In mid-2015, to the amazement of the scientific community, large volumes of brown algae reached the shores of the Mexican Caribbean. The turquoise blue of the sea turned brown as a result of the decay of these organisms.

A harvesting machine, extraction belts and a series of collection guidelines issued by the Ministry of Environment and Natural Resources (Semarnat) were among the first proposals to address a problem whose environmental effects were still unknown.

In 2016 and 2017, the bloom of sargassum in the sea decreased considerably and its impact on the coasts was minimal, so there was a pause in the search for solutions, explained Rosa María Rodríguez Martínez, a researcher at the Academic Unit of Reef Systems of the National Autonomous University of Mexico (UNAM) and a pioneer in the analysis of the impacts of sargassum.

However, in 2018, high volumes of algae overflowed off the coast of Quintana Roo. That year recorded the highest peak of sargassum bloom in the ocean, with more than 20 million tons, according to the record of the Marine Oceanography Laboratory of the University of South Florida (USF). In the following years, the arrival has been in smaller numbers, but with significant effects.

The blossoming of sargassum begins between the months of February and March and its highest peaks in summer, showing a decrease in the months of September and October, according to the behavior pattern recorded by the USF. For this year, large numbers are already being observed in the Riviera Maya area and the east coast of Cozumel.

In Playa del Carmen, the foul smell of seaweed extends up to 400 meters into the urban area, where the hotels are located and the bad image scares tourists away.

The white beaches and the shade of the sea are the region's main tourist asset, which annually attracts more than 14 million tourists, according to data from the Ministry of Tourism of Quintana Roo.

Sargassum represents one of the greatest environmental and economic threats in the medium and long term, with no solutions on the table so far, Rodríguez Martínez said.

Impact of algae

Brigitta van Tussenbroek, also a pioneer in sargassum research and an academic at the Reef Systems Unit of the UNAM in Puerto Morelos, explained that algae has always reached Mexican shores in smaller quantities, coming from the Sargasso Sea, an ecosystem located in the North Atlantic. The first record of these algae dates back to 1,492, at the Christopher Columbus crossing.

However, the species of sargassum that make mass landfall on the Caribbean coast are a new phenomenon, which began to be monitored in 2011. It is a sargassum belt that originates in the South Atlantic, between the coasts of Brazil and Africa.

The specialist explained that there is a big difference between the 'original' Sargasso Sea and the pelagic sargassum that currently affects beaches. The first is an ecosystem in the open ocean that functions as a great refuge for biodiversity.

On the other hand, the recent phenomenon of Sargassum completely transforms the coastal ecosystem. The decomposition of seaweed on the coast loads the water with nutrients and heavy metals and removes available oxygen, a combination harmful to living organisms adapted to pure water.

“Sargassum itself is not harmful, what hurts are the enormous masses that reach our shores and begin to decompose. The release of gases, bacteria, lack of oxygen, causes stress to different organisms,” said Van Tussenbroek, an expert in macroalgae.

Among the main recorded problems is the death of seagrasses, which have high environmental relevance to prevent coastal erosion, are food for multiple species such as sea turtles, shelter for small marine organisms and carbon dioxide collectors.

Another of the impacts already visible is the reduction of sandy areas, Van Tussenbroek said. In addition to the death of seagrass, during the manual collection process of sargassum, quantities of sand are also collected daily.

An investigation led by Rosa Rodríguez Martínez, carried out between 2018 and 2019, with the analysis of 63 samples, showed that sargassum contains elements such as arsenic, copper, manganese and molybdenum.

In addition, an analysis by Rodríguez Martínez found specimens of at least 72 dead species among algae, mainly fish and crustaceans.

Another of the main concerns, he said, is the mismanagement of sargassum that is collected from beaches, since it is deposited in Sascaberas, landfills or unauthorized sites.

During the algae decomposition process, leached liquids are released, which, due to the characteristics of the regional soil, can easily reach the aquifer and contaminate the water.

The massive arrival of brown algae to the coasts of the Mexican Caribbean coincides with the outbreak of the coral disease White Syndrome in the Mesoamerican Reef. Although Rodríguez indicated that there is no data to associate sargassum as a cause of the disease, he pointed out that poor water quality contributes to the vulnerability of corals.

Without strategies or solutions

Since 2015, to address the problem, City Councils have been responsible for cleaning public beaches, while beach dealers, such as hotels and restaurants, are responsible for keeping their fronts clean.

The government of Quintana Roo, through the Secretariat of Ecology and Environment (SEMA), is responsible for placing containment barriers.

In 2019, the President of the Republic, Andrés Manuel López Obrador, tasked the Secretariat of National Defense (Sedena) with coordination and actions to resolve the effects of sargassum. The agency, in turn, implemented collection work at sea.

For Rosa Rodríguez, harvesting at sea is currently inefficient and expensive, since the volume of algae collected is minimal. “The distance covered by the ship is 15 kilometers, which is clearly not enough,” he said. The coastline of Quintana Roo covers 1,176 kilometers.

Alejandro Bravo, oceanologist and one of the creators of the first pilot project for the containment of sargassum, recognizes that the actions currently being carried out 'have fallen short' to control the problem, in addition to the costs they represent.

“It hasn't worked. We have to look for other alternatives. I think that the most viable is harvesting from the sea, because once you have it on the coast it's already a problem,” said the specialist, who is also a member of the State Advisory Council created to design public policies for the care of sargassum.

Both Rodríguez and Bravo agree that it is necessary to allocate a public budget to research and tools to control sargassum, before its effects on the coasts are irreversible.

“Municipalities charge an Environmental Sanitation Right and it must be used for this, there are resources, it's just that we don't know what it's being spent on,” Rodríguez said. “You can't expect different results if you keep doing the same thing,” he added.

Another of the pending issues is the elaboration of an Official Mexican Standard (NOM) for the collection, management and use of sargassum for commercial purposes, at the proposal of the State Advisory Council, which must be issued by the National Advisory Committee for the Standardization of Environment and Natural Resources (Comarnat).