Data from: Symbiont community stability through severe coral bleaching in a thermally extreme lagoon

Coral reefs are threatened by climate change as coral-algal symbioses are
currently living close to their upper thermal limits. The resilience of
the algal partner plays a key role in determining the thermal tolerance of
the coral holobiont and therefore, understanding the acclimatory limits of
present day coral-algal symbioses is fundamental to forecasting corals’
responses to climate change. This study characterised the symbiont
community in a highly variable and thermally extreme (Max = 37.5 °C,
Min = 16.8 °C) lagoon located in the southern Persian/Arabian Gulf using
next generation sequencing of ITS2 amplicons. Despite experiencing extreme
temperatures, severe bleaching and many factors that would be expected to
promote the presence of, or transition to clade D dominance, the symbiont
communities of the lagoon remain dominated by the C3 variant, Symbiodinium
thermophilum. The stability of this symbiosis across multiple genera with
different means of symbiont transmission highlights the importance of
Symbiodinium thermophilum for corals living at the acclimatory limits of
modern day corals. Corals in this extreme environment did not undergo
adaptive bleaching, suggesting they are living at the edge of their
acclimatory potential and that this valuable source of thermally tolerant
genotypes may be lost in the near future under climate change.

珊瑚礁正受到气候变化的威胁，因为珊瑚-藻类共生体（coral-algal symbioses）目前正处于其热耐受上限附近。藻类共生伙伴的抗逆性在决定珊瑚共生体（coral holobiont）的热耐受能力方面发挥着关键作用，因此，明晰当代珊瑚-藻类共生体的驯化极限，是预测珊瑚对气候变化响应的核心基础。本研究针对波斯湾/阿拉伯湾南部一处环境高度多变且热胁迫极端（最高温37.5℃，最低温16.8℃）的泻湖，利用ITS2扩增子下一代测序（next generation sequencing）技术对其中的共生藻群落进行了表征。尽管该泻湖环境经历了极端温度波动、严重珊瑚白化，以及诸多被认为会促进D类群（clade D）优势定植或群落向D类群转变的环境因子，但其中的共生藻群落仍以C3变异型——嗜热虫黄藻（Symbiodinium thermophilum）为主导。这种共生关系在多个具有不同共生体传播方式的珊瑚属中保持稳定，凸显了嗜热虫黄藻对于生活在当代珊瑚驯化极限环境中的珊瑚的重要性。该极端环境中的珊瑚并未发生适应性白化（adaptive bleaching），这表明它们正处于自身驯化潜能的临界边缘，而这种极具价值的耐热基因型资源，在未来不久的气候变化背景下可能会永久丧失。