Otolith elemental evidence for spatial structuring in a temperate reef fish population

Abstract

Elemental fingerprints of calcified structures can provide useful insight into dispersal, structure and connectivity of fish and invertebrate populations, but an assumption must be made that fingerprints reflect local physico-chemical conditions at the time of accretion. Physiological control of elemental uptake and temporal variability in environmental conditions can confound interpretation of spatial patterns. Multiple lines of evidence suggest that a commercially important temperate reef fish Parapercis colias (Forster 1801) (Pinguipedidae) in the New Zealand fjords forms discrete subpopulations at the mesoscale (10 to 20 km). We investigate otolith microchemistry as a tool to elucidate population structure and connectivity in the southern fjords. Concentrations of 12 elements (Li, B, Mg, P, S, Ca, Mn, Cu, Zn, Sr, Ba and Pb) were measured at the otolith edge (the most recently accreted region) using laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Demographic and temporal variability were accounted for before spatial patterns were investigated. P:Ca, Sr:Ca and Ba:Ca ratios were positively correlated while Li:Ca was negatively correlated with age. Inter-annual variability in signatures within a single site was widespread. Independent of demography, fingerprints differed between inner and outer fjord subpopulations in Bradshaw-Thompson, Breaksea and Dusky Sounds but not in Doubtful Sound or Long Sound-Preservation Inlet. Solution and laser ablation ICP-MS were similarly able to discriminate between subpopulations of fish in a subset for which one sagitta was analysed by each technique. The assumption that fingerprints represent environmental conditions at the time of accretion is supported by a relocation study between habitats in Doubtful Sound. These results have important implications for temperate reef fish management and support the adoption of spatially explicit measures such as those in place in the New Zealand fjords. © Inter-Research 2011.