NO. 2 HARTMAN, BARNARD: BENTHIC FAUNA OF DEEP BASINS 223 



after removal of the San Nicolas basin data. Nevertheless sipunculids 

 are more than five times as abundant in the basins as on the shelf. 



The question might arise that crustaceans, as surface dwellers and 

 not deep burrowers, and as excellent swimmers, would be lost from 

 the samples when the grab strikes bottom or as it is drawn to surface. 

 No doubt large fast swimming demersals such as euphausiids and large 

 amphipods are able to escape the grab, but they are able to do so in 

 shallow water as well. Almost all of the crustaceans recovered are 

 known as shallow burrowing types; but the ratio of abundance is still 

 quite low in the basins. 



It must be concluded, from the sparsity of crustaceans and the 

 higher ratio of polychaetes and sipunculids, that the basins are a habitat 

 favoring populations of wormlike organisms. 



It is probable that polychaetes are better adapted for bathyal and 

 abyssal existence because of their sedentary lives and reduced activities, 

 thus requiring less food and living longer than do most crustaceans, 

 which are active movers and great food consumers. Parenthetically, 

 isopods may be an exception, for they are a conspicuous part of abyssal 

 faunas. 



The striking preponderance of polychaetes in the shelf, slope and 

 basin faunas, with increase in relative faunal abundance with increased 

 depth, suggests that abyssal areas may have a far larger polychaete 

 population than previously considered. The sparsity of such records 

 from abyssal areas is partly the consequence of a lack of quantitative 

 deep burrowing grab samples. 



NUMBER OF SPECIES IN THE BASINS 



The trend of decrease of existing animal species in the ocean with 

 increasing depth is well known but poorly documented in the literature. 

 It is a monumental task to tally all species of the oceans by depth and 

 draw a graph to represent the information. Ekman (1953, p. 274) 

 reproduces information from the CHALLENGER Expedition to 

 document the trend sketchily. We are able to offer some information 

 in this regard but only as an issue aside from the overall picture of the 

 ocean, for the basins cannot be considered a typical part of the ocean 

 floor, with such depths as representative of all similar oceanic depths. 

 This is apparent for two reasons: first, the basins are close to shore 

 and probably have higher food supplies than similar depths far from 



