The effects of acidic seawater on three species of lamellibranch mollusc

Abstract

Three species of commercial bivalve mollusc, Ostrea edulis, Crassostrea gigas and Mytilus edulis, were maintained in seawater over a pH range of 5.4–8.2 (control), normally for 30 days. Significant mortalities occurred in C. gigas at pH <6, in M. edulis at pH <6.6, in O. edulis young at pH ⩽6.9 (after 60 days) and spat at pH <7 after 18 days. Survival at a given pH level reduced with time of exposure and with increased temperature, and increased with size of animal. Growth suppression, tissue weight loss, reduced shell size, shell dissolution and suppressed feeding activity occurred at pH ⩽ 7. Abnormal behaviour analogous to narcosis (excessive shell gaping, torpor) occurred at pH ⩽6.5, possibly attributable to CO 2 excess. These and other collated results confirm that seawater at pH <7 is intolerable to bivalve molluscs.