Effects of Hypoxia and Low-Frequency Agitation on Byssogenesis in the Freshwater Mussel Dreissena polymorpha (Pallas)

The effect of variations in PO2 and agitation rate on byssogenesis, motility, and survival of the zebra mussel (Driessena polymorpha) was investigated. Mussels exposed to a PO2 {le} 15.4 torr exhibited increased mortality, reduced motility, and significant suppression of byssogenesis. At 7.7 and 15.4 torr, mean survival times were 5.2 and 5.8 days, maximum survival times being 15 and 16 days, respectively. After 21 days at a PO2 of 23.1 torr, sample mortality was 33.3% and declined to 18.2% at 30.9 torr. There was no mortality at full air O2 saturation (~ 154.3 torr). Adult zebra mussels exhibited the highest rate of byssogenesis in still water (0 cycles per minute [CPM]). Rate of byssogenesis progressively decreased as agitation rate increased. At 30 and 40 CPM, rate of byssal thread production was significantly lower than at 0 CPM. After 21 days, means of 58.6 and 44.8 byssal threads/mussel were found in the byssal mass of specimens exposed to 30 and 40 CPM, respectively, significantly fewer than the mean of 92.7 threads/mussel recorded in still water. Suppression of byssogenesis in D. polymorpha under hypoxic conditions is a response similar to that reported for the marine mytilid Mytilis edulis; however, suppression of byssogenesis with elevated agitation rate is the opposite response to that reported for M. edulis.