MEPS 297:273-281 (2005)  -  doi:10.3354/meps297273

Elevated levels of trace elements in cores of otoliths and their potential for use as natural tags

Benjamin I. Ruttenberg1,*, Scott L. Hamilton1, Michael J. H. Hickford1,2, Georges L. Paradis3, Michael S. Sheehy1, Julie D. Standish1, Ofer Ben-Tzvi4,5, Robert R. Warner1

1Department of Ecology, Evolution and Marine Biology and Marine Science Institute, University of California, Santa Barbara, California 93106, USA
2Marine Ecology Research Group, School of Biological Sciences, University of Canterbury, PB 4800, Christchurch, New Zealand
3Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, California 93106, USA
4The Institute for Nature Conservation Research, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
5The Interuniversity Institute for Marine Sciences in Eilat, PO Box 469, Eilat 88103, Israel

ABSTRACT: Variation in the chemical composition of fish otoliths has been used in recent years to address a range of ecological questions, including levels of stock mixing, variation in habitat use, and rates of larval exchange. While some of these questions have been answered with varying success, the degree to which discrete populations are connected via larval exchange remains unknown. To identify larval sources using natural variation in otolith chemistry, we must distinguish and measure the chemical composition of the otolith core, the portion of the otolith formed at the spawning site. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we found that the core regions of otoliths from 6 different species of fishes were highly enriched in manganese (Mn), and elevated in magnesium (Mg) and barium (Ba), relative to adjacent regions of the otolith. These patterns were consistent for species drawn from different taxonomic groups, which inhabit temperate and tropical regions, are found in marine and freshwater, and utilize a variety of spawning modes. Variation among species in Mn concentration in the core also corresponds to maternal investment, measured by egg size. These data suggest that core enrichment may be a general characteristic of otoliths, and that the chemical composition of the otolith core is fundamentally different from other regions of the otolith. The localized elemental enrichment of the core underscores the importance of methods that analyze the core region in small, discrete samples if otolith chemistry is used to address questions of larval exchange among populations.

KEY WORDS: Otolith chemistry · Otolith core · Trace metal · Trace element · Larvae · LA-ICPMS

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