Pelagic Sargassum as an emerging vector of high rate carbonate sediment import to tropical Atlantic coastlines

• Published in: Global and planetary change Vol. 195; p. 103332
• Main Authors: Salter, Michael A., Rodríguez-Martínez, Rosa E., Álvarez-Filip, Lorenzo, Jordán-Dahlgren, Eric, Perry, Chris T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2020
• Subjects: Atlantic Ocean; Bryozoa; calcium carbonate; Caribbean; Caribbean Sea; Coastal sediment supply; coastal sediments; coastal water; coasts; confidence interval; epiphytes; Macroalgal bloom; Marine carbonates; Mexico; Rhodophyta; Sargassum; Sargassum epiphyte communities; seagrasses; shorelines; socioeconomics; Tropical sediment sources; Caribbean; Mexico; Atlantic Ocean; Sargassum epiphyte communities; Marine carbonates; Coastal sediment supply; Caribbean Sea; Tropical sediment sources; Macroalgal bloom
• DOI: 10.1016/j.gloplacha.2020.103332
• ISSN: 0921-8181

Since 2011, pelagic Sargassum has inundated Caribbean, West African, and northern Brazilian shorelines in increasing volumes. These events are linked to the emergence of a major new Sargassum bloom region in the Atlantic Ocean, and annual high-volume Sargassum beachings are seemingly becoming an established norm. Resultant socio-economic and ecological implications are widespread and potentially serious, but an important question that has so far received no attention is whether these Sargassum inundations might represent a new source of carbonate sediment in affected coastal areas. This sediment derives from calcareous epiphyte communities that colonise Sargassum (e.g., bryozoans, serpulid worms, and red algae), and if volumetrically significant, may help to counteract aspects of Sargassum beachings thought to reduce sediment supply and decrease coastal stability. Here we determine the carbonate contents of Sargassum from coastal waters of the Mexican Caribbean. Integrating these with volumetric data on beached Sargassum, we then estimate total epiphytic carbonate import during 2018 at 11 sites along a 60 km section of the Quintana Roo coast, Mexico. Based on measured mean carbonate content of Sargassum (2.09% wet weight; 95% confidence interval [CI]: 1.83–2.32), and estimates of annual beached Sargassum (7.0 × 103 kg drained weight·m−1 of shoreline; 95% CI: 6.9–7.2), our findings indicate that Sargassum beachings in the Mexican Caribbean contributed an average of 179 kg CaCO3·m−1 of shoreline (95% CI: 173–185) in 2018: close to our upper estimate of seagrass epiphyte contributions (210 kg·m−1). Although quantitative data on Sargassum beachings from other locations are sparse, numerous media reports suggest the scale of these events is comparable for many exposed tropical Caribbean and Atlantic shorelines. This represents the first documentation of pelagic Sargassum as a major vector of coastal sediment import, the significance of which has likely only arisen since the onset of large-scale inundations in 2011. [Display omitted] •Recent emergence of major new central Atlantic and Caribbean Sargassum bloom region.•Unprecedented widespread coastal Sargassum inundations are potentially a new norm.•We quantify Sargassum and carbonate epiphyte arrivals on Caribbean shorelines.•Sargassum imported an estimated 179 kg CaCO3 per metre of shoreline in 2018.•Represents a novel and potentially major vector of tropical coastal sediment import.