From local discovery to global insights: deep-sea amphipod diversity in a high-seas marine protected area and its conservation implications

The deep ocean, while home to a remarkable diversity of life, remains one of the least understood environments on Earth. This profound lack of information hampers our ability to protect and manage deep-sea ecosystems effectively, especially as they face escalating threats from human activities such as resource extraction, pollution, and climate change. In light of these knowledge gaps, this study investigates the diversity of benthic amphipods collected from abyssal depths within the recently established North Atlantic Current and Evlanov Sea basin (NACES) high-seas marine protected area (MPA). Amphipods, with their brooding reproductive strategy and absence of a dispersive larval stage, are potentially limited in their distribution. This makes them valuable for biogeographic studies as biographic histories are maintained over longer periods of time. A total of 253 amphipod cytochrome c oxidase subunit I (COI) sequences were newly generated; these include 99 from the NACES MPA, 43 from the Labrador Sea, 42 from the Azores as well as 69 eusirids from other populations in the Atlantic, Pacific, Indian Ocean, and Antarctic. A single epibenthic sledge haul from the NACES MPA in 3,677 m depth revealed 47 amphipod molecular operational taxonomic units (MOTUs) from 98 sequenced individuals, with Chao1 estimates exceeding 120 species. This highlights unexpectedly high benthic diversity at local scales. The majority of these species could not be unambiguously assigned to known species, but many of these are probably new to science. Two of these species are formally described, Cleonardo helga sp. nov. and Cleonardo davinci sp. nov., and a dichotomous key to all known Cleonardo species worldwide is provided. Biogeographic links were studied for species of the family Eusiridae Stebbing, 1888 by comparing the NACES MOTUs to newly sequenced data from the North Atlantic and all existing COI sequences from GenBank and Barcode of Life Data Systems (BOLD). Of the eight NACES eusirid MOTUs, four were recorded also from other abyssal regions including the Labrador Sea, the Azores, the Arctic, and North and West Pacific. By linking the discovery of local species to broader global distribution patterns, this research enhances our understanding of deep-sea marine ecosystems and underscores the importance of conservation efforts in safeguarding these vulnerable marine habitats.