Spatially Explicit Estimates of In Situ Filtration by Native Oysters to Augment Ecosystem Services during Restoration

Matthew Gray,Emily Lemagie,Philine zu Ermgassen,Chris Langdon,Jonathan Gair,Jim Lerczak

doi:10.1007/s12237-019-00515-3

Abstract

US west coast populations of the native Olympia oyster Ostrea lurida declined precipitously in the late nineteenth and early twentieth centuries and were often replaced by the non-native Pacific oyster (Crassostrea gigas) by the aquaculture industry. Recovery of native oyster ecosystem services derived from their suspension feeding activities (termed “filtration services” (FS)) often serves as a powerful incentive for restoration of populations of O. lurida along the US west coast despite uncertainty about the potential effects of their filtration activities on concentrations of suspended particulate matter. Here, we provide an improved FS model for O. lurida and C. gigas in Yaquina Bay, OR, that is based on both in situ feeding behavior and the complex hydrodynamics of the estuary. The total area and the order of locations chosen for oyster restoration in Yaquina Bay were examined to determine how oyster FS could be maximized with limited resources. These modeling efforts quantified estimates showing (1) native oysters, if restored in Yaquina Bay to historic levels, may contribute nearly an order of magnitude greater FS than previously estimated; (2) C. gigas contributes significantly greater FS than O. lurida, especially during the wet season; (3) FS provided by either species is highly dependent upon seasonal river forcing and salinity; (4) spatial variation in FS arises from the hydrodynamics of the system, uneven oysters distributions, and upstream pre-filtering. We found that spatially explicit models demonstrated the benefits of prioritizing restoration to areas with the greatest FS potential, rather than placing oysters randomly within historic habitats. Directing restoration in this manner used between 75% (dry season) and 60% (wet season) less of the restored area needed to achieve comparable FS with randomly placed oysters.

Highlights

Oysters are considered keystone species due to the numerous ecosystem services (ESS) they provide in coastal environments
The first attempt to model O. lurida and C. gigas in Yaquina Bay was made by zu Ermgassen et al (2013a) in which historic populations of O. lurida were estimated to clear a very small proportion of Yaquina Bay (1% of bay cleared per estuary residence time) during the summer when environmental conditions were modeled to elicit maximum feeding activity
The updated FS model presented in this study suggests that O. lurida and C. gigas could clear a much larger fraction of the estuary than previously estimated by zu Ermgassen et al (2013a), but that these services vary substantially between species, season, scale of restoration, and area of the estuary in which the oysters are restored

Summary

Introduction

Oysters are considered keystone species due to the numerous ecosystem services (ESS) they provide in coastal environments. Restoration efforts throughout the USA are currently underway with the explicit goal of enhancing the ESS provided by oysters, including those of Olympia oyster (Ostrea lurida), Estuaries and Coasts (2019) 42:792–805 which is the only native oyster on the US west coast This species was once abundant in estuaries and bays of the Pacific Northwest (PNW) but populations were heavily impacted by overharvesting, habitat degradation, and pollution (White et al 2009). The ability of restored native oysters to effectively exert top-down control over phytoplankton blooms and improve water quality in coastal ecosystems remains somewhat equivocal and has sparked considerable debate within the literature (e.g., Newell 2004; Newell et al 2004, 2007; Pomeroy et al 2006, 2007; Coen et al 2007; Mann and Powell 2007), largely due to uncertainty about spatial and temporal mismatch between oyster filtration and phytoplankton abundance and the access of oyster to the overlaying water. The Pacific oyster is widely farmed on the west coast and has become the dominant oyster species (Pauley et al 1988) and may offer considerably different ESS than O. lurida (Ruesink et al 2006; Banas et al 2007)

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Results

Conclusion