Seasonal variation in morphotype composition of pelagic Sargassum influx events is linked to oceanic origin

Abstract

The recent proliferation of pelagic Sargassum spp. in the Tropical Atlantic causes major ecological and socioeconomic impacts to the wider Caribbean when it washes ashore, with regional fisheries and tourism industries particularly affected. The Caribbean influxes have been tracked to a new bloom region known as the North Equatorial Recirculation Region (NERR) encompassing the area between the South Equatorial Current and the North Equatorial Counter Current and extending from Africa to South America. The vast biomass of Sargassum presents serious problems when it washes ashore but also represents significant commercial opportunities, especially with biofuel and fertilizer. The floating Sargassum mats are themselves diverse ecosystems that vary both in their biodiversity and biochemical attributes. Two major species (Sargassum fluitans and S. natans) have been identified as well as several distinguishable morphotypes of each. Oceanic mixing tends to blend the morphotypes together making it difficult to determine if there are regions of the NERR that favour bloom and growth of the distinct types. In this study, we quantify the species and morphotype composition of Sargassum strandings in Barbados and test if this is related to separate oceanic origins and routes travelled using a backtracking algorithm based on ocean drifter data. We found significant seasonal variation in the relative abundance of three morphotypes and this could be traced to two distinct easterly sub-origins and/or transport pathways; one area around 15° N that travels directly E–W across the Atlantic, and another area generally south of 10° N that takes a more meandering route coming close the coast of South America. These findings contribute towards our understanding of why the Tropical Atlantic bloom is presently occurring as well as towards addressing valorisation constraints surrounding variation in the supply of the three commonly occurring morphotypes.

Changes in holopelagic Sargassum spp. biomass composition across an unusual year

“…During Caribbean sargassum influxes, S. natans I and VIII, and S. fluitans III have been shown to be the dominant morphotypes, and their relative abundance varied across seasons, years, and regions (31)(32)(33)(34)(35). S. fluitans III was the predominant morphotype on the Mexican Caribbean coast between September 2016 and May 2020 (31).…”

“…The EU-Roadmap for the blue economy reported that the seasonal variation in biomass composition is a characteristic of seaweeds that can affect the scalability of production and the logistical processes (24). In the last few years, there have been increasing reports on seasonal variations of the biochemical (25)(26)(27) and elemental (28)(29)(30) composition of sargassum, as well as on seasonal changes in the morphotype abundance (31)(32)(33)(34)(35).…”

Skillful Seasonal Forecast of Sargassum Proliferation in the Tropical Atlantic

“…The choice to consider varying internal nutrient quotas (C:N:P stoichiometry) is motivated by observations suggesting that Sargassum , like other brown algae, is able to store some nutrients in its tissues (Hanisak, 1983; Lapointe, 1995; Lapointe et al., 2021). In situ observations have also revealed that three different morphotypes are involved in the proliferation ( Sargassum fluitans III, Sargassum natans I, and Sargassum natans VIII e.g., Alleyne et al., 2023; Dibner et al., 2022; García‐Sánchez et al., 2020; Schell et al., 2015). The eco‐physiological features are species dependent, and it has been shown that Sargassum fluitans III, which has been the dominant morphotype over the recent years (García‐Sánchez et al., 2020), grows significantly faster than the Sargassum natans morphotypes (Changeux et al., 2023; Corbin & Oxenford, 2023; Magaña‐Gallegos et al., 2023a, 2023b).…”

Science and policy lessons learned from a decade of adaptation to the emergent risk of sargassum proliferation across the tropical Atlantic

“…In 2023, it is only now evident that the most dominant sargassum morphotype in peak Caribbean sargassum seasons has been S. fluitans III [48,55,56]. Nevertheless, morphotype composition of sargassum rafts is highly variable across space and time [48,57], and the quality and quantity of commercially important compounds such as mannitol, alginates, fucoidans and fucoxanthin vary among morphotypes [51,56].…”