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The growing threat of global warming on coral reefs underscores the urgency of identifying heat‐tolerant corals and discovering their adaptation mechanisms to high temperatures. Corals growing in intertidal rock pools that vary markedly in daily temperature may have improved heat tolerance. In this study, heat stress experiments were performed on scleractinian coral Porites lutea from subtidal habitat and intertidal rock pool of Weizhou Island in the northern South China Sea. Thermotolerance differences in corals from the two habitats and their mechanisms were explored through phenotype, physiological indicators, ITS2, 16S rRNA, and RNA sequencing. At the extremely high temperature of 34°C, rock pool P. lutea had a stronger heat tolerance than those in the subtidal habitat. The strong antioxidant capacity of the coral host and its microbial partners was important in the resistance of rock pool corals to high temperatures. The host of rock pool corals at 34°C had stronger immune and apoptotic regulation, downregulated host metabolism and disease‐infection‐related pathways compared to the subtidal habitat. P. lutea, in this habitat, upregulated Cladocopium C15 (Symbiodiniaceae) photosynthetic efficiency and photoprotection, and significantly increased bacterial diversity and coral probiotics, including ABY1, Ruegeria, and Alteromonas. These findings indicate that rock pool corals can tolerate high temperatures through the integrated response of coral holobionts. These corals may be 'touchstones' for future warming. Our research provides new insights into the complex mechanisms by which corals resist global warming and the theoretical basis for coral reef ecosystem restoration and selection of stress‐resistant coral populations. [ABSTRACT FROM AUTHOR]

Coral skeleton δ13C is a routinely measured indicator in modern insolation change research, but the knowledge of environmental and climatic signals recorded in its seasonality during geological time is sparse. In this study, we present eight Porites coral δ13C records from the mid‐late Holocene to the present from the northern South China Sea (NSCS). Compared with the main control factors for modern δ13C changes, coral δ13C seasonality in the NSCS since the mid‐Holocene shows a long‐term decreasing trend, which is consistent with the change trend as orbital‐induced (precession) insolation seasonal amplitude. By excluding other influencing factors, we speculate that the stronger coral δ13C seasonality (18.8%) over the mid‐Holocene than modern period is attributable to the metabolic effect, which predicts the stronger coral δ13C seasonality under stronger insolation seasonality. Our study has implications for coral δ13C seasonality as a potential indicator to record past insolation information under different climatic backgrounds. Plain Language Summary: Numerous studies have documented the seasonal features of fast‐growing modern coral skeleton δ13C in response to insolation variation. The environmental and climatic signals recorded by coral δ13C seasonality in the geological period remain unclear owing to the relatively short length of observation records. Here we present monthly resolved δ13C records in seven fossil Porites corals (5.6–3.6 ka BP, before 1950 CE) and one modern Porites coral (1987–2001 CE) from the northern South China Sea (NSCS). Compared with the widely accepted prevailing control factors for modern coral δ13C, our results indicated that the stronger coral δ13C seasonality (18.8%) over the mid‐Holocene compared to the modern period is consistent with the orbital‐induced (precession) insolation changes, which indicate a declining seasonality from the mid‐Holocene to present. By excluding other influencing factors, we infer that a tendency toward higher δ13C seasonality during the mid‐Holocene was primarily driven by the metabolic fractionation caused by the enhanced insolation seasonality. This study highlighted coral δ13C seasonality as a potential indicator for recording past insolation information. Key Points: The seasonal variation of modern coral skeleton δ13C in the northern South China Sea (NSCS) is primarily controlled by solar insolationCoral δ13C seasonality in the NSCS since the mid‐Holocene shows a long‐term decreasing trendThe decrease of orbital‐induced (precession) insolation seasonal amplitude led to the declining trend of δ13C seasonality [ABSTRACT FROM AUTHOR]

High-latitude coral communities have attracted much attention due to their potential as refuges during global climate change. However, this function is being constrained by the combined pressure of global climate and anthropogenic activities. To determine how the reef has developed, we conducted a long-term monitoring study on coral communities along the Bailong Peninsula in the northern South China Sea. The results showed that the distribution area of corals was 3.67 km2 and that corals extended about 4.7 km along the coastline. The coral distribution pattern is scattered and uneven. Our results showed that the growth of reef-building corals and coral recruitment are improving, indicating that coral recruitment plays an important role in regulating the structure of adult coral populations and promoting the development of coral communities. Bailong Peninsula is expected to become a refuge for corals provided that human activities impacting coral restoration potential are controlled. [ABSTRACT FROM AUTHOR]

