四屬軟珊瑚於熱壓力下之共生體變動研究

Abstract

隨著氣候變遷加劇，海洋熱浪日益頻繁，對珊瑚礁生態系造成衝擊。過去研究多集中於石珊瑚，近年研究指出，軟珊瑚在白化事件中可能具有更高的耐受性，甚至可能取代石珊瑚成為優勢族群。過往於野外調查發現，四屬常見軟珊瑚，Sarcophyton、Lobophytum、Sclerophytum 以及 Litophyton 表現出不同的敏感性，其中以Litophyton 最為敏感，Sarcophyton 則相對穩定。珊瑚的共生體組成，特別是共生藻與共生細菌，可能與此密切相關。本研究以此為基礎，針對四屬軟珊瑚進行熱壓力水缸實驗，結合生理指標（顏色分數與光合作用效率）、共生藻 ITS2 與細菌 16S rRNA V6–V8 區域之高通量定序資料，評估其在熱處理下的敏感性差異，並進一步探討共生體群落與宿主反應之潛在關聯。結果顯示，四屬軟珊瑚在共生藻與細菌群落組成上皆呈現明顯的物種特異性，且與宿主間的親緣關係趨於一致。整體而言，Litophyton 為對熱壓力反應最敏感，在宿主生理、共生藻量及細菌群落組成皆出現明顯變動，突顯其共生體系統在熱擾動下的不穩定性，有助於理解珊瑚共生體的熱反應機制。相較之下，其餘三屬則表現出較高的穩定性與耐受性，此差異可能與物種型態特徵有關。核心菌群分析指出，Ruegeria 屬細菌穩定存在於 Sarcophyton、Lobophytum 與 Sclerophytum 中，卻在 Litophyton 中幾乎完全缺失。Ruegeria 為已知具抗氧化與抗病原潛力之潛在珊瑚益生菌，其缺乏可能削弱 Litophyton 面對熱壓力時的微生物緩衝能力，亦可能與其微生物共生關係的演化歷程有關。另一方面，Litophyton 中的Endozoicomonas 可區分為兩個類群，且這兩群在熱壓力反應下展現出不同的動態變化，顯示其內部可能具有演化上的分化與功能上的異質性。

As climate change intensifies, marine heatwaves are becoming increasingly frequent, posing serious threats to coral reef ecosystems. While previous studies have largely focused on hard corals, recent research suggests that soft corals may exhibit greater tolerance to bleaching events and could potentially replace hard corals as dominant reef builders. Field surveys have revealed varying thermal sensitivities among four common genera of soft corals, Sarcophyton, Lobophytum, Sclerophytum, and Litophyton, with Litophyton being the most sensitive and Sarcophyton relatively stable. The composition of coral symbionts, particularly Symbiodiniaceae and associated bacteria, may be closely related to this variation. Based on these observations, this study conducted tank experiments on four genera of soft corals under heat stress. By integrating physiological indicators (color score and photosynthetic efficiency) with high-throughput sequencing data of the Symbiodiniaceae ITS2 region and the bacterial 16S rRNA V6–V8 region, we assessed their sensitivity to thermal stress and further explored potential associations between symbiotic community dynamics and host responses. Results showed strong species-specific patterns in both Symbiodiniaceae and bacterial community composition, largely consistent with host phylogeny. Litophyton exhibited the strongest response to thermal stress, with pronounced changes in host physiology, symbiont abundance, and bacterial community structure, indicating instability of its symbiotic system under thermal disturbance. In contrast, the other three genera showed higher levels of stability and tolerance, possibly associated with morphological traits.Core microbiome analysis revealed that Ruegeria, a genus known for its antioxidant and antimicrobial potential, was consistently present in Sarcophyton, Lobophytum, and Sclerophytum, but nearly absent in Litophyton. Its absence may reduce microbial buffering capacity under stress and reflect evolutionary differences in symbiotic partnerships. Notably, Endozoicomonas associated with Litophyton can be categorized into two groups that respond differently to thermal stress, indicating possible evolutionary divergence and functional heterogeneity within the genus.