title: Comparative mitochondrial and chloroplast genomics of a genetically distinct form ofSargassumcontributing to recent "Golden Tides" in the Western Atlantic.
abstract: Over the past 5 years, massive accumulations of holopelagic species of the brown macroalgaSargassumin coastal areas of the Caribbean have created "golden tides" that threaten local biodiversity and trigger economic losses associated with beach deterioration and impact on fisheries and tourism. In 2015, the first report identifying the cause of these extreme events implicated a rare form of the holopelagic speciesSargassum natans(formVIII). However, since the first mention ofS. natans VIIIin the 1930s, based solely on morphological characters, no molecular data have confirmed this identification. We generated full-length mitogenomes and partial chloroplast genomes of all representative holopelagicSargassumspecies,S. fluitans IIIandS. natans Ialongside the putatively rareS. natans VIII, to demonstrate small but consistent differences betweenS. natans IandVIII(7 bp differences out of the 34,727). Our comparative analyses also revealed that bothS. natans IandS. natans VIIIshare a very close phylogenetic relationship withS. fluitans III(94- and 96-bp differences of 34,727). We designed novel primers that amplified regions of thecox2andcox3marker genes with consistent polymorphic sites that enabled differentiation between the twoS. natansforms (IandVIII) from each other and both fromS. fluitans IIIin over 150Sargassumsamples including those from the 2014 golden tide event. Despite remarkable gene synteny and sequence conservation, the threeSargassumforms differ in morphology, ecology, and distribution patterns, warranting more extensive interrogation of holopelagicSargassumgenomes as a whole.
authors.affiliation: Marine Biological Laboratory Josephine Bay Paul Center for Comparative Molecular Biology and Evolution Woods Hole MA USA; Department of Earth, Environmental, and Planetary Sciences Brown University Providence RI USA.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Amaral-Zettler
authors.affiliation: Sea Education Association Woods Hole MA USA.
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Dragone
authors.affiliation: Sea Education Association Woods Hole MA USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Schell
authors.affiliation: Marine Biological Laboratory Josephine Bay Paul Center for Comparative Molecular Biology and Evolution Woods Hole MA USA.
authors.forename: Beth
authors.initials: B
authors.lastname: Slikas
authors.affiliation: Marine Biological Laboratory Josephine Bay Paul Center for Comparative Molecular Biology and Evolution Woods Hole MA USA.
authors.forename: Leslie G
authors.initials: LG
authors.lastname: Murphy
authors.affiliation: St. George's University Grenada West Indies.
authors.forename: Clare E
authors.initials: CE
authors.lastname: Morrall
authors.affiliation: Sea Education Association Woods Hole MA USA; Oekologia Environmental Research & Education Falmouth MA USA.
authors.forename: Erik R
authors.initials: ER
authors.lastname: Zettler
keywords: Sargasso Sea; accumulations; chloroplast genome; macroalgae; mitogenome; strandings