Sargassum Differentially Shapes the Microbiota Composition and Diversity at Coastal Tide Sites and Inland Storage Sites on Caribbean Islands.

Vincent Hervé,Pascal Jean Lopez,Damien Alain Devault,Josie Lambourdière,Malika René-Trouillefou

doi:10.3389/fmicb.2021.701155

Abstract

Rafts of drifting pelagic Sargassum that are circulating across the Atlantic Ocean are complex ecosystems composed of a large number of associated species. Upon massive stranding, they lead to various socio-environmental issues including the inflow of contaminants and human health concerns. In this study, we used metabarcoding approaches to examine the differences in both the eukaryotic- and prokaryotic-associated communities from Sargassum present in two islands of the Lesser Antilles, namely Guadeloupe and Martinique. We detected significant differences in microbial community structure and composition between landing Sargassum, the surrounding seawater, and Sargassum from inland storage sites. In total we identified 22,214 prokaryotic and 17,679 eukaryotic OTUs. Among them, functional prediction analyses revealed a number of prokaryotes that might contribute to organic matter decomposition, nitrogen cycling and gas production, including sulfate-reducing bacteria at coastal landing sites, and methanogenic archaea at inland storage sites. We also found that Metazoan was the most abundant group in Sargassum samples, with nematode clades that presented exclusive or specific richness and abundance patterns depending on their Sargassum substrate. Together, these molecular inventories of the micro- and meiofauna communities provide baseline information for further characterization of trophic interactions, algal organic matter decomposition and nutrient transfers at coastal and inland storage sites.

Highlights

Numerous seaweeds, including benthic and drifting pelagic Sargassum species, are becoming invasive in various regions of the world, creating potential threats to native species and local resources, and causing economic and health concerns (Hu and Fraser, 2016)
When comparing the communities associated to Sargassum collected at tide sites compared to Sargassum from inland storage sites, we identified 146 prokaryotic and 32 eukaryotic operational taxonomic units (OTUs) with differential abundance (Figures 5C,D and Supplementary Table 2)
Among the 24 OTUs that were significantly associated with the TS-sarg samples, we found one OTU assigned to a toxic dinoflagellate of the Amphidinium carterae species, another to Ulvella that are endophytic microalgae, one related to the raphid diatom genus Aneumastus, one OTU with the best BLASTN results as Sargassococcus simulans, an epiphyte on floating Sargassum thallus, isolated in the Sargasso Sea, one to the copepod genus Zaus, which are organisms living in the phytal zone, and five OTUs belonging to Hydrozoans, which are frequently encountered as Sargassum epibionts (Huffard et al, 2014)

Summary

Introduction

Numerous seaweeds, including benthic and drifting pelagic Sargassum species, are becoming invasive in various regions of the world, creating potential threats to native species and local resources, and causing economic and health concerns (Hu and Fraser, 2016). The whole Caribbean region and the west coast of Africa have been faced with massive tides of Sargassum (Wang et al, 2019). These holopelagic macroalgae shoals contains several morphotypes, with the most common one being S. fluitans and S. natans (Parr, 1939; Schell et al, 2015; Amaral-Zettler et al, 2017; Martin et al, 2021). The microbial communities that are associated with the seaweeds can thrive in new habitats, as postulated for the export of surface-dwelling fauna associated with Sargassum from the surface down to the seafloor (Baker et al, 2018)

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