Under the dual effects of climate change and anthropogenic activities, coral reefs in the South China Sea (SCS) are at serious risk of degradation. Galaxea fascicularis is a widely distributed species in the SCS, and the study of its genetics, survival, and adaptability is conducive to further understanding the future characteristics of coral reefs in the SCS. In this study, 146 G. fascicularis samples were selected from 9 survey stations across 12 latitudes in the SCS, and 8 pairs of microsatellite markers were used to characterize their genetic diversity and structure. The results showed moderate genetic diversity index values (A r = 3.444–4.147, H e = 0.634–0.782, H o = 0.367–0.586). The AMOVA results and pairwise F ST values showed a moderate level of genetic differentiation (Φ ST = 0.119, P < 0.05) among G. fascicularis populations in the SCS, whereas its genetic structure showed high genetic differentiation (F ST = 0.062–0.225) among relatively high-latitude populations (n = 3) and low genetic differentiation (F ST = 0.012–0.064) in low-latitude populations (n = 6). The living environment of relatively high-latitude populations is disturbed by high-intensity human activities, leading to the specialization of local populations. Mantel test results showed a significant positive correlation between genetic differentiation among G. fascicularis populations and sea surface temperature (SST) variance (R2 = 0.4885; Mantel test, p = 0.010 < 0.05) in addition to geographical distance (R2 = 0.1134; Mantel, test p = 0.040 < 0.05), indicating that SST and geographical isolation were primary factors affecting the genetic structure of this species in the SCS. The lower genetic diversity and limited gene flow of G. fascicularis indicate limited genetic adaptation, and corresponding vulnerability may be more pronounced under future environmental changes. These findings provide a theoretical basis for the conservation and restoration of coral reefs in the SCS. [Display omitted] • Galaxea fascicularis show moderate genetic diversity and differentiation in South China Sea. • Under climate change, the local degradation risk of G. fascicularis in SCS is high. • Genetic structure of G. fascicularis is shaped by SSTs and geographical isolation. • Higher latitude populations of G. fascicularis are specialized to human activity. [ABSTRACT FROM AUTHOR]

Investigating the potential and mechanisms of thermal adaptability in scleractinian corals is critical for aiding corals in dealing with global warming and improving the efficiency of coral reef restoration efforts. Although thermal acclimation facilitates the resistance of branching corals to thermal stress, little is known about the physiological processes of massive and platy corals in the South China Sea or their ability to adapt to heat stress. In this study, we conducted indoor short-term thermal acclimation simulation experiments on three types of corals: massive Porites lutea , platy Pavona decussata , and branching Pocillopora damicornis. Subsequently, we studied the responses and adaptive mechanisms of the three corals to heat stress and explored the effects of short-term thermal acclimation using physiological and biochemical markers. The results showed that the three corals exhibited comparable phenotypic and physiological responses to heat stress, including tentacle retraction and decreases in zooxanthellae density, maximum quantum efficiency of photosystem II, and glutathione content, along with increases in antioxidant activity (catalase and superoxide dismutase), ammonium assimilation (glutamine synthetase), and apoptosis (lipid peroxide and caspase-3). Additionally, heat tolerance differed among the different species of coral. Furthermore, the physiological markers performed better in all three coral types after acclimation, and the effects of short-term acclimation decreased from P. lutea to P. damicornis to P. decussata. We propose that short-term thermal acclimation enhances the heat tolerance of corals by affecting their metabolism and antioxidant capacity. Leveraging short-term thermal acclimation in coral reef restoration efforts could help corals adapt to the threats posed by global warming and enhance restoration efficiency. • Coral reefs are in rapid decline in the context of global pressures. • Different types of scleractinian corals display similar responses to heat stress. • Short-term thermal acclimation enhances the coral antioxidant capacity. • Porites lutea and Pocillopora damicornis have better thermal acclimatization. [ABSTRACT FROM AUTHOR]