Interaction between top-down and bottom-up control in marine food webs

Area of Science:

• Marine Ecology
• Ecosystem Modeling
• Climate Change Impacts

Background:

• Climate change and resource exploitation alter bottom-up and top-down forces in ecosystems.
• Trophic control patterns in complex food webs are emergent and often counterintuitive.

Purpose of the Study:

• To develop a statistical model for simulating trophic control in the North Sea ecosystem.
• To investigate the influence of fishing mortality and climate variables on ecosystem dynamics.
• To understand the interplay of bottom-up and top-down forces in a heavily impacted marine environment.

Main Methods:

• Developed a statistical, non-deterministic model incorporating time-series data (>40 years) for plankton, fish, and bird groups.
• Model driven by fishing mortality and climatic variables.
• Simulated ecosystem component changes under various stressor scenarios.

Main Results:

• Top-down fishing pressure is crucial for fish population dynamics.
• Bottom-up climatic processes predominantly control plankton dynamics.
• Planktivorous fish act as a central link, initiating cascading effects across trophic levels.

Conclusions:

• Fishing impacts on predators indirectly affect plankton abundance.
• Bottom-up and top-down forces are not mutually exclusive in marine ecosystems.
• Integrated models can simulate complex long-term ecosystem changes under combined stressors.