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Pilot Study on the Incidence of Algal Toxins (ASP, DSP and PSP Toxins) in Scottish Brown Crab Cancer Pagurus

Integrin Advanced Biosystems Ltd
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This research project aims to provide the Food Standards Agency Scotland with data relating to the uptake of biotoxins by Cancer pagurus and the occurrence of amnesic shellfish poisoning (ASP), diarrhetic shellfish poisoning (DSP) and paralytic shellfish poisoning (PSP) in crabs harvested from areas known to be affected by shellfish biotoxins.
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The Food Standards Agency has the statutory responsibility under EU legislation to monitor shellfish from classified production areas for the presence of algal toxins.

Toxins belonging to the ASP, DSP and PSP toxin groups are regularly monitored as part of the statutory monitoring programme, which focuses on bivalve shellfish such as mussels, scallops and oysters. Bivalve shellfish have provided the usual route of toxic transfer for human poisoning by algal toxins in the UK.

However, there are frequent reports from other parts of the world of people being poisoned through other vectors, particularly fish and crabs. Recently, there was a serious outbreak of DSP in Norway caused by contaminated brown crabs (Cancer pagurus). These crabs had probably been feeding on contaminated mussels.

Cancer pagurus is a major target of creel fisheries in the UK and is sold in various forms including 'Cromer' crab where the viscera are used along with white meat. Therefore, there is a possibility of crab-related poisonings in the UK.

However, crabs are not routinely sampled as part of the monitoring programme and there is no data on UK crab toxicity that could inform whether or not such monitoring is necessary and, if it is, at what frequency it should be employed.

The purpose of this study is to provide Food Standards Agency Scotland with data on the incidence of algal toxins in Cancer pagurus in Scottish waters during the 2005 and 2006 monitoring seasons. Information will also be gathered to provide the FSA with a good knowledge of crab fisheries and processing in Scotland so that the risk of algal toxin transfer to humans via brown crabs can be better evaluated. This information will be used to inform the FSA of the possible need for a UK-wide study to investigate the occurrence of algal toxins in edible crustaceans.

Research Approach:
The following approaches will be employed to investigate the potential contamination of brown crabs by ASP, PSP and DSP which are summarised below.

  • targeted sampling of wild crabs from areas where contaminated mussels are found both routinely and periodically
  • laboratory feeding experiments to investigate the potential for, and in vivo localisation of these toxins and to generate material for analytical studies
In addition, a study of the Scottish crab fishery will be carried out to map where, when and how many crabs are being fished. This will be followed by a study of the fate of Scottish crabs following capture.

Results and findings:
Amnesic, Diarrhetic or Paralytic Shellfish Poisoning (ASP, DSP, PSP respectively) is normally associated with the consumption of bivalve molluscs. However, in 2002, there was an outbreak of DSP in Norway caused by contaminated brown crabs (Cancer pagurus). Cancer pagurus is a major target of creel fisheries in the UK. The purpose of this study was to provide Food Standards Agency Scotland with data on the incidence of algal toxins in Cancer pagurus collected from Scottish fishing grounds. During 2005 and 2006, brown crabs were collected from areas around Scotland that were historically known to have problem with these toxins in shellfish, or reactively from areas suffering from a toxic event (as identified by levels in shellfish near to, or above, the regulatory limit), and then analysed for ASP, PSP or DSP. Feeding studies to artificially contaminate crabs were also carried out to examine toxin uptake in more detail.

Algal biotoxins including DSP are regularly detected in bivalve molluscs harvested in Scotland, but very little is known about their prevalence in other vectors. An incident of Diarrhetic Shellfish Poisoning (DSP) in Norway due to the consumption of brown crab prompted the Food Standards Agency Scotland (FSAS) to commission this study to investigate the potential for crabs from Scottish waters to act as a vector for algal biotoxins.

Crabs were sampled from a variety of locations around Scotland during 2005 and 2006, and the brown meat analysed for all three groups of algal biotoxins (ASP, DSP and PSP). During 2005, it was found that both PSP and ASP toxins were frequently detected in wild crabs although only a very small number of crabs were found to contain levels that were over the regulatory limit set for bivalves for these toxins. In crabs containing high toxin levels in the brown meat, the white claw meat was also tested. However, no ASP, and only trace levels of PSP were detected. DSP toxins were not detected in any of the crabs sampled during 2005. Again, during 2006 ASP and PSP toxins were regularly detected at low concentrations in the brown meat, with only a small number found to be over the regulatory limit for bivalves. Trace levels of DSP toxins were also detected in the brown meats of crabs sampled during 2006.

Laboratory feeding studies demonstrated that accumulation of both ASP and DSP toxins occurred in crabs fed exclusively on toxic shellfish. This study has highlighted the potential for crabs to be contaminated with all three groups of algal biotoxins, although the findings suggest that toxicity is almost exclusively associated with the brown meat. Further work is required to determine the implications of these findings for human health.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number
Natural Toxins
Bacterial Pathogens