Seasonal dynamics of cyst formation of strombidiid ciliates in alpine Lake Mondsee, Austria

Abstract

The seasonal dynamics of strombidiid ciliates in alpine Lake Mondsee, Austria, were studied from September 1999 to November 2000 and in April/May 2001. Simultaneously, their resting cysts were collected in sediment traps. Concentrations of active strombidiids at 0 to 20 m depth ranged from 50 cells 1-1 (February) to 2100 cells 1-1 (May). The genera Pelagostrombidium and Limnostrombidium coexisted during all seasons, with Pelagostrombidium being the dominating taxon, contributing 70 and 83% to total strombidiids in September 1999 and May 2001, respectively. Throughout the study period, only 1 cyst type was observed, which in size and shape matched a previous description of Pelagostrombidium cysts. Maxima of cyst production (up to 2 × 105 cells m-2 d-1) occurred in October/November, while virtually no cysts were detected in winter, spring and early summer. The absence of a spring maximum of cyst formation contrasts with earlier observations from pre-alpine Lake Constance. We explain this finding by a different timing of strombidiid development, relative to the phytoplankton spring bloom in both lakes.