Production potential of seaweed and shellfish integrated aquaculture in Narragansett Bay (Rhode Island, US) using an ecosystem model

Integrated aquaculture systems combining macroalgae with traditional fish and shellfish production represent an ecologically sound and economically attractive solution for farmers. To evaluate the potential of growing sugar kelp (Saccharina latissima) at existing oyster (Crassostrea virginica) farms in Narragansett Bay (NB; Rhode Island, U.S.), we developed an ecosystem model based on individual Dynamic Energy Budget models for kelp and oysters forced offline by a coupled 3D hydrodynamic-water quality model. Kelp growth during the cold winter months provides ecosystem services through the removal of nutrients in the bay as well as serving as an additional source of revenue for farmers. Locations with the most nutrient-rich waters at the northern end of the bay seem most suitable for kelp aquaculture, with oyster growth also reaching maxima at the same locations. Predictions of kelp biomass grown on lines ranged from 0.97 kgWW m-1 at the easternmost site at the Bay Entrance to 2.03 kgWW m-1 at the northernmost site in the Upper Bay, or 1.6 and 3.4 tons ha-1 on 6 m spaced line-farms, respectively. For denser production in 1.5 m spaced line-farms, estimates ranged between 6.5 and 13.5 tons ha-1. Depending on the different farm setups, we estimated the potential profits (based on delivered cost for consumer product) at $4,468 for a 6 m spaced line-farm of 1 ha and $17,872 for a 1.5 m spaced line-farm. The N and C fixation of kelp ranged depending on spacing of longlines and time of harvest but reached maximum values of 1117 and 6184 kg ha-1, respectively. These estimates offer valuable information that should help producers and managers in their decision to direct efforts and investments into this developing activity in the U.S.