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Regime Shifts in Marine Ecosystems

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Regime Shifts in Marine Ecosystems DRAFTPRE-RELEASE! ! DRAFT ! DRAFT PRE-RELEASE! ! DRAFT ! DRAFT Directorate-GeneralPRE-RELEASE! !Fo r DRAFTinternal Policies POLICY DEPARTMENT Directorate-General For internal Policies STRUCTURAL AND COHESION POLICIES B POLICY DEPARTMENT AgricultureAgriculture and Rural and Development Rural Development STRUCTURAL AND COHESION POLICIES B CultureCulture and Education and Education Role The Policy Departments are research units that provide specialised advice Fisheries to committees, inter-parliamentary delegations and other parliamentary bodies. Fisheries RegionalRegional Development Development Policy Areas TransportTransport and andTourism Tourism Agriculture and Rural Development Culture and Education Fisheries Regional Development Transport and Tourism Documents Visit the European Parliament website: http://www.europarl.europa.eu/studies PHOTO CREDIT: iStock International Inc., Photodisk, Phovoir DIRECTORATE GENERAL FOR INTERNAL POLICIES POLICY DEPARTMENT B: STRUCTURAL AND COHESION POLICIES FISHERIES REGIME SHIFTS IN MARINE ECOSYSTEMS: HOW OVERFISHING CAN PROVOKE SUDDEN ECOSYSTEM CHANGES WORKSHOP This document was requested by the European Parliament's Committee on Fisheries. AUTHORS Christian MÖLLMANN Institute for Hydrobiology and Fisheries Science, University of Hamburg, Germany Michele CASINI Swedish University of Agricultural Sciences, Department of Aquatic Resources, Institute of Marine Research, Sweden Georgi M. DASKALOV Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences (IBER- BAS), Bulgaria Brad DE YOUNG Physics and Physical Oceanography, Memorial University, Canada RESPONSIBLE ADMINISTRATOR Irina POPESCU Policy Department Structural and Cohesion Policies European Parliament E-mail: [email protected] EDITORIAL ASSISTANCE Virginija KELMELYTE LINGUISTIC VERSIONS Original: EN Translation: DE, ES, FR, IT, PT ABOUT THE EDITOR To contact the Policy Department or to subscribe to its monthly newsletter please write to: [email protected] Manuscript completed in November 2011. Brussels, © European Parliament, 2011. This document is available on the Internet at: http://www.europarl.europa.eu/studies DISCLAIMER The opinions expressed in this document are the sole responsibility of the author and do not necessarily represent the official position of the European Parliament. Reproduction and translation for non-commercial purposes are authorized, provided the source is acknowledged and the publisher is given prior notice and sent a copy. DIRECTORATE GENERAL FOR INTERNAL POLICIES POLICY DEPARTMENT B: STRUCTURAL AND COHESION POLICIES FISHERIES REGIME SHIFTS IN MARINE ECOSYSTEMS: HOW OVERFISHING CAN PROVOKE SUDDEN ECOSYSTEM CHANGES WORKSHOP Abstract Regime shifts, i.e. sudden changes in the structure and function of ecosystems, are of growing concern for fisheries management. This workshop reviewed the present state of our understanding of regime shifts in marine ecosystems, focusing on shifts which largely took place as a result of overfishing. The workshop presented examples of shifts in overexploited marine ecosystems around the world and provided recommendations for management responses. Two case studies discussed the Baltic and Black Sea ecosystem shifts, which are among the most prominent regime shifts recorded so far. November 2011 PE 474.557 EN Regime shifts in marine ecosystems CONTENTS FOREWORD 5 ECOSYSTEM REGIME SHIFTS TRIGGERED BY OVERFISHING Christian MÖLLMANN 7 ECOSYSTEM SHIFTS IN THE BALTIC SEA Michele CASINI 45 ECOSYSTEM SHIFTS IN THE BLACK SEA Georgi M. DASKALOV 83 MANAGEMENT RESPONSES TO REGIME SHIFTS IN MARINE ECOSYSTEMS Brad DE YOUNG 123 3 Policy Department B: Structural and Cohesion Policies 4 Regime shifts in marine ecosystems FOREWORD Sudden changes in the structure and function of marine ecosystems, termed regime shifts, have been increasingly reported from all parts of the world's oceans. Regime shifts are commonly defined as abrupt changes between contrasting, persistent states of ecosystems. Far from being an abstract scientific concept, they are of growing concern for fisheries management both because of their suddeness (making it difficult for management to respond) and their persistency (meaning that they have to be dealt with for a long time, decades or longer). Regime shifts can lead to the collapse of commercially important fish stocks, generating significant economic and social effects. Moreover, regime shifts could lead to the large-scale redistribution of marine species, and this potential should be considered in fisheries management and international agreements. The workshop "Regime shifts in marine ecosystems: how overfishing can provoke sudden ecosystem changes" was