Marine megafauna (cetaceans, turtles, seabirds & elasmobranchs) associate with pelagic Sargassum off Suriname

Marine megafauna associating with Sargassum in Suriname

Abstract

Recent atypical blooming events of the macroalgae Sargassum have affected humans and animals within the wider Caribbean region. Little is known how Sargassum affects marine megafauna offshore in Suriname. Data from dedicated marine megafauna surveys were pooled (2012 and 2015; May - September). A significant higher presence of Sargassum was found in May and July and particularly over the Demerara plateau. Sargassum constituted localised ‘hot-mats’ for biodiversity: 77 sightings comprising 25 species associated with Sargassum mats. Young green turtles (Chelonia mydas) basked in Sargassum at a farthest reported (global) distance from the coast. Cetaceans were significantly more abundant in waters with Sargassum. Dolphins (Stenella longirostris and S. attenuata) showed higher abundance indices in presence of Sargassum, while deep diving cetaceans showed higher indices without Sargassum. All three species of booby (Sulasp.) foraged on flying fish in Sargassum. Terns (Onychoprion fuscatus) and shearwaters (Calonectris diomedea, Puffinus gravis, P. lherminieri) foraged amongst Sargassum. Manx shearwater (P. puffinus) and red-billed tropicbird (Phaethon aethereus) were flying low over Sargassum. Using bird transect-data we found that in 2012, Sargassum attracted significantly larger groups of foraging seabirds compared to 2015. These differences may have been affected by mat-morphology (2012: ‘loose’ vs 2015: ‘dense’). It is unknown how mat-morphology may affect marine megafauna during future blooming-events. It has been reported that Sargassum natans VIII provides less suitable feeding-mats than other forms, but more research is needed. Nevertheless, Sargassum offers opportunities to a diverse marine megafauna community in what are otherwise relative nutrient-poor tropical offshore waters.