Judit Daniela Huenten, Ariana Belén Alarcón Saavedra, María Carla de Aranzamendi, Timothy O’Hara, Martín Ignacio Brogger

Hidden biodiversity in the Southwestern Atlantic Ocean: brittle stars from the Mar 2 del Plata Submarine Canyon, Argentina

Introduction

Hidden biodiversity in the southwestern atlantic ocean: brittle stars from the mar 2 del plata submarine canyon, argentina. Uncover hidden biodiversity of brittle stars (Ophiuroidea) in Argentina's Mar del Plata Submarine Canyon, SW Atlantic. Reveals 56 species, doubling known records.

Abstract

Among the phylum Echinodermata, the class Ophiuroidea is the most diverse, with brittle stars being widely distributed across benthic environments worldwide. However, this trend is not consistently observed in the Southwestern Atlantic, where other echinoderm classes are reported to be more prevalent. The apparent low biodiversity may be due to insufficient studies and sampling in the deep sea, particularly in small and localized environments like submarine canyons. These geomorphic features of the continental margins are known to support unique marine communities and high biodiversity, as shown by oceanographic expeditions to the Continental Shelf of Argentina on the research vessel Puerto Deseado (CONICET) over ten years ago. These explorations significantly expanded our knowledge of benthic fauna diversity in the Southwest Atlantic. Subsequent studies have reported new fauna records and species, revealing a complex and largely uncharacterized environment, especially regarding brittle stars, a topic still pending thorough study in this area. The present study aims to enhance our understanding of ophiuroid species richness in this deep-sea environment, providing essential data for generalization and biogeographic studies globally. The study area includes the Argentine Continental Slope and the Mar del Plata Submarine Canyon in the Southwestern Atlantic Ocean. We examined samples from 64 stations at depths ranging from 200 to 3,447 meters. Ophiuroids were found in 81% of the surveys, with approximately 6,000 specimens collected. The study area reveals a potential richness of 56 ophiuroid species, including 32 validly recognized species (16 new records for the Argentine Sea) and 24 unidentified or partially identified species. These data more than doubles the known ophiuroid species in the region, highlighting that deep-sea environments are key biodiversity hotspots and could contain significant biodiversity in the Southwestern Atlantic Ocean.

Review

This study makes a significant contribution to our understanding of deep-sea biodiversity in the Southwestern Atlantic Ocean, an area historically considered less diverse in ophiuroids compared to other echinoderm classes. The authors effectively highlight the critical knowledge gap resulting from insufficient sampling, particularly in complex habitats like submarine canyons. By focusing on the Mar del Plata Submarine Canyon and the adjacent Argentine Continental Slope, the research directly addresses the hypothesis that perceived low diversity is an artifact of limited exploration. The premise that deep-sea environments and specific geomorphic features act as biodiversity hotspots is well-established, and this paper provides compelling regional evidence for this general ecological principle, setting the stage for crucial advancements in regional biogeography. The methodological approach, encompassing 64 stations across an impressive depth range (200 to 3,447 meters), is commendable and represents a substantial sampling effort. The collection of approximately 6,000 ophiuroid specimens from 81% of the surveys underscores the abundance and widespread presence of these brittle stars in the study area. The most striking finding is the potential richness of 56 ophiuroid species, which includes 32 validly recognized species – notably, 16 of these are new records for the Argentine Sea. Furthermore, the identification of 24 unidentified or partially identified species strongly suggests that the true diversity is even higher. These figures are transformative, effectively more than doubling the previously known ophiuroid species in the region and decisively demonstrating that the deep Southwestern Atlantic is far from depauperate. Overall, this research successfully uncovers a previously "hidden biodiversity," strongly supporting the idea that deep-sea environments in the Southwestern Atlantic are significant biodiversity hotspots. The identification of numerous new records and potentially new species not only redefines our understanding of regional ophiuroid diversity but also provides essential baseline data for future conservation efforts and more detailed biogeographic analyses. The presence of a substantial number of unidentified species signals an urgent need for dedicated taxonomic work and further exploration. This paper serves as a vital call to action for increased research investment in deep-sea habitats, as it conclusively demonstrates that vast amounts of biodiversity remain undiscovered, even within well-studied phyla like Echinodermata.

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