Project: Ribbed mussel nutrient bioextraction in the Bronx River Estuary, New York CityDates: 2011-2017Team: National Fish and Wildlife Foundation, Maine Shellfish R&D, Rocking the Boat, NOAA, Long Island Sound Study, Gaia InstituteFunding: New York State Office of the Attorney General, NOAA Fisheries Office of Aquaculture (https://www.fisheries.noaa.gov/about/office-aquaculture)
Project summary:Ribbed mussels are a shellfish species native to Long Island Sound and New York City, with historically large populations providing important services such as reducing nutrients and stabilizing shorelines. As these shorelines have become developed, most of the salt marshes that used to be ribbed mussel habitat have been lost to bulkheads, ports, and other waterfront infrastructure. By putting a raft stocked with mussels into the Bronx River Estuary, our goal was to restore some of the ecosystem functions that were once provided by historic ribbed mussel populations. At the same time, the project team’s researchers were interested in the ribbed mussel species because their notoriously poor taste reduces the likelihood of people eating them. Therefore they can be safely grown in places like the Bronx where high numbers of bacteria make shellfish aquaculture for human food not possible.
This project was a pilot study designed to address as many practical questions related to the use of ribbed mussels for nutrient bioextraction as possible. The researchers learned that, although ribbed mussels naturally grow in the intertidal zone where they are regularly exposed to air, ribbed mussels can grow constantly submerged underwater using methods typical of blue mussel aquaculture. The team monitored small local ribbed mussel populations in the Bronx and found that they were healthy even in an environment highly impacted by humans, and that local ribbed mussels naturally reproduce in June and July. It used a technique called stable isotope analysis to determine that the nitrogen used by the ribbed mussels to grow their tissues and shell originally came from human sources. This finding was good news for local nitrogen management programs that are focused on reducing excess nitrogen coming from human activities on land. The team also found that growing mussels in the water instead of on the seafloor reduced the amount of metals and organic contaminants such as pesticides that ended up in mussel tissue.
The project showed that ribbed mussels on a single 20×20 foot mussel raft could filter more than 3 million gallons of water every day. Harvest of the mussels on that raft would remove 140 pounds of nitrogen contained in their shell and tissue. Given these impressive results, the researchers were very interested to also discover that our location at Hunts Point was not an ideal place to grow mussels. Particles in the water that were filtered by mussels were dominated by sediments and other inorganic material, instead of mussel food such as plankton and other organic material. The mussels were able to adapt to these challenging conditions by increasing the amount of time they spent sorting through the particles they filtered, selecting food to ingest and rejecting material that was not food. But a different location with more food available may have resulted in faster mussel growth.
Some questions remain following our study. The project team tried a variety of methods to catch young ribbed mussels in the natural environment to stock our raft, but none of them worked. This was identified as a key bottleneck to future implementation projects. Recent research by Rutgers University and the Partnership for the Delaware Estuary have made great progress in reducing this bottleneck. The question of what to do with ribbed mussels after harvest also remains. Obviously the hope is that the mussels would be able to be recycled instead of ending up in a landfill. Some options for using the mussels include as feed for other animals and as fertilizers or compost. Researchers in Europe have studied the use of blue mussels for chicken and pig feed, and found that adding mussel meal as a supplement improved the quality of the feeds. It is possible that parts of the mussel could be used as supplements for plant-based fish feeds, such as the omega-3 fatty acids in the mussel tissue, but this is an area needing more research.
Link to scientific publication:
Links to recent media stories about the project:
Paul Greenberg features the Bronx project prominently in his book, The Omega Principle
Links to older media stories about the project:
Project: Use of Sugar Kelp Aquaculture in Long Island Sound and the Bronx River Estuary for Nutrient ExtractionProject Dates: 2012-2013Project Team: Jang K. Kim, George P. Kraemer, and Charles Yarish
Project Summary:
Following Kim et al.’s (2014) study quantifying the usefulness of Gracilaria tikvahiae in open water nutrient bioextraction farm systems in the Long Island Sound (LIS) and Bronx River Estuary (BRE), Kim et al. investigated the effectiveness of the cold water kelp species, Saccharina latissima, for nutrient bioextraction through seaweed aquaculture.
Nitrogen concentration in Long Island Sound and New York City estuaries is lowest during the summer months and begins to increase from late August to early September, with peaks during the winter months (January−February). This suggests that management strategies to reduce nutrients may be more effective if nutrients in Long Island Sound can be removed during the winter months before the spring phytoplankton bloom that accompanies peak nutrient levels. The goal of this study is to evaluate the feasibility of growing Saccharina latissima for nutrient bioextraction under different environmental conditions in urbanized estuaries like the Long Island Sound and coastal waters of New York City during the fall to spring growing season. Saccharina latissima, known as sugar kelp, is a cold temperate brown algal species.
Saccharina latissima seed string was outplanted on two 50m longlines at two near shore sites in the Long Island Sound (Fairfield and Branford, CT) and at the mouth of the Bronx River Estuary. The kelp was suspended at 2 different depths (0.5 and 1.0 m) to determine the depth that maximizes productivity and nutrient bioextraction. Researchers monitored water quality for inorganic nutrients, temperature, and salinity; tissue carbon (C), phosphorus (P), and nitrogen (N) contents; and evaluated productivity of cultured Saccharina latissima at each site by measuring the fresh weight biomass of kelp per longline at final harvest.
