Food web structure and ecosystem multifunctionality in a subsidized coastal ecosystem

The structure and functioning of all ecosystems face growing threats, ranging from local development to global climate change. Ecosystems with little to no in situ primary production may be disproportionately dependent on resources from other ecosystems. We examined the role of basal resource availability on community structure and ecosystem multifunctionality of sandy beaches. We hypothesized that substantial marine macrophyte wrack inputs from productive nearshore ecosystems, like kelp forests, would drive recipient beach ecosystem structure and function. Using piecewise structural equation modeling, we found wrack abundance had a strong positive effect on beach food web diversity and biomass of detritivorous and predatory macroinvertebrates as well as ecosystem multifunctionality, an integrative measure of ecosystem functioning. Resource inputs and biodiversity both explained ecosystem multifunctionality, but the role of biodiversity was strongly underpinned by wrack inputs. The diversity and abundance of top predators, shorebirds, responded similarly to resource availability. Our findings suggest the influence of marine foundation species, such as giant kelp, can extend to recipient ecosystems as detrital subsidies. The highly coupled nature of these coastal ecosystems increases the likelihood that negative impacts to donor ecosystems will cascade to affect the structure and function of subsidized recipient ecosystems.