Spatial patterns and regional affinities of coral communities at the Kermadec Islands Marine Reserve, New Zealand—a marginal high-latitude site

The Kermadec Islands Marine Reserve (29 to 31° S), New Zealand, harbours one of the world’s highest latitude scleractinian coral communities, situated close to the lower thermal limits for coral survival. An understanding of how and why similarities and differences exist between so-called ‘marginal’ coral communities can provide insight into the physical and biological factors that influence coral distributions. In this study, a depth-stratified survey of benthic community structure and coral species assemblages was conducted at 9 sites around the Kermadec Islands. All coral species identified were subtropical non-reef building species, or species with a wide geographic range. Scleractinian coral cover (16 species) was low and variable between sites and depths (5.3 ± 13.9%, mean ± SD) with macroalgae contributing between 36 to 95% of the benthic cover. Multivariate analyses revealed small-scale spatial variability between closely located sites. Resulting data on coral species diversity were compared to published data from coral communities at other ‘marginal’ locations, as well as those from a range of Australian locations. On a global scale, the Kermadec Islands coral community exhibits greatest affinity with southeastern Australian sites. In comparison, there was a lack of affinity for Australian tropical sites and other high latitude sites, both in Australia and globally. Our analyses suggest that the low diversity, highly variable coral communities of the Kermadec Islands are likely shaped by their isolation and high wave energy, in addition to the low annual temperatures experienced.