Recent Sargassum Inundation Events in the Caribbean: Shipboard Observations Reveal Dominance of a Previously Rare Form

Factors controlling the seasonal distribution of pelagic Sargassum

“…The backwards-timestep particles and connectivity analysis presented here also support the hypothesis that Sargassum in the tropics has a southern source. Different morphological forms of S. natans appear to be dominant in the Sargasso Sea versus the Western Tropics (Schell et al 2015), which is consistent with this two-source hypothesis. Additional observational studies would be helpful in determining if Sargassum biomass is present in the proposed seed regions year-round, and whether the genetic diversity of Sargassum fluitans and Sargassum natans supports this hypothesis.…”

“…More recently, Sargassum distribution throughout the annual cycle has been mapped via satellite (Gower & King 2011, Gower et al 2013, Wang & Hu 2016. The remote sensing derived distributions also suggest that changes in biomass and southern range expansion have occurred in recent years (Gower et al 2013, Wang & Hu 2016, and field observations suggest this may be influencing species and morphotype composition in the Caribbean (Schell et al 2015). In situ observations confirm that Sargassum natans occurs off the coast of Brazil, south of the presumed range (Széchy et al 2012, Sissini et al 2017.…”

Pelagic Sargassum in the Tropical North Atlantic

“…Although pelagic Sargassum was previously reported in the tropical North Atlantic (Taylor 1960), it had never been observed in such large quantities as occurred in 2011 (Franks et al 2011). Since there were no documented reports of pelagic Sargassum being transported in large quantities on currents from the North Atlantic Gyre into the tropical Atlantic, and lacking evidence to the contrary from either in situ observations or satellite imagery, indications were strong that the Sargassum bloomed (Schell et al 2015) in an area we identified as the North Equatorial Recirculation Region (NERR, Franks et al 2011; Figure 1). The NERR is substantially larger than could be expected to produce Sargassum blooms via coastal eutrophication (Smetacek and Zingone 2013).…”

Remote Sensing of Sargassum Biomass, Nutrients, and Pigments

“…Early Sargassum biomass estimations mainly come from ship-based samplings using neuston tows (Butler et al, 1983;Butler & Stoner, 1984;Parr, 1939;Stoner, 1983). More recently, the Sea Education Association collected neuston measurements in both Sargasso Sea and tropical Atlantic over the last 50 years and observed significant abundance changes especially in the tropical Atlantic (Schell et al, 2015;Siuda, 2011). Stoner conducted another quantitative study and reported a major decrease of Sargassum biomass (Stoner, 1983), which was later attributed to the geographic variations within the Sargasso Sea and the sampling method (Butler & Stoner, 1984).…”