Benthic macrofauna succession under mussels, Mytilus edulis L. (Bivalvia), cultured on hanging long-lines

Cultures of the mussel Mytilus edulis produce accumulations of feces as well as mussels on the sea floor below the cultures. Changes in the sediment composition and benthic community structure under such cultures were studied over a three-year period on the Swedish west coast. Deposition of organic matter created several centimetres of sediment each year, resulting in production of H2S in the uppermost layer. Originally, the benthic fauna was dominated (as per numbers of individuals) by Nucula nitidosa and (as per biomass) by Echinocardium cordatum and Ophiura spp. After 6–15 months of mussel culturing these and other species disappeared and were replaced by opportunistic polychaetes (Capitella capitata, Scolelepis fuliginosa, and Microphthalmus sczelkowii). The abundance of these species fluctuated due to changes in the position of the redoxcline and their annual life cycle. The anaerobic sediments and mass occurrence of opportunistic polychaetes were localized to a zone under and 5–20 m around the cultures. After harvesting of the mussels only limited recovery was observed after a one and a half year.