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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]

To better understand the long-term survival of modern coral reefs under global warming, the history of past coral bleaching events prior to modern marine ecological surveys must be investigated. Here, 11 dead Porites and 2 Porites with growth hiatuses growing in the 20th century were collected from the Nansha Islands, southern South China Sea (SCS) for monthly Sr/Ca, δ18O and δ13C analyses to explore the climatic conditions and metabolic information corresponding to these growth structures. Among the 13 episodes, the results showed that 8 mortalities occurred in the summers, coral MJ8 died in spring, and the other 2 mortalities and 2 growth hiatuses occurred in the cooling season. In addition to the dead surface of the coral mortalities, stress bands with significantly reduced growth rates could also be observed in the corals. Negative shifts in δ13C occurred prior to 5 coral mortalities and most stress bands were caused in summer, suggesting a sharp reduction in photosynthesis by decreased symbiotic zooxanthellae or photosynthetic pigments. Overall, the mortalities can be concluded to have occurred in summer and stress bands with abrupt δ13C decreases in the last century were mainly caused by thermal coral bleaching in the southern SCS. This in turn suggests that the repeated coral bleaching and mortalities occurred much earlier before the 1980s, which is a longer-term response to modern global warming during the last century. [ABSTRACT FROM AUTHOR]

Beachrock is considered a good archive for past sea-levels because of its unique formation position (intertidal zone). To evaluate sea-level history in the northern South China Sea, three well-preserved beachrock outcrops (Beigang, Gongshanbei, and Hengling) at Weizhou Island, northern South China Sea were selected to examine their relative elevation, sedimentological, mineralogical, and geochemical characteristics. Acropora branches with well-preserved surface micro-structures were selected from the beachrocks and used to determine the ages of these beachrocks via U-series dating. The results show that the beachrocks are composed of coral reef sediments, terrigenous clastics, volcanic clastics, and various calcite cements. These sediments accumulated in the intertidal zone of Weizhou Island were then cemented in a meteoric water environment. The U-series ages of beachrocks from Beigang, Gongshanbei, and Hengling are 1712–768 ca. BP, 1766–1070 ca. BP, and 1493–604 ca. BP (before 1950 AD) respectively. Their elevations are 0.91–1.16 m, 0.95–1.24 m, and 0.82–1.17 m higher than the modern homologous sedimentary zones, respectively. Therefore, we concluded that the sea-level in the Meghalayan age (1766–604 ca. BP) was 0.82–1.24 m higher than the present, and that the sea-level over this period showed a declining trend. [ABSTRACT FROM AUTHOR]

Summary: Environmental conditions between the outer reef slope (ORS) and lagoon in tropical atolls are significantly different, but the variations of juvenile coral‐microbiomes in the two environments and their relationship with coral thermal acclimatization are poorly understood. We explored this issue based on local water conditions and the microbiome of juvenile corals in the ORS and lagoon in the central South China Sea. Coral‐symbiotic Symbiodiniaceae showed significant differences among coral species; Pocillopora verrucosa and Pachyseris rugosa in the ORS, and Acropora formosa in the lagoon were dominated by Durusdinium, but other corals were dominated by Cladocopium. Although A. formosa in the ORS were dominated by Cladocopium (C3u), they were dominated by Durusdinium (D1/D1a) and Cladocopium (C50) in the lagoon. Other coral species were both dominated by Cladocopium in the lagoon and ORS. The relative abundance of bacteria in the Deinococcus–Thermus was generally higher in the lagoon corals than in the ORS corals. Our study indicates that P. verrucosa, P. rugosa and Porites lutea may have high thermal tolerance based on the relatively high abundance of heat‐tolerant Durusdinium and Thermus scotoductus. Likewise, A. formosa in the lagoon may acclimatize to the thermal environment based on a high relative abundance of heat‐tolerant Durusdinium. [ABSTRACT FROM AUTHOR]

