e r a n c e range, i s a b l e t o occupy t i d e p o o l s a t a l l l e v e l s w h i l e 0. s n y d e r i . w h i c h has a narrow range, i s r e s t r i c t e d t o p o o l s h a v i n g l o w e r and more s t a b l e t e m p e r a t u r e r e g i m e s . A l t h o u g h a g r e a t d e a l o f a t t e n t i o n has been g i v e n t o c r i t i c a l t h e r m a l l i m i t s , i t must be borne i n mind t h a t many i m p o r t a n t f u n c t i o n s o f p o l k i l o t h e r m i c organisms may be ad-v e r s e l y a f f e c t e d by tempe r a t u r e extremes l o n g b e f o r e c r i t i c a l t h e r m a l maxima a r e r e a c h e d . F o r example, i t has been shown t h a t w i t h i n the l i m i t s o f c r i t i c a l t h e r m a l maxima and minima of c e r t a i n f i s h e s , swimming speeds a r e maximal a t s p e c i f i c o p t i m a l t e m p e r a t u r e s ( F r y and H a r t , 1948; B r e t t , 1967). D i r e c t l y r e l a t e d t o t h e s e r o u t i n e performance a c t i v i t i e s a r e fundamental p h y s i o l o g i c a l p r o c e s s e s such as nerve c o n d u c t i o n and b i o c h e m i c a l t r a n s f o r m a t i o n s o f f o o d i n t o energy. The. e x a c t n a t u r e o f temperature e f f e c t s on th e s e and o t h e r p r o -c e s s e s i n whole organisms i s d i f f i c u l t t o a s c e r t a i n . Thus, 0. maculosus. as w e l l as 0. s n y d e r i , may s u f f e r l o n g term e f f e c t s 119 o f r e p e a t e d exposure i n i n t e r t i d a l p o o l s t o n a t u r a l tempera-t u r e extremes w h i c h a r e n o t o b v i o u s i n some o f t h e l a b o r a t o r y e xperiments o A comparison o f the oxygen consumption r a t e s o f 0. s n y d e r i and 0. maculosus o b t a i n e d by M o r r i s (1961) i n d i c a t e l o w e r l e v e l s o f consumption f o r the l a t t e r s p e c i e s as shown by l a t e r a l d i s p l a c e m e n t o f the r a t e - t e m p e r a t u r e c u r v e s . Graham (1970) c i t e s s e v e r a l i n v e s t i g a t i o n s ( S c h o l a n d e r , e t a l . , 1953; B a r l o w , 196l; M o r r i s . 1961) w h i c h show t h a t marine f i s h from h a b i t a t s o f v a r i a b l e and h i g h t e m p e r a t u r e regimes a l s o d i s p l a y l o w e r Q10 v a l u e s . A l t h o u g h no Q10 d i f f e r e n c e s were a p p a r e n t , t h e s e d a t a i m p l y t h a t 0. maculosus i s b e t t e r a d a p t e d p h y s i o l o g i c a l l y t o warmer and/or more v a r i a b l e t h e r m a l r e g i m e s . F o r a c o m p a r a t i v e l y s t e n o t h e r m a l s p e c i e s such as 0. s n y d e r i , t h e mode and time o f i n i t i a l h a b i t a t i o n o f the i n t e r t i d a l by r e t u r n i n g p o s t - l a r v a e i s e s p e c i a l l y c r i t i c a l . V e r y l i t t l e i s known o f the e a r l y l i f e h i s t o r y o f 0. s n y d e r i , as w e l l as o f 0. maculosus, and t h e e x a c t n a t u r e o f " s e t t l e -ment" by p o s t - l a r v a e I n t i d e p o o l s remains p r o b l e m a t i c a l . E a r l y works on the r e c r u i t m e n t o f l e v e l - b o t t o m m arine com-m u n i t i e s