Latitudinal diversity gradients in the deep sea with special reference to North Atlantic nematodes

The discovery of global-scale latitudinal gradients of declining biodiversi ty from the tropics to the pole for bivalves, gastropods and isopods in the deep North Atlantic has created a high degree of interest and controversy. This is because such gradients are commonly associated with solar energy-t emperature gradients in terrestrial and shallow water systems and it is dif ficult to see how these processes might apply to a diversity gradient in th e deep North Atlantic, where productivity increases northwards but diversit y declines. Here, we compare biodiversity patterns from marine nematodes, t he most abundant deep-sea metazoan, from the deep North Atlantic with previ ous results and show that rarefaction is potentially unsuitable for large-s cale biogeographic pattern analysis. We obtain a different pattern from tha t previously obtained for mollusc and isopod data. Nematode diversity, as m easured by species count, shows a positive gradient between 13 to 56 degree s N, which is consistent with the hypothesis that this pattern is related t o the productivity gradient in the food-starved deep North Atlantic. The No rwegian Sea appears to be an area of low diversity for reasons connected to historical geographical processes.