Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 1
Ecosystem Concepts for Sustainable Bivalve Mariculture Summary Almost 50% of all seafood eaten worldwide today is farm raised, compared to only 9% in 1980, primarily from the expansion of aquaculture in China (Food and Agriculture Organization of the United Nations, 2006). In the United States in 2007, mariculture—the cultivation of organisms in the marine environment—produced approximately 15,000 metric tons (meat weight) of bivalve molluscs, mostly oysters, clams, and mussels (National Oceanic and Atmospheric Administration, 2009a). Mariculture production of bivalve molluscs in the United States has roughly doubled over the past 25 years. Increasing domestic seafood production in the United States in an environmentally and socially responsible way will likely require the use of policy tools, such as best management practices (BMPs) and performance standards. These policy tools are commonly utilized to reduce effects associated with the use of natural resources in commercial activities like mariculture. Although mariculture operations may expand the production of seafood without additional exploitation of wild populations, they still depend upon and affect natural ecosystems and ecosystem services. BMPs and performance standards are useful for protecting the environment while increasing mariculture production. Bivalve mariculture can have both positive and negative ecological impacts on the marine environment. For instance, culture operations and the associated gear can alter water flow, composition of the sediment, and rate of sedimentation and in some cases can disturb the benthic flora, including seagrass, which provide habitat for fish and
OCR for page 2
Ecosystem Concepts for Sustainable Bivalve Mariculture invertebrates. However, bivalve mariculture can enhance production in seagrass beds by increasing water clarity through filtration and by fertilizing the beds through biodeposition. Mariculture gear increases the availability of hard substrates, thereby supporting higher densities of fish and invertebrates that associate with structured habitat, but the presence of artificial hard substrates can also promote colonization and spread of introduced species, such as nonnative tunicates. Such a mix of beneficial and negative effects illustrates the complexity of ecosystem responses to mariculture operations. Many laws and regulations currently govern bivalve mariculture. At the federal level, the U.S. Army Corps of Engineers issued a nationwide permit for existing mariculture under the Clean Water Act. Implementation is subject to regional conditions to address regional concerns and protect important resources. Because most bivalve operations occur in coastal waters, mariculture also falls under state jurisdiction, with details of regulatory requirements varying from state to state. Inconsistent and confusing laws from multiple layers of local, county, state, and federal jurisdictions can produce an uncertain legal environment for the mariculture industry. In some cases, regulators may be in the conflicted position of promoting the development of the industry, preventing conflicts with other uses, and maintaining terrestrial and marine environments. The National Park Service asked the National Research Council to investigate the potential ecosystem effects of bivalve shellfish mariculture and recommend best practices to maintain ecosystem integrity. This report examines how ecological effects vary in magnitude and type with the environment, the species cultured, and the habitat type and describes the uncertainties that characterize our current understanding of mariculture’s effects. The report reviews how bivalve mariculture can affect wild stocks and what socioeconomic factors influence mariculture operations, and it identifies the most important topics for future research to minimize negative and maximize beneficial environmental impacts (see Appendix A for the full statement of task). The committee acknowledges and draws from many efforts by industry, government, nongovernmental organizations, and academia from around the world to identify best practices and establish ecologically sustainable policies for bivalve shellfish mariculture. The report provides an overview of the scientific issues that should be considered in assessing the effects of bivalve mariculture on estuarine and coastal ocean ecosystems and builds on recent efforts, such as those initiated by the Food and Agriculture Organization of the United Nations, to develop an ecosystem-based approach to management of bivalve shellfish mariculture. Ecosystem-based management considers the web of direct and indirect interactions among the living and non-living elements of an ecosystem, including human
OCR for page 3
