What was long interpreted as a simple change in the color of the Mar Menor waters is, in reality, a profound process of ecological degradation. A team of scientists from the Spanish Institute of Oceanography and the University of Murcia has demonstrated, for the first time worldwide, that the so-called 'white patch' is not merely a visual phenomenon, but is severely altering the seabed and the life it supports.
The study, published in the journal Marine Pollution Bulletin , reveals that the continuous precipitation of calcite microcrystals, caused by an increase in the water's pH, has generated a layer of sediment that now covers 12,3 square kilometers of the lagoon . This area is equivalent to 9% of the Mar Menor and has led to the near-total loss of underwater vegetation in a core area of 6,7 square kilometers.
A phenomenon that goes beyond the color of the water
The turbidity in the affected area is up to nine times higher than normal, drastically reducing the amount of sunlight reaching the seabed. During the analyzed period, only 3,9% of solar radiation reached the seabed, compared to 18,3% in the control areas. This lack of light, along with the progressive burial under calcite , has left an area of 6,7 km² completely devoid of seagrass meadows.
Víctor Orenes-Salazar, a researcher at the IEO-CSIC and lead author of the study, points out that "the magnitude of the seagrass loss is especially worrying." He explains that the phenomenon "is not limited to changing the color of the water," but also drastically reduces the amount of light reaching the bottom and continuously deposits calcite particles onto the plants. In fact, the data indicate that the vegetation has completely disappeared in the central core of the affected area.
Devastating consequences for marine life
The disappearance of seagrass meadows has a direct effect on fish, as these vegetated areas are essential as refuge and breeding grounds. To quantify this impact, researchers from the University of Murcia analyzed more than 4.000 specimens over the course of a year. The results are conclusive: while 21 different species were identified in healthy areas, only ten appeared at the edge of the affected area, and within the most impacted core, only three survived.
Species closely linked to seagrass meadows, such as the river needlefish and the wrasse, have practically disappeared from the area, while more generalist species, such as the black goby, have increased in number. Adrián Guerrero-Gómez, a researcher in the Department of Zoology at the University of Murcia (UMU ), points out that this phenomenon is not occurring in an intact ecosystem: “The white patch is not affecting an untouched ecosystem; it comes after decades of changes and loss of deep habitats . Our results suggest that this phenomenon is further simplifying communities that had already undergone significant transformations.”
The authors emphasize that the study constitutes the first empirical demonstration, internationally, that a chronic whiting episode can persist for years and cause far-reaching ecological changes in a coastal ecosystem. The research was carried out thanks to state, regional, and European funding through the BELICH and GRASSREC projects and contracts with the Directorate General for the Mar Menor of the Autonomous Community of Madrid.
The research team considers it a priority to maintain constant monitoring of the white patch's evolution, assess whether it could spread to more sensitive areas of the lagoon, and determine if the underwater vegetation will be able to regenerate over time. Continuous monitoring is crucial to prevent further deterioration and to determine if the Mar Menor ecosystem can recover from this new environmental blow.
