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New Hampshire IMTA study shows oysters reduce nitrogen in shrimp farming

A scientist at the University of New Hampshire (UNH)’s College of Life Sciences and Agriculture (COLSA) is studying how integrated multi-trophic aquaculture (IMTA) has found oysters help control the production of nitrogen produced from farming shrimp.

IMTA is a system in which two or more organisms are farmed together. This process could make shrimp farming more sustainable and support the growth of this industry in the United States.

Elizabeth Martin, a graduate student in the marine biology program at COLSA is studying IMTA systems that pair farmed shrimp with water-filtering species, like oysters, to determine if the grouping will cut down on the amount of ammonia and phosphorus that remains in the water as part of the farming process.

UNH graduate student Elizabeth (Lizzy) Martin tests water samples from a shrimp aquaculture study she conducted at UNH’s Coastal Marine Lab in 2023. (Photo: University of New Hampshire)

“Much of the shrimp we consume comes from overseas, where they don’t need to follow the same environmental regulations as we do here in the U.S.,” said Martin. “And shrimp is also one of the highest valued seafood imports for the U.S., so developing a local industry would help reduce reliance on these overseas markets.”

Although shrimp produce ammonia naturally, there are other ammonia contributors including shrimp feed, which is often high in nitrogen, the natural decomposition of the shrimp feed, dead organisms, faeces and other materials found within the large artificial ponds where shrimp are commonly raised. 

This water is then discharged into the surrounding environment, resulting in the effluent entering waterways and, in the U.S., potentially violating regulations like the EPA’s Clean Water Act. In natural environments, water-filtering species, like shellfish, help clean the water of excess nutrients. 

Martin tested if a similar method could be used in more of a closed farming system, in which native oysters and nonnative red seaweed could grow alongside Pacific white shrimp.

“We had three treatments — shrimp with the seaweed, shrimp with the seaweed and an oxygenator and shrimp with the seaweed and oysters,” said Martin, who conducted her experiment at the UNH Coastal Marine Lab in New Castle, New Hampshire. “And what we found was that the final treatment, the shrimp with the seaweed, which absorbs and stores nitrogen, and the oysters resulted in a reduced level of nitrogen (including ammonia, nitrite and nitrate) over time.”

The oysters controlled nitrogen production better, resulting in significantly lower amounts over a 30-day window, compared to the other two treatments.

Graph showing total nitrogen count for the three different treatments over a timespan of more than 30 days. (Photo: Elizabeth Martin)

This method has the potential to grow shrimp sustainably and produce marketable products like seaweed and oysters. The products can diversify the revenue streams for aquaculture farms while contributing positively to the environment.

Although the implementation of such systems faces challenges, including regulatory issues and environmental concerns unique to the U.S. compared to traditional shrimp farming practices in Asia, the study provides a pathway for more sustainable practices that could be adopted widely, including in New England.

Michael Chambers, a research associate professor with the UNH School of Marine Science and Ocean Engineering and Martin’s graduate advisor said her research—which demonstrates a new IMTA approach to culture shrimp in a closed recirculating aquaculture system—allows it to be grown inside a barn, greenhouse or even a basement to provide fresh seafood to local restaurants at a premium price.