Cosmopolitism, rareness and endemism in deep-sea marine nematodes

Nematodes represent the most abundant benthic metazoan of all seas and oceans, and their relative importance increases with increasing water depth. Understanding the biodiversity patterns of this dominant phylum could be a critical step towards our comprehension of the evolutionary patterns across the largest biome of the biosphere. For instance, it has been assumed for a long time that nematodes are ubiquitous across depths, latitudes and biogeographic regions, but there is still little scientific evidence for this lack of endemism. The present study is based on a meta-analysis of nematode biodiversity data collected from 246 deep-sea sites of the Atlantic Ocean and Mediterranean Sea. We explored the cosmopolitanism, rareness and potential endemism of nematode genera in deep-sea sediments. The results of this analysis indicate that only one-third of nematode families are widely distributed and could potentially be cosmopolitan, whereas 94% of the nematode genera are linked to specific habitats or bathymetric ranges. Singleton nematode genera (i.e. genera presenting as a single individual only in one specific habitat) increased in importance with increasing water depth. We conclude that rareness and endemism may be a far more common feature than previously thought in deep-sea nematode assemblages and hypothesise that the deep ocean interior could be a huge reservoir of endemic nematode species.

Automated summary

Nematodes, as the most abundant benthic metazoan in the seas and oceans, play a crucial role in the deep-sea ecosystem. This study conducted a meta-analysis of nematode biodiversity data from deep-sea sites in the Atlantic Ocean and Mediterranean Sea, revealing that only a small portion of nematode families are widely distributed, while the majority of nematode genera are linked to specific habitats or bathymetric ranges. It suggests that rareness and endemism are more common features in deep-sea nematode assemblages than previously thought.