Shifts in patterns of shell utilization by the hermit crab Clibanarius erythropus following the arrival of a non-native gastropod

Hermit crabs rely on gastropod shells for protection and survival in rocky coastal habitats. This study evaluates the arrival of the non-native Phorcus sauciatus influences patterns of shell selection of the hermit crab Clibanarius erythropus along the southern coast of São Miguel Island, Azores (NE Atlantic). Field sampling from four intertidal sites revealed that P. sauciatus accounted for 22.4% of the shells occupied by hermit crabs, marking a significant shift in shell utilization since the species introduction in 2013. Morphometric analyses compared P. sauciatus shells with four others commonly used gastropod shells, revealing that P. sauciatus provides favorable characteristics, such as a high internal-to-mass ratio, which likely enhances hermit crab survival and motility. Temporal comparisons with studies from 2000 and 2009 indicate substantial changes in shell utilization, with P. sauciatus becoming a key resource. P. sauciatus establishment provides a greater diversity of shells available to C. erythropus. This study underscores the ecological consequences of non-native species, showing how they can alter resource availability and create new exploitable niches for native species, such as hermit crabs on the rocky shores of São Miguel.