Deep-sea nematode assemblages from a commercially important polymetallic nodule area in the Central Indian Ocean Basin

Abstract

The Central Indian Ocean Basin (CIOB) is an important area for prospective mining for polymetallic nodules. However, little is known about the biodiversity or community structure of abyssal benthic assemblages in the area. The aim of this study was to investigate nematode assemblages inhabiting nodule fields in the CIOB in terms of species composition, diversity, density, biomass, size spectra and sex ratio. Samples were collected by box corer from a depth of 5000–5100 m during the 39th cruise of RV Akademik Boris Petrov in 2009. In total, 1066 individuals were examined from 4 stations and 16 samples. The total average density of nematodes recorded in the CIOB was considerably lower than reported from other deep-sea regions (27.17 ± 2.7 inds/10 cm2). Nematode diversity was comparable with that of other deep-sea regions and the composition of the dominant taxa was typical for oceanic basins. A total of 284 morphotypes belonging to 113 genera and 30 families were identified. Chromadoridae (29.6%), Xyalidae (19.3%), Oxystominidae (6.6%) and Desmoscolecidae (5.0%) were the dominant families. Among the genera, Acantholaimus (23.2%), Halalaimus (5.7%), Desmoscolex (4.8%), Theristus (3.5%) and Daptonema (3.4%) were the most numerous. The majority of specimens had a body length in the range of 1000–1500 µm, which is also in accordance with other deep-sea studies. Females were three times more abundant than males at all CIOB stations. Average total nematode biomass (52.39 ± 10.0 mg/m2) was comparable with macrofauna biomass from the same area.