Abstract
The ciliate–metazooplankton trophic coupling is well documented from both laboratory and field experiments. The knowledge about these relationships during winter ice-covered periods is very scarce. The abundance and composition of planktonic ciliates, rotifers and crustaceans were studied during the ice-covered and ice-free periods in the Łuczański Canal (Masurian Lakeland, Poland). We hypothesised that in winter, rotifers play a major role in the top-down control of ciliates and that ciliate–metazooplankton relationships differ not only between the ice-covered and ice-free periods, but also between ice-covered months. Our study showed that ciliates formed a significant part of zooplankton biomass during the winter ice-covered period when crustaceans occurred in very low abundances. Despite cold water temperature and the presence of ice cover, time was probably a cue that initiates zooplankton development. The ciliate, rotifer and crustacean numbers and biomass, as well as chlorophyll a concentrations, were lower in February than in ice-free periods. In the winter month with ice cover, bottom-up control by resources was more important than top-down control by zooplankton grazing in regulating ciliates. In the spring month with ice cover, crustaceans and rotifers may include ciliates as an important part of their diets. In April, the studied groups of organisms were not related to each other in contrast to the summer, when zooplankton communities were closely related to each other. In autumn, rotifers may play an important role in controlling ciliates. The abundance, composition and ciliate–metazoan relationships can vary considerably not only across seasons, but also across ice-covered months.
Different Roles of Top-Down and Bottom-Up Processes in the Distribution of Size-Fractionated Phytoplankton in Gwangyang Bay
