Spatial Portfolios in Coral Metapopulations Are Shaped by Spatiotemporal Asynchrony in Environmental Conditions

Identifying the drivers and timescales of population synchrony is critical for understanding metapopulation resilience. Using wavelet analyses of a 19-year coral community timeseries from Moorea, French Polynesia, we quantified timescale-specific population synchrony in four common coral genera and evaluated the predictors of spatial portfolio effects. We detected synchrony within genera associated with synchrony in degree heating days, diurnal temperature range (DTR) and macroalgal cover at different timescales. Synchrony in DTR and macroalgal cover was associated with lower synchrony of Pocillopora and Porites populations, respectively. Population (for three of four genera) and environmental synchrony were stronger within than among habitats across timescales, underscoring the role of habitat-specific conditions in driving spatial synchrony and spatial portfolios. These results describe how the spatial and temporal scales of heterogeneity in environmental and ecological conditions determine synchrony in coral population dynamics and support a spatial portfolio effect, which may buffer coral metapopulations from island-scale collapse.