Timing of Holocene sea-level highstands by mass spectrometric U-series ages of a coral reef from Leizhou Peninsula, South China Sea

Systematic mass spectrometric 230Th ages are reported for a Porites coral reef terrace from Dengloujiao,Leizhou Peninsula, South China Sea. Seven episodes of coral growth were recognized in this terrace: 7125±96, 6764±29,5826±37, 5006±54, 2543±24, 1915±15, and 1513±22 calendar years before present (cal. aBP). 50% of the coral age population fall between 7200 and 6600 cal. aBP, marking post-glacial stabdization of global sea level. Considering the facts that ( i ) Dengloujiao reef fiat was measured at 1.6-2.5m above modern tidal datum plane; (ii) modern Porites corals in the South China Sea are living at least ～1 m below the modern tidal datum plane; (iii) the top 20-30 cm of the reef was eroded; and (iv) crustal subsidence in the region since mid-Holocene was negligible, we conclude that the above age groups record at least two major periods (7200-5000 and 2500-1500 cal. aBP) of high sea-level at least 2.9-3.8 m above the present-day level.     

Assessment of coral bleaching using symbiotic zooxanthellae density and satellite remote sensing data in the Nansha Islands,South China Sea

Coral bleaching,characterized by a significant loss of symbiotic zooxanthellae,is the primary cause of mass coral mortality and reef degradation throughout the world.The characteristics,processes,and resistance of corals to bleaching varies significantly and is dependent on environmental conditions.We documented a mass coral bleaching event in June 2007 at the Meiji and Zhubi Reefs,Nansha Islands (NS),South China Sea using ecological surveys and measurement of coral zooxanthellae density and sea surface temperatures (SST).More than 35 species of corals (between 0-20 m in depth) were bleached.These bleached corals accounted for 15.6% of total corals in the investigated quadrats.The branching corals Pocillopora and Acropora were the most vulnerable species whereas the massive corals Porites and Favia were more tolerant of the high SSTs.Surprisingly,we found no evidence of bleaching in Agariciidae corals suggesting that this family is resistant to thermal stresses.The bleached corals had lost 72%-90% of their symbiotic zooxanthellae.Furthermore,corals that had no visual signs of bleaching had also lost 31%-53% of their zooxanthellae suggesting that most corals were experiencing the early stage of bleaching.The monthly mean SST during June 2007 was 30.8°C,the highest since 1998.Based on measurements of SST and the Hotspots and DHW data (NOAA),we conclude that it the extremely high SSTs triggered this coral bleaching event.Our results suggest that the previously accepted temperature thresholds used to predict coral bleaching based on satellite data are likely to underestimate the extent and intensity of coral bleaching,at least in the NS.     

Using the Acropora digitifera genome to understand coral responses to environmental change

Despite the enormous ecological and economic importance of coral reefs, the keystone organisms in their establishment, the scleractinian corals, increasingly face a range of anthropogenic challenges including ocean acidification and seawater temperature rise. To understand better the molecular mechanisms underlying coral biology, here we decoded the approximately 420-megabase genome of Acropora digitifera using next-generation sequencing technology. This genome contains approximately 23,700 gene models. Molecular phylogenetics indicate that the coral and the sea anemone Nematostella vectensis diverged approximately 500 million years ago, considerably earlier than the time over which modern corals are represented in the fossil record (～240 million years ago). Despite the long evolutionary history of the endosymbiosis, no evidence was found for horizontal transfer of genes from symbiont to host. However, unlike several other corals, Acropora seems to lack an enzyme essential for cysteine biosynthesis, implying dependency of this coral on its symbionts for this amino acid. Corