Impacts of ocean acidification on hermit crab communities through contrasting responses of Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843)

Ocean acidification (OA) is predicted to decrease the abundance of calcified organisms such as gastropods. Since hermit crabs utilize gastropod shell as mobile shelter, OA has indirect impacts on hermit crab population. To examine the impacts of OA on hermit crab communities, which use calcified shell as the mobile shelter, we conducted field surveys and laboratory experiments using volcanic CO2 seeps in Shikine Island, Japan. By comparing hermit crab community structures and shell availability among five intertidal rocky shores with different degrees of acidification, Paguroidea abundance and species richness were simplified in acidified areas. Rearing experiments comparing survival rates of two Paguroidea species, Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843), at both adult and larval stages, between acidified and ambient aquaria revealed that acidified seawater reduced larval survival rate of C. virescens. Overall, the results indicated that the species-specific direct effect in elevated C. virescens larval mortality could simplify the Paguroidea species composition. In addition, such direct effect would also lead to reduction of Paguroidea abundance, along with indirect effects though a decrease in shell availability.