Distribution patterns and habitat suitability of the non-native brittle star Ophiothela mirabilis Verrill, 1867 along the Western Atlantic

Abstract The Pacific epizoic brittle star Ophiothela mirabilis Verrill, 1867 has successfully established itself along the Southwestern Atlantic. While reports of this species show high densities and an expanding range throughout the Western Atlantic, specific knowledge regarding populations and their potential for distribution is scarce. We assess herein the current distribution and abundance patterns of O. mirabilis along the subtropical SW Atlantic coast while simultaneously employing ecological niche models (ENMs) to predict suitable habitats in the future. Ophiothela mirabilis is currently distributed in both poly- and euhaline estuarine and inner continental shelf areas. Population densities tend to increase from the inner shelf (≤ 492 individuals.m−2) to estuarine habitats (≥ 815 individuals.m−2), characterized by a 53.38% mean habitat suitability index, until being limited by unsuitable environmental habitats. Octocoral species are the most densely and frequently colonized hosts (up to 3.6 individuals.cm−2 of host's area). Currently, occurrence records for O. mirabilis encompass disjunct habitats from Santa Catarina (S Brazil) to Southeast Florida (USA). Our ENMs predicted that O. mirabilis has the potential to further spread across the warm marine provinces of the Western Atlantic, as they are characterized by ≥40.72% of environmentally suitable habitats. The occurrence of the species correlates mainly to mean calcite concentration and mean sea surface temperature, which accounts for 56.97% of the performance of the ENMs. The high spreading capacity and the maintenance of dense abundances on hosts raises questions about its effects on recipient biodiversity and systems.