Metazoan diversity in the Atacama and Kermadec trenches through eDNA (metabarcoding of 18S and COI)

Our current understanding is that marine faunal diversity decreases with depth, but a significant part of the deep ocean has not yet been explored. We assessed the faunal diversity in the water column of the Atacama Trench, from the high-productive near-surface down to ~8000 m depth, using environmental DNA. Our results indicate that in the Atacama Trench the genetic diversity of metazoans in waters below 4000 m depth is as high as in waters above, with a dominance of hydrozoans and copepods. They also revealed several unknown phylogenetic clades within the abyssal and hadal dominant groups. Similar observation in the less productive Kermadec Trench, however, do not show a higher diversity in deep waters. The combined results thus suggest the occurrence of high endemism in ultra-deep pelagic waters influenced by high primary production. They also underline the need to continue exploring and studying these remote ecosystems to understand better their ecology and uncover their hidden biodiversity.