The influence of environmental factors on the growth of holopelagic Sargassum in the Great Atlantic Sargassum Belt (GASB)

In 2011, the first massive holopelagic Sargassum spp. (herein Sargassum) bloom was reported in the central Atlantic. Over the following years, the bloom developed into the Great Atlantic Sargasum Belt (GASB), extending from West Africa to the Gulf of Mexico. The Sargassum establishment in the GASB has raised questions about the main drivers associated with the blooms. It is hypothesized that an increase in nutrient input from rivers (e.g. Amazon, Orinoco, Congo), atmospheric dust (e.g. Saharan dust), or upwelling waters could significantly contribute to the rise in open-ocean Sargassum accumulations. However, direct evidence of the impact of these nutrient sources on Sargassum performance remains lacking. Access to the GASB from our research cruise, during the summer of 2024 from Guadeloupe to Cape Verde, gave us the opportunity to study these regional drivers. We performed controlled physiological experiments onboard, comparing the performance of oligotrophic “open ocean” Sargassum against its exposure to the Amazon River plume water, ocean water plus Saharan dust, and nutrient-rich “upwelled water” collected from below the mixed layer. By analyzing data on nutrient concentrations in the water, growth rate determination and photosynthetic efficiency through different experiments enabled us to assess the influence of these sources on the Sargassum performance. The results of this study explore the impact of different nutrient sources on the Sargassum growth and physiology and provide essential insights into the mechanisms underlying their dramatic proliferation in the region.

Presentation Preference: Oral

Primary Presenter: Fabio Nauer, Royal Netherlands Institute for Sea Research (NIOZ) (fabio.nauer@nioz.nl)

Authors:

Fabio Nauer, NIOZ Royal Netherlands Institute for Sea Research  (fabio.nauer@nioz.nl)

Edén Magaña-Gallegos, Instituto de Ciencias del Mar y Limnología-UNAM  (eden.maga@cmarl.unam.mx)

Juliane Vasconcelos, Universidade Federal de Pernambuco  (bernardijuliane@gmail.com)

Jesser de Souza-Filho, Universidade Federal de Pernambuco  (jesser.fidelis@ufpe.br)

Erik Zettler, NIOZ Royal Netherlands Institute for Sea Research  (erik.zettler@nioz.nl)

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

Linda Amaral-Zettler, NIOZ Royal Netherlands Institute for Sea Research  (linda.amaral-zettler@nioz.nl)