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The toxic dinoflagellate Gymnodinium catenatum: an invader in the Mediterranean Sea

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Over the last few decades, Mediterranean marine biodiversity has been undergoing rapid alterations due to climate change and human impact (TURLEY 1999), and has become exceptionally susceptible to fish, invertebrate or macroalga invasions (BIANCHI and MORRI 2000, GALIL 2000, MEINESZ et al. 2001, BOUDERESQUE and VERLAQUE 2002). In the pelagic ecosystem, it is to be expected that a change in nutrient ratios will shift the phytoplankton composition to non-siliceous species such as flagellates and dinoflagellates (TURLEY 1999, BÉTHOUX et al. 2002). Consequently, together with a modification of the coastal habitats, an increase in red tide events is expected, in conjunction with the spread of toxic dinoflagellates, as already reported (GARCÉS et al. 2000, VILA et al. 2001). Since the early 1900s, at least 16 exotic species of phytoplankton has become an integral part of European Atlantic waters (NEHRING 1998, ELBRÄCHTER 1999). However in the Mediterranean Sea, little is known about the invasion of exotic phytoplankton taxa. Gymnodinium catenatum Graham is a naked, chain-forming dinoflagellate that produces saxitoxin, the first metabolite responsible for Paralytic Shellfish Poisoning intoxication (PSP). The species produces cysts that survive prolonged darkness and nutrient-poor conditions and can travel considerable distances in ships´ ballast water (HALLEGRAEFF 1998). Many studies have reported the historical presence of the species in European Atlantic waters based on cysts (NEHRING 1995), but these records corresponded to non-toxic species Gymnodinium nolleri Ellegaard et Moestrup further described (ELLEGAARD and MOESTRUP 1999). The origin of Gymnodinium catenatum in Atlantic European waters is still unresolved. The taxon was for first time reported in 1976 after a PSP event in the Galician Rías (NW Spain) (ESTRADA et al. 1984). WYATT (1992) hypothesised that the taxon was introduced by the Galician fishing fleet, which during the 70s operated in Argentinan waters, where this species is common.

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