MEPS 153:259-271 (1997)  -  doi:10.3354/meps153259

Spatial and temporal validation of settlement-marks in the otoliths of tropical reef fishes

Wilson DT, McCormick MI

The link between the timing of settlement (transition from the pelagic to the benthic environment) and the formation of the 'settlement-mark' in fish otoliths was examined in order to validate the use of this microstructural feature for the back-calculation of settlement patterns and planktonic larval durations. The formation of the settlement-mark was validated to occur at settlement in 2 pomacentrids, Pomacentrus amboinensis, P. nagasakiensis, and less conclusively in 13 other species from 7 families. Within these species, 3 distinct settlement-mark durations were identified: a single-increment mark (P. amboinensis, P. nagasakiensis); a 2-increment mark (P. coelestis); and a zonal, 14-increment mark (Acanthurus sp. 2, probably A. blochi). The structure of settlement-marks for P. amboinensis and P. nagasakiensis were compared among 4 to 5 locations on the northern Great Barrier Reef, Australia (maximum of 20 km apart). Otolith increment profiles differed minimally over spatial scales of 20 km in these species, with Lizard Island fish possessing increment profiles different to those from other locations. This pattern of minimal variation in profiles occurred despite the fact that the planktonic larval duration of one species (P. nagasakiensis) differed among locations (range of mean values: 22.4 to 26.3 d). Further, at Lizard Island, increment profiles of P. amboinensis showed statistically significant, although minor, differences among local populations around the island and between successive lunar recruit cohorts. Our evidence suggests that the structure of the increment transitions associated with settlement are taxon specific, although the optical contrast of settlement-marks (determined by increment width) may show subtle spatial and temporal variation.

Settlement-mark validation · Tropical reef fish · Metamorphosis · Otolith · Recruit

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