Deep reefs are not refugium for shallow-water fish communities in the southwestern Atlantic

1. The deep reef refugia hypothesis (DRRH) predicts that deep reef ecosystems may act as refugium for the biota of disturbed shallow waters. Because deep reefs are amongst the most understudied habitats on Earth, formal tests of the DRRH remain scarce. If the DRRH is valid at the community level, the diversity of species, functions and lineages of fish communities of shallow reefs should be encapsulated in deep reefs.

2. We tested the DRRH by assessing the taxonomic, functional and phylogenetic diversity of 22 Brazilian fish communities between 2 and 62m depth. We partitioned the gamma diversity of shallow (<30m) and deep reefs (>30m) into independent alpha and beta components, accounted for species’ abundance, and assessed if beta patterns were mostly driven by spatial turnover or nestedness.

3. We recorded 3821 fishes belonging to 85 species and 36 families. Contrary to DRRH expectations, only 48% of the species occurred in both shallow and deep reefs. Alpha diversity of r...