Shellfish Culture is Good for the Environment

For those of us who grow shellfish, this statement has been a no-brainer for years, but proving it has been another matter. Finally we are starting to get some scientific proof to back up our claims. Oysters clean the water, remove nitrogen, accelerate denitrification, enhance water clarity, promote eelgrass survival, and provide excellent habitat for myriad juvenile fish and crustaceans. All this and they taste great and are good for you too!

Watch a great video on the Environmental Benefits of Shellfish Aquaculture.

Download our Environmental Benefits brochure in pdf format.

View a series of Power Point presentations from the 2008 National Symposium on Shellfish and the Environment held in Warwick, Rhode Island on June 9-10, 2008.

There is an increasingly large body of science to support the assertion that shellfish aquaculture is good for the environment. Brett Dumbauld came out with a nice review in 2009, entitled "The ecological role of bivalve shellfish aquaculture in the estuarine environment: A review with application to oyster and clam culture in West Coast (USA) estuaries."

In 2004 University of Rhode Island graduate student Brian Kilpatrick compared the abundance and diversity of organisms congregating around eelgrass with those on the oyster cages at the Moonstone Oysters Narragansett growing site in Point Judith Pond. His thesis research showed that the abundance of small fish, crustaceans, and invertebrates in the oyster cages was about ten times that in the eelgrass beds, and that the diversity indices at the two sites were about the same. He counted thousands of fish, crabs, and lobsters in the oyster cages, including hundreds of juvenile tautog, black seabass, and other commercially important species. Kilpatrick's paper appeared in vol. 23 of the Journal of Shellfish Research.

Subsequently, in 2007 Jessica Tallman showed that oyster cages were similar to artificial reefs and natural cobble reefs in terms of habitat quality for scup and tuatog in an article published in the Transactions of the American Fisheries Society.

View an annotated bibliography of articles pertaining to shellfish aquaculture assembled by Bob Rheault. If it's missing any good references please let us know!

Denitrification

In 2002, Roger Newell and colleagues at the University of Maryland suggested that bacteria in the sediment around oyster bars remove at least 20 percent of the nitrogen in oyster wastes through denitrification, the same process used in modern wastewater treatment plants.

"It's mind-boggling what the potential would be if we had a large oyster population in the (Chesapeake) Bay," Newell said.

Oysters are seen as one of the most important species in the Chesapeake. Their filtering clears the water, letting more light penetrate to eel grass beds, while their reefs provide important marine habitat. Earlier work by Newell showed that historical oyster populations filtered the entire Chesapeake Bay in three to six days.

Newell acknowledges that most of the nutrients filtered from the water by oysters are recycled back into the water column, but the flux of undigested plant matter to the sediments stimulates bacterial processes known as nitrification and denitrification: the processes of turning the fertilizer ammonia into nitrate and then into harmless nitrogen gas, which escapes into the atmosphere instead of stimulating phytoplankton blooms.

These findings suggest that if a large oyster population could be restored, it could play an important role in helping to achieve the nitrogen reductions needed to help clean up the Chesapeake. Newell said, "You need to do everything you can do to control nutrients on the land, but then, once the nutrients get into the water column, what do you do to get them out? One way may be managing your oyster resource..."

For more information on this topic, see "Influence of simulated bivalve biodeposition and microphytobenthos on sedimentary nitrogen dynamics: a laboratory study," from the September 2002 issue of Limnology and Oceanography.

Nutrient removal at harvest

Since oysters are 1.4 percent nitrogen by weight, when a grower harvests 10,000 oysters for weekly deliveries to customers he is removing about 23 pounds of nitrogen and 2.3 pounds of phosphate and shipping it out. This is equivalent to the annual nitrogen output of a single waterfront homeowner!

Odd Lindahl presented an economic analysis of a mussel farm in Sweden that removed 39 Tons of nitrogen from a fjord annually at a substantial savings compared with a proposed land-based sewer treatment upgrade.

The ECSGA supports the development of a system for trading nitrogen credits for shellfish farmers.

Old news but good news...

Good news from the courts! In 2002 the Ninth Circuit Court in the state of Washington decided a case in favor of a mussel farm. The farm was being sued by a group of waterfront homeowners who claimed that raft-grown mussels were polluting the water with feces and shell. The court found that "...feces and chemicals exuded from live mussels have not been shown in the record significantly to alter the character of Puget Sound waters, and the record suggests instead that the mussel-harvesting operations generally purify the waters."

In 2004 the Environmental Protection Agency (EPA) issued Effluent Guidelines for Aquatic Animal Production Facilities, concluding that shellfish aquaculture does not need new effluent limitations guidelines or regulations, since shellfish "...remove nutrients (in the form of algae) from ambient waters by filtration."

Special thanks to Mike Rice, John Kraeuter, Bill Dewey, and others who contributed countless hours on the JSA EPA Aquaculture Effluent Task Force Molluscan Shellfish Technical Subgroup.