As a gauge for ocean precipitation conditions, sea surface salinity (SSS) is suspected to be an excellent indicator for variations in the global hydrological cycle. The SSS conditions in the South China Sea (SCS) are closely related to precipitation changes of the East Asian monsoon. However, the characteristics and driving mechanisms of the meridional pattern of East Asian monsoon rainfall during the warm periods of the late Holocene are not well understood because of a lack of high-resolution proxies from the SCS. Here, we present three precise chronologies of monthly stable coral skeleton oxygen isotopes (δ18O) and pair them with established composite strontium/calcium (Sr/Ca) records from the Xisha Islands to obtain a continuous reconstruction of the residual δ18O (Δδ18O, regarded as seawater δ18O) during 1980–2007 CE (Common Era), 1149–1205 CE, and 2070–2011 a BP (years before 1950 CE). The results confirm that coral Δδ18O is a good tracer for reconstructing SSS and precipitation changes in the northern SCS on seasonal and interannual timescales, with higher Δδ18O values implying more saline conditions and less precipitation. The mean value of fossil coral Δδ18O for 1149–1205 CE was higher than that of modern coral, suggesting the existence of salty surface waters and notable dry climate episodes in the northern SCS during the late Medieval Climate Anomaly (MCA). In contrast, the average coral Δδ18O for 2070–2011 a BP was significantly lighter by about 0.404‰ compared to that of recent decades, indicating that less saline and more humid conditions occurred in the northern SCS during the early Roman Warm Period (RWP). Synthesizing our coral records with other published precipitation reconstructions from eastern China suggested a meridional dipole spatial pattern of moisture variation over East Asia during the historical warm periods of the Holocene. During the MCA, drier conditions generally prevailed in the region south of the Yangtze River, and more humid conditions in the north. This may be closely related to the contemporaneous strong El Niño activity occurring at this time, which probably enhanced the East Asian summer monsoon (EASM) and caused a northward shift of the intertropical convergence zone (ITCZ), possibly inducing increased water vapor transport from the SCS to North China. During the RWP, the relatively weak El Niño–Southern Oscillation (ENSO) variability may weaken the intensity of the EASM and shift the ITCZ southward, possibly resulting in a spatial pattern of "wet south and dry north" in East Asia. • 145-year monthly seawater δ18O derived from corals in the northern South China Sea. • Salty surface waters for 1149–1205 CE and less saline for 2070–2011 a BP. • Meridional pattern of moisture over East Asia for the warm periods of late Holocene. • El Niño-Southern Oscillation modulates the strength of East Asian monsoon. [ABSTRACT FROM AUTHOR]

Coral bleaching heat stress products provide real-time and rapid coral bleaching alerts for coral reefs globally. However, geographical variations in the alert accuracy of multi-source coral bleaching heat stress products exist. Taking the coral reefs in the South China Sea (SCS) as the study area, we evaluated and improved the coral bleaching alert capabilities of two coral bleaching heat stress products: Coral Reef Watch (CRW) and Coral Reef Temperature Anomaly Database (CoRTAD). Using in situ coral bleaching survey data and evaluation indicators, the optimized thresholds of degree heating weeks (DHWs) for coral bleaching alerts were determined. The results in the SCS indicated that, first, CRW was better than CoRTAD for coral bleaching event alerts. However, both products underestimated coral bleaching events using the common DHW thresholds of 4°C-weeks and 8°C-weeks. Second, the DHW optimized threshold for CRW was 3.32°C-weeks for coral bleaching event alerts and 4.52°C-weeks for severe coral bleaching event alerts. For CoRTAD products, the DHW optimized threshold was 2.36°C-weeks for coral bleaching event alerts and 4.14°C-weeks for severe coral bleaching event alerts. This study proposed a method to evaluate and optimize the alert capability of multi-source coral bleaching heat stress products, which can provide more accurate basic data for coral reef ecosystem health assessment and contribute to global coral reef ecosystem protection and restoration. • A method to evaluate and optimize the alert capability of coral bleaching heat stress products in the SCS. • Optimized DHW thresholds for coral bleaching alerts were 3.32°C-weeks for CRW and 2.36°C-weeks for CoRTAD. • Optimized DHW thresholds for coral severe bleaching alerts were 4.52°C-weeks for CRW and 4.14°C-weeks for CoRTAD. • CRW was better than CoRTAD for coral bleaching event alerts in the SCS. [ABSTRACT FROM AUTHOR]

