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. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In press.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.</p>

Studier visar att dagens elever känner oro inför framtiden och de klimatförändringar vår värld utsätts för. Skolverkets nationella kartläggning utav miljöundervisning i skolan visar dock att cirka hälften av de tillfrågade gymnasielärarna inte bedriver någon undervisning i ämnet. Denna studie beskriver en alternativ modell för undervisning i klimatfrågor. Elever ges genom modellering av ekosystem möjlighet att fördjupa sin förståelse kring klimatförändringar i samband med exploatering av topp-predatorer. Detta är ett realistiskt problem då en mängd studier visar att dagens ekosystem utsätts för en mängd stressfaktorer, med ursprung i klimatförändringar, och att exploatering av topp-predatorer kan leda till konsekvenser med artutdöende som följd. Modellen som används i undersökningen är en generell Lotka-Volterra-modell vilken fungerar som analytiskt verktyg. Skolverket betonar matematikens roll som ämnesöverskridande verktyg och modellekosystem ger elever möjlighet att använda matematiska kunskaper i ett verkligt scenario. I studien undersöks även hur pass stor exploatering topp-predatorer kan utsättas för i takt med ökade klimatförändringar. De undersökta områdena inbegriper tre- och fyr-artssystem i marina och terrestra miljöer. Resultaten visar att exploateringen måste minska i takt med ökade klimatorsakade förändringar i samtliga fall, undantag terrestra tre-artsystem som utsätts för förändrade interaktionsstyrkor. / Studies show that today's students are worried about the future and the increasing climate change. A survey made by the Swedish National Agency for Education about environmental education shows that approximately half of the surveyed secondary school teachers are not engaged in teaching in the field. This study describes an alternative model for teaching environmental issues. Students are by the modeling of ecosystem given an opportunity to deepen their understanding of climate change associated with the exploitation of top predators. This is a realistic problem, numerous studies show that today's ecosystems are exposed to a variety of stressors, with the origin of climate change, and the exploitation of top predators can lead to serious consequences with extinction as a result. The model used in this study is a generalized Lotka-Volterra model which works as an analytical tool. The Swedish National Agency for Education emphasizes the role of mathematics as interdisciplinary tools and model ecosystem gives students the opportunity to use math skills in a real scenario. The study also investigated how much exploitation top predators can be exposed to in line with increased climate change. The research sites include three-and four-species system of marine and terrestrial environments. The results show that the exploitation must be reduced in line with increased climate-caused changes in all cases, except terrestrial three-species system exposed to changes in interaction strengths.

Se ha estudiado la dinámica del fitoplancton en las lagunas costeras de Aiguamolls de l'Empordà. El fitoplancton esta sujeto principalmente al control "bottom-up", la variabilidad hidrológica y la disponibilidad de nutrientes tienen una mayor influencia en la composición y distribución de tamaños del fitoplancton, que el zooplancton. La concentración de materia orgánica disuelta es el factor ambiental más correlacionado con el crecimiento de la biomasa fitoplanctónica. Dada la proximidad entre las lagunas costeras y el mar, donde la ocurrencia de Proliferaciones de Algas Nocivas es cada vez más frecuente, se realizan un inventario general de las especies más abundantes del fitoplancton y se llevan a cabo análisis extensivos de la toxicidad. La mayoría de especies de dinoflagelados encontradas son potencialmente nocivas. Hay pocas especies en común entre el mar y las lagunas, sin embargo, existen especies productoras de PANs características de los ambientes lagunares. / The phytoplankton dynamics in the coastal lagoons of Empordà salt marshes was studied. The phytoplankton was mainly subject to the "bottom-up" control, the hydrologic variability and the nutrients availability have a greater influence in the composition and size distribution of the phytoplankton, than zooplankton. The concentration of dissolved organic matter was the environmental factor more correlated with the phytoplanktonic biomass growth. Due to the proximity between the coastal lagoons and the sea environment, where the occurrence of Harmful Algae Blooms is frequent, a general inventory of the most abundant species of the phytoplankton was made and an extensive monitoring of the toxicity was carried out. Most of dinoflagellates species found were potentially harmful. There were few species in common between the sea and the lagoons, nevertheless, some HABs species, characteristic of coastal lagoons, were found.