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Abstract:
This study represents the efforts of a network of researchers to characterise the large, floating Sargassum (Fucales, Phaeophyceae) biomass that had reached the Brazilian coast in 2014 and 2015. Material collected during these events was identified as Sargassum natans and S. fluitans using morphological characteristics; ITS2 sequences showed low divergence (0%–3%) with sequences of nine other Sargassum species. Several epiphytic macroalgae, invertebrates and fishes were associated with the floating Sargassum. Satellite images did not support the hypothesis of slicks moving south from the Sargasso Sea in the northern Atlantic Ocean. This strengthens the hypothesis that there is a matrix of pelagic Sargassum in the central Atlantic Ocean and that biomass accumulation should be considered a result of the combination of physicochemical seawater conditions and biological interactions. The biomass accumulation of the stranded Sargassum was estimated during four events, peaking in 98 kg m−2 wet weight on a beach on the Amazonian coast. The landing of huge Sargassum biomass represents a potential source of environmental stress, as it can lead to an increase in oxygen demand and eventually synthesise and release chemical compounds with allelopathic properties. On the other hand, these floating islands are a fundamental element of the biogeography and macroecology of tropical environments in the Atlantic Ocean, providing connectivity south/north and east/west among marine biodiversity from Atlantic reef environments. Studies concerning Sargassum effects on local communities are necessary for the proper management of this phenomenon.
ACKNOWLEDGEMENTS
Financial support was provided by CNPQ (National Council for Scientific and Technological Development) (PROSPECMAR 458548/2013-8). M.N.S. was granted with a scholarship from CNPq (383753/2014-7). P.H. thanks the CNPq grant as well as CNPq/PROTAX, Coordination for the Improvement of Higher Education Personnel (CAPES), Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina (FAPESC), PELD and Fundação Grupo Boticário de Proteção à Natureza for financial support. M.C.O. thanks CNPq and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for financial support. The authors also thank the opportunities provided by INCT REDECLIMA, REBENTOS and CORAL VIVO for providing network maintenance and developing.
DEDICATION
We dedicate this work to the coauthor, friend and exemplary phycologist, Rafael Riosmena-Rodrígues.
SUPPLEMENTARY DATA
Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/16-92.1.s1.