The study presents a detailed record of foraminiferal faunas from CK2 core, a 928.75 m long core drilled in the center of Xisha Islands, South China Sea, for biostratigraphy and palaeoenvironmental reconstruction of the study area. Coupling foraminiferal biostratigraphy and bulk-sediment strontium-isotope chronologic age revealed that carbonate deposition occurred from Early Miocene (~19.6 Ma) to present. Examination of 281 petrologic thin sections and 246 unconsolidated sediment samples revealed 141 foraminiferal taxa, among which the foraminiferal abundance and simple diversity peaked in the Middle Miocene and Pliocene to early Pleistocene strata. Nine foraminiferal assemblages (FAs) were distinguished, documenting eight distinct facies that indicated five intervals in the development of Xisha Islands. At the initial interval (19.6–17 Ma), a coral, coralline algal and shallow-water larger foraminifers (FA1 and FA2) association colonized the shallow platform facies, forming an aggrading sequence in response to tectonic subsidence and sea-level rise. Platform development slowed from 17 to 10.19 Ma, dominated by the miliolids and small benthic foraminifers as well as larger benthic foraminifers (FA3 and FA4) representing lagoonal to reef-flat facies with agradation to progradation (backreef infilling) associated with sea-level fall. At 10.19–4.35 Ma, a deepening sequence was indicated by the change from shallow-water benthic foraminifers (FA5) upward to deeper dwelling species (FA6), as a result of climatic cooling and abrupt sea-level fluctuation. As sea level rose, the platform was drowned from 4.35 to 2.18 Ma, as indicated by abundant planktic foraminifers and large, flat benthic foraminifers (FA7 and FA8). At 2.18–0.089 Ma, the platform aggraded rapidly with sea level fall indicated by the appearance of thick benthic foraminifers (FA9) and increased coral. The close association between the biofacies and regional paleobathymetry, which was in phase with the long-term global sea-level change, suggest that foraminiferal morphology and assemblage composition are ideal parameters for paleobathymetric and paleo-depositional environmental interpretations. • Nine foraminiferal assemblages were distinguished, documenting eight carbonate biofacies. • Two major transgressive-regressive palaeobathymetry cycles were recorded since about 19.6 Ma. • Five development phases of Xisha carbonate succession since Early Miocene were revealed. • Eustasy, tectonics, paleoclimatic and paleooceanographic change are the main factors affecting the carbonate production. [ABSTRACT FROM AUTHOR]

Reconstructing the precise timing of sea level fall is important for understanding earth system during the geologic time. However, previous studies are limited by the absence of effective indicators for sea level fall. To overcome this limitation, we investigated the 87Sr/86Sr and petrologic features of carbonate strata in a 928.75-m-long coral reef core (CK2) from Xisha Islands, northern South China Sea and their relationship to sea level fluctuations. Ten exposed surfaces were identified by their petrologic features. The Mn and Sr content, Mn/Sr, Sr/Ca and δ18O suggest that most of the coral reef carbonate in the CK2 core preserved the original seawater 87Sr/86Sr except at intervals of 672–616, 596–575, 521–491, 423–414, and 192.5–161 m, which suffered alteration of meteoric water and showed higher 87Sr/86Sr during low sea level period. The 160 carbonate 87Sr/86Sr showed a continuously increasing trend, which is consistent with that of seawater over the same period. The continuously increasing 87Sr/86Sr curve of CK2 was divided into seven units by six 87Sr/86Sr hiatuses. Inconsistency between the sedimentation rate of CK2 and tectonic subsidence rate in the Xisha area suggest that the continuously increasing 87Sr/86Sr was controlled by the coupled effect of tectonic subsidence and sea level change, and the hiatus and higher 87Sr/86Sr interval in the 87Sr/86Sr curve were controlled by sea level fall. The higher 87Sr/86Sr usually produced during low sea level (<5 m), 87Sr/86Sr hiatus usually produced when sea level changed from deeper to shallower. The depth of hiatuses and higher intervals of 87Sr/86Sr correspond well with the exposed surface in CK2 core, verifying that the hiatuses and higher intervals of 87Sr/86Sr in the coral reef carbonate succession provide an effective indicator of sea level fall. Using this indicator and the CK2 87Sr/86Sr profile, we identified eleven large-scale sea level falls and three dramatic regressions during 19.6–0.2 Ma and constrained the age based on strontium isotope stratigraphy. These interpreted sea level falls are mostly consistent with other records of global sea level changes, confirming the reliability of our records. The 87Sr/86Sr profile of a coral reef carbonate is an efficient indicator of past sea level falls, including their timing. • 87Sr/86Sr ratios of carbonate in a coral reef core from Xisha Islands. • The core indicated five hiatuses and six anomalously high ratios in Sr isotope. • Hiatus and high ratios in reef carbonate Sr isotope were produced by sea level fall. • Eleven major lower sea level and three dramatic regressions found during 19.6–0.2 Ma. • This method provides an effective indicator of past sea level fluctuation. [ABSTRACT FROM AUTHOR]

