Alternative stable states and trophic
cascades in the Baltic Sea
– do we need an alternative approach
to fisheries management?
Rovfisk(e) i Östersjön
Swedish
Board of Fisheries
FiVs
”skarpsillprogram”
Magnus Appelberg, Andrea Belgrano, Mikaela Bergenius, Ingemar
Berglund, Ulf Bergström, Patrik Börjesson, Michele Casini, Anna
Gårdmark, Joakim Hjelm, Lars Ljunggren, Johan Lövgren
WGIAB 2008
Baltic open sea food web
Fishery
common guillemot
Climate
cod
Top-down
Bottom-up
herring
sprat
nektobenthos
zooplankton
phytoplankton
nutrients
Research and Development
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
800
80
60
40
b
Zooplankton
Sprat
600
400
200
0
c
Research and Development Year
25
20
15
10
5
0
0
45
40
35
30
25
20
15
10
5
0
600
0.3
400
0.2
200
0.1
0
0.0
5
30
Sprat biomass (10 tons)
35
10
100
Cod
Sprat
Sprat abundance (10 ind.)
a
-1
3
Cod biomass (10 tons)
20
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
-3
Zoopl. biomass (mg m )
120
Chl. a (mg l )
-3
Zoopl. biomass (mg m )
Changes in open sea at all trophic levels
800 1 3 5 7 9 111315171921232527293133
0.4
Zooplankton
Chlorophyll a
From HELCOM/ICES WGIAB
Cod biomass regulates top-down/bottom-up
High cod
82
89
500
87
79
400
Low cod
91
84
78
80
300
88
86
200
81 90
75
01 00
83
02
99
97
76
77
85
03
04
98
100
96
95
0
0
5
10
15
20
25
30
35
40
10
Sprat abundance (10 individuals)
Abiotic driven
bottom-up
Research and Development
Sprat driven
top-down
45
Casini et al. 2006
3
Zooplankton bio. (mg/m )
600
Changes in open coastal areas
- Baltic Proper
Reduced recruitment
success of predatory fish in
coastal fish communities
Increased growth of
epiphytic macro-algae
in coastal areas
Research and Development
Reduced landings of major coastal
predatory fish in the Baltic Proper
Baltic Proper (27, 28, 25)
tonnes
Annual catch
(tonnes) of pike
and perch
120
Perch
100
80
Pike
60
40
20
2004
2002
2000
1998
1996
1994
0
Swedish landings of perch and pike in the Baltic
Proper
Research and Development
Bothnian Bay
Recruitment of
perch and pike
(Juvenile fish surveys
1996-2003)
Baltic Proper
Large scale
recruitment failure
(open coast and outer
archipelago)
Ljunggren et al. unpubl.
Research and Development
Reduced abundance of perch larvae and juveniles in
open coastal areas of the Baltic Proper
numbers/m2
Abundance of different lifestages -Perch
1000
Baltic proper
100
Baltic proper
inner basins
Bothnian bay
10
1
0,1
0,01
eggs
Research and Development
larvae
juveniles
Ljunggren et al. unpubl.
Recruitment failure of predatory fish coincide with
high abundance of grazer
and zooplankton feeders
Abundance (nr x net
-1
)
Small
bodied
All
small
bodied
grazer
feeders
grazer eaters
Sticklebacks
Sticklebacks
1500
1000
500
0
0.6
May epiphytes
0.5
Filamentous algae (%)
2000
high abundance of
epiphytic macro-algae
August epiphytes
0.4
0.3
0.2
0.1
0
G> P
Disturbed
areas
Field data
Research and Development
G< P
Undisturbed
areas
G>P
Disturbed
areas
G<P
Undisturbed
areas
from Swedish Bd of Fisheries, collated by Eriksson et al. in prep
A relation between fishery and the
environment?
Research and Development
Reversible or…. Alternative Stable State
Research and Development
Mittelbach et al. 2006
Planktivore management
- linking food web dynamics to fisheries
A governmental research project run by Swedish Bd
of Fisheries together with Swedish EPA and
international research organisations:
a) investigate if and how we can reinstate fish predator
dominated coastal and offshore ecosystems in the Baltic
Sea?
b) identify the indirect ecosystem effects of changing the
abundances of predatory fish in the coastal and offshore
ecosystems?
Research and Development
Project outline
Five work packages
WP 1. Spatial and temporal variation in key food web
components
WP 2. Field experiments
WP 3. Laboratory experiments
WP 4. Modelling
WP 5. Syntheses, management evaluation and
dissemination
Research and Development
Field experiments
Exclosure experiments in Planktivore thinning outside
recruitment areas
recruitment areas
Reference area
Exclosure
Exclosure
Planktivore thinning
Exclosure
Exclosure
Objectives
- explore if the state of the coastal system can be
altered by manipulating zooplanktivore density,
- determine where predation of zooplankton takes
place;
- explore the cascading effects in the coastal
ecosystem from piscivores down to filamentous algae,
Research and Development
Modelling objectives:
Use dynamic ecosystem models to identify and analyse the mechanisms that
govern the dynamics of coastal and open sea food webs by analysing:
- occurrence of alternative stable states,
- mechanisms causing and maintaining alternative stable states,
- mechanisms reverting the current zooplanktivore dominated state into a
piscivore dominated state, and
- the indirect ecological effects (e.g. trophic cascades) of altered piscivore
and zooplanktivore abundances.
Saduria
Cod
Egg
Larvae
Juveniles
2 weeks
5-15 cm
Pseudocalanus
Larvae/Juveniles
Sprat
Juveniles/Adults
Age 1
Acartia
Research and Development
Juveniles/Adults
20 cm?
Mysis
Larvae/Juveniles
Juveniles/Adults
14-15 cm
???
Herring
Syntheses, Management Evaluation and
dissemination
The overall objective is to develop an ecosystem based fisheries
management (EBFM) of Baltic Sea piscivores by synthesising the
results from the other WPs using
–
management strategy evaluation under alternative ecological and
climatic scenarios,
–
risk analytical modelling,
–
socio-economic analyses
–
stakeholder involvement and dissemination
Research and Development
Predatory fish back in the Baltic?
Research and Development