Abstract
As the problem of ocean warming worsens, the environmental adaptation potential of symbiotic Symbiodiniaceae and bacteria is directly related to the future and fate of corals. This study aimed to analyse the comprehensive community dynamics and physiology of these two groups of organisms in the coral Pocillopora sp. through indoor simulations of heat stress (which involved manually adjusting the temperature between both 26 °C and 34 °C). Heat treatment (≥30 °C) significantly reduced the abundance of Symbiodiniaceae and bacteria by more than 70%. After the temperature was returned to 26 °C for one month, the Symbiodiniaceae density was still low, while the absolute number of bacteria quickly recovered to 55% of that of the control. At this time point, the Fv/Fm value rose to 91% of the pretemperature value. The content of chlorophyll b associated with Cyanobacteria increased by 50% compared with that under the control conditions. Moreover, analysis of the Symbiodiniaceae subclade composition suggested that the relative abundance of C1c.C45, C1, and C1ca increased during heat treatment, indicating that they might constitute heat-resistant subgroups. We suggest that the increase in the absolute number of bacteria during the recovery period could be an important indicator of coral holobiont recovery after heat stress. This study provides insight into the cross-linked regulation of key symbiotic microbes in the coral Pocillopora sp. during high-temperature stress and recovery and provides a scientific basis for exploring the mechanism underlying coral adaptation to global warming.
Highlights
IntroductionWith global climate warming, rising sea surface temperature (SST) is a major threat to the survival and development of coral reefs [1,2,3,4]
The coral nubbins endured the stress of the high-temperature threshold, and their tentacles were in a state of tight contraction
The heat stress would quickly disrupt the symbiotic relationship between coral host and microorganism (Symbiodiniaceae and bacteria)
Summary
With global climate warming, rising sea surface temperature (SST) is a major threat to the survival and development of coral reefs [1,2,3,4]. Many large-scale coral bleaching events are related to the abnormal rise in SST [5,6,7], with the frequency and severity of coral bleaching tending to increase [8]. The most direct impact of high SST is the large-scale expulsion of endosymbiotic dinoflagellates (family Symbiodiniaceae) by coral, resulting in a loss of pigmentation and a disruption in the coral energy supply [9,10] and leading to coral bleaching or mortality. Some species of coral hosts are adaptable and resistant to environmental stress [11,12], primarily because their symbiotic microorganisms
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