Understanding carbon fixation rates and biodiversity in and around wild and aquafarmed holopelagic Sargassum as crucial step towards resource valorisation

While Sargassum accumulations cause economic and environmental issues in the Caribbean, the macroalgae is discussed as a carbon dioxide removal option. Early cultivation attempts were made but the impact of Sargassum aquafarms on the surrounding biodiversity is poorly understood. To better understand its potential, it is crucial to quantify carbon fixation under different conditions both in the wild and in aquaculture. We investigated the carbon fixation rates of the three Sargassum morphotypes both during a cruise across the GASB and within an aquafarm in St Vincent and the Grenadines using 13C measurements. While controlled conditions lead to similar carbon fixation rates in GASB S. fluitans III and S. natans I, S. natans VIII showed significantly lower carbon uptake rates (p < 0.05). No significant differences between carbon fixation rates of aquafarmed and wild Sargassum could be observed in St Vincent. Using eDNA, we investigated the impact of wild and aquafarmed Sargassum on biodiversity of adjacent waters. While the wild algae present a unique habitat for a Sargassum-specific community, they do not impact the biodiversity of adjacent waters. We found that a Sargassum aquafarm does not change the biodiversity of surrounding waters in St Vincent. Our results indicate that aquafarmed Sargassum efficiently fixes carbon, even for an extended time period, without impacting the biodiversity of its surrounding environment. Our findings support the algae’s potential as a candidate for carbon dioxide removal, shifting its perception from harmful algae to valuable resource.

Presentation Preference: Oral

Primary Presenter: Katharina Paetz, Alfred-Wegener-Institut (katharina-paetz@gmx.net)

Authors:

Katharina Paetz, Alfred Wegener Institute (AWI)  (katharina-paetz@gmx.net)

Laura Laier, Alfred Wegener Institute (AWI)  (laierl@uni-bremen.de)

Jasmin Behnke, Alfred Wegener Insitute (AWI)  (jamsin.behnke@uni-oldenburg.de)

Miriam Philippi, Alfred Wegener Institute  (miriam.philippi@awi.de)

Franziska Elmer, Seafields Solutions Ltd  (Franziska.Elmer@seafields.eco)

Julia Schnetzer, Alfred Wegener Institute (AWI)  (jschnetzer@gmail.com)

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

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

Mar Fernández Méndez, Alfred Wegener Institute (AWI)  (mar.fernandez-mendez@awi.de)