Quantitative Valuation of Ecosystem Services Provided by Oyster Reefs in Mobile Bay, Alabama

Abstract

Oyster reef services have been acknowledged for their ecosystem services, but globally oyster reefs are at risk due to rapid anthropogenic and natural changes. Conservation decisions for these important habitats often require cost-benefit analysis to evaluate trade-offs associated with various restoration strategies. Evaluating economic values of ecosystem services is desirable to for this purpose. The objectives of this dissertation were to estimate: 1) The value (in dollars) of fish and crustacean production enhancement associated with current oyster reefs in Mobile Bay, Alabama; 2) The nitrogen removal services provided by these oyster reefs, and; 3) The consequences of increasing the oyster (Crassostrea virginica) harvest size limit on provision of ecosystem services by oyster reefs in Mobile Bay, Alabama. This study estimated that when compared to unstructured habitats, oyster reefs in Mobile Bay resulted in enhancement of 354.09±182.62 (mean±1sd) g m-2 yr-1 of fish and crustaceans. The production attributed to commercial and recreational landings was 64.55±68.55 g m-2 yr-1 and 105.80±63.63 g m-2 yr-1, respectively. The economic benefit estimated for the 1,045 ha of oyster reefs in the bay was $267,000 - $739,000 yr-1 from commercial landings and $3.7 - $12.3 million yr-1 from recreational fishing. In addition, the oyster reefs also were estimated to remove 26,666±2,919 kg N yr -1 through denitrification, the burial of biodeposits into sediments, and via oyster harvest, comprising an additional $106,397±11,646 yr-1 in economic benefit. Results from a model that evaluated oyster growth indicated that a proposed change to an 89mm harvest size limit would lower harvest production from 46% to 72% compared to the 76mm size limit. The economic benefit from nitrogen removal services associated with changing the harvest regulation was very small ($8,127 yr-1) compared to the loss of oyster production ($308,000 - $482,000) due to estimated high natural mortality associated with poor water quality for oysters Results (e.g., fish enhancement, nitrogen removal benefits) can be used by decision makers or the public to estimate the economic return of oyster habitat restoration investment in Alabama. Oysterrowth models did not support increasing harvest size limit to 89mm but fishery managers could monitor oyster mortality in the bay to reduce uncertainty related to proposed changes in harvest size limit in the future.