Growth experiments of two Sargassum genotypes (S. fluitans III and S. natans VIII) and study of the impacts of exposure to metals (iron, arsenic) in the Great Atlantic Sargassum Belt (GASB)

Since 2011 the northern tropical Atlantic in the North Equatorial Recirculation Region (NERR) has seen repeating blooms of holopelagic Sargassum species, creating the ‘Great Atlantic Sargassum Belt’ extended for 8850-km length which stretches from tropical Africa to the Gulf of Mexico. Sargassum's ability to absorb metals, including arsenic (As) and iron (Fe), raises concerns about potential physiological impacts, especially on its growth. Arsenic is a toxic metalloid, and iron, though essential for cellular processes like photosynthesis, can be harmful in high concentrations. This study aimed to (i) develop a growth system for Sargassum onboard a research cruise, (ii) investigate the effects of metal bioaccumulation on growth rates, and (iii) determine the speciation of bioaccumulated arsenic. Morphotype S. fluitans III and S. natans VIII were grown for five days under controlled conditions with seawater from different locations along the cruise and various iron and arsenic concentrations. Growth parameters such as wet weight, number of bladders, number of secondary branches, thickness of primary strand and branch lengths were evaluated, while metal concentrations were measured in sargassum tissues as well as in water using simultaneously DGTs and water samples. Growth rates were determined as a percentage of growth. Initial findings indicate that iron and arsenic contamination result in complex growth adaptations in Sargassum, with different responses in each growth parameter depending on the presence or absence of contamination.

Presentation Preference: Oral

Primary Presenter: Marine Guilbaud, La Sorbonne Université (guilbaudmarine.pro@gmail.com)

Authors:

Marine Guilbaud, La Sorbonne Université  (guilbaudmarine.pro@gmail.com)

Magalie Baudrimont, Université de Bordeaux  (magalie.baudrimont@u-bordeaux.fr)

Débora Héroin, Université de Bordeaux  (debora.heroin@u-bordeaux.fr)

Linda Amaral-Zettler, NIOZ  (linda.amaral-zettler@nioz.nl)

Yann Combes, Université de Bordeaux  (yann.combes@u-bordeaux.fr)

Emilie Dassié, Université de Bordeaux  (emilie.dassie@u-bordeaux.fr)

Benoit Simon-Bouhet, La Rochelle Université  (bsimonbo@univ-lr.fr)

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

Pierre-Yves Pascal, Sorbonne Université  (pierreyves.pascal@gmail.com)