Contemporary Impacts of Climate Change: Sargassum in the Mexican Caribbean Sea

Climate change is often framed as a futuristic problem. The ambitious target of limiting global warming to 1.5 degrees by 2100 gives the impression that the adverse effects of climate change will occur in the future, or that they will not arise if we reach the 1.5-degree target. The planet has, however, already reached an average warming of 1 degree Celsius since pre-industrial times. Even though this does not create the disastrous effects that even higher temperatures will create, climate change’s adverse impact already occurs around the world.

Sargassum. Credit: US Fish & Wildlife Service

Some events with direct links to climate change have received the media attention they deserve. The fires in the Amazonian rainforest and the Australian bushfires were widely reported, while coral bleaching and the species extinction gains increasing media coverage. Many other adverse contemporary impacts of climate change are, however, relatively unknown.

In 2011, the Mexican Caribbean Sea started experiencing climate change impacts by a sudden influx of Sargassum. Sargassum is a macroalgae – a type of seaweed – which is important for ecological functions in many parts of the world. The seaweed provides essential habitats and serves as a hotspot for biodiversity while providing food for a diverse set of fish and invertebrates. Since 2011, million tons of Sargassum continues to flow the coastline and beaches in countries situated in the Mexican Caribbean sea. The sudden arrival of such large quantities of Sargassum creates severe problems for Mexico and the Caribbean countries.

Since Sargassum is not native to the Mexican Caribbean Sea, the environmental effects are adverse. The impacts of Sargassum’s sudden influxes leads to biodiversity loss, degradation of coral reefs and associated ecosystems, and negatively affects sea turtle nests. Moreover, many small fishes, invertebrate animals, and other algae are associated with Sargassum. Therefore, Sargassum might be a transport[1] for introducing exotic and invasive species. In addition, Sargassum depletes oxygen in nearshore waters and reduce the visibility of the water column[2], blocking algae and fauna from absorbing sunlight.

Humans also experience adverse effects due to the large flow of Sargassum to the Mexican Caribbean Sea. The main cause of Sargassum’s adverse human effects is how it floods the beaches and ruins coastal areas. A study[3] examining the Sargassum on the Coast of Caribbean countries found that the seaweed produces large amounts of toxic gas after 48 hours on the shore, including hydrogen sulphide and ammonia. In Guadeloupe, doctors reported more than 3341 cases of acute exposure to the toxic gas between January and August 2018. In Martinique, more than 8061 cases were reported.

Moreover, the economic damage is substantial. The cost of clean up is huge, leading to coastal management challenges of over US$ 100 million in 2018 in the Caribbean[4]. Sargassum makes the beach unattractable to tourists while fishing becomes harder, causing large losses of income for locals and national economies.

The causes of the increase of Sargassum in the Mexican Caribbean Sea are numerous, and showcase how complex and interconnected many impacts of climate change are. Since the phenomenon emerged out of nowhere quite recently, the answers to why Sargassum suddenly appeared in the Mexican Caribbean Sea are still not fully determined, or what the most substantial cause is. Scientists[5] have, however, determined that it is most likely due to a wide range of interconnected causes – which are further driven by climate change.

A scientific paper[6] published in 2020 attributes the initial cause of Sargassum’s massive flow to extreme winds, which triggered a biosphere tipping point. The winds brought the Sargassum from the Sargasso Sea to the Mexican Caribbean Sea. The first arrival of Sargassum in the Mexican Caribbean Sea in 2011 gave rise to the Sargassum seed population in the area, which now causes recurrent blooms every year[7]. Human pollution, mainly from spillage from the Amazon River and West Africa, provides nutrient enrichment for the Sargassum, allowing it to flourish further. Changes in oceanographic conditions – such as temperature changes in the ocean – improves the conditions even more for Sargassum to blossom in the Mexican Caribbean Sea.

The influx of Sargassum in the Mexican Caribbean Sea shows how climate change causes problems that might not be as direct as large forest fires or loss in species. Sargassum is important in many parts of the world. However, due to climate change events and human pollution, it is now appearing and spreading to parts of the world where Sargassum contributes to ecological and socio-economic disturbances.

The problem with Sargassum in the Mexican Caribbean Sea shows how complex the issue of climate change is. The impacts of climate change occur in ways that we might not be aware of, and it might take some time until people notice what happens or that climate change was the main driver to an issue. The problems Sargassum brings has a broader perspective – how seemingly harmless forces such as changes in where certain types of seaweed occur can create such large problems. Events similar to the influx of Sargassum in the Mexican Caribbean Sea occurs in many other parts of the world and propose a severe threat to the future of the seas[8] as we know them. More attention needs to be given to the impacts of climate change since it creates adverse consequences on both the ecosystem and human societies – that are already detrimental in many parts of the world. If 1-degree warming creates these kinds of problems, it is clear how severe higher temperature rises will be.