Hidden gems of the abyss: first species of azooxanthellate scleractinian coral (Scleractinia: Deltocyathidae) attached to polymetallic nodules in the eastern Pacific Ocean

Abstract Species in the genus Deltocyathus occur in every ocean basin except the Arctic and around Antarctica. They are most commonly found within 200 to 1000 m depth, with the deepest recorded species, Deltocyathus parvulus, found at 5080 m deep. Most Deltocyathus species are free-living, except for the Atlantic species Deltocyathus halianthus. Using an integrative taxonomic approach, here we describe Deltocyathus zoemetallicus sp. nov., collected at abyssal depths in the Clarion-Clipperton Zone and with a distribution spanning around 1000 km. This region of the central Pacific contains abundant mineral accretions known as polymetallic nodules that provide a significant source of hard substrate for sessile fixed species, including the species described herein. Seabed imagery transects on nodule fields were used to estimate standing stocks, with higher densities found in areas characterized by small nodules that almost completely cover the seafloor. These findings suggest that the abundance of D. zoemetallicus might depend on the density of polymetallic nodules. Consequently, despite its broad geographic range that may confer resilience at a large scale, this new coral species could be locally vulnerable to potential deep-sea mining activities.