High species richness and unique composition of the tanaidacean communities associated with five areas in the Pacific polymetallic nodule fields

Abstract

The benthic fauna associated with polymetallic nodule fields is scarcely studied. Studies on species richness and distribution patterns are indispensable for the conservation of the abyssal ecosystem and for the development of management strategies for sustained commercial activities in the future. Here, we analysed the distribution patterns and diversity of tanaidacean communities associated with four International Seabed Authority licenced areas (BGR, IOM, GSR, Ifremer) located in the Clarion-Clipperton Fracture Zone (North-East equatorial Pacific) and the one Area of Particular Environmental Interests (APEI3). The study was based on 34 box core samples collected at depths ranging from 4200 to 5000 m. Altogether, 98 species (446 individuals) were recorded, of which 47 were singletons. Most tanaidaceans (78 species) were unique to a specific area. The highest densities, species richness and diversity were recorded in the BGR license area, while the lowest values were found in the APEI3. Our results correspond to the differences in productivity observed among the five areas. Species accumulation curves demonstrated substantial undersampling, and the final conclusions about tanaidaceans diversity in the CCFZ should be treated with caution, requiring further studies with higher sampling effort. The extremely low densities (2.3 ± 2.3 ind./0.25 m2) and species richness (five species) recorded in the APEI3 suggest a need for the revision of planned conservations strategies in the CCFZ, although it was the most scarcely sampled area and our results are therefore not representative of the entire site.