Seston Removal by Natural and Constructed Intertidal Eastern Oyster (Crassostrea virginica) Reefs: A Comparison with Previous Laboratory Studies, and the Value of in situ Methods

Abstract

An important ecological role ascribed to oysters is the transfer of materials from the water column to the benthos as they feed on suspended particles (seston). This ecosystem service has been often touted as a major reason for many oyster restoration efforts, but empirical characterization and quantification of seston removal rates in the field have been lacking. Changes in chlorophyll a (chl a) concentrations in the water column were measured in May 2005 and June 2006 in South Carolina using in situ fluorometry and laboratory analysis of pumped water samples taken upstream and downstream as water flowed over natural and constructed intertidal oyster reefs. Both methods gave similar results overall, but with wide variability within individual reef datasets. In situ fluorometer data logged at 10 to 30-s intervals for up to 1.3 h over eight different reefs (three natural and five constructed) showed total removal (or uptake) expressed as % removal of chl a ranging from −9.8% to 27.9%, with a mean of 12.9%. Our data indicate that restored shellfish reefs should provide water-quality improvements soon after construction, and the overall impact is probably determined by the size and density of the resident filter feeder populations relative to water flow characteristics over the reef. The measured population-level chl a removal was converted to mean individual clearance rates to allow comparison with previous laboratory studies. Although direct comparisons could not be made due to the small size of oysters on the study reefs (mean shell height, 36.1 mm), our calculated rates (mean, 1.21 L h −1 ) were similar to published laboratory measured rates for oysters of this size. However, the wide variability in measured removal by the oyster reefs suggests that individual oyster feeding rates in nature may be much more variable than in the laboratory. The proliferation of ecosystem-level models that simulate the impacts of bivalves on water quality based only on laboratory-feeding measurements underscores the importance of further research aimed at determining ecologically realistic feeding rates for oysters in the field. Because in situ methods provide many replicate measurements quickly, they represent a potentially powerful tool for quantifying the effects of oyster reefs, including all suspension-feeding taxa present, on water quality.

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

“…In order to account for field conditions in our model, we used the field measurements of seston uptake over natural oyster reefs reported in Grizzle et al (2006Grizzle et al ( , 2008 to estimate filtration rates. Grizzle et al measured seston drawdown over reefs with a known mean oyster SH and density, and under optimal temperature conditions.…”

“…SH to dry tissue mass conversions from the respective regions (South Carolina and Florida) were applied. Field data were collected on intertidal reefs during both ebb and flood tides (Grizzle et al 2006(Grizzle et al , 2008 and therefore captured the impact of the tidal cycle (Dame et al 1984(Dame et al , 1992. Negative values caused by waves or other disturbances were excluded.…”

“…In order to make broad, estuary-scale estimates of the volume of water filtered by oyster populations nationally, we derived a model of oyster filtration based on the only in situ measurements of oyster filtration currently available (Grizzle et al 2006(Grizzle et al , 2008. We use this model to explore the estimated delivery of this ecosystem service historically versus presently across 13 US estuaries.…”

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

“…Both oysters and the complex physical habitats they build may provide a number of important ecosystem services, including the direct provision of food, filtration of the water column (Grizzle et al 2008), enhanced denitrification rates (Newell et al 2002), the enhancement of non-oyster fish stocks (Peterson et al 2003), and coastal protection (Scyphers et al 2011). Most detailed studies on these services have focused on Crassostrea virginica (Gmelin, 1791) reefs on the Atlantic and Gulf coasts of the United States (see Coen et al 2007); yet, similar benefits are attributed to other oyster species, such as the Olympia oyster, Ostrea lurida Carpenter 1864 on the Pacific coast (White et al 2009).…”

Ecosystem services are lost when facilitation between two ecosystem engineers is compromised by oil

“…Because the fishery value of nearshore oysters in the northern GoM is limited (although these areas have the potential to serve as a de facto spawning sanctuary that 'seeds' areas of harvest), the loss of ecosystem functions and services is the pressing concern for resource managers. Extensive literature now exists on the ecological benefits of oyster reefs (see Coen et al 2007, Grabowski et al 2012 for recent reviews) and supports that the loss of habitat can have effects on nutrient cycling (Piehler & Smyth 2011, Beseres Pollack et al 2013, Kellogg et al 2013), fish and invertebrate production (Peterson et al 2003), water clarity (Ne well & Koch 2004, Grizzle et al 2008, and shoreline stabilization (Scyphers et al 2011). Collectively, the annual economic value of these services (excluding oyster harvest) was recently estimated to total US $5500−99 000 ha −1 (Grabowski et al 2012).…”