Quantifying the historic contribution of Olympia oysters to filtration in Pacific Coast (USA) estuaries and the implications for restoration objectives

Abstract

The Olympia oyster, Ostrea lurida Carpenter, was formerly widespread in many US Pacific coast estuaries. Following dramatic declines in the late 1800s and early 1900s, this species is now the focus of renewed restoration efforts. Restoration is undertaken for brood stock rehabilitation as well as a range of ecosystem services such as filtration; however, these ecosystem services are as yet poorly quantified. We present the first laboratory measurements of filtration rates (FR) for O. lurida, to which we fit a model of FR as a function of dry tissue weight and water temperature. We find that O. lurida has a FR at optimum temperature similar to previously established means across oyster species at 1 g dry tissue weight (DTW), but lower than many Crassostrea species. We also find that the allometric exponent relating FR to DTW in O. lurida is lower than the previously published mean across oyster species. Based on our derived filtration rates and historical data, we estimate the historic impact of filtration by O. lurida in five Pacific coast estuaries. We find that historic O. lurida populations did not have the capacity to filter the full volume of the estuary within the estuary residence time in any of the estuaries examined. This result is primarily driven by the low water temperatures and the short estuary residence times that typify the Pacific coast. We conclude that, unlike Crassostrea virginica Gmelin on the Atlantic and Gulf coasts, the Olympia oyster was not historically a dominant force in regulating seston concentrations at large scales in Pacific coast estuaries. Given the differences in the ecological role and habitat structure of these two oyster species, we recommend that analogies between them be drawn with caution. We discuss the implications of our results for developing restoration objectives.

Beyond residence time: quantifying factors that drive the spatially explicit filtration services of a “pristine” oyster population

“…For example, Gray et al (2019) estimated native Olympia oysters to filter 28% of Yaquina Bay, OR within a single residence time after accounting for hydrodynamics. This estimate is substantially larger than that of an earlier study (1% per residence time) by zu Ermgassen et al (2013) who used a much simpler method when accounting for hydrodynamics (tidal prism method), which likely underestimated the residence time of the ecosystem (Lemagie and Lerczak 2015). Aside from residence time, the frequency at which a parcel of water was exposed to filterfeeding activity of oysters before exiting the estuary, termed encounter rate by Gray et al (2019), was also considered to be important when estimating oyster FS but was not quantified.…”

Population structure, genetic connectivity, and adaptation in the Olympia oyster (Ostrea lurida) along the west coast of North America

“…The Olympia oyster ( Ostrea lurida , Carpenter 1864) is a native estuarine bivalve found from Baja California to the central coast of Canada, patchily distributed over strong environmental gradients (Chan et al, 2017; Schoch et al, 2006). Oysters are ecosystem engineers in estuaries, providing structured habitat and removing suspended sediments (zu Ermgassen et al, 2013; Coen et al, 2011). Unlike other oysters where both males and females spawn gametes (e.g., Crassostrea ), the females fertilize eggs with sperm from the water column and initially brood larvae in the mantle cavity.…”

The benefits of bivalve reef restoration: A global synthesis of underrepresented species

“…Even within species, there can be substantial differences in ecosystem service delivery between geographies, as evidenced by the regional differences in fish and mobile invertebrate production from C. virginica reefs in the Gulf of Mexico relative to the South and Mid‐Atlantic USA (zu Ermgassen, Grabowski, Gair, & Powers, 2016). The environmental setting can also play a critical role in the degree of service delivery; for example, oysters are unlikely to have played as important a role in water quality on the Pacific coast of the USA relative to the Atlantic coast, not only because the native species of oyster, O. lurida , has slower clearance rates, but also because Pacific coast estuaries tend to have lower residence times (zu Ermgassen, Gray, Langdon, Spalding, & Brumbaugh, 2013). As such, there is a strong case for building a greater quantitative knowledge for each species, despite having confidence that certain ecosystem services are likely to arise from universal ecosystem engineering properties.…”