21/12/2011 Ecosystem Shifts in the Baltic Sea 1

ECOSYSTEM SHIFTS IN THE BALTIC SEA

Michele CasiniSwedish University of Agricultural Sciences

21/12/2011 Ecosystem Shifts in the Baltic Sea 2

The area

Central Baltic Sea

25

27

29

28

26

Sweden

Latvia

Estonia

Finland

GermanyPoland

Russia

Lithuania

Denm

ark

Gulf of Finland

Gulf of Riga

21/12/2011 Ecosystem Shifts in the Baltic Sea 3

Changes in the ecosystem

SpratAcartia

CodHerring

Pseudocalanus

Möllmann et al. 2009

1974 2005Climate

21/12/2011 Ecosystem Shifts in the Baltic Sea 4

Climate

Salinity in spring

6.5

7.0

7.5

8.0

8.5

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

Year

Salin

ity 0

-60

m (p

su)

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

Salin

ity 6

0-10

0 m

(psu

)

0-60 m60-100 m

Surface temperature in spring

0

1

2

3

4

5

6

7

8

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

Year

Tem

pera

ture

0-5

0 m

(°C

)

SMHI database

21/12/2011 Ecosystem Shifts in the Baltic Sea 5

Nutrients

0

100000

200000

300000

400000

500000

600000

700000

800000

1850

1860

1870

1880

1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

Year

Nitr

ogen

load

s (to

nnes

/yea

r)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Pho

spho

rus

load

s (to

nnes

/yea

r)NitrogenPhosphorus

Winter inorganic nitrogen and phosphorus, Landsort deep 0-10 m

0

4

8

12

16

1950 1960 1970 1980 1990 2000 2010

DIN

(µM

)0.00.10.20.30.40.50.60.70.80.91.0

DIP

(µM

)

DINDIP

Human emissions Concentration in the system

Ulf Larsson (Stockholm University)Baltic Nest Institute

21/12/2011 Ecosystem Shifts in the Baltic Sea 6

Oxygen Anoxic areas september 2010

Anoxic areas

SMHI 2010

21/12/2011 Ecosystem Shifts in the Baltic Sea 7

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

Year

Clu

peid

bio

mas

s (1

000

tons

)

0

100

200

300

400

500

600

700

800

Cod

bio

mas

s (1

000

tons

)

SpratHerringCod

Commercial fish species

From ICES 2011

21/12/2011 Ecosystem Shifts in the Baltic Sea 8

Cod

• High fishing pressure• Reduced reproductive volume• Reduced larval prey

Fishing mortality

0.0

0.3

0.6

0.9

1.2

1.5

1.8

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

Year

F (a

ges

4-7)

Fmsy

Fpa

Reproductive volume

0

100

200

300

400

500

600

700

800

1960

1964

1968

1972

1976

1980

1984

1988

1992

1996

2000

2004

2008

Year

Rep

rodu

ctiv

e vo

lum

e (K

m 3

)

Gotland BasinGdansk DeepBornholm Basin

ICES 2011 Maris Plikshs, Latvian Institute of Food Safety

21/12/2011 Ecosystem Shifts in the Baltic Sea 9

Cod

• High fishing pressure• Reduced reproductive volume• Reduced larval prey

Fishing mortality

0.0

0.3

0.6

0.9

1.2

1.5

1.8

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

Year

F (a

ges

4-7)

Fmsy

Fpa

ICES 2011 ICES 2010

21/12/2011 Ecosystem Shifts in the Baltic Sea 10

Sprat

• Reduced cod predation• Increased temperature

0

200

400

600

800

1000

1200

1400

1600

1800

0 80 160 240 320 400 480 560 640 720 800

Cod SSB (1000 tons)

Spra

t SSB

(100

0 to

ns)

ICES 2011

From ICES 2011 ICES 2010

21/12/2011 Ecosystem Shifts in the Baltic Sea 11

Herring

• High fishing pressure• Increased competition with sprat• Decreased salinity• Coastal eutrophication

Fishing mortality

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

Year

F (a

ges

3-6)

Fmsy

Fpa

Mean body weight

0.00

0.02

0.04

0.06

0.08

0.10

0.12

1974

1978

1982

1986

1990

1994

1998

2002

2006

Year

Mea

n w

eigh

t (K

g)

Age 8+Age 7Age 6Age 5Age 4Age 3Age 2Age 1

Body weight

ICES 2011

21/12/2011 Ecosystem Shifts in the Baltic Sea 12

Trophic cascade

• Top-down regulations, driven by predation

• Inverse relationshipsbetween trophic levels

-

+

+

-

+

−

Casini et al. 2008

21/12/2011 Ecosystem Shifts in the Baltic Sea 13

Fish body growth:

Side effect of trophic cascade: density-dependence

Mean body weights

0

5

10

15

20

25

30

35

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

Year

Spr

at w

eigh

t, ag

e 3

(g)

0

10

20

30

40

50

60

70

80

Her

ring

wei

ght,

age

3 (g

)

SpratHerring

From ICES 2011

0

5

10

15

20

0 50 100 150 200 250 300 350 400 450

Sprat abundance (ind. *10 9)

Spra

t wei

ght (

g)

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400 450

Sprat abundance (ind. *10 9)

Her

ring

wei

ght (

g)

21/12/2011 Ecosystem Shifts in the Baltic Sea 14

Cod

Zooplankton

Phytoplankton

N

Anoxic areas

P

Recent state (1990s-2000s)

HerringSpratT

Fishery

S

Drivers of ecosystem state

Cod

Zooplankton

Phytoplankton

N

Anoxic areas

P

Previous state (1970s-1980s)

HerringSpratT S

Fishery

21/12/2011 Ecosystem Shifts in the Baltic Sea 15

Potential feedback loops (“vicious circles”)

Cod

Zooplankton

Sprat

Hydrology

Herring

21/12/2011 Ecosystem Shifts in the Baltic Sea 16

Potential feedback loops (“vicious circles”)_1

Cod

Zooplankton

Sprat

Hydrology

Negative effects of sprat on cod• Competition for food • Predation on cod eggs• Effect of cod growth

Herring

21/12/2011 Ecosystem Shifts in the Baltic Sea 17

Shift in functioning: alternative stable states?

Sprat-dominated

Climate stressor (Salinity, oxygen, etc...)

Biological feature(Zooplankton,Fish growth,

Cod recruitment)

Cod-dominatedBiological

feature

Hydrology

Sprat

Biologicalfeature

Hydrology

Sprat

1970-1980s

1990-2000s

From Casini et al. 2010

21/12/2011 Ecosystem Shifts in the Baltic Sea 18

Phytoplankton

Nutrientsin system

Anoxia

Humanemissions

Potential feedback loops (“vicious circles”)_2

21/12/2011 Ecosystem Shifts in the Baltic Sea 19

Phytoplankton

Nutrientsin system

Anoxia

Humanemissions

Low cod

Trophic cascade

Potential feedback loops (“vicious circles”)_3

21/12/2011 Ecosystem Shifts in the Baltic Sea 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

21/12/2011 Ecosystem Shifts in the Baltic Sea 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.

21/12/2011 Ecosystem Shifts in the Baltic Sea 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 oxygen-

deficient areas.

21/12/2011 Ecosystem Shifts in the Baltic Sea 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 ecosystemrecovery in the long run.