The biological state of the Baltic Sea 2010

The time series on species composition and biomass or abundance of phyto- and zooplankton as well as macrozoobenthos in Kiel Bight, Mecklenburg Bight and the Baltic Proper, existing since 1979, was continued in 2010.

The phytoplankton spring bloom start in Kiel Bight at the end of January anr reaches its maximum with almost 7 g/L in the mid of March, mainly with Rhizosolenia setigera, Skeletonema costatum and Coscinodiscus radiatus. The share of Mesodinium rubrum in the spring bloom increases towards the east. In comparison with previous years, Dictyocha
speculum and Chrysochromulina sp. have strongly diminished. The usual diatom summer bloom was not found. Cyanobacteria were dominant in the Arkona Sea temporarily. Strong diatom but no dinoflagellate blooms occurred in November 2010. The bloom-forming diatom was Pseudosolenia calcar-avis in Kiel Bight and Mecklenburg Bight and
Coscinodiscus granii in the Arkona Sea.

The chlorophyll a method was changed. It is strongly recommended to use only the data corrected for pheopigment (Chl.a-kor) until 2009. Since the year 2010 we apply a new fluorometric method which delivers data called “Chl.a-tot-NEU”. Parallel measurents performed in 2010 showed that no break in data series occurred by the change.

Sedimentation records of organic matter in the Arkona Basin over the year 2010 displayed sedimentation maxima in spring and autumn. Mainly due to the high input of resuspended material the total annual flux for the single elements exceeded the values of the previous year by far and amounted to 628 mmol C, 68 mmol N, 228 mmol Si and 6.7 mmol P m^-2 a^-1 at a mass flux of 133 g dry mass m^-2 a^-1.

The total number of mesozooplankton taxa amounted to 41 from the beginning of the BSH financed monitoring, with most taxa found in 1998 and 2010. In 2010, the number increased by six in comparison to the previous year. New neozoans were not found. The declining tendency of mesozooplankton abundance since the early 1990s is still continuing, probably additionally caused by the strong winter and the too early sampling time of the July-cruise in respect to cladocerans.

The 118 species found in the macrozoobenthos in 2010 mark a very low diversity within the 20 years of zoobenthos monitoring conducted by the IOW. A defaunation process due to an oxygen deficit situation was observed in 2010 in the Fehmarnbelt and Mecklenburg Bight. The abundances varied in respect to the area between 91 and 7.000 ind./m². The biomasses (ash free dry weight) ranged from 1 g/m² in the central Arkona Basin to 91 g/m² in Kiel Bight. At the 8 monitoring stations altogether 19 species of the Red List could be observed. 4 indigenous species were observed during the 2010 sampling.

Dr. Norbert Wasmund, Dr. Falk Pollehne, Dr. Lutz Postel, Dr. Herbert Siegel, Dr. Michael L. Zettler