Invasive species encroach on the habitats of native organisms, displacing them and often leading to their decline or disappearance. In the case of the river crab, a non-native competitor has already claimed about 95% of its space in Spanish ecosystems, highlighting the pressure from American crayfish that were introduced decades ago.
A research team at the Doñana Biological Station (EBD) of the Higher Council for Scientific Research (CSIC) studied shifts in the distributions and ecological niches of three crayfish species introduced to Spain over time. The focus centers on the Italian crayfish, which arrived in the 16th century and is often mischaracterized as native. Two North American species, the red crayfish and the signal crayfish, were introduced in the 1970s.
The findings, published in the Journal of Animal Ecology, indicate that the shared ecological niche of these two American species now covers more than 95% of the Italian crayfish’s niche. The report notes that only small headwater refuges remain for the latter.
To conduct the study, researchers compiled systematic data on crayfish presence spanning the past 200 years, integrating a range of historical and contemporary sources.
“Although discussions often center on native crayfish, the Peninsula actually hosts no native species of crayfish,” explains researcher Miguel Clavero from EBD-CSIC. “Recent work suggests that the species thought to be native is in fact the Italian crayfish, scientific name Austropotamobius fulcisianus.” he notes.
Crabs since the time of Philip II
This crayfish species was introduced to King Henry II, who sought to fill the ponds of his newly built palaces with striking animals encountered in Dutch and Italian sites. Spain received the Italian crayfish in the late 16th century at the king’s request. The privilege to stock ponds endured as new introductions followed, a process not fully documented until now. The species became a common source of seafood.
While the Italian crayfish spread widely between 1850 and 1960, its ecological niche in 1850 already closely resembled its profile in 1960. The 20th century saw sustained introductions of Italian crayfish, with the Franco regime promoting fishing interests.
“Likely due to overexploitation, many Italian crayfish populations began to decline or vanish in the early 1970s,” notes researcher Duarte Viana, the study’s lead author.
“This triggered concern in a society with a strong affection for crabs and helped justify the introduction of two North American species, the red crayfish and the signal crayfish. After the arrival of the American crabs, the Italian crayfish’s distribution contracted to higher, more mountainous river sources and coastal zones.”
Crayfish as Disease Carriers
The ecological niches of the two American species show clear complementarity: the signal crayfish (Pacifastacus leniusculus) thrives in colder northern environments, while the red crayfish (Procambarus clarkii) favors warmer, lower-altitude habitats.
The combination of global warming and the ongoing spread of American species could render small streams, once safe havens for the Italian crayfish, uninhabitable. Like many invasive taxa, these crabs are associated with a pathogen known as the crayfish plague, a deadly disease for all European crayfish, including the Italian species.
American specimens carry the crayfish plague, a disease fatal to all European crabs.
“Ecosystems are continually shifting, a pattern intensified by current climate change,” explains Viana. “Species can adjust their niches in response to environmental changes, and understanding these shifts helps biodiversity conservation. Although a species’ niche is often viewed as fixed, it can change under changing conditions.”
Long-term data on changes in species’ ecological niches have been sparse. Much biodiversity information has only recently been collected in standardized ways, so earlier changes may be overlooked. This crayfish study demonstrates how historical data can illuminate species distributions and ecological processes during less-studied periods. The researchers emphasize that a long-term perspective is essential for assessing human impacts on natural systems and establishing reference conditions for biodiversity conservation.
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