Identifying 120 years of decline in ecosystem structure and maturity of Great South Bay, New York using the Ecopath modelling approach

► We constructed four mass balanced models of GSB, NY over different time periods. ► We assessed changes in ecosystem structure and maturity and shifts in keystone species. ► GSB experienced declines in ecosystem maturity and connectivity to the ocean. ► GSB has lost keystone species and become dominated by low trophic level organisms. ► These changes undermine ecosystem services and increase conflicts over resources.