Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
Bundesamtes für Seeschifffahrt und Hydrographie, Hamburg, Rostock
(Federal Maritime and Hydrographic Agency of Germany, Hamburg, Rostock)
The time series an species composition and biomass or abundance of phyto- and zooplankton as well as
macrozoobenthos in the Belt Sea and the Baltic proper, existing since 1979, was continued in 2003.
The phytoplankton (Skeletonema costatum) spring bloom developed exceptionally early (in February 2003)
in Mecklenburg Bight and the Arkona Sea, perhaps owing to the inflow of saline bottom water which raised the
pycnocline. In the Bornholm Sea and in the southem Gotland Sea it occurred only in the second half of March.
The summer bloom of large diatoms was dominated by Guinardia flaccida and Dactyliosolen fragilissimus
in Mecklenburg Bight. The. typical cyanobacterial blooms (Nodularia spumigena, Aphanizomenon sp.)
spread in the first half of July from the northem Gotland Sea towards the southem Arkona Sea and drifted into
the Mecklenburg Bight by early August. The autumn bloom in Mecklenburg Bight is characterised by the coexistence
of dinoflagellates (Ceratium tripos) and diatoms (Proboscia alata).
Whereas the share of diatoms in the spring blooms was very Iow in the 1990s in the southem Baltic proper, its
increase since the year 2000 increases. On the other hand, dinoflagellates and Mesodinium rubrum reduced
their share in the spring bloom in this area.
In March, late summer and autumn 2003 the number of mesozooplankton taxonomic groups slightly increased in
comparison to the last four years due to previous saltwater inflows. Some species like Oithona similis
indicated the spreading of saline water in the basins of the central Baltic Sea. Polychaet and bivalve larvae
reached highest concentration in March and October respectively. The average total abundance in 2003 significantly
remained below the long-term mean at analysed stations in the central Arkona Sea and the eastern Gotland Sea caused
by missing mass development of rotifers and cladocerans. Calanoid copepods never changed in total abundance in the
last years but relative shifts occurred within taxa as usual.
The quick recovery of macrozoobenthos after the oxygen depletions in 2002 in the western Baltic and the
re-colonisation of the Bornholm Sea after five years are remarkable. Since the beginning of the macrozoobenthos
monitoring in 1991, 156 taxa were proved. Three species (Halicryptus spinulosus, Bylgides sarsi,
Diastylis rathkei) showed high presence during all the years. The long-term tendencies in species number
and Shannon-Wiener-Index since 1980 are displayed at one station in the Arkona Basin. The development of the
abundance of Pygospio elegans and Macoma balthica in the south-eastern Arkona Sea from 1991 to
2003 is shown.
The complete report is available in German on the internet at:
http://www.bsh.de/de/Meeresdaten/Beobachtungen/MURSYS-Umweltreportsystem/PDF/osretro042004.pdf (895 KB)