Massive influxes of Pelagic Sargassum in the Wider Caribbean Region

from Massive influxes of Pelagic Sargassum in the Wider Caribbean Region

By Mariana C. León Pérez, PhD

Since 2011, massive quantities of Sargassum algae have been accumulating on shores throughout the Wider Caribbean Region, covering the crystal-clear waters with rotting seaweed. These unprecedented annual events have been detrimental to the natural environment and are threatening coastal communities and economies. Affected communities are responding to these historic influxes of Sargassum with a variety of mitigation measures, but face an unsettled and confusing regulatory and policy framework as they attempt to deal with this growing phenomenon.

What is Sargassum and where does it originate?

Sargassum is a brown macroalga (seaweed). The two species found in Sargassum influxes in the Wider Caribbean Region are Sargassum fluitans and Sargassum natans. These species are pelagic, meaning that they spend their lives floating freely at or near the ocean surface. Pelagic Sargassum accumulates into dense mats that serve as important habitat for fish, sea turtles and other organisms, and are dispersed by ocean currents and wind.

Coastlines (yellow areas) in West Africa and the Caribbean Antilles are illustrated using the entire country coastline. Coastlines in continental America are illustrated by the specific sargassum accumulation areas reported within each country. Data sources: https://www.unep.org/events/unep-event/sargassum-caribbean-and-west-africa-key-challenges-responses-and-collaborations and http://sargassummonitoring.com/.

Historically, pelagic Sargassum is found in the Sargasso Sea, an area in the North Atlantic. However, since 2011, Sargassum has established a new production system off the coasts of western Africa and Brazil known as the North Equatorial Recirculation Region (NERR) and are accumulating in concentrations never-before seen. Evidence suggests that an anomaly in the strength and direction of winds and currents in the Sargasso Sea during 2009 and 2010 resulted in displacement of Sargassum mats, which eventually reached the NERR. There, persistent favorable environmental conditions have resulted in recurrent yearly blooms. Sargassum mats from this new source are then transported by currents and winds into the Caribbean Sea, Gulf of Mexico and West Africa, forming the Great Atlantic Sargassum Belt. In 2018, this belt extended more than five thousand miles and carried more than 20 million metric tons of Sargassum biomass, the equivalent of more than 200,000 blue whales!

Why it is a concern?

Although Sargassum can serve as an important habitat, massive influxes can also act as a Harmful Algal Bloom (HAB) when it accumulates in near shore waters, causing ecological damage, as well as threatening the health, economy and wellbeing of impacted coastal communities.

Decomposing Sargassum can decrease the light, pH, and oxygen of nearshore waters. Increases in seawater temperature, turbidity, and nutrients also occur. Collectively, these impacts can lead to eutrophication (nutrient enrichment) and low (or no) oxygen environments, which are harmful to marine life and may persist long after the Sargassum is gone. Fish kills, coral mortality and seagrass die off have been reported as a result of these changes, which can have serious implications for the long-term sustainability of coastal marine ecosystems. Sargassum accumulations also represent a physical obstruction for some animals, such as adult sea turtles nesting on the beach and sea turtle hatchlings that struggle to make it through thick Sargassum accumulations on their way to sea.

Beached Sargassum mats also represent a threat to human health. On the shore, Sargassum decomposition produces high concentrations of ammonium and hydrogen sulfide gasses that can trigger irritation of the eyes and respiratory system. When in direct contact with Sargassum some people may experience allergic reactions. These are caused by hydroids, small organisms related to jellyfish.

Further, in much of the Caribbean, the economy is dependent on coastal and marine resources that have deteriorated with Sargassum influxes. Economic impacts in the tourism sector, for example, include an increase in cancellations in hotels, restaurants, and tours near Sargassum accumulation areas. Fishers have also been impacted by Sargassum, which can become entangled in fishing gear and boat propellers, and may affect fishing effort. In addition, the hydrogen sulfide released by Sargassum decomposition corrodes metals present in electrical appliances and jewelry. To reduce these impacts, Sargassum clean up efforts have been implemented, and for example, in 2018 were estimated to cost $120 million to the Caribbean Economy, according to the Jamaica’s Minister of Tourism.

What has been done to address it?

Diverse efforts have taken place throughout the region to reduce the negative impacts of Sargassum influxes. These include preventing the accumulation of Sargassum on the coast by installing floating boom barriers and/ or removal by boats (sea harvest), manually and mechanically removing accumulated Sargassum on beaches and disposing of or even using this seaweed for commercial purposes. In addition, several international initiatives to understand, share knowledge and develop solutions have recently emerged.

Main challenges

The mitigation of Sargassum impacts represents an economic challenge to the nations, states and territories of the Wider Caribbean Region. Specialized equipment and infrastructure are needed for the containment, removal, transportation and disposal or use of Sargassum. However, the greater obstacle in many instances is the absence of a clear legal framework to guide the implementation of effective mitigation strategies both within and across jurisdictions, as well as in international waters. Although international initiatives have yielded several creative solutions, particularities in each legal system may inhibit implementation in some jurisdictions.

The National Sea Grant Law Center is collaborating with national and international partners to clarify the laws and policies that apply to the management of Sargassum, including any needed reforms, and in identifying best practices in dealing with impacts, under the current international and domestic law.

Acknowledgments

References

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Please cite as: León-Pérez, M.C., McLaughlin, R., Chaparro, R., Krimsky, L., Klein, Z., Myers, A., Ankersen, T.T. 2021. Massive influxes of Pelagic Sargassum in the Wider Caribbean Region. National Sea Grant Law Center.

Thanks to Dr. Hector Ruiz for providing technical assistance on the Sargassum species illustrations. This publication was in part made possible by the National Oceanic and Atmospheric Administration – Center for Coastal and Marine Ecosystems (NOAA CCME) award number NA16-SEC4810009. Its contents are solely the responsibility of the award recipient and do not necessarily represent the official views of the U.S. Department of Commerce, National Oceanic and Atmospheric Administration. UPRSG-G-320