Patterns of spacing in a coral reef fish in two habitats on the Great Barrier Reef

Patterns of spacing in the butterflyfish Chaetodon trifasciatus (Pisces, Chaetodontidae) were studied in two habitats on the southern Great Barrier Reef. Pairs of fish were found to defend territories at reef slope and lagoon study sites. Territories were 2·7–3·7 times larger in the lagoon than on the reef slope, where population density and food abundance were greater. No significant changes occurred in the sizes of territories in either habitat over on year, but patterns of spacing were generally more variable in the lagoon habitat. This was interpreted as a response to low population density and poor habitat quality.