s u g g e s t e d a scheme o f random s e t t l i n g o f l a r v a l i n -v e r t e b r a t e s f o l l o w e d by a s t r u g g l e f o r s u r v i v a l a g a i n s t the v a r i o u s e n v i r o n m e n t a l parameters (Thorson, 1957). A c c o r d i n g t o Thorson (1957). t h i s v i e w i s no l o n g e r h e l d as such works as t h a t o f W i l s o n (1952) have shown t h a t numerous I n v e r t e b r a t e s p e c i e s a r e a b l e t o d e l a y metamorphosis u n t i l s u i t a b l e s u b s t r a t e 120 i s f o u n d . F i e l d c o l l e c t i o n s ( l a t e A ugust, 1968.) have y i e l d e d p o s t - l a r v a l 0. maculosus and what a r e b e l i e v e d t o be p o s t -l a r v a l 0. s n y d e r i , w h i c h had r e c e n t l y i n v a d e d t i d e p o o l s n e a r the r e s e a r c h s i t e . The l a t t e r s p e c i e s were f o u n d i n l o w e r t i d e p o o l s (<Cabout 8.0 f o o t l e v e l ) w h i l e the p o s t - l a r v a e o f 0. maculosus were c o l l e c t e d o n l y i n t h e upper t i d e p o o l s . C l o s e . o b s e r v a t i o n o f the immediate a r e a . r e v e a l e d no s i g n s o f mass m o r t a l i t i e s o f p o s t - l a r v a e . These f i e l d o b s e r v a t i o n s s u g g e s t t h a t both; s p e c i e s do n o t randomly Invade p o o l s a t a l l v e r t i c a l l e v e l s . R a t h e r , i t appears t h a t the p o s t l a r v a e o f 0. maculosus and 0. s n y d e r i i n v a d e t i d e p o o l s o f s p e c i f i c v e r t i c a l p o s i t i o n . The i m p l i c a t i o n o f t h i s s u g g e s t i o n i s t h a t the " t h r e s h o l d " l e v e l s o f m i c r o e n v i r o n m e n t a l f a c t o r s s u c h as t e m p e r a t u r e a r e d e t e r m i n e d e a r l y i n the l i f e h i s t o r y o f t h e two s p e c i e s . A l -though o p t i m a l t e m p e r a t u r e ranges f o r a s p e c i e s v a r y w i t h g e n e t i c p o t e n t i a l , age and p r e v i o u s t h e r m a l h i s t o r y , i t would appear t h a t f o r a d u l t 0. maculosus and 0. s n y d e r i , such d i f -f e r e n c e s w h i c h may o c c u r a r e n o t o f suc h magnitude t o cause g r e a t d e v i a t i o n s from t h e i r p o s t - l a r v a l m l c r o d l s t r l b u t i o n p a t -t e r n s . A c l e a r s e p a r a t i o n o f g e n e t i c and e n v i r o n m e n t a l l y i n -duced d i f f e r e n c e s i n t h e r m a l p h y s i o l o g y l n t h e two s p e c i e s i s not p o s s i b l e a t t h i s t i m e . The c o m p l e x i t y o f t h i s problem has been p o i n t e d o u t by S c h n e i d e r (1964) who has d i s t i n g u i s h e d between g e n e t i c e f f e c t s , i r r e v e r s i b l e p h e n o t y p i c a d a p t a t i o n s ( i e , l o n g term compensatory changes i n d u c e d by the environment and f i x e d i n e a r l y embryonic s t a g e s ) and r e v e r s i b l e p h e n o t y p i c a d a p t a t i o n s ( i e . r e v e r s i b l e s h o r t term compensatory changes 121 i n m e t a b o l i s m o c c u r r i n g d u r i n g p o s t - e m b r y o n i c s t a g e s and w h i c h a r e o f a temporary n a t u r e ; a c c l i