The Fish Communities of a Coral Reef Transect

Abstract

As a contribution to the discussion on the causes of the high fish species diversity found on coral reefs, a coast-to-sea transect has been studied in the lagoon of Moorea Island (French Polynesia) in order to uncover the spatial scales at which recurrent assemblages (i.e., communities) can be identified. The transect was divided into 22 stations where fishes were sampled. According to the null hypothesis (chaos), the fish species should be distributed at random along the transect. This was tested first by a method of constrained clustering that performs a statistical test of cluster fusion, based on a null hypothesis that corresponds to chaos. Groups of stations were found with, at most, a 5% chance of resulting from a random distribution of species among the groups. The distribution of species among the stations pro vided a second test of the null hypothesis; the observed number of ubiquitous species was found to be significantly smaller than expected under the hypothesis of chaos and, in the same way, the species limited to a single group of stations were found to be significantly more numerous than expected under chaos. Both patterns are consistent with reports from other reefs of the Indo-Pacific.