PHYSIOLOGICAL CHARACTERS OF MA- 

 RINE ANIMALS FROM DIFFERENT 

 DEPTHS * 



By Prof. V. E. Shelford, 

 University of Illinois, Urbana, III. 



I. — INTRODUCTION. 



The sea is the largest single type of habitat and on 

 account of its vastness we are accustomed to think of its 

 life as comparatively uniform for slightly different 

 depths, and of its conditions as essentially the same for 

 closely connected parts and opposite sides of compara- 

 tively narrow channels. It was a matter of much sur- 

 prise to the writer to find that marine fishes showed 

 marked sensitiveness to slight differences in acidity and 

 alkalinity, and that, as compared with the difference to 

 which they respond, the differences in this respect be- 

 tween the two sides of the channel south of Brown's 

 Island, Puget Sound (Friday Harbor, Wash.),f which 

 is only about a fourth of a mile wide, are great. The 

 water on the north side of the island is uniformly 

 alkaline and suited to the development of the eggs of fish- 

 es and invertebrates which require an alkaline medium, 

 while the water of the south side is acid much of the 

 time and the eggs of various animals do not develop 

 well. This difference is correlated with striking differ- 

 ences in vegetation and animal life which the casual 

 observer would attribute to the difference in current and 

 bottom, the south side being most strongly swept by the 

 tide and rocky, while the north side is sandy and escapes 

 the main force of the tide. In a paper by the writer 

 and Mr. E. B. Powers, attention was called to the fact 

 that slight contamination of the sea can have pronounced 

 effects. 



* Contribution from the Puget Sound Marine Station. 

 t Biol. Bull. XXVIII: 315-334; also reprinted in Fishing Gazette, 

 March and April, 1916. 



