The influence of oceanic and lagoonal plume waters on otolith chemistry

Abstract

To determine how ocean and lagoonal plume waters from within the same reef were reflected in the chemical composition of otoliths, we conducted an experiment over three consecutive summers where conditions of temperature and food were held constant. Presettlement Pomacentrus coelestis were held in replicate tanks of the two water masses for 9 days. The sagittae were then analyzed at high spatial resolution (5 μm x 50 μm x 4 μm) using laser ablation inductively coupled plasma mass spectrometry. Ba/Ca and Sr/Ca varied between water masses and the rank of these elemental ratios changed among years. Although the reason for this change in rank is not known, likely mechanisms include upwelling and (or) the episodic appearance of phytoplankton blooms inside the lagoon. This is the first demonstration that the elemental signatures of otoliths can vary significantly over small spatial scales in reef systems in the absence of confounding factors, thus complicating studies attempting to discriminate reef-based stocks or elucidate natal origins using otolith chemistry.