Practical Applications of Nutrient Bioextraction

Seaweed Farming in Long Island Sound and Other East Coast Locations

Watch a video from Science Friday on how GreenWave trains “3D Ocean Farmers” here.

Global seaweed aquaculture accounts for about 20 percent of the total marine aquaculture production by weight, according to Kim et al. (2017). Seaweed aquaculture has been growing in popularity in the U.S. in recent years, most notably in Connecticut, Rhode Island, Massachusetts, and Maine on the East Coast, as existing aquaculturists want to diversify their existing crop and prospective aquaculturists are interested in entering new markets. As of 2017, nearly 20 open water kelp farms were operating in the Northeast, with nearly all locally grown products going to US markets (Yarish et al. 2017).

Seaweed species such as Gracilaria and sugar kelp have the ability to improve water quality through ecosystem services such as nutrient bioextraction. Seaweed has the ability to store nutrients such as nitrogen and phosphorus within its tissue. When the seaweed is harvested, the excess nutrients in the water column are effectively removed from the system. In addition to the ecosystem services provided by nutrient bioextraction, the cultivation of seaweed provides ancillary ecosystem services such as increasing the local species diversity and richness, and creating habitat for invertebrates and juvenile/small vertebrates.

Founded in 2014, GreenWave is a non-profit organization that focuses on ocean-farmer training and education, policy development, and research and development. It replicates polyculture vertical farming system (which it calls “3D Ocean Farming”) by growing a mix of seaweeds and shellfish that require zero inputs while sequestering carbon, taking up excess nutrients, and rebuilding ecosystems. GreenWave’s training program provides new ocean farmers with permitting support, personalized technical assistance, hands-on trainings, and free kelp seed grown in its Connecticut kelp hatchery as they work to deploy their farms, including in Long Island Sound. With its partners, GreenWave studies the impacts of 3D Ocean Farms, measures ecosystem services, builds kelp hatcheries, and helps farmers sustainably scale their operations.

In 2018, GreenWave kicked-off a partnership with Stony Brook University on Long Island to help oyster farmers in Peconic Bay incorporate sugar kelp (Saccharina latissima) into their operations. This partnership is helping to advance commercial seaweed-farming policy in the state and diversify ocean farms with a promising marine specialty crop, while enhancing ecosystem services and sequestering nutrient runoff, including nitrogen and phosphorus, in Peconic Bay.



  • Kim, J.K., Yarish, C., Hwang, E.K., Park, M., Kim, Y. (2017). Seaweed Aquaculture: Cultivation Technologies, Challenges and its Ecosystems Services. Algae, 32(1), 1-13.
  • Yarish, C., Kim, J.K., Lindell, S., Kite-Powell, H. (2017). Developing an Environmentally and Economically Sustainable Sugar Kelp Aquaculture Industry in Southern New England:From Seed to Market. 1-49.

Shellfish Aquaculture to Reduce Nitrogen Loads in Mashpee, MA (Cape Cod)

Members of AmeriCorps Cape Cod planting quahog in Great River. Credit: Rick York

In 2015, the town of Mashpee, Massachusetts completed their Comprehensive Watershed Nitrogen Management Plan, (CWNMP) which includes the Wastewater Management Plan that utilizes a hybrid approach to maximize the use of shellfish aquaculture, and construction of new sewage treatment infrastructure to meet their nitrogen load reduction requirements based on the Massachusetts Estuaries Project (MEP) reports for Popponesset Bay and Waquoit Bay.  The project area includes all of Mashpee and portions of the neighboring communities of Barnstable, Falmouth and Sandwich that fall within the Popponesset Bay watersheds or eastern Waquoit Bay watersheds. The plan is predicated on the use of shellfish in the following areas: Popponesset Bay/ Popponesset Creek, Ockway Bay, Mashpee River and Shoestring Bay in the Popponesset Bay watersheds, and in Hamblin Pond, Little River, Jehu Pond and Great River in the Waquoit Bay watersheds. Prior to implementation, the town conducted an extensive benthic survey to pre-identify locations that would be suitable for shellfish survival and growth, based on bottom type.

