The unusual massive beaching of Sargassum around Dakar Peninsula (Senegal, Africa) in autumn 2022: opportunity or threat
Résumé
Huge strandings of holopelagic Sargassum along the Senegalese coast were observed throughout the
summer of 2022. The unusual nature of such stranding has mobilized the community, sparking questions
from civic society and industrialists. We report on this Sargassum arrival to participate in a global
scientific endeavour and to inform local stakeholders. Volunteers reported stranding from north to south
of Senegal, harming the coastal life, including turtle fatalities. We analyzed the stranded biomass for
taxonomic identity and heavy metal concentrations (As, Cd, Pb and Hg). We differentiated the
Sargassum collected into six morphotypes based on morphological details. We noticed the presence of
the species S. natans I, S. fluitans III and S. natans VIII. Chemical nuclear magnetic resonance (HRMAS
NMR) fingerprintings were obtained to compare morphotypes and sampling sites. In comparison
to previous studies throughout the tropical Atlantic Ocean, preliminary analyses revealed low quantities
of arsenic and high concentrations of cadmium and mercury in the thalli. For all these heavy metals
except lead, the concentrations are higher in S. natans I. Arsenic concentrations were variable between
sampling sites but lead and mercury concentrations were spatially homogeneous. For agricultural
purposes, the maximum values for As and Cd were above some recommended limits. For animal feed,
all As concentrations were below the permissible level (40 ppm EU, European Union). Additional
analyses are underway to validate these first results and study the biochemical composition of the
samples.
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