At NIOZ we aim to elucidate the composition of the Sargassum holobiome and determine the nature of the host-microbe interactions in holopelagic Sargassum. We use techniques such as amplicon sequencing, metagenomics, and metatranscriptomics to explore the Sargassum holobiome.

The golden floating rainforest

Sargassum is one of the most diverse marine macroalgal genera with over 350 recognized benthic species but only two holopelagic (floating) species: S. fluitans and S. natans. Sometimes referred to as the 'Golden floating rainforest of the Atlantic Ocean', holopelagic Sargassum is considered an essential habitat for both attached and mobile fauna that contribute to its unique biodiversity. However, the holopelagic species of Sargassum that are normally associated with the Sargasso Sea, have begun forming unprecedented accumulations and subsequent strandings on the western coast of Africa, several islands in the Caribbean, including the Netherlands Antilles, Mexico, the Gulf of Mexico, and northern Brazil.

Local threats

These accumulations threaten local biodiversity and trigger economic losses associated with beach deterioration and impact on fisheries, tourism and national marine sanctuaries. An important realization is that in these strandings it is not only the macroalga Sargassum that washes ashore on the coasts of the Caribbean but the Sargassum holobiome: a rich collection of organisms including the microbial communities that reside on Sargassum. Microbial communities can have beneficial environmental functions in macroalgae, for example being responsible for nitrogen fixation. However, certain groups of marine macroalgae-associated microbes can also be pathogenic and a potential source of disease. Questions remain on how Sargassum microbial communities differ on the basis of species and biogeography. Moreover, microbial interactions between hosts and microbes in the Sargassum holobiome are largely unknown.