Farmed mussels

© Muckairn Mussels

Algal toxins (also known as biotoxins) are natural compounds produced by certain species of marine algae. They are of concern because shellfish such as mussels, cockles and oysters can accumulate them when they feed, and this has the potential to affect human consumers. However, when toxins are detected in shellfish by the statutory monitoring programme (Figure 4.19), appropriate management measures are taken to protect shellfish consumers. Despite some concern that high levels of nutrients could increase the occurrence of harmful algal blooms in which the toxins are produced, a recent study concluded that the abundance of the harmful algal bloom species in UK and Irish coastal waters is not related to nutrient enrichment from human sources. Essentially, harmful algal blooms are a natural phenomenon beyond our control and, as such, will occur. However, we will need to continue with monitoring programmes to protect public health and shellfish production, particularly as climate change may alter the frequency of toxic blooms.

For this assessment we used data from comprehensive biotoxin monitoring programmes covering the period 2005 to 2008. These include monitoring for relevant phytoplankton species in all regions of the UK to comply with EU legislation. (The testing methods employed by all official monitoring laboratories on behalf of the competent authority follow United Kingdom National Reference Laboratory [UKNRL] protocols [where these exist] and are accredited to ISO17025 standards where possible.) We did not include data from additional studies outside this three-season programme.

We did not include historical data in this assessment, so have not reported trends in toxicity observed in shellfish. We found that marine biotoxins and toxic algae were present in samples from all monitored areas in England and Wales, Northern Ireland and Scotland during the three years of study, but they did not increase either temporally or spatially. However, the number of samples in which toxins were detected was small, generally fewer than 5% and less than 1% in some years.

There were no incidents of human toxicity and thus we conclude that the current monitoring regime within the UK (which monitors the three classes of shellfish toxins responsible for amnesic shellfish poisoning, ASP; diarrhetic shellfish poisoning, DSP; and paralytic shellfish poisoning, PSP – see Figure 4.20) provides sufficient protection for human consumers of shellfish in respect of ASP, DSP and PSP toxins. Other algae occur in UK waters which generate additional toxins; notably the azaspiracids and spirolides and the toxins responsible for neurotoxic shellfish poisoning. Current monitoring arrangements do not include these, so we need further research to assess the risk they pose and whether they should be monitored in the future.