ALKOR AL594

In the context of climate change and increasing anthropogenic use, the Baltic Sea has experienced and, compared to the rest of the world, is undergoing particularly rapid changes, such as warming, acidification, eutrophication, increasing oxygen deficiency, overfishing, and the spread of non-indigenous species. The ecological and economic consequences of these long-term changes are difficult to monitor scientifically through short-term projects. All the more important are long-term data series that also depict decadal patterns. The integrative research work during cruise AL594 continous one of the best available multi-disciplinary long-term data series for the pelagic Baltic Sea with focus on the deep basins of the Baltic Sea with main focus on the Bornholm Basin with consistent methodology in pelagic trawling with single fish surveys, length measurement series and fish sampling, food web sampling (phytoplankton, seston, zooplankton including ichthyoplankton, gelatinous zooplankton, nekton), oceanographic/hydrographic measurements and hydroacoustic recordings, since 1986. The resulting sample and data sets are used to investigate changes in (1) species composition, including the distribution of non-native species, (2) phenology within the phenology of fish and plankton communities, (3) biodiversity (including genetic diversity) of zooplankton and fishes, (4) the structure and function of food webs and (5) physical/hydrographical parameters. The coupling of these interdisciplinary data sets for causal analyses plays a central role here. Additional focal points of the cruise are sampling of pelagic microbes and trace compounds (vitamins) for subsequent analysis along the salinity gradient, and of fish for the subsequent reassessment of the ecology and selection-induced changes at the population level using molecular bioanalytical isotope-chemical approaches. With the continuation of the integrative long-term data series AL594 contributes to various projects of the department "Marine Evolutionary Ecology" at GEOMAR and forms the basis for collaborations with various partners in the Baltic Sea region.