Quantifying Ecosystem Functions of Shellfish Habitats within the South-East England

Decline in Flat Oyster (Ostrea edulis) populations since the 1960s by 90% globally has resulted in momentum to restore this species to coastal areas. One justification for Native Flat Oyster restoration is ecosystem function and services shellfish can provide, but restoration of this species is questioned as Pacific Oyster (Crassostrea gigas) populations continue to rise on UK coastlines (Beck et al., 2011). The Crassostrea species has been the primary focus of oyster-based studies, as a result ecosystem function data are heavily assumed for O. edulis with no evidence to support the possibility for species differentiation. Mesocosm and field experiments were conducted to quantify these ecosystem functions. Mesocosms involved a comparison between live oyster with a shell layer, live oyster alone, and bare sediment in relation to nutrient (nitrogen) cycling for C. gigas only. Mesocosm results for microbial communities inconclusive but did however show a significant change in N compounds within sediments, based on presence of oyster communities dependent on day. In-situ field experiments compared species C.gigas vs O.edulis and density of oysters in 10x10m2 plots (living oyster to dead shell ratio = 1:4 - densities of living oyster 1, 5, 10, 15 per m2). Field experiments showed high variation in sediment-stored inorganic carbon content for both species at all densities with overall no significant difference. Biodiversity measured as animal abundance showed insignificant difference based on density and based on base oyster species, but showed variation in abundance as C. gigas displays overall higher abundance with O. edulis having higher richness. C. gigas show trend of higher functionality than O. edulis in higher densities potentially due to size and site placement, but data inconclusive.