Interregional variation of free-living nematode assemblages in tropical coral sands

Nematode assemblages were studied in tropical lagoonal carbonate sands at f our regions in the Pacific Ocean. This material was compared to other descr ibed nematode assemblages originating from ecologically similar sites. Data were aggregated to a range of hierarchical taxonomic levels. The contribut ion of different environmental variables to the variability of nematode ass emblages was estimated at local, regional (four studied regions) and global scales (this study plus other available data). All nematode assemblages we re significantly different at species and generic levels between different study regions. At higher taxonomic levels (family and order) most regions w ere not distinguishable and the assemblages were dominated by Desmodoridae, Chromadoridae and Xyalidae. Multivariate analysis showed that mean grain s ize, silt content and depth contributed mostly to the variability of nemato de assemblages at the local scale whereas geographical coordinates were mos t important at regional and global scale. However, the weak relationship be tween sediment characteristics, co-ordinates and biota suggests that other variables are important in structuring nematode assemblages at a global sca le.