ECOSYSTEM SHIFTS IN THE BALTIC SEA Michele Casini Swedish University of Agricultural Sciences 21/12/211 Ecosystem Shifts in the Baltic Sea 1
The area Central Baltic Sea Finland Sweden 29 Gulf of Finland Estonia Denmark 25 27 26 28 Gulf of Riga Lithuania Latvia Russia Germany Poland 21/12/211 Ecosystem Shifts in the Baltic Sea 2
Changes in the ecosystem Climate Sprat Acartia 1974 25 Cod Herring Pseudocalanus Möllmann et al. 29 21/12/211 Ecosystem Shifts in the Baltic Sea 3
Climate Salinity -6 m (psu) 8.5 8. 7.5 7. 6.5-6 m 6-1 m Salinity in spring 11. 1.5 1. 9.5 9. 8.5 8. 7.5 Salinity 6-1 m (psu) Temperature -5 m ( C) 8 7 6 5 4 3 2 1 Surface temperature in spring 196 1965 197 1975 198 1985 199 Year 1995 2 25 21 196 1965 197 1975 198 1985 Year 199 1995 2 25 21 SMHI database 21/12/211 Ecosystem Shifts in the Baltic Sea 4
Nutrients Human emissions Concentration in the system Nitrogen loads (tonnes/year) 8 7 6 5 4 3 2 1 185 186 187 188 Nitrogen Phosphorus 189 19 191 192 193 Year 194 195 196 197 198 199 2 5 45 4 35 3 25 2 15 1 5 Phosphorus loads (tonnes/year) DIN (µm) 16 12 8 4 Winter inorganic nitrogen and phosphorus, Landsort deep -1 m DIN DIP 195 196 197 198 199 2 21 1..9.8.7.6.5.4.3.2.1. DIP (µm) Baltic Nest Institute Ulf Larsson (Stockholm University) 21/12/211 Ecosystem Shifts in the Baltic Sea 5
Oxygen Anoxic areas september 21 Anoxic areas SMHI 21 21/12/211 Ecosystem Shifts in the Baltic Sea 6
Commercial fish species Clupeid biomass (1 tons) 2 18 16 14 12 1 8 6 4 2 8 7 6 5 4 3 2 1 Cod biomass (1 tons) Sprat Herring Cod 1966 197 1974 1978 1982 1986 Year 199 1994 1998 22 26 21 From ICES 211 21/12/211 Ecosystem Shifts in the Baltic Sea 7
Cod High fishing pressure Reduced reproductive volume Reduced larval prey F (ages 4-7) 1.8 1.5 1.2.9.6.3. Fishing mortality Fpa Fmsy Reproductive volume (Km 3) 8 7 6 5 4 3 2 1 Reproductive volume Gotland Basin Gdansk Deep Bornholm Basin 1966 197 1974 1978 1982 1986 199 Year 1994 1998 22 26 21 196 1964 1968 1972 1976 198 1984 Year 1988 1992 1996 2 24 28 ICES 211 Maris Plikshs, Latvian Institute of Food Safety 21/12/211 Ecosystem Shifts in the Baltic Sea 8
Cod High fishing pressure Reduced reproductive volume Reduced larval prey 1.8 1.5 Fishing mortality F (ages 4-7) 1.2.9.6.3. 1966 197 1974 1978 1982 1986 199 1994 1998 22 26 21 Year Fpa Fmsy ICES 211 ICES 21 21/12/211 Ecosystem Shifts in the Baltic Sea 9
Sprat Reduced cod predation Increased temperature 18 ICES 211 Sprat SSB (1 tons) 16 14 12 1 8 6 4 2 8 16 24 32 4 48 56 64 72 8 Cod SSB (1 tons) From ICES 211 ICES 21 21/12/211 Ecosystem Shifts in the Baltic Sea 1
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).4.3.2.1. 1974 1978 1982 1986 199 1994 1998 Year Fpa 22 Fmsy 26 21 Mean weight (Kg).8.6.4.2. 1974 1978 1982 1986 199 1994 Year 1998 22 26 Age 8+ Age 7 Age 6 Age 5 Age 4 Age 3 Age 2 Age 1 ICES 211 21/12/211 Ecosystem Shifts in the Baltic Sea 11
Trophic cascade Top-down regulations, driven by predation Inverse relationships between trophic levels - + + - + Casini et al. 28 21/12/211 Ecosystem Shifts in the Baltic Sea 12
Fish body growth: Side effect of trophic cascade: density-dependence 2 Mean body weights Sprat weight (g) Herring weight (g) 15 1 5 6 5 4 3 2 1 5 1 15 2 25 3 35 4 45 Sprat abundance (ind. *1 9 ) Sprat weight, age 3 (g) 35 3 25 2 15 1 5 Sprat Herring 8 7 6 5 4 3 2 1 Herring weight, age 3 (g) 1974 1978 5 1 15 2 25 3 35 4 45 Sprat abundance (ind. *1 9 ) Year From ICES 211 21/12/211 Ecosystem Shifts in the Baltic Sea 13 1982 1986 199 1994 1998 22 26 21
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
Potential feedback loops ( vicious circles ) Cod Sprat Herring Zooplankton Hydrology 21/12/211 Ecosystem Shifts in the Baltic Sea 15
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
Shift in functioning: alternative stable states? Biological feature (Zooplankton, Fish growth, Cod recruitment) 197-198s Cod-dominated Sprat-dominated Biological feature Hydrology Biological feature Sprat Sprat 199-2s Hydrology Climate stressor (Salinity, oxygen, etc...) From Casini et al. 21 21/12/211 Ecosystem Shifts in the Baltic Sea 17
Potential feedback loops ( vicious circles )_2 Phytoplankton Human emissions Anoxia Nutrients in system 21/12/211 Ecosystem Shifts in the Baltic Sea 18
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
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
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
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
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