In 2014, Kim et al. reported that the warm temperate red seaweed, Gracilaria, removed 28 and 94 kg N ha−1 from the western Long Island Sound and the Bronx River Estuary sites respectively, over the 90-day growing season, if it was cultivated with 2m spacing between longlines. The results of this study showed that at the same locations (western Long Island Sound and the Bronx River Estuary sites), Saccharina latissima is estimated to respectively remove 70 and 180 kg N ha−1 at 0.5m depth, and 67 and 140 kg N ha−1 at 1.0m depth, with 1.5m spacing between longlines. Together, Saccharina latissima and Gracilaria would have the potential to remove 98 and 274 kg N ha−1 yr−1 from the western Long Island Sound and the Bronx River Estuary sites respectively, if Gracilaria and Saccharina culture were alternated in different seasons.
The results of this study demonstrated the suitability of seaweed aquaculture as a nutrient management tool, using the cold water species Saccharina latissima. There are three main advantages of sugar kelp aquaculture in highly urbanized estuaries: (1) the growing season of sugar kelp rarely overlaps with summer recreational boat activities; (2) non-overlap between the sugar kelp growing season and shellfish farming season, and (3) minimum maintenance effort for cultivation, and therefore, minimum costs. This study highlighted the benefits of alternating culture of warm- and cold- water species, suggesting this practice would maximize the nutrient bioextraction capacity of seaweed aquaculture throughout the year.
This project was funded by the U.S. EPA Long Island Sound Study’s Long Island Sound Futures Fund, the Connecticut Sea Grant College Program, the National Fish and Wildlife Foundation, and NOAA SBIR I and II.
Project: Field Scale Evaluation of Seaweed Aquaculture as a Nutrient Bioextraction Strategy in Long Island Sound and the Bronx River EstuaryProject Dates: 2011-2012Project Team: Jang K. Kim, George P. Kraemer, and Charles Yarish
Despite management efforts to reduce nutrient loading, such as the Total Daily Maximum Load (TDML) concept, which has significantly reduced nitrogen inputs through upgrades to waste water treatment facilities, the Western Long Island Sound still suffers from prolonged hypoxic events during summer months. As these environmental problems continue to persist, there is a need to manage other sources of nutrients entering into the aquatic systems, including atmospheric deposition, storm water discharge, excess fertilizer flows, etc. The goal of this study was to evaluate the performance of the red seaweed Gracilaria tikvahiae in open water nutrient bioextraction farm systems in the Long Island Sound and Bronx River Estuary. Drs. Kim and Yarish investigated Gracilaria as a candidate species for nutrient bioextraction because it is easy to propagate, has relatively high growth rates, has a high capability of storing N concentrations in its tissue, and has a wide tolerance to a range of environmental conditions.
Gracilaria was grown in the Long Island Sound, near Fairfield, CT, and in the Bronx River Estuary on two 50 m long lines at depths of 0.5m and 1.0m in 2011 and two 50m long lines at depths of 0.25m and 0.5m in 2012 during the summer to fall growing season. Researchers monitored water quality, subsurface irradiance using a LiCor LI-185A PAR meter, aerial irradiance, and wet weight of Gracilaria at each harvest. Once Gracilaria was harvested, growth rates were estimated, percentage of nitrogen and carbon in the tissue were determined, and N stable isotopes ratios in samples were analyzed the University of California Davis Stable Isotope Facility.
Gracilaria was estimated to remove 28 and 94 kg N ha−1 at the Long Island Sound and Bronx River Estuary sites, respectively, over the 90-day growing season. Kim et al. determined that Gracilaria grew up to 16.5% day−1 at Bronx River Estuary and 4.8% day−1 at the Long Island Sound site in July 2012 and the tissue N contents at the same periods were 3.7% (Bronx River Estuary) and 1.5% (Long Island Sound), respectively. Interestingly, the different growth rates of Gracilaria are likely due to different inorganic nutrient regimes at the two sites. While nutrients fueled the growth of new Gracilaria tissue at the Bronx River Estuary site, they appeared to limit growth at the Long Island Sound site during the summer months. Additionally, the estimated carbon removal by Gracilaria at the Bronx River Estuary and Long Island Sound sites were up to 727 kg ha−1 and 300 kg ha−1, respectively. The data showed that the greatest nutrient extraction, which is a function of ambient temperature, light, and N concentration, likely occurred during May–July. Data showed that growth was light-limited at 1.0 m depth, particularly at the Bronx River Estuary site. Data from the horizontal lines showed depth significantly influenced growth rate, tissue N and C concentration, N and C removal rates for both the Bronx River Estuary and Long Island Sound sites.
The results of this study demonstrate that Gracilaria aquaculture can be a useful technique for nutrient bioextraction in urbanized coastal waters, such as the estuaries of New York City (Bronx River Estuary) and Long Island Sound. This study highlighted spatial and temporal differences in the variables measured, suggesting the importance of site selection to maximize the capacity for nutrient bioextraction by Gracilaria.
This project was funded by the U.S. EPA Long Island Sound Study’s Long Island Sound Futures Fund, the New York State Office of the Attorney General through the Bronx River Watershed Initiative, and the National Fish and Wildlife Foundation.
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