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

Abstract

The discovery of global-scale latitudinal gradients of declining biodiversity 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-temperature gradients in terrestrial and shallow water systems and it is difficult to see how these processes might apply to a diversity gradient in the deep North Atlantic, where productivity increases northwards but diversity declines. Here, we compare biodiversity patterns from marine nematodes, the most abundant deep-sea metazoan, from the deep North Atlantic with previous results and show that rarefaction is potentially unsuitable for large-scale biogeographic pattern analysis. We obtain a different pattern from that previously obtained for mollusc and isopod data. Nematode diversity, as measured by species count, shows a positive gradient between 13 to 56°N, which is consistent with the hypothesis that this pattern is related to the productivity gradient in the food-starved deep North Atlantic. The Norwegian Sea appears to be an area of low diversity for reasons connected to historical-geographical processes.