Otolith chemistry of the non-dispersing reef fish Acanthochromis polyacanthus: cross-shelf patterns from the central Great Barrier Reef

Abstract

The influence of cross-shelf gradients, within and among distance strata, on the otolith chemistry of the non-dispersing reef fish Acanthochromis polyacanthus was examined on the Great Barrier Reef. Most of the variation in elemental ratios (Mg/Ca, Cu/Ca, Sr/Ca, Ba/Ca) was at the level of sites within reefs; some broad patterns of otolith chemistry were found cross-shelf. Sr/Ca and Ba/Ca ratios increased with distance from shore. Highest ratios of Mn/Ca and Cu/Ca were found at the outermost shelf sites at Myrmidon Reef, but Mn levels were generally greatest within 45 km of shore. Elevated ratios of Ba/Ca at Myrmidon Reef were persistent over 3 yr and are likely indicative of upwelling, which is known to occur in the area. The Ba/Ca ratios were the highest ever reported in marine fish otoliths, and accuracy of our estimates was confirmed in a paired laboratory test. The robustness of reef-wide chemical signatures in fish was weak, but unique signatures were found within reefs. High resolution elemental records could help to identify sites affected by upwelling and the periodicity of upwelling events.