Effect of repeated Exposure to low oxygen on respiratory metabolism and vertical movements in the pen shell Atrina lischkeana

We exposed pen shells (Atrina lischkeana) to repeated periods of low-oxygen for 30 d and measured their survival, behavior, glycogen content, and organic acid concentration. Exposure to low-oxygen had no effect on survival. Animals moved upward above the sediment under low-oxygen conditions and downward under aerobic conditions, repeating these movements for 19 d. The difference in shell height above the sediment before and after low-oxygen exposure gradually decreased; after 20 d there was no significant difference. Low-oxygen exposure also resulted in a significant decrease in glycogen content and in concentrations of malate and fumarate. Thus, repeated exposure of pen shells to low-oxygen conditions reduces glycogen content, alters metabolism, and affects vertical movements, all of which may cause ecological dysfunction. We suggest that hypoxia might be one factor contributing to the collapse of pen shell resources.