m a t i o n , , ) I n c o n c l u s i o n , i t i s hoped t h a t the i n f o r m a t i o n p r e -s e n t e d i n t h i s s t u d y w i l l p r o v i d e a d i r e c t i o n f o r f u t u r e , more b a s i c i n v e s t i g a t i o n s i n I n t e r t i d a l a d a p t a t i o n s o f t i d e -p o o l f i s h e s o A t t h i s p o i n t , the number o f v a r i a b l e s has been r e d u c e d and s e v e r a l i m p o r t a n t q u e s t i o n s c o n c e r n i n g the m i c r o -h a b i t a t r e q u i r e m e n t s and v e r t i c a l z o n a t i o n among t i d e p o o l f i s h e s r a i s e d . These i n c l u d e : 1. What i s the mode and t i m i n g o f p o s t - l a r v a l s e t t l e -ment o f t i d e p o o l f i s h e s ? 2. A t what s t a g e i n the l i f e c y c l e a r e the m i c r o -environment r e q u i r e m e n t s o f t i d e p o o l f i s h e s f i x e d ? 3. How a r e i n t e r s p e c i f i c d i f f e r e n c e s i n the t h e r m a l p h y s i o l o g y o f t i d e p o o l f i s h e s a f f e c t e d by m i c r o -e n v i r o n m e n t a l t e m p e r a t u r e s ? 4. What a r e the l o n g term e f f e c t s o f c y c l i c t e m p e r a t u r e v a r i a t i o n s on the t h e r m a l p h y s i o l o g y o f t i d e p o o l f i s h e s ? 122 • Suranary 1. The u b i q u i t o u s t i d e p o o l d i s t r i b u t i o n o f O l i g o c o t t u s macu-l o s u s i s n o t t h e d i r e c t r e s u l t o f i t s h i g h t i d e d e p t h p r e f e r e n c e p e r se. R a t h e r , a c o m b i n a t i o n o f s h a l l o w ' w a t e r p r e f e r e n c e s and a r h y t h m i c p e r i o d o f l o c o m o t o r a c -t i v i t y f a c i l i t a t e s a wide exposure o f t h i s s p e c i e s t o t i d e p o o l s a t most i n t e r t i d a l l e v e l s . 2. The r e s t r i c t e d t i d e p o o l d i s t r i b u t i o n o f O l l g o c o t t u s • s n y d e r l i s n o t a d i r e c t r e f l e c t i o n o f d e p t h s e l e c t i o n d u r i n g p e r i o d s o f h i g h t i d e . 3. The s u b s t r a t e - c o v e r p r e f e r e n c e o f 0. maculosus f o r a r o c k y m i c r o e n v i r o n m e n t does n o t r e s t r i c t t h i s s p e c i e s t o t h i s p a r t i c u l a r m i c r o h a b l t a t . T h i s f l e x i b i l i t y I n c h o i c e o f m i c r o e n v i r o n m e n t and t h e c o l o r o f t h i s s p e c i e s a l l o w s i t t o r e a d i l y adapt t o most t i d e p o o l s i t m i g h t be - exposed t o . 4. The s u b s t r a t e - c o v e r p r e f e r e n c e o f 0. s n y d e r l f o r dense m a c r o p h y t i c c o v e r i s r i g i d , and l i m i t s the o c c u r r e n c e o f t h i s s p e c i e s t o t i d e p o o l s w i t h such c o v e r . The p a r t i c u -l a r l y b r i g h t c o l o r s o f t h i s s p e c i e s a r e n o t p r o t e c t i v e i n most t i d e p o o l s d e v o i d o f m a c r o p h y t e s . 5. The r e s t r i c t i o n o f 0. s n y d e r l t o t h e l o w e r t i d e p o o l s i s n o t r e l a t e d t o t h e s u b s t r a t e - c o v e r f a c t o r s i n c e t h i s s p e c i e s does n o t o c c u r i n h i g h e r t i d e p o o l s w i t h dense beds o f e e l g r a s s . 