Ostrea edulis has become considerably depleted throughout its range in areas of former abundance through disease, overexploitation, habitat loss and interactions with introduced species. 0. edulis has been included in the UK Species Biodiversity Action Plan and efforts towards its regeneration have shown potential for success. The Come estuary has a long history of oyster cultivation, is part of the Essex Estuaries European Marine Site, a controlled area for Bonamia ostreae and contains designated shellfish waters. Fragmented patches of 0. edulis were sparsely distributed in the estuary, within the species' range of acceptable salinity. Maximum densities were lower than those observed historically in Essex estuaries and the Solent, but slightly greater than former fishery areas in Northern Ireland. Ostrea appeared to form part of an extensive, but declining metapopulation of oysters in the region. Availability of hard substrata was found to be an important driver of spatial variation on a local scale. Key areas for settlement of 0. edulis were identified close to the estuary mouth, however, modification of the benthos by dredging to resuspend fine particulates and increasing coarse sediment by planting out cultch did not increase recruitment. Larval densities were low during the reproductive season and were concluded to be limiting recruitment. Biodiversity increased in association with 0. edulis density and availability of coarse substrata, demonstrating the value of the 0. edulis habitat for settlement and recruitment of sessile and epizootic macrofauna in an estuary composed substantially of fine sediments. Crepidula Jornicata dominated the sublittoral zone of the Come on coarse substrata and Polychaetae were abundant on fine sediments. Despite habitat overlap between C. Jornicata and O. edulis, no evidence was apparent of spatial competition between the species. Crassostrea gigas dominated large areas within the littoral zone, however the habitats of C. gigas and 0. edulis overlapped minimally in shallow subtidal areas. Adoption of strategies to increase broodstock and therefore larval supply was recommended to promote natural regeneration of 0. edulis in the Colne estuary.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:654462 |
| Date | January 2014 |
| Creators | Hardy, Malcolm J. |
| Publisher | University of Essex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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