Ontogenetic habitat use in labrid fishes: an ecomorphological perspective

We examined the extent to which wave exposure and swimming ability shape the ontogenetic distribution patterns of wrasses across the Great Barrier Reef at 2 spatial scales: cross-shelf and within-habitat. Visual censuses were used to record the distribution of juveniles and adults among shelf habitats, and their relative position in the water-column within a single, wave-swept habitat zone. Pectoral fin shape was used as a measure of swimming ability. Examination of fins from a broad size range of individuals indicated an ontogenetic shift in swimming ability in 5 of the 8 species examined. Despite apparent differences in their swimming abilities, juveniles and adults of each species displayed similar distributions across the 11 shelf habitats. Significant differences in habitat distributions were only apparent among species. Microhabitat use within the reef flat, however, displayed a distinct trend of increasing water-column use with increasing size in those 5 species that displayed a marked ontogenetic shift in swimming ability. This shift in microhabitat use appeared to be due largely to flow-refuging behaviour in the small individuals and slow-swimming species