A spatial and temporal assessment of sargassum blooms in the tropical Atlantic

Abstract

Since 2011, sargassum algae blooms have been occurring in the Tropical Atlantic basin from North and Central America, through the Caribbean Sea and across to the Gulf of Guinea. The blooms are aggregated and transported by wind and currents, and deposited on coastlines across the region. They pose threats to ocean and coastal biodiversity, human health, coastal stability, industries such as tourism and aquaculture, and ultimately the livelihoods of coastal communities. Since the emergence of this new social-environmental challenge, there has been an increase in research and knowledge of sargassum. Most research has focused mainly on the Gulf of Mexico, the Caribbean and North Atlantic Ocean and significant regional knowledge gaps exist. For example, in the Gulf of Guinea and Central America, there is much we do not know about sargassum. More specifically, in the under-researched geographic areas further data are needed on beaching events, different species and morphotypes, chemical composition, volume of sargassum, and the drivers of the blooms across the basin. This thesis aims to address these knowledge gaps by developing methods and creating datasets to improve the spatial and temporal understanding of the distribution of sargassum blooms across the Tropical Atlantic. Research questions asked are: How can we improve monitoring and detection of sargassum events at multiple scales?; How can we better detect and track sargassum pathways across the Tropical Atlantic?; What opportunities exist to improve beach detection and monitoring in cloud covered regions? Data are collected from: field campaigns in Ghana and Barbados, time-series analysis of sargassum in West Africa, and GPS tracking of floating sargassum blooms. Results show that i) there is a distinct seasonal pattern to sargassum blooms in the Eastern Tropical Atlantic and a co-variance of the occurrence of blooms with atmospheric and oceanic events; ii) there are alternative methods of detecting blooms which overcome spatial and temporal limitations of remote sensing, including cloud cover; iii) decomposition stages of beached sargassum have distinct spectral profiles which has value for supporting monitoring and improving valorisation potential; and iv) there is a need for more freely available high resolution imagery to monitor smaller blooms in open-ocean areas. It is expected that this information will contribute to effective management of sargassum blooms through tracking floating mat movements and aggregations, providing information for forecasting sargassum events and development of a risk management strategy, and supporting opportunities to valorise sargassum.

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Identifiers

ORCID for Yanna Alexia Fidai: orcid.org/0000-0003-3561-4718

ORCID for Jadu Dash: orcid.org/0000-0002-5444-2109

ORCID for Emma Tompkins: orcid.org/0000-0002-4825-9797

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