Patterns and scales of connectivity: temporal stability and variation within a marine metapopulation

Because many marine invertebrates have a dispersive planktonic phase, the spatial scale of demographic, connectivity among local populations remains a key, but elusive, parameter driving population and metapopulation dynamics. However, temporal variation in the scale of connectivity remains largely undocumented, despite its recognized importance for predicting population responses to environmental changes. To assess the temporal stability of metapopulation connectivity, we conducted a large-scale survey of a blue mussel (Mytilus spp.) metapopulation for five years along a 100-km section of coastline of the Gaspé Peninsula, Québec, Canada. For each year, we estimated the scale of demographic coupling among 27-29 sites within our study region, using the spatial cross-covariance between adult abundance and recruit density across sites. Despite large interannual variability in overall recruit abundance, our analysis revealed stationary spatial distributions of adult and recruit abundance. More importantly, our analysis revealed a consistent demographic coupling among populations at a distance ranging from 12 to 24 km in all but one of the five years studied. The scale of connectivity in this system is thus temporally stable, but can occasionally show irregular fluctuations, and our results provide evidence in support of the integration of time-varying connectivity to marine metapopulation and reserve network theories.