脊椎作為魚類生活史代謝紀錄器之可行性開發驗證

Abstract

海洋生物的代謝反應其能量使用情形，與其生活環境以及生活史策略相關，例如物種的分佈、環境溫鹽、生物交互作用、個體體型、運動能力強弱、及繁殖策略等，因此了解海洋生物在各種環境和人為壓力下的能量用以及相關生理反應至關重要。為了調查野外海洋生物的新陳代謝率，前人的研究應用了來自生物碳酸鹽中所紀錄的δ13C值計算出代謝指標（Cresp），如魚耳石、雙殼綱殼體和烏賊骨板，而本研究旨在擴展Cresp在海洋脊椎動物中的應用潛力，並企圖驗證脊椎的結構碳酸鹽也可以用作代謝記錄器。為此，我們進行了兩項實驗來評估其可行性，(1)分析了27種野生魚類的耳石和脊椎中所記錄的δ13C值，探討兩個結構δ13C值的可比性；(2)進行了為期一年的黑鯛（Acanthopagrus schlegelii）養殖實驗，建立脊椎結構碳酸鹽Cresp值與耗氧量建立關係式。首先，本研究觀察到在跨物種的比較中，耳石和脊椎之間的δ13C值在不同魚種中呈高度相關。其次，由黑鯛脊椎樣本計算的Cresp值與耗氧量之間的關係遵循退化模型的上升模式(a decay model in an increasing form)，這與前人在耳石上進行的驗證實驗結果相似。這些結果證實了脊椎也可以用作魚類生活史代謝率的紀錄器，並且本研究所建立的δ13C代謝指標可應用於沒有耳石的物種，如鯊魚和海洋哺乳類等脊椎動物。發展δ13C代謝指標方法及應用有助於評估野生海洋生物的行為和生理，並可用於預測海洋脊椎動物在環境變化下的種群動態。

The metabolism reflects the energy use of a marine organism, which is associated with multiple variables, such as species distribution, environmental conditions, prey-predator interaction, body size, activity, reproduction, and fitness. Thus, it is crucial to understand the physiological responses of marine organisms exposed to various environmental and anthropogenic pressures. To investigate the physiological traits of marine organisms in the field, previous studies applied a metabolic proxy (Cresp) derived from the δ13C value in the biogenic carbonate, e.g., fish otolith, bivalve shell, and cuttlefish cuttlebone. This study aims to extend the use of Cresp in marine vertebrates and attempt to prove that the vertebral carbonate can also be used as a metabolic recorder. Thus, two experiments are conducted to evaluate the feasibility. (1) Field observations are to compare the δ13C value recorded in otolith and vertebrae in wild-caught fish across 27 species. (2) A one-year rearing experiment is to link Cresp to the oxygen consumption rate during the ontogeny of the black porgy (Acanthopagrus schlegelii). First, a strong correlation of δ13C values between otolith and vertebrae across teleost species is observed. Second, the relationship between vertebra-derived Cresp and oxygen consumption rate follows the decay model in an increasing form comparable to the previous validation experiment on otolith. These results strongly suggest that the vertebrae can also be used as a chemical archive, and the δ13C metabolic proxy holds the potential to apply to those species without otolith, e.g., sharks and marine mammals. The development of the δ13C metabolic proxy facilitates evaluating behavioral and physiological responses of marine organisms in the wild and predicting the population dynamic of marine vertebrates under the changing climate.