Revealing growth increments in fossil and modern otoliths with backscattered electron imaging
Abstract
Otoliths, the functional earstones of teleost fishes, record growth in the form of microscopic increments, making them key archives of individual life histories. While increment analysis is commonly applied to modern otoliths, studies of fossil (Holocene) otoliths remain limited. Traditional methods such as light microscopy (LM) and secondary electron (SE) imaging often fail to resolve microincrements, leading to underestimation and inconsistent findings. We used backscattered electron (BSE) imaging to examine modern and radiocarbon‐dated Holocene otoliths of the black goby (Gobius niger Linnaeus, 1758) from the northern Adriatic Sea. Our aim was to assess whether BSE imaging improves microincrement visibility. Standard BSE imaging outperformed LM, detecting 22.6% more increments than in thin‐sectioned and 55.7% more increments than in surface‐polished Holocene otoliths. High‐resolution BSE imaging with extended scan times and optimized settings revealed over 250% more increments than a standard BSE workflow. These results show that imaging quality and scan strategy significantly influence microincrement detection, and that optimized BSE workflows greatly improve the resolution of growth records. Notably, microincrement visibility in the Holocene otoliths was unaffected by post‐mortem alteration or radiocarbon age, indicating robust internal preservation. In contrast, LM imaging of thin‐sectioned modern otoliths yielded higher increment counts than the BSE method due to…
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