GLOBEC-Germany - Trophic interactions between Zooplankton and Fish under the influence of Physical Processes

“Trophic Interactions between Zooplankton and Fish under the Influence of Physical Processes in the Baltic and North Sea (2002 – 2007)”

The international Global Ocean Ecosystem Dynamics (GLOBEC) programme was initiated in 1991 by the Scientific Committee on Oceanic Research and the Intergovernmental Oceanographic Commission of the UNESCO. It is a core project of the International Geosphere-Biosphere Project (IGBP) with its research topics aiming at understanding how global change impacts abundance, diversity and productivity of marine populations (Barange & Harris 2003).

GLOBEC-Germany is the national German contribution to this core project focussing on the Baltic Sea and North Sea, to which Germany has adjoining coastlines. The two seas exhibit a gradient from marine (North Sea) to almost fresh water conditions (outer ends of the Baltic Sea). Main topic of the project was the investigation of interactions between zooplankton and fish under the influence of physical processes (Alheit 2004). Main sampling areas were located in the southern North Sea and German Bight, as well as in the Bornholm Basin in the Baltic Sea (Tamm et al. 2007).

In these areas herring (Clupea harengus L.), sprat (Sprattus sprattus L.) and cod (Gadus morhua L.) as well as numerous copepod populations experienced high fluctuations in recruitment and biomass since the middle of the 20th century (Alheit et al. 2005). Whereas a substantial decrease of individual weight of herring and sprat at high biomass was documented in the Baltic Sea, no such similarities were observed in the North Sea. It was assumed that this phenomenon is caused by food limitation (mainly copepods) in the Baltic Sea. However, it was not clear whether this was due to direct effects of trophic interactions (internal dynamics) in the rather simple food web of the Baltic Sea, or whether the decrease of some copepod populations is a consequence of physical processes (external forcing).

An interdisciplinary team of fishery biologists, planktologists, physiologists, geneticists, physical oceanographers and modellers investigated these questions in concerted actions. Field studies, experimental approaches and modelling were combined and applied to investigate the influence of physical processes and trophodynamic interactions. Top-down and bottom-up processes were studied comparatively in both ecosystems. Results were used to elucidate principal mechanisms accounting for the high variability of copepod production and success in fish recruitment. They also form the basis for strategic modelling and estimating recruitment success of fish. Numerous scientific studies, including results from PhD and diploma theses, were conducted and have improved our current understanding of mechanisms governing population dynamics on short time scales (Alheit 2007).

To insure sustainable and citeable storage the GLOBEC data were imported into the PANGAEA database of the World-Data-Centre (WDC) Mare.