ECOSYSTEM SHIFTS IN THE BALTIC SEA

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1 ECOSYSTEM SHIFTS IN THE BALTIC SEA Michele Casini Swedish University of Agricultural Sciences 21/12/211 Ecosystem Shifts in the Baltic Sea 1

2 The area Central Baltic Sea Finland Sweden 29 Gulf of Finland Estonia Denmark Gulf of Riga Lithuania Latvia Russia Germany Poland 21/12/211 Ecosystem Shifts in the Baltic Sea 2

3 Changes in the ecosystem Climate Sprat Acartia Cod Herring Pseudocalanus Möllmann et al /12/211 Ecosystem Shifts in the Baltic Sea 3

4 Climate Salinity -6 m (psu) m 6-1 m Salinity in spring Salinity 6-1 m (psu) Temperature -5 m ( C) Surface temperature in spring Year Year SMHI database 21/12/211 Ecosystem Shifts in the Baltic Sea 4

5 Nutrients Human emissions Concentration in the system Nitrogen loads (tonnes/year) Nitrogen Phosphorus Year Phosphorus loads (tonnes/year) DIN (µm) Winter inorganic nitrogen and phosphorus, Landsort deep -1 m DIN DIP DIP (µm) Baltic Nest Institute Ulf Larsson (Stockholm University) 21/12/211 Ecosystem Shifts in the Baltic Sea 5

6 Oxygen Anoxic areas september 21 Anoxic areas SMHI 21 21/12/211 Ecosystem Shifts in the Baltic Sea 6

7 Commercial fish species Clupeid biomass (1 tons) Cod biomass (1 tons) Sprat Herring Cod Year From ICES /12/211 Ecosystem Shifts in the Baltic Sea 7

8 Cod High fishing pressure Reduced reproductive volume Reduced larval prey F (ages 4-7) Fishing mortality Fpa Fmsy Reproductive volume (Km 3) Reproductive volume Gotland Basin Gdansk Deep Bornholm Basin Year Year ICES 211 Maris Plikshs, Latvian Institute of Food Safety 21/12/211 Ecosystem Shifts in the Baltic Sea 8

9 Cod High fishing pressure Reduced reproductive volume Reduced larval prey Fishing mortality F (ages 4-7) Year Fpa Fmsy ICES 211 ICES 21 21/12/211 Ecosystem Shifts in the Baltic Sea 9

10 Sprat Reduced cod predation Increased temperature 18 ICES 211 Sprat SSB (1 tons) Cod SSB (1 tons) From ICES 211 ICES 21 21/12/211 Ecosystem Shifts in the Baltic Sea 1

11 Herring High fishing pressure Increased competition with sprat Decreased salinity Coastal eutrophication.6.5 Fishing mortality.12.1 Body weight Mean body weight F (ages 3-6) Year Fpa 22 Fmsy Mean weight (Kg) Year Age 8+ Age 7 Age 6 Age 5 Age 4 Age 3 Age 2 Age 1 ICES /12/211 Ecosystem Shifts in the Baltic Sea 11

12 Trophic cascade Top-down regulations, driven by predation Inverse relationships between trophic levels Casini et al /12/211 Ecosystem Shifts in the Baltic Sea 12

13 Fish body growth: Side effect of trophic cascade: density-dependence 2 Mean body weights Sprat weight (g) Herring weight (g) Sprat abundance (ind. *1 9 ) Sprat weight, age 3 (g) Sprat Herring Herring weight, age 3 (g) Sprat abundance (ind. *1 9 ) Year From ICES /12/211 Ecosystem Shifts in the Baltic Sea

14 Drivers of ecosystem state Previous state (197s-198s) Recent state (199s-2s) Fishery Fishery Cod Cod T Sprat Herring S T Sprat Herring S Zooplankton Zooplankton Phytoplankton Anoxic areas Phytoplankton Anoxic areas N P N P 21/12/211 Ecosystem Shifts in the Baltic Sea 14

15 Potential feedback loops ( vicious circles ) Cod Sprat Herring Zooplankton Hydrology 21/12/211 Ecosystem Shifts in the Baltic Sea 15

16 Potential feedback loops ( vicious circles )_1 Cod Sprat Herring Zooplankton Hydrology Negative effects of sprat on cod Competition for food Predation on cod eggs Effect of cod growth 21/12/211 Ecosystem Shifts in the Baltic Sea 16

17 Shift in functioning: alternative stable states? Biological feature (Zooplankton, Fish growth, Cod recruitment) s Cod-dominated Sprat-dominated Biological feature Hydrology Biological feature Sprat Sprat 199-2s Hydrology Climate stressor (Salinity, oxygen, etc...) From Casini et al /12/211 Ecosystem Shifts in the Baltic Sea 17

18 Potential feedback loops ( vicious circles )_2 Phytoplankton Human emissions Anoxia Nutrients in system 21/12/211 Ecosystem Shifts in the Baltic Sea 18

19 Potential feedback loops ( vicious circles )_3 Low cod Trophic cascade Phytoplankton Human emissions Anoxia Nutrients in system 21/12/211 Ecosystem Shifts in the Baltic Sea 19

20 Conclusions Large changes in the Baltic ecosystem Effects of fisheries: direct & via trophic cascade Effects of hydro-climate and eutrophication: reinforcing the trophic cascade Change in ecosystem functioning: feedback loops tend to maintain the new biological state 21/12/211 Ecosystem Shifts in the Baltic Sea 2

21 Recommendations Actions for ecosystem recovery Fishing pressure on cod should be kept low (EU management plan). Fishing pressure on herring should be reduced. Fishing pressure should be adaptive to the hydro-climate conditions. Anthropogenic nutrient inputs, both nitrogen and phosphorus, should be reduced. 21/12/211 Ecosystem Shifts in the Baltic Sea 21

22 Recommendations Expected effects In the current hydro-climate conditions, recover of cod stock at relatively high levels. Enhancement of the herring stock. Increase of total zooplankton. Decrease of algal blooms and oxygendeficient areas. 21/12/211 Ecosystem Shifts in the Baltic Sea 22

23 Recommendations Potential external hinders The effective reduction of anoxia extent may require periods of oxygen-rich water inflows. Hydro-climate will aid or counteract the management actions. Projected long-term climate changes (decrease in salinity and increase in temperature) may hinder the ecosystem recovery in the long run. 21/12/211 Ecosystem Shifts in the Baltic Sea 23