Preconditioning improves bleaching tolerance in the reef‐building coral Pocillopora acuta through modulations in the programmed cell death pathways

Abstract

Reef-building stony corals live in a mutually beneficial partnership with photosynthetic algae that is the core energetic driver of coral reefs. Stressful conditions such as high temperature lead to the disruption of this symbiosis known as coral bleaching, and eventual coral death (Brown, 1997). Climate change-related mass bleaching events have become increasingly common, affecting about 75% of coral reefs in Hawaiʻi and 93% of surveyed corals in the Great Barrier Reef, with over 50% mortality in some regions (Couch et al., 2017;Hoegh-Guldberg et al., 2015). Current climate-change mitigation measures (e.g., the Paris agreement), aiming to limit global warming to 2℃ are unlikely to effectively moderate impacts on coral reefs. As temperature stress events become more frequent and severe, most reefs are projected to face near-annual bleaching by mid-century, leaving these ecosystems under an imminent threat of collapse and

Thermal preconditioning in a reef-building coral alleviates oxidative damage through a BI-1 mediated antioxidant response

“…Like most organisms, corals have the ability to acclimatize to environmental change, which reduces the severity of bleaching and mortality during thermal stress [34][35][36][37][38]41,55 . However, this natural phenomenon may be genotype-specific 39 and could be lost under future climatechange scenarios 40 .…”

“…To exclude non-specific effects of the siRNA treatment, we analyzed the correlation of pa-BI-1 expression with 4 genes (pa-HSP70, pa-Bcl-2, pa-BAK, pa-BAX) previously found to be involved in coral bleaching 41,50,51 and which follow a similar expression patterns as pa-BI-1 in PC and NPC corals upon heat stress, and with pa-NFKBI (NFkB inhibitor) that was differentially expressed ( 41 , We hypothesized that if the siRNA treatment is not specific to the pa-BI-1 gene or impacts the whole bleaching pathway, we would observe a shift in multiple genes involved in the coral bleaching cascade. Upon siBI-1 treatment, the expression of none of these genes changed significantly (Fig S3B ), supporting the specificity of the siRNA treatment to siBI-1 gene expression.…”

“…However, the coral host control of the level of oxygen radicals and ROS is likely a major component in the dynamics of coral-algal symbiosis maintenance 19,31 and activation of DNA damage response pathways is a hallmark of thermal stress in corals 32 Intra-generational plasticity is critical for mitigating stress in corals, which have a limited ability to avoid stressful environmental conditions, highlighting the importance of acclimatization for the long-term persistence of coral reefs by 'buying time' for adaptive change 33 . While many corals show improved thermal tolerance after pre-exposure to sublethal temperatures [34][35][36][37][38][39][40][41] , the molecular triggers and consequences of this process remain poorly understood.…”

Growth and survival among Hawaiian corals outplanted from tanks to an ocean nursery are driven by individual genotype and species differences rather than preconditioning to thermal stress

“…There is some optimism that individual acclimatization or population adaptation of corals to rising ocean temperatures will drive reef resilience to climate change ( Coles et al, 2018 ; Majerova et al, 2021 ; Middlebrook, Hoegh-Guldberg & Leggat, 2008 ; Thomas et al, 2018 ), and while there are probable limits ( Ainsworth et al, 2016 ; Hughes et al, 2017 ), various intervention strategies are attempting to direct that effort ( Hagedorn et al, 2021 ; Hancock et al, 2021 ; van Oppen et al, 2017 ; van Oppen et al, 2015 ). Because Kāne‘ohe Bay again experienced elevated temperatures and subsequent bleaching throughout the bay and around HIMB (where the nursery trees were located) during the summer and fall of 2019, we examined the response between individual and groups of corals with and without a history of previous exposure to elevated temperatures.…”

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).…”