Ecosystem Concepts for Sustainable Bivalve Mariculture activities. The committee’s review of the science is intended, therefore, to inform policy makers about this web of ecosystem consequences so that the implications of alternative policies and management goals will be more transparent. From organism to ecosystem, there is no free lunch—every additional animal has an incremental effect arising from food extraction and waste excretion. The scope of impacts of cultured bivalves is a function of the scale and location of mariculture operations, a fact that needs to be recognized and quantified. Some effects may be beneficial to the ecosystem, while others may be detrimental, depending on the scale and location of the bivalve farm. All impacts need to be considered in a policy context that appropriately weighs the values of seafood production and of changing ecosystem state so that the costs and benefits of choices about mariculture can be compared. BEST MANAGEMENT PRACTICES AND PERFORMANCE STANDARDS BMPs represent one approach to protecting against undesirable consequences of mariculture. Most BMPs for bivalve mariculture have been prepared by industry groups, nongovernmental organizations, and governments with the common goal of sustainability. Industry guidelines mostly address ways to sustain production, but this may not be sufficient to sustain other ecosystem components or to safeguard other societal goals. An alternative approach to voluntary or mandatory BMPs is the establishment of performance standards for mariculture. Variability in environmental conditions makes it difficult to develop BMPs that are sufficiently flexible and adaptable to protect ecosystem integrity across a broad range of locations and conditions. An alternative that measures performance in sustaining key indicators of ecosystem state and function may be more effective. Because BMPs address mariculture methods rather than monitoring actual ecosystem responses, they do not guarantee that detrimental ecosystem impacts will be controlled or that unacceptable impact will be avoided. Fixed BMPs can also result in a stifling of innovation. By contrast, adoption of performance standards is likely to encourage innovation among growers. With performance standards, mariculture operations are managed adaptively to maintain key indicators within acceptable bounds, through direct monitoring of ecosystem indicators rather than tracking compliance with specific management practices. However, the monitoring required for implementing performance standards is costly, and this additional expense could serve as a disincentive to the expansion of bivalve mariculture in the United States.
OCR for page 4
Ecosystem Concepts for Sustainable Bivalve Mariculture Finding: Performance standards are generally more efficient than BMPs because they allow for innovation and track ecosystem responses. However, implementation of performance standards usually involves additional, and potentially costly, requirements for monitoring and enforcement. Many of the issues surrounding bivalve shellfish mariculture are location specific and may not be addressed effectively by broad national standards. Technically oriented BMPs have in some cases been shown to increase efficiency and hence profitability, while reducing environmental impacts. However, no single BMP or standard can address the many contingencies raised by different mariculture techniques, the species in culture, and the environmental conditions that are unique to various regions or sites. Recommendation: Performance standards that set parameters based on carrying capacity (size of population or biomass that the environment can support; see definition in Chapter 5) should be developed and implemented at the ecosystem level because they can be applied to bivalve mariculture more generally with adjustments for the specific conditions of each mariculture operation, species, and culture technique. Recommendation: Management of bivalve mariculture should employ performance standards to address carrying capacity concerns at the scale of the water basin but may find the use of BMPs to be more practical and efficient at the local scale, especially where the industry consists of large numbers of small growers. Because BMPs tend to be specific to the type of mariculture operation and the environmental conditions on site, it is not practical for this report to recommend a set of BMPs to suit all circumstances. Instead the report identifies general principles for best practices and performance standards. In the cases where there are best practices or standards that apply across the range of cultured species and conditions, the committee provides recommendations for managers and practitioners (Table S.1). ECOLOGICAL EFFECTS OF BIVALVE MARICULTURE Culturing of suspension-feeding bivalves has effects on the plants, animals, biogeochemical processes, food webs, and habitats of estuarine and coastal ocean ecosystems. Suspension-feeding bivalves gain nourishment by filtering suspended particles, including phytoplankton, organic detritus, and inorganic particles, from the water column. By-products of suspension feeding include excreted, dissolved ammonium and biodeposits of feces and pseudofeces. This filtration and excretion-deposition process affects the food web and the biogeochemical cycling. Further-
OCR for page 5
