Sargassum(Fucales, Phaeophyceae) in Mauritius and Réunion, western Indian Ocean: taxonomic revision and biogeography using hydrodynamic dispersal models

Abstract

Mauritius and Réunion are part of the Mascarene Islands situated in the southwestern Indian Ocean, c. 800 km east of Madagascar. A total of 44 different Sargassum species and subspecific taxa was listed in the literature for these islands. This was a remarkable number for such isolated and small islands, and was more than have been recorded from Madagascar or other East African countries. The first aim of our study was to revise these species lists using newly collected specimens to provide a reliable and illustrated tool for the identification of the Mauritian and Reunion Sargassum On the basis of morphological and molecular analyses, a total of six taxa was identified as S. cymosum f. borbonicum S obovatum, S. pfeifferae (reinstated), S. polycystum, S. portierianum and S. robillardii (stat. nov.). A seventh taxon S scopula, was identified from a herbarium collection but not re-collected. As a result of our taxonomic revision, we concluded that most of the species listed in the literature for both Mauritius and Réunion were misidentifications or synonyms, and we proposed three new taxonomic synonyms. The biogeography of the six Sargassum taxa was further investigated using local and regional hydrodynamic dispersal models. Results underlined the isolated position of the Mascarene Islands with (1) unlikely import o[ Sargassum in present-day conditions, (2) likely dispersal/exchanges withm the archipelago and (3) a two-pronged export of Sarga.ssum to the east coast of Madagascar and the Seychelles with a major stream northwestward and a weaker stream south westward. These oceanic conditions had probably shaped the Sargassum diversity of the Mascarene Islands and in particular explained the endemicity of 5. cymosum f borbonicum and restricted distribution of S. obovatum, S. pfeifferae, S. robillardii and S. scopula.

A revision of the genus Sargassum (Fucales, Phaeophyceae) in South Africa

“…Examination of Linnaeus' type of S. lendigerum (LINN1274.44) led us to the conclusion that Grunow's specimens collected from Port Natal by Gueinzius (Grunow, 1916, p. 139) could have been a misidentification of S. elegans. Similarly, the record of S. portierianum f. lendigerioides Setchell (= S. portierianum Zanardini, see Mattio et al, 2013) from Port Natal by Setchell in Børgesen (1941) may have been a misidentification of an ecotype of the same species. The taxonomic confusions pertaining to taxa belonging to the "cymosum-lendigerumportierianum" group is discussed by Mattio et al (2013).…”

“…Samples were preserved in silica gel and processed in part at the Central Analytical Facility, DNA sequencer, Stellenbosch University (South Africa) following Mattio et al (2013) and in part at the Systematic Lab, Department of Biological Sciences, University of Cape Town (South Africa) following . The nuclear ITS-2 (Internal Transcribed Spacer 2), chloroplastic partial RuBisCO operon, mitochondrial cox3 (Cytochrome c Oxydase subunit 3) and mt23S (mitochondrial ribosomal DNA 23S subunit) regions were PCR amplified using primers listed in Mattio et al (2013).…”

“…The nuclear ITS-2 (Internal Transcribed Spacer 2), chloroplastic partial RuBisCO operon, mitochondrial cox3 (Cytochrome c Oxydase subunit 3) and mt23S (mitochondrial ribosomal DNA 23S subunit) regions were PCR amplified using primers listed in Mattio et al (2013). All PCR products were purified and sequenced at the Central Analytical Facility using respectively the NucleoFast membrane (Machery-Nagel, Düren, Germany) on a Freedom Evo robot (Tecan Group Ltd., Männedorf, Switzerland) and the BigDye Terminator v3.1 sequencing kit (Life Technologies, Johannesburg, South Africa).…”

“…Literature pertaining to the listing and description of species in South Africa and the region (Bory de Saint-Vincent, 1828; Von Suhr, 1840;Kützing, 1861;Grunow, 1868Grunow, , 1915Grunow, , 1916Juel, 1918;Stephenson et al, 1937;Papenfuss, 1940;Stephenson, 1944Stephenson, , 1948Papenfuss, 1952;Isaac, 1957;Isaac and Chamberlain, 1958;Price et al, 1978;Seagrief, 1984;Stegenga, 1987, 1990;Jackelman et al, 1991;Farrell et al, 1993;Silva et al, 1996;Stegenga et al, 1997;De Clerck et al, 2005;Oliveira et al, 2005;Mattio et al, 2013), further studies including information on within taxon morphological variation (Mattio et al, 2008, and additional historical diagnoses of various species for the genus (Agardh, 1820(Agardh, , 1824(Agardh, , 1848(Agardh, , 1889 were used for preliminary identification of morphotaxa. Phylogenetic trees were then used to challenge the grouping of specimens based on morphological analysis, as well as a tool to help with identification when sequences clustered with published reliably identified specimens, or sequences obtained from type localities.…”

“…Phylogenies of the genus have been built using various selections of nuclear (ITS), chloroplastic (psaA, RuBisCO spacer, rbcL) and mitochondrial (COI, cox3, 23S-tRNA Val spacer and partial mt23S) markers (e.g. Phillips and Fredericq, 2000;Stiger et al, 2000;Mattio et al, 2008Mattio et al, , 2013Cho et al, 2012). Several significant changes in the classification of the genus as well as a number of new taxonomic synonymies have been proposed, tending towards a simplification of the genus' taxonomy and a reduction in the number of species recorded in areas studied (e.g.…”