The Spanish Institute of Oceanography warns of the risk of another episode of massive death of fish in the Mar Menor

Algae in the Mar Menor, in the area near San Javier, a week ago. SAN JAVIER CITY COUNCIL (Europa Press)

The Spanish Institute of Oceanography (IEO-CSIC) has warned this Tuesday of the risk that the Mar Menor runs of suffering another episode of massive death of fish and other organisms.

The CSIC center has prepared a report to assess the state of the salty lagoon after the torrential rains in March, the conclusions of which point to the fact that the increase in nutrients and organic matter drives the eutrophication of this aquatic ecosystem, a process that translates into the increase of algae, the depletion of oxygen and, finally, in the death of animals.

The last major similar episode took place in August 2021, while in recent days, the scientific committee that monitors the lagoon has warned of a dangerous increase in algae in the area.

“There is a high probability that an episode like the one last August will occur,

but we don't know when it will be.

In the current circumstances, nothing can be done to avoid it”, summarizes Juan Manuel Ruiz, research professor at the IEO-CSIC and one of the authors of the report.

The document, prepared at the request of the Ministry for the Ecological Transition, updates the previous studies carried out by the IEO-CSIC on the scientific monitoring of the state of the Mar Menor.

The authors of the study —also P. Clemente-Navarro and R. García Muñoz— point out that any analysis of the situation of the lagoon must be contextualized in the process of eutrophication that it has been suffering in recent decades due to the massive contribution of nutrients from of human activity, mainly due to intensive agriculture and excessive tourism.

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These substances, mainly nitrogen and phosphorus, enter the lagoon through surface runoff in the boulevards, through groundwater or through the dragging of water and materials from the basin during torrential rains, such as those that have occurred in recent months.

"The rains drag tons of materials from nearby agricultural land into the lagoon, which are very rich in nitrogen and phosphorus, which is what activates the growth of phytoplankton," Ruiz points out.

"Furthermore, the runoff crosses the urban centers, where it saturates the sanitation networks, which are undersized, and causes all that water contaminated with sewage and other urban pollutants to end up in the Mar Menor," he continues.

In fact, according to data from Ecological Transition, the month of March was the wettest in the Region of Murcia in the last 62 years and has also coincided with two particularly intense haze episodes.

These climatic anomalies, together with the high concentration of nutrients already existing in the salty lagoon, form a perfect cocktail for the rapid growth of species such as macroalgae, and are the clearest exponent of the eutrophication process that the area is undergoing.

In addition, the document warns that the heavy rains have also caused a sharp drop in salinity, a variable that for scientists is of great importance in the Mar Menor.

After the rainfall, and as a result of the rise in the water table -the upper layer of the aquifer-, the contributions of fresh water with a high content of nutrients to the lagoon continue, which, according to scientific projections, will also interfere with the seasonal dynamics of salinity.

Scientists warn that these problems will occur more and more.

“This type of episode has become more frequent since 2016, when the ecosystem collapsed, because the Mar Menor is in a more vulnerable, more unstable state and, therefore, more susceptible to suffering from anoxia —lack of oxygen—,” he points out. the scientist.

"With climate change it will get worse, because there will be more and more extreme phenomena, such as heat waves and torrential rains, which will end up having an impact on the lagoon as well," he concludes.

On the other hand, the IEO-CSIC experts have detected a notable increase in the turbidity of the water column as of February of this year.

This new episode is due, above all, to the contributions of materials during the rainy episodes, but it could continue in the coming weeks or even months due to the development of phytoplankton communities —living beings of plant origin that live floating in the water— .

In addition, there is a sharp increase in chlorophyll that is likely to continue to grow due to the increase in temperatures and hours of sunshine typical of spring.

Alert in the last days

Last week, experts in the Mar Menor sounded the alarm over the rapid growth of algae known as angel hair (

mixed with ovas (another type of algae) in various areas, including La Manga del Mar Menor.

This plant appears when there is an excess of nitrogen in the water, which is caused in the lagoon by the discharges that arrive through different streams, loaded with the remains of the fertilizers used in agriculture.

The latest measurements indicate that "very high values" of nitrogen are entering, around 21,000 kilos per day, according to what Emilio Maria Dolores, president of the scientific committee that monitors the lagoon, made up of politicians and experts, warned on Wednesday.

This alarming situation “marks the beginning of eutrophication”, which if it is not stopped will probably mean that “the situation is the same as or worse than last year”, in reference to the episode experienced in August.

The strip of algae detected in the La Manga area is located about 100 meters from the coast and is about two kilometers long and an average of about 50 meters wide, the Platform for the Mar Menor has calculated.

The regional government has been removing the algae for more than three weeks, the only method that exists to prevent it from decomposing on the shores, forming a slime that moves and that, with the appearance of phytoplankton (composed of microscopic organisms), leads to a decrease in oxygen.

So far, more than 10,000 tons of biomass and algae have been removed.

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