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 reorganization.
An Ecopath with Ecosim Baltic Proper food—web model (Balt-
ProWeb) 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
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
reorganization 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.