Structure and biodiversity of nematode assemblages in the SW lagoon of New Caledonia

Meiofaunal density and the taxonomic composition of nematodes were investigated in three bottom types of the SW lagoon of New Caledonia (SW Pacific). Meiofaunal density was significantly higher in white-sand bottoms than in other biotopes (grey-sand and muddy bottoms). Thirty-three nematode families and 172 genera were identified. Species diversity indices were significantly lower in back-reef white-sand than in seagrass grey-sand and coastal mud. The familial, generic and species diversity were analysed in relation to ecological and biotic parameters by multivariate factorial correspondence analysis and hierarchical clustering. The analysis at familial level was unable to discriminate between stations and biotopes. The analysis at generic level detected three main nematode associations related to microphytobenthic primary productivity, macrophyte biomass and silt content. Taxonomic composition of one white-sand station (Mebere reef) differed from all others in relation to an increased chlorophyll/pheophytin ratio and a lower silt content. Grey-sand stations were split in two distinct groups. The first combined two of the three white-sand stations and the grey-sand stations, all of which were characterised by a medium silt content and a medium productivity. The second group combined the muddy bottom stations and the siltiest grey-sand stations which were characterised by a high silt content, a lower macroflora biomass and low productivity.