Ecosystem Concepts for Sustainable Bivalve Mariculture more, this filtration and deposition activity has impacts on the physical and chemical environment, modifying various habitats and their ecological functioning. Submerged aquatic vegetation (SAV) and other benthic plant production can be enhanced by greater penetration of light through reductions in turbidity from suspension feeding and also by fertilization of the bottom through biodeposition by the bivalves. Structures associated with mariculture typically suppress SAV beneath them by shading, and human disturbance associated with mariculture operations, such as foot and boat traffic, can degrade SAV habitat. Impacts on the benthos can occur if mariculture structures substantially modify deposition patterns by altering currents or the cultured organisms transfer organic materials to the bottom through biodeposition, which can either enhance food supplies for some deposit-feeding benthic invertebrates in soft sediments or induce mortality of benthic invertebrates under conditions of limited flow and high-stocking densities. The structures used by bivalve mariculturists to hold and protect molluscs during grow-out provide novel hard substrates for epibiotic attachment and can attract fish and crustaceans to the structural habitat and to the attached epibiota. Many of these mobile organisms have been shown to feed upon structure-produced prey, but there is no definitive conclusion on whether or not the “artificial reef” effect reflects simple attraction of fish and crustaceans or actual enhancement of their production. Nonetheless, widespread recognition has emerged that such structures enhance production of benthic prey and provide hiding places for fish and crustaceans that feed on these prey. Information on the potential effects of mariculture on birds, marine mammals, and marine turtles is largely based upon a general understanding of wildlife ecology and the relationships of these species to the physical and biological environment rather than on studies to test explicitly the effects of mariculture operations. Potential positive impacts include increased food availability for birds attracted to the fouling organisms on mariculture gear. Some potential negative impacts include entanglement and drowning in nets and other gear and disturbance, removal, or displacement of wildlife whose breeding or foraging habitats occur near mariculture operations. Historically, bivalve mariculture, especially of oysters, led to numerous examples of both intentional and inadvertent introductions of non-native species. The intentional importation of nonnative species, such as oysters, used in mariculture represents a species introduction, and historically several of these bivalves reproduced and established self-sustaining populations. The imported bivalves often carried unintended “hitch-hiker” species, some of which established self-sustaining populations that spread out from the mariculture facilities. However, the development
OCR for page 6
Ecosystem Concepts for Sustainable Bivalve Mariculture TABLE S.1 Best Practices and Standards That Can Be Applied Across Bivalve Species and Conditions Potential Problem Impact Best Management Practice Excessive localized organic loading to sediments via biodeposits from bivalve mariculture Low oxygen (hypoxia) in sediments and loss of benthic biota Site selection (e.g., tidal flushing rate, currents) and limiting bivalve biomass to levels below carrying capacity for biodeposits Integrate bivalve mariculture with seaweed culture Decreased planktonic biomass by overstocking Shift planktonic composition; reduce turbidity allowing greater light penetration and hence more benthic plant production; deprive native suspension feeders of food Site selection (highly productive area) Manage stocking density based on carrying capacity for filtration Loss of carbonate shell from coastal waters Less habitat for larval settlement and oyster reef biota; reduced buffering capacity for maintaining pH Recycle shell from shucking operations and restaurants, taking precautions to prevent spread of nonnative species Introduction and transmission of disease organisms Large losses of cultured bivalves; transmission of disease to native species with possible biodiversity losses and reduction in wild stocks of bivalves Largely limit transfer to eyed larvae screened for disease; minimize transfer of adults and only after screening Establishment of breeding populations of nonnative bivalves introduced through culture Loss of native biodiversity resulting from competition, predation, and habitat modification Culture sterile triploids Regulate transport and processing of live animals Spread of nonnative species associated with mariculture Loss of biodiversity resulting from competition, predation, and habitat modification Limit stocking to clean seed or eyed larvae (no adults) Regular cleaning and land-based or other appropriate disposal of fouling organisms
OCR for page 7
