Mixotrophy, allelopathy and the population dynamics of phagotrophic algae (cryptophytes) in the Darss Zingst Bodden estuary, southern Baltic

Abstract

Seasonal plankton dynamics in the Darss Zingst Bodden Chain (DZBC), a southern Baltic estuary, are characterised by summer cyanophyte/chlorophyte dominance, but with winter blooms of mixotrophic cryptophytes, particularly associated with periods of ice cover. Analysis and simulation of a mixotrophic Lotka-Volterra competition model shows that coexistence of algae and cryptophytes is unlikely under static conditions, with seasonal or stochastic variation in parameters, as well as with time lags. However, incorporating production by cyanophytes/chlorophytes of non- toxic allelopathic substances allows stable coexistence of algae and mixotrophs. When parameterised using empirical DZBC data for light, temperature and ice cover, the model gives a good represen- tation of cryptophyte dynamics and bloom formation. We conclude that both mixotrophy and allelopathy are necessary ingredients of community coexistence and dynamics in the DZBC.