Widely regarded as one of the planet’s most dangerous invasive alien species for its economic toll and ecological disruption, the zebra mussel has now been detected along eight of Spain’s fifteen hydrographic borders, after adults were found in the Segura basin.
The Segura Hydrographic Confederation notes that the Talave reservoir in Albacete may be partially emptied to a level where zebra mussels typically survive at depths around two to five meters. Drying out existing specimens is seen as a measure to slow or halt their spread.
Data from the Ministry of Ecological Transformation confirms the zebra mussel is present at the borders of several basins, including the Andalusian Mediterranean Basin, Guadalquivir, Guadalete and Barbate, and areas around Tinto, Odiel and Piedras, plus the Júcar, Ebro and Catalonia River Basin Region.
Occurrences extend to Miño-Sil, the Galician coast, the Eastern Cantabria area, Western Cantabria, the Duero, and the Tagus and Guadiana basins. In short, the so called silica portion of Spain has seen incursions.
Concha Durán, head of the Júcar Hydrographic Confederation Technical Service and an expert on this invader, notes that the zebra mussel tends to settle in calcareous environments because it requires calcium carbonate to form its shell.
The zebra mussel ranks among the top ten most dangerous invasive species worldwide due to significant socioeconomic and ecosystem impacts; it does not pose a direct threat to human health, but wherever it appears it brings bad news, Durán emphasized.
The Segura boundary has been one of the few borders still largely free from invasion, possibly thanks to stringent boat controls and ongoing species monitoring, Durán added, stressing the need for firm action when outbreaks are detected.
Brutal ecological impact
Beyond preventive unloading, the temporary cessation of use at the Talave reservoir for fishing and navigation is part of an extensive study to map how far the mussel population has progressed.
Durán shared practical wisdom: initial tough measures are essential, because early intervention shapes the long-term ability to manage the problem.
And there is a caveat. When a population is confirmed, experts expect dispersal to mirror patterns seen in neighboring basins, with continuous efforts to curb the invasive species.
According to researchers, the mollusk can release more than a million larvae per year, while predators are sparse in some waters, amplifying the potential socio economic damage to sectors like agriculture in a basin such as Segura.
Several confederations have already spent tens of millions of euros on direct management, and a study at the Ebro Hydrographic Confederation estimates indirect losses exceed one point six billion euros. These figures illustrate why action is critical.
Boating and fishing restrictions
A restricted reservoir level, along with comprehensive sampling, is being used to determine the true extent of the population. Temporary prohibitions on activities that could spread larvae, including boating and sport fishing, are part of the containment strategy.
It is noted that the zebra mussel is likely to reach the Segura basin via the Tajo-Segura transfer, as streams from infected areas in the Júcar river basin continually feed the Talave reservoir.
Officials say the first adult specimen was detected only a few weeks ago. So far, only larvae with notable morphological damage and low concentrations have been observed. The head of the Segura Hydrographic Confederation Water Quality Service, Sonia Hernandez, says the early detection is encouraging.
To reduce the chance of spread, the water level will be lowered by six to seven meters, partially emptying the reservoir and causing regional samples to die off due to drought. Comprehensive checks will continue both in the affected reservoir and downstream to monitor progress.