THE CYSTS OF CERATIUM-HIRUNDINELLA - THEIR DYNAMICS AND ROLE WITHIN AEUTROPHIC (LAKE SEMPACH, SWITZERLAND)

The dynamics of the Ceratium hirundinella population and the abundance of dinocysts in the plankton and sediments were studied in Lake Sempa ch in 1988. In 1987, a rich population of Ceratium (380 cells ml-1) ac companied by Peridinium spp. developed in the lake. The dinocysts were found entrapped in a kind of flocs, in the deepest part of the lake, in the upper flocculent layer. The number of viable cysts of Ceratium in the sediments decreased gradually from April to July 1988. The Cera tium population increased slowly starting in April, and reached a maxi mum number in August (31 cells ml-1). Peridinium willei reached 100 ce lls ml-1. Newly formed cysts of Ceratium were recorded in the plankton and sediments at the end of July - beginning of August. They appear i n the sediments as separate cells. Their number increased gradually, r eaching a maximum of 600 cysts l-1 at the end of October. Ceratium for med more cysts than did Peridinium, but the rate of survival of the Ce ratium cysts appears to be lower than that of Peridinium cysts. In add ition to their biological functions, the cysts also have an impact on the ecosystem as carriers of nutrients from down to up and from up to down.