University of Virginia Charlottesville, VA, United States
Abstract: Cross-ecosystem subsidies are critical to ecosystem structure and function, especially in ecosystems where they are the primary source of organic matter to the food web of the recipient system. Subsidies are indicative of physical processes connecting ecosystems and can couple ecological dynamics across system boundaries. However, the degree to which such flows can induce cross-ecosystem cascades of spatial synchrony, the tendency for system fluctuations to be correlated across locations, is not well understood. Synchrony has destabilizing effects on ecosystems, adding to the importance of understanding how widely synchrony can be transmitted, and by what mechanisms. In order to understand whether and how spatial synchrony cascades across the marine-terrestrial boundary via resource subsidies, we studied the relationship between giant kelp forests on rocky nearshore reefs and sandy beach ecosystems that receive resource subsidies in the form of kelp wrack (detritus). By applying wavelet-based analyses, we found that synchrony cascades from rocky reefs to sandy beaches, with spatiotemporal patterns mediated by fluctuations in kelp supply, wave action, and beach width. Moreover, wrack deposition synchronized aggregations of shorebirds that consume wrack-associated invertebrates, demonstrating that synchrony due to subsidies propagates across trophic levels in the recipient system. Respectively, these mechanisms explained up to 80% and 50% of synchrony in wrack deposition and shorebird aggregations across seasonal to interannual timescales. Synchronizing resource subsidies likely play an underappreciated role in the spatiotemporal structure, functioning, and stability of ecosystems. Changes to the magnitude and timing of cross-ecosystem flows due to climate change and other disturbances may alter ecosystem synchrony and stability in a variety of systems.