DOMOIC ACID UPTAKE AND DEPURATION IN DUNGENESS CRAB (CANCER-MAGISTER DANA 1852)

The patent marine neurotoxin domoic acid (DA) was detected in razor cl ams and Dungeness crabs on the Pacific Coast of the United States in 1 991, resulting in temporary closures of these fisheries. Closures prot ect the health of human consumers of clams and crabs but impose signif icant economic losses to the communities that are dependent on these f isheries. Widespread closures, and in the case of the clams long-lasti ng ones, were necessary risk management strategies because our knowled ge of DA uptake and movement through the food web is very limited. In order to resolve some of these issues and provide health managers with better information concerning this toxin, experiments were conducted on the accumulation and fate of DA in Dungeness crabs. Such informatio n could provide enhanced safety, permit more efficient closures, and l essen the economic effect of future outbreaks. In the first study, raz or clams, containing known concentrations of DA, were fed to Dungeness crabs for 5 days to determine the uptake of the toxin by the crabs. T wenty-four hours after the crabs ingested an initial 960 mu g of toxin , 260 mu g of DA (27%) was found in the hepatopancreas (HP) of the cra bs. At the end of 6 days, 68% (2,850 mu g), from an accumulated 4,220 mu g of ingested toxin, was present in the HP. DA was never found in t he hemolymph or edible muscle of crabs in this experiment, but DA was found in the feces, indicating a route of depuration. The second study examined the depuration of DA by crabs under fed and starved conditio ns. Crabs fed DA-contaminated clams for 4 days achieved an average con centration of 69.5 mu g of DA/g of HP. After 7 days, crabs that were f ed toxin-free clams three times per week showed a 38% reduction in DA concentration, to 43.4 mu g of DA/g, whereas the average toxin concent ration in the HP of crabs that were starved was reduced by only 4%, to 66.9 mu g of DA/g. In the last sampling, taken at 21 days, the concen tration of DA in the HP of fed crabs decreased by 89% of the initial D A concentration to 7.6 mu g of DA/g, but that of the starved crabs dec reased by only 57%, to 29.7 mu g of DA/g. Differences in mean concentr ations between starved and fed crabs at 7, 14, and 21 days were signif icant. Additional measurements at 21 days showed the average weight of a starved crab's HP was only 53% of the fed crab's HP (25.7 vs. 48.7g ). Although the mean weight of the starved crabs (770 g) was greater t han that of the fed crabs (730 g), the difference was not significant.