The marine environment supports a range of microscopic plants called phytoplankton or algae. Some algae produce natural chemicals that are toxic to humans. These toxins do not represent a problem in algal cells as the toxin concentrations are low and not in a form consumed by humans. However they may be concentrated in the tissues of filter feeding shellfish (eg oysters, mussels, scallops and clams) thus providing a means by which high and potentially fatal concentrations of toxin may be ingested by humans. The shellfish themselves are relatively insensitive to the toxins.
The toxins produced by algae can cause four significant syndromes when concentrated by shellfish and consumed by humans: Paralytic Shellfish Poisoning (PSP), Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP) and Amnesic Shellfish Poisoning (ASP). The symptoms of these syndromes range from mild illness to death in susceptible consumers.
The TSQAP has developed a biotoxin management plan to better protect shellfish consumers from the risk of biotoxin poisoning, The biotoxin management plan focuses heavily on monitoring for biotoxins in meats and is supported by algal monitoring and chemical testing as required.
TSQAP Biotoxin Management Plan (693Kb)
Biotoxins in Tasmania
In 1980 the toxic dinoflagellate Gymnodinium catenatum appeared in southern Tasmanian waters. Regular and sometimes prolonged closures of shellfish farms have occurred in some growing areas in Tasmania since this date, focussing mainly in the south east.
Several mild cases of PSP occurred during 1986 and 1993 following massive blooms of Gymnodinium catenatum. G. catenatum is the only toxic organism causing regular closures of shellfish farms, although DSP toxins have caused one marine farm closure, and have been found at elevated levels outside marine farm zones in south-east Tasmania.
Potentially toxic algae that have been found in Tasmania are Alexandrium catenella, A. cf tamerense, A. ostenfeldii, A. minutum, Gymnodinium catenatum, Dinophysis fortii, D. acuminata, D. caudata, D. acuta, Prorocentrum lima and Psuedo-nitzschia spp.