Neighboring colonies influence uptake of thermotolerant endosymbionts in threatened Caribbean coral recruits

Abstract

Intervention strategies to enhance coral resilience include manipulating the association between corals and their algal endosymbionts. While hosting thermotolerant Durusdinium trenchii can increase bleaching thresholds in adults, its effects remain largely unknown during the early life stages of Caribbean corals.Here, we tested if Orbicella faveolata recruits could establish symbiosis with D. trenchii supplied by nearby "donor" colonies and examined the resulting ecological trade-offs to evaluate early Symbiodiniaceae manipulation as a scalable tool for reef restoration. We exposed aposymbiotic recruits to 29°C or 31°C and to fragments of either Montastraea cavernosa (containing Cladocopium) or Siderastrea siderea (containing D. trenchii). After 60 days, recruits reared with D. trenchii donors hosted nearly three times more D. trenchii than those with Cladocopium donors, suggesting that recruits can acquire Symbiodiniaceae from nearby corals of different species. Temperature did not affect D. trenchii uptake.Next, donor colonies were removed and surviving recruits were maintained for three months at ambient temperatures, after which a subset was exposed to a 60-day heat stress trial. Recruits previously reared at 31°C survived twice as long at 34°C as those reared at 29°C, suggesting that pre-exposure to heat can prime recruits to withstand future thermal stress. In addition, recruits hosting primarily D. trenchii survived twice as long at 34°C as those hosting little or no D. trenchii. However, the proportion of D.trenchii hosted was negatively correlated with polyp size and symbiont density, indicating a trade-off between growth (of both host and symbiont) and heat tolerance. These findings suggest that, while donor colonies may be effective sources for seeding coral recruits with thermotolerant symbionts, practitioners will need to balance the likely benefits and costs of these approaches when designing restoration strategies.

Gregarious larval settlement mediates the responses of new recruits of the reef coral Acropora austera to ocean warming and acidification

“…These results suggest the complex role of larval aggregation in shaping post-settlement performance of corals in response to ocean warming and acidification, and provide direct evidence for the benefits and tradeoff associated with coral chimerism in determining the recruitment success under future climate change. Uptake of algal symbionts and symbiosis establishment are of paramount importance to the early success and resilience of broadcast spawning corals (Suzuki et al, 2013;Yuyama and Higuchi, 2014;Hazraty-Kari et al, 2022), while this process is particularly susceptible to the ongoing ocean warming (Abrego et al, 2012;Yuyama et al, 2016;Yorifuji et al, 2017;Sun et al, 2020;Jiang et al, 2021;Williamson et al, 2021). Consistent with these aforementioned studies, our results also showed detrimental effects of heat stress on symbiont infection process, with symbiont infection rates being reduced by 50% at 30.5°C.…”

“…Consistent with these aforementioned studies, our results also showed detrimental effects of heat stress on symbiont infection process, with symbiont infection rates being reduced by 50% at 30.5°C. It is important to note that the experimental inoculation method used here may differ from what would happen on natural reefs with a high diversity of free-living Symbiodiniaceae, and this could greatly influence the symbiont selection and acquisition in early stages of corals (Williamson et al, 2021;Matsuda et al, 2022). Furthermore, we found a significant interaction between increased temperature and pCO 2 on algal uptake.…”

Effect of species, size, and chimerism on the susceptibility of Caribbean brain coral recruits to stony coral tissue loss disease (SCTLD)

“…If a specific taxon (i.e. Breviolum ) is implicated in SCTLD infection, managers may choose to provide recruits with sources of alternative taxa during initial symbiosis establishment (Williamson et al, 2021).…”

“…After settlement, recruits were provisioned with Symbiodiniaceae. Fragments of Orbicella faveolata hosting Durusdinium trenchii were placed in aquaria with D. labyrinthiformis recruits to serve as symbiont sources (Williamson et al, 2021). The C. natans recruits were inoculated with approximately one million cells per liter of cultured Breviolum and D. trenchii twice per week, until all recruits were visibly infected (approximately three weeks).…”

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

“…Stress memory in corals was first discovered in eastfacing surfaces of small massive corals that bleached during a summer heatwave whereas west-facing surfaces receiving higher light dosesdid not [50]. Whilst some studies have since demonstrated that moderate thermal [51][52][53] and acidification [54] stress can also enhance tolerance to subsequent thermal stress, others have shown pre-conditioning is not a guarantee to boosting stress tolerance [55]. On balance, given the potential for enhancing stress tolerance through careful environmental exposure, preconditioning seems useful for reef restoration during the larval and early recruit rearing phase of sexually produced coral stock, but also for asexual adult propagation by carefully choosing the location of in situ nurseries (Propagation and planting).…”