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 (calculation without correction for pheopigments). Method instructions see
Phytoplankton counting was carried through until 17.6.2008 by use of the counting programme PhytoWin and since 26.6.2008 with OrgaCount. The continuity of the data series is retained as both programmes are based on the HELCOM-biovolume factors (Olenina et al. 2006), which were updated in April 2008 by the Phytoplankton Expert Group of HELCOM. The analytical specifics of the chlorophyll-a-determination
are published by Wasmund et al. (2006). According to the decision of BLMP-subgroup "Quality Assurance” from 11.9.2008 we show here the chlorophyll a data which are not corrected for pheopigments.
Microscopical analysis was not possible in 12 samples because of high sediment portions, caused by wind-induced sediment resuspension at the shallow station. Chlorophyll measurements were, however, always possible. Only on 2.12.2008, the sampling was cancelled because of a storm.
The phytoplankton biomass was very low in the first few weeks of the year. It was mainly composed of cryptophyceae (Plagioselmis prolonga, Teleaulax spp., Hemiselmis spp.) on 8.1.2008. Since week 3 (15.1.2008), Gymnodiniales appeared, and since week 5 (29.1.2008) also Ceratium tripos and Porosira glacialis. Remarkably, a quick change within the diatoms occurred from Porosira glacialis to Rhizosolenia setigera
from week 5 to 6, and back to Porosira glacialis in week 7. Obviously, different water bodies with different species signature drifted along the station. Since week 7 (12.2.2008), Mesodinium rubrum developed and reached a biomass of 118 mg/m³ in week 8. On 26.2.2008 (week 9), Mesodinium rubrum, Porosira glacialis, Eutreptiella sp., Teleaulax spp.
and Guinardia delicatula contributed more than 10 mg/m³ in each case. Unfortunately, no detailed information on the start of the spring bloom was possible because the sample from 4.3.2008 could not be evaluated.
On 11.3.2008, the spring bloom has reached already its peak (3415 mg/m³). Astonishingly, it was not dominated by diatoms but by the euglenophyceae Eutreptiella spp. (2440 mg/m³). Besides this, the diatoms Rhizosolenia setigera and Rhizosolenia hebetata forma semispina, and the photoautotrophic ciliate Mesodinium
rubrum were important. Also Teleaulax spp., Gyrodinium spirale, Protoperidinium depressum, Ceratium tripos and Proboscia alata are worth mentioning.
The quick disappearance of the spring bloom might have been affected by a transport of water bodies because the species composition differed very much from the 11.3.2008 (week 11) to the 18.3.2008 (week 12). Eutreptiella spp. was suddenly almost completely absent, whereas the silicoflagellate Dictyocha speculum appeared with 722 mg/m³. As it occured mainly in its "naked" form, its identification is not sure;
also the genera Chattonella, Verrucophora or Pseudochattonella could be possible. Important diatoms were Rhizosolenia hebetata forma semispina, Proboscia alata, Rhizosolenia setigera and Guinardia delicatula. An unusual early appearance of the peak of Dictyocha speculum was also noticed in 2007. Generally, the Dictyocha bloom is expected only after the diatom bloom in April. Already in 2007, it suppressed
the diatom bloom and also dinoflagellates could not develop properly (Wasmund et al. 2008). The unusual development of 2007 shows up also in 2008 and could establish as a permanent phenomenon (regime shift ?).
By the 25.3.2008 (week 13), also Dictyocha speculum disappeared. Suddenly, Skeletonema costatum became dominant (270 mg/m³). It is regularly one of the most important spring diatoms. However, a diatom spring bloom was not found in 2008. Despite a taxonomic revision of the Skeletonema-species (vgl. Sarno et al., 2005) we keep the old name Skeletonema costatum preliminarily.
The diatoms vanished completely by the 15.4.2008 (week 16). Mixotrophic organisms appeared, like cryptophyceae (Plagioselmis prolonga) and prymnesiophyceae (Chrysochromulina spp.). Perhaps also the dominating ciliate Mesodinium rubrum belongs to this mixotrophic group.
The next change occurred until the 29.4.2008 (week 18): Mesodinium rubrum and Cryptophyceae were absent, but Chrysochromulina spp. developed. Dinoflagellates (Heterocapsa triquetra, Heterocapsa rotundata) became dominant. The early appearance of Aphanizomenon sp. (12 mg/m³) is worth mentioning. The phytoplankton composition was similar on 20.5.2008 (week 21).
On 3.6.2008 (week 23), Chrysochromulina spp. has vanished. Small unidentified unicells dominated. Perhaps also small hardly recognizable Chrysochromulina spp. were counted into this group, but it was mainly composed of coccoid cyanobacteria.
The phytoplankton biomass declined further by the end of June. The dominating "Unidentified" were mainly made up by small coccoid cyanobacteria (< 2 µm) and very thin filamentous cyanobacteria (< 1 µm).
On 8.7.2008, Chrysochromulina sp. and Proboscia alata were suddenly dominant. The latter was still on 22.7.2008 (week 30) the dominating diatom. The spontaneous appearance of the flagellate Eutreptiella sp. without corresponding chlorophyll signal was striking.
The samples from 12.8. to 2.9.2008 (week 33 - 36) were characterised by high diatom biomass, with a succession from Dactyliosolen fragilissimus to Coscinodiscus granii, Guinardia flaccida and to Pseudo-nitzschia seriata-group. Ceratium tripos developed slowly as expected. The unidentified unicells were particularly large (> 2 µm) and therefore counted, whereas they were
smaller (< 2 µm) before and after this date and therefore not counted.
On 7.10.2008 (week 41), mainly Cerataulina pelagica, Coscinodiscus granii and Pseudo-nitzschia pungens appeared. The latter developed a biomass of 448 mg/m³ until 21.10.2008 (week 43). On 28.10.2008, the dinoflagellates Ceratium tripos, Ceratium lineatum and Ceratium fusus and on 11. - 18.11.2008 (week 46 - 47), the diatom
Cerataulina pelagic dominated. Also Mesodinium rubrum was important.
The late occurrence of an autumn bloom of Coscinodiscus granii only on 16.12.2008 (week 51) was astonishing. We would expect it at outflow from the Baltic Sea, but the high salinity of 13.3 suggests rather inflow or upwelling.
Our data from the first half of the year 2008 showed again that this coastal station Heiligendamm is not optimal for recording the phytoplankton succession. The general phytoplankton development is well reflected (e.g. timing of the bloom, magnitude of biomass). However, abrupt changes in species composition cannot be considered in the sense of succession. They are based on macro-scale differences in species composition which become apparent if
the different water bodies are drifting along the fixed station. A combination with monitoring data from the open sea and with currents data would allow to describe even spatial heterogeneities. The data of the HELCOM monitoring are, however, available only with a long delay.
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.
Sarno, D., Kooistra, W.H.C.F., Medlin, L., Percopo, I., Zingone, A. (2005). Diversity in the genus Skeletonema (Bacillariophyceae). II. An assessment of the taxonomy of S. costatum-like species with the description of four new species. J. Phycol. 41, 151-176.
Wasmund, N., Topp, I., Schories, D. (2006): Optimising the storage and extraction of chlorophyll samples.
Oceanologia 48: 125-144.
Wasmund, N., Pollehne, F.; Postel, L., Siegel, H., Zettler, M.L. (2008): Biologische Zustandseinschätzung der Ostsee im Jahre 2007. Meereswiss. Ber., Warnemünde, 74, 88 pp.
Figure 1: Composition of the phytoplankton biomass and concentration of chlorophyll a from 2.1. to 16.12.2008 at sea-bridge Heiligendamm.