Latitudinal trends in the species richness of free-living marine nematode assemblages from exposed sandy beaches along the coast of Chile (18-42 °S)

The latitudinal pattern of species richness of free-living marine nematodes from exposed sandy beaches along the coast of Chile between 18 and 42 degrees S was examined. Unlike many other examinations of latitudinal gradients, this study is not based on data mined from the literature, but on samples collected specifically to examine these themes. Five replicate quantitative 50 cm3 samples of sediment were taken from the zone of retention of 66 exposed sandy beaches. The free-living nematode fauna was identified and quantified to species level. The data were then examine using ordinary least squares and simultaneous autoregressive model (SARerr) regression methods, examining the associations between species richness and latitude, coastline complexity, and sea surface temperature, primary productivity of the adjacent coastal waters and mean latitudinal range size. The species richness of free-living marine nematodes from exposed sandy beaches along the coast of Chile decreased with increasing latitude and was strongly associated with mean annual sea surface temperature. Mean latitudinal range size increased with increasing latitude, supporting Rapoports rule, and decreased with increasing species richness. The results suggest that the nematode fauna of exposed sandy beaches is derived from a low latitude fauna that has dispersed to higher latitudes, but that many species may be physiologically constrained, by temperature, from dispersing further south.