Monica M. Moritsch1, Rod Fujita1, Kristen Davis2
1Environmental Defense Fund, San Francisco, CA 94105, USA, 2University of California Irvine, Department of Civil and Environmental Engineering, Irvine, CA 92697, USA
Correspondence: Monica M. Moritsch, mmoritsch@edf.org
There is an urgent need to remove carbon dioxide from the atmosphere, reduce greenhouse gas emissions, produce food, restore fisheries, and improve conditions of marine ecosystems. Seaweed products can contribute to all of these goals, though not without tradeoffs. To increase seaweed products’ ability to provide climate benefits and other environmental benefits, production needs to be scaled up. Expansion of seaweed farming operations to include offshore waters could help address this need and avoid spatial constraints present in heavily used nearshore waters. We mapped where seaweed could be farmed throughout the world’s Exclusive Economic Zones (nearshore and offshore) to support decision-making and investment related to expanding seaweed farming. We used spatial analysis to identify confluences of high productivity, low costs, and ecological co-benefits. We combined models of seaweed production and cost with historical data on ocean acidification, eutrophication, dissolved oxygen, future water temperatures, shipping activity, and fishing intensity. We scaled all variables from 0 to 100 (100 being most favorable) and combined them to create a composite favorability score for seaweed farming. To assign variable weights, we used four scenarios, which prioritized production, environmental stressor amelioration (co-benefits), avoidance of spatial conflicts, or future climate suitability for seaweed farming. A fifth scenario weighted the four priorities equally. We identified locations that scored in the top 20th percentile across all five scenarios and explored geographic differences between scenarios. The resulting maps will assist in identification of opportunity areas for seaweed farming to benefit the climate and the marine environment.