Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
The results of weekly sampling at the Heiligendamm pier (54°08,55' N; 11°50,60' E, 300 m off shore, 3 m water depth), performed by the Baltic Sea Research Institute Warnemünde (IOW), are shown in Figure 1. The line reflects the chlorophyll a concentration, and the columns the phytoplankton wet weight. The phytoplankton biomass was determined by microscopic counting, and the chlorophyll a concentration by ethanolic extraction and fluorometric measurement according to the HELCOM manual (http://www.helcom.fi/Monas/CombineManual2/CombineHome.htm).
Quantitative microscopic counting was not possible in weeks 3, 4, 7, 22, 29 and 48 because of high concentrations of
resuspended sediments in the samples due to strong wind.
As expected, phytoplankton biomass was low in January and February. A relatively large amount of
Cryptophyceae (Teleaulax spp.), besides the dinoflagellate Heterocapsa rotundata, occurred only on 17.2.2004 (week 8). On 9.3.2004 (week 11), the spring bloom reached its peak. It was dominated by Thalassiosira nordenskioeldii (1473 mg/m³), besides much lower biomasses of Skeletonema costatum (101 mg/m³), Chaetoceros cf. debilis (93 mg/m³), and Porosira glacialis (67 mg/m³). As early as 17.3.2004, Thalassiosira nordenskioeldii dropped to 87 mg/m³, while the biomass of Skeletonema costatum increased to 305 mg/m³. On 23.3.2004 (week 13), the bloom was over, which was confirmed by the chlorophyll a data. In 2003, the spring bloom occurred much earlier (on 26.2.2003) and was dominated by Skeletonema costatum (=1662 mg/m³). The biomass of the photoautotrophic ciliate Mesodinim rubrum stayed low, as in 2003.
On 6.4.2004, the naked form of the Chrysophyceae species Dictyocha speculum occurred, at 429 mg/m³. It remained the dominant or sub-dominant species until 29.6.2004 (week 27). The large diatom Dactyliosolen fragilissimus developed strongly from 2.6.2004. It increased to a peak biomass of 2757 mg/m³ by 22.6.2004 (week 26) but disappeared almost completely by 6.7.2004 (week 28). It was replaced by the large diatom Cerataulina pelagica (316 mg/m³) on 20.7.2004 (week 30). By 3.8.2004, it had decreased to 56 mg/m³ while the summer cyanobacteria Nodularia spumigena, Aphanizomenon sp. and Anabaena spp. developed. However, in contrast to the previous year, the cyanobacteria did not form a bloom. By 10.8.2004 (week 33), concentrations of the cyanobacteria Nodularia spumigena, Aphanizomenon sp. and Anabaena spp. had already decreased. Also the summer diatoms (Cerataulina pelagica, Proboscia alata, Dactyliosolen fragilissimus) disappeared, whereas the slow growth of the typical dinoflagellate Ceratium tripos continued. Cryptophyceae (Plagioselmis prolonga) developed as well. All species decreased by 24.8.2004 (week 35). A large biomass of dinoflagellates (Ceratium tripos, Prorocentrum micans, Heterocapsa rotundata) appeared on 31.8.2004 but decreased only one week later. Surprisingly, Nodularia spumigena reappeared in week 37 but finally disappeared in week 39 (21.9.2004). Dinoflagellates (Ceratium tripos, C. fusus, Prorocentrum micans) continued to grow. An unusual bloom of the potentially toxic diatom Pseudonitzschia cf. pungens (349 mg/m³) was observed; the last bloom of this species was recorded in October 1999. At the same time (5.10.2004, week 41), also Cerataulina pelagica, Guinardia flaccida and Ceratium tripos were frequent.
The typical autumn dinoflagellates (Ceratium tripos, C. fusus, Prorocentrum micans) dominated on 19.10. and 2.11.2004 (weeks 43 and 45). Afterwards, their biomass decreased sharply. Nevertheless, the diversity was rather high in mid-December, with more than 40 identified
taxa. It consisted mainly of diatoms (Proboscia alata, Guinardia flaccida, Thalassiosira anguste-lineata, Thalassionema nitzschioides, Chaetoceros curvisetus, Ditylum brightwellii, Cerataulina pelagica), dinoflagellates (Ceratium tripos, Heterocapsa rotundata) and cryptophyceae (Teleaulax sp., Plagioselmis prolonga).
Figure 1: Chlorophyll a concentration and composition of phytoplankton biomass
(wet weight) from 6.1. to 28.12.2003 at the coastal station Heiligendamm (surface water).