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