STRUCTURE AND BIODIVERSITY OF NEMATODE ASSEMBLAGES IN THE SW LAGOON OF NEW-CALEDONIA

Meiofaunal density and the taxonomic composition of nematodes were inv estigated in three bottom types of the SW lagoon of New Caledonia (SW Pacific). Meiofaunal density was significantly higher in white-sand bo ttoms than in other biotopes (grey-sand and muddy bottoms). Thirty-thr ee nematode families and 172 genera were identified. Species diversity indices were significantly lower in back-reef white-sand than in seag rass grey-sand and coastal mud. The familial, generic and species dive rsity were analysed in relation to ecological and biotic parameters by multivariate factorial correspondence analysis and hierarchical clust ering. The analysis at familial level was unable to discriminate betwe en stations and biotopes. The analysis at generic level detected three main nematode associations related to microphytobenthic primary produ ctivity, macrophyte biomass and silt content. Taxonomic composition of one white-sand station (Mebere reef) differed from all others in rela tion to an increased chlorophyll/pheophytin ratio and a lower silt con tent. Grey-sand stations were split in two distinct groups. The first combined two of the three white-sand stations and the grey-sand statio ns, all of which were characterised by a medium silt content and a med ium 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.