Using naturally occurring climate resilient corals to construct bleaching-resistant nurseries

Abstract

Ecological restoration of forests, meadows, reefs, or other foundational ecosystems during climate change depends on the discovery and use of individuals able to withstand future conditions. For coral reefs, climate-tolerant corals might not remain tolerant in different environments because of widespread environmental adjustment of coral physiology and symbionts. Here, we test if parent corals retain their heat tolerance in nursery settings, if simple proxies predict successful colonies, and if heat-tolerant corals suffer lower growth or survival in normal settings. Before the 2015 natural bleaching event in American Samoa, we set out 800 coral fragments from 80 colonies of four species selected by prior tests to have a range of intraspecific natural heat tolerance. After the event, nursery stock from heat-tolerant parents showed two to three times less bleaching across species than nursery stock from less tolerant parents. They also retained higher individual genetic diversity through the bleaching event than did less heat-tolerant corals. The three best proxies for thermal tolerance were response to experimental heat stress, location on the reef, and thermal microclimate. Molecular biomarkers were also predictive but were highly species specific. Colony genotype and symbiont genus played a similarly strong role in predicting bleaching. Combined, our results show that selecting for host and symbiont resilience produced a multispecies coral nursery that withstood multiple bleaching events, that proxies for thermal tolerance in restoration can work across species and be inexpensive, and that different coral clones within species reacted very differently to bleaching.

Symbiont community diversity is more variable in corals that respond poorly to stress

“…Given the mortality suffered by Worst‐27, there is no indication that Durusdinium types provided that genet with tolerance to elevated temperature, p CO 2 , additions of V. owensii , or combinations thereof in this experiment. Although significant hopes for the survival of reefs into the future often rest upon corals acclimatizing to stress by harboring Durusdinium symbionts, this finding and some other studies indicate that hosting Durusdinium is not a panacea; only some Durusdinium types/species may impart stress tolerance to some coral hosts under certain circumstances and/or abundances (e.g., Hoadley et al, ; LaJeunesse et al, ; Morikawa & Palumbi, ). If complementarity effects are important in coral–Symbiodiniaceae mutualisms, then symbiont community diversity metrics may help reveal particular contexts in which Durusdinium (or other Symbiodiniaceae) types/species contribute to holobiont stress tolerance.…”

Resilience in reef‐building corals: The ecological and evolutionary importance of the host response to thermal stress

“…Similarly, Baums et al () found that larvae of Acropora palmata from different parental crosses differed in their swimming speed and development rates under thermal stress. Recent work has also documented the stability of fixed effects over time, where thermal tolerance is consistent despite the potential for acclimatization under cooler conditions (Morikawa & Palumbi, ; Schoepf et al, ).…”

Signatures of selection in the coral holobiont reveal complex adaptations to inshore environments driven by Holocene climate change

“…The projected severity of these impacts therefore depends on whether coral holobionts (coral, photosymbionts and associated bacteria 7,8 ) can adapt fast enough to maintain the integrity of reef ecosystems 9,10 . A key factor that might improve the adaptive outlook for corals is the existence of stress-tolerant populations which could fuel adaptation in conspecifics through assisted or natural gene flow [11][12][13][14] . Ironically, many of these resilient coral populations are threatened because they are found in inshore environments 13,15,16 where they face additional pressures from reduced water quality [17][18][19] that can exacerbate susceptibility to elevated temperature 20,21 .…”