EFFECTS OF DOMOIC ACID ON HEMOLYMPH PH, PCO2 AND PO2 IN THE PACIFIC OYSTER, CRASSOSTREA-GIGAS AND THE CALIFORNIA MUSSEL, MYTILUS-CALIFORNIANUS

The physiological effects of domoic acid on marine invertebrates which are known to accumulate this neurotoxin have not been investigated previously. Changes in haemolymph pH, PCO2, and PO2 were measured in Crassostrea gigas and Mytilus californianus when exposed continuously to the domoic acid producing diatom, Pseudonitzschia pungens f. multiseries, for 48 h followed by a 120 h clearance period. A general stress response by C. gigas was characterized by a respiratory acidosis from shell closure bs h after introduction of the algae. Haemolymph pH in the oyster returned to control levels after 36 h exposure and although hypoxic conditions persisted during 48 h exposure PO2 levels returned to normal only after 24 h of clearance, Substantial hypercapnia and elevated haemolymph bicarbonate occurred after 8 h exposure which was rectified during the remaining period of exposure. Body burden of domoic acid was greatest in the oyster after 4 h of exposure. At 120 h of continuous clearance the gill, muscle, and soft tissue still revealed detectable levels of domoic acid. M. californianus exhibited no significant change in haemolymph pH on exposure to the alga although a slight alkalosis occurred, which is associated normally with increased filtration (feeding) and gas exchange. Haemolymph PCO2 and PO2 were within the range of established control values throughout the experiment, Domoic acid was assimilated to the highest level in gill tissue and no detectable concentration of toxin was observed in any tissue after 120 h of clearance.