2003年から2005年までの有明海におけるたいらぎ類の浮遊幼生および稚貝の分布

抄録

The spatial distribution and abundance of planktonic larvae and spats of pen shells (Atrina lischikeana and Atrina pectinata) were investigated in Ariake Bay, southern Japan, from 2003 to 2005, to determine the recruitment stage of spats in relation to larval supply and spat survival after settlement. The distribution type was an aggregated distribution for both the larval and spat stages. However, spatial patterns of occurrence for larvae and spats were different. The planktonic larvae were broadly distributed in Ariake Bay, particularly in the middle of the bay during high summer. The spats were observed from the northern part to the eastern coast of Ariake Bay. In particular, spats over 25 mm in shell length were mainly obtained from the eastern coast of the bay. The umbo-stage larvae were frequently observed at the middle or the bottom layer of the water column in depths of more than 5 m, and full-grown larvae were obtained only from the bottom layer. The survival of spats was related to several parameters concerning sediment, especially concerning low values of acid volatile sulfide (AVS). The broad distribution of larvae in Ariake Bay was due to dispersion with a tidal residual current and a long planktonic period of more than one month. On the contrary, the narrow distribution of spats along the eastern coast of Ariake Bay may be affected by the bottom sediment conditions. These results suggest that spat recruitment is definitive in the post settlement stage, at 25 mm in shell length, and recruitment also depends on the ambient sea floor environment rather than larval supply in Ariake Bay.