The massive influx of sargassum to the beaches of the Yucatan Peninsula generates economic and environmental damage, so it is necessary to have long-term forecasts that serve to establish early warnings and make decisions related to the ecological impact, tourism, and the collection of this alga, among others.

For this reason, the oceanologist and member of the Laboratory of Engineering and Coastal Processes of the Sisal Academic Unit of the UNAM's Institute of Engineering, María Eugenia Allende Arandía, works with numerical models with which she seeks to explain the physical factors that modulate their arrival to the Mexican coasts and that the information contributes to the formation of an early warning system of the upwelling.

The models simulate ocean currents and use as tools inert particles that are "released" in the regions where sargassum patches are observed by satellite images. These particles move as a function of current and wind speed.

"Under different scenarios of wind conditions, we see how far they go, we find accumulation zones, arrival times, connectivity zones, trajectories, how many particles move. Research so far suggests that only one percent of the magnitude of the wind over the ocean surface is needed for the particles to reach the Mexican coasts and they will take approximately three to four months from the Equatorial Atlantic," he said.

They do not have biological properties, that is to say, we do not consider the buoyancy of the algae, how fast it reproduces, what its growth rate is, but it is important to explain the factors that modulate the arrival of sargassum to the Mexican coasts, added the specialist in Ocean-Atmosphere Interaction.

Oceanic dynamics

The expert explained that the oceanic dynamics of the Equatorial Atlantic basin -where these spots are formed- has been studied, the main currents are known; however, more aspects need to be analyzed.

"It is a basin with a lot of atmospheric activity, we have trade winds -those that blow between the tropics-, hurricane generation zone, tropical cyclones and it is important to know how much these seasonal issues and the interaction between the ocean and the atmosphere, plus the terrestrial contributions can make these large sargassum patches move to the Caribbean".

We study how they are transported on the ocean surface and how their trajectory changes depending on the wind, what is the minimum wind intensity needed for them to enter the Caribbean and then reach the Mexican coasts, at what time of the year, and how much sargassum could arrive," she said.

Exponential growth theories

It is an alga that moves superficially, there is still no precise data on how deep it can go, biological characteristics that experts are studying. It is also an ecosystem of its own that offers rest for some organisms and is a feeding and reproduction zone for others. It dies when it reaches the coasts. It has an exponential reproduction, from the time that patches are generated in the Equatorial Atlantic and migrate towards the northeast through the Atlantic basin.

She also works in climate process modeling and commented that there are several theories about the causes that generate the massive influxes of sargassum; however, there is still no certainty. One is the deforestation of the Amazon, which generates a large contribution of sediments and nutrients to the ocean that have favored its growth. Another possible explanation is that the change in water temperature in the ocean favors its growth, and the last one is related to the impact of urbanization in coastal areas.

Impact on the marine ecosystem

The Laboratory of Engineering and Coastal Processes of the Sisal Academic Unit of the Institute of Engineering also has a video monitoring system for the coastal zone. One station is located at the Sisal academic unit, and the other at the Institute of Marine Sciences and Limnology, in Puerto Morelos, Quintana Roo; both are UNAM stations. In them, images are obtained that allow observing the arrival of sargassum, the change of the coastline, the sand bars, the movement of coastal dunes, among others.

"We calculate, by means of image analysis methods, how wide the mass of sargassum is that reaches the coast and how at certain times of the year the storms carry the seaweed away; it is a seasonal cycle," Allende Arandía said.

The massive influx of seaweed coincides with important periods such as turtle nesting in Quintana Roo, which has raised the alarm among social and governmental organizations because they do not allow the turtles to reach the beach.  "This has an impact that goes beyond being able to collect the algae or not," emphasized the expert. When the algae begin to decompose, she continued, it emits gases that are quite uncomfortable and affect the well-being of the local communities, because the beaches that are generally cleaned are those of the hotel zones and not the public ones.

"The algae die when it reaches the coast because it no longer has oxygenation, the nutrients no longer circulate and a layer of decomposing algae is formed that does not allow light to penetrate the interior of the water column and everything below begins to die. If this upwelling reaches a reef zone, for example, where part of its vital functions depends on how much light reaches it, it could die in a matter of hours or days", warned the expert.

Utility of sargassum

One of the lines of research that has been strengthened is related to the use that could be made of it since it is already used in the pharmaceutical, agricultural, textile and food industries. An important element is to know if a balance can be established between the amount that can be collected annually and the products that could be produced, as well as the investment required.

So far, it is not attractive to invest in these projects because seaweed is not an available resource, of which it is known how much will arrive and at what date. The investment that has to be made by the private sector or the government to process it is too much to not know if the raw material will be available, he considered.

"For example, in 2018, 522 thousand 226 tons of sargassum were collected, with an investment of 332 million pesos; however, these are figures that have been historical in the Mexican coasts. It is very important to take this into account because the more decomposed it is, the less processable this seaweed is", warns the expert.

She insists that the massive influxes of sargassum are a national problem that requires attention and synergies between the federal and state governments, the private sector, and non-governmental organizations that promote projects for decision making. In addition, to provide early warnings, it is necessary to continue studying sargassum inflows not only nationally but also internationally, as the phenomenon affects several countries such as Brazil, Central America, Mexico, and the United States.

"We must join efforts to do more research, promote transdisciplinary teams and see the coasts as a socio-ecosystem: society, the coast, the sea, and the sargasso are a set of factors that interact all the time, we cannot separate them," she concluded.