We have previously shown that the coralline algal assemblages (CAAs) of the South China Sea may indicate post-Pliocene paleo-water depth changes; however, the pre-Pliocene coralline algal compositions and related sea-level significance remain to be elucidated. In the present study, we explore the Miocene coralline algal compositions and their role in recording the sea level, and show the distribution, classification, type, abundance, and diversity of Miocene coralline algae from 213 petrologic thin sections using a coral-reef carbonate sequence from the northern South China Sea. The diversity and abundance of coralline algae in the early and late Miocene are higher than those in the middle Miocene. Eleven genera were identified and grouped into seven CAAs, showing a water depth range from <5 m to >25 m. At 18.67–17.98 Ma, the coral reef was in a stagnation/drowning stage, with rising sea levels exceeding the development of the coral reef. At 17.98–16.78 Ma, the coral reef was in a rapid development during a rapid rise in sea level. Additionally, at 16.78–14.79 Ma, low coralline algal abundance was observed, and the corals were sporadically distributed at a relatively stable sedimentation rate, suggesting a decline in coral reef development. At 14.79–10 Ma, the coral reef development was remarkably slow or stagnant. Furthermore, at 10–5.3 Ma, the coral reefs developed slowly, indicating a gradual rise in the sea level. The sea-level changes indicated by coral reef development are consistent with the long-term global sea-level changes, indicating that the composition and assemblage of Miocene coralline algae can be used to accurately relay the sea-level history. • Eleven coralline algal genera were identified in a Miocene carbonate sequence. • Miocene coralline algae were divided into 7 coralline algal assemblages (CAAs). • Sea-level changes due to coral reef development were consistent with global values. [ABSTRACT FROM AUTHOR]

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]

The East Asian Monsoon (EAM) has significantly influenced various depositional and diagenetic processes in carbonate sediments in much of East and South Asia during the Cenozoic. The relationship between the EAM and marine carbonate platforms, which are widely developed in this region, however, remains largely unknown. Based on petrographic, mineralogical, and geochemical analyses of the carbonate succession (∼237 m thick) on the Xisha Islands, South China Sea, meteoric diagenesis and its relationship with the East Asian Summer Monsoon (EASM) during the Pleistocene were studied. Various petrographic features, stable isotopes (δ13C, δ18O), and trace elements (Sr, Fe, Mn, Rare Earth Elements and Y) indicate that this succession was extensively altered by meteoric diagenesis, producing four exposed surfaces embedded in the shallow coral reef sediments. Given this data, we suggest that the meteoric diagenesis that affected this succession occurred during periods of low sea-level, and was potentially related to the relative intensity of the EASM. During strong EASM periods, particularly during the Mid-Pleistocene Transition ∼0.9 Ma, meteoric diagenesis was intense, as suggested by the complete alteration of unstable minerals, extreme dissolution, the presence of reddish-brown iron oxides, and a large negative excursion of δ13C (−6.2‰). The influence of the EASM on meteoric diagenesis of Pleistocene carbonate platforms can be identified throughout the South China Sea. This study sheds light on the relationship between meteoric diagenesis and paleo-climate conditions in carbonate platform regions that are influenced by monsoons. • Meteoric diagenesis was controlled by the relative intensity of EASM. • The sensitivity of geochemical parameters to meteoric diagenesis is different. • EASM had influenced meteoric diagenesis since Pleistocene. • Meteoric diagenetic transformation of Xisha platform was most intense at ∼0.9 Ma. [ABSTRACT FROM AUTHOR]

Despite organophosphate esters (OPEs) are widely prevalent in the environment, however, limited information is available regarding their occurrence, trophodynamics, and exposure risks in coral reef ecosystems. In this study, 11 OPEs were investigated in a tropical marine food web (7 fish species and 9 benthos species) from the Xisha (XS) Islands, South China Sea (SCS). The ∑ 11 OPEs were 1.52 ± 0.33 ng/L, 2227 ± 2062 ng/g lipid weight (lw), 1024 ± 606 ng/g lw, and 1800 ± 1344 ng/g lw in seawater, fish, molluscs, and corals, respectively. Tris (2-chloroisopropyl) phosphate (TCIPPs) were the dominant OPEs in seawater, fish, and molluscs, while tris (2-butoxyethyl) phosphate (TBOEP) predominated in coral tissues. Abiotic and biotic factors jointly affect the OPEs enrichment in marine organisms. Trophic magnification factors (TMFs) (range: 1.31–39.2) indicated the biomagnification potency of OPEs. A dietary exposure risk assessment indicated that OPEs at current levels in coral reef fish posed a low risk to human health but were not negligible. Overall, this study contributes to a further understanding of the environmental behaviors of OPEs in coral reef ecosystems. [Display omitted] • OPEs profiles in seawater and marine organisms are different. • Fish tend to enrich Cl-alkyl OPEs and benthos prefer to accumulate aryl OPEs. • Abiotic and biotic factors jointly affect the OPEs enrichment in marine organisms. • OPEs pose a low risk to human health by coral reef fish ingestion. • Emerging pollutants are dominating the pollution status in the Xisha Islands. [ABSTRACT FROM AUTHOR]

