Multi-level trophic cascades in a heavily exploited open marine ecosystem
Anthropogenic disturbances intertwined with climatic changes can have a large impact on the upper trophic; levels of marine ecosystems, which may cascade down the food web. So far it has been difficult to; demonstrate multi-level trophic cascades in pelagicmarine environments.Using field data collected during a; 33-year period, we show for the first time a four-level community-wide trophic cascade in the open Baltic; Sea. The dramatic reduction of the cod (Gadus morhua) population directly affected its main prey, the; zooplanktivorous sprat (Sprattus sprattus), and indirectly the summer biomass of zooplankton and; phytoplankton (top-down processes). Bottom-up processes and climate–hydrological forces had a weaker; influence on sprat and zooplankton, whereas phytoplankton variation was explained solely by top-down; mechanisms.Ourresults suggest that in order todampenthe occasionally harmful algal bloomsof the Baltic,; effort should be addressed not only to control anthropogenic nutrient inputs but also to preserve structure; and functioning of higher trophic levels.