Microhabitat Heterogeneity and Population Ecology of Ribbed Mussels (Geukensia demissa) Near Their Northern Range Limit (Maritime Canada)

Population dynamics of sessile marine invertebrates are potentially affected by variation in abiotic variables among microhabitats. The ribbed mussel (Geukensia demissa), an ecosystem engineer in salt marshes from Cape Cod to northern Florida, inhabits two microhabitats in salt marshes near its northern range limit, Maritime Canada: the exposed seaward edge of the marsh (edge) and the edge of creeks (creek). To determine differences in population dynamics of ribbed mussels between these microhabitats, population, demographic, and abiotic variables were measured at multiple sites over 1 to 2 years. Water flow was higher, temperature less variable, and winter shoreline disturbance less prevalent along creeks than edges. Mussels showed some minor demographic differences between microhabitats: a slightly delayed onset of gametogenesis, and a tendency to lower female reproductive output and more settlers (although overall numbers were low) within creeks. These differences did not translate into consistent differences in population variables across microhabitat types, namely density, size structure, and individual growth of juveniles and adults. Although creeks appear to be more suitable habitat based on abiotic variables measured, mussel population variables may be limited by a combination of temperature and food availability or quality, or some other factor. Overall, population dynamics of ribbed mussels are similar between creek and edge microhabitats in salt marshes in Maritime Canada. This study contributes a first assessment of the dynamics of a potentially key salt marsh species near its northern range limit.