Baltic Sea food web dynamics and response to environmental change

PhD plan

Susa Niiranen28th July 09, Bornholm

Photographs: Hirvonen, A. and Lastumäki, I.

Aim to

• 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

Spring phytoplankton

Bacteria

Microzoopl.

Mysids

Meiobenthos

Seals

Detritus sed

Age 0

Age 0

Age 0

Eggs/larvae

Pseudocalanus

Acartia

Temora

Other...

Macrozoobenthos

Cyanob. Other...

Age 1

Herring

Age 2 etc..

Age 2, etc

Age 1

Cod

Age 2, etc...

Age 1

Sprat

DOM

Spr_fleet

Cod_fleet

Her_fleet

Temp/Climate

/Salinity

SAL

RV

O2

?

N, P

Planned studies

1. model robustness

2. past dynamics

3. alternative trophic

mechanisms

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

shift)?

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.

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1970 1990 2010 2030 2050 2070 2090

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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

ECOSUPPORT model hierarchy

www.baltex-research.eu/ecosupport

Timetable

2009/10 2010/11 2011/12 2012/13

PhD essay: literature study

Papers 1 and 4

Papers 2 and 3 Paper 5 Paper 6

PhD thesis

Papers 2 and 3

Licenciate thesis

PhD thesis

PhD defence

e-mail: susa.niiranen@mbox.su.se Hirvonen, A. and Lastumäki, I.

BONUS project ECOSUPPORT is acknowledged for financing this PhD study(www.baltex-research.eu/ecosupport)

Collaboration:

• 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)