Recent studies have indicated that coral mucus plays an important role in the bioaccumulation of a few organic pollutants by corals, but no relevant studies have been conducted on organochlorine pesticides (OCPs). Previous studies have also indicated that OCPs widely occur in a few coral reef ecosystems and have a negative effect on coral health. Therefore, this study focused on the occurrence and bioaccumulation of a few OCPs, such as dichlorodiphenyltrichloroethanes (DDTs), hexachlorobenzene (HCB) and p , p ′-methoxychlor (MXC), in the coral tissues and mucus as well as in plankton and seawater from a coastal reef ecosystem (Weizhou Island) in the South China Sea. The results indicated that DDTs were the predominant OCPs in seawater and marine biota. Higher concentrations of OCPs in plankton may contribute to the enrichment of OCPs by corals. The significantly higher total OCP concentration (∑ 8 OCPs) found in coral mucus than in coral tissues suggested that coral mucus played an essential role in resisting enrichment of OCPs by coral tissues. This study explored the different functions of coral tissues and mucus in OCP enrichment and biodegradation for the first time, highlighting the need for OCP toxicity experiments from both tissue and mucus perspectives. [Display omitted] • OCPs were firstly studied in coral mucus in the South China Sea. • Plankton may have an influence on coral enrichment of OCPs. • Obvious higher ∑ 8 OCPs occurred in coral mucus than in coral tissues. • Coral mucus showed lower metabolic capability of DDTs than coral tissues. • Coral mucus may resist the enrichment and metabolism of OCPs by coral tissues. [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]

As one of the most abundant metals in heavy oils, Ni has suffered so notably increasing impacts from industrial and traffic activities that anthropogenic Ni emissions have altered natural geochemical processes. The coral Ni/Ca has become a reliable proxy for characterizing marine pollution, but this potential has been unexploited for highlighting oil pollution. Here, we utilized a high-resolution record of geochemical parameters (Ni/Ca, δ18O, and δ13C) in a Porites coral of an offshore island in the northern South China Sea to reconstruct of Ni distribution patterns in surface seawater from 1984 to 2015. The coral Ni/Ca ratios exhibit minor fluctuations, except for multiple mutation peaks (0.20 ± 0.42 μmol/mol) during the period from 1984 to 1993. The ratio was low and stable (0.10 ± 0.09 μmol/mol) from 1994 to 2008, and then increased rapidly with significant variations (1.60 ± 4.56 μmol/mol) from 2009 to 2015. The coral Ni/Ca ratios captured all significant Ni discharges, and this demonstrates its potential for recording oil spill episodes. The historical variations in the contributions of Ni indicate that industrial and traffic activities should be responsible for changes in the anthropogenic input. The leaks and consumptions of petroleum likely account for the primary Ni emission sources. [Display omitted] • Anthropogenic Ni input has altered the geochemical processes of oceanic Ni. • Coral Ni/Ca records have potentials to be novel proxies for surface winds. • Temporal emissions of anthropogenic Ni can be captured by coral Ni/Ca records. [ABSTRACT FROM AUTHOR]

The levels, fate, and potential sources of 22 organochlorine pesticides (OCPs) in coral tissues and the surrounding air-seawater system from the South China Sea (SCS) were elucidated for the first time. ∑ 22 OCPs (total concentration of 22 OCPs) (16.1–223 pg L−1) was relatively higher in coastal seawater than in offshore seawater, which may be the widespread influence of coastal pollution inputs under the western boundary current. The atmospheric ∑ 22 OCPs were predominantly distributed in the gas phase (48.0–2264 pg m−3) and were mainly influenced by continental air mass origins. The air-seawater exchange of selected OCPs showed that OCPs tended to migrate from the atmosphere to seawater. The distribution of ∑ 22 OCPs in coral tissues (0.02–52.2 ng g−1 dw) was significantly correlated with that in air samples, suggesting that OCPs may have a migration pattern of atmosphere-ocean corals in the SCS. Corals exhibited higher bioaccumulation ability (Log BAFs : 2.42–7.41) for OCPs. Source analysis showed that the new application of technical Chlordanes (CHLs) was primarily responsible for the current levels of CHLs in the surrounding environment over the SCS, while historical residues were the primary sources of other OCPs. [Display omitted] • Pioneer OCPs study of coral tissues from the South China Sea (SCS). • Corals presented a higher bioaccumulative ability to OCPs. • Ocean currents and monsoons played essential roles in the OCPs' spatial distribution. • Net atmospheric deposition of OCPs occurred in the coral reef regions (CRRs), SCS. • OCPs may have a migration pattern of atmosphere-ocean-corals in the CRRs, SCS. [ABSTRACT FROM AUTHOR]