Ecosystem Concepts for Sustainable Bivalve Mariculture Performance Standard Approach Desired Outcome Monitoring for hypoxia in sediments Limit organic accumulation in sediments, yet fertilize submerged aquatic vegetation (SAV) Carrying capacity model for estimating stocking density Maintain or restore biodiversity and natural food web structure; enhance water clarity via filtration and improve SAV habitat Monitor for change in plankton composition and performance of native suspension feeders Maintain baseline shell-based habitat and carbonate balance of estuaries and coastal lagoons; compensate for shell removed by harvesting wild bivalve stocks Monitor for disease organisms Avoid spread of disease; maintain health of cultured and native bivalves Monitor for nonnatives in areas near mariculture operations Protect native species and ecosystem structure Monitor for nonnatives at mariculture operations and in areas near operations Protect native species and ecosystem structure
OCR for page 8
Ecosystem Concepts for Sustainable Bivalve Mariculture Potential Problem Impact Best Management Practice Overfishing, depleted stocks, and habitat degradation and loss Reduction in seafood supply Use mariculture to create habitat and build up brood-stock sources; restore filtering capacity and water clarity; enhance SAV; increase seafood supply Food web changes and biodiversity loss Displacement of native species and/or predation on cultured stock Disturbance of birds, marine mammals, and marine turtles Site selection (avoid areas near breeding and feeding areas) Confine activities to less sensitive time periods Visual impact Social discord Employ submerged culture structures and adoption of industry and intergovernmental codes of practice have greatly reduced threats of new unintentional introductions. In addition, artificial hard substrate habitat (e.g., cages, racks, lines, netting) facilitates the spread and high abundance of nonnative epibiotic organisms in soft-sediment environments. Disease organisms can still be transferred with bivalve seed used in mariculture, but International Council for the Exploration of the Sea protocols for the transport of eyed larvae from hatcheries with rigorous disease inspection programs and producing seed in quarantine greatly reduce the potential for disease transmission. Diseases that occur at low levels within wild populations can flourish in mariculture populations because of altered conditions, such as crowding and temperature fluctuations. Lastly, the introduction of nonnative bivalve species for the purposes of mariculture can affect the genetics of native populations through the interbreeding of wild and cultured organisms. Finding: Research that takes a broader landscape-scale and ecosystem-based approach would provide a better understanding of how the scale and intensity of bivalve mariculture influence the natural ecosystem structure and processes. To achieve this goal, methods for accurate estimation of ecosystem carrying capacity will be vital. In addition, further study of the impacts of high-density (intensive)
OCR for page 9
Ecosystem Concepts for Sustainable Bivalve Mariculture Performance Standard Approach Desired Outcome Monitor prices and demand for wild and cultured bivalves Recreate some of the historic habitat and nutrient cycling functions of oysters and other bivalves Potentially reduce fishing pressure on wild stocks Assess sensitivity to disturbance and population resilience of native species Minimize negative interactions between mariculture and protected species Provide more effective environmental water-quality regulations to prevent microbial contamination of bivalves and wild waters Establish visual design standards Increase compatible uses of coastal areas Enhance social acceptance mariculture on local biodiversity would help decision makers and managers anticipate changes in the ecosystem that could influence social attitudes and public acceptance. Recommendation: Efforts should be directed at studying effects of bivalve mariculture at appropriate landscape and ecosystem scales that would facilitate managing mariculture at these scales instead of current management scales, which often focus on the scale of the individual lease or even the individual potentially impacted species. Future research efforts should assess how modification of habitat by bivalve mariculture affects aquatic vegetation and mobile fish and invertebrates at larger spatial and longer temporal scales, especially life stages of the guild(s) of fish and crustaceans known to associate with structure and hard substrates. Additionally, mariculture structures, such as racks, lines, bags, and the cultured shellfish should be studied to determine whether they act only as attractants or also enhance productivity of species known to aggregate around structures. Finding: Continued research efforts could develop appropriate culturing techniques for native bivalve species, as well as enhance ways of restoring and then sustainably managing depleted native stocks. It is important to develop a better understanding of the potential of nonnative bivalve molluscs used in mariculture to become natural-
OCR for page 10
