ANIMAL LIFE OF THE DEEP SEA BOTTOM 



187 



ceeded our wildest hopes; our jars were filled with several thousand 

 animals of at least 220 different species, and half of them were from 

 depths beyond 6,000 metres, in short from the actual trench depths. 



The Kermadec Trench thus gave us more than twice as many species 

 as the four other trenches put together. This means that we now have 

 a real basis for studying the dependence of the species on the depths — 

 or pressure, because in this rather limited region we can disregard the 

 other influencing factors, in the first place food supply and in the second 

 oxygen supply, temperature, and the minor factor of salinity. 



The general impression obtained is that the number of species dimin- 

 ishes rapidly with the depth. In the deepest trawl we obtained 18 species, 

 but in the four shallowest — at 4,510, 4,410, 2,630, and 2,470 metres — 

 there were, respectively, 57, 51, 55, and 45 species. Furthermore, we 

 know that the trawl at 2,530 metres which yielded 45 species was a good 

 deal richer, because we lost the bulk of the catch, which was so large that 

 it burst one of the bindings of the trawl-bag. The trawls between 4,520 and 

 8,2 10 metres yielded at the most 38 species per trawl, so that the tendency is 

 quite clear — a rapidly diminishing number of species with a rapidly in- 

 creasing depth. The reason must chiefly be sought in the greater or lesser 

 ability of the various species to live under very high pressure. 



Bivalve, seen from above and from the side; 3,590 metres. Snail, from 2,630 metres. 



