Demersal fish community diversity off New Zealand: Is it related to depth, latitude and regional surface phytoplankton?

Recent studies of basin-scale patterns of diversity of benthic macrofauna reported strong latitudinal gradients of diversity in the deep North Atlantic, in contrast to regionally variable patterns in the Southern Hemisphere. Here we use data from fisheries research trawl surveys to examine spatial patterns of species richness, Shannon-Wiener diversity index, and evenness of demersal fish communities in relation to latitude and depth from 80 to 898 m off south-east New Zealand. We found species richness decreased latitudinally within regions in the poleward direction, and increased with depth. Areas of high species richness were concentrated along the margins of the Chatham Rise and were associated with current intensification in regions of enhanced surface phytoplankton pigment concentration. Species richness was highest between the 500 and 1000 m contours on the Chatham Rise, where enhanced surface phytoplankton pigment is associated with a major oceanographic feature, the Subtropical convergence. A predominance of species-rich locations was found on the more steeply shelving northern margin of the Chatham Rise. The regional latitudinal pattern of diversity appears to be correlated with regional production, and to be influenced by mesoscale oceanographic features constrained by the bathymetry, although the proximal causes for high diversity remain speculative.