海洋浮游動物體內的微量金屬元素

Trace metals in marine zooplanktons

林佩萱(Pei-Hsuan Lin)

指導教授 ： 溫良碩

國立臺灣大學/理學院/海洋研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02055

摘要

微量金屬元素參與海洋生物體內的各種生理反應，當浮游植物進食後，微量元素即隨著食物鏈傳遞並累積在生物體內，而未被浮游動物利用的元素則經由代謝和排泄回到海水中。因此，了解浮游動物的代謝作用和攝食行為，探討微量元素在海洋浮游動物體內的反應，可讓我們進一步窺探海洋環境中微量元素生地化循環。本研究利用超純淨採樣分離方法（Ultraclean Size Fraction Techniques），以體型大小為基準，在台灣海峽至西菲律賓海海域間，採集浮游生物並區分為不同生長階段（10~63、63~153、>153、363~500、500~1000、1000~2000、>2000 μm），剖析基本元素及微量金屬元素含量。根據浸洗實驗得知，浮游動物體內的微量元素約佔73%，剩餘約27%則吸附在外骨骼表面上。浮游動物的Fe、Zn、Cu、Ni、Cd平均含量各為361±455、98.87±60.61、8.43±4.10、5.53±3.18以及3.02±2.02μg g-1，且隨著空間和生物體型大小改變，而有顯著差異。幾乎在所有研究海域中，Cu、Ni、Cd皆是大體型者含量較低，且Cd含量隨著每個食階提昇（體型增加）後約下降64%~79%，下降趨勢顯著；再者，隨著浮游動物食階增加，不同金屬和C、N、S的比值（TM/C、TM/N、TM/S）分布亦隨之改變。橈足類活體、殼體和碎屑金屬含量皆不同，Fe、Cu、Ni似乎多分布於殼體上，佔橈足類活體中各66%、64%與75%；相反地，殼體Cd 金屬只佔1%，其餘99%可能皆分布於軟組織內。餵食培養實驗亦發現，浮游動物體內的金屬含量將隨著食物來源的不同而產生差異。由此可知，浮游動物對於不同金屬的吸收、代謝和排除機制似乎不同。綜合實驗研究可知，不同食階之浮游動物對不同金屬的需求與反應作用顯然不同，微量元素累積程度會受到環境、體型、生理代謝反應與食物來源等因素影響。此外，浮游動物會主動累積必需元素，亦會主動排除毒素，影響海洋中微量元素的生地化循環。

關鍵字

食階 ； 浮游動物 ； 微量金屬 ； 生物累積 ； 台灣海峽 ； 西菲律賓海

並列摘要

Bioactive trace elements (Fe, Zn, Cu, Ni and Cd) were taken up by phytoplankton in euphotic zone through various biological processes. Accumulation in the zooplanktons mainly through feeding process (trophic transfer), any unassimilated trace elements will be rapidly packaged into fecal pellets and transported out to surface waters. However, zooplankton bio-concentration or trophic transfer of trace metals, whether caused by dietary behavior or metabolic function remain a main issue for trace metals biogeochemical cycle in marine environment. In this study, using ultraclean techniques, elemental and metals concentration of selected zooplanktons at various sizes (sizes in μm: 10~63, 63~153, 153~363, 363~500, 500~1000, 1000~2000, >2000) were analyzed. It was found, on average, that only ~73% of trace metals were intercellular, remained ~27% were adsorbed on exoskeleton. Concentrations of Fe, Zn, Cu, Ni and Cd in zooplanktons increased with sizes, on average, 361±455、98.87±60.61、8.43±4.10、5.53±3.18 and 3.02±2.02 μg g-1 respectively, with various metal to elemental ratios (TM:C, TM:N and TM:S). Fecal pellets, exoskeletons, and intracellular materials all show distinctive diverse metal concentration levels. Fe, Cu and Ni were mostly in exoskeleton (Fe: 66%, Cu: 64%, Ni:75%); but, only 1% for Cd. Incubation experiments also revealed that zooplanktons have different trace metals requirement at various growth stages, due to environmental conditions, trophic levels, metabolism mechanisms and food sources. Over all, these findings suggest that zooplankton were deliberately accumulated essential metals, not passively as previously believed. Metal detoxification is actively involved in its life cycles which have profound impact on biogeochemistry of trace metals in the ocean.

並列關鍵字

zooplankton ； trophic level ； trace metal ； bioaccumulation ； Taiwan Strait ； western Philippine Sea

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