Settlement and Metamorphosis of the Ribbed Mussel, Geukensia demissa, in Response to Environmental Cues

Ribbed mussels are typically found in Spartina alterniflora salt marshes and can form dense aggregations along low marsh shorelines and tidal creeks. The presence of ribbed mussels within marshes is well documented, and many studies have examined their importance in these ecosystems. However, it is not known whether mussels settle preferentially in S. alterniflora habitat and what factors influence observed aggregations of mussels. Knowing this is important for current efforts in salt marsh restoration. Therefore, we conducted experiments with competent larvae to test whether chemical or physical cues of S. alterniflora or adult conspecifics stimulate settlement and metamorphosis. More larvae settled and metamorphosed in the presence of a S. alterniflora leaf, although not on the leaf, and in water conditioned with S. alterniflora than in seawater controls. The presence of chemical or physical cues from conspecifics had no effect on settlement and metamorphosis relative to controls. Larvae settle and metamorphose in response to chemical cues from S. alterniflora, resulting in ribbed mussels being found predominantly in S. alterniflora habitat. However, because there was no response to conspecifics, other factors are likely responsible for their aggregated distribution. Further work is required to determine the factors resulting in mussel aggregation, including movement of juvenile mussels and environmental filtering.