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 DOES OVERFISHING PROMOTE ALGAL BLOOMS? NOTE This document was requested by the European Parliament's Committee on Fisheries. AUTHOR Britas Klemens ERIKSSON Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, University of Groningen The Netherlands RESPONSIBLE ADMINISTRATOR Irina POPESCU Policy Department Structural and Cohesion Policies European Parliament E-mail: [email protected] EDITORIAL ASSISTANCE Virginija KELMELYTE LINGUISTIC VERSIONS Original: EN Translations: 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 DOES OVERFISHING PROMOTE ALGAL BLOOMS? NOTE Abstract This note provides scientific evidence for a connection between overfishing and the development of algal blooms, and presents several European case-studies supporting this hypothesis. Overfishing has contributed to the increasing problem of algal blooms in Europe. Over- exploitation of offshore stocks has changed the structure of many marine ecosystems, which has promoted the accumulation of algal biomass. Today, detrimental effects of overfishing on offshore food webs are spreading to coastal ecosystems, causing problems with near shore water quality and habitat loss. IP/B/PECH/IC/2011-105 November 2011 PE 474.461 EN Does overfishing promote algal blooms? CONTENTS LIST OF ABBREVIATIONS 5 LIST OF FIGURES 7 LIST OF TABLES 9 EXECUTIVE SUMMARY 11 1. INTRODUCTION 15 2. TYPES AND EFFECTS OF ALGAL BLOOMS 19 2.1. What are algal blooms? 19 2.2. Ecological effects of algal blooms 19 2.3. Harmful algal groups 20 2.4. General societal problems and costs 22 2.5. Specific effects on fisheries in Europe 23 3. THE ECOLOGY OF ALGAL BLOOMS 27 3.1. A natural process that increases in frequency with eutrophication 27 3.2. Nutrients and grazing together control algal bloom development 30 3.3. Decreases in top predatory fish coincide with increases in algae 32 3.4. Trophic cascades depend on resources and predator diversity 33 4. DOES OVERFISHING CONTRIBUTE TO ALGAL BLOOMS IN EUROPE? 37 4.1. Modelling effects of overfishing and eutrophication 37 4.2. The North Sea case study 40 4.3. The Black Sea case study 42 4.4. The Kattegat case study 46 4.5. The Baltic Sea – offshore case study 49 4.6. The Baltic Sea – coastal case study 53 5. CONCLUSIONS AND RECOMMENDATION 57 REFERENCES 61 3 Policy Department B: Structural and Cohesion Policies 4 Does overfishing promote algal blooms? LIST OF ABBREVIATIONS ASP Amnesic Shellfish Poisoning CFP Ciguatera Fish Poisoning CPUE Catch Per Unit Effort DSP Diarrhetic Shellfish Poisoning EBM Ecosystem-Based Management FK Fish Killing algal blooms GLM General Linear Model HAB Harmful Algal Bloom HBT High Biomass Toxic algal blooms HBNT High Biomass Non-Toxic algal blooms NAO North Atlantic Oscillation PSP Paralytic Shellfish Poisoning NSP Neurotoxic Shellfish Poisoning ST Seafood Toxic algal blooms 5 Policy Department B: Structural and Cohesion Policies 6 Does overfishing promote algal blooms? LIST OF FIGURES Figure 1: Potential effects of overfishing on marine food-web structure showing a connection between fisheries and algal blooms 16 Figure 2: Groups of organisms and different types of harmful algal blooms. 19 Figure 3: An increased in algal biomass over time in the Black Sea 27 Figure 4: Duration of the algal bloom season in the Wadden Sea 29 Figure 5: Areal extent of the peak cyanobacterial bloom in the Baltic Sea 1997-2009. 30 Figure 6: The relative effect of grazers on the biomass of algae. 31 Figure 7: Fishery induced declines in top predators coincide with abrupt increases in the standing stock of algae in the north Atlantic, Baltic Sea and Black Sea. 32 Figure 8: Nutrient enrichment accumulate on different trophic levels depending on the number of trophic levels in the ecosystem. 35 Figure 9: Generic food web of a temperate pelagic nearshore ecosystem. 38 Figure 10: Generic food web of a temperate pelagic nearshore ecosystem. 