• Open Access

Overfishing of top predators eroded the resilience of the Black Sea system regardless of the climate and anthropogenic conditions

Authors

  • MARCOS LLOPE,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway
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    • 1Present address: M. Llope, Instituto Español de Oceanografía (IEO), Centro Oceanográfico de Cádiz, Puerto Pesquero, Muelle de Levante s/n, PO Box 2609, E-11006 Cádiz, Andalucía, Spain.

  • GEORGI M. DASKALOV,

    1. CEFAS Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK
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    • 2Present address: Laboratory of Marine Ecology, Institute of Biodiversity and Ecosystem Research (Bulgarian Academy of Sciences), 18 Makedonia Str 9002, Varna, Bulgaria.

  • TRISTAN A. ROUYER,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway
    2. Centre de Recherche Halieutique Méditerranéenne et Tropicale, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Avenue Jean Monnet, BP 171, 34203 Sète cedex, France
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  • VESSELINA MIHNEVA,

    1. Institute of Fisheries and Aquaculture, Varna, PO Box 72, Varna 9000, Bulgaria
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  • KUNG-SIK CHAN,

    1. Department of Statistics and Actuarial Science, University of Iowa, 263 Schaeffer Hall, Iowa City, IA 52242, USA
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  • ALEXANDER N. GRISHIN,

    1. Southern Scientific Research Institute of Marine Fisheries and Oceanography (YugNIRO), 2, Sverdlov Street, 98300 Kerch, Crimea, Ukraine
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  • NILS CHR. STENSETH

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway
    2. Flødevigen Marine Research Station, Institute of Marine Research (IMR), NO-4817 His, Norway
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Nils Chr. Stenseth, Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway, tel. +47 22 854584, fax +47 22 854001, e-mail: n.c.stenseth@bio.uio.no

Abstract

It is well known that human activities, such as harvesting, have had major direct effects on marine ecosystems. However, it is far less acknowledged that human activities in the surroundings might have important effects on marine systems. There is growing evidence suggesting that major reorganization (i.e., a regime shift) is a common feature in the temporal evolution of a marine system. Here we show, and quantify, the interaction of human activities (nutrient upload) with a favourable climate (run-off) and its contribution to the eutrophication of the Black Sea in the 1980s. Based on virtual analysis of the bottom-up (eutrophication) vs. top-down (trophic cascades) effects, we found that an earlier onset of eutrophication could have counteracted the restructuring of the trophic regulation at the base of the food web that resulted from the depletion of top predators in the 1970s. These enhanced bottom-up effects would, however, not propagate upwards in the food web beyond the zooplankton level. Our simulations identified the removal of apex predators as a key element in terms of loss of resilience that inevitably leads to a reorganization. Once the food web has been truncated, the type and magnitude of interventions on the group replacing the apex predator as the new upper trophic level have no effect in preventing the trophic cascade. By characterizing the tipping point at which increased bottom-up forcing exactly counteracts the top-down cascading effects, our results emphasize the importance of a comprehensive analysis that take into account all structuring forces at play (including those beyond the marine system) at a given time.

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