Lipid biomarker signatures as tracers for harmful cyanobacterial blooms in the Baltic Sea

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.

The Holocene sedimentary record of cyanobacterial glycolipids in the Baltic Sea: an evaluation of their application as tracers of past nitrogen fixation

“…4a, summarized in Table 1), agrees well with the HG distribution in cultures of Nodularia, Aphanizomenon and Anabaena as well as other members of the Nostocaceae family (Table 1), including those that have been isolated from the Baltic (Bauersachs et al, 2009a(Bauersachs et al, , 2017. These cultures generally also synthesized minor amounts of the C 26 keto-ol HG, as was seen in the MoWP sediments.…”

“…The C 28 diol was often dominant and both the C 26 and C 28 keto-ol were present in a higher proportion than during the Bauersachs et al (2009a). b Bauersachs et al (2017). c Wörmer et al (2012).…”

“…Bauersachs et al (2017) have recently analyzed the HGs of eight representative heterocystous cyanobacterial strains isolated from the Baltic Sea, and the six C 6 HGs targeted in our study (a) (b) Figure 4. Distribution of HGs, displayed as fractional abundance (%) vs. depth (in cm) for (a) the MUC P435-1-4 core and (b) the GC 303 600 core.…”

Reconstructing N<sub>2</sub>-fixing cyanobacterial blooms in the Baltic Sea beyond observations using 6- and 7-methylheptadecanes in sediments as specific biomarkers

“…However, the profile was dominated by 7Me-C17:0 and 6-methylheptadecane (6Me-C17:0), which together accounted for 65% to 88% of 85 all hydrocarbons. As 6Me-C17:0 and 7Me-C17:0 were not detected in the other heterocystous cyanobacteria investigated (with the exception of 7Me-C17:0 occurring in minor abundance in the Aphanizomenon strain), they can be considered as most diagnostic for tracing planktonic cyanobacteria of the genus Nodularia in the Baltic Sea (Bauersachs et al, 2017). Indeed, 7Me-C17:0 has been found in the surface waters of the central Baltic Sea (Landsort Deep) in summer (Berndmeyer et al, 2014).…”

“…Branched alkanes, most commonly as 7-methylheptadecane, were predominantly observed in particular clades including heterocystous, ramified and some filamentous cyanobacteria, and rarely in unicellular cyanobacteria (Liu et al, 2013;Coates et al, 2014). Recently, Bauersachs et al (2017) examined the lipid profiles of heterocystous cyanobacteria strains belonging to the genera Dolichospermum, Aphanizomenon and Nodularia, isolated from the Baltic Sea. Mid-chain branched alkanes were not detected in any of the investigated Dolichospermum strains, although 7-methylheptadecane (7Me-C17:0) and 8-80 methylheptadecane (8Me-C17:0) have been reported in a representative of this genus before (Coates et al, 2014;Fehler and Light, 1970).…”