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Seaweed Pilot Project Summaries

Sugar Kelp Project

Project: Use of Sugar Kelp Aquaculture in Long Island Sound and the Bronx River Estuary for Nutrient Extraction
Project Dates: 2012-2013
Project 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 openwater nutrient bioextraction farm systems in the Long Island Sound (LIS) and Bronx River Estuary (BRE), researchers Kim, Kraemer, and Yarish at the University of Connecticut and Purchase College investigated the effectiveness of the cold water kelp species, Saccharina latissimi, for nutrient bioextraction through seaweed aquaculture.

Nitrogen concentration in LIS 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 LIS 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 latissimi for nutrient bioextraction under different environmental conditions in urbanized estuaries like LIS and coastal waters of NYC during fall to spring growing season. Saccharina latissimi, known as sugar kelp, is a cold temperate brown algal species. Drs. Kim, Kraemer, and Yarish chose to investigate Saccharina latissimi as it has recently been successfully cultivated in the Atlantic Ocean.

Researcher Kim, Kraemer, and Yarish grew native Saccharina latissimi seed using the nursery rearing technology developed at the University of Connecticut. When plants reached 1mm in size, Saccharina latissimi seed string were outplanted on two 50 meter longlines at two near shore sites in the LIS (Fairfield and Branford, CT) and at the mouth of the BRE. 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 LIS and the BRE 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 LIS and the BRE sites), Saccharina latissima is estimated to respectively remove 70 and 180 kg N ha−1 at 0.5 m depth, and 67 and 140 kg N ha−1 at 1.0 m depth, with 1.5 m 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 LIS and the BRE 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 latissimi. 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. Additionally, opportunities for integrated multitrophic aquaculture systems may enhance nutrient bioextraction capacity in urbanized estuaries.

Citation: Kim, J.K., Kraemer, G.P., & Yarish, C. (2015). Use of Sugar Kelp Aquaculture in Lose Island Sound and the Bronx River Estuary for Nutrient Extraction. Marine Ecology Progress Series, 531, 155-166.

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.

For more information, contact Charles Yarish at charles.yarish@uconn.edu.

Gracilaria Project

Project: Field Scale Evaluation of Seaweed Aquaculture as a Nutrient Bioextraction Strategy in Long Island Sound and the Bronx River Estuary
Project Dates: 2011-2012
Project Team: Jang K. Kim, George P. Kraemer, and Charles Yarish

Project Summary:
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 openwater nutrient bioextraction farmsystems in the Long Island Sound (LIS) and Bronx River Estuary (BRE). 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 (salinity, temperature and nutrients). Additionally, Gracilaria is an economically important species (~ $400 million annual value) and is a commercial source of agar for the food and biotech industries

Researchers Charles Yarish and Jang Kim at the University of Connecticut (UConn) grew seed stock of the native red seaweed, Gracilaria, in the Seaweed Marine Biotechnology Laboratory at UConn (Stamford) and the Bridgeport Regional Aquaculture Science and Technology Education Center (BRASTEC). Some of this seed stock was then used to grow Gracilaria in the LIS, near Fairfield, CT, and in the Bronx River Estuary on two 50-meter long lines at depths of 0.5 meters and 1.0 meters in 2011 and two 50-meter long lines at depths of 0.25 meters and 0.5meters 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 LIS and BRE sites, respectively, over the 90-day growing season. Kim et al. determined that Gracilaria grew up to 16.5% day−1 at BRE and 4.8% day−1 at the LIS site in July 2012 and the tissue N contents at the same periods were 3.7% (BRE) and 1.5% (LIS), 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 BRE site, they appeared to limit growth at the LIS site during the summer months. Additionally, the estimated carbon removal by Gracilaria at the BRE and LIS 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 BRE 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 BRE and LIS 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 (BRE) 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.

In addition to the ecosystem services provided by nutrient bioextraction, the cultivation of Gracilaria provides ancillary ecosystem services by increasing the species diversity and richness within an embayment.

Citation: Kim, J.K., Kraemer, G.P., & Yarish, C. (2014). Field Scale Evaluation of Seaweed Aquaculture as a Nutrient Bioextraction Strategy in Long Island Sound and the Bronx River Estuary. Aquaculture, 433, 148-156.

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.

 For more information, contact Charles Yarish at charles.yarish@uconn.edu.

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