|NCDMF CHPP - Chapter 3. Shell bottom
3.2. Ecological Role and Functions
Water Quality Enhancement
Shell bottom provides direct and indirect ecosystem services that benefit coastal fisheries through water filtration, benthic-pelagic coupling, and sediment stabilization (Coen et al. 1999; Newell 2004; ASMFC 2007; Coen et al. 200). The filtering activities of oysters and other suspension feeding bivalves remove particulate matter (both organic and inorganic), phytoplankton, and microbes from the surrounding water column (Coen et al. 1999; Wetz et al. 2002; Nelson et al. 2004; Newell 2004; Coen et al. 2007; Wall et al. 2008). Fouling organisms on shell bottom are often suspension feeders as well and contribute to the water filtration capacity of this habitat (ASMFC 2007). Small-scale additions of oysters in tidal creeks of North Carolina have been demonstrated to reduce total suspended solids and chlorophyll a concentrations downstream of transplanted oyster reefs (Nelson et al. 2004). In addition, laboratory investigations have found that environmentally realistic densities of oysters, hard clams, and blue mussels (Mytilus edulis) lower chlorophyll a concentrations and increase light penetration to levels that facilitate the growth of SAV (Wall et al. 2008).
Modeling efforts of the effects of oyster filtration on water quality in Chesapeake Bay have suggested that oysters play an important role in determining water clarity, phytoplankton biomass, and dissolved oxygen (DO) dynamics in that system (Newell and Koch 2004; Cerco and Noel 2007). Cerco and Noel (2007) found that a tenfold increase in oyster biomass would result in a system-wide reduction of chlorophyll a concentration by 1 mg m-3, an increase in deepwater DO by 25 g m-3, and a 20% increase in summer SAV biomass. Newell and Koch (2004) came to similar conclusions for the addition of oysters suggesting that a modest increase in oyster biomass in Chesapeake Bay would reduce suspended sediment concentrations by an order of magnitude and increase the depth at which SAV was predicted to grow, but found that the influence of hard clams on reducing turbidity was much less than oysters due to their lower weight-specific filtration rate. The results of water quality models such as these and in situ measurements of filtration capacities has lead numerous authors conclude that oysters exert top-down grazer control of phytoplankton blooms (Coen et al. 1999; Newell 2004; Newell and Koch 2004; Cerco and Noel 2007; Coen et al. 2007). However, several investigators have recently questioned the validity of this conclusion stating that oyster filtration rates have been overestimated due to spatial and temporal mismatches between oyster and phytoplankton biomass and the lack of filtration access to all but the shallow bay water (Pomeroy et al. 2006; Fulford et al. 2007). Nevertheless, filtration by oysters has been demonstrated to improve water quality and clarity in both laboratory and field settings (Coen et al. 1999; Wetz et al. 2002; Nelson et al. 2004; Newell 2004; Coen et al. 2007; Wall et al. 2008). An economic analysis is needed that compares the cost saving of oyster restoration and sanctuary development with that of wastewater treatment capacity, along with the added fishery production of associated finfish species and oyster harvest in the remaining open shellfish harvesting waters. The results of one such analysis are pending (J. Grabowski/GMRI, pers. com., January 2009).
Shell bottom also enhances water quality through coupling benthic and pelagic processes (Newell et al. 2002; Newell 2004; Porter et al. 2004; Newell et al. 2005; ASMFC 2007; Coen et al. 2007; DMF 2008a). Suspension feeding bivalves consume seston from the water column and their biodeposits accumulate on the sediment surface (Newell 2004; Porter et al. 2004; Newell et al. 2005). The nitrogen (N) and phosphorous (P) excreted by the bivalves can become buried in the sediment or may be lost via bacterially mediated nitrification-denitrification (Newell et al. 2002; Newell 2004; Porter et al. 2004; Newell et al. 2005). The net ecosystem loss of N and P results in bottom-up nutrient control of phytoplankton production through alterations in nutrient regeneration processes (Newell 2004; Newell et al. 2005). However, bivalve biodeposits can be released back into the water column by erosion, sediment reworking by animals, or resuspension with possible uptake by adjacent SAV and phytoplankton (Peterson and Peterson 1979; Newell 2004).
ASMFC (Atlantic States Marine Fisheries Commission). 2007. The importance of habitat created by molluscan shellfish to managed species along the Atlantic coast of the United States. Habitat Management Series 8 , 108p.
Cerco, C. F. and M.R. Noel. 2007. Can oyster restoration reverse cultural eutrophication in Chesapeake Bay? Estuaries and Coasts 30(2): 331-343.
Coen, L. D., R.D. Brumbaugh, D. Bushek, R. Grizzle, M.W. Luckenbach, M.H. Posey, S.P. Powers, and S.G. Tolley. 2007. Ecosystem services related to oyster restoration. Marine Ecology Progress Series 341: 303-307.
Coen, L. E., M.W. Luckenbach, and D.L. Breitburg. 1999. The role of oyster reefs as essential fish habitat: a review of current knowledge and some new perspectives. p. 438-454 in L.R. Benaka (ed.). Fish habitat: Essential fish habitat and rehabilitation. American Fisheries Society, Bethesda, MD, Symposium 22 , 459 p.
Fulford, R. S., D.L. Breitburg, R.I.E. Newell, W.M. Kemp, and M. Luckenbach. 2007. Effects of oyster population restoration stratagies on phytoplankton biomass in Chesapeake Bay: a flexible modeling approach. Marine Ecology Progress Series 336: 43-61.
Kirby, M. X. and H.M. Miller. 2005. Response of a benthic suspension feeder (Crassostrea virginica Gmelin) to three centuries of anthropogenic eutrophication in Chesapeake Bay. Estuarine, Coastal and Shelf Science 62(4): 679-689.
Nelson, K. A., L.A. Leonard, M.H. Posey, T.D. Alphin, and M.A. Mallin. 2004. Journal of Experimental Marine Biology and Ecology. Using transplanted oyster (Crassostrea virginica) beds to improve water quality in small tidal creeks: a pilot study 298(2): 347-368.
Newell, R. I. E. 1988. Ecological changes in the Chesapeake Bay: are they the result of overharvesting the Amercian oyster? p. 536-546 in M.P. Lynch and E.C. Krome (eds.). Understanding the estuary: advances in Chesapeake Bay research. Chesapeake Bay Research Consortium, Baltimore, MD, Publication 129 .
Newell, R. I. E. 2004. Ecosystem influence of natural and cultivated populations of suspension-feeding bivalve molluscs: a review. Journal of Shellfish Research 23(1): 51-61.
Newell, R. I. E. and E.W. Koch. 2004. Modelling seagrass density and distribution in response to changes in turbidity stemming from bivalve filtration and seagrass sediment stabilization. Estuaries 27(5): 793-806.
Newell, R. I. E., J.C. Cornwell, and M.S. Owens. 2002. Influence of simulated bivalve biodeposition and microphytobenthos on sediment nitrogen dynamics: a laboratory study. Limnology and Oceanography 47(5): 1367-1379.
Newell, R. I. E., T.R. Fisher, R.R. Holyoke, and J.C. Cornwell. 2005. Influence of eastern oysters on nitrgen and phosphorus regeneration in Chesapeake Bay, USA. p. 93-120 in R. Dame and S. Olenin (eds.). The comparative roles of suspension feeders in ecosystems. Springer, The Netherlands, 47 .
Peterson, C. H. and N.M. Peterson. 1979. The ecology of intertidal flats of North Carolina: A community profile. U.S. Fish and Wildlife Service, OBS-79/39 , 73 p.
Pomeroy, L. R., C.F. D'Elia, and L.C. Schaffner. 2006. Limits to top-down control of phytoplankton by oysters in Chesapeake Bay. Marine Ecology Progress Series 325: 301-309.
Porter, E. T., J.C. Cornwell, and L.P. Sanford. 2004. Effect of oysters Crassostrea virginica and bottom shear velocity on benthic-pelagic coupling and estuarine water quality. Marine Ecology Progress Series 271: 61-75.
Wall, C. C., B.J. Peterson, and C.J. Gobler. 2008. Facilitation of seagrass Zostera marina productivity by suspension-feeding bivalves. Marine Ecology Progress Series 357: 165-174.