Optimal monitoring of coral biodiversity at Christmas Island

Abstract. Coral reefs are one of the most biodiverse ecosystems in the world and are increasingly at risk due to a range of threats. Detailed species-level data is essential in developing effective management strategies for the conservation of coral reef biodiversity. For hard corals, this critical information is rarely available due to the high degree of expertise, time and costs involved in collecting species-level data, hence, the development of proxy metrics which accurately and reliably reflect coral species richness are imperative. At Christmas Island, in the north-easternIndian Ocean, little species-level baseline data is available to inform managers regarding spatial (or temporal) variations of coral diversity. Here we examine the ability of four proxy metrics to reflect patterns in hard coral species richness, compared across depth gradients at eight sites around Christmas Island using regression analysis. Generic richness measured on a belt transect was the strongest explanatory variable for species richness (68–88% variation explained) regardless of the scale of analysis. Percent live hard coral cover has traditionally been used to assess and monitor coral reef health; however, our results suggest that it is not related to coral species richness asa significant linear function. Overall, at Christmas Island, monitoring generic richness on replicated belt transects offers the simplest and most robust proxy metric for estimating species richness