1Nippon Total Science, Inc., Hiroshima 721-0957, 2Faculty of Applied Biological Science, Hiroshima University, Hiroshima 739-8528, Japan
Effects of oxygen deficient water on the settlement and survival of the spionid polychaete Polydora cornuta were investigated, based on benthos and plankton samples obtained at 5 stations in Fukuyama Harbor, between April 1998 to March 1999. Low oxygen saturation was observed in the bottom layer during the period from late spring to autumn. Anoxic water occurred at the eutrophic inner part of the harbor in summer. Both benthic individuals and pelagic larvae distributed mainly at the inner part, and showed a different seasonal change: the former was present from January to June, but the latter appeared throughout the year. In summer, the benthic individuals disappeared, and the center of larval distribution migrated from the inner to the central parts. Thus the death of benthic individuals and the escape of pelagic larvae were due mainly to oxygen saturation lower than 50% and 10%, respectively.