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

The dynamics of the Ceratium hirundinella population and the abundance of dinocysts in the plankton and sediments were studied in Lake Sempach in 1988. In 1987, a rich population of Ceratium (380 cells ml-1) accompanied 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 Ceratium population increased slowly starting in April, and reached a maximum number in August (31 cells ml-1). Peridinium willei reached 100 cells ml-1. Newly formed cysts of Ceratium were recorded in the plankton and sediments at the end of July - beginning of August. They appear in the sediments as separate cells. Their number increased gradually, reaching a maximum of 600 cysts l-1 at the end of October. Ceratium formed more cysts than did Peridinium, but the rate of survival of the Ceratium cysts appears to be lower than that of Peridinium cysts. In addition 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.