- Oyster reefs provide an array of ecosystem services. Specifically, they provide structurally complex habitat for fish and invertebrate species such as the commercially important Dungeness crab, Metacarcinus magister. This ecosystem service, once provided by the native oyster Ostrea lurida, is now provided by the commercially cultured oyster Crassostrea gigas in many estuaries on the U.S west coast. An economic investigation was conducted examining the ecosystem services provided by oyster habitat, common economic valuation theories and techniques, and tradeoffs between oyster restoration and aquaculture expansion. A scientific investigation, comprised of three studies, was also conducted to examine Dungeness crab production as an ecosystem service provided by oyster habitat.
Because natural ecosystems, such as oyster reefs, provide beneficial goods and services through time, they should be valued as any other economic asset or capital. Until recently many of these beneficial services have not been accounted for within resource management plans, often resulting in the over-exploitation of those resources. Activities such as coastal development, dredging, aquaculture expansion, or even habitat restoration can affect estuarine ecosystems. While valuing the ecosystems themselves might be difficult, valuation of the services they provide can be a useful tool for identifying and protecting key ecosystem services while implementing plans with minimal negative impact.
The oysters, O. lurida and C. gigas inhabit different regions of the tidal zone. O. lurida is predominantly found in subtidal and low intertidal regions whereas C. gigas is predominantly found in intertidal regions. The shift in the dominant species has resulted in a subsequent shift of available recruitment habitat for M. magister. We conducted an across-estuary study to examine settlement of M. magister in existing O. lurida, C. gigas, eelgrass, and open mud habitats in Willapa Bay, WA, Netarts Bay, OR, and Coos Bay, OR, to determine tradeoffs in crab production between habitat types. A second study using shell bags as settlement substrate at various tidal elevations was conducted in Yaquina Bay, OR, to obtain density data of M. magister by depth. We used these densities, in combination with pre-existing data from Willapa Bay, to compare the production of Dungeness crab as an ecosystem service historically provided by O. lurida habitat and production currently provided by C. gigas habitat in Willapa Bay, WA. A third study using shell piles was conducted in Yaquina Bay, OR to estimate survival of juvenile M. magister. The results of these three studies generally support prior research indicating that densities of juvenile M. magister are greater in oyster and eelgrass habitats than in open mud, and are generally greater in oyster habitat than in eelgrass. The Yaquina Bay shell bag study indicated greater densities of juvenile M. magister in subtidal regions, while the shell pile study indicated greater densities in higher intertidal regions.