Evidence from both terrestrial and marine ecosystems demonstrates that ecosystem engineers strongly affect natural communities and ecosystem properties by modifying physical conditions. Research on ecosystem engineering has mostly focused on effects of single dominating engineering species. However, natural communities often contain diverse ecosystem engineers that operate on different spatial scales and that may act in synergy or have antagonistic effects on local habitat conditions and associated species. With a large-scale experiment we investigated interactive effects of three common marine engineers (cockles, Cerastoderma edule L., lugworms, Arenicola marina L., and mussels, Mytilus edulis L.) on the functioning and community structure of an intertidal ecosystem. We manipulated a total of 2.400 m2 by adding 64.000 lugworms and 800.000 cockles to different 25 m2plots, both in the plumes of biodeposits created by mussel beds and in sandy areas without mussels.
Results/Conclusions
We found that interactive engineering effects of cockles, mussels and lugworms significantly affected primary producers, bivalve recruitment and the functional composition of the macrobenthic community. Specifically, cockles and mussel beds facilitated phytobenthic production and bivalve recruitment by decreasing sediment erosion. Cockle beds increased sediment stability locally, while mussel reefs alleviated hydrodynamic stress on larger scales. Furthermore, through opposite effects on sediment organic matter content and bed level stability, cockles, lugworms and mussels together increased habitat heterogeneity, which eventually led to niche partitioning among different functional groups of the macrobenthic community. Our results demonstrate that changes in environmental conditions caused by the interaction of species-specific engineering effects of cockles, lugworms and mussels translate to large-scale changes in the community structure and ecosystem functioning, and highlight the role of engineering networks in structuring coastal ecosystems.