Shellfish aquaculture — In praise of sustainable economies and environments

We write to extol the virtues of filterfeeding bivalve shellfish – clams, mussels, oysters and scallops – to give them their due as key players in ecologically sustainable aquaculture in the marine environment and as environmentally sensitive monitors and water purifiers. Shellfish are successfully farmed throughout the world and shellfish culture represents a legitimate use of the marine environment for sustainable food production. An equally compelling case can be made for the primary grazers such as abalone and sea urchins. In recent years it has become all too common for the press and some scientific literature to focus only on the negative aspects of man’s use of the environment. Unless we as humans decide to eat substantially less seafood, which is contraindicated by the latest in health and nutrition research, aquaculture is here to stay; seafood production is a key to our present and future food supply. Worldwide, the demand for seafood continues to surpass supplies of wildcaught fish and shellfish, and appetites for these products are growing steadily at a time when the world is increasingly looking to the sea to provide food. Promoting ecologically sustainable shellfish culture is promoting sound resource stewardship and a clean environment. There is a critical need worldwide to bring ecological balance to some forms of aquaculture and an urgent challenge to foster aquaculture as an environmentally sound and socially acceptable practice in the United States. Marine/estuarine shellfish culture is an optimally environmentally sustainable form of aquaculture. In 1999, bivalves represented nine percent of total world fishery production, and 27 percent by volume or 18 percent in value of total world aquaculture production. World bivalve production (capture + culture) has increased continuously and substantially over the past half century, rising from approximately one million tons in 1950 to about 11 million tons in 1999. This growth is primarily due to aquaculture (Anderson 2002). As the global population continues to grow, demand and production of food, especially seafood from aquaculture will continue to be an essential element in the future of our food security. Unfortunately and quite unfairly, aquaculture has become an all inclusive term, especially when used by special interest and advocacy groups to rail against the perceived impacts of some coastal farmers on the environment. All aquaculture is not created equal and should not be treated as such. The various attributes and intricacies of different forms of aquaculture need to be understood. Aquaculture is a broad term that encompasses the farming of many aquatic species such as fish, shellfish and seaweeds, not only for food but also for medicinal and nutraceutical purposes. Filter-feeding bivalves have unique requirements for growth compared to other aquaculture-reared organisms such as fish and seaweeds and, consequently, they have different interactions and impacts on the coastal waters, habitats and food webs in which they are grown. Given this fact, these various attributes and potential beneficial interactions amongst the various species under culture need to be considered on their own merits in order for the continued sustainable aquaculture production of seafood. Cultured shellfish are one of the few forms of marine aquaculture to get a solid thumbs up of approval for ecological stewardship from the Audubon Society, Monterey Bay Aquarium’s Seafood Watch and Eco-Fish. The broad-brush approach of lumping all aquaculture impacts together is too simplistic an approach to what is actually a complex set of issues. Molluscan shellfish aquaculture is, by definition, a ‘green’ industry. Shellfish growers are committed to water quality – quality of their product and quality of the environment – from the day the molluscs spawn to the day the finished product is eaten by the consumer. Shellfish grown in approved, certified waters provide a safe, nutritious, healthy food source. In addition, the act of shellfish feeding (biofiltering) improves water quality by removing particulates and some unwanted nutrients from the water column. Shellfish feed at the base of the food chain as first-order consumers they are vegetarians. Filter-feeding bivalve molluscs are an essential link between the bottom-dwelling aquatic communities and phytoplankton production in the water column. Shellfish are highly efficient water filters that directly remove particulate material thus reducing turbidity and both directly and indirectly removing nitrogen and other nutrients. Via this process, these highly efficient water purifiers remove or reduce organic matter, nutrients, silt, bacteria and viruses, and improve clarity and light transmission which, in turn, improves the condition of critical habitat, including survival of critical habitat species such as seagrasses and other submerged vegetation. Thus they provide a net gain for the environment. As with any living organism, too many shellfish in a given area can result in