Multi-objective zoning for aquaculture and biodiversity.

Aquaculture is the fastest growing food production industry in the world yet research and guidance demonstrating strategic multi-objective zoning for sector expansion is scarce. Quantifying and mitigating conflicts and impact on sensitive coastal environments through jointly-optimized objectives for aquaculture and biodiversity simultaneously has not been tested yet. We here develop and evaluate six alternative planning scenarios for one of the European Union's highest priority bivalve shellfish aquaculture areas, the Emilia-Romagna Region in Italy. We i) develop an aquaculture profitability surface as a function of the distance from main ports, and in parallel build a fine-scale aquaculture suitability distribution surface for important commercial species using multi-criteria analysis; ii) prioritize protected areas for biodiversity while testing how different considerations of human impacts influence priorities; iii) simultaneously plan for aquaculture and biodiversity while minimizing impacts on other maritime activities. We compare results from different scenarios according to how well they capture suitable aquaculture habitats and minimize impacts. We introduce a new evaluation method for scenario comparison in spatial optimization using a nearest-neighbor analysis for spatial pattern similarities. Lastly, we test the "value of information" provided by our investment in developing the fine-scale suitability surface to improve efficiencies. We find that an integrated multi-objective zoning approach, which simultaneously optimizes for biodiversity and aquaculture, supports more efficient planning than traditional sector specific growth strategies. We also discovered that the fine-scale suitability model delivered a 5% more efficient solution than the simple distance function, highlighting the role of proxy cost surfaces and diminished returns from investing in comprehensive habitat suitability analysis in regions without much variation in key parameters. We offer evidence of improved efficiency and practical guidance for integrated planning in Blue Growth agendas. Our analysis can be applied in any context where multiple objectives occur for aquaculture sector growth and biodiversity conservation.