Benthic animals

Abstract

The species composition and distribution of macrobenthic fauna in the East Sea (Japan Sea) are summarized and briefly introduced in this chapter from many investigations in both small scale local areas including coastal bays and shallow subtidal areas and large scale areas extending from shelf to bathyal and abyssal depths. There have been few studies on benthic organisms in the deep bottoms of the East Sea, and some recent investigations have not been completed or the target benthic fauna were restricted to a particular faunal group such as bivalves, polychaetes, sipunculids and pericarid crustaceans. Because both the faunal composition and the distribution of the benthic fauna are closely related to the sedimentary facies they inhabit, there were complex benthic faunal assemblages in the southwestern shelf area of the East Sea. The East Sea contains various benthic environments from shallow coastal zones to bathyal and abyssal depths and the distribution of macrobenthic fauna clearly represents the diversity of environmental factors related to the depth gradient. It is expected that when the water depth increased, the abundance and diversity of macrobenthic fauna decreased, although this conclusion is based on only a few fragmental fauna data. From the recent research by Russian investigators on bathyal and abyssal fauna, it can be concluded that there was no real abyssal fauna in the East Sea because they are different from fauna commonly found at near abyssal depths in the North Pacific Ocean. The macrobenthic fauna communities in the ocean dumping areas responded to the organic enrichment of sediments, and thus a few opportunistic species like Capitella capitata occurred in a temporally closed region of the dumping area for several years as well as in the present dumping area in the southwest of the East Sea.