Holocene coral reef development is valuable to understanding the behavior and impacts of paleoclimate and sea level changes. This study focuses on the Holocene carbonate sequences of a drill core extracted from Well CK2 in the northern South China Sea (SCS). This drill core consists of an 873.55 m thick carbonate layer overlying 55.20 m of volcanic basement. High precision U-series dating of 22 coral samples suggests that the Holocene coral reef, which has a thickness of 16.7 m, initiated at ~7800 yr BP (years before 1950 CE) and stopped vertical accretion at 3900 yr BP. The mean vertical accretion rate in the Holocene in Well CK2 was 3.48 m kyr−1, varying from 6.44 m kyr−1 during 7800–6000 yr BP to 0.87 m kyr−1 during 6000–3900 yr BP. After 3900 yr BP, the vertical development of the reef ceased, indicating that the reef development likely involved lateral accretion. The Holocene section mostly consists of unconsolidated coarse sediments, mainly including corals, coralline algae, large benthic foraminifera, and mollusks. Based on the relationship between coral reef development and sea level, together with the age profile, we determined that the relative sea level near Chenhang Island rose rapidly between 7800 and 6000 yr BP, slowed at ~6000 yr BP, and reached a position of about 2 m above the present-day mean sea level by 3900 yr BP. After 3900 yr BP, the sea level was stable or fell, resulting in a cessation in the reef's upward development. • 22 230Th ages of a SCS reef core suggest the Holocene reef initiated at 7800 yr BP. • Vertical development decreased from 6.44 to 0.87 m kyr−1 at 3900 yr BP. • Sea level at 7800 yr BP was ~13.8 m below present and rose rapidly. • Sea level has stabilized/fallen since 3900 yr BP, as indicated by reef development. [ABSTRACT FROM AUTHOR]

Global warming and sea-level rise (SLR) induced by rising atmospheric CO2 concentrations can cause coral bleaching, death, and submergence of the world's coral reefs. Adopting the GIS and RS methods, we modeled how these two stressors combine to influence the future growth of the atolls and table reefs of three archipelagoes in the South China Sea (SCS), based on geomorphic and ecological zones. A large-scale survey of the coral communities in Xisha Islands in 2014, Dongsha Islands in 2014–2016 and Nansha Islands in 2007 provided zone-specific process datasets on the range of reef accretion rates. Sea surface temperature and extreme (minimum and maximum) SLR data above 1985–2005 levels by 2100 in the SCS were derived from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) models forced with the Representative Concentration Pathways (RCPs). Our model projected that: (1) the Xisha Islands and Dongsha Islands may have a better growth status, because the reef flat biotic sparse zone may be recolonized with hard coral and become a biotic dense zone; (2) the southern Nansha Islands reefs have a risk of stopping growing due to their earlier annual bleaching years. The increasing of water depths of these reefs is stronger in the RCP with more emissions. Our approach offers insights into the best-case and worst-case impacts of two global environmental pressures on potential future reef growth under a changing climate. [ABSTRACT FROM AUTHOR]

Coral probiotics can improve the tolerance of corals to heat stress, thus mitigating the process of coral thermal bleaching. Sensitive and specific detection of coral probiotics at low abundances is highly desirable but remains challenging, especially for rapid and on-site detection of coral probiotics. Since the electrochemical biosensor has been recently used in the field of environmental DNA (eDNA) detection, herein, an efficient electrochemical biosensor was developed based on CoS 2 /CoSe 2 -NC HNCs electrode material with a specific DNA probe for the C. marina detection. After optimization, the lower limit of detection (LOD) values of such biosensors for the target DNA and genomic DNA were 1.58 fM and 6.5 pM, respectively. On this basis, a portable device was constructed for the practical detection of C. marina eDNA, and its reliability and accuracy were verified by comparison with the ddPCR method (P > 0.05). For each analysis, the average cost was only ∼ $1.08 and could be completed within 100 min with reliable sensitivity and specificity. Overall, the biosensor could reflect the protective effect of probiotics on coral heat stress, and the proposed technique will put new insights into the rapid and on-site detection of coral probiotics to assist corals against global warming. [ABSTRACT FROM AUTHOR]

