Depth and latitudinal diversity gradients in seamount benthic communities of the South Atlantic

Aim

Although latitudinal and bathymetric species diversity gradients in the deep sea have been identified and investigated, studies have rarely considered these gradients across seamount and oceanic island ecosystems. This study aimed to identify whether the current understanding of latitudinal and bathymetric gradients in α-diversity (species richness) apply to South Atlantic seamount ecosystems, as well as ascertaining whether identifiable trends were present in seamount β-diversity along a bathymetric gradient.

The South Atlantic Ocean.

2013-2019

Benthic communities.

Drop camera images from 39 transects, collected between 250 m and 950 m, were used to characterise species richness from within the Exclusive Economic Zones of Ascension Island, Saint Helena and Tristan da Cunha, spanning 8°S to 40°S. We subsequently applied linear modelling to test possible environmental drivers across latitudinal and bathymetric ranges (see transect metadata for variables). An Analysis of Similarity was employed to investigate the beta-diversity gradient, and the level of species turnover with depth.

Surface primary productivity and substrate hardness both had significant positive effects on species richness, and there was significantly higher species richness at temperate latitudes. No significant relationship between species richness and depth was detected, but there was a significant species turnover with depth.

Seamounts and oceanic islands do not conform to established depth-diversity relationships within the depth range studied. However, despite their isolation and small sizes, seamounts and oceanic islands in the South Atlantic appear to follow latitudinal patterns of deep-sea species richness established for specific taxonomic groups in different ecosystems.