Eudiaptomus gracilis in Italy: how, where and why

Eudiaptomus gracilis, one the most widely distributed calanoid copepod species in Europe, was not reported in Italy prior to the late 1980s. Since then, E. gracilis has spread to an increasing number of Northern Italian water bodies where an indigenous calanoid copepod, E. padanus, was commonly present and abundant. In some instances, the former species has displaced the latter. Morphological and ecological similarities between the two species suggest that competitive exclusion may explain this substitution. The establishment of E. gracilis seems to be limited to relatively small, eutrophic water bodies, which represent the majority of floodplain lakes in Northern Italy. The very recent colonization of oligo-mesotrophic Lake Maggiore - one of the largest Italian lakes - may allow for an examination both of the invasion process and its consequences for the abundant E. padanus population. Establishment of E. gracilis in Lake Maggiore could accelerate the spread of the species to other lakes in the region. Indeed, due to its high connectivity, Lake Maggiore could become an invasion hub in a manner consistent with that reported for other invaders in lakes around the world.