The island of Rapa presents an interesting lens through which to investigate human decisionmaking and resource-use patterns in a marginal environment. In addition to being small and isolated, Rapa is climatically marginal, being positioned on the southern fringe of the tropical Indo-West Pacific marine province. Most obviously, this geographical situation translates to restricted species diversity, with a great many common tropical taxa not able to survive the conditions. However, as pointed out by Preece (1995:345), it would be a mistake to see the marine fauna of marginal Polynesian islands as simply an impoverished subset of the tropical Indo-West Pacific community. Indeed, Paulay and Spencer (1988, in Irving 1995:321) suggest that there is a belt of islands in the central-eastern Pacific (including Easter Island, the Pitcairn Islands, Kermadecs, Rapa and Lord Howe) that have a littoral fauna specifically adapted to cooler conditions. Such species include a number of endemics, as well as species restricted solely to the islands listed above. The dominant mollusc within the Tangarutu assemblage - Nerita morio - is one such species (see below for discussion).