[Display omitted] • Blue light increases the thermal bleaching tolerance of coral holobiont. • Blue light decreases photosynthesis, respiration and ROS release of Symbiodiniaceae under heat stress. • Blue light reduces respiration and lipid peroxidation of host under heat stress. • The up-regulation of the DAO gene indicates a coral bleaching model that dependents on the host. Given the high degree of heterogeneity of coral bleaching, there is potential for abiotic approaches to improve the thermal tolerance of coral. However, there is limited knowledge about such factors and causes that regulating acclimation of coral to warming. Here, a study was conducted on the reef building coral Acropora tenuis to investigate the impact of light qualities on the physiological, cellular, and molecular biochemical responses of the coral holobiont to heat stress. The results showed that after subjecting the samples to heat stress at 32 ℃ for 9 days, over 90% corals exposed to compound light experienced bleaching on the fifth day, while corals exposed to blue light showed no significant signs of bleaching even on the ninth day. This indicates that blue light may enhanced the coral's thermal bleaching tolerance. Further analysis revealed blue light primarily increased coral's resistance to thermal bleaching by remodeling the interactions between Symbiodiniaceae (i.e. decreased photosynthesis, respiration and ROS release) and coral (i.e. decreased respiration and lipid peroxidation). The study also found that the host's of reactive oxygen species (ROS) played a role in causing coral bleaching besides the ROS released by Symbiodiniaceae. The up-regulation of the DAO gene (encoding D-amino-acid oxidase, up-regulated nearly 1000 times under warming conditions) in the host highlights the mechanism of coral bleaching, whereby the catalysis of amino acids by the D-amino-acid oxidase produces ROS. In summary, the present study reveals novelty insights into the molecular processes related to thermal bleaching of coral, identifies blue light as a positive environmental factor that enhances coral's tolerance to global warming. [ABSTRACT FROM AUTHOR]

Most studies on coral bleaching alerts use common Degree Heating Week (DHW) thresholds; however, these may underestimate historical patterns of heat stress for coral reef ecosystems. Taking an optimized DHW threshold for coral bleaching alerts for Coral Reef Watch (CRW) and Coral Reef Temperature Anomaly Database (CoRTAD) products, we analyzed the precise spatial and temporal pattern of heat stress on China's coral reefs from 2010 to 2021 in the South China Sea (SCS) and the Beibu Gulf (BG). We compared acute heat stress using common and optimized thresholds. Results indicated that the ocean warming rate in 2010–2021 was approximately 0.43 ± 0.22 °C/10a, showing a significant increase in the northern SCS and the BG. More severe bleaching events were predicted by the optimized thresholds and the high-frequency areas were mainly in the northern SCS. The number and intensity of years with severe heat stress anomalies was in the order 2020 > 2014 > 2010 > 2015. Heat stress duration was the longest in the Xisha Islands among offshore archipelagos, and longest in 2020–2021 in Weizhou Island in BG in the relative high-latitude inshore reefs. These abnormal events were mainly caused by El Niño, but La Niña was also involved in 2020. • The most intense severe heat stress anomaly years were 2010 > 2014>2020 > 2015. • The anomaly duration of offshore islands was Xisha > Dongsha > Zhongsha > Nansha Islands. • High-latitude reefs were predicted not to be future thermal refuges for SCS reefs. • The optimized DHW threshold more accurately predicted spatiotemporal heat stress. [ABSTRACT FROM AUTHOR]

The coral reef crisis has significantly intensified over the last decades, mainly due to severe outbreaks of crown-of-thorns starfish (COTS). Current ecological monitoring has failed to detect COTS densities at the pre-outbreak stage, thus preventing early intervention. In this work, we developed an effective electrochemical biosensor modified by a MoO 2 /C nanomaterial, as well as a specific DNA probe that could detect trace COTS environmental DNA (eDNA) at a lower detection limit (LOD = 0.147 ng/μL) with excellent specificity. The reliability and accuracy of the biosensor were validated against the standard methods by an ultramicro spectrophotometer and droplet digital PCR (p > 0.05). The biosensor was then utilized for the on-site analysis of seawater samples from SYM-LD and SY sites in the South China Sea. For the SYM-LD site suffering an outbreak, the COTS eDNA concentrations were 0.33 ng/μL (1 m, depth) and 0.26 ng/μL (10 m, depth), respectively. According to the ecological survey, the COTS density was 500 ind/hm2 at the SYM-LD site, verifying the accuracy of our measurements. At the SY site, COTS eDNA was also detected at 0.19 ng/μL, but COTS was not found by the traditional survey. Hence, larvae were possibly present in this region. Therefore, this electrochemical biosensor could be used to monitor COTS populations at the pre-outbreak stages, and potentially serve as a revolutionary early warning method. We will continue to improve this method for picomolar or even femtomolar detection of COTS eDNA. [ABSTRACT FROM AUTHOR]

