TOXICITY IN PERIDINIUM ACICULIFERUM ‐ AN ADAPTIVE STRATEGY TO OUTCOMPETE OTHER WINTER PHYTOPLANKTON?

Abstract

Rengefors, K.1 & Legrand, C.2 1Limnology, Department of Ecology, Ecology Building, Lund University, SE‐223 62 Lund, Sweden; 2Department of Biology and Environmental Science, University of Kalmar, Barlastgatan 1, SE‐391 82 Kalmar, SwedenFreshwater dinoflagellates may form dense blooms during winter in ice‐covered lakes. Unlike their marine counterparts freshwater dinoflagellates are rarely considered as potential toxin producers. Here we tested if the winter species Peridinium aciculiferum produces a toxin(s)and investigated the potential adaptive function of that toxin ‐ i.e. predator defense or inhibition of competitors (allelopathy). We found that P. aciculiferum produces a toxin(s). Using traditional toxicity bioassays (Artemia toxicity test and haemolytic activity assay), we detected the production of a toxic substance by P. aciculiferum cells from both the field and from laboratory cultures. Cultures deprived of phosphorus showed most toxicity. Potential predators, such as Daphnia galeata (Cladocera) and Eudiaptomus graciloides (Copepoda), were apparently not harmed by P. aciculiferum toxicity. However, a competitor, the flagellate Rhodomonas lacustris (Cryptophyceae), which co‐occurs with P. aciculiferum was killed (allelopathy) by the P. aciculiferum toxin. The toxin(s) caused the cells of R. lacustris to swell and burst. We concluded that allelopathy may be an adaptive strategy of winter dinoflagellates, allowing them to outcompete other phytoplankton species, and thereby dominate the algal biomass.