Abstract
Seasonal change of zooplankton was investigated for 14 months from February 1996 to March 1997 at a fixed station in the Tama-river estuary. The results indicated that zooplankton at the station increased in summer and decreased in winter. The dominant taxa was Copepoda followed by larvae of polychaetous Annelida, those of Bivalvia, and Cirripedia. Twenty-four copepod species/groups belonging to five orders were identified including marine, brackish, and freshwater species. Acartia omorii and Sinocalanus tenellus were abundant from winter to spring, Centropages abdominalis was found most in winter, while Paracalanus parvus and Pseudodiaptomus inopinus increased from autumn to winter. Acartia sinjiensis, Oithona davisae, and the Ergacilidae were abundant in summer. A drastic decrease in estuarine zooplankton was observed immediately after the typhoon which was asocciated with heavy rainfall and river swelling; however, the number of zooplankton recovered within two weeks.