Ecosystem Concepts for Sustainable Bivalve Mariculture ized under changing environmental, climatic, and other conditions. Additionally, there is a general lack of information on community-and ecosystem-level responses to mollusc introductions and how those responses compare to native species. Recommendation: To prevent unintentional and probably irreversible establishment of breeding populations of introduced species, mariculture operators should use sterile triploids as much as possible when they grow nonnative bivalves in areas where the cultured species either has not been introduced or has not established a reproductive population. More attention should be directed toward the eradication of undesirable nonnative species, and a greater emphasis should be placed on studies of ecosystem-level effects of nonnative bivalve introductions. Finding: Assessments of the impacts of disturbance from bivalve mariculture on birds, marine mammals, and marine turtles are constrained by insufficient baseline data on habitat use by these species and further, by a lack of data both on spatio-temporal variation in disturbance events and on the longer-term consequences of these disturbances on populations of these species. Recommendation: Managers should recognize that previous studies have limited power to detect adverse effects of disturbance and that a precautionary approach should be taken in order to minimize potential disturbance. Future decision making would benefit from targeted research that incorporates spatially explicit studies of the activities of mariculturists; the individual behavioral responses of birds, marine mammals, and marine turtles using these coastal habitats; and the population consequences of any observed behavioral changes. BIVALVE MARICULTURE CONTRASTED WITH WILD FISHERIES Many ecological effects of bivalve mariculture closely parallel the corresponding ecological effects of wild-stock harvests. The similarity is greatest when comparing wild harvest to mariculture operations that raise bivalves in or on natural bottom habitats because similar or identical harvesting methods are typically used. Impacts of dredge-harvest gear on the benthic communities are greater than for any other bottom-disturbing fishing gear, and the intensity and duration of such impacts of harvest disturbance vary with bottom type. Mariculture conducted on lines, racks, or cages does not require dredging and is thus less damaging to the ecosystem than wild-stock harvesting. In a bivalve mariculture operation, the shell habitat is largely maintained by replacing harvested bivalves with new juveniles. In contrast, the exploitation of wild stocks of oysters has
OCR for page 11
Ecosystem Concepts for Sustainable Bivalve Mariculture caused the degradation and loss of oyster-reef habitat over time. Hence, fisheries that target species, such as oysters, which create biogenic habitat, can have and have had net negative impacts on habitat quality and quantity. Wild-stock harvests tend to be more frequent and more dispersed, thus causing greater damage to the ecosystem than the less frequent, more localized, and managed harvest of cultured bivalves. Basic economics suggests that increasing supply through mariculture will reduce seafood prices if other factors remain unchanged. Lower prices will tend to reduce economic incentives to harvest the wild population, thereby reducing fishing pressure on the wild stock. However, this effect can be masked in practice if wild-harvest fisheries remain profitable even at lower prices, if overall demand for the product increases, or if a strong niche market develops for the wild-harvest product. Increasing imports of cultured salmon into the United States since the mid-1990s correlate with falling prices for wild-stock salmon, and a similar pattern of price decline followed the increased domestic production of cultured hard clams. Finding: Although the effects of disturbance to benthic communities caused by bivalve mariculture activities and those from wild harvest are relatively well understood at local scales, there are few direct comparisons, and less is known about cumulative effects at larger spatial and longer temporal scales. Recommendation: Direct comparisons of the effects of bivalve mariculture and wild harvest should be conducted in systems with both activities to better understand their effects in comparable environments. Studies at larger spatial scales and over longer periods of time should also be undertaken. Finding: Economic theory suggests that mariculture production will tend to increase supply and reduce the price of the cultured species, thereby reducing economic incentives to harvest wild populations. The effect of lower prices on fishing pressure depends on the condition and management of the wild fishery. Empirical evidence for these effects is largely limited to observations of price trends with increases in supply, but there has been little formal analysis of responses of either markets or wild fisheries to the expansion of mariculture. Recommendation: Policy makers and marine resource managers should anticipate possible linkages between wild harvest and mariculture production in shellfish markets when developing forecasts. Managers should monitor changes in market prices to assess the effects of mariculture on supply, product quality and availability, and the response of wild-harvest fisheries to these changes in market conditions.
