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Multiple forces drive the Baltic Sea food web dynamics and its response to environmental change
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding the interaction of multiple drivers and their compounded effects on ecosystem dynamics is a key challenge for marine resource management. The Baltic Sea is one of the world’s seas most strongly impacted by effects from both human activities and climate. In the late 1980’s changes in climate in combination with intensive fishing initiated a reorganization of the Central Baltic Sea (CBS) food web resulting in the current sprat-dominated state. In the future, climate change is projected to cause drastic changes in hydrodynamic conditions of the world oceans in general, and the Baltic Sea in particular.  

In this thesis, CBS food web responses to the combined effects of fishing, nutrient loads and climate were tested for the past (1974-2006) and projected into the future (2010-2098). A new food web model for the CBS (BaltProWeb) was developed using extensive monitoring data across trophic levels. This model described the past food web dynamics well, and was hence also used for future (2010-2098) projections. Different ensemble modeling approaches were employed when testing the food web response to future scenarios.

The results show that regardless the climate change, the management of nutrient loads and cod fishing are likely to determine the food web dynamics and trophic control mechanisms in the future Baltic Sea. Consequently, the variation in the food web projections was large, ranging from a strongly eutrophied and sprat-dominated to a cod-dominated CBS with eutrophication levels close to today’s values. The results also suggest a potential risk of abrupt ecosystem changes in the future CBS, particularly if the nutrient loads are not reduced. Finally, the studies illustrate the usefulness of the ensemble modeling approach, both from the perspective of ecosystem-based management as well as for studying the importance of different mechanisms in the ecosystem response.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2013. , 28 p.
Keyword [en]
Baltic Sea, climate change, Ecopath with Ecosim, food web interactions, multiple drivers, regime shift, trophic control
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-92541ISBN: 978-91-7447-744-3 (print)OAI: oai:DiVA.org:su-92541DiVA: diva2:642488
Public defence
2013-10-04, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In press. Paper 5: Submitted.

Available from: 2013-09-12 Created: 2013-08-08 Last updated: 2013-09-12Bibliographically approved
List of papers
1. Ecosystem flow dynamics in the Baltic Proper-Using a multi-trophic dataset as a basis for food-web modelling
Open this publication in new window or tab >>Ecosystem flow dynamics in the Baltic Proper-Using a multi-trophic dataset as a basis for food-web modelling
2012 (English)In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 230, 123-147 p.Article in journal (Refereed) Published
Abstract [en]

The Baltic Proper is a semi-enclosed, highly productive basin of the Baltic Sea with a low biodiversity, where only a few key species drive the system's dynamics. Recently, an ecosystem regime shift was described having pronounced changes at all trophic levels, driven by changes in fishery and climate and leading to a food-web reorganisation. An Ecopath with Ecosim Baltic Proper food-web model (BaltProWeb) was developed to simulate and better understand trophic interactions and their flows. The model contains 22 functional groups that represent the main food-web components. BaltProWeb was calibrated to long-term monitoring data (1974-2006), covering multiple trophic levels and is forced by fisheries and environmental drivers. Our model enables the quantification of the flows through the food-web from primary producers to top predators including fisheries over time. The model is able to explain 51% of the variation in biomass of multiple trophic levels and to simulate the regime shift from a cod dominated to a sprat dominated system. Results show a change from benthic to more pelagic trophic flows. Before the reorganisation macrozoobenthos was identified as an important functional group transferring energy directly from lower trophic levels to top predators. After the regime shift, the pelagic trophic flows dominated. Uncertainties and limitations of the modelling approach and results in relation to ecosystem-based management are discussed.

Keyword
Ecosystem dynamics, Food-web interactions, Trophic flows, Regime shift, Ecopath with Ecosim
National Category
Environmental Sciences
Identifiers
urn:nbn:se:su:diva-76059 (URN)10.1016/j.ecolmodel.2011.12.014 (DOI)000302517200012 ()
Note
4Available from: 2012-05-08 Created: 2012-05-08 Last updated: 2017-12-07Bibliographically approved
2. Uncertainties in a Baltic Sea Food-Web Model Reveal Challenges for Future Projections
Open this publication in new window or tab >>Uncertainties in a Baltic Sea Food-Web Model Reveal Challenges for Future Projections
2012 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 41, no 6, 613-625 p.Article in journal (Refereed) Published
Abstract [en]

Models that can project ecosystem dynamics under changing environmental conditions are in high demand. The application of such models, however, requires model validation together with analyses of model uncertainties, which are both often overlooked. We carried out a simplified model uncertainty and sensitivity analysis on an Ecopath with Ecosim food-web model of the Baltic Proper (BaltProWeb) and found the model sensitive to both variations in the input data of pre-identified key groups and environmental forcing. Model uncertainties grew particularly high in future climate change scenarios. For example, cod fishery recommendations that resulted in viable stocks in the original model failed after data uncertainties were introduced. In addition, addressing the trophic control dynamics produced by the food-web model proved as a useful tool for both model validation, and for studying the food-web function. These results indicate that presenting model uncertainties is necessary to alleviate ecological surprises in marine ecosystem management.

Keyword
Food-web, Baltic Sea, Uncertainty, Model sensitivity, Ecopath with Ecosim, Ecosystem-based management
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:su:diva-81248 (URN)10.1007/s13280-012-0324-z (DOI)000308039100009 ()
Note

AuthorCount:4;

Available from: 2012-10-15 Created: 2012-10-15 Last updated: 2017-12-07Bibliographically approved
3. Biological ensemble modeling to evaluate potential futures of living marine resources
Open this publication in new window or tab >>Biological ensemble modeling to evaluate potential futures of living marine resources
Show others...
2013 (English)In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 23, no 4, 742-754 p.Article in journal (Refereed) Published
Abstract [en]

Natural resource management requires approaches to understand and handle sources of uncertainty in future responses of complex systems to human activities. Here we present one such approach, the biological ensemble modeling approach,'' using the Eastern Baltic cod (Gadus morhua callarias) as an example. The core of the approach is to expose an ensemble of models with different ecological assumptions to climate forcing, using multiple realizations of each climate scenario. We simulated the long-term response of cod to future fishing and climate change in seven ecological models ranging from single-species to food web models. These models were analyzed using the biological ensemble modeling approach'' by which we (1) identified a key ecological mechanism explaining the differences in simulated cod responses between models, (2) disentangled the uncertainty caused by differences in ecological model assumptions from the statistical uncertainty of future climate, and (3) identified results common for the whole model ensemble. Species interactions greatly influenced the simulated response of cod to fishing and climate, as well as the degree to which the statistical uncertainty of climate trajectories carried through to uncertainty of cod responses. Models ignoring the feedback from prey on cod showed large interannual fluctuations in cod dynamics and were more sensitive to the underlying uncertainty of climate forcing than models accounting for such stabilizing predator-prey feedbacks. Yet in all models, intense fishing prevented recovery, and climate change further decreased the cod population. Our study demonstrates how the biological ensemble modeling approach makes it possible to evaluate the relative importance of different sources of uncertainty in future species responses, as well as to seek scientific conclusions and sustainable management solutions robust to uncertainty of food web processes in the face of climate change.

Keyword
climate change, Eastern Baltic cod, environmental variation, exploitation, fisheries management, food web models, Gadus morhua callarias, model uncertainty, scenario analysis, species interactions
National Category
Environmental Sciences Ecology
Identifiers
urn:nbn:se:su:diva-92132 (URN)10.1890/12-0267.1 (DOI)000320105100005 ()
Note

AuthorCount:11;

Available from: 2013-07-22 Created: 2013-07-19 Last updated: 2017-12-06Bibliographically approved
4. Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web
Open this publication in new window or tab >>Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web
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2013 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 11, 3327-3342 p.Article in journal (Refereed) Published
Abstract [en]

Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multi-model approach to project how the interaction of climate, nutrient loads and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, while low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, non-linearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

Keyword
Baltic Sea, climate change, food web, fishing, eutrophication, nutrient loads, Ecopath with Ecosim
National Category
Ecology Environmental Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-92833 (URN)10.1111/gcb.12309 (DOI)000325567100009 ()
Note

AuthorCount: 9;

Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2017-12-06Bibliographically approved
5. The potential risk of regime shifts and changes in ecosystem dynamics in the future Baltic Sea
Open this publication in new window or tab >>The potential risk of regime shifts and changes in ecosystem dynamics in the future Baltic Sea
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(English)Article in journal (Refereed) Submitted
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-92834 (URN)
Available from: 2013-08-20 Created: 2013-08-20 Last updated: 2017-03-08Bibliographically approved

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