Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
(Dr. Norbert Wasmund, Susanne Busch, Ina Topp, Regina Hansen)
The Leibniz Institute for Baltic Sea Research conducts a coastal monitoring programme with weekly samplings at the sea-bridge Heiligendamm (54°08,55' N; 11°50,60' E; 300 m off shore, 3 m water depth). The Department of Marine Biology analyses the surface samples, taken by means of a bucket, for phytoplankton composition and biomass and for chlorophyll a.
The phytoplankton biomass is determined by microscopical counting (UTERMÖHL method) and the chlorophyll a concentration by ethanol extraction and fluorometric measurement. Method instructions see:
Phytoplankton counting was carried through by use of the counting programme OrgaCount and is based on the HELCOM-biovolume factors which are annually updated: http://www.ices.dk/env/repfor/index.asp (basics see in Olenina et al. 2006). The analytical specifics of the chlorophyll a determination are published by Wasmund et al. (2006). According to the
decision of the BLMP-subgroup "Quality Assurance” from 11.9.2008 we show here chlorophyll a data which are not corrected for pheopigments.
Microscopical analysis was not possible in 2 samples because of high sediment portions, caused by wind-induced sediment resuspension at the shallow station. Sampling was completely impossible on 18 January 2011 (week 6) because on an storm event.
The results are shown in Figure 1.
As expected, phytoplankton biomass stayed low in the cold month of January 2011. In the first weeks, diatoms (Diatomophycee) of the genus Actinocyclus sp. dominated, followed by a growth of Mesodinium rubrum. On 1.2.2011 (week 5), Eutreptiella braarudii appeared (Image 1), but it disappeared after the storm event.
Image 1: Eutreptiella braarudii
Until 8.3.2011 (week 10), phytoplankton biomass stayed low. We have to admit that the samples contained much sand grains which impair the microscopical counting results. However, the low chlorophyll-a-concentrations confirm our phytoplankton data. Within the diatoms, Rhizosolenia setigera dominated in weeks 8 and 9 and Achnanthes taeniata in week 10.
The spring bloom started on 15.3.2011 (week 11) which is one week later than in the previous year. At the time of its maximum (on 22.3.2011) it was dominated by Achnanthes taeniata (654 mg/m³, see Image 2), Detonula confervacea (472 mg/m³, see Image 3) and Chaetoceros spp. (212 mg/m³).
Skeletonema costatum and the Euglenophycee Eutreptiella sp. were astonishingly low in this spring bloom in comparison with that of the year 2010. Instead, Dictyocha speculum (Image 4) occurred with a biomass up to 388 mg/m³, predominantly in its naked form. This species was counted to Chrysophyceae in Figure 1 and accounts for approximately 80 % in this group. It belongs to the common spring plankton, but it was exceptionally
low in 2010.
The diatom bloom decreased quickly, and the so far dominating groups (diatoms as well as the species Dictyocha speculum and Mesodinium rubrum) were successively replaced by dinoflagellates (Peridiniales, frequently Peridiniella danica, Image 5). Besides of these, Dictyocha speculum appeared again on 12.4.2011 (week 15) with high biomass.
Image 2: Achnanthes taeniata
Image 3: Detonula confervacea (Light- and electronmicroscopical image)
Image 4: Dictyocha speculum: spiny cell besides of two "naked" cells
Image 5: Peridiniella danica
A succession from diatoms to dinoflagellates within the spring bloom is rather common in the western Baltic Sea. The spring bloom was terminated by the 19.4.2011 (Week 16)
Olenina, I., Hajdu, S., Andersson, A.,Edler, L., Wasmund, N., Busch, S., Göbel, J., Gromisz, S., Huseby, S., Huttunen, M., Jaanus, A., Kokkonen, P., Ledaine, I., Niemkiewicz, E. (2006): Biovolumes and size-classes of phytoplankton in the Baltic Sea. Baltic Sea Environment Proceedings No.106, 144pp.
Wasmund, N., Topp, I., Schories, D. (2006): Optimising the storage and extraction of chlorophyll samples. Oceanologia 48,125-144.
Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Seestr. 15, D-18119 Rostock-Warnemünde
Figure 1: Composition of the phytoplankton biomass and concentration of chlorophyll a from 4.1. to 26.4.2011 at sea-bridge Heiligendamm.