Long-Term Trends of the Offshore Ecosystems

Long-term data sets are crucial in assessing the state of the marine systems and its ecological processes, to disentangle human-induced and natural changes, short-term fluctuations and long-term trends. A clear trend was observed in phytoplankton composition. The dominant phytoplankton classes in the Baltic Sea, diatoms and dinoflagellates, showed an opposing trend in the spring bloom of the open Baltic Proper. Diatoms decreased and dinoflagellates increased suddenly since the late 1980s. Nearly at the same time, also a shift in the macrozoobenthos occurred in the southern Baltic Sea. The biocenotic shift in the second half of the 1990s for various members of the food chain, both in pelagic and benthic habitats, is apparently a widespread phenomenon, as it has been observed even in the eastern North and Central Atlantic. It represents probably a second ecosystem regime shift within the investigation period, which is less remarkable and less known than the first one, but nevertheless needs attention.