Ecosystem engineers can affect habitat structure and resource availability by strongly modifying abiotic conditions across space. In theory, this can affect the abundance and spatial distribution of other species and their consumers, indicating strong effects of ecosystem engineers on biodiversity and food-web structure. However, in many intertidal soft-sediment systems, these species have disappeared, due to multiple anthropogenic disturbances, and many associated species disappeared with them. The goal of this study was to empirically investigate the importance of spatial extended habitat modification by reef-builders in explaining the distribution of four avian predators and their benthic prey in the Wadden Sea – one of the world’s largest intertidal soft-sediment ecosystems. We applied Structural Equation Modeling (SEM) to identify important direct and indirect interactions between the different components of the system.
Results/Conclusions
We found strong spatial gradients in sediment properties into the surrounding area of mixed blue mussel (Mytilus edulis) and Pacific oyster (Crassostrea gigas) reefs, indicating large-scale (100s of m) engineering effects. The benthic community was significantly affected by these gradients, with the abundance of several important invertebrate prey species increasing with sediment organic matter and decreasing with distance to the reefs. Distance from the reef, sediment properties and benthic food abundance simultaneously explained significant parts of the distribution of oystercatchers (Haematopus ostralegus), Eurasian curlews (Numenius arquata) and bar-tailed godwits (Limosa lapponica). The distribution of black-headed gulls (Chroicocephalus ridibundus) – a versatile species with many diet options – appeared unaffected by the reefs. These results suggest that intertidal reef builders can affect consumer-resource dynamics far beyond their own boundaries. Our study emphasizes that conservation and restoration of ecosystem engineers should be considered a crucial step in the restoration of intertidal soft-sediment ecosystems.