6. The f o r m a t i o n o f h a l o c l l n e s i n most t i d e p o o l s a f t e r . p e r -i o d s o f r a i n f a l l p r o v i d e s a means by w h i c h b o t h 0. macu-l o s u s and Oo s n y d e r i c o u l d a v o i d h y p o s a l i n e w a t e r s . ?. The c a p a c i t y o f 0 . maculosus and-.>0. s n y d e r i t o w i t h s t a n d h y p o s a l i n e w a t e r (7.5 °/oo) f o r c o m p a r a t i v e l y l o n g p e r -i o d s w o u l d a l l o w b o t h , t o s u r v i v e most c o n d i t i o n s o f un-s t r a t i f i e d h y p o s a l i n i t y w h i c h a l s o o c c u r s i n c e r t a i n t i d e p o o l s . 8. The v e r t i c a l d i s t r i b u t i o n s o f b o t h 0 . maculosus and 0. s n y d e r i a t P o r t Renfrew a r e n o t a f f e c t e d by s a l i n i t y as t h e bottom s a l i n i t i e s o f most t i d e p o o l s do n o t g r e a t l y d i f f e r f r o m t h e on-shore s e a w a t e r o r between v e r t i c a l l e v e l s . < 9. The d i s t r i b u t i o n o f 0 . maculosus i s n o t r e s t r i c t e d by t i d e p o o l t e m p e r a t u r e s a t P o r t Renfrew. The c o m p a r a t i v e l y g r e a t t o l e r a n c e and r e s i s t a n c e o f t h i s s p e c i e s t o tempera-t u r e extremes e n a b l e s i t t o s u c c e s s f u l l y i n h a b i t h i g h e r as w e l l as t h e l o w e r l e v e l t i d e p o o l s . 10. The d i s t r i b u t i o n o f 0 . s n y d e r i i s l i m i t e d by i t s i n a b i l i t y t o w i t h s t a n d h i g h t e m p e r a t u r e extremes w h i c h a r e more c h a r a c t e r i s t i c o f h i g h e r l e v e l t i d e p o o l s . 11. I n t e r s p e c i f i c ,,irit<araotions: s u c h as c o m p e t i t i o n and a g g r e s -s i v e b e h a v i o r do n o t appear t o be o f i m p o r t a n c e i n de-t e r m i n i n g t h e r e s p e c t i v e d i s t r i b u t i o n o f 0. maculosus and Q. s n y d e r i . 1 2 4 L l t e r a t u r e C i t e d A l l e e , W.C. 1 9 2 2 . Some p h y s i c a l f a c t o r s r e l a t e d t o the d i s t r i b u t i o n o f l i t t o r a l i n v e r t e b r a t e s . 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S e l e c t i o n mechanisms a s s o c i a t e d w i t h i n t e r s p e c i f i c s h e l l v a r i a t i o n i n L i t t o r i n a p i c t a . E v o l . , 22:459-480, Thorson, G. 1957. Bottom communities. I n : J . Hedgepeth ( E d . ) i T r e a t i s e on M a r i n e E c o l o g y and P a l e o e c o l o g y . V o l , Ec o l o g y . The G e o l o g i c a l S o c i e t y o f A m e r i c a , Mem. 67: 461-534. V e r n b e r g , P.J.. 1962. Comparative p h y s i o l o g y : L a t i t u d i n a l e f f e c t s on p h y s i o l o g i c a l p r o p e r t i e s o f a n i m a l p o p u l a t i o n s . Ann. Rev. P h y s i o l . , 24:517-546. . Widdowson, T.B. 1965. A s u r v e y o f the d i s t r i b u t i o n o f i n t e r -t i d a l a l g a e a l o n g a c o a s t t r a n s i t i o n a l i n r e s p e c t t o s a l i n i t y and t i d e f a c t o r s . J o u r n . F i s h , Res. Bd. Can,, 22:1425-1454. W i l l i a m s , G.C, 1957. 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