Eastern Gotland Basin
Central Baltic
Latitude:   57.0000     Longitude:   20.2000

 Associated Investigators:
Gunta Rubene (BIOR) ,
Solvita Strake (LHEI) ,   Georgs Kornilovs (BIOR)  

The Eastern Gotland Basin sampling site is located in the central Baltic Sea, ICES Subdivision 28. Zooplankton biomass (wet weight) was sampled using a Juday net (0.36 m opening diameter, 160 mm mesh). Individual hauls were carried out in vertical steps, resulting in full coverage of the water column to a maximum depth of 100 m. Sampling has been conducted in spring (May), summer (August), and autumn (October/November) since 1959.

The dominant zooplankton species in the central Baltic Sea are the copepods Acartia spp., Temora longicornis, and Pseudocalanus acuspes. Since the early 1970s, high positive biomass anomalies were observed for P. acuspes, followed by a drastic decline after 1990. At the same time, an opposite trend was observed for T. longicornis. Changes in temperature (increasing) and salinity (decreasing) are considered to be the reason for the shift in zooplankton species composition from P. acuspes to T. longicornis. Similarly, the species composition of the central Baltic fish community shifted from cod (Gadus morhua), which was dominant during the 1980s, to sprat (Sprattus sprattus), which became dominant during the 1990s (Mollmann et al., 2003, 2005). Water temperatures in the survey area have been increasing since the 1900s, with some variability, and are currently warmer than any measured during the last century. Increased precipitation and river run-off have accompanied the warmer temperatures. This affects the Baltic and its zooplankton communities by directly freshening surface waters and preventing inflows of saline and oxygenated water from the Kattegat and North Sea (Matthaus and Schinke, 1999).

REFERENCES:

Matthaus, W., and Schinke, H. 1999. The influence of river runoff on deep water conditions of the Baltic Sea. Hydrobiologia, 393: 1-10.


Mollmann, C., Koster, F. W., Kornilovs, G., and Sidrevics, L. 2003. Interannual variability in population dynamics of calanoid copepods in the Central Baltic Sea. ICES Marine Science Symposia, 219: 220-230.