organised by the European Parliament's Policy Department B at the request of the Committee on Fisheries (PECH), and was held at the PECH meeting on 20 December 20111. The workshop reviewed the present state of our understanding of regime shifts in the ocean in the context of fisheries management, focusing on regime shifts which, to a large extent, took place as a result of overfishing. It was intended to present Members of the European Parliament with examples of shifts in overexploited marine ecosystems around the world and to provide recommendations for management responses to regime shifts. Two case studies gave particular attention to the Baltic and Black Sea ecosystem shifts, which are among the most prominent regime shifts recorded so far. The workshop was structured around four briefing notes: Ecosystem regime shifts triggered by overfishing (Christian MÖLLMANN, Institute for Hydrobiology and Fisheries Science, University of Hamburg, Germany) Case study: Ecosystem shifts in the Baltic Sea (Michele CASINI, Swedish University of Agricultural Sciences, Department of Aquatic Resources, Institute of Marine Research, Sweden) Case study: Ecosystem shifts in the Black Sea (Georgi M. DASKALOV, Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria) Management responses to regime shifts in marine ecosystems (Brad DE YOUNG, Physics and Physical Oceanography, Memorial University, Canada) Although algal blooms do not represent ecosystem shifts sensu stricto, an additional briefing note entitled "Does overfishing promote algal blooms?" was presented and discussed at the workshop2. 1 The record of the workshop can be accessed online at http://www.europarl.europa.eu/ep-live/en/committees/video?event=20111220-0900-COMMITTEE- PECH&category=COMMITTEE&format=wmv 2 B.K. Eriksson, 2011. Does overfishing promote algal blooms? European Parliament, Policy Department B - Structural and cohesion policies, 68 pp. http://www.europarl.europa.eu/committees/en/studiesdownload.html?languageDocument=EN&file=65911 5 Policy Department B: Structural and Cohesion Policies The briefing notes presented at the workshop indicate that different factors contribute to regime shifts. Overfishing is shown to be a major driver, causing regime shifts directly or by degrading the resilience of the ecosystem, i.e. its ability to resist disruption without changing state. Other drivers can also be involved, such as climate, eutrophication and species invasion. Most commonly, regime shifts are triggered by a combination of these factors acting together, e.g. overfishing/hydro-climatic changes/eutrophication in the Baltic Sea (Casini, this volume) or overfishing/climate/eutrophication/introduction of the invasive jellyfish Mnemiopsis in the Black Sea (Daskalov, this volume). The common internal mechanism of regime shifts is a trophic cascade, defined as the top down reorganisation of the food web. The collapse of a predatory species at the top of the food web due to overfishing can provoke an explosive increase in its prey, which becomes the dominant species. Cascading effects are transmitted down the food web, with up to four trophic levels affected (piscivorous fish, planktivores (fish and jellyfish), zooplankton and phytoplankton), as is the case in the Baltic and the Black Sea. Trophic cascades can also change the food web regulation from bottom up (resource controlled) to top down (consumer controlled). Vulnerability to overfishing-induced trophic cascading appears to be higher in the case of marine ecosystems with lower species diversity and relatively simple food webs, for which the Baltic and the Black Sea are good examples. After a regime shift, a marine ecosystem is unlikely to return to the previous state, as there are so many available states. The ecosystem will evolve in response to local forcing and its internal dynamics, which may be different following the shift. Nevertheless, the recovery of collapsed stocks is possible, if the fishing pressure is sufficiently low and the general hydro- climatic and trophic conditions are favourable. The cod stock in the Baltic has shown signs of some recovery in recent years, following the EU cod management plan. Also, planktivorous fish in the Black Sea (mainly anchovy) have partially recovered after the drastic reduction of the fishing capacity in the area in the early 1990's and the decrease of the Mnemiopsis population. However, partial recovery of the collapsed stocks is not a reasonable ecosystem objective in itself, as further changes may drive the system into the next catastrophic loop. Although the briefing notes have been produced independently, they all converge on a similar conclusion: recognizing that fishing affects not only the state of the targeted fish stocks but a whole range of complex interactions that
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