Recovery rates of UK seabed habitats after cessation of aggregate extraction.
Marine aggregate extraction and benthic fishing are the two largest causes of physical disturbance to the UK seabed. Aggregate dredging is a damaging but highly spatially heterogeneous pressure, with a footprint < 1 % of bottom fishing (2001–2007). To understand the impacts of aggregate dredging, international literature was reviewed for recovery rates of the seabed following cessation of dredge activity, in a range of habitats, hydrodynamic conditions and dredge intensities. Physical recovery (TPhys) was determined as the period for dredge tracks to become undetectable and sediment composition to return to either pre-dredge or reference site conditions. Biological recovery (TBio) was defined as the period for establishment of a community consistent with non-impacted sites, or 90 % of pre-dredge condition. Results of the review were used to estimate recovery times for the types of marine landscape targeted by the aggregate industry in UK waters. Ninety-six percent of aggregate extraction in the UK occurred in sand or coarse sediment. Fifty percent of all extraction activity targeted coarse sediment plains of moderate tidal stress, which were found to have the longest period of TPhys (20 yrs) and the second longest TBio (8.7 yrs). In shallow coarse sediments with weak tidal stress, approximately 21 % of the habitat supported high intensity dredging and the habitat had the longest mean TBio, 10.75 yrs. Aggregate extraction affects less than 1 % of most landscapes, but six percent of the area of estuaries; the latter having the shortest TPhys and TBio. Maintenance dredging data were not included.
Marine Ecology Progress Series, 390, 15-26