Notes on the morphological variation of the rotifer species Keratella cochlearis (Gosse) s.l. in one eutrophic pond

Abstract

The standing crop and photosynthetic activity of Microcystis aeruginosa Kütz. in both the plankton and sediment were investigated from November 1979 to May 1982 in Lake Kasumigaura, Japan. The number of planktonic colonies of this species decreased from early autumn to early spring, but increased in the sediment during late summer and autumn. The overwintering colonies in the sediment were −100–1000 times greater per unit area than those in lake water. No photoinhibition of photosynthesis could be observed in overwintering Microcystis. The values of the initial slopes of photosynthesis-light (P-I) curves were similar to those of the summer population, although the maximum photosynthetic rate (P_max) measured at 20°C was lower than that of the summer planktonic population. In winter the values of initial slope of the P-I curve, and the ratio of phycobilin to chlorophyll a sorted from sediment were higher than in colonies from the plankton.