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Sargassum: Golden rainforest or nuisance?

GEF/UNDP/IOC/SSC Strengthening the Stewardship of the Sargasso Sea

By IW:LEARN

June 7^th, 2023

Sargassum has garnered a lot of bad press lately – CBS news reported that a 13.5 million metric ton blob of seaweed was set to wash up this summer on the west coast of Florida.

These catastrophic inundations have been occurring since 2011 – and they’re not limited to the US coast – mass strandings of Sargassum have devastated the coasts of many Caribbean states, the coast of Brazil, and the coast of West Africa from Senegal to Nigeria.

The effect of such large inundations can be catastrophic to inshore ecosystems as well as to human health. Washing in Sargassum can create a ‘brown tide’ that smothers coral reefs and seagrass beds.

Sargassum smells as it rots on the beach, impacting tourism, and releasing hydrogen sulfide gas, which can irritate the skin and even cause respiratory and neurocognitive issues. There are also challenges in disposing of Sargassum as it has been found to contain high levels of arsenic.

Sargassum: Golden rainforest or nuisance?

At the same time, in its natural habitat in the Sargasso Sea, Sargassum provides the basis to a unique and highly biodiverse ecosystem. To be clear, here we are talking about Sargassum natans and Sargassum fluitans, the two holopelagic species of Sargassum which are adapted to a high seas lifestyle, never attaching to the bottom at any point in their life cycle.

Sargassum provides a safe haven for small animals on the high seas, supporting ten endemic species, and providing critical developmental habitat for many species of pelagic fish that grow to be ocean giants, and at least three species of Atlantic sea turtle. This thriving Sargassum community in turn supports other organisms that feed beneath it, acting as the basis for the iconic Sargasso Sea ecosystem.

Modeling and satellite data have shown that the Sargassum that inundates beaches in Western Africa, the Caribbean, and the Eastern US comes from an area to the south of the Sargasso Sea, between the north equatorial current and the equator, commonly called the Great Atlantic Sargassum Belt.

The Great Atlantic Sargassum Belt has bloomed annually since 2011, stretching from the West Coast of Africa to the Gulf of Mexico.

While the cause of the blooms is not certain, scientists have suggested that nutrients introduced to the ocean from sewage and farm run-off may be a contributing factor.

While Sargassum originating from elsewhere may be receiving bad press, the Sargasso Sea is worthy of positive attention.

As negotiations on a high seas treaty recently concluded in New York, the Sargasso Sea is poised as a flagship implementation site for a new era in high seas governance.

Strengthening the Stewardship of the Sargasso Sea, a child project of the Common Oceans Programme, is funded by the Global Environment Facility, with UNDP and IOC-UNESCO as implementing and executing agencies respectively.

This project will produce the first Socio-Ecosystem Diagnostic Analysis (SEDA) for a high seas ecosystem – an ambitious adaptation of the GEF International Waters TDA/SAP methodology. Based on this, and working with stakeholders of the Sargasso Sea, including the Sargasso Sea Commissioners, ten governmental signatories to the Hamilton Declaration and more, the project will produce a comprehensive Strategic Action Programme to conserve this iconic area of the ocean.

You can have too much of a good thing, as the negative impacts of strandings of the Great Atlantic Sargassum Belt prove, but the Sargasso Sea and its Sargassum are unique, valuable, and surely deserving of protection.

In addition to Sargassum’s role in supporting endemic species and acting as a nursery for developing fish and turtles, the wider Sargasso Sea also acts as the only spawning ground for the endangered European and American anguillid eels, and provides a migratory corridor for many species of sharks, rays, dolphins, and whales.

The Sargasso Sea also acts as a significant carbon sink, representing ca. 7% of the global biological carbon pump, and this is aided by the sinking of Sargassum to the deep sea when it reaches the end of its life cycle.

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About the GEF/UNDP/IOC/SSC Strengthening the Stewardship of the Sargasso Sea

“Strengthening stewardship through cooperation in an economically and biologically significant high seas area – the Sargasso Sea” is part of the GEF Council Areas Beyond National Jurisdiction (ABNJ) programme entitled "Common Oceans - Sustainable utilisation and conservation of biodiversity in areas beyond national jurisdiction"; the programme is financed under the GEF's International Waters focal area.

The United Nations Development Programme (UNDP) is the GEF implementing agency for the project, with the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organisation (IOC-UNESCO) as executing agency.

The project collaborates with the Bermuda Institute of Ocean Sciences, the Duke University Marine Geospatial Ecology Lab, the Imperial College London Centre for Environmental Policy, the University of Edinburgh, the World Maritime University, and the French Global Environment Facility (FFEM).

The overall objective of the nearly $3 million GEF/UNDP/UNESCO/IOC Sargasso Sea project is to facilitate a collaborative, cross-sectoral, and sustainable stewardship mechanism for the Sargasso Sea through the improvement of the knowledge base and strengthened frameworks for collaborative management and governance.