TY - JOUR

T1 - Coral host physiology and symbiont dynamics associated with differential recovery from mass bleaching in an extreme, macro-tidal reef environment in northwest Australia

AU - Jung, E. Maria U.

AU - Stat, Michael

AU - Thomas, Luke

AU - Koziol, Adam

AU - Schoepf, Verena

PY - 2021

Y1 - 2021

N2 - As marine heatwaves increasingly threaten coral reefs worldwide, some extreme reef environments naturally expose corals to high-temperature fluctuations and can therefore provide important insights into the mechanisms underlying coral heat tolerance. Coral reefs in the Kimberley region in northwest Australia experience the world's largest tropical tides and are therefore exposed to highly fluctuating temperatures in the intertidal. In contrast, the subtidal remains mostly submerged, resulting in moderate daily temperature fluctuations. A marine heatwave in 2016 triggered wide-spread bleaching in the Kimberley. Intertidal corals bleached less and recovered faster than adjacent subtidal corals; however, the mechanisms underlying this differential bleaching and recovery response remain poorly understood. Here we assessed both host- and symbiont-based indicators of bleaching resilience in the coral Acropora aspera. We tagged visibly healthy and bleached colonies from both environments in April 2016 and measured symbiont community composition, cell density, chlorophyll a, total biomass and host tissue energy reserves (lipids, protein and carbohydrates) during bleaching in April and in November 2016. Bleaching severity was higher in the subtidal than in intertidal, and while Cladocopium dominated all corals, symbiont community compositions differed significantly between environments and between bleached and healthy subtidal corals. Interestingly, bleaching resilience seemed decoupled from energy reserves, even though high levels of energy reserves and/or sufficient consumption during bleaching are widely thought to increase resistance to and recovery from bleaching. Although all bleached/recovered corals showed a general pattern of catabolizing protein reserves, distinct environment-specific trends were observed: subtidal corals that suffered extensive mortality also catabolized energy-poor carbohydrate reserves. In contrast, intertidal corals recovered rapidly after bleaching and maintained energy reserves. Total biomass remained unchanged between bleached and healthy corals in both environments. Overall, the findings of this study demonstrate that the consumption of energy reserves during bleaching is not always a reliable indicator of bleaching resilience.

AB - As marine heatwaves increasingly threaten coral reefs worldwide, some extreme reef environments naturally expose corals to high-temperature fluctuations and can therefore provide important insights into the mechanisms underlying coral heat tolerance. Coral reefs in the Kimberley region in northwest Australia experience the world's largest tropical tides and are therefore exposed to highly fluctuating temperatures in the intertidal. In contrast, the subtidal remains mostly submerged, resulting in moderate daily temperature fluctuations. A marine heatwave in 2016 triggered wide-spread bleaching in the Kimberley. Intertidal corals bleached less and recovered faster than adjacent subtidal corals; however, the mechanisms underlying this differential bleaching and recovery response remain poorly understood. Here we assessed both host- and symbiont-based indicators of bleaching resilience in the coral Acropora aspera. We tagged visibly healthy and bleached colonies from both environments in April 2016 and measured symbiont community composition, cell density, chlorophyll a, total biomass and host tissue energy reserves (lipids, protein and carbohydrates) during bleaching in April and in November 2016. Bleaching severity was higher in the subtidal than in intertidal, and while Cladocopium dominated all corals, symbiont community compositions differed significantly between environments and between bleached and healthy subtidal corals. Interestingly, bleaching resilience seemed decoupled from energy reserves, even though high levels of energy reserves and/or sufficient consumption during bleaching are widely thought to increase resistance to and recovery from bleaching. Although all bleached/recovered corals showed a general pattern of catabolizing protein reserves, distinct environment-specific trends were observed: subtidal corals that suffered extensive mortality also catabolized energy-poor carbohydrate reserves. In contrast, intertidal corals recovered rapidly after bleaching and maintained energy reserves. Total biomass remained unchanged between bleached and healthy corals in both environments. Overall, the findings of this study demonstrate that the consumption of energy reserves during bleaching is not always a reliable indicator of bleaching resilience.

KW - Coral bleaching

KW - Recovery capacity

KW - Energy reserves

KW - Symbiont dynamics

KW - Extreme reef environments

KW - Kimberley region

KW - WESTERN-AUSTRALIA

KW - TISSUE BIOMASS

KW - ZOOXANTHELLAE

KW - SYMBIODINIUM

KW - PATTERNS

KW - STRESS

KW - CARBON

KW - SPECIFICITY

KW - TOLERANCE

KW - DIVERSITY

U2 - 10.1007/s00338-021-02094-x

DO - 10.1007/s00338-021-02094-x

M3 - Journal article

VL - 40

SP - 893

EP - 905

JO - Coral Reefs

JF - Coral Reefs

SN - 0722-4028

IS - 3

ER -