Holopelagic species of the brown macroalga Sargassum create a vital and biodiverse habitat in the open Atlantic Ocean. However, over the past decade, floating Sargassum has started to produce nuisance blooms resulting in mass strandings on continental coastlines across the tropical and subtropical Atlantic. Hypotheses regarding the causes of these blooms, include the influence of nutrient runoff from the Amazon and Congo rivers, and a changing climate and oceanographic regimes, with the latter recently being experimentally supported. To understand the influence of nutrient increases on the growth of holopelagic Sargassum, we conducted ecophysiology experiments on board of a research vessel in the Great Atlantic Sargassum Belt (GASB), and ex-situ experiments on the Caribbean island of Curaçao. Our initial results reveal increases in the growth rates of Sargassum natans VIII and Sargassum natans I after the addition of nitrate, phosphate, and Saharan dust. Furthermore, the holopelagic Sargassum microbiomes undergo significant changes after nutrient pulses of phosphate and nitrate, possibly due to physiological changes in the Sargassum host. We combined our growth measurements with measurements of physiological and stoichiometric changes in Sargassum to better quantify the influence of varying nutrients on Sargassum ecophysiology and how this may differ per Sargassum species.

Primary Presenter: Tom Theirlynck, University of Amsterdam, NIOZ Institute (tom.theirlynck@nioz.nl)

Authors:

Tom Theirlynck, University of Amsterdam, NIOZ Institute  (tom.theirlynck@nioz.nl)

Lotte Staat, University of Amsterdam  (lotte.staat@student.uva.nl)

Dhaishendra Servania, University of Amsterdam  (dhaishendra_13@hotmail.com)

Marta Garcia Sanchez, Instituto de Ingeniería, UNAM  (martagarciasanchez81@gmail.com)

Erik Zettler, NIOZ Institute  (erik.zettler@nioz.nl)

Ricardo Leite, Instituto Gulbenkian de Ciência  (rleite@igc.gulbenkian.pt)

Brigitta van Tussenbroek, Instituto de Ciencias del Mar y Limnología-UNAM  (vantuss@cmarl.unam.mx)

Aschwin Engelen, Centro de Ciências do Mar  (aengelen@ualg.pt)

Petra Visser, University of Amsterdam  (p.m.visser@uva.nl)

Gerard Muyzer, University of Amsterdam  (g.muijzer@uva.nl)

Linda Amaral-Zettler, University of Amsterdam, NIOZ Institute  (linda.amaral-zettler@nioz.nl)