Over the course of 25 years, the town of Mashpee will implement five distinct phases of the plan and the extent of traditional wastewater infrastructure and shellfish can be adjusted can be made through the adaptive management program. Shellfish aquaculture is targeted for early implementation as shellfish aquaculture will improve water quality needed in the waterbodies due to nitrogen impacts.

In order to restore water quality in the Popponesset and Waquoit Bay estuary systems and meet TMDL nitrogen load reduction requirements, a total of about 17,000 kg of nitrogen per year needs to be removed the project areas. The plan proposed the use of 35.53 million quahogs and eastern oysters, and some new sewage treatment infrastructure across the project areas. Based on water quality monitoring results, shellfish assessments and nitrogen content analysis, adjustments in additional shellfish, other nitrogen removal measures, or sewer and treatment plant construction will be implemented as needed.

For over 20 years, the waters of Popponesset and Waquoit bays have failed to meet regulatory standards due to excess nitrogen mostly from septic systems, causing increases in algae, low levels of oxygens, and ultimately fish kills in the highly nitrogen loaded Mashpee River. Since the Town established an oyster aquaculture project in the Mashpee River 2005, there have not been any fish kills. To start implementation of the CWNMP in 2016, the town of Mashpee increased seed aquaculture and planting quahogs in Great and Little River/Hamblin and Jehu Pond area on the east of side of Waquoit Bay to restore water quality, and for recreational and commercial fisheries harvesting. The plan is to grow and harvest enough quahogs to completely restore water quality in that area. Water quality monitoring assessment data from 2017 showed improvement in the quahog project area while other areas were getting worse. Additionally, new commercial oyster farm sites have been licensed by the Town, and more are planned. The Town of Mashpee is also collaborating with the Mashpee Wampanoag Tribe’s Natural Resources Department on restoration and monitoring, which also includes the University of Massachusetts Dartmouth, School for Marine Science and Technology (SMAST) as a collaborator.  SMAST is conducting a study to quantify the enhanced denitrification in the oyster aquaculture areas.  The Tribe received an EPA Healthy Communities Grant to fund oyster restoration in Shoestring Bay.


Oyster Harvesting to Reduce Nitrogen, Phosphorus and Sediment Loads in the Chesapeake Bay

Credit: Oyster Recovery Partnership

The Chesapeake Bay Program (CBP) has approved the use of eastern oysters as a best management practice (BMP) in the Bay watershed and local jurisdictions can use oysters as part of their Watershed Implementation Plans (WIPs). WIPs require nitrogen, phosphorus, and sediment reductions to help improve water quality in the Bay.

The CBP approved recommendations made by the Oyster BMP Expert Panel, comprised of 13-members and coordinated by the Oyster Recovery Partnership. The Expert Panel is responsible for providing recommendations on and applying a decision framework to quantify the nutrient (nitrogen and phosphorus) and suspended sediment reduction effectiveness of oyster practices, including aquaculture and restoration activities, where there is sufficient science, for BMP application in the Chesapeake Bay Total Maximum Daily Load (TMDL).

The Expert Panel recommended that off-bottom culture, bottom culture, and bottom culture with substrate addition are the only private oyster aquaculture BMPs at this time. Additionally, there are a number of qualifying conditions for TMDL use, such as, only oyster aquaculture in tidal waters is eligible, and oysters have to be alive when harvested. The Expert Panel set baywide nitrogen and phosphorus reductions associated with tissue harvested from private oyster aquaculture practices. Based on existing scientific data and research, the Expert Panel determined the nutrient reduction effectiveness of diploid (2 chromosome) and triploid (three chromosome) oysters at different size classes based on the oyster’s biomass and percent nitrogen and phosphorus content in the tissue. They determined that the tissue assimilation capacity of various class sizes of diploid and triploid oysters conservatively ranged from 110-1,477 pounds of nitrogen and 22-154 pounds of phosphorus per one million oysters, respectively.

In the coming months, the expert panel will be issuing a second set of recommendations about shell, denitrification associated with restored reefs and aquaculture operations, and nutrient removal via the public fishery.


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