The influence of biotic and abiotic factors on the seasonality of meso-zooplankton in Lake Tovel (Trentino, Italy)

摘要

Lake Tovel, famous for its past red summer blooms of the dinoflagellate Glenodinium sanguineum Marchesoni, represents an unusual lentic ecosystem, naturally subject to strong seasonal water-level fluctuations and a very fast lake renewal time. These factors permit Lake Tovel to be classified a fluvial lacustrine environment (Corradini et al. 2001). Both underground and surface inlets in the Red Bay collect the water of the catchment area. Since Baldi's work (1941) Lake Tovel has been considered a rotifer lake due to the high abundance of rotifers in contrast to Crustacea. In the lake, 18 different pelagic rotifer taxa are present in contrast to two species of cladocera, B. longirostris and D. longispina, and one species of copepoda, Cyclops strenuus. Rotifers play an important role as grazers, suspending feeders and predators in the zooplankton community. In terms of biomass rotifers can not compete with the larger Crustacea (Herzig 1987), but their short development time gives rotifers a decisive time advantage when the food conditions for development are favourable (Walz 1995). The relationship among suspension feeding rotifers, cladocerans and copepods is important because they compete for food resources of similar size (Herzig 1987) and, through exploitative competition, cladocera are able to suppress rotifers (Conde-Porcuna et al. 1994). Many studies show that temperature, oxygen content, pH and the availability of suitable food are also key factors in restricting rotifer occurrence and vertical distribution of rotifers (Hofmann 1977, Urabe 1992). In artificial reservoirs water-level fluctuations affect food availability (bottom-up effects) and the pressure of predators (top-down effects; Naselli-Flores & Barone 1997) but little is known about the consequences of water-level changes on rotifers and Crustacea in lakes of temperate regions. The purpose of this study was to relate the temporal distribution of rotifers and cladocera to the hydro-logical situation of the lake.