CYANOBACTERIAL HETEROCYST GLYCOLIPIDS ASSOCIATED WITH THE FLOATING MACROALGA SARGASSUM

Summary Species of the floating macroalga Sargassum occur in a range of marine settings, in particular the tropical North Atlantic. Recently, inundations of Sargassum washing ashore particularly in the Caribbean, have been a socio-economic and ecological concern. Since abundance records of floating Sargassum are limited, geological sediment cores could provide clues as to the causes of the accumulations and help with predicting future growth dynamics. Open-ocean Sargassum sinks as it ages with remnants observed both on the seabed and buried in sediments. Floating Sargassum provides a habitat for many microorganisms, including N2 fixing cyanobacteria. Heterocyst glycolipids (HGs) have proven to be highly specific biomarkers for heterocystous N2 fixing cyanobacteria. HGs with hexose (C6) head groups are generally associated with free-living cyanobacteria while those with pentose (C5) head groups have been found mainly in endosymbiotic species (found within diatoms). These HGs have been used to trace the cyanobacterial occurrence and activity back in the geological record. We hypothesize that past occurrence of Sargassum can be traced in the sediment record using HGs as a quasi-biomarker for Sargassum. In this study, we looked at the HG distribution in two Sargassum species collected across the tropical North Atlantic and in associated underlying surface sediments.