Acute physiological effects of zebra mussel (Dreissena polymorpha) infestation on two unionid mussels, Actinonaias ligamentina and Amblema plicata

Our laboratory studies of the physiological effects of zebra mussel (Dreissena polymorpha) infestation on the freshwater mussels Actinonaias ligamentina and Amblema plicata (Unionidae) show that (i) zebra mussel infestation causes stress and symptoms of starvation in unionid mussels, (ii) unionid species are affected unequally, and (iii) symptoms of starvation are greater when initial condition is low. Nutritive stress in infested unionid mussels was indicated by shifts to lower metabolic rates, more protein-based metabolism (lower O:N ratios), and compensatory increases in grazing rates. Starvation may be the result of local food depletion and (or) increased metabolic cost. Actinonaias ligamentina (subfamily Lampsilinae) was more sensitive to infestation than Amblema plicata (subfamily Ambleminae), as indicated especially by changes in oxygen uptake rate and grazing rate. The effects of infestation were greater in mussels that were already in low condition. Our results indicate that the decline in diversity of unionid mussels since the introduction of zebra mussels is due to species-specific rates of starvation.