Economic modelling as a tool to support macroalgal bloom management: a case study (Sacca di Goro, Po river delta)

Abstract

During the last 20 years, intensive mollusk farming has been developed in coastal waters, mostly in sheltered bays and lagoons. Often, mollusk stocks are threatened by frequent anoxic events from macroalgal blooms. Here, a decision support tool is described to select the optimal short-term strategy to control algal biomasses. Even though long-term and detailed studies of the lagoon systems are required to provide reliable, biologically based policies, we have here developed a simplified analysis that overlooks most of the ecological complexity, but explicitly includes environmental variability and uncertainty in parameter estimation in the economic assessment of the performances of different management strategies. The aim is to quickly screen management alternatives of harvesting Ulva rigida biomass in terms of the control measures considered, i.e. the number of vessels used (the harvesting effort) and the U. rigida density at which the vessels start to operate. The decision support tool was applied to the Sacca di Goro, the southernmost coastal lagoon of the Italian Po river delta, where intensive farming of the clam Tapes philippinarum occurs. The results of the analysis indicate that an intermediate number of vessels should start operating as soon as U. rigida biomass exceeds low thresholds.