Hemocyte changes in the Pacific oyster, Crassostrea gigas, caused by exposure to domoic acid in the diatom Pseudo-nitzschia pungens f. multiseries

The physiological effects of domoic acid on the immune system of marine invertebrates, which are known to accumulate this neurotoxin, have not been investigated previously. Changes in the number and relative phagocytic activity of circulating haemocytes in Crassostrea gigas exposed to domoic acid in the diatom Pseunonitzschia pungens f. multiseries for 48 hr, followed by clearance for 240 hr, were investigated using chemiluminescence. An initial stress response to the toxin assimilation was characterized by a marked increase in number and activity of haemocytes with 4 hr of exposure to the algae. Although the toxin level in the oyster increased during the 48 hr exposure, both number and activity of haemocytes declined from the 4 hr peak values to those significantly lower than control values after 24 hr clearance. This suppression in number and activity of circulating haemocytes following the initial toxin response was rectified only after 48 hr clearance, when domoic acid levels in the oyster tissue had declined to trace levels, allowing blood cells to regain their normal characteristics.