Many marine benthic invertebrates undergo a passive pelagic larval stage. As opposed to sessile adults, larvae can travel over great distances, transported by currents. However, patterns of ocean currents are known to vary across temporal scales, seasonally, inter-annually. Moreover, such variability is predicted to increase with ongoing climate change. Metapopulation theory predicts how the average and spatial distribution of connectivity can alter the stability of metapopulations, but little is known about the importance of spatiotemporal heterogeneity in connectivity and how it can affect metapopulation stability and persistence. To answer such question, we used a stochastic and stage-structured metapopulation models, with and without density-dependence in subpopulation growth. We derived and simulated the stochastic metapopulation growth rate in relation to the regional mean and to the spatial clustering of temporal covariance of pairwise population connectivity. We then applied our model to the British Columbia (Canada) coastal system and quantified the connectivity between sites from 1998-2007 with a biophysical model (Regional Oceanic Modeling System), and then assessed pairwise connectivity covariance and its spatial clustering over that period. We further varied the spawning time and pelagic larval duration to assess how clusters of connectivity covariance are affected by species intrinsic traits related to connectivity.
Results/Conclusions
Our results revealed the importance of connectivity covariance for both density-dependent and density-independent growth. In both cases, negative connectivity covariance reduced the spatial variance in population density and thus promoted persistence. However, the sensitivity of variance in population density to connectivity depended on local growth rates, but also on spatial variance in carrying capacities and on the cluster size distribution of connectivity covariance. When applied to simulated trajectories of sea cucumber larvae along the British Columbia coastline, our results suggest that (1) natural coastal systems can be characterized by significant covariance in connectivity fluctuations that could impact long-term metapopulation growth. They also show that (2) the number and size of covariance clusters that impact long-term growth depend on species traits (larval duration and spawning time). Trait-based biophysical and ecological models of connectivity fluctuations can contribute to the design of marine reserve networks, and will improve predictions of species response to scenarios of future climate and ocean transport variability.