Ecosystem services trade-offs informing impacts of marine aquaculture development in the southern Caspian Sea

Humans have always benefited from marine ecosystems and the use of their services has increased over time. The principal challenge of managing ecosystem services is that they are not independent of each other. Attempts to optimize a single service have often led to the reductions or losses of other services; in other words, they are “traded-offs”. Based on the purpose of assessing the impacts of marine aquaculture development in the Southern Caspian Sea, 3 management scenarios were utilized to model 3 categories, including marine aquaculture, Water Quality (WQ) and Habitat Risk Assessment (HRA) through marine Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST). Marine aquaculture model was first considered for Oncorhynchus mykiss that the results were as follows: in the baseline scenario with 9 farms, the amounts of the total weight of fish produced and Net Present Value (NPV) measured during 1 year equaled 1970 tons and 2,247,000 dollars; in the conservation scenario with 4 farms, their amounts were 800 tons and 1 million dollars; in the expansion scenario with an increased number of farms (20 farms), their amounts were estimated to be 4000 tons and 5 million dollars, respectively. The results of the marine aquaculture model were utilized as the inputs both to WQ (amount of BOD released from each farm) and HRA (habitats of four species of fish (Rutilus frisii kutum, Acipenser stellatus, Acipenser persicus, and Huso huso) models. The results revealed 41%, 16%, and 60% of WQ reductions and 35%, 20%, and 45% of HRA changes in the baseline, conservation, and expansion scenarios, respectively. Considering the current production of 9 existing farms (1970 tons per year) and the impact of this production on water quality (41%) and habitat risk (35%), it is recommended to reduce this production volume and doing aquaculture development in the Southern Caspian Sea without considering and managing negative consequences can have dangerous consequences for this sensitive ecosystem.