Brazil's Invisible Invaders: Are Craspedacusta Jellyfish a Ticking Ecological Bomb?

ABSTRACT The invasive freshwater jellyfish Craspedacusta sowerbii , likely of Asian origin, is globally distributed, yet its invasion history in South America remains poorly understood. Following a mass mortality event of tilapia ( Oreochromis niloticus ) during a jellyfish bloom in Paraná, Brazil, in March 2022, we conducted morphological and molecular analyses on C. sowerbii from two southern Brazilian states (Paraná and Santa Catarina). We generated the first mitochondrial cytochrome c oxidase subunit I (COI) gene sequences for this species in Brazil. Morphological analysis confirmed the species identity, with the Paraná population consisting exclusively of females. Phylogenetic analysis revealed two distinct genetic lineages, indicating at least two separate introduction events. The Paraná population clustered with haplotypes from Chile, whereas the Santa Catarina population was closely related to haplotypes from southern Asia (Singapore and China). These findings underscore the complex, human‐mediated, and yet not fully understood invasion pathways of C. sowerbii , highlighting the need for further monitoring to understand its distribution and ecological impacts.