What Does the Haired Keel on the Shell Whorls of Potamopyrgus antipodarum (Gastropoda, Tateidae) Mean?

In several ecosystems, Potamopyrgus antipodarum (Gray, 1853) (Gastropoda, Tateidae) is considered among the worst invasive species. Its tolerance to a broad range of environmental conditions has favoured its success in colonising new environments worldwide. However, population
 crashes may occur, leading to significant fluctuations in snail densities. Such crashes might be linked to morphological changes in the shell whorls, like the emergence of a haired keel (carinatus morphotype). In this study, we investigated the link between the appearance of the carinatus
 morphotype and the crashes in population densities over three years, based on field observations. The presented results show that after the emergence of the so-called carinatus morphotype, the population of P. antipodarum collapsed and did not recover for the next two years.
 This may indicate that the carinatus morphotype is a defensive reaction to extremely unfavourable environmental conditions.