OCR for page 12
Ecosystem Concepts for Sustainable Bivalve Mariculture CARRYING CAPACITY AND BIVALVE MARICULTURE Carrying capacity as it applies to bivalve mariculture can be defined as the maximum population or biomass that an area will support sustainably, as set by available space, food, and other potentially limiting resources but within the limits set by the capacity of the ecosystem to process biological wastes and by social tolerance for the change in environmental attributes. The concept of carrying capacity is increasingly and appropriately invoked as a quantitative guide to identify limits to stocking densities of bivalves in mariculture operations. Suspension-feeding bivalves remove phytoplankton and suspended detrital and inorganic particles while producing and releasing nutrients in dissolved and biodeposited forms. These biogeochemical functions provide the ecological basis for scaling impacts of different biomass loadings of the cultured bivalves. Application of a carrying capacity concept to setting mariculture stocking limits requires a determination on what represents acceptable versus unacceptable impacts. In many estuaries, the historical baseline abundances of oysters and other bivalve molluscs, and hence their collective filtration capacity, was dramatically higher before harvesting reduced these stocks. If cultured bivalves were used to help restore baseline conditions of filtration, there could be substantial improvements in the ecosystem state through enhanced water clarity and reductions in algal blooms and hypoxia. Carrying capacity models can be used to optimize production of the cultured bivalves; reduce the ecological impacts on the food web; or maintain societal values, such as scenic amenity or recreational opportunity. All carrying capacity approaches require models of the mariculture activity and its interactions with living and non-living components of the ecosystem. Although several carrying capacity models have been developed for bivalve mariculture, the uncertainties associated with ecosystem-based models remain large. Monitoring to test model predictions and adaptive modification of the models and of management decisions are thus critical components of implementing site-specific limits to bivalve stocking. Finding: Assessment of bivalve mariculture has occurred mostly at the local scale by measuring the “footprint” of the shellfish farm. Scaling up these effects to whole systems has been limited by the difficulty in identifying a signal attributable solely to mariculture and by the capacity and resources to make meaningful measurements over larger areas. Similarly, most of the potential measures of ecological carrying capacity consider only a single or a few ecosystem components. Our understanding of factors that affect ecological carrying capacity will evolve as scientists learn more about the functioning of marine ecosystems.
OCR for page 13
Ecosystem Concepts for Sustainable Bivalve Mariculture Recommendation: Managers should utilize models based on empirical data that can estimate carrying capacity relative to bivalve production, ecosystem, and social constraints. The models provide an approach for addressing many of the issues that are associated with understanding multiple farm interactions and cumulative effects of other coastal zone activities at a scale relevant to coastal ecosystems. Recommendation: Further development and refinement of models for estimating carrying capacity should be encouraged. This will require a coordinated and sustained measurement effort to provide the empirical data necessary for iterative modification of these models and to validate projections produced by the models. Models should be designed to address the needs of managers and mariculturists alike. In addition, model parameters and general model outputs should be presented in clear and concise terms that are understandable and acceptable to all users. ECONOMIC AND POLICY FACTORS AFFECTING BIVALVE MARICULTURE A complex set of laws, regulations, and policies governs bivalve mariculture in the United States and affects jurisdictional areas, including (a) leasing and tenure policy; (b) land use, zoning, and tax policies; (c) interstate transport policies; and (d) offshore mariculture policy. The estuarine and nearshore coastal waters most appropriate for bivalve mariculture are typically regulated at the state, county, or town level. In most states, the intertidal or shallow subtidal bottom and overlying waters in which mariculture operations are located are owned by the public with the state acting as trustee. A federal permit may be required if mariculture gear could represent an obstruction to navigation or if the operation is located in federal waters. Because mariculture operators in most coastal states do not own the bottom they use in their businesses, uncertainty over leasing and tenure in the long term represents an impediment to investment and may reduce opportunities to obtain financing. At least 120 federal laws and more than 1,200 state statutes across 32 states, plus local regulations, affect mariculture. Some states have identified a lead agency or established an interagency coordinating committee to help guide prospective culturists through the complex permitting process. Some states exempt mariculture from sales or use taxes or encourage mariculture by special zoning or waterfront revitalization programs. Other states have enacted legislation or constructed regulations to reduce interference with commercial fishing often by restricting potential leasing to areas outside of productive mariculture grounds.
