Abstract
Cyanobacteria are found worldwide in various habitats. Members of the picocyanobacteria genera Synechococcus and Prochlorococcus dominate in oligotrophic ocean waters. Other picocyanobacteria dominate in eutrophic fresh or brackish waters. Usually, these are morphologically determined as species of the order Chroococcales/clade B2. The phytoplankton of a shallow, eutrophic brackish lagoon was investigated. Phytoplankton was dominated by Aphanothece-like morphospecies year-round for more than 20 years, along a trophy and salinity gradient. A biphasic approach using a culture-independent and a culture-dependent analysis was applied to identify the dominant species genetically. The 16S rRNA gene phylogeny of clone sequences and isolates indicated the dominance of Cyanobium species (order Synechococcales sensu Komárek/clade C1 sensu Shih). This difference between morphologically and genetically based species identifications has consequences for applying the Reynolds functional-groups system, and for validity long-term monitoring data. The literature shows the same pattern as our results: morphologically, Aphanothece-like species are abundant in eutrophic shallow lagoons, and genetically, Cyanobium is found in similar habitats. This discrepancy is found worldwide in the literature on fresh- and brackish-water habitats. Thus, most Aphanothece-like morphospecies may be, genetically, members of Cyanobium.
Highlights
Cyanobacteria live in most habitats worldwide and are important primary producers
We identified the dominant planktonic cyanobacteria of the Darß-Zingst Bodden chain (DZBC), using both culture-dependent and -independent approaches
Other brackish waters with described Aphanothece-like species are the Curonian Lagoon and Vistula Lagoon, which are located on the southern Baltic coast
Summary
Cyanobacteria often dominate the phytoplankton under meso- or eutrophic conditions. Very small single-cell cyanobacteria (< 2 μm; picocyanobacteria = APP) are most abundant in the oligotrophic open oceans. Most of these are assigned as species of Synechococcus and Prochlorococcus (Chisholm et al, 1992). But closely related, Synechococcus-like cyanobacteria succeed in eutrophic coastal waters (Caroppo, 2015 and references therein). Different cyanobacteria inhabit and can sometimes dominate almost all aquatic systems, even under highly contrasting conditions. Most of these cyanobacteria are only assigned as Synechococcus-like organisms, knowing that the genus Synechococcus is polyphyletic (see Komárek et al, 2014 and references therein)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
