Institute of Marine Research, Nordnes, Bergen, Norway.
Department of Fisheries Resources, National Marine Fisheries Research Institute, Gdynia, Poland.
PLoS One. 2021 Apr 1;16(4):e0248711. doi: 10.1371/journal.pone.0248711. eCollection 2021.
The isotopic composition of inorganic carbon in otoliths (δ13Coto) can be a useful tracer of metabolic rates and a method to study ecophysiology in wild fish. We evaluated environmental and physiological sources of δ13Coto variation in Icelandic and Northeast Arctic (NEA) cod (Gadus morhua) over the years 1914-2013. Individual annual growth increments of otoliths formed at age 3 and 8 were micromilled and measured by isotope-ratio mass spectrometry. Simultaneously, all annual increment widths of the otoliths were measured providing a proxy of fish somatic growth. We hypothesized that changes in the physiological state of the organism, reflected by the isotopic composition of otoliths, can affect the growth rate. Using univariate and multivariate mixed-effects models we estimated conditional correlations between carbon isotopic composition and growth of fish at different levels (within individuals, between individuals, and between years), controlling for intrinsic and extrinsic effects on both otolith measurements. δ13Coto was correlated with growth within individuals and between years, which was attributed to the intrinsic effects (fish age or total length). There was no significant correlation between δ13Coto and growth between individuals, which suggests that caution is needed when interpreting δ13Coto signals. We found a significant decrease in δ13Coto through the century which was explained by the oceanic Suess effect-admixture of isotopically light carbon from fossil fuel. We calculated the proportion of the respired carbon in otolith carbonate (Cresp) using carbon isotopic composition in diet and dissolved inorganic carbon of the seawater. This approach allowed us to correct the values for each stock in relation to these two environmental baselines. Cresp was on average 0.275 and 0.295 in Icelandic and NEA stock, respectively. Our results provide an insight into the physiological basis for differences in growth characteristics between these two cod stocks, and how that may vary over time.
耳石中无机碳的同位素组成（δ13Coto）可以作为代谢率的有用示踪剂，并可用于研究野生鱼类的生态生理学。我们评估了 1914 年至 2013 年期间冰岛和东北北极（NEA）鳕鱼（Gadus morhua）耳石中 δ13Coto 变化的环境和生理来源。使用同位素质谱仪对 3 岁和 8 岁时形成的耳石的每年个体生长增量进行微磨和测量。同时，还测量了所有耳石的每年生长增量宽度，为鱼类体生长提供了替代指标。我们假设，反映在耳石同位素组成中的生物体生理状态的变化会影响生长速度。我们使用单变量和多变量混合效应模型，在控制了对耳石测量的内在和外在影响的情况下，估计了碳同位素组成与不同水平（个体内、个体间和年际间）鱼类生长之间的条件相关性。δ13Coto 与个体内和年际间的生长呈正相关，这归因于内在效应（鱼类年龄或总长度）。δ13Coto 与个体间的生长没有显著相关性，这表明在解释 δ13Coto 信号时需要谨慎。我们发现，通过整个世纪，δ13Coto 呈显著下降趋势，这可以用海洋苏斯效应来解释，即化石燃料中较轻的碳同位素的混合。我们使用饮食中的碳同位素组成和海水中的溶解无机碳，计算了耳石碳酸盐（Cresp）中呼吸碳的比例。这种方法允许我们根据这两个环境基准来校正每个种群的值。在冰岛和 NEA 种群中，Cresp 分别平均为 0.275 和 0.295。我们的研究结果深入了解了这两个鳕鱼种群在生长特征上的差异的生理基础，以及这种差异可能随时间的变化而变化。
