The positive correlation between sediment particle-size diversity (a measure of habitat heterogeneity) and deep-sea macrofaunal diversity was first demonstrated two decades ago. The causality of this relationship was not elucidated because of the potential influence of macrofauna on sediment granulometry. Here we test the generality of this correlation using smaller organisms with limited mobility and limited ability to change the physical structure of sediments. Results of partial regressions accounting for the effect of water depth and food availability showed that nematode species and genus diversity were positively correlated with sediment particle-size diversity on the continental slope of New Zealand. Trophic diversity was not correlated with sediment particle-size diversity, however, which could suggest that the relationship between habitat heterogeneity and diversity was not the result of food partitioning between species/genera. Our findings provide support for the importance of small-scale habitat heterogeneity in the maintenance of local diversity in the deep sea, one of the few known environmental factors that may directly influence species co-existence in this biome.
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