Elemental signatures of Pomacentrus coelestis otoliths at multiple spatial scales on the Great Barrier Reef, Australia

Abstract

Elemental signatures in both the natal and post-settlement regions of otoliths from newly settled Pomacentrus coelestis were measured from multiple sites, reefs, years and reef clusters at different latitudes on the Great Barrier Reef, Australia. Significant differences in latitude and year were found for Sr/Ca and Ba/Ca in the post-settlement portion of the otoliths, and discriminant function analyses identified clear separations in otolith signatures from different reef clusters and years. The spatial and annual variation found in the post-settlement signatures was similar to that determined for the brooding damselfish Acanthochromis polyacanthus, and suggests that these 2 species record environmental variation in a similar manner. This similarity also extended to reefs, although some reefs showed persistent trends for individual elemental ratios. However, the natal portion of the otoliths proved less useful in discriminating groups, and appeared to be decoupled from the post-settlement portion of the otoliths. Such a decoupling could be the result of differences in the food source during the natal period, protein content of the 2 otolith portions which could potentially influence affinity for trace elements, or ontogenetic changes in the depositional process itself. Our findings indicate that robust elemental signatures are likely to be found among clusters of reefs rather than individual reefs, which has important ramifications for future studies attempting to discriminate reef fish populations.