Macrozoobenthic communities of the deep sea sediments in the northeastern Pacific Ocean

Abstract

Macrobenthos were collected at 7 stations located from 5°N to 10°N with 1° interval along the longitude of 131°W using a box corer with sampling area of 0.25 m2 in July, 1999. In order to see the vertical distribution of macrobenthos in sediments, each subcore sample was divided into 5 layers with 1 cm interval up to 6 cm depth. Each subcore sample was sieved through 0.3 mm mesh screen and fixed with 10% Rose Bengal added formalin. A total of 22 faunal groups in 11 phyla were sampled and the average density was 959 ± 584 ind./m2. Foraminiferans comprised 34.8% of total specimens were the most abundant fauna, and followed by nematodes (27.5%), polychaete worms (15.7%), and benthic harpactoid copepods (10.4%). A latitudinal trend was shown in the distribution of macrobenthos; the maximum density of 1,832 ind./m2 appeared at station N06 and the most poverished community occurred at station N09 with the density of 248 ind./m2 . The density of typical macrofaunal taxa except foraminiferans and nematods was 116 ind./m2. In the vertical distribution of macrobenthos, more than 70% of macrobenthos occurred in the upper 2 cm layer, and upper 4 cm layer contained about 90% of macrofauna. Polychaete worms consisted of 22 families, and cirratulid and paraonid worms were dominant polychaete species. The prominant feeding guilds of polychaete worms were SDT (surface, descretely motile, tenaculate feeding) and SMX (surface, motile, non-jawed); they comprised more than 50% of polychaete abundance. These feeding guilds of polychaete worms suggests that the deep sea benthos should be well adapted the newly settled deposits from water column, but this should be clarified by the further studies.