Host-microbe interactions in the holopelagic brown macroalga Sargassum

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. 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, but also its associated microbial communities. Microbial communities can have beneficial environmental functions in Sargassum, 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. So far knowledge of the diversity and biogeography of Sargassum-associated microbial communities is limited. Moreover, microbial interactions between the host and microbe in the Sargassum holobiont are largely unknown. Therefore, this project aims to elucidate the composition of the microbial community and the nature of the host-microbe interactions in holopelagic Sargassum and its associated epifauna.

Scientists involved in this research

Tom Theirlynck (NIOZ-UvA)
Linda Amaral-Zettler (NIOZ-UvA)
Gerard Muyzer
Petra Visser
Henk Bolhuis (NIOZ)
Evelien Jongepier

In cooporation with

Aschwin Engelen (CCMAR, Faro, Portugal)
Klaas Timmermans (NIOZ)


  1. Diversity of the holopelagic Sargassum microbiome from the Great Atlantic Sargassum Belt to coastal stranding locations.

    Tom Theirlynck, Inara Regina W. Mendonça, Aschwin H. Engelen, Henk Bolhuis, Ligia Collado-Vides, Brigitta I. van Tussenbroek, Marta García-Sánchez, Erik Zettler, Gerard Muyzer, Linda Amaral-Zettler,Harmful Algae,Volume 122,2023,102369,ISSN 1568-9883,