Cultured, heat-evolved symbionts can increase the fitness of coral juveniles
Creators: name: Spencer Altice, Miranda
Publisher: name: Southern Cross University
Year: 2024
Subjects: Symbiodiniaceae
Symbionts
Coral larvae
Coral reef restoration
Assisted evolution strategies
Coral juveniles
Climate change
Coral bleaching

description: Scleractinian corals depend on a mutualistic relationship with microalgal symbionts from the family Symbiodiniaceae for growth and survival. Elevated sea temperatures can cause symbiont expulsion, leading to coral bleaching and potential mortality. As corals struggle to adapt to climate change, researchers are exploring assisted evolution strategies to enhance coral resilience. One approach involves exposing microalgal symbionts to increasing temperatures to develop heat tolerance. This study investigates whether scleractinian corals can acquire heat-evolved symbionts during early life stages and the minimum densities required for uptake. The impact of hosting heat-evolved versus wild-type symbionts on coral growth and survival was also explored.
description: Results showed that all four tested coral species could uptake symbionts, with significant variability across symbiont genera, types, and inoculation densities. Durusdinium exhibited higher uptake rates than Cladocopium, regardless of symbiont type, density, or coral species. There was no significant difference in the uptake of wild-type versus heat-evolved symbionts, indicating minimal discrimination in uptake. Survival rates were high in three out of four coral species, with no discernible differences between symbiont types six days post-inoculation. However, settlement success was influenced by symbiont and density treatments, particularly with Durusdinium at the highest densities (10³ and 10⁴ cells mL⁻¹). The study also found that symbiont treatment significantly impacted coral growth three months post-settlement, with differential effects observed between species and life stages of inoculation. A. kenti, particularly during the spat stage, was influenced by density treatments, while P. daedalea exhibited superior growth under all conditions. Durusdinium showed substantial growth in both coral species, while Cladocopium lagged.
description: These findings indicate that corals can readily acquire heat-evolved symbionts during early ontogeny, influencing growth and survival. While uptake, survival, and growth correlated with increasing inoculation densities, symbiont treatments had a more significant influence, especially for larvae-inoculated corals. The results suggest that inoculations at the spat stage may offer greater benefits than at the larval stage, providing guidance for coral inoculation in reef restoration. Durusdinium treatments positively affected the growth of P. daedalea and A. kenti when inoculated at both life stages, demonstrating the species-specific nature of coral-symbiont interactions. Higher symbiont densities were associated with increased coral fitness, particularly at certain levels. These insights contribute to enhancing the fitness of scleractinian corals for coral husbandry and reef restoration, laying the groundwork for further research in assisted evolution strategies.