Although the majority of phytoplankton are harmless to humans, some contain toxins that can cause illness and even death in extreme cases through the consumption of contaminated shellfish.
In Ireland shellfish poisoning is presently a year round occurrence with most closures being attributed to Dinophysis species. However other toxic species that are problematic to the Irish aquaculture industry are Pseudo-nitzschia, Alexandrium and Protoperidinium species.
You can download an identification sheet (PDF, 177KB) including details of these species.
Species |
Associated Toxins |
Symptoms |
Comments |
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Dinophysis species and Prorocentrum lima
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Diarrhetic Shellfish Poisoning (DSP)
caused by Okadaic acid (OA) and Dinophysis toxins (DTXs) |
diarrhoea, nausea, vomiting, |
Known to cause most closures of bays in Ireland.
Dinophysis can be observed throughout the year, although are most present during the summer months.
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Pseudo-nitzshia species |
Amnesic Shellfish Poisoning (ASP)
caused by Domoic Acid (DA) |
diarrhoea, nausea, vomiting, abdominal pain, short term memory loss |
They are found in all areas of the Irish coast.
Have to occur in numbers in excess of 50,000 plus cells per litre to cause toxicity in shellfish.
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Alexandrium species |
Paralytic Shellfish Poisoning (PSP)
Caused by Saxitoxins and Gonyautoxins |
Headaches, dizziness, diarrhoea, nausea, vomiting leading on to muscular paralysis. In severe cases respiratory failure may occur |
Can produce toxins in relatively low no’s
PSP has not been observed in any other part of Ireland apart from Cork Harbour despite Alexandrium being observed along the west and south coasts.
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Protoperidinium species
(possibly) |
Azaspiracid Poisoning (AZP)
Caused by Azaspiracids |
Same as DSP but more acute, with headaches and chills |
It is still to be confirmed if this species is the cause of AZP, studies are ongoing. |