Coral reef research has predominantly focused on the effect of temperature on the breakdown of coral-dinoflagellate symbioses. However, less is known about how increasing temperature affects the establishment of new coral-dinoflagellate associations. Inter-partner specificity and environment-dependent colonization are two constraints proposed to limit the acquisition of more heat tolerant symbionts. Here, we investigated the symbiotic dynamics of various photosymbionts in different host genotypes under “optimal” and elevated temperature conditions. To do this, we inoculated symbiont-free polyps of the sea anemone Exaiptasia pallida originating from Hawaii (H2), North Carolina (CC7), and the Red Sea (RS) with the same mixture of native symbiont strains (Breviolum minutum, Symbiodinium linucheae, S. microadriaticum, and a Breviolum type from the Red Sea) at 25 and 32 °C, and assessed their ITS2 composition, colonization rates, and PSII photochemical efficiency (Fv/Fm). Symbiont communities across thermal conditions differed significantly for all hosts, suggesting that temperature rather than partner specificity had a stronger effect on symbiosis establishment. Overall, we detected higher abundances of more heat resistant Symbiodiniaceae types in the 32 °C treatments. Our data further showed that PSII photophysiology under elevated temperature improved with thermal pre-exposure (i.e., higher Fv/Fm), yet, this effect depended on host genotype and was influenced by active feeding as photochemical efficiency dropped in response to food deprivation. These findings highlight the role of temperature and partner fidelity in the establishment and performance of symbiosis and demonstrate the importance of heterotrophy for symbiotic cnidarians to endure and recover from stress.

珊瑚礁研究主要集中在温度对珊瑚-甲藻共生体分解的影响上。然而，人们对温度升高如何影响新的珊瑚-甲藻协会的建立知之甚少。伴侣间特异性和依赖环境的定植是提出的两个限制条件，以限制获得更耐热的共生体。在这里，我们研究了在“最佳”和高温条件下不同宿主基因型中各种光共生体的共生动力学。为此，我们将来自夏威夷 (H2)、北卡罗来纳 (CC7) 和红海 (RS) 的海葵 Exaiptasia pallida 的无共生息肉接种到相同的天然共生菌株混合物 ( Breviolum minutum、Symbiodinium linuchae)、S. microadriaticum和来自红海的Breviolum类型）在 25 和 32 °C，并评估了它们的 ITS2 组成、定植率和 PSII 光化学效率 ( Fv/Fm )。所有宿主的热条件下的共生群落都存在显着差异，这表明温度而非伴侣特异性对共生建立的影响更大。总体而言，我们在 32 °C 处理中检测到更高丰度的耐热共生科类型。我们的数据进一步表明，高温下的 PSII 光生理学随着热预曝光（即更高的Fv/Fm)，然而，这种影响取决于宿主基因型，并受到主动进食的影响，因为光化学效率因食物匮乏而下降。这些发现强调了温度和伴侣忠诚度在共生的建立和表现中的作用，并证明了异养对于共生刺胞动物忍受压力和从压力中恢复的重要性。