Possible mechanisms for a marine benthic regime shift in the North Sea

A sharp regime shift from a brittle star Amphiura filiformis dominated state to a burrowing mud shrimp Callianassa subterranea dominated situation was observed in a region of the North Sea known as the Frisian Front in the mid-1990s. No indications exist that food levels or other relevant conditions in this part of the North Sea had changed significantly. However, the new state has persisted until the present. This could suggest that this regime shift represents a transition between alternative stable community states. We propose a potential explanation for the existence of 2 stable states, which agrees with experimental and field observations. We demonstrated experimentally that sediments inhabited by burrowing shrimps are more susceptible to sediment resuspension by tidal currents and wave forces than sediments inhabited by brittle stars. Although the burrowing shrimps apparently thrive under these conditions, successful recruitment of brittle stars may be hampered on such unstable frequently resuspended sediments. This implies a positive feedback; brittle stars promote sediment stability, which favors their persistence. We created a model to demonstrate that this feedback between the benthic community and sediment stability may cause both the shrimp dominated state and the brittle star dominated state to be stable under the same external conditions.