Seagrass burial by dredged sediments: Benthic community alteration, secondary production loss, biotic index reaction and recovery possibility

In 2005, dredging activities in Arcachon Bay (France) led in burying 320,000 m2 of Zostera noltii intertidal seagrass. Recovery by macrobenthos and seagrass was monitored. Six months after works, seagrass was absent and macrobenthos drastically different from surrounding vegetated stations. Rapidly and due to sediment dispersal, disposal area was divided into a sandflat with a specific benthic community which maintained its difference until the end of the survey (2010), and a mudflat where associated fauna became similar to those in adjacent seagrass. Macrobenthic community needs 3 years to recover while seagrass needs 5 years to recover in the station impacted by mud. The secondary production loss due to works was low. In this naturally carbon enriched system, univariate biotic indices did not perform well to detect seagrass destruction and recovery. Multivariate index MISS gave more relevant conclusions and a simplified version was tested with success, at this local scale.

► Macrobenthos and seagrass are monitored after sediment burial by dredging activities. ► Macrobenthos recovers within 3 years when buried under mud while seagrass needs 5 years. ► The secondary production loss related to seagrass destruction was low. ► Biotic Indices neither performed well nor agreed in detecting seagrass destruction and recovery. ► A derived version of MISS index was successfully tested.