Metapopulation theory predicts that demographic connectivity can strongly influence local and regional dynamics in spatially structured metapopulations. However, a mechanistic understanding of the processes driving variation in connectivity and the consequences of this variation for metapopulation dynamics has been constrained by a paucity of comprehensive spatiotemporal data on these processes for most species. To test several predictions from metapopulation theory, we described patterns of patch extinction and colonization for the giant kelp Macrocystis pyrifera across 32 years (1984–2016) and nearly 900 km of coastline in southern California using a satellite-based time series of giant kelp abundance. We calculated connectivity among kelp patches using novel population fecundity estimates from diver-calibrated satellite imagery and spore dispersal estimates from a high-resolution ocean circulation model.
We made three primary discoveries that provide new insight into metapopulation theory. (1) Consistent with our predictions, spatial asynchrony in local population dynamics stabilized regional dynamics despite frequent extinction due to stochastic disturbances. (2) Demographic connectivity among populations strongly structured local population dynamics. Large, unfragmented, and highly-connected patches had lower risks of extinction and greater chances of colonization than small, fragmented, and isolated patches. (3) Fluctuations in population fecundity, rather than fluctuations in dispersal, were the dominant driver of variation in connectivity and contribute substantially to population recovery and persistence. Thus, ignoring fluctuations in fecundity may overestimate connectivity and population resilience and stability. Through the analysis of long-term data, our studies provide novel empirical support for metapopulation theory, clarify the mechanisms structuring giant kelp metapopulations, and offer guidelines to improve the conservation, mitigation, and restoration of giant kelp forests.