Short-range diversity and invasion dynamics of the invasive freshwater jellyfish Craspedacusta sowerbii in Lake Kinneret and its watershed – field sampling combined with hydrodynamical simulations

The hydrozoan Craspedacusta sowerbii , native to the Yangtze River system in China, has become an invasive species in freshwater ecosystems worldwide. Multiple genetic lineages have been introduced globally, yet the species’ taxonomic identity remains unresolved. Its life cycle alternates between a benthic polyp stage and a pelagic medusa stage, the latter being the primary focus of most distributional studies. In Israel, the species was previously reported from the Kinneret watershed, though recent records are lacking. Here, we surveyed streams and ponds in the Golan Heights for both medusae and polyps and conducted genetic analyses on collected specimens. Three mtDNA-haplotypes were identified, corresponding to those previously described from European populations. Most sites exhibited homogeneous haplotype composition, suggesting limited admixture and restricted short-distance dispersal. While our survey did not confirm the presence of C. sowerbii in its pelagic stage, the detection of polyps in multiple inflowing streams suggests that colonization of Lake Kinneret is likely. Toward planning a proper monitoring program, we first performed 3D hydrodynamical simulations of the lake dynamics, incorporated with both transport processes, injected from the major inflowing streams. The simulations suggest specific positions for yearly and seasonally coastal ‘hotspots’ of jellyfish distributions. Furthermore, the simulations indicate seasonal variations in the penetration potential of jellyfish into the lake. In winter, they penetrate deeper and away from the coasts, whereas in summer they remain concentrated near the lake surface and close to the coasts.