Deepwater population structure and reproductive state of quagga mussels (Dreissena bugensis) in Lake Erie

Quagga mussel (Dreissena bugensis) population structure and reproductive status were assessed at deepwater (37 and 55 m) sites in eastern Lake Erie during July 1996. Mussels occupied similar to 70% of soft substrates at 37-m sites and between 63 and 90% at 55-m sites. Shell length and dry mass frequency distributions were similar at both sites, although recruits less than or equal to 5 mm comprised a larger proportion of the population at the deeper site. The population surveyed here allocated disproportionately less mass to shell and more to soft tissues relative to zebra mussels (Dreissena polymorpha) from shallow-water sites in eastern Lake Erie and from Lake St. Clair. The population at 55 m was slightly skewed toward male mussels (58%). Female mussels that were examined for reproductive state contained mature oocytes (80%) or had spent gonads (20%). Because water temperature at the site was only 4.8 degrees C, this survey provides the first evidence of gonadal development and spawning by quagga mussels at low temperature. These findings contrast with most reports of spawning by congeneric zebra mussels at temperatures greater than or equal to 12 degrees C but are consistent with distributions of the species in different basins of the lake.