Domoic acid: a fascinating marine toxin.

There are indications that toxic algal blooms are increasing because of pollution of coastal waters and worldwide shipping. This mini-review deals with the marine biotoxin domoic acid, also known as amnesic shellfish poison, and its main producing pennate diatom genus Pseudo-nitzschia (Bacillariophyceae). Besides contamination of seafood, these organisms have also been involved in human and marine wildlife mortality. The article aims to give an overview of all biological and environmental factors that should be considered when trying to evaluate a possible increase in toxic blooms of Pseudo-nitzschia spp. Pseudo-nitzschia blooms characteristically occur in a low light regime, at a time when the temperature is falling and at a wide range of salinities. Laboratory studies have shown that the production of domoic acid, a water-soluble amino acid, is related to silicon, phosphorus, nitrogen and trace metal (mainly iron) availability. Domoic acid has no known function in defence or primary metabolism; a role in excretion of excess photosynthetic energy or as a binding ligand for trace metals is suggested. The variability in domoic acid production by different Pseudo-nitzschia spp., or the presence of toxic and non-toxic strains of the same species, cannot be explained. The conclusion is drawn that an increase in toxic blooms of Pseudo-nitzschia spp. might be possible, especially because of the expected increase in nutrient availability from pollution and desert dust. Global warming may have an influence as well by lengthening the growth period for Pseudo-nitzschia, enlarging their global distribution and increasing the dust load through desertification.