Spatial distribution of chaetodontid fish in coral reefs of the Ryukyu Islands, southern Japan

The spatial patterns of butterflyfish assemblages (Chaetodontidae) were exa mined within and between five islands of the Ryukyu Archipelago, southern J apan. Despite being the northernmost reef communities in the world and desp ite the severe natural and human-induced disturbances that have affected th em since the 1970s, the coral reefs of the Ryukyu Islands have one of the m ost diversified assemblages of chaetodontids in the world. A total of 30 sp ecies were identified, and species richness per island ranged from 20 to 25 species. On each of the 45 stations prospected, between four and 17 specie s were recorded, and between 0.75 and 21.75 ind 250 m(-2) were counted. Var iation in species composition, species richness and abundance between islan ds was less pronounced than the variation within islands, where assemblages of the major reef environments (i.e. the reef flat, the reef edge, and the reef slope) were distinguished. The highest species richness and abundance were found on the reef slope and the reef edge. Canonical correspondence a nalysis revealed that depth, substrate complexity and live coral cover infl uenced the distribution of chaetodontid fishes. These factors accounted for 20% of the variation in the species data matrix.