La Duero Hydrographic Confederation has put updated figures on a problem that continues to grow: invasive species in the Duero basinA recent work confirms the presence of 108 taxa of flora y 20 fauna non-native plants with the capacity to expand and have effects on riverbanks, rivers and reservoirs.
The diagnosis is based on extensive research and a review of multiple sources. The results reveal that in the 56,7% of the sections analyzed, at least one exotic species of fauna appears, a clear indicator of the pressure exerted by these allochthonous populations on river biodiversity.
Fieldwork and scope of the study
The technical teams visited more than 320 locations distributed between 130 rivers and streams y 15 reservoirs and slow-flowing water bodies (often conditioned by transversal obstacles). The sampling network covered sub-basins such as Adaja, Águeda, Cega, Duratón, Esla, Huebra, Pisuerga, Sabor, Támega, Tormes, Tuela, Valderaduey and Zapardiel, in addition to the Duero itself and its minor tributaries.
In addition to field work, information was collected from regional administrations and specific monitoring programs, integrating previous records of exotic species and the National Catalogue of Invasive Alien Species to draw as complete a picture as possible.
Invasive fauna under the microscope
Among the animal species that are most repeated are the two American crabs (signal and red), the american mink and Asian clamIts success is explained by its ecological plasticity and by the role of the great rivers (Duero, Esla, Pisuerga, Tormes or Órbigo) as authentic dispersal corridors.
El crab sign (Pacifastacus leniusculus) —introduced to replace decimated native populations— thrives in headwater sections with faster currents, lower conductivity, less silt and clear waters. It presents striking abundances in Avila and Segovia, and also in Zamora, where it impacts the river naiad (Daisy margaritifera), an endangered bivalve.
El Red crab (Procambarus clarkii) is a very efficient predator that degrades habitat and competes with native fauna. In addition to its ecological effect, it can cause agricultural damage (for example in rice paddies) by altering margins and soils.
El american mink (Neovison mink), which arrived in its day through the fur industry, occupies today middle sections of large rivers, with a notable presence in the sub-basins of the Esla and Pisuerga and on slopes of the Cantabrian Mountains, the Iberian System and the Central System. It poses a direct threat to the iberian desman (Galemys pyrenaicus), an endemic species in a critical situation.
La Asian clam (Corbicula fluminea) concentrates its dense nuclei in the Douro river, especially near the mouths of the Pisuerga, Adaja and Valderaduey, as well as in Sequillo. In many places it dominates the substratum and displaces other threatened native mollusks.
The inventory also includes other exotic presences, such as the Florida pond turtle (Trachemys scripta) And the asian hornet (Vespa velutina). The expansion is favored by intentional or accidental introductions associated with different human activities.
The invasive ichthyofauna is wide: at least one is confirmed dozens of fish of the National Catalogue with extensive distributions, and there are also exotic species not catalogued in the demarcation, such as the tench (Tinca tenca), the Red fish (Carassius auratus) or the Danube salmon (Hucho hucho). Among the most problematic are the catfish (Ameiurus melas) And tent (Cyprinus carpio), whose presence is linked to the fishery and relocations for recreational purposes.
Exotic flora gaining ground
The census of invasive plants amounts to 108 species, with several especially widespread in the river network. They stand out Ailanthus altissima (tree of heaven), Azolla sp. Populus × canadensis, Conyza canadensis, medicago sativa, Isatis tinctoria and Mimosa (acacia dealbata).
Conyza canadensis, native to North America, is a herbaceous plant that colonizes rapidly altered and nutrient-rich areas. Even with variable ecological impact, it competes with crops and can generate losses in certain farms.
medicago sativa —wild alfalfa from Türkiye and Central Asia— is used as forage and has found a niche in mighty rivers like the Duero, Pisuerga, Esla, Cea o Tormes, where it is established in borders and gravel pits.
Isatis tinctoria, historically linked to obtaining indigo, can exceed one meter in height and form dense patches which prevent the regeneration of native vegetation; it has been detected in rivers Arlanza y Lobos.
La Mimosa (acacia dealbata) is widely distributed in the channels of the demarcation in the province of Ourense (Támega area), where it colonizes burned slopes and valley bottoms, replacing riparian vegetation.
The greatest diversity of exotic flora is concentrated near urban centers , the Zamora, Valladolid, León o Palencia, where environmental degradation facilitates their settlement. A singular focus appears in the Arrives del Duero, favored by a warmer microclimate than in other areas of the demarcation.
Impact, entry pathways and management
Most of these species arrive by human action: deliberate releases, escapes, trade in Pets, gardening, restocking for fish farming purposes or movements associated with infrastructure such as reservoirs and pipelinesOnce established, they take advantage altered habitats to expand.
Consequences include competition with native species, predation, transmission of pathogens and physical changes in the habitat. In particularly fragile river systems, these processes can lead to local extinctions and transformations that are difficult to reverse, which underlines the usefulness of maps and tracking which is promoted by the CHD to guide actions.
The report paints a resounding picture: many entry routes, river corridors that facilitate expansion and a host of species - from crabs and minks to ailanthus, mimosas or Azolla— which already determine the health of the Duero rivers. With 108 invasive plants and 20 animals identified and critical areas near large cities and in enclaves such as the arrivals, the demarcation faces a conservation challenge of the first order.