Developing comparative indices, valuation of nitrogen bioextraction ecosystem services, and scenario modeling to support decision-making in the Texas oyster mariculture industry

This dissertation aims to develop information that supports decision-making surrounding oyster aquaculture in Texas. Each chapter presents a different product, valuation, or modeling approach that addresses concerns or management of oyster aquaculture. The first research chapter developed a four-part index composed of production, policy, and economic attributes related to oyster aquaculture in the U.S. Data used in this index was derived from two studies comparing GIS tools and policy attributes of American aquaculture, and two more sections using both qualitative and quantitative data were developed as part of this study. The results of this index found that the U.S. Mid-Atlantic and New England regions have the greatest number of resource and policy attributes to facilitate and support oyster aquaculture. Among policy attributes, Texas differed from other U.S. states as lease transferability and applicant guides are not found in the state. Additionally, publicly available GIS map viewers, which are currently in development, can assist in decision-making. The second research chapter in this dissertation focused on nitrogen bioextraction as an ecosystem service provided by cultivated oysters. First, eutrophication screening was performed using the Assessment of Estuarine Trophic Status (ASSETS) model, with results indicating that Copano Bay is a candidate for eutrophication treatment based upon high levels of expression of influencing factors. Nitrogen estimates were found using Farm Aquaculture Resource Modeling (FARM), with a representative 7-acre farm capable of removing around 4,400 -6,500 lbs. of nitrogen from the water through assimilation into tissue and shell, based upon different environmental extremes in Copano Bay. A valuation model using five wastewater treatment plant (WWTPs) with two cost estimates were used to derive a monetary range of nitrogen bioextraction. The potential monetary range in value from $37,532 to $212,887 (based on various levels of WWTP efficiencies), depending on environmental growing conditions. This represents $11.49-$32.69 per pound of removed nitrogen, a valuable ecosystem service that will expand with subsequent leases as oyster aquaculture expands in Texas.
The final research chapter utilized the FARM model to simulate oyster farming under different environmental and cultivation scenarios. Historically, some risks, such as hurricanes, low salinity events, or Vibrio outbreaks, have occurred more often in summer, which may be mitigated by planning seeding and harvest dates to avoid warmer months. Model results indicate that persistent low salinity, such as that found in Copano Bay in 2010, can delay harvests due to poor growth that extends past the simulated 270-day grow-out cycle. Seeding of oysters during periods of moderate temperatures in April resulted in faster growth rates than in January or October. Increasing initial oyster stocking densities from 200 to 250 oysters m-2 resulted in ≤ 1% decrease in oyster length. Triploid oysters grew slightly slower (4-5%) than diploids, based upon 270-day crop cycles. Chlorophyll a did not appear to be a limiting factor for oyster growth, even using a high oyster stocking density scenario of up to 1,000 oysters m-2. Salinity was the most apparent factor influencing oyster growth in scenario modeling; understanding freshwater inflow is among the most critical factors for long-term aquaculture siting. Together, the results from this dissertation can be used to inform policy, understand ecosystem service value, and demonstrate the utility of scenario modeling to evaluate cultivation strategies that mitigate risk with predictable harvests.