Population dynamics of the ribbed mussel (Geukensia demissa) near its northern range limit, Maritime Canada

Abstract

Ribbed mussels (Geukensia demissa) are important ecosystem engineers in salt marshes along the east coast of North America, but their populations are not well studied at their northern range limit, Maritime Canada. To learn more about ribbed mussel populations in Maritime Canada, I monitored their population dynamics over 2 years at several salt marshes in 2 microhabitats (the exposed seaward marsh edge and the edge of marsh creeks). I also reared larval ribbed mussels in the laboratory to monitor their survival, growth, and settlement at a range of temperatures (15–28°C). I then used survival, growth, and age data from my research and the scientific literature to parameterize a matrix model for ribbed mussel populations in two regions: Maritime Canada and southern New England/New York. Density of individuals, population size structure and demographic variables of ribbed mussels in Maritime Canada were variable within and among sites, but were not consistently affected by different microhabitats. Larval ribbed mussels had high mortality at low temperatures and grew significantly faster and settled earlier at higher temperatures. Elasticity analyses of my matrix model indicated that ribbed mussel populations, independent of the region examined, were more sensitive to fluctuations in adult survival than recruitment. However, ribbed mussel populations in Maritime Canada were more sensitive to fluctuations in adult survival than those in southern New England and New York; ribbed mussels in Maritime Canada are more affected by winter disturbance (ice scour and storms), but nevertheless appear to have a longer life span potentially because of low predation pressure and absent intraspecific competition. Overall, this thesis provides the first integrated assessment of ribbed mussel population dynamics at their northern range limit, Maritime Canada.