The bioprotective properties of the blue mussel (Mytilus edulis) on rocky shore platforms

Abstract:

Biogeomorphological processes are an important component in the geomorphic evolution of rocky coasts. Sessile organisms, including those which form dense biological covers, enhance and retard weathering and erosion. The common blue mussel (Mytilus edulis) is found on rocky-shores around the globe, typically in large beds several centimetres thick. Unlike other canopy forming marine organisms, the influence of mussels on processes of rock breakdown lacks quantitative analysis. This study assesses the potential of M. edulis to act as a bioprotective agent through a combination of simulated weathering experiments and field trials on a rocky shore platform in Wales, UK.

Monitoring on the shore platform showed that daily near-surface temperature maxima, range and short-term variability were significantly lower on surfaces colonised by mussels compared to those that were bare. This finding was supported by laboratory simulations which showed that (artificial) mussel colonisation consistently reduces the internal temperature of rock samples at a variety of depths during low-tide periods. As mechanical weathering processes are influenced by surface and sub-surface temperature regimes, it is inferred that these stabilising effects may translate to a reduction in the efficiency of particular types of rock deterioration at colonised surfaces compared to bare surfaces. Rock hardness measurements collected from the shore platform using a Schmidt hammer and Equotip support this assertion as colonised surfaces were found to be significantly harder than bare surfaces, indicating they had experienced less deterioration over long time periods.

A supplementary field experiment, which used gypsum ‘domes’ to indirectly measure the influence of mussel colonisation on local wave hydrodynamics, reinforces the overall contention that mussels exhibit some bioprotective properties, as the results indicate that mussel beds reduce the amount of rock disintegration caused by waves.

This study presents some of the first empirical evidence of the bioprotective potential of mussels through the moderation of near-surface microclimate regimes and wave movement.