Abstract

Massive Sargassum influxes into the Wider Caribbean Region and West African coast have negatively affected both social and ecological systems since 2011. Current monitoring efforts using satellite data are being conducted but are mainly limited to offshore waters. Therefore. we developed a method to characterize Sargassum accumulations along the coastline and to understand their spatial and temporal dynamics. Using the online platform Google Earth Engine. we analyzed Sentinel-2 MultiSpectral Instrument (MSI) satellite imagery for Sargassum occurrence from 2015 to 2021 for La Parguera. Puerto Rico. A combination of MSI reflectance bands and several vegetation and water quality indexes were used with a Random Forest classification algorithm. Field data was collected to calibrate and validate the classification product. which achieved 90% overall accuracy. Our classification model can identify both fresh and decomposing Sargassum. as well as the brown tide (chromophoric dissolved organic matter) generated from decomposing Sargassum. We identified hotspots of Sargassum accumulation that persisted throughout the study period and assessed their spatial and temporal dynamics. Findings of this research provides high spatial resolution information for resource managers and researchers to understand the impacts of these ongoing events and to identify areas where mitigation efforts are needed to be focused.

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