By Steve Cranwell, 13 Oct 2016
Rapa and its surrounding islets is a very remote place. It is almost 1500 from Tahiti, the main island in French Polynesia. This isolation together with other geophysical characteristics has resulted in the evolution of a highly unique flora and fauna. As for other islands of the eastern Pacific, there are no mammals, instead these are replaced by birds and a diversity of specialised plants, invertebrates and terrestrial molluscs. For a relatively small island (c.40km2) endemism is extraordinarily high. 3 birds, 100 molluscs, 31% of all plants and 67 Miocalles (beetles) species or subspecies only occur on Rapa (Meyer et al 2014). The island is an IBA and a KBA.
However, almost all of this flora and fauna is considered highly threatened. Believed to have been colonised as late as the 1500’s Rapa was the last island to be permanently occupied (by Polynesians) and while tremendous damage has been wrought it is perhaps this relatively recent human history that has allowed this unique fauna and flora to cling on. Reasons for these declines is a story replicated throughout the Pacific; habitat loss associated with the clearance of land for agriculture, uncontrolled fires and the introduction of invasive alien species that continue to degrade habitats, compete for resources and prey directly on native wildlife.
Rapa and the nearby Marotiri islets are the most important islands for seabirds in the Australs with the highest diversity for the archipelago, but also the greatest level of (sub-specific) endemism. The Rapa shearwater (Puffinus newelli myrtae) has recently been recognised as more closely related to the Endangered Newell’s Shearwater (formerly Little Shearwater Puffinus assimilis) which occurs in Hawaii, Rapa constituting an extremely distant population. Fregetta grallaria titan the local form of White-bellied Storm Petrel is also considered to have sub-specific differences due to its larger body size however, it’s had very little taxonomic attention and distinct characteristics including vocalisations may warrant a separate species.
The Endangered White-throated Storm Petrel (Nesofretta fuliginosa) is also present and, while there’s been no thorough seabird survey of Rapa for over 25 years, numbers then were perilously low. With the consistent effects of introduced rodents and feral cats, goats, rabbits, cattle and horses these populations will have continued to decline.