Hidden biodiversity in the Southwestern Atlantic Ocean: ophiuroids from the Mar del Plata Submarine Canyon, Argentina

HUENTEN DANIELA; ALARCÓN SAAVEDRA, ARIANA B.; DE ARANZAMENDI, M. CARLA; OHARA, TIMOTHY

Revista del Museo Argentino de Ciencias Naturales, nueva serie

Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"

Lugar: Buenos Aires; Año: 2025 vol. 27 p. 183 - 195

1853-0400

Among the phylum Echinodermata, the class Ophiuroidea is the most diverse, with ophiuroids beingwidely distributed across benthic environments worldwide. However, this trend is not consistently observed inthe Southwestern Atlantic, where other echinoderm classes are reported to be more prevalent. The apparent lowbiodiversity may be due to insufficient studies and sampling in the deep sea, particularly in small and localized en-vironments like submarine canyons. These geomorphic features of the continental margins are known to supportunique marine communities and high biodiversity, as evidenced by oceanographic expeditions to the Argentinecontinental slope on the research vessel Puerto Deseado (CONICET) conducted over a decade ago. These expe-ditions significantly expanded our knowledge of benthic fauna diversity in the Southwest Atlantic. Subsequentstudies have reported new fauna records and species, revealing a complex and largely uncharacterized environ-ment, particularly with regard to ophiuroids, a topic still pending thorough study in this area. This study aimsto enhance our understanding of ophiuroid species richness in deep-sea environments, providing essential datafor broader and biogeographic studies globally. The study area encompasses the Argentine Continental Slope,including the Mar del Plata Submarine Canyon in the Southwestern Atlantic Ocean. We examined samples from64 stations at depths ranging from 200 to 3,447 meters. Ophiuroids were identified in 81% of the surveys, withapproximately 6,000 specimens collected. The study area reveals a potential richness of 56 ophiuroid species,including 28 validly recognized species (12 new records for the Argentine Sea) and 28 unidentified or partiallyidentified species. These data more than doubles the known ophiuroid species in the region, underscoring theimportance of deep-sea environments as biodiversity hotspots and suggesting that the ophiuroid diversity in theSouthwestern Atlantic Ocean is underestimated and may be significantly diverse as in other regions.