Exploring the Diversity of Temperate Mesophotic Rocky Reefs From ARMS and Water eDNA in Central Chile

ABSTRACT Humans rely heavily on marine ecosystems for essential goods and services. However, the diversity and composition of mesophotic ecosystems (ME) across temporal and spatial scales remain poorly understood. Upper (UME; 20–50 m) and lower (LME; 50–150 m) MEs, despite the diversity they host and the threats they face, remain largely unprotected. At two locations in central Chile, we first contrast the diversity and composition of rocky reef invertebrate communities between the UME and the LME using eDNA from ARMS and second compare the invertebrate diversity and composition collected from water eDNA and ARMS eDNA. Alpha diversity was greater in the LME except at one of the sites; the LME contained the highest number of exclusive families with the greatest taxa turnovers detected between LME and UME; and community composition differences were mainly driven by sponges (Callyspongiidae) and crabs (Pilumnoididae, Porcellanidae) in the UME and habitat formers such as sponges (Halisarcidae, Suberitidae) and hydroids (Bougainvilliidae, Pandeidae), feather duster worms (Sabellidae), squat lobsters and sea urchins (Arbaciidae) in the LME. Regarding the eDNA diversity and composition between water and ARMS, little diversity was shared between media. Most of the families characterizing the water eDNA community encompassed pelagic copepods (e.g., Acartiidae, Claussocalanidae), whereas ARMS eDNA revealed primarily benthic taxa, such as fan worms (Sabellidae), polychaetes (Terebellidae) and flatworms (Notocomplanidae). This study contributes to our knowledge of the spatial distribution of UME and LME taxa in the central Humbolt current system, justifying the richness and uniqueness of these unprotected ecosystems. Furthermore, this study provides a comparison between water and ARMS eDNA in ME, highlighting the need to sample multiple media to obtain more complete diversity estimates in marine systems.