Genetic affinities, ecophysiology and toxicity of Prorocentrum playfairii and P. foveolata (Dinophyceae) from Tasmanian freshwaters

The freshwater dinoflagellates Prorocentrum playfairii (corrected from the original spelling playfairi) and P. foveolata from two lagoons in Tasmania, Australia, have been successfully cultured for the first time. Cultures were established in order to elucidate their possible toxicity, ecophysiology and genetic affinities with better-known marine congeneric species. Growth experiments indicated P. playfairii to be a slow-growing [0.09 divisions (div.) d-1], truly freshwater species that will only grow in salinities of 0-5 practical salinity units (psu). In contrast, P. foveolata tolerated salinities of 0-30 psu and exhibited a significantly faster growth rate (0.47 div. d-1). Both P. playfairii and P. foveolata grew under a wide temperature range (10-30C and 10-25C, respectively), indicating a tolerance to temperature fluctuations typical of shallow, enclosed water bodies. Both species were negative for toxins such as those from marine species of Prorocentrum causing diarrhetic shellfish poisoning in humans. Molecular sequencing of the large-subunit ribosomal DNA suggested that P. playfairii and P. foveolata are more closely related to toxic benthic marine Prorocentrum (such as P. lima and P. cf. belizeanum), than pelagic marine Prorocentrum (such as P. gracile, P. rhathymum, P. triestinum and P. compressum). We speculate that P. playfairii and P. foveolata most likely evolved from a common ancestor to marine benthic Prorocentrum and have since adapted to freshwater habitats.