The New York State Office of the Attorney General, through the Bronx River Watershed Initiative, has funded Carter Newell, a commercial shellfish farmer, and Rocking the Boat, a local youth-development organization, to install a raft in the Bronx River with ropes to catch and grow ribbed mussels. These mussels naturally live along the Bronx River shoreline, but have lost most of their salt-marsh habitat as human populations and industry have expanded along the river. Ribbed mussels now exist at much lower abundance than they did historically.
Mussels feed on plankton, and when they grow they incorporate into their shells and meat nutrients that are in excess in the urban waters around New York City. These excess nutrients come from sources such as wastewater and storm runoff. When the mussels are harvested, this harvest will also remove the excess nutrients from the environment that have been incorporated into their shells and tissue, thereby improving water quality for other marine life.
NOAA aquaculture scientists from the Milford Laboratory in Connecticut are helping to evaluate the effectiveness of these mussels at removing nutrients from the Bronx River. Such harvest of cultivated aquatic animals and plants for the purpose of removing nutrients from the environment is referred to as “nutrient bioextraction,” and this project in the Bronx River is one of the first in the region to test the effectiveness of this relatively new technology.
The ribbed mussel raft was installed in August 2011 and mussels were harvested in October 2012. The raft system was used during winter 2012-2013 as part of the co-located seaweed project, but has since been removed from the Bronx River.
1. Can ribbed mussels live on a commercial, blue mussel aquaculture raft?
Ribbed mussels naturally live on the shoreline, in salt marshes, and are regularly exposed to the air during low tide. When they are grown on a typical mussel raft they will be constantly underwater, so it was important to determine if this would interfere with their growth. Laboratory experiments with ribbed mussels showed that after three days of submersion, there were no differences in feeding between the intertidal and submerged mussels. These results have been reviewed and published in the scientific journal Aquaculture International (see link here). These results support the use of ribbed mussels for bioextraction purposes using traditional mussel aquaculture techniques.
2. Is mussel health impacted by living in such an urban environment?
The native ribbed mussel populations were studied by a shellfish pathologist and compared to a population in a suburban environment to look at occurrence of physiological abnormalities and disease. There were no significant differences in the health of the urban and suburban mussels. These results have also been reviewed and published in the scientific journal Estuaries and Coasts (see link here).
3. Is the Bronx River a good place to grow mussels?
Researchers from the Milford lab investigated this question using a combination of water testing and experiments with native mussel populations. During the summer of 2012, water was sampled weekly for temperature, salinity, dissolved oxygen, dissolved and particulate nutrients, chlorophyll, plankton abundance and community composition. A series of feeding experiments with native mussel populations were performed during the summers of 2011 and 2012. These experiments allowed NOAA researchers to determine how quickly and efficiently the mussels consume food that is naturally available in the water.
By combining the mussel feeding data with measurements of environmental conditions, researchers were able to determine that the Bronx is not an optimal site for mussel growth. The raft was located at the point where the Bronx and East Rivers meet, and the dynamic water movement at this site resulted in high levels of silt and sand in the water. These inorganic particles inhibited growth of the phytoplankton on which ribbed mussels typically feed. Mussels at the Bronx site proved to be highly adaptable, however, and were able to sort through the silt and sand in the local water to feed on the available food as efficiently as mussels from a more favorable suburban site. These results are provided in greater detail in the Estuaries and Coasts article described above.
These results demonstrate the high tolerance of ribbed mussels for a wide range of environmental conditions. For this reason, researchers believe the ribbed mussel is a good candidate for use in future nutrient bioextraction projects.
Researchers were also able to use measurements of mussel feeding to determine positive effects of the raft on the local environment. The mussels on a fully stocked, one-acre raft would filter 19 million gallons of water every day, removed 1,358 pounds of particles. For details about these calculations, see the final report of this project at the bottom of this page.
4. Are the mussels from the raft contaminated?
Harvested mussels will be sent to a contract laboratory and tested for a wide range of contaminants, including heavy metals, PCBs and flame retardants. These results can be compared to those from the nearby Throgs Neck Bridge, which is a long-term mussel contaminant monitoring site that is part of the NOAA Status and Trends program.
5. What do we do with the mussels once they are harvested?
Ribbed mussels are not eaten by people because of their poor taste, and the waters around Hunts Point are not approved for shellfish consumption. Therefore, alternative uses must be identified for future shellfish production from urban waters such as New York City. The NOAA Aquaculture Program funds an alternative finfish feeds program, based in the NOAA Northwest Fisheries Science Center. Harvested mussels from the raft have been sent to the NOAA Seattle Lab for evaluation as a potential fish feed. Other potential uses of bioextraction-related mussel meat are being explored in Sweden, and include chicken feed and compost.
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