Heat-Evolved Microalgal Symbionts Increase Thermal Bleaching Tolerance of Coral Juveniles Without a Trade-Off Against Growth

Heat‐evolved algal symbionts enhance bleaching tolerance of adult corals without trade‐off against growth

“…While heat‐evolved C. proliferum (SS8) has been experimentally evolved (Chakravarti et al., 2017) and maintained at 31°C for ~10 years, it can form a symbiosis with adult GBR G. fascicularis , to which it is a heterologous symbiont. SS8 can also colonize aposymbiotic coral larvae and juveniles of a taxonomically distant species ( A. tenuis ) (Buerger et al., 2020; Quigley et al., 2023; Quigley & van Oppen, 2022), indicating it can potentially be a reef restoration resource applicable to corals across taxa and life stages. Consistent with previous studies (Puntin et al., 2023; Scharfenstein et al., 2022; Wang et al., 2012), menthol treatment was an effective way to produce corals with minimal native Symbiodiniaceae (<1%–2% of pre‐bleaching densities), but did not produce fully aposymbiotic corals.…”

“…(2020) inoculated Acropora tenuis larvae with 10 different strains of heat‐evolved C. proliferum (SS1–10), three of which (SS1, 7, 8) enhanced larval bleaching tolerance compared to those inoculated with wild‐type C. proliferum (WT10) in the laboratory. Furthermore, A. tenuis juveniles (2 or 10 months old) inoculated with heat‐evolved strains (SS1 or SS8) survived better or had less bleaching than those inoculated with WT10 under elevated temperatures (31 or 32°C) in the laboratory (Quigley et al., 2023; Quigley & van Oppen, 2022). While these findings are promising, it is unclear whether they can be extrapolated to other coral species and to the adult life phase, given larvae/juveniles and adults differ significantly physiologically.…”

Horizon scan of rapidly advancing coral restoration approaches for 21st century reef management

“…A possible solution is to augment thermal tolerance of homologous Symbiodiniaceae isolates ex hospite (in culture) via experimental evolution [ 59 ] ( Figure 1 ), followed by the reintroduction of the heat-evolved isolates into coral. This procedure has already been shown to increase thermal tolerance in coral larvae [ 60 ] and juveniles [ 61 ]. Thus, for reef restoration, aposymbiotic coral early life stages could be inoculated with heat-evolved symbionts to boost their thermal tolerance prior to deployment onto degraded reefs.…”

Assisted evolution of algal symbionts to enhance coral reef bleaching tolerance: A success story

“…Perhaps the most alarming of these threats is anthropogenic global warming, which is leading to severe effects on coral, disrupting the association between coral host and symbiont microalgae and resulting in bleaching of coral and potential coral death (Hughes et al., 2018). The survival of corals hinges on their ability to maintain symbiotic associations with microalgae from the Symbiodiniaceae family, as these microalgae provide vital carbon and nitrogen to their hosts (Quigley et al., 2023). Symbiodiniaceae possess physiological properties that can provide protection to their hosts during stress events, such as increased tolerance to high temperatures.…”

“…In anticipation of the severe ocean warming and acidification expected for the near future (IPCC, 2022), advanced techniques to maintain coral reefs are actively being explored. Human-assisted evolution is a new area of research aiming to transplant manipulated coral into the natural environment to establish resilient coral reefs (van Oppen et al, 2015). The host-associated microbiome has been revealed as essential for the adaptation of corals to their environment, making it a significant consideration in conservation biology.…”