Despite their cosmopolitan distribution, knowledge on cyanobacteria in the family Coelosphaeriaceae is limited. In this study, a single species culture of a coelosphaeran cyanobacterium isolated from a brackish rock pool in the Baltic Sea was established. The strain was characterized by morphological features, partial 16S rRNA sequence and nonribosomal oligopeptide profile. The bioactivity of fractionated extracts against several serine proteases, as well as protein-serine/threonine phosphatases was studied. Phylogenetic analyses of the strain suggested a close relationship with Snowella litoralis, but its morphology resembled Woronichinia compacta. The controversial morphologic and phylogenetic results demonstrated remaining uncertainties regarding species division in this cyanobacteria family. Chemical analyses of the strain indicated production of nonribosomal oligopeptides. In fractionated extracts, masses and ion fragmentation spectra of seven possible anabaenopeptins were identified. Additionally, fragmentation spectra of cyanopeptolin-like peptides were collected in several of the fractions. The nonribosomal oligopeptide profile adds another potential identification criterion in future inter- and intraspecies comparisons of coelosphaeran cyanobacteria. The fractionated extracts showed significant activity against carboxypeptidase A and trypsin. Inhibition of these important metabolic enzymes might have impacts at the ecosystem level in aquatic habitats with high cyanobacteria densities.

Studies of rock pools tend to focus on the surrounding emergent habitat. Moreover, research on phytoplankton in small, nutrient-rich water bodies is limited. Summer phytoplankton species, functional groups and life strategies, as well as physicochemical variables potentially influencing the phytoplankton, were surveyed in 34 brackish rock pools. Except from total nitrogen and total phosphorus, the pools were chemically quite similar. Phytoplankton abundance and biovolume consisted mainly of charophytes (Zygnematales), unidentified small flagellates, cyanobacteria, chlorophytes and dinoflagellates. Many of the phytoplankton functional groups were representative of shallow, nutrient-rich and light-abundant environments. The majority of the common and abundant species were classified as C-strategists (invasive opportunists). Total nitrogen, total phosphorus and phytoplankton biomass varied greatly between the rock pools, and were positively related. The rock pool depth and macrovegetation presence–absence played a central role in shaping the phytoplankton species distribution. Frequently occurring species, present in the majority of the rock pools, seldom dominated the phytoplankton. Species dominating the phytoplankton rock pool assemblages were not common components of the phytoplankton flora.

Phytoplankton temporal fluctuation and vertical distribution were studied by seasonal and close interval siphon sampling (May-Sep) in a shallow lake dominated by common water milfoil (Myriophyllum sibiricum). Factors potentially regulating phytoplankton primary production were investigated in situ in 2 enrichment bioassays. The results suggest that the macrophyte vegetation provided an unfavourable habitat for large colonial chlorophytes. Small species, mainly cryptophytes but also small chlorophytes and cyanobacteria, characterised the summer phytoplankton. Phytoplankton abundance as well as primary production were considerable and remained in the mesotrophic range. The total nitrogen to total phosphorus ratio during the growth season, and the enrichment bioassays, showed that phosphorus was a significant regulator of primary production. Small-celled species had competitive advantages in the dense vegetation, and the canopy structure created by dense stands of common water milfoil allowed phytoplankton growth. Hence, although the macrophytes altered the physical and chemical conditions in the lake, coexistence of small-celled algae and macrophytes was possible.