Theses and Dissertations

Title: The effects of oyster structure and bio activity on transient fish biomass

Name: Jackson, Anthony R.

Degree: MS

Chair: David Rouse


University: Auburn University

Location: Auburn, Alabama

Date: 2003

Pages: 63

Keywords: Oyster structure,BioActivity,Biomass


A number of studies have demonstrated that oyster reefs play an important role in the trophic dynamics of surrounding ecosystems. However, debate remains whether structure or bioactivity has a greater effect and as to the value of oyster reefs as compared to other habitat types. The intent of this experiment was to differentiate the effects of oyster reef structure from the effects of oyster bioactivity (filtration and excretion) and the ultimate impact on fish growth.The study was conducted on Dauphin Island near the mouth of Mobile Bay, Alabama (30.25 N, 88.07 W). The experiment consisted of twelve 68-L tanks lined with sand and equipped with a flow-through system drawing water from the bay. There were three treatments, each with four replicates. Treatments included a control without shell nor oysters, a shell reef representing structure effects, and a live oyster reef representing bioactivity effects. After a one-week period for community establishment, four juvenile mullet (Mugil cephalus) were added to each replicate to represent a transient herbivorous species. Four juvenile spot (Leiostomus xanthurus) were added one week later as transient benthic predators. Parameters measured in the experiment included dissolved macronutrients (NO3-N, NO2-N, NH4-N, PO4-P), sediment nutrients (inorganic C, total N, Mg, Ca, K, PO4), phytoplankton, periphyton, annelid density and biomass, and fish weight.In this experiment, the bioactivity of the oysters resulted in differences from the control for almost all parameters and in most compared to structure. Structure was not significantly different from the control for almost all parameters. Ammonia was commonly twice as high in the tanks with the oyster treatment. The other dissolved macronutrients fluctuated but were higher with the oyster treatment when a significant difference was present. In the sediments, the oyster treatment, on average, resulted in three times as much total nitrogen and twice as much carbon and organic matter. Significant differences over the control but not structure included: phosphorus, potassium, and calcium. Periphyton was oftenvtwice as dense and phytoplankton was reduced significantly with the oyster treatment. Annelids populations were twice as dense and had three times as much biomass on average in the treatment containing the oysters. Almost all fish lost weight during the experiment but the combined effects resulted in the juvenile spot losing only 5.4% of their weight on average in the oyster treatment as opposed to approximately 14% in the control and shell treatments. Juvenile mullet lost an average 18.2% of weight with the oyster treatment and appeared to have suffered from interspecific competition for microalgae. The mullet lost only 8.6% of their weight with the shell treatment as compared to 11% in the control.In this experiment, oyster bioactivity clearly exerted more of an effect than oyster structure. The impact of oyster bioactivity on trophic dynamics indicates a need to reassess the value of the ecological services that oysters perform.

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