Recovery rates of UK seabed habitats after cessation of aggregate extraction

Marine aggregate extraction and benthic fishing are the 2 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 to 2007). To understand the impacts of aggregate extraction, international literature was reviewed for recovery rates of the seabed following cessation of dredging in a range of habitats, hydrodynamic conditions and dredge intensities. Physical recovery (T-Phys) and biological recovery (T-Bio) were determined as the mean time-period for recovery to pre-dredge or reference site conditions. Recovery times were then estimated for marine landscapes targeted by the aggregate industry in UK waters. Maintenance dredging data were not included. Aggregate extraction affects 6% of estuarine areas and <1% of all other landscapes. Ninety-six percent of extraction occurred in sand or coarse sediment. Fifty percent targeted coarse sediment plains with moderate tidal stress, which had the longest period of T-Phys (20 yr) and the second longest T-Bio (8.7 yr), Shallow coarse sediments with weak tidal stress had the longest mean T-Bio, (10.75 yr), but 21% of the habitat supported high intensity dredging. The most intense dredging (>90 h) was in estuaries, which have the shortest recovery times: T-Phys 1.67 yr and T-Bio 5.25 yr. At present, licensed areas do not appear to be located to avoid the most sensitive marine landscapes nor to target the least sensitive areas. Linking information on habitat recovery potential to marine landscapes and aggregate activity provides a practical tool for use in marine spatial management.