Limits to top-down control of phytoplankton by oysters in Chesapeake Bay

Abstract

Restoration of the oyster Crassostrea virginica population in Chesapeake Bay is often advocated as an easy solution for controlling phytoplankton blooms. Even at their pre-colonial densities, oysters are unlikely to have controlled blooms, despite the fact that sediment cores suggest that pre-colonial spring blooms were smaller than at present. Lack of access to all bay water and low springtime filtration rates would make it impossible for oysters to control the spring bloom and the resulting summer hypoxia. Previous studies have overestimated potential oyster filtration rates, because they extrapolated summer rates to spring conditions that are 20°C cooler. Previous studies have also assumed that oysters have access to all phytoplankton, without considering the spatial separation. In Chesapeake Bay, oysters and the spring bloom are separated horizontally owing to the size of the bay and its small tidal amplitude. Indeed, a multi-species guild of suspension feeders now present in the bay should have a filtration capacity approaching that of pre-colonial oysters, but it does not control the bloom. Actual oyster filtration potential must be lower than many advocates of oyster restoration assume, and replenishing the bay with oysters is not the means of controlling blooms and hypoxia. KEY WORDS: Chesapeake Bay · Hypoxia · Oysters · EutrophicationResale or republication not permitted without written consent of the publisher

Quantifying the Loss of a Marine Ecosystem Service: Filtration by the Eastern Oyster in US Estuaries

“…However, even when undisturbed, estuaries exhibit high variability in sediment load, planktonic productivity, depth, residence time, and natural abundance of oysters (Bricker et al 2007;zu Ermgassen et al 2012), all of which influence the extent to which oyster filtration may impact water quality (Officer et al 1982;Pomeroy et al 2006;Cerco and Noel 2007). Temporal mismatching between phytoplankton production and peak oyster filtration may also limit the potential for oyster populations to have a regulating influence.…”

“…Temporal mismatching between phytoplankton production and peak oyster filtration may also limit the potential for oyster populations to have a regulating influence. Additionally, the impact of filtration on seston drawdown on large scales cannot be directly inferred from filtration rates due to the influences of wave action (Porter et al 2004), the unequal distribution of oysters (Cerco and Noel 2007), and imperfect mixing within the estuary (Pomeroy et al 2006). This in turn may lead to variable impacts of oyster filtration on nutrient cycling within the bay, as the biodeposition of seston may stimulate enhanced denitrification and anammox in the sediments (Dame 2011).…”

Changes in Sediment Characteristics upon Oyster Reef Restoration, NE Florida, USA

“…Therefore, restoration of oyster reefs has received increasing attention and investment from coastal municipalities. However, the wisdom of pursuing restoration is controversial [11][12][13][14][15][16]. Part of this disagreement may stem from differences in how the goals of each restoration project are defined, the complexity of ecosystem services rendered by oysterreefs, and whether benefits from all of these services are includedin the assessment of restorationsuccess [1,2].…”

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debated [11,12,14,15], but less research has been devoted to the effect of oyster reefs on the surrounding sediment. Reefs act to attenuate wave energy, possibly facilitating deposition of fine sediment [8]; this process may work in concert with oyster filtration to increase light penetration that may then shift ecosystems towards more benthic primary producers [6].

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Top-down control of phytoplankton by oysters in Chesapeake Bay, USA: Reply to Newell et al. (2007)

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ABSTRACT: Recently published models, which allow for spatial and temporal matching of oyster and phytoplankton populations in mainstream Chesapeake Bay, support the conclusion of Pomeroy et al (2006; Mar Ecol Prog Ser 325:301-309) that oysters cannot, and could not, control the spring blooms that are the ultimate cause of summer hypoxia. We enlarge upon our earlier exposition of how top-down and bottom-up processes interact in Chesapeake Bay to permit the occurrence of phytoplankton blooms in spring, but not in summer.

KEY WORDS: Oyster · Hypoxia · Filter-feeders · Phytoplankton blooms

Resale or republication not permitted without written consent of the publisher

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