39 Figure 11: Trends in landings of large and small fish in the North Sea 41 Figure 12: Trends in landings of large pelagic species in the North Sea 41 Figure 13: Trends in landings of large demersal species in the North Sea 41 Figure 14: Trends in abundance of algae in the North Sea 42 Figure 15: Trends in mean trophic level of landings in the North Sea 42 Figure 16: Trends in landings of tuna and billfishes from Black Sea fisheries 44 Figure 17: Trends in landings of small and medium sized pelagic species in the Black Sea 44 Figure 18: Trends in mean trophic level of landings in the Black Sea 45 Figure 19: Trends in the relative biomass of zoo- and phytoplankton in the Black Sea 45 7 Policy Department B: Structural and Cohesion Policies Figure 20: Trends in landings of Cod and other large predatory fish in Kattegat 47 Figure 21: Trends in total biomass of cod in Kattegat 47 Figure 22: Trends in the abundances of shore crabs and medium sized fish from coastal monitoring at Ringhals in Kattegat 47 Figure 23: Relation between offshore cod and coastal populations of medium sized predators in Kattegat 48 Figure 24: Relation between spring temperatures and coastal populations of medium sized predators in Kattegat 48 Figure 25: Trends in the dominating fish populations in the Baltic Sea 50 Figure 26: Biomass of zoo- and phytoplankton in the Gotland Sea, S Baltic Sea 50 Figure 27: Intensity of the spring bloom in the Gotland Sea, S Baltic Sea 50 Figure 28: The relative importance of different biological and environmental factors for determining the density of sprat in the Baltic Sea 51 Figure 29: The relative importance of different biological and environmental factors for determining the density of zoo- and phytoplankton in the southern Baltic Sea 52 Figure 30: Decline in perch on the Swedish coast in the southern Baltic Sea 54 Figure 31: Decline in pike on the Swedish coast in the southern Baltic Sea 54 Figure 32: Trends in the abundance of larger coastal predatory fish at Kalmar in the southern Baltic Sea 55 Figure 33: Trends in offshore abundances of cod, sprat and stickleback 55 Figure 34: Abundance of stickleback and the percentage of area overgrown by filamentous algae depending on the density of top predators 56 Figure 35: Removing perch and pike together with eutrophication increase the development of filamentous bloom forming algae 56 8 Does overfishing promote algal blooms? LIST OF TABLES Table 1: Reports of algal bloom incidents in the Mediterranean and the Black Seas 28 Table 2: The relation between larger pelagic predators and lower trophic levels in the Black Sea over time 45 Table 3: The relation between adjacent trophic levels in the Baltic Sea between 1974 and 2006 51 9 Policy Department B: Structural and Cohesion Policies 10 Does overfishing promote algal blooms? EXECUTIVE SUMMARY Background Algal bloom is a collective name for an event of rapid excessive growth of algae and photosynthesizing bacteria. As such, the specific organisms producing algal blooms are only remotely related, and belong to a highly variable group of photosynthesizing aquatic organisms. Algal blooms may cause significant nuisance to humans by affecting valuable parts of ecosystems negatively - a harmful algal bloom (HAB). Summing up available data from European marine waters shows that the total socio-economic impact of harmful algal blooms is at least 850 million euro per year. However, this does not include all countries in Europe and do not account for non-listed events. The frequency of algal blooms has increased with global eutrophication, and in Europe negative effects of harmful algal blooms have increased significantly since the 1950s. Negative effects of algal blooms can be divided into two broad categories: High density blooms: Large visible accumulations of algae or bacteria that colour the water and cause nuisance by sheer abundance. High biomasses of algae can be detrimental to the ecosystem in various ways, for example by forming drifting algal mats and excess loads of mucus that clog waters and accumulate together with foam on beaches, and by inducing post-bloom anoxia from the decomposition of the large amounts of accumulated organic matter. Toxin producers: Highly potent algal toxins are produced by a group of unicellular algae dominated by the algal group dinoflagellates. Such toxins are responsible for extensive mortality in fish and shellfish and can have a strong impact on human health by accumulating in the food web, especially through shellfish poisoning.