Text of Baltic Sea food web dynamics and response to environmental change PhD plan Susa Niiranen 28th July...
Baltic Sea food web dynamics and response to environmental change
Susa Niiranen28th July 09, Bornholm
Photographs: Hirvonen, A. and Lastumäki, I.
• Study the past food web mechanisms of the open Baltic Sea ecosystem and their response to external forcing
• Study the food web changes induced by changes in future climate, fishery and nutrient input.
• Address management from an ecosystem point of view
• Place the study results into a more global perspective
Questions in food web studies
• What are the roles of external forces and direction of trophic cascades?
• Combined effects of control most likely: e.g. “bottom-up” control creates basis for food web structure (e.g. TLs) and production potential platform for ”top-down” control (Carpenter and Kitchell, 1984; Oksanen, 1988)
• What influences what? what are the thresholds? Relevance to management (fishery, nutrient inputs and change in climate)
Baltic Sea food web
• A relatively simple and species-poor food web
• Ecosystem heavily exposed to human-impact e.g. intensive fishing and eutrophication ”management matters”.
• Ecosystem has gone through major transitions in state
• The most recent shift (late 1980s) when cod and sprat due to:
• overfishing and spawning habitat deterioration (cod)• Change in winter climate T ZP (sprat)
• Ecopath with Ecosim-approach (www.ecopath.org):
- Ecopath (mass-balance)
P = Mp+ F + Mother + BA + migration
C = P + Unass. food + R
- Ecosim (simulation)
• Input parameters: B, P/B, C/B, diet• In the Baltic e.g. Harvey et al., 2003; Sandberg et al. 2007 and
2008; Hansson et al., 2007
Food-web modelling approach
Age 2 etc..
Age 2, etc
Age 2, etc...
1. model robustness
2. past dynamics
3. alternative trophic
6. spatial dimension
5. future climate effects
4. ensemble modelling
2. Disentangling the effects of multiple drivers influencing Baltic Proper food web
• Aim to understand the mechanisms behind past food web dynamics
• Future food web effects cannot be projected and appropriate management options selected without understanding the past
• Different combinations of external forcing (fishing, T, sal etc.) will be applied on the food web model
What factors and combinations could reproduce the observed model dynamics (incl. late 1980s
Acartia spp. herring
spring T F
3. Identifying critical knowledge gaps for our understanding of the Baltic Sea food web dynamics
• Central fw mechanisms unknown
Aim: What management effect will alternative fw assumptions have?
• Possible mechanisms to study:
• ZP feeding on cyanobacteria• spatial sprat/cod overlap• Invasive species
• Potential future fw changes tested? Photo: FIMR
4. Ensemble food web and multi-species models
• Aim to identify knowledge gaps in our understanding of the Baltic Sea system dynamics
• Comparing the results of different multi-species and fw models
• A common set of scenarios with varying environmental forcing (cc) and fishing pressure
• Study is part of the work of ICES WGIAB.
1970 1990 2010 2030 2050 2070 2090
ICES WGIAB report 2009
5. How can the future climate affect the Baltic Sea ecosystem and does this create new needs for policy-making?
• Aim to describe the potential food web effects of future changes in climate and nutrient load
• Does management need to adapt to cc e.g. for sustainable fishery or “de-eutrophication”?
• Knowledge on comparative ecosystems is reflected in the analyses of the modelling results.
• Scenario output from the ECOSUPPORT project is used Multi-model ensemble simulations
BONUS project ECOSUPPORT is acknowledged for financing this PhD study(www.baltex-research.eu/ecosupport)
• Alf Norkko (benthic-pelagic coupling)• Maiju Lehtiniemi (mysid and Mnemiopsis dynamics)• Brian MacKenzie, John Havenhand (ECOSUPPORT)• ICES WGIAB (Integrated assessment)• Fiskeriverket – Anna Gårdmark et al. (fish dynamics)• Georgi Daskalov (Black Sea)• SMHI – Markus Meier et al. (climate scenarios)