Restoration that targets function as opposed to structure: replacing lost bivalve production and filtration

Abstract

Abundant suspension-feeding bivalves have a dominant organizing role in shallow aquatic systems by filtering overlying waters, affecting biogeochemical processing, and diverting production from the water column to the benthos. In degraded aquatic systems where bivalve populations have been reduced, successful restoration of ecosystem functions may be achieved by targeting the revival of bivalve populations. The 'North Cape' oil spill on the coast of Rhode Island (USA) provides an opportunity to demonstrate the feasibility of scaling bivalve restoration to meet quantitative goals of enhanced production. After this oil spill, mortalities of bivalves were estimated by impact assessment modeling of acute toxicity, and results were confirmed by comparisons with counts of dead and moribund animals on local beaches. Computation of lost bivalve production included future production expected from affected animals, had they lived out their expected life spans. This calculation of production forgone required a demographic model that combined age-specific mortality with individual growth. Application of this modeling approach to surf clams Spisula solidissima, the species that comprised 97% of the total loss of bivalve production from the spill, illustrates the detailed implementation of scaling restoration to match estimates of losses. We consider the factors known to limit abundance and production of surf clams and other marine bivalves (hard clams, American oysters and bay scallops) and review the advantages of hatchery stocking, transplantation, habitat restoration, and reduction of fishing pressure in selecting a reliable and efficient restoration action. Age-specific estimates of the scale of population enhancement required to restore production showed that fewer additional animals were needed when larger (older) animals were added, but at the expense of greater grow-out requirements. Relaxation of fishing was most effective for hard clams. Accurate scaling of restoration was most sensitive to mortality rate, and the most efficient restoration involving seeding of small bivalves would be accomplished using surf clams. Monitoring of the restoration option chosen to compensate for the bivalve loss following the 'North Cape' oil spill can serve to test the underlying demographic assumptions and accuracy of the restoration scaling.

Hypoxia in Chesapeake Bay Tributaries: Worsening effects on Macrobenthic Community Structure in the York River

“…The infauna in the York and Rappahannock Rivers filter the water and provide food for higher trophic levels, along with other secondary services such as geochemical processing, denitrification, and bioturbation. Many infaunal organisms remove particulates from the water through filter or suspension feeding (McCay et al 2003), which increases the clarity of the water and has positive effects on other species, particularly submerged aquatic vegetation (Kemp et al 2005). All of these main functions are influenced by the abundance, biomass, and species composition of the benthic infauna.…”

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

“…One of the major ecological functions of suspensionfeeding bivalve molluscs such as oysters is their potential to improve water quality by filtering plankton and other suspended particles (seston) from the water column (Dame 1996;Kennedy 1996;Harsh andLuckenbach 1999, Dame et al 2001;French McCay 2003;Newell and Koch 2004). Ongoing and planned oyster restoration projects in many areas emphasize ecosystem services such as waterquality improvements, instead of or at least in addition to, the historical role of oysters as a commercial resource (Luckenbach et al , 2005Brumbaugh et al 2000;Luckenbach 2000, Coen et al 2007;Grabowski and Peterson 2007).…”

Setting Goals and Measuring Success: Linking Patterns and Processes in Stream Restoration

“…As a result, many studies of stream systems have inferred prevalent ecological processes from instantaneous collections of physical, chemical, and biological data (e.g., Dole-Olivier et al, 1994;Tockner & Bretschko, 1996). This is a perilous undertaking when the spatial or temporal scale of measurement does not coincide with the relevant process (McKee & Faulkner, 2000;French McCay et al, 2003). This dilemma is evident in many aspects of river ecology (Minshall, 1988;Palmer & Poff, 1997).…”

“…Researchers are beginning to move beyond the rhetoric of advocating the use of process-based ecological indicators to quantitatively assessing measures such as biogeochemical cycles (McKee & Faulkner, 2000), primary production (French-McCay et al, 2003), and organic matter breakdown (Gessner & Chauvet, 2002) as ecological indicators of restoration success. Use of these processes facilitates the examination of long-term and cumulative impacts on aquatic communities from the base of the food web.…”