Newly designed glass apparatus to conduct stepwise dissolution experiment for radiocarbon using fish otoliths

Abstract

Isotopes and trace elements extracted from fish otoliths have been widely used to understand different fish habitats. Otoliths can track the life-long histories of fish habitats and can supplement the information that is often difficult to reconstruct using tagging methods. Due to the advancement of radiocarbon measurement techniques, small quantities can be prepared for this purpose, and radiocarbon can be used to understand the migration history by referring to the variations of radiocarbon in the surface ocean. One major drawback of otolith isotope methods is the length of time it takes to collect samples by milling before each sample can be measured by accelerator mass spectrometry. Sequential acid digestion systems can potentially offer a solution whereby each dissolution step can provide information of otolith growth. Here we designed a glass apparatus that can be used for this purpose. We tested the otoliths from the western Pacific roughy (Hoplostethus japonicus) caught in Suruga Bay off the coast of Japan to see if their otoliths can provide reliable information in reconstructing their life history. The results show radiocarbon concentrations in the otoliths gradually decreased, indicating the habitat depth of analyzed individuals gradually shifted from deep to shallow water demonstrating the promise of this method to understand fish habitats. This is consistent with expected behavior considering the oceanography of the region. Thus, stepwise dissolution using a newly designed glass apparatus, proposed here, can aid marine fish ecological studies using otoliths.