Resilience of the trophic cascades in the Black Sea and Baltic Sea regime shifts – lessons from their recent history

Abstract

The Black Sea and the Baltic Sea are two European lake-like marine systems where regime shifts have occurred. Both ecosystems show similar features and hold comparable long-term records for the main food web components and external pressures. Here we analyse Black Sea and Baltic Sea multi-trophic time series applying the same statistical tool, which allowed us to characterize tipping points and quantify the main dynamics ruling each regime phase. In both systems a trophic cascade, consequence of overfishing, drove a shift between regimes. This paper focuses on the robustness of this ecological mechanism. By simulating environmental scenarios we tested whether enhanced bottom-up effects could counteract the development of the trophic cascades once these has been triggered. We found that under certain environmental settings the trophic cascade signals blur at different levels suggesting that the observed changes resulted from a combination of heavy fishing and unfavourable conditions. Through the outlook of one single methodology applied to two different but comparable systems we discuss the obstacles we may find if we are to promote a more desirable state and management measures considering synergistic effects of fishing and future climate change.