錦花軟珊瑚於白化事件後的生物表徵及微生物群探討

Abstract

在氣候變化的情況下，夏季海洋熱浪引發更頻繁、更劇烈的白化事件。在2020年，臺灣經歷了歷史上最嚴峻且最廣泛的白化事件。處在亞熱帶地區的北臺灣，在淺水區的珊瑚受到了輕微的影響，而更深的水域（水下5公尺以下）則幾乎不受影響。唯有一類的珊瑚例外：錦花軟珊瑚（Litophyton sp.）在15公尺深處依然展現明顯的白化。因此，本研究將為期一年追蹤此珊瑚於白化事件後的復原狀況。珊瑚的採集於2020年9月（T1）、2021年1月（T2）、5月（T3）和8月（T4）在北臺灣鼻頭進行季節性的採樣，測量了其珊瑚內微生物的組成及性能的表徵，包括：珊瑚宿主的穩定碳和氮同位素、有機質、葉綠素a和c濃度、內共生藻類含量、宿主蛋白和內共生藻類蛋白質濃度。此次研究也與2019 年 4 月（T0）對同種珊瑚在同一地點的研究中之生物表徵數據合併，以了解白化事件所帶來之影響。此外，此研究也調查了從T1到T4這些與珊瑚相關微生物群的差異，並探究其主要影響組成的分類群。研究結果表明所有測量的表徵在不同的採樣時間下都有顯著的變化，特別是在T1-T2和T0-T3-T4之間。這兩組在主成分分析中也易於區分，相對於對照組（T0）可分為珊瑚忍受白化影響（T1和T2）和從白化中恢復（T3和T4）時期。然而，綜觀所有採樣期間，有些特徵呈現的數值仍然與T0有所差異。在微生物方面，在T2呈現高度多樣性的群落明顯不同於其他採樣時期。然而，就相對豐度而言，T4的微生物群組成在視覺上似乎與T1和T3不同。未來的研究應針對微生物組的組成是影響生物表徵的原因，還是受生物表徵影響的結果。此研究表明錦花軟珊瑚可呈現出對白化事件有一定程度的忍受和恢復之能力，可讓此物種因應在日益溫暖的海洋環境中之生存策略。

Under climate change, summer marine heatwaves trigger more frequent and intense bleaching episodes. In 2020, Taiwan underwent the most severe and widespread bleaching event in its recent history. Northern subtropical assemblages were mildly impacted in shallow waters, but deeper waters (< 5m) were almost unaffected. Litophyton sp. was the exception as this octocoral presented obvious signs of bleaching down to -15 m. Fortunately, this octocoral was part of a long-term survey of octocoral organismal performance. Therefore, I scrutinized directly how this species endured and recovered from the bleaching event. Colonies of Litophyton sp. were seasonally sampled in September (T1), January (T2), May (T3) and August (T4) from 2020 to 2021 at Bitou, Taiwan. Organismal traits depicting organismal performance were measured in individual colonies, including host δ13C and δ15N values, organic matter, chlorophyll a and c concentrations, algal endosymbiont content, host protein and algal endosymbiont protein concentrations. Organismal trait composition was tested for differences among sampling periods and merged the dataset from an earlier study on the same species and site in April 2019 (T0). Finally, I looked at variations in microbiome communities associated with those corals from T1 to T4 and identified influential taxa of changes. The results showed obvious differences in all organismal traits, especially between T1-T2 and T3-T4, which were similar to T0 on pigment concentration, algal endosymbiont content and δ15N values. Those two groups were distinguished in a Principal Component Analysis with vector’s characteristics discriminating colonies enduring (T1 and T2) and recovering (T3 and T4) from bleaching with regard to T0. Yet, some traits such as organic matter still differed with T0 through all the sampling periods. Regarding individual microbiome, high alpha diversity was delineated at T2. Furthermore, beta diversity can clearly be distinguished from a community delineated by other sampling periods. Nevertheless, community composition at T4 seems visually to differ from T1 and T3 in terms of relative contribution. Yet, my study indicates that Litophyton sp. presents a certain ability to endure and recover from bleaching, shedding light on an important strategy that may allow this species to be naturally selected in a warmer ocean. Future works should decipher whether the microbiome composition is a cause or a consequence of organismal performance.