Northward Redistribution of Warm-Affinity Marine Fauna in the Iberian Atlantic: Insights from a Recent Northern Occurrence of the Hermit Crab Dardanus calidus.

Poleward shifts in species distributions are increasingly reshaping marine communities worldwide. Along the Atlantic coast of the Iberian Peninsula, recent observations suggest ongoing biogeographical changes affecting a wide range of marine organisms. Here, we document the occurrence of the warm-water hermit crab Dardanus calidus in Galician waters (NW Spain), based on a single female collected in the region. Morphological and molecular analyses confirmed its identification, with the COI sequence showing high similarity to previously published Atlantic and Mediterranean sequences. The Galician record represents the northernmost occurrence of the species currently documented in the Atlantic Iberian region. Given the conspicuous nature of D. calidus and the comparatively well-documented hermit crab diversity of northwestern Iberia, the specimen is unlikely to reflect a common but previously overlooked component of the regional fauna. Although this single record does not demonstrate colonization or a sustained northward expansion, it adds to the increasing number of warm-affinity marine species recently reported beyond their historically documented ranges in northwestern Iberia and is consistent with broader evidence of ongoing biogeographical reorganization in the region. This finding highlights the value of integrating faunistic observations and molecular tools to track contemporary changes in marine species distributions.