Abstract

Pelagic Sargassum spp. constitutes important habitat and nutrient source for marine biodiversity in the oligotrophic waters of the Atlantic Ocean and Caribbean Sea. Influx of floating Sargassum to the Gulf of Mexico and the Caribbean Sea have been historically influenced by trade winds, and have reached coasts and beaches of the Caribbean islands and Central America. However, since 2011 exceptional biomass of floating Sargassum have been reported along the Caribbean coast, including Mexico and West Indies. These abnormal events have affected biodiversity (p.e. sea turtles, fishes and dolphins) and economic sectors such as fisheries and tourism. Negative effects of these influxes might be higher at insular contexts such as the Archipelago of San Andrés, Providence and Santa Catalina Islands, because human population wellbeing depends more on the quality of marine ecosystems that are the basis of economic activities as tourism and fishery. In Colombia, occasional influxes of Sargassum have been reported for 2014 and 2015 at San Andres Island, as well as at Serranilla Island by 2017. This year 2018, other events were observed in San Andres Island, during April and begging of May. Average width extension of Sargassum bands were determined on beaches, as well as dry average biomass. We estimated that around 188.000 kg of Sargassum humid biomass arrived at the island´s beaches, and around 618.000 kg per event along the entire east coast of the island. Effects of these events on nutrient input to seawater could be positive for productivity, but negative effects on shallow seagrass meadows and nearby coral reefs, as well for economic activities like tourism or fisheries should be assessed. More research is needed to understand causes and effects of these events at San Andrés and the entire Caribbean region.

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