Massive decline of invasive apple snail populations after blue crab invasion in the Ebro River, Spain Céspedes, Vanessa Bernardo‑Madrid, Rubén Picazo Mota, Félix Vilá, Montserrat Rubio, Cristóbal García, María Sanz, Ismael Gallardo, Belinda Callinectes sapidus Ebro River Overpredation The negative interaction between multiple invasive species, when an invasive predator benefits from a previously introduced and abundant prey, poses unanticipated challenges for the joint management of invaders. To illustrate this question, we describe the surge and collapse of the invasive apple snail Pomacea maculata population before and after the arrival of the invasive blue crab, Callinectes sapidus, in the Ebro River (NE Spain). These two invaders have coincided for the first time beyond their respective native and prior invasive ranges, and thus lack any previous shared eco-evolutionary history facilitating coexistence. We leverage data from a 9-year apple snail removal programme (2014–2022) conducted by authorities to evaluate the effectiveness of the management programme and describe the apple snail temporal dynamics in the Ebro River. Since its arrival in 2013, the apple snail population increased exponentially along the river and adjacent rice-fields despite labour-intensive eradication efforts. Unexpectedly, riverine populations of the apple snail declined by 90% in 2018 relative to the prior year without apparent association with previous management efforts. Simultaneously, the blue crab was first recorded in the Ebro River in 2018, and its distribution rapidly overlapped the whole area invaded by apple snails. We suggest that over-predation by the blue crab is the main cause of the decline observed in the apple snail, and discuss the implications of this new invader-invader interaction for management. This study underscores the unforeseen consequences of subsequent waves of invasion, and the importance of supporting management with a deeper understanding of ecological interactions among invasive predator and prey species. 2024-07-23T11:21:41Z 2024-07-23T11:21:41Z 2024-05-21 journal article Céspedes, V., Bernardo-Madrid, R., Picazo, F. et al. Massive decline of invasive apple snail populations after blue crab invasion in the Ebro River, Spain. Biol Invasions (2024). [https://doi.org/10.1007/s10530-024-03334-1] https://hdl.handle.net/10481/93407 10.1007/s10530-024-03334-1 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional Springer Nature