Census of heat tolerance among Florida's threatened staghorn corals finds resilient individuals throughout existing nursery populations

Abstract

The rapid loss of reef-building corals owing to ocean warming is driving the development of interventions such as coral propagation and restoration, selective breeding and assisted gene flow. Many of these interventions target naturally heat-tolerant individuals to boost climate resilience, but the challenges of quickly and reliably quantifying heat tolerance and identifying thermotolerant individuals have hampered implementation. Here, we used coral bleaching automated stress systems to perform rapid, standardized heat tolerance assays on 229 colonies of Acropora cervicornis across six coral nurseries spanning Florida's Coral Reef, USA. Analysis of heat stress dose–response curves for each colony revealed a broad range in thermal tolerance among individuals (approx. 2.5°C range in F v /F m ED50), with highly reproducible rankings across independent tests ( r = 0.76). Most phenotypic variation occurred within nurseries rather than between them, pointing to a potentially dominant role of fixed genetic effects in setting thermal tolerance and widespread distribution of tolerant individuals throughout the population. The identification of tolerant individuals provides immediately actionable information to optimize nursery and restoration programmes for Florida's threatened staghorn corals. This work further provides a blueprint for future efforts to identify and source thermally tolerant corals for conservation interventions worldwide.

Variation in Coral Thermotolerance Across a Pollution Gradient Erodes as Coral Symbionts Shift to More Heat-Tolerant Genera

“…This approach has been shown to determine differences in coral thermotolerance similarly to a classic longterm heat stress assay (Voolstra et al, 2020;Evensen et al, 2021). We chose to use this 1-day ramp-hold assay in 2019 rather than repeat the 2014-style assay due to the logistical advantage of a 1-day assay and to be more comparable to recent studies using CBASS (Voolstra et al, 2020(Voolstra et al, , 2021Cunning et al, 2021;Evensen et al, 2021;Savary et al, 2021). This assay consists of four replicate tanks to test three experimental temperature treatments and one control, for a total of eight tanks.…”

Building Consensus around the Assessment and Interpretation of Symbiodiniaceae Diversity

“…For example, recent high-throughput approaches for assessing thermal tolerance at the whole coral level (e.g., coral bleaching automated stress systems (CBASS; Voolstra et al, 2020) and single cell levels (Behrendt et al, 2020) have incorporated short thermal challenges followed by stress characterization through the measurement of 1-2 physiological variables such as maximum PSII photochemical efficiency (Fv/Fm) and cell density. While single-phenotype assays can be informative within the context of ecosystem service values (e.g., identifying thermally tolerant corals for nursery propagation; Cunning et al, 2021), identification of functionally distinct Symbiodiniaceae phenotypes will benefit from measuring a broader spectrum of physiological metrics (Hoadley et al, 2021). Phenotypic characterization using multiple photosynthetic metrics can provide some species-specific resolution (Suggett et al, 2015), and the non-invasive nature of chlorophyll a fluorometry lends itself to high-throughput approaches.…”

“…Single-cell transcriptomics (i.e., isolating individual cells and sequencing their transcriptomes) could solve this issue as gene expression could be explored within and among each symbiont cell in hospite. The generation of a cell atlas for the coral Stylophora pistillata enabled the characterization of fine-scale metabolic interactions between symbionts and host gastrodermal cells (Levy et al, 2021). Single-cell sequencing can also enable high-resolution interrogations of how Symbiodiniaceae and host cells interact during symbiosis establishment, maintenance, and breakdown, particularly when Symbiodiniaceae cells can be isolated from different parts of the host coral that exhibit contrasting physiologies.…”

Evidence for adaptive morphological plasticity in the Caribbean coral,Acropora cervicornis

“…This decline has prompted a global effort to understand factors that promote coral survival and persistence under changing ocean conditions. Both differences in fitness-related traits among common-gardened genotypes and of clones under different conditions (30)(31)(32)(33) suggests that some individuals or environments could be used to reestablish the structure and function of reefs (34)(35)(36). However, as corals experience new conditions, via translocation during reef restoration (37,38) or through climate change (39,40), it is unclear whether top performing genotypes will maintain their status (41,42) or if variation in plasticity will result in new 'winners' and 'losers' (43).…”