VERTICAL-DISTRIBUTION OF MACROBENTHIC ORGANISMS IN THE SEDIMENT OF WAKASA BAY, SEA OF JAPAN

The vertical distribution of macrobenthic organisms in the sediment was studied at three sampling stations at two different depths (100 m and 200 m) using core samples obtained with a USNEL box corer. Although organisms were heavily concentrated in the near-surface layer, as found in most previous studies of this type, there was an obvious difference in the vertical profile among various taxonomic groups: while more than 80% of the crustaceans present occurred within the upper 2 cm of the sediment, polychaetes tended to penetrate deeper. In the case of polychaetes the vertical profiles differed greatly between the stations at 100 m and 200 m. At the deeper station the cumulative level was lower than that at the shallower stations through the sediment depth down to about 10 cm. An analysis of the faunal characteristics of each station clearly showed that at the deep station there is an extreme scarcity of species which depend entirely upon the surface of the sediment to live. The reason for this is discussed with respect to the thick aggregation of some megalobenthic ophiuroids and spatangoids at that station as well as to the silty condition here.