Image courtesy of Lynton Land, Ph.D.
Excessive nutrient concentration has stimulated an overgrowth of microscopic plants in the bay, and scientists point to nitrogen and phosphorous as the major culprits. This nutrient pollution comes from sources ranging from wastewater treatment plants and septic tanks to fertilizer and manure runoff from farms, and from atmospheric deposition from burning fossil fuels.
Now a team of researchers from Virginia Commonwealth University and Virginia Tech has shown how to directly quantify the nutrient removal capacity of aquacultured oysters as a means to offset those sources.
As they grow, oysters remove nitrogen-containing compounds from the water. These nutrients are then permanently removed from the water-system when the oysters are harvested and sold to the seafood market.
In a study, published online in the January-February issue of the Journal of Environmental Quality, Colleen Higgins, a Ph.D. life sciences candidate, her mentor and corresponding author for the study, Bonnie Brown, Ph.D., professor and associate chair for the VCU Department of Biology, and economist Kurt Stephenson, Ph.D., with the Department of Agricultural and Applied Economics at Virginia Tech, reported that they could estimate this nutrient removal mechanism with a high degree of confidence by measuring the shell length of aquacultured oysters.
Higgins said that total length is a common market measurement already used by growers, so it would not require a costly or time-consuming effort on the part of growers to verify the amount of nutrient removal. They would just need to verify the quantity of oysters harvested of different size classes, for example cocktail, regular and jumbo.
“Oyster aquaculture can offset inputs and have an impact at the local tributary scale where inputs are measured and targets are set, but this would require a large scale-up of production,” said Higgins.
“Although in the bigger picture of the bay, nutrient loads are so massive that reducing them requires changing the habits of all of the people that live in the watershed, from how we grow our food to how much water we use,” explained Higgins.
“Oyster biomass removal can make a dent, but can only do so much. Now that it has been quantified, bay managers can decide the utility of oyster cultivation as an in situ removal mechanism and if it should be added to the tool box of measures aimed at curbing nutrient pollution in the bay,” she said.
Oyster aquaculture production is more common in places like the U.S. Pacific coast, Australia, Prince Edward Island in Canada, and in Australia and Europe, where cultivation of oysters and mussels is a much larger portion of the local economy, according to Higgins.
“In the bay, there has been less acceptance of shellfish aquaculture, but that might be changing,” she said.
This work was supported in part by funds from U.S. Environmental Protection Agency’s Targeted Watershed Grant Program and administered by the National Fish and Wildlife Foundation.