Biodiversity of nematodes in the Western Indian Ocean (WIO): taxonomy and assemblages

Abstract

During the Netherlands Indian Ocean Program (NIOP) 1990-1995, benthic sampling was carried out to assess among other things, meiofauna densities, sediment community oxygen consumption and nematode assemblages. Four transects were sampled along the Kenyan coast in the Western Indian Ocean (WIO), from north to south: Kiwayu, Tana, Sabaki and Gazi. Samples were taken during two seasons: South East monsoon in June/July and the onset of the North East monsoon in November/December at depths: 20m, 50m, 500m, 1000m and 2000m. The samples were taken using a box core or lander. From each box two subsamples were taken to a depth of 5 cm using a plastic core 2.6 cm internal diameter. The two sub-samples from each box were mixed and fixed in hot, 4 % formaldehyde. In the laboratory, they were centrifuged in Ludox and nematodes were separated and enumerated. Between 100-200 nematodes were picked and processed using standard methods for slide preparation. They were then identified to genera level. Genus composition and distribution in the transects, in the two seasons and in depth were studied. Genus diversity was estimated using Hills diversity numbers (N0, N,, N2, H’). From some selected families (Chromadoridae, Comesomatidae, Microlaimidae and Molgolaimus), the nematodes were identified to species level and where well represented they were described. For the selected families (Chromadoridae, Comesomatidae, Microlaimidae and Molgolaimus), genera and species composition and distribution were studied in the two periods, four transects and in depth. Species diversity was estimated using Hills diversity numbers and Hierarchical diversity. Environmental data from the same area (WIO) were obtained from published work or unpublished data analysed in other institutes. This included sediment community oxygen consumption (SCOC), DNA:RNA ratio, oxygen concentration and saturation, organic carbon, C:N ratio and sediment composition.