AN OUTLINE OF THE DISTRIBUTION OF PACIFIC 

 DEEP-SEA ANIMALS 



By Anton Fr. Bruun 



University Zoological Museum 

 Copenhagen K, Denmark 



When it is remembered that the existence of a deep-sea fauna has 

 been known for less than a century, that the Pacific Ocean covers 50 per 

 cent of all seas, and that the Pacific deep-sea fauna has been studied 

 relatively less than those of the Indian and Atlantic Oceans, it is no 

 wonder that an outline of the distribution of the animals must rest 

 on a very scanty material. 



We shall only consider true deep-sea animals, i.e. those living at 

 2000 meters or deeper, the abysso-pelagic and abyssal fauna. In this 

 way are excluded such species as may be considered to have their main 

 distribution on the continental slopes. Again this means by far the 

 greater part of the Pacific, 87.3 per cent, as the continental shelves cover 

 only 5.7 per cent and the continental slopes 7.0 per cent of this ocean 

 (Sverdrup, Fleming & Johnson 1946). 



Ekman (1953a, p. 303) is of the opinion that "the open-sea abyssal 

 can be divided zoogeographically into only three or four main regions: 

 an Atlantic, Pacific, Arctic and perhaps Antarctic region." And on 

 p. 291: "Not even for the most extreme abyssal species of the benthos 

 call a cosmopolitan distribution, however, be considered as the rule. 

 The lack of common species between the Atlantic and the other oceans 

 may up to a point be due to the insufficient knowledge of the fauna, 

 but this is only partly true." When the term "Pacific" is used in this 

 connection, Ekman means "an Indo-Pan-Pacific region" (p. 292). 



The echinoderms are especially well suited for consideration re- 

 garding the distribution of deep-sea animals because they are numerous 

 qualitatively as well as quantitatively, and they are easily caught. 

 Therefore, it is of special interest to compare the conclusions of Mad- 

 sen (1953) with Ekman's statements above. Madsen is of the opinion 

 "that the known distribution of the deep-sea Echinoderms strongly fa- 

 vours the view that the main zoogeographical regions of the extreme 

 deep-sea of today are, on the one hand, the Pacific, and, on the other 

 hand, the combined Atlantic and Indian Oceans. As the deep-sea re- 

 gion next in importance to these comes the Antarctic deep-sea region, 

 but other regions of the deep-sea I think it difficult to define from the 



365 



