Effect of oysters Crassostrea virginica and bottom shear velocity on benthic-pelagic coupling and estuarine water quality

Abstract

Increasing the biomass of bivalve suspensions feeders has been proposed as a means to improve water quality in eutrophic estuaries such as the Chesapeake Bay. However, water quality impacts are likely to be determined by the balance of bivalve feeding and the deposition and sediment regeneration of nutrients from particulate organic matter. In shallow-water environments, benthic and pelagic processes are closely coupled and water flow can regulate the supply of seston to the bivalves. In addition, such flow may regulate benthic-pelagic nutrient fluxes through mass transfer limitation and resuspension. We studied the interacting effects of juvenile oysters Crassostrea virginica and bottom shear velocity on phytoplankton biomass and on nutrient regeneration in a series of three 4 wk long comparative experimental ecosystem experiments. All mesocosms had a 1000 l water volume, a 1 m 2 sediment surface area, and a 1 m water-column depth, and the same realistic water-column mixing (turbulence intensity 1 cm s -1 ). The systems included a multi-component mesocosm with moderate bottom shear velocity (0.6 cm s -1 ) and 2 standard cylindrical tanks with an unrealistically low bottom shear velocity (0.1 cm s -1 ). Oysters shifted processes to the sediments by decreasing phytoplankton biomass without stimulating additional blooms and by increasing light penetration to the bottom. Through complex and indirect relationships, the interaction of oysters and enhanced shear velocity significantly affected microphytobenthos biomass. Light, as enhanced by the oyster feeding on phytoplankton, increased microphytobenthos biomass; a moderate bottomshear velocity eroded the biomass. Microphytobenthos biomass decreased nutrient regeneration from the sediments to the water column and may have implications for water quality in low-energy parts of shallow-water estuaries such as Chesapeake Bay. Enhanced bottom shear in more energetic parts of shallow estuaries negatively affects microphytobenthos biomass and may increase nutrient regeneration from the sediments.

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

“…The areal NH 4 fluxes we report here are from the low position only, and are likely to vary seasonally and spatially, and so more research is needed to characterize NH 4 fluxes or predict effects on N2 production rates. Rather, these results highlight the potential for altered N-cycling upon reef construction, and the importance of benthic algal uptake in mediating benthic-pelagic coupling [6,7]. This is likely to be especially important for intertidal reefs such as the one in this study, which receive abundant sunlight.…”

“…In addition to direct revenue from oyster harvesting, oysters provide hard substrate for sessile organisms, habitat complexity and refuge for small mobile organisms, and attenuation of wave energy for shoreline protection [1,2]. Furthermore, the filtering capacity of oysters is thought to improve water clarity and influence the structure of estuarine ecosystems with respect to recycling of organic matter and nutrients [3][4][5], benthicpelagic coupling, and energy flow to the microbial loop [6,7]. At the creek-level scale, oyster communities have been shown to significantly affect concentrations of particulate and dissolved nutrients and organic matter, though effects often depended on season and tidal state [5,8].…”

“…Finer particles and much higher organic matter (OM) content in oyster-associated sediments suggests a substantial role for carbon and nutrient removal by burial [8,17] and benthic algal uptake where light penetration is sufficient [6]. However, mesocosm experiments show that physical factors such as bottom shear can influence sediment resuspension and benthic micro-algal biomass, making the system more complex and the likelihood of OM burial versus remineralization more difficult to predict [7]. Several recent studies suggest that sediments associated with natural and restored oyster reefs have high rates of denitrification and may thus represent important sites for long term nitrogen removal [17][18][19][20].…”

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

“…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).…”

Overfishing, disease, habitat loss, and potential extirpation of oysters in upper Chesapeake Bay

“…Oysters are ecosystem engineers, constructing habitat for themselves as well as for a multitude of other organisms (Coen et al 1999, Peterson et al 2003, Grabowski et al 2005, Fulford et al 2010. They also provide important ecosystem services like nutrient cycling (Dame & Libes 1993, Fulford et al 2007) and benthic-pelagic coupling (Baird & Ulanowicz 1989, Porter et al 2004. Additionally, increasing oyster populations may have a substantial influence on reducing effects of anthropogenic eutro phication (Cerco & Noel 2007, Fulford et al 2010.…”