Morphological and Molecular Characters Differentiate Common Morphotypes of Atlantic Holopelagic Sargassum

• Published in: Phycology
• Main Authors: Amy N. S. Siuda, Aurélie Blanfuné, Skye Dibner, Marc Verlaque, Charles-François Boudouresque, Solène Connan, Deborah S. Goodwin, Valérie Stiger-Pouvreau, Frédérique Viard, Florence Rousseau, Valérie Michotey, Jeffrey M. Schell, Thomas Changeaux, Didier Aurelle, Thierry Thibaut
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2024
• Subjects: holopelagic Sargassum; North Atlantic Ocean; phylogeny; Sargassum natans var . wingei; Neurosciences. Biological psychiatry. Neuropsychiatry; RC321-571; Biology (General); QH301-705.5; North Atlantic
• Online Access: https://doi.org/10.3390/phycology4020014; https://doaj.org/article/784536a703b945c0b389c54f44508f7e

Since 2011, massive new strandings of holopelagic Sargassum have been reported on the coasts of the Caribbean, northern Brazil, Guiana, and West Africa, causing severe economic and ecological damage. Three common morphotypes ( S. fluitans III, S. natans I, and S. natans VIII) were identified as responsible for these catastrophic events, with dominance shifts between them over time. However, the taxonomic status of these holopelagic Sargassum morphotypes remains unclear. Using an integrative taxonomy framework, combining a morphological study and molecular analyses, this study aimed to clarify their taxonomic status. Morphological analyses of 54 characters revealed no intermediate form between the three morphotypes, with the overall shape, nature of the axis, and size and shape of blades and vesicles being the most discriminating. An analysis of mitochondrial ( IGS , cox2 , cox3 , mt16S rRNA , and nad6 ) and plastid ( rbcL ) markers confirmed the genetic divergence among the three morphotypes, with a lower level of divergence between the two S. natans morphotypes. Without additional molecular characterization, these morphotypes cannot be classified as three distinct species. However, due to their distinct morphological characteristics and sympatry within drifting aggregations, a revision of holopelagic species names is proposed, with Sargassum fluitans var. fluitans (for S. fluitans III), Sargassum natans var. natans (for S. natans I), and S. natans var. wingei (for S. natans VIII ) . This revision provides necessary clarity on the species involved in inundations of the tropical Atlantic.