Characteristics of foraminiferal communities in the western Clarion–Clipperton Zone revealed by eDNA metabarcoding

The Clarion-Clipperton Zone (CCZ) has attracted growing commercial interest because of its huge reserves of polymetallic nodules and has therefore become an important seabed area for global biodiversity conservation. Foraminifera, significant members of abyssal benthic communities, have been listed as an object of environmental assessment in the specification ISBA/25/LTC/6 issued by the International Seabed Authority due to their high sensitivities to environmental conditions. However, previous ecological studies of CCZ foraminifera were mainly based on morphological analysis and rarely on DNA sequences. Here, we obtained the first DNA metabarcoding dataset of foraminifera in the western CCZ using high-throughput sequencing and focused on the diversity and distribution of hard-shelled foraminifera, which have excellent fossil records and are widely used for paleoenvironmental reconstructions. A total of 806 hard-shelled foraminiferal OTUs were assigned to 36 taxa at the family level and 77 taxa at the species level. The family Eggerellidae and species Nonionellina labradorica had a high relative abundance in all study sites. The taxonomic composition of hard-shelled foraminifera showed spatial heterogeneity, and the alpha diversity between sites was significantly different (p < 0.01). Mantel test showed that Bray-Curtis dissimilarity was positively correlated with the distance separation (p = 0.014; r = 0.461), indicating that the compositional variation of the hard-shelled foraminiferal assemblages increased with increasing geographic distance. Our research is an important supplement to the genetic data of foraminifera in the western CCZ and an enhancement of the information on foraminiferal assemblages in this poorly studied area.