Re-evaluation of species diversity patterns of free-living marine nematodes

Nematode species diversity was analysed for 55 data points ranging from local studies to large-scale faunal surveys. Multiple regression analysis uses latitude, investigated area, sampling effort and depth as independent variables. Species diversity in a biotope (or alpha-diversity) is about twice as high in the deep sea, while the main source of diversity in shallow waters is heterogeneity of biotopes (beta-diversity). For sites deeper than 100 m, regional species richness shows a unimodal (hump-shaped) latitudinal pattern, with the highest diversity at 30degrees to 60degreesN. Species diversity in shallow waters does not show any prominent gradients throughout the world ocean. These patterns possibly reflect the diversity-productivity relationships. Different approaches to estimation of species diversity are discussed.