Coral bleaching susceptibility is predictive of subsequent mortality within but not between coral species

Abstract

18Marine heat waves instigated by anthropogenic climate change are causing increasingly frequent 19 and severe coral bleaching events that often lead to widespread coral mortality. While 20 community-wide increases in coral mortality following bleaching events have been documented 21 on reefs around the world, the ecological consequences for conspecific individual colonies 22 exhibiting contrasting phenotypes during thermal stress (e.g. bleached vs. not bleached) are not 23 well understood. Here we describe the ecological outcomes of colonies of the two dominant reef-24 building coral species in Kāne ohe Bay, Hawai i, Montipora capitata and Porites compressa, 25 that exhibited either a bleaching susceptible phenotype (bleached) or resistant phenotype (non-26 bleached) following the second of two consecutive coral bleaching events in Hawai i in 2015. 27Conspecific pairs of adjacent bleaching susceptible vs. resistant corals were tagged on patch 28 reefs in two regions of Kāne ohe Bay with different seawater residence times and terrestrial 29 influence. The ecological consequences (symbiont recovery and mortality) were monitored for 30 two years following the peak of the bleaching event. Bleaching susceptible corals suffered higher 31 partial mortality than bleaching resistant corals of the same species in the first 6 months 32 following thermal stress. Surprisingly, P. compressa had greater resilience following bleaching 33 (faster pigment recovery and lower post-bleaching mortality) than M. capitata, despite having 34 less resistance to bleaching (higher bleaching prevalence and severity). These differences 35 indicate that bleaching susceptibility of a species is not always a good predictor of mortality 36 following a bleaching event. By tracking the fate of individual colonies of resistant and 37 susceptible phenotypes, contrasting ecological consequences of thermal stress were revealed that 38 were undetectable at the population level. Furthermore, this approach revealed individuals that 39 underwent particularly rapid recovery from mortality, including some colonies over a meter in 40 diameter that recovered all live tissue cover from >60% partial mortality within just one year. 41These coral pairs continue to be maintained and monitored in the field, serving as a "living 42 library" for future investigations on the ecology and physiology of coral bleaching. 43 44 45 46 102 2008; Bahr et al., 2017; Hughes et al., 2017). Kāne ohe Bay, Hawai i, located on the northeast 103 coast of O ahu, is an opportune system for investigating this question of how intraspecific 104 variability in coral responses to thermal bleaching events driven by climate change influence 105 coral survival. The two dominant reef-building coral species in the bay, Montipora capitata and 106Porites compressa, both exhibit differences in thermal performance within and between species 107 during bleaching (Grottoli et al., 2006; Cunning et al., 2016; Wall et al., 2019). Differences in 108 5 symbiont associations and nutritional plasticity a...

Physiological and transcriptomic variability indicative of differences in key functions within a single coral colony

“…These plastic responses by genetically identical polyps can then be communicated through the coenosarc to the rest of the colony to allow for enhanced resource sharing [106-108]. Such plasticity may aid in colony recovery after partial mortality events, such as those due to bleaching [109], and may be integral to adaptation to environmental change [110]. Further, the expression patterns underlying the tested micro-environmental differences are found to be evolutionary conserved in the distantly-related stony corals S. pistillata and Acropora spp.…”

Metabolomic signatures of coral bleaching history

“…Individual Montipora capitata colonies were tagged during the 2015 bleaching event in Kāneʻohe Bay, Hawaiʻi (Matsuda et al 2019). These tagged corals represent pairs of colonies immediately adjacent to each other where one coral completely bleached while the other remained visibly healthy ( Figure S1B).…”

“…However, our understanding of longer-term impacts of past bleaching is limited (Pinzón et al 2015; Thomas and Palumbi 2017), and differences between thermally resistant and susceptible phenotypes in unstressed conditions is largely unexplored. Corals exhibit a broad range of thermal tolerance (Howells et al 2016;Matsuda et al 2019), which can be used as a framework to investigate the dynamics of resilience and leveraged for restoration. The identification of the drivers and latent effects of bleaching are fundamental for restoration efforts (van Oppen et al 2017) and development of tools for resilience-based management (Anthony et al 2015) under a changing climate.…”

“…Here, we applied an untargeted metabolomics approach to examine the effects of past bleaching and experimental heat stress on the coral holobiont. We sampled pairs of adjacent corals with different historical bleaching phenotypes on a patch reef in Kāneʻohe Bay, Hawaiʻi four years after a bleaching event ( Figure S1) (R Cunning, Ritson-Williams, and Gates 2016; Matsuda et al 2019) and identified a strong signature of bleaching history in the metabolomic data that was primarily driven by the abundance of a class of highly saturated betaine lipids in resilient corals. Host immune response molecules were also significantly different between bleaching phenotypes and correlated strongly with algal-derived metabolites.…”

Marine heatwaves depress metabolic activity and impair cellular acid-base homeostasis in reef-building corals regardless of bleaching susceptibility

“…Short intervals between heatwaves can also change the relative performance between coral species, as differential investments in resistance versus recovery strategies (e.g. (Matsuda et al 2020)) may enable some species to withstand single but not repeat bleaching events (Grottoli et al 2014).…”