不同季節硨磲貝共生微生物群落與弧菌屬菌群之動態變化

Abstract

硨磲貝是珊瑚礁生態系中獨特的底棲生物，其殼體可供海洋生物庇護，而排泄物中所含共生藻能被珊瑚或硨磲貝幼體吸收，作為自身共生藻使用。硨磲貝與體內微生物共同構成共生體，其中共生藻和細菌與宿主間具有高度相關性。然而，近年來全球暖化使水溫急遽上升，導致硨磲貝面臨環境壓力。此外，弧菌屬為海洋生物常見致病菌，前人研究顯示，高溫加熱而瀕臨死亡的硨磲貝體內，弧菌屬相對豐度高於健康個體。雖然珊瑚與其體內微生物的相互作用已被廣泛研究，但針對硨磲貝在季節性溫度變化下共生微生物的群落組成與變化仍相對缺乏，而共生藻與細菌在組織中的空間分佈亦尚無更詳盡的描述。因此本研究旨在探討硨磲貝於不同季節下之共生微生物 (共生藻、共棲細菌) 的群落組成，並利用qPCR及FISH定量方法分析弧菌屬豐度變化。同時，透過FISH觀察共生藻與細菌在組織中的空間分佈。此研究為排除個體間之差異，均採用已標定硨磲貝之外套膜進行分析。結果顯示，於春季時，共生藻之群落組成發生改變，且Clade C (Cladocopium)與Clade D (Durusdinium) 相對豐度呈現上升趨勢。在細菌群落方面，弧菌屬相對豐度於夏季時較高，冬季則呈現下降趨勢，而弧菌屬qPCR定量顯示其在秋季時的含量較其他階段高，但未觀察到顯著差異。此外，FISH定量結果與次世代定序具有一致性，且於影像中觀察到細菌與共生藻在外套膜內具有高度緊密之空間分佈關係，暗示共生微生物之間亦具有共存關係，未來研究可深入探討兩者間的交互作用。

Giant clams are special benthic invertebrates in coral reef ecosystem. Their shells can provide refuges for reef organisms, and fecal pellets contain viable Symbiodiniaceae that can be acquired by coral and giant clams’ larvae and maintained as their own symbionts. Giant clams form a holobiont together with their associated microbiome. However, global warming–driven increases in seawater temperature have led to environmental stress in giant clam holobionts. Vibrio are common pathogen of marine organisms, and previous studies have shown that the relative abundance of Vibrio is higher in dying giant clams than in healthy individuals. Although coral-associated microbiome interaction has been widely studied, shift in the composition and abundance of giant clam’s microbiome across seasonal temperature variations remain less explored, particularly regarding the spatial distribution of Symbiodiniaceae and bacteria within host tissues. Therefore, this study aims to investigate the Symbiodiniaceae and bacteria community dynamics of giant clams across different season. Moreover, qPCR and FISH were employed to quantify changes in Vibrio abundance, while FISH imaging was used to examine the tissue-level spatial distribution. To control for individual variation, each giant clam in the field was tagged to ensure repeated sampling of the same individuals. The results demonstrate that Symbiodiniaceae community composition changed in spring, with increased relative abundance of Clade C (Cladocopium) and Clade D (Durusdinium). Relative abundance of Vibrio was higher in summer but decrease in winter; qPCR indicates higher abundance in autumn. FISH result aligned with sequencing and revealed close spacial distribution between Symbiodiniaceae and bacteria. This suggests that symbiotic microbiome may also exhibit a coexistence relationship, and future studies could investigate the interactions between the two.