Author
 |
COEN, LOREN - Sanibel-Captiva Conservation Foundation |
|
Dumbauld, Brett |
|
JUDGE, MICHAEL - Manhattan College |
|
Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 12/31/2010 Publication Date: 11/1/2011 Citation: Coen, L.D., Dumbauld, B.R., Judge, M.L. 2011. Expanding shellfish aquaculture: A review of the ecological services provided by and impacts of native and cultured bivalves in shellfish dominated ecosystems. In: Shumway, S.E. editor. Shellfish Aquaculture and the Environment. Hoboken, NJ: Wiley-Blackwell. p. 239-318. Interpretive Summary: Aquaculture is making an increasing contribution to world-wide demand for bivalve shellfish while efforts are being made to restore wild shellfish populations because they are declining. The sometimes negative impacts of shellfish culture to natural systems have been evaluated, but both native and cultured shellfish are also being recognized for positive ecosystem services which they can provide such as their ability to filter and potentially increase water clarity, their ability to stabilize shorelines and their contribution to habitat for many other species of fish and invertebrates. A summary and evaluation of what is known about the impacts of bivalve shellfish and these positive ecosystem services in places where these shellfish are the dominant organisms is given. Two examples, one for oysters (both native Ostrea lurida and cultured Crassotrea gigas) in Willapa Bay, Washington and a second one for hard clams (Mercenaria mercenaria) in tidal creeks of South Carolina suggest that both impacts and services vary depending on system characteristics. The role of oysters in the Willapa Bay ecosystem clearly changed when native oysters were harvested and removed and Pacific oysters were introduced. Pacific oysters are larger in size, can filter more water and can form large reefs. Further, the location where these oysters are found in the estuary differs and Pacific oysters are repeatedly planted and harvested over time. Effects of Pacific oysters on native eelgrass habitat and carrying capacity due to their filtration capacity have also been shown to be influenced greatly by the ocean along the U.S West Coast. In the case of hard clams grown in small tidal creeks along the US southeast coast, the cages in which the clams were grown had significant effects on water flow which altered sediment characteristics and chlorophyll a concentrations directly within the cultured area. The biomass of small invertebrates inhabiting the mud in addition to clams themselves however was little affected by these high density clam pens. Both cases showed that aquaculture can provide enhanced structured habitat that parallels that provided by native bivalve dominated communities and provide similar ecosystem services, but the effects of this structured habitat should be evaluated in each system at appropriate temporal and spatial scales. While use of native bivalve species is desirable because it reduces the chance of other unwanted effects and potentially restores native wild stocks, a great deal more site specific research needs to be directed at examining sustainable aquaculture and shellfish restoration practices including emphasis on both positive and negative impacts at the landscape or ecosystem scale. Technical Abstract: Aquaculture is making an increasing contribution to world-wide demand for bivalve shellfish at the same time that substantial efforts are being made to restore wild shellfish populations because they are declining. Impacts of shellfish culture to natural systems have been evaluated, but both native and cultured shellfish act as ecosystem engineers and provide multiple ecosystem services including the ability to filter and potentially influence eutrophied waters, the ability to stabilize shorelines and a significant contribution to above ground habitat for many other species of fish and invertebrates. An overview and evaluation of what is known about ecosystem services provided by bivalve shellfish and impacts to shellfish dominated systems in the U.S. is given. Two examples for oysters (both native Ostrea lurida and cultured Crassotrea gigas) in Willapa Bay, Washington and for hard clams (Mercenaria mercenaria) in tidal creeks of South Carolina suggest that impacts and services provided vary depending on system characteristics. The role of oysters in the Willapa Bay ecosystem has clearly changed over time as the native oyster was removed and Pacific oysters introduced due to the larger size, filtration and reef forming capacity of the introduced oysters, their location in the landscape, as well as the planting and harvest practices employed in their culture. Effects on native eelgrass habitat and carrying capacity due to their filtration capacity have also been shown to be influenced greatly by the ocean driven system they inhabit along the US West Coast. This differs from the case study of hard clams in small tidal creeks along the US southeast coast which showed that the large concentrations of three dimensional cages in which clams were grown had significant effects on the hydrodynamic regime and altered sediment characteristics and chlorophyll a concentrations in the immediate area of the culture activity. Nonetheless, infaunal biomass exclusive of the clams themselves was little affected by the high density clam pens. Both cases showed that aquaculture can provide enhanced structured habitat that parallels that provided by native bivalve dominated communities and can provide similar ecosystem services, but the effects of structured habitat should be explicitly evaluated at appropriate temporal and spatial scales. While use of native species is desirable because it reduces the chance of other unwanted effects and potentially restores native wild shellfish stocks, a great deal more site specific research needs to be directed at examining sustainable aquaculture and shellfish restoration practices including emphasis on both positive and negative impacts at the landscape or ecosystem scale. |
