Spatial patterns of meiofauna and diversity of nematode species assemblages in the Uvea lagoon (Loyalty Islands, South Pacific)

Meiofauna assemblages were investigated at 15 stations on triplicated samples in the Uvea Atoll (Loyalty Islands) in relation to 9 selected environmental parameters. Spatial patterns and variability of meiofauna density were quantified according to location, macrofauna and nematode species assemblages. Meiofauna was dominated by ciliates and nematodes. Densities of total meiofauna and of most of the meiofauna taxa were significantly higher in the back reef North Pléiades stations than the leeward side of the Island. The highest correlation between biotic patterns and environmental parameters that best explains the pattern was with sediment thickness and to a lesser extent organic matter, C/N ratio and depth. One hundred and thirty-four nematode species were identified with four dominant species Chromadora macrolaimoides, an undescribed species of Bolbonema, Daptonema svalbardense and Prochromadorella septempapillata. Three significantly different nematode species assemblages were detected in two of the previously described macrofauna assemblages by cluster analysis and multidimensional scaling methods suggesting that nematodes are more sensible ecological indicators than macrofauna. Diversity indices based on dominance were not significantly different among the three nematode species assemblages but indices based on species richness and rarefaction were significantly higher leeward of Uvea Island. Estimates of total species richness showed no sign of stabilizing with sample size. However, rare species stabilized very quickly, whereas abundant species were added with increasing sampling coverage, indicating a high spatial variability of the local composition of nematodes.