Beyond food: a foundation species facilitates its own predator

Facilitation by foundation species can play a critical role in structuring ecological communities. As environmental stress increases, generally more organisms become dependent on the stress buffering provided by foundation species. As such, foundation species may even facilitate their own predators, an interaction that can influence the functioning and structure of the foundation species population and thereby the facilitated organisms. This work presents a case study on the blue mussels and sea stars, where we tested to what extent a foundation species (i.e. blue mussels) may facilitate its own predator (sea star) when exposed to a gradient of environmental stress (hydrodynamic forces). Amelioration of hydrodynamic stress by mussels facilitated sea stars, allowing them to persist on a soft bottom in highly dynamic environment, which would not be possible in the absence of mussels. Moreover, sea stars continue preying on mussels when environmental stress increases. The results suggest that a foundation species may interact with its own predator beyond the role of food source, by ameliorating environmental stress, creating an additional dependence link between the foundation species and the predator, which potentially has major implications for ecosystem structure and stability.