Reconstruction of temperature experienced by Pacific bluefin tuna Thunnus orientalis larvae using SIMS and microvolume CF-IRMS otolith oxygen isotope analyses

Abstract

This study aimed to reconstruct temperatures experienced during the larval period by adult Pacific bluefin tuna Thunnus orientalis using high-resolution otolith stable oxygen isotope (δ18O) analysis. A novel otolith sample preparation protocol for secondary ion mass spectrometry (SIMS) analysis developed in this study reduced the background noise of SIMS measurements, enabling analyses of >10 times higher resolution around the otolith core compared to previous studies using conventional isotope ratio mass spectrometry (IRMS). The values obtained from SIMS were compared to those obtained by microvolume δ18Ootolith analysis using micromilling and conventional continuous-flow IRMS (CF-IRMS). There was a systematic offset (average 0.41‰ with SIMS resulting in lower values) most likely caused by matrix effects on SIMS δ18Ootolith values that can be calibrated using a strong linear relationship between SIMS and CF-IRMS measurements (r2 = 0.78, p < 0.001). The core-to-edge δ18Ootolith of 5 Pacific bluefin tuna revealed fine-scale seasonal variations in water temperature agreeing with known migration patterns. In addition, the ambient water temperature experienced during larval stages (about 10-20 d post hatch) estimated from otolith core δ18O ranged from 26.7 to 30.7°C, overlapping with temperatures associated with the occurrence of larval Pacific bluefin tuna. Combining SIMS and microvolume CF-IRMS δ18O otolith analyses offers a microscale examination of fish ecology that is not possible with conventional IRMS techniques. This novel method is particularly useful for understanding the early life history of fish that may be affected by climate change and reconstructing a well-resolved migration history for fish species that have small otoliths and/or narrow growth increments.

Accuracy of Otolith Oxygen Isotope Records Analyzed by SIMS as an Index of Temperature Exposure of Wild Icelandic Cod (Gadus morhua)

“…There are two possible reasons for the analytical bias causing the small divergence between measured and predicted δ 18 O otolith values. One could be the matrix effect of the SIMS method, whereby the different chemical compositions and structures of the otolith relative to the reference material can introduce a bias [Hane et al (2020) and references therein]. This matrix effect is unavoidable in the absence of a matrix-matched reference material had been available.…”

Otolith δ18O Composition as a Tracer of Yellowfin Tuna (Thunnus albacares) Origin in the Indian Ocean

“…SIMS requires high precision in sample preparation because smooth and even surfaces are needed for proper quantification, so that any irregularity in the sample surface (e.g., cracks, bubbles, reliefs, inclinations, etc.) can be avoided [42,51]. The otolith was embedded in a rectangular box following the same methodology as described above.…”

“…One of the major challenges of the SIMS technique, is the difficulty in preparing suitable samples. Data quality from SIMS analyses depends on high quality sample surface condition [42,51] and samples that do not meet these high standards may need to be discarded. Yellowfin tuna have fragile, thin, and elliptic otoliths that require particular care during sectioning and polishing so preparing transverse sections is an extremely delicate process.…”

“…One of the limitations of IRMS is that it relies on obtaining a minimum amount of calcium carbonate powder from otolith milling. As a result, the technique does not allow for fine temporal scale resolution (i.e., the signal corresponding to several months must be integrated) or fine scale life history reconstructions (i.e., core to edge transects) [42]. Thanks to recent analytical advances, it is now possible to measure stable isotopes with higher spatial/temporal resolution using secondary ion mass spectrometry (SIMS).…”

“…Thanks to recent analytical advances, it is now possible to measure stable isotopes with higher spatial/temporal resolution using secondary ion mass spectrometry (SIMS). This technique requires more preparation of the samples to be analysed [42], but in return offers a promising tool to unravel migration patterns and life history characteristics at much shorter timescales [43][44][45][46]. When water temperature and oxygen isotopic composition are known, it is possible to delineate isoscapes (i.e., spatial maps of predicted isotopic variation) that can be used to track potential movements across water masses with distinct isotopic signatures [47].…”