OCR for page 14
Ecosystem Concepts for Sustainable Bivalve Mariculture Rules governing the interstate importation of bivalve seed vary widely among states, creating confusion, misinformation, and often noncompliance. The lack of a comprehensive national policy has contributed to the spread of bivalve diseases, along with variability in the capacity of states to test for diseases. To avoid nearshore pollution and use conflicts, mariculturists have become interested in offshore mariculture in federal waters, beyond the jurisdiction of the states. Despite growing interest in offshore mariculture, regulation remains unsettled, and the lack of a settled and transparent regulatory framework and uncertainty over legal tenure inhibits this enterprise. Most mariculture operators in the United States target high-price regional and local markets for specialty, value-added products. Passage of laws to require labeling of bivalves by country of origin may increase demand locally for home-grown products, including cultured bivalves. Local traditions and nearshore use conflicts often play an important role in bivalve mariculture. Recreational activities, such as boating and swimming, and aesthetic considerations regarding ocean and bay views often affect public acceptance of existing operations and the permitting of new mariculture operations. Bivalve growers can increase societal acceptance and reduce political opposition to mariculture leases by engaging constructively with the local community and by designing their operations to minimize visual impacts. Mariculture operations that restrict foot or boat traffic in nearshore waters or tidal areas face issues of public use and access rights. In some states, mariculture is given lower priority in the resolution of use conflicts. Education of the local community about the ecological benefits of bivalve mariculture may increase public acceptance, particularly in locations where excess nutrient input has caused eutrophication problems, where wild stocks have been depleted, or where seagrass has declined greatly from historical baselines. Finding: While some laws and regulations may constrain bivalve mariculture development, others can serve to advance its growth. Local traditions and use conflicts can have this dual effect as well. Recommendation: States should streamline the permitting process for bivalve mariculture in state waters and identify areas within state waters where such activities are encouraged. Shellfish growers should engage the local community and design their operations to minimize conflicts. ECOSYSTEM SERVICES OF BIVALVES Suspension-feeding bivalves have the ability to reduce turbidity through their filtration, fertilize benthic habitats through biodeposition,
OCR for page 15
Ecosystem Concepts for Sustainable Bivalve Mariculture induce denitrification, counteract some detrimental effects of eutrophication in shallow waters, sequester carbon, provide structural habitats for other marine organisms, and stabilize habitats and shorelines. These ecosystem services of bivalves, along with recognition that oysters, clams, and scallops have been depleted dramatically below historical baselines in many estuaries, explain why bivalve mollusc restoration has become an important component of many programs for restoring impaired estuaries and some coastal waters. Finding: There is a need for improved quantifying of ecosystem service values so that markets for these ecosystem services could be further explored. Through a market-based approach, the present practice of externalizing the lost value could be changed to a system that assesses the true costs to those who contribute to the deterioration of natural estuarine and coastal marine ecosystems services. Recommendation: Research at the interface of biology and natural resource economics should be aggressively supported to explore the various proposed ecosystem services of bivalve molluscs and to develop rigorous economic methods of putting values on those services. This could include methods that specify market values for those services that yield to this approach and methods involving “willingness to pay” and other public preference approaches where markets do not exist. This research should then be utilized by policy makers to achieve social equity in putting costs of service losses on those responsible and using fees paid for lost services to restore those ecosystem services and thereby preserve them for the general public trust. Finding: Many estuaries suffer from eutrophication and potentially could benefit from increasing the biomass of suspension-feeding bivalves to provide resilience to eutrophication and reduce the symptoms of excessive nutrient and sediment loading. In addition to limiting effects of eutrophication and sedimentation, restoring the beneficial biogeochemical functioning of suspension-feeding bivalves, especially oysters, could provide additional ecosystem services associated with filtration of phytoplankton and inorganic particles from the water column and deposition of organic biodeposits. These effects will be greatest in shallow and well-mixed water bodies, such as those typically found in estuaries, coastal bays, and lagoons. Recommendation: Policies should be developed to encourage restoration of the biogeochemical filtration functions associated with suspension-feeding bivalves in estuaries. Such policies should consider both recovery of wild stocks and mariculture of (preferably
OCR for page 16
Ecosystem Concepts for Sustainable Bivalve Mariculture native) suspension-feeding bivalves to restore the filtration functions and associated ecosystem services. For restoration purposes, particular attention should be given to (1) establishing genetic husbandry guidelines to prevent loss of genetic diversity; (2) avoiding negative effects of disturbance of vertebrates and other valued species; (3) controlling spread of nonnative fouling organisms, especially certain tunicates; (4) regulating bivalve stocking to require use of eyed larvae from certified hatcheries with an effective and comprehensive disease inspection or to first-generation seed spawned from adult bivalves under quarantine conditions in order to minimize species introductions and disease spread; (5) insuring that bivalve shellfish loading does not exceed levels that have unacceptable negative impacts on the benthos through excessive organic loading or on other components of the ecosystem through clearance of planktonic foods and organic particles from the water column; (6) preventing unacceptable damage to bottom habitat by harvest gear; and (7) assessing the social tolerance for mariculture on a site-specific basis.