Promoting self-facilitating feedback processes in coastal ecosystem engineers to increase restoration success: Testing engineering measures

Coastal ecosystem engineers often depend on self-facilitating feedbacks to ameliorate environmental stress. This makes the restoration of such coastal ecosystem engineers difficult. We question if we can increase transplantation success in highly dynamic coastal areas by engineering measures that promote the development of self-facilitating feedback processes. Intertidal blue mussels Mytilus edulis are a typical example of ecosystem engineers that are difficult to restore. A lack of self-facilitating feedbacks at low densities limits establishment success when young mussels are transplanted on dynamic mudflats. In a large field experiment, we investigated the possibility of increasing transplantation success by stimulating the formation of an aggregated spatial configuration in mussels, thereby reducing hydrologically induced dislodgment and the risks of predation. For this, we applied engineering measures in the form of fences that trapped wave dislodged mussels. Mussel loss rates were significantly lower when mussels were placed between both artificial fences, and in high densities (4.2 kg/m²) compared with mussels placed in areas without fences and in low densities (2.1 kg/m²). The fences induced the formation of a banded pattern with high local mussel densities, which locally reduced predation. Synthesis and applications. Our results underline the importance of actively promoting the development of self-facilitating processes, such as aggregation into patterns, in restoration projects of ecosystem engineers. In particular, the current study shows that engineering measures can help to initiate these kinds of self-facilitating interactions, especially in highly dynamic areas.