Abstract
Toxic harmful algal bloom events across the globe seem to be increasing, even in what have been considered to be relatively clean aquatic environments, such as the Swan Canning Estuary in Perth. After a series of blooms of potentially toxic dinoflagellate Alexandrium sp., local regulatory bodies collaborated to investigate the potential impact of blooms on the socially iconic blue swimmer crab (Portunas armatus) in order to provide scientifically sound advice on consumption of crabs in the presence of an Alexandrium outbreak.
In particular, the consortium was interested in whether crabs actually become intoxicated with paralytic shellfish toxins (PSTs) at a level that would warrant a public health response and, if so, what happened to those toxins when crabs were prepared for consumption.
Toxin analysis of crab tissues using LC-MS/MS revealed that PSTs accumulated only in the hepatopancreas when crabs were exposed to PST levels double the regulatory limit. PST concentration was not affected by cooking, the interaction between freezing and cooking, or the size or sex of the crabs. Freezing crabs significantly reduced the total PST concentration in the hepatopancreas (F1,23 = 10.60, P < 0.001) possibly due to use of a ‘thawing by flushing’ technique on frozen material. Analysis of individual toxins showed that freezing significantly reduced the concentration of relatively toxic GTX2 (F1,23 = 8.54, P < 0.05) and GTX3 (F1,23 = 10.87, P < 0.05) but not less toxic C1 (F1,23 = 4.56, P > 0.05) or C2 (F1,23 = 0.28, P > 0.05) analogs. There were no apparent effects of either cooking or freezing on the toxin profile. No PSTs were detected in the cooking broth. These findings suggest that current recommendations to remove the head, gut, and gills before cooking P. armatus crabs exposed to toxic Alexandrium spp. blooms should prevent human ingestion of PSTs.