Français
The phenomenon of sargassum stranding in the Caribbean in general, and on Saint-Barthélemy in particular, remains a matter of deep concern. For economic reasons, since the massive arrival of this brown algae on the coasts disrupts tourist activity, but also for ecological reasons. Stranded sargassum covers underwater biodiversity, but also causes significant damage when it enters the decomposition phase. However, we are currently investigating another factor that can have a detrimental effect on the ecosystem. The effects of collecting stranded seaweed on beaches. Sargassum also removes large quantities of sand.
Scientist Anaïs Coulon is attached to the Geography and Planning Laboratory at the University of Montpellier, and is working as a doctoral student on coastal dynamics. on coastal dynamics in Saint-Barthélemy with the Agence territoriale de l'environnement. For several months now, she has been conducting a study on the effects of sand collection associated with sargassum harvesting. This study is ongoing, and the conclusions are still far from being established.
Preserving biodiversity
Thirteen samples were taken by hand, using a backhoe and the Barber system. The samples were taken from several of the island's beaches. The aim was to compare the sargassum collected at the start of collection, during collection and at the very end of the operation. The samples collected were rinsed to recover the sand and separate it from the sargassum, then oven-dried so that the percentage of sand contained in a fixed-weight sample could be weighed. "The most important sand sampling usually occurs at the end of the collection, when the beach is thoroughly cleaned and no sargassum is left behind", emphasizes the scientist. This observation confirms that already established in a similar study carried out in both Guadeloupe and Martinique by scientist Franck Dolique. He wrote: "The comings and goings of heavy machinery, fitted with large tires, compact the sand, confirming the trend towards topographical degradation. ONCFS (Office nationale de la chasse et de la faune sauvage) also assumes that this compaction would have a consequent impact on the destruction of sea turtle egg-laying nests (ONCFS, 2015; Josso, 2016) and probably also, more broadly, on the beach ecosystem. "In his article, Franck Dolique makes a number of recommendations. During mass strandings, large volumes need to be collected quickly, as they act as a reflection wall for the waves, boosting their energy and causing significant demaigrination of the sand with export to the foreshore. In periods of average or low beachings, manual collection is preferred, with partial spreading of plant waste over the entire beach. He adds: "The thinness of the plant fibers then favors the propagation of the shore jet, effectively trapping the sand and contributing to the fertilization of the backshore plant banks as well as the foreshore seagrass beds. "
To sum up, collection cannot be carried out in a crude manner if the aim is to preserve coastal biodiversity. The results of the current study will certainly provide a better understanding of what is at stake in such a practice.
