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Abstract

Jackson, A.R., D.B. Rouse and G. Ozbay. 2007. The effects of oyster (Crassostrea virginica) structure and bioactivity on water Quality, sediment nutrients, infaunal communities, and transient fish biomass. JEMREST 4:00-00

The objective was to differentiate the effects of oyster reef structure from the effects of oyster bioactivity and the ultimate impact on fish growth. The three treatments included a control without shell nor oysters, a shell reef representing structure effects and a live oyster reef representing bioactivity effects. After two weeks, four juvenile mullets (Mugil cephalus) as a transient herbivorous fish species and one week later four juvenile spots (Leiostomus xanthurus) as transient benthic fish predators were added to each replicate. Parameters measured in the experiment included dissolved macronutrients (NO₃-N, NO₂-N, NH₄-N, and PO₄^-4-P), sediment nutrients (inorganic C, total N, Mg⁺², Ca⁺², K⁺, and PO₄^-4-P), phytoplankton, periphyton, annelid density and biomass, and fish weight. The bioactivity of the oysters resulted in significant differences (P<0.05) from the control and the shell treatment for almost all parameters. Structure was not significantly different from the control for almost all parameters. Dissolved macronutrients were significantly higher with the oyster treatment. In the sediments, the oyster treatment resulted three times as much total nitrogen and twice as much carbon and organic matter as values in control and shell treatments. Periphyton and annelids were twice as dense, but phytoplankton was reduced significantly with the oyster treatment. Almost all fish lost some weight during the experiment, but the juvenile spot lost only 5% of their weight on average in the oyster treatment as opposed to 14% in the control and shell treatments. Juvenile mullet lost more weight (18%) with the oyster treatment and appeared to have suffered from inter-specific competition for microalgae. Oyster bioactivity clearly exerted more of an effect than oyster structure and in most cases had positive impacts on oyster habitats. More information about possible benefits and detriments to coastal ecosystems will help to shape the future fate and structure of shellfish restoration nationwide.