When politics benefit marine ecosystems: MPAs in the long-suffering Aegean Sea

The Aegean Sea is a transboundary marine system facing increasing ecological pressure from overfishing, habitat degradation, pollution, and climate change, while fisheries management remains fragmented between neighbouring jurisdictions. Marine Protected Areas (MPAs) have therefore emerged as a key policy tool for supporting ecosystem recovery and sustainable fisheries. Recent initiatives by Greece and Türkiye provide a timely opportunity to evaluate how alternative spatial protection strategies may influence ecological and fisheries outcomes in a shared marine basin. Using an established Ecopath with Ecosim (EwE) model and its spatial module (Ecospace), we assessed five hypothetical MPA scenarios reflecting individual (country based) and combined protection configurations associated with recent proposals and designations, relative to a baseline scenario representing current management. To allow direct comparison among alternative spatial designs, the additional MPAs were implemented as hypothetical no-fishing zones, with fishing excluded for all modelled fleets from 2025 to 2035, followed by a return to baseline management conditions until 2040. By 2040, five years after the additional MPA restrictions ended, changes in total ecosystem biomass were small across scenarios, while spatially localized and functional group-specific responses persisted. The magnitude and direction of responses varied among spatial configurations and functional groups, with both positive and negative legacy effects on biomass and catches. The combined transboundary spatial configuration produced stronger and more extensive persistent spatial responses than the individual configurations tested. These findings underscore the importance of spatial design and cross-border considerations when evaluating MPA strategies for reconciling conservation and fisheries objectives in the Aegean Sea.