Long-term fluctuations in mollusk populations before and after the appearance of the alien predator Euspira fortunei on the Tona coast, Miyagi Prefecture, northern Japan.
The impact of Euspira fortunei as an alien predator on fluctuations in population densities of prey mollusks between 2001 and 2010 on the Tona coast, northern Japan, was investigated. This species increased dramatically from 2002 to 2004. In contrast, prey species such as Ruditapes philippinarum and Macoma incongrua decreased rapidly from 2001 to 2004, whereas Pillucina pisidium and Batillaria cumingii did not show a significant decrease during this period. Using a laboratory experiment, we were able to show that these decreases in the population densities of some species of mollusks but not other species were the result of species-selective predation by E. fortunei, as the experiment revealed that E. fortunei preferred to attack R. philippinarum and M. incongrua rather than P. pisidium, although the predator did expand its diet to include P. pisidium after it had consumed 16 of the 20 preferred prey available (i.e., R. philippinarum and M. incongrua). This case study suggests that invasive naticid predators have the potential to affect the population density and community structure of prey mollusks in recipient coastal ecosystems through predation.