Abstract

Otolith chemistry has gained increasing attention as a tool for analyzing various aspects of fish biology, such as stock dynamics, migration patterns, hypoxia and pollution exposure, and connectivity between habitats. While these studies often assume otolith elemental concentrations reflect environmental conditions, physiological processes are increasingly recognized as a modulating and/or controlling factor. In particular, biomineralization—the complex, enzyme-regulated construction of CaCO₃ crystals scaffolded by proteins—is believed to play a critical role in governing otolith chemical patterns. This review aims to summarize the knowledge on otolith composition and biophysical drivers of biomineralization, present hypotheses on how biomineralization should affect element incorporation, and test the validity thereof with selected case studies. Tracers of environmental history are assumed to be dominated by elements that substitute for Ca during crystal growth or that occur randomly trapped within the crystal lattice. Strontium (Sr) and barium (Ba) largely comply with the biomineralization-based hypotheses that otolith element patterns reflect environmental concentrations, without additional effects of salinity, but can be influenced by physiological processes, typically exhibiting decreasing incorporation with increasing growth. Conversely, tracers of physiology are assumed to be elements under physiological control and primarily occur protein-bound in the otolith’s organic matrix. Physiological tracers are hypothesized to reflect feeding rate and/or growth, decrease with fish age, and exhibit minimal influence of environmental concentration. The candidate elements phosphorus (P), copper (Cu) and zinc (Zn) confirm these hypotheses. Magnesium (Mg) is believed to be randomly trapped in the crystal structure and hence a candidate for environmental reconstruction, but the response to all examined drivers suggest Mg to be coupled to growth. Manganese (Mn) substitutes for Ca, but is also a co-factor in matrix proteins, and therefore exhibits otolith patterns reflecting both environmental (concentration and salinity) and physiological (ontogeny and growth) histories. A consistent temperature response was not evident across studies for either environmental or physiological tracers, presumably attributable to variable relationships between temperature and fish behavior and physiology (e.g., feeding rate, reproduction). Biomineralization thus has a controlling effect on otolith element concentrations for elements that are linked with somatic growth, but not for elements that substitute for Ca in the crystal lattice. Interpretation of the ecological significance of patterns from field samples therefore needs to consider the impact of the underlying biomineralization processes of the element in question as well as physiological processes regulating the availability of ions for inclusion in the growing crystal lattice. Such understanding will enhance the utility of this technique to address fisheries management questions.

摘要

耳石化学作为分析鱼类生物学各个方面的工具越来越受到关注，例如种群动态、迁移模式、缺氧和污染暴露以及栖息地之间的连通性。虽然这些研究通常假设耳石元素浓度反映环境条件，但生理过程越来越被认为是调节和/或控制因素。特别是生物矿化——CaCO ₃复杂的酶调控结构由蛋白质支撑的晶体被认为在控制耳石化学模式中起着关键作用。本综述旨在总结有关耳石成分和生物矿化的生物物理驱动因素的知识，提出关于生物矿化如何影响元素掺入的假设，并通过选定的案例研究测试其有效性。环境历史的示踪剂被假定为由在晶体生长过程中替代 Ca 或随机出现在晶格内的元素主导。锶 (Sr) 和钡 (Ba) 很大程度上符合基于生物矿化的假设，即耳石元素模式反映环境浓度，没有盐度的额外影响，但会受到生理过程的影响，通常随着生长的增加而减少掺入。相反，生理学示踪剂被认为是生理控制下的元素，主要发生在耳石有机基质中的蛋白质结合中。生理示踪剂被假设为反映摄食率和/或生长，随着鱼的年龄而减少，并且对环境浓度的影响最小。候选元素磷 (P)、铜 (Cu) 和锌 (Zn) 证实了这些假设。镁 (Mg) 被认为是随机捕获在晶体结构中，因此是环境重建的候选者，但对所有检查驱动因素的反应表明，镁与生长相关。锰 (Mn) 替代 Ca，但也是基质蛋白中的辅助因子，因此表现出反映环境（浓度和盐度）和生理（个体发育和生长）历史的耳石模式。在环境或生理示踪剂的研究中，一致的温度响应并不明显，这可能归因于温度与鱼类行为和生理学（例如摄食率、繁殖）之间的可变关系。因此，生物矿化对与体细胞生长相关的元素的耳石元素浓度具有控制作用，但对替代晶格中 Ca 的元素没有影响。因此，对来自现场样品的模式的生态意义的解释需要考虑相关元素的潜在生物矿化过程以及调节离子可用性的生理过程的影响，以包含在不断增长的晶格中。