Natali Claezon (MSc Thesis 2019)

Epibiotic Colonisation of Oyster Cages and Settlement Plates in the Solent.

Historic decline of the European flat oyster Ostrea edulis populations has led to an interest in re-stocking efforts. The once abundant ecosystem engineer is of both commercial and ecological vale, providing services of water purification, increasing biodiversity, and as a food resource. The growing sector of oyster cultivation along with the benefits brought by restoration of biogenic oyster reefs, highlights the need for a combined approach to sustainable management of shellfish aquaculture inclusive of coastal and estuarine ecosystem health. Research into combined approaches for improving coastal marine ecosystems in conjunction with increasing fishery productivity is a topical area. This work builds on an existing trial of restocking O. edulis in the Solent, English Channel. Lesser attention has been addressed to the role of epibiotic organisms that colonise the artificial structures involved in cultivating oysters, whether for commercial or restorative purposes. This study addresses the composition of epibiotic communities on the substrates associated with this re-stocking project with focus locations within the Beaulieu Estuary. Using a combination of settlement plates and samples from the exterior of cages containing oysters and micro reefs; structures from within these cages, epibiotic communities were compared. PRIMER software was used for multi-dimensional scaling for comparison of taxonomic diversity in assemblages recorded. Findings from this exploratory work suggest that the variability of species colonising, and their level of succession varied depending on substrate shape and fluctuation conditions. Settlement plates up-river revealed large variations in biomass and fouling and were dominated by amphipods of the Corophium genus and the hydroid Tubularia. Whereas the communities on the oyster cages had more diverse assemblages that were dominated by rhodophytes and tunicates. Understanding these dynamic epiphytic colonisations and community’s composition on artificial reef structures, enables better informed decision making feasible for the management of coastal oyster fisheries in highly utilised coastal zones and estuaries.