Influence of Asari clam (Ruditapes philippinarum) abundance increase caused by cover-net on the nematode assemblages on a tidal flat

Abstract

Macrobenthos including Asari clam (Ruditapes philippinarum) and meiobenthos inside and outside of cover-nets on the Minami tidal flat, Yamaguchi Bay were examined to study the effect of the nets on the benthos. Cover-net (5×7 m, 9 mm mesh size) have remained for five–seven years to protect from predation by fishes. The density of R. philippinarum and gastropods in the cover-net area were higher than those outside of the cover-net area. The density of nematodes in the cover-net was higher than outside area. Considering three sizes of nematodes (63–125, 125–250, and ≧250 μm), the percentage of the smaller size increased in the cover-net area, and the percentage of the large size tended to be low. The nematode family composition in the cover-net area differed from that in the outside area. The nematode density of Xyalidae, Comesomatidae and Oncholaimidae in the cover-net increased. The percentage of 1B nematode feeding type (non-selective deposit feeder) in the cover-net area was higher than outside area. This suggests that the cover-net not only affects the density of R. philippinarum and nematodes but also changes the nematode family composition.