Harmful Algal Blooms
There are over 5000 species of tiny single celled plants that make up the marine phytoplankton. These are at the start of virtually all marine food chains and are essential to support marine life.
Harmful phytoplankton produce a range of toxic biochemicals. These are harmless to shellfish, which filter feed on the phytoplankton and in doing so can concentrate toxins in their tissue . Some very serious neurological and gastrointestinal sicknesses result in people if they eat contaminated shellfish.
Diarrheic Shellfish Poisoning (DSP)
Amnesic Shellfish Poisoning (ASP)
Paralytic Shellfish Poisoning (PSP)
There is a fourth category, Azasparacid Shellfish Poisoning (AZP), which causes symptoms similar to DSP in low doses. The toxins which cause the most problems in western Europe are those which result in DSP. This group of toxins comprises okadaic acid and its derivatives (DTX1, DTX2, DTX3, etc.). Most often contamination is linked with the presence of Dinophysis, particularly Dinophysis acuminata and Dinophysis acuta. These species have a very distinctive appearance under a microscope. The ASP toxin, domoic acid, is produced by the diatom Pseudo-nitzschia whereas PSP toxins are mainly produced by species from the genus Alexandrium, which is a very small, innocuous phytoplankton that along with Dinophysis belongs to a group known as the dinoflagellates. The toxin produced by Alexandrium tamarense found around the Northern Isles of Britain is highly potent indeed.
|Dinophysis acuta||Dinophysis acuminata|
The diatom Pseudo-nitzschia is a small spindle shaped cell which often occurs in chains of slightly overlapping cells. The cells in these images are 70 micrometres long and about 6 micrometers wide (0.07 x 0.006 mm).<
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