A team of environmental researchers discovered three specimens during fieldwork in the Nalón-Narcea basin of Asturias. The discovery includes a marble crab, a species native to the Americas and never before seen in Spain’s rivers. The crab is notable for its high reproductive capacity, a trait that could enable rapid population growth and potentially threaten the region’s indigenous aquatic species.
One of the specimens is slated for genetic sequencing to determine its origin. The goal of the study, as explained by the project lead, is to establish whether the crabs were released from an aquarium or if they belong to a marble crab population already established somewhere in Europe. This information will also help assess survivability in this particular area and guide any necessary conservation actions in the river systems of Asturias.
The marble crab is among 272 species listed as potentially invasive in continental waters of Spain and Portugal, identified under the Life Invasaqua initiative. This program, funded in part by European resources, aims to raise awareness and educate the public about invasive alien species affecting freshwater and estuarine environments across the Iberian Peninsula.
The discovery site features both the physical samples and the attendant context of the investigation, highlighting the role of regional authorities in monitoring incursions that could disrupt local ecosystems. Agency records note that the marble crab originates from the Americas and has been bred for the ornamental aquatics industry. In Spain, it has not been observed in the wild until now. The genetic sequencing will reveal clues about the source of the organisms and help determine whether they are tied to captive populations that escaped or to a breeding population in Europe.
If the specimens are connected to European populations, the crabs may encounter conditions better suited to their survival, which could accelerate their establishment in local waterways. In that scenario, regional authorities plan to conduct river surveys across the Asturian river network to detect additional individuals and map any potential expansion. The presence of this species could create competition for native freshwater fauna and expose them to new parasites and pathogens carried by the crab or its shell, potentially affecting ecosystem balance. Some researchers warn that the marble crab reproduces by parthenogenesis, a mode of reproduction in which females can produce viable offspring without fertilization. In practical terms, a single female could seed a new population, generating hundreds of offspring in a short period.
The Life Invasaqua project, a collaborative effort co-funded with European funds, emphasizes public education and policy measures to mitigate the spread and impact of invasive species in Spain and Portugal. The current study underscores the importance of early detection, rapid assessment, and coordinated response to protect native biodiversity in Iberian waters.