Cook Islands

Abstract

The Cook Islands are located in the southern Pacific Ocean, east of Fiji and west of the Society Islands. They consist mostly of coral atolls in the north and high basaltic islands in the south. The islands have a narrow fringing reef, a shallow-reef area several hundred meters wide sloping gently to a depth of about 30 m, and a precipitous drop-off extending to 200 m or more. Research on fishes in mesophotic coral ecosystems (MCEs) in Rarotonga, the largest and most populous island, were documented during expeditions from 1989 to 2012 using conventional SCUBA and technical diving, resulting in the discovery of many new species. Very little is known about other groups in MCEs, but data downloaded from the Global Biodiversity Information Facility (GBIF) reveals a clear pattern of undersampling on MCEs for all taxonomic groups. Patterns of diversity and species richness among fishes are similar to those for reef fishes in general, but differ in several ways, including an underrepresentation of Gobiidae (likely due to sampling bias) and an overrepresentation of Acanthuridae. The primary threats to Cook Islands MCEs are the same general threats that apply to shallow reefs, as well as all reefs at all depths worldwide (i.e., climate change, ocean acidification, and overfishing of food fishes). Over the course of more than 20 years of direct, albeit qualitative, observations in Rarotonga, there have been no major changes in the overall health, abundance, and diversity of organisms on shallow or MCE habitats.