Feedback of higher trophic levels and overharvesting
Theme 2 aims to answer the following questions:
- Are the indirect effects of climate change via organic carbon and nutrients affecting fish predation? Where has it gone the opposite: What is the effect of increased planktivores on the biodiversity of the planktonic food web?
- How is regulation of fish communities and cascading effects on the food web affected by harvesting and climate-induced changes in productivity?
- Do long-term monitoring data at lower trophic levels correlate with long-term data on fish, particularly for the Bothnian Sea? What are the recruitment habitats of perch and pike? And can they be defined through isotope analyses? How can the results be used for ecosystem-based fisheries management?
Photo: Kerstin Jonsson/Azote
Summary of results (so far)
Coastal wetlands - a key to pike recruitment and nutrient reduction
Pike recruitment in the coastal Baltic Sea is improved by restoration of wetlands. Increasing the abundance of pike will have a top-down effect on the coastal ecosystem by reducing zooplanktivorous fish. The recruitment of pike can be focused to specific coastal areas of interest as the pike shows natal homing behavior. Coastal wetlands can be optimized for nutrient reduction and pike recruitment simultaneously as the same key variables are important for both processes (vegetation type, patchy distribution of vegetation, shallow depth, high temperature and large wetland area).
Stickleback predation behind perch recruitment failure on the coast
By combining field studies (on resource dynamics, temporal and spatial changes in larval perch and three spine stickleback densities) in spawning areas in the coastal zone and a large scale pond experiments, we have showed that three spine sticklebacks can have strong negative effects on perch recruitment via predation on larval perch. We have thus identified the main mechanism behind suggested correlative patterns of recruitment failures linked to increasing densities of sticklebacks in coastal areas.