IMPROVED SITING OF KELP AQUACULTURE USING N15 STABLE ISOTOPE ANALYSIS    

The time has come to gain a better understanding of the opportunities and limitations for seaweed harvesting along urbanized coastlines. Interest in wild harvest of seaweed, and farming it using aquaculture techniques, has skyrocketed in the Americas and Europe. As such, more research is needed to determine how land use along these coastlines could influence decisions regarding optimal siting of seaweed farms or the identification of best areas for wild harvest. The objective of this study was to test if nitrogen isotopes measured in the tissue of sugar kelp (Saccharina latissimi) grown in strategic locations could be used to improve siting of future kelp farms. The small curved embayment of Saco Bay, Maine was selected as the field site for this study because it is akin to many developed coastlines. It has a strong tourism industry, historic industrial operations, and it receives water from a major river, effluent from 6 wastewater treatment plants (WWTPs), water from tidal pools and salt marshes, and runoff from residential developments.

Buoys were deployed along two perpendicular transects in Saco Bay and mature kelp was attached to each buoy, along with temperature, light, and salinity sensors. Tissue samples were collected from the kelp every two weeks, and following rain events greater than 1 in. Samples were excised from the meristem, mid part, and distal tissue of the kelp and analyzed for their N15/N14 ratio. These results were compared with effluent data from the area's wastewater treatment plants, discharge measurements from the Saco River, and ocean current velocity hindcast in a spatial analysis tool to identify relationships between predicted dispersion of anthropogenic nitrogen and observed nitrogen isotope ratios in kelp grown on the buoys. Results from this and other parallel efforts may help to inform a management plan for wild or farmed seaweed harvest in the region.