Abstract
The recent proliferation of harmful cyanobacterial blooms (cyanoHABs) in the Baltic and other marginal seas poses a severe threat for the health of infested ecosystems as e.g. the massive export and decay of cyanobacterial biomass facilitates the spread of bottom water hypoxia. There is evidence that cyanoHABs occurred repeatedly in the Baltic Sea but knowledge of their spatiotemporal distribution and the cyanobacteria that contributed to them is limited. In this study, we examined representatives of the major bloom-forming heterocystous cyanobacteria (i.e. Aphanizomenon, Dolichospermum (formerly Anabaena) and Nodularia) to establish lipid fingerprints that allow tracking these environmentally important diazotrophs in the modern and past Baltic Sea. The distribution of normal and mid-chain branched alkanes, fatty acid methyl esters, bacteriohopanepolyols and heterocyst glycolipids permitted a clear chemotaxonomic separation of the different heterocystous cyanobacteria but also indicated a close phylogenetic relationship between representatives of the genera Aphanizomenon and Dolichospermum. Compared to the discontinuous nature of phytoplankton surveys studies, the distinct lipid profiles reported here will allow obtaining detailed spatiotemporal information on the frequency and intensity of Baltic Sea cyanoHABs as well as their community composition using the time-integrated biomarker signatures recorded in surface and subsurface sediments. As heterocystous cyanobacteria of the genera Aphanizomenon, Dolichospermum and Nodularia are generally known to form massive blooms in many brackish as well as lacustrine systems worldwide, the chemotaxonomic markers introduced in this study may allow investigating cyanoHABs in a great variety of contemporary environments from polar to tropical latitudes.
Highlights
Massive accumulation of unicellular and/or filamentous cyanobacteria—known as harmful cyanobacterial blooms—have significantly increased in abundance, intensity and duration in both brackish and freshwater environments over the last decades [1,2,3]
These results are well in line with the previously reported hydrocarbon distribution in freshwater representatives of this genus [34]. n-Heptadecane has been reported to be among the most prominent hydrocarbons in various cultured unicellular and filamentous heterocystous cyanobacteria [49,50,51]. It occurred in high abundances in hypersaline microbial mats [52] as well as hot springs [53, 54] and in such extreme environments is generally considered to be of cyanobacterial origin
N-C17:0 is present in many aquatic algae and photosynthetic bacteria [55] and in nonextreme environments it may not serve as an indicator for a cyanobacterial contribution to the sedimentary organic matter
Summary
Massive accumulation of unicellular and/or filamentous cyanobacteria—known as harmful cyanobacterial blooms (cyanoHABs)—have significantly increased in abundance, intensity and duration in both brackish and freshwater environments over the last decades [1,2,3]. In the modern Baltic Sea, cyanoHABs are frequent and during summer can cover large areas of surface water with profound impacts on the health of the aquatic ecosystem [4, 5]. The major bloom-forming diazotrophs in the contemporary Baltic Sea belong to three genera of filamentous heterocystous cyanobacteria including Aphanizomenon, Dolichospermum (previously classified as Anabaena) and Nodularia [11, 12] Representatives of these genera are considered important sources of combined N, as they add an estimated 180–420 Gg N yr-1 to the surface waters of the Baltic Sea, which is similar in magnitude to the entire riverine load and twice the atmospheric input [12, 13]. Current estimates on the future development of cyanobacterial blooms and their consequences for the Baltic Sea show, large uncertainties due to our incomplete understanding of the spatiotemporal distribution of cyanoHABs in the Baltic Sea over time and the anthropogenic as well as environmental controls that promote bloom formation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
