A comparison of juvenile dungeness crab (Metacarcinus magister) habitat provided by contemporary oyster aquaculture versus historical native oyster habitat in a U.S. West Coast estuary

Authors: Dumbauld, Brett; MURPHY, JESSICA - Oregon State University; MCCOY, LEE - Us National Park Service; LEWIS, NATHANIEL - Oregon State University

Submitted to: Journal of Shellfish Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2021
Publication Date: 5/3/2021
Citation: Dumbauld, B.R., Murphy, J., McCoy, L., Lewis, N. 2021. A comparison of juvenile Dungeness crab (Metacarcinus magister) produced in current oyster aquaculture versus historical native oyster habitat in a U.S. West Coast estuary. Journal of Shellfish Research. 40(1):161-175. https://doi.org/10.2983/035.040.0116.
DOI: https://doi.org/10.2983/035.040.0116

Interpretive Summary: Both oysters and seagrasses provide valuable nursery habitat for juvenile fish and invertebrates like Dungeness crab in US West coast estuaries. Oyster habitat was historically provided by the native Olympia oyster in many of these estuaries like Willapa Bay in Washington State. Native oysters are found in low intertidal areas and were the target of a large fishery in the late 1800’s, but have since been replaced by Pacific oyster aquaculture which typically occurs at higher tidal elevations in these estuaries. This research was conducted to understand how this shift in habitat may have affected juvenile Dungeness crab production in these habitats and inform current management of both oyster and eelgrass habitats at the estuary scale. Comparable densities of juvenile crab were found in surveys of remnant or restored native oyster habitats and cultured oysters, but this density was higher than that in nearby seagrass. A broader survey showed that juvenile crab recruitment within oyster habitat was highest near the mouth of the estuary and at lower tidal elevations. Historical native oyster habitat was estimated to produce up to three times more juvenile crab than current oyster aquaculture using maps to extrapolate these results to the estuary scale, but both oyster habitats produced more crab than seagrass or open mud habitat. Managers can use this information to provide context for current decisions about permitting both oyster aquaculture and native oyster restoration, but should consider similar ecosystem scale evaluations for other resources.

Technical Abstract: Oysters and seagrasses provide structurally complex estuarine habitat for fish and invertebrate species. On the U.S. west coast, complex oyster habitat was historically provided by the native Olympia oyster, Ostrea lurida, but is now provided by the commercially cultured oyster Crassostrea gigas. O. lurida is found in subtidal and low intertidal areas whereas C. gigas is predominantly cultured at higher intertidal elevations resulting in a potential shift in available habitat for other fish and invertebrates that utilize this intertidal habitat. This potential shift was examined for juvenile Dungeness crab, Metacarcinus magister and results showed; 1) comparable crab densities in remnant and restored populations of O lurida and cultured C. gigas shell habitats in two estuaries, 2) generally higher crab densities in both shell habitats than those observed in eelgrass or open mud habitat, 3) contemporary juvenile crab density in intertidal areas of Willapa Bay was most influenced by distance from the estuary mouth (declining with increasing distance) but also declined with increasing tidal elevation, and 4) when extrapolated to the estuarine ecosystem scale historical O. lurida habitat potentially produced three times more juvenile crab than those currently produced in cultured C. gigas habitat. Nonetheless both intertidal oyster habitats contribute more to juvenile crab production than eelgrass or open unstructured mud and the ecosystem services associated with the placement of native and commercial oyster beds should be considered when defining goals for and permitting both aquaculture and native oyster restoration in Willapa Bay and other US west coast estuaries. Managers should consider this shifting temporal baseline in intertidal habitat provision, but also conducting similar evaluations at this broader estuary scale when evaluating habitat value for other resources that utilize these habitats differently.