Seasonal changes in species composition of ciliate in the Lake Nakaumi

Abstract

It is known that various species of organisms inhabit the brackish-water Lake Nakaumi. Lake Nakaumi has been subjected to the influence of reclamation and desalination projects. Consequently, its ecosystem has been modified to a great extent, but investigations on protozoan biota have not been conducted so far. In this research, the species diversity and occurrence of ciliate protozoans were examined at 12 fixed points over the course of a year. As a result, spatial distribution of ciliates, species compositions, and their seasonal changes became clear in the whole region of the lake. The species of frequent occurrence were divided to 5 assemblages. Among the environmental factors examined (water temperature, salinity, and pH), salinity showed the strongest influence on the species composition of ciliates. In the Honjo area that is artificially isolated from the main stream of seawater by a system of dikes, some species of ciliates, which normally appears in the inner bay or at high salinity, were seen.