First record of hybrid Eriocheir specimens (crustacea, decapoda, varunidae) in the Mediterranean sea

Two specimens of Eriocheir sp. were captured on December 11, 2024, in L’Albufera of Valencia, a shallow, hypereutrophic coastal lagoon in the Mediterranean Coast of Spain. The specimens were adult males. An adult female was also captured on January 2nd, 2025. Although the initial morphological examination led to its identification as members of a cryptic Eriocheir species, subsequent COI sequence analysis and the re-checking of some morphological characters identified the specimens as hybrids of E. sinensis and E. japonica. These hybrids have previously been recorded in East Asia—specifically in Russia, Japan, and South Korea—as well as in several European locations including Germany, Poland, North Wales and The Netherlands, suggesting that historical records of E. sinensis in both its native and invasive distributions may include misidentified hybrids. Multiple introduction pathways are considered, including ballast water discharge, larval dispersal, and potential human-mediated escape or deliberate introduction. Additionally, a catastrophic storm in October 2024 may have facilitated the transport of these crabs from freshwater systems into the lagoon. The establishment of a self-sustaining Eriocheir population could impose significant ecological pressures on the lagoon’s ecosystem and adversely affect local stakeholders, notably professional fishermen and rice cultivators. These findings highlight the urgent need for comprehensive monitoring and management strategies in vulnerable coastal ecosystems.