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Niclas Johansson1 & Edna Granéli2 1Dept. of Limnology, Lund University, Ecology Building, SE-223 62, Lund, Sweden 2Marine Sciences Dept., Kalmar University, Box 905, SE-391 29, Kalmar, Sweden
The marine haptophyte Prymnesium parvum is known to produce a set of highly potent exotoxins commonly called prymnesins. These toxins have been shown to have several biological activities, including ichthyotoxic, neurotoxic, cytotoxic, hepatotoxic and hemolytic activity towards a range of marine organisms, mainly gill breathing animals such as fish, shellfish and molluscs. If prymnesins can act as allelopathic substances inhibiting the grouth of other phytoplankton species is however not known. Earlier studies have shown that the toxicity of P. parvum is enhanced when the cells are grown under N- or P-limited conditions. In this study, Thalassiosira weissflogii, Prorocentrum minimum, Rhodomonas sp. and a strain of Prymnesium patelliferum known to produce prymnesins, were incubated with cell-free filtrate of P. parvum cultures grown under nutrient limiting (N or P) or non limiting conditions. Addition of filtrate from P. parvum cultures grown under N- or P-limitation inhibited the growth of all tested species, except P. patelliferum, which was not negatively affected under any conditions. Also, addition of filtrates from the non-limited cultures did not have a negative influence on the growth of any of the tested species. This differing activity of the Prymnesium toxins suggests that prymnesins may play an allelopathic role in nature. Thus, production of prymnesins is a valuable weapon in Prymnesium- species to avoid grazing pressure and to outcompete co-occuring phytoplankton species.
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