Rahanna Juman,
Institute of Marine Affairs
For yet another year, massive quantities of sargassum are seen washing up along our coasts and is causing concern among fisherfolk and other beach users. This new source of sargassum is now linked to climate change and ocean eutrophication, and these are likely to continue supporting significant sargassum blooms into the future. As such, annual mass influxes of sargassum into the Caribbean Sea are now being considered as the new normal, requiring sustainable management responses and long-term adaptation (Desrochers et al. 2020).
Pelagic (free-floating) sargassum, a brown algae from the equatorial Atlantic, comprises a mixture of two or possibly three different sargassum species, namely sargassum fluitans III, sargassum natans I, and sargassum natans VIII (Schell, Goodwin, and Siuda 2015) that forms large floating mats often referred to as “golden tides.” These species are unique in that they are the only sargassum species to spend their entire lifecycle afloat, instead of attached to the seafloor. As such, they are considered to be holopelagic, and to only occur in the Atlantic Ocean (Desrochers et al. 2020). The Atlantic holopelagic sargassum is also thought to only reproduce vegetatively through growth and fragmentation, and is able to double its biomass very quickly under the right conditions (nine to 20 days; Hanisak and Samuel 1987, Lapointe 1986).
Field surveys and satellite maps have indicated that sargassum blossoms naturally in the warm waters of the Atlantic Ocean; the Tropical South Atlantic and in the North Atlantic including the Sargasso Sea. Since 2011, there have been several episodes of unusual quantities of sargassum reaching the coasts of many of the islands of the Caribbean Sea and West Africa, but where is it coming from?
In 2013, satellite images showed sargassum concentrated in the tropical North Atlantic over 600 km offshore from South America, to the north and west of the mouth of the Amazon River. For about 18 months prior to landing in 2013, a trace from the sargassum sighting location was made using a high-resolution numerical ocean current model, which pointed to waters near the North Equatorial Recirculation Region (NERR) (Johnson et al. 2013). Sargassum may be aggregating in the NERR region and blooming there.
More recent satellite images revealed increasing trends in sargassum amounts in both the tropical Atlantic and the Caribbean through 2018. Floating sargassum travels with ocean currents and is influenced by surface winds. However, the currents that have resulted in the movement of more sargassum into the Eastern Caribbean and Northwest African coastlines are not clear at this time (UNEP, 2018).
Massive sargassum pile up has disrupted fisheries and has had devastating impacts on tourism, damaged critical nearshore ecosystems and coastal livelihoods, as well as caused significant health challenges for populations exposed to rotting sargassum (UNEP 2018). The ecological impacts are