Nutrient enrichment is a widely recognized threat to coastal coral reefs. Yet its impact on open ocean reefs is largely unknown due to the lack of long-term observations at remote sites and the entanglement of various environmental factors affecting coral growth. Here we determined growth rates and the carbonate chemistry of calcifying fluid (CF) of massive corals over the last 550 years at a remote South China Sea reef ecosystem. We show that large growth variations cannot be fully explained by changes in seawater pH or temperature due to the antiphase relationship between growth rate and pH cf as well as small sea surface temperature variations before the 1960s. Instead, coral growth rate decreases proportionally with past seabird populations over the past centuries. We suggest that excess nutrient loads through monsoon pumping and seabird migration played an important role in controlling coral growth at this remote reef ecosystem. Specifically, episodic eutrophication as indicated by a ∼ 3 per mil increase in coral δ13C has depressed coral growth by ∼30% during 15th to 18th centuries, which is comparable to the modern decline. Thus, accurate projections of future coral growth for remote reefs under ongoing human activities and climate change needs to take into account the history of past nutrient inputs into these ecosystems under pre-anthropogenic conditions, which has been overlooked previously due to a lack of historical observations. • Coral cores from an open ocean reef that grew from ∼1450 to present were analyzed. • Temperature affects multi-decadal variability in coral calcifying fluid DIC but not pH. • Reef-water pH modified by monsoon controls calcifying fluid pH and [CO 3 2−] • Eutrophication caused by monsoon and seabirds depressed coral growth during the Little Ice Age • An analog to the responses of corals to the projected rise in anthropogenic nutrient inputs. [ABSTRACT FROM AUTHOR]

Multiple environmental pressures caused by global warming and human activities have aroused widespread concern about PAHs pollution in tropical marine coral reef regions (CRRs). However, the trophodynamics of PAHs in the food webs of the CRRs and the related influence factors have not been reported. This study investigated the occurrence, trophic amplification, and transmission of PAHs in various organisms selecting between at least representative species for each level in CRRs of the South China Sea (SCS); revealed their driving mechanisms; and explored the trophodynamics of PAHs in the food web of the coral reef ecosystem. Results showed that more PAHs can be accumulated in the mantle tissue of Tridacnidae, and the proportion of mantle tissue of Tridacnidae increases with the increase of latitude (y = 0.01x + 0.17, R2 = 0.49, p < 0.05). Latitude drives the differential occurrence level and bioaccumulation of PAHs in tropical marine organisms, and also affects the trophodynamics of PAHs in aquatic ecosystem food webs. PAHs undergo trophic amplification in the food webs of tropical marine ecosystems represented by coral reefs, thus further aggravating the negative environmental impact on coral reef ecosystems. The cancer risk caused by accidental ingestion of PAHs by humans through consumption of seafood in CRRs is very low, but we should be alert to the biomagnification effect of PAHs. [Display omitted] • Reported PAHs' occurrence in the coral reef food web for the first time. • Latitude affected PAHs' occurrence and bioaccumulation in the organisms. • Latitude drove the PAHs' trophodynamics in aquatic ecosystem food webs. • PAHs underwent trophic amplification in the food webs of coral reef ecosystems. [ABSTRACT FROM AUTHOR]

Ciguatera poisoning is mainly caused by the consumption of reef fish that have accumulated ciguatoxins (CTXs) produced by the benthic dinoflagellates Gambierdiscus and Fukuyoa. China has a long history of problems with ciguatera, but research on ciguatera causative organisms is very limited, especially in the Beibu Gulf, where coral reefs have been degraded significantly and CTXs in reef fish have exceeded food safety guidelines. Here, five strains of Gambierdiscus spp. were collected from Weizhou Island, a ciguatera hotspot in the Beibu Gulf, and identified by light and scanning electron microscopy and phylogenetic analyses based on large and small subunit rDNA sequences. Strains showed typical morphological characteristics of Gambierdiscus caribaeus, exhibiting a smooth thecal surface, rectangular-shaped 2′, almost symmetric 4″, and a large and broad posterior intercalary plate. They clustered in the phylogenetic tree with G. caribaeus from other locations. Therefore, these five strains belonged to G. caribaeus, a globally distributed Gambierdiscus species. Toxicity was determined through the mouse neuroblastoma assay and ranged from 0 to 5.40 fg CTX3C eq cell−1. The low level of toxicity of G. caribaeus in Weizhou Island, with CTX-contaminated fish above the regulatory level in the previous study, suggests that the long-term presence of low toxicity G. caribaeus might lead to the bioaccumulation of CTXs in fish, which can reach dangerous CTX levels. Alternatively, other highly-toxic, non-sampled strains could be present in these waters. This is the first report on toxic Gambierdiscus from the Beibu Gulf and Chinese waters and will provide a basis for further research determining effective strategies for ciguatera management in the area. [ABSTRACT FROM AUTHOR]