90 Pub. Puget Sound Biol. Sta. Vol. 2, No. 37 



Relation to oxygen 



Although blennies seem easily to withstand long confinement in a 

 limited amount of shallow water, they are sensitive to the changed condi- 

 tions in a deeper tub. At one time nearly all of a large number died be- 

 fore the laboratory was reached. The oxygen demand must be very 

 high or diffusion slow. This, however, is compensated by the nature of 

 the Ulva beds where the blenny feeds. The Ulva naturally releases 

 great amounts of oxygen, especially in sunlight. In tests made from the 

 beds on the north shore of Brown Island at low tide the oxygen content 

 reached as high as 11.66 cc. per liter. One was 10.5 cc, and the surface 

 near the shore gave 5.17 cc. per liter. This is much higher tlian the 

 waters farther out. Shelf ord and Powers (1915) found in 1914 that the 

 waters of the vicinity in general contained les.s than 5 cc. of oxygen 

 per liter. 



Conclusions 



It has been made clear by these experiments that blennies differ 

 much from deeper water fish in the response to certain stimuli which 

 differ in the lower Laminarian and shore belts. It is apparent that 

 this may explain in great degree at least why blennies are found in 

 the shore environment. The species studied are negative to bright light 

 and show a remarkably low degree of sensitivity, for marine fishes, to 

 changes in temperature. They withstand living out of water for periods 

 of time much greater than the intervals between high tides and have great 

 resistance to fresh water. 



There seems to be little reason for doubting that behavior, that is, 

 reaction to definite environmental stimuli, is responsible for the existence 

 of blennies in this unusual habitat. Of the several factors presenting them- 

 selves as possible causes, perhaps the varying amount of carbon dioxide 

 in connection with the oxygen demand constitutes the chief one. The 

 oxygen and carbon dioxide in turn depend upon other conditions. Carbon 

 dioxide in the shore waters depends both upon the temjjerature of the 

 water and the activity of the Ulva. An increasing amount of decompo- 

 sition will increase the hydrogen sulphide, and this lowers the CO., content. 

 While the oxygen is more or less constant at the surface, the activity of 

 the Ulva controls the oxygen content of the water washing it. This 

 activity naturally varies with day and night. 



It seems tenable that these fish are most active among the Ulva 

 while the tide is in or the light permits the green plants to work actively, 

 l^ater they rest quietly beneath stones, thus avoiding a greater concen- 

 tration of carbon dioxide in the deeper water as the tide recedes. In 



