Scallop dredging has profound, long-term impacts on maerl habitats

Maerl beds are mixed sediments built by a surface layer of slow-growing, un attached coralline algae that are of international conservation significanc e because they create areas of high biodiversity. They are patchily distrib uted throughout Europe (to similar to 30 m depth around the British Isles a nd to similar to 120 m depth in the Mediterranean) and many are affected by towed demersal fishing. We report the effects of Newhaven scallop dredges on a previously unfished maerl bed compared with the effects on similar gro unds that have been fished commercially in the Clyde Sea area; Scotland. Se diment cores were taken to assess the population density of live maerl thal li prior to scallop dredging on marked test and control plots. These plots were then monitored biannually over a four-year period. Live maerl thalli w ere sparsely distributed at the impacted site, and experimental dredging ha d no discernible effect on their numbers. The previously unfished ground ha d dense populations of live maerl and scallops (both Aequipecten operculari s and Pecten maximus). While counts of live maerl remained high on the cont rol plot, scallop dredging led to a >70% reduction with no sign of recovery over the subsequent four years. The vulnerability of maerl and associated benthos (e.g., the delicate bivalve, Limaria hians) is discussed in relatio n to towed demersal fishing practices. (C) 2000 International Council for t hc Exploration of tho Sea.