SUMMER ZOOPLANKTON COMPOSITION, VERTICAL DISTRIBUTION AND BIOMASS IN LAKE IKEDA, SOUTHERN KYUSHU, JAPAN

Abstract

Summer zooplankton composition, vertical distribution and biomass of limnetic zooplankton in Lake Ikeda, Japan were investigated during September 2006. A total of eleven species including four copepods, five cladocerans and two rotifers occurred. Cladocera was most dominant group followed by Copepoda and Rotifera; they represented 63%, 33% and 4% respectively. Diaphanosoma brachyurum, Bosmina longirostris and Eodiaptomus japonicus were found abundantly. The Cadocera Daphnia galeata is newly recorded for the first time from Lake Ikeda. Vertical distribution showed that most of zooplankton population preferred either deep epilimnion (10 m) or hypolimnion (20 m) but, avoided surface water. Biomass was highest at 10 m depth. According to Carlson’s trophic state index (TSI) Lake Ikeda is still mesotrophic lake, however, appearance of Daphnia galeata, a new invader, indicates that process of eutrophication is prevailing.