Fishes of the Remote Southwest Palau Islands: A Zoogeographic Perspective

Abstract

Fishes of the Southwest Palau Islands (SWPI) recorded from the SWPI Expedition of 1992 were analyzed for patterns of distribution, species richness, diversity, evenness, and similarity between island localities. Fifty-three timed visual transects and supplemental observations were made at Helen Reef (Hotsarihie Atoll) and the islands of Tobi, Merir, Pulo Anna, Sonsorol, and Fanna. A total of 602 species was observed, including 596 species and morphs on transects. Fifty-four new records were identified, including nine species new to Micronesia. The species reported compose 64.1% of the known Palauan fish fauna. A latitudinal gradient in species richness, decreasing from north to south, is apparent. Species diversity is less pronounced latitudinally, is significantly different between island localities in most pairwise comparisons, and is seemingly dependent upon the degree of habitat complexity. This complexity may be a function of locality relative size. Patterns of similarity in faunal composition also appear to be related to relative size of locality. Helen Reef had the most distinct fauna, followed by Tobi. Merir and Sonsorol, and Pulo Anna and Fanna, respectively, were more similar to each other.