Respiratory and acid - base consequences of zebra mussel infestation on the valves of unionids

Infestations of the zebra mussel (Dreissena polymorpha) on the valves of unionids purport to cause the eventual death of the host, although the means is uncertain. We examined the blood acid–base and respiratory gas state in a sample of the unionid bivalve Elliptio complanata, both with zebra mussels attached to the valves and with zebra mussels removed. Both sets of clams were exposed for 24 h to the following three environmental gas treatments: normoxia–normocapnia ( 153 torr, 0.3 torr), moderate hypoxia–hypocapnia ( 35 torr, 0 torr), and severe hypoxia–hypercapnia ( 8 torr, 2.5 torr). Blood pH, , , total CO2, and osmolality were determined. Although the effects of gas treatment were profound, zebra mussel infestation had no effects on any of the variables measured. Zebra mussel infestation increased with size of the unionid host, but we detected no relationship between the degree of infestation and any blood variable. This suggests that competition for oxygen in the medium or reduction in ventilatory c...