Shell bioerosion in high-latitude low-energy environments: Firths of Clyde and Lorne, Scotland

The agents of bioerosion in the Firths of Clyde and Lorne include endolithic algae, Cliona, phoronids, Acmaea virginea, Lepidopleurus asellus and regular echinoids which directly and indirectly cause shell disintegration and the production of calcareous sediments. Algae and Acmaea are very effective in shell erosion, but are confined to the photic zone where over 90% of the shells have suffered from their attack. Other bioerosion agents are not depth-restricted but individually affect a lesser number of shells. The photic limit (approx. 30 m) is estimated from the disappearance of the deepest growing algae “Conchocelis” and Ostreobium. The density of algal boring is high due to the low energy at the bottom. It is shown that algal borings and Acmaea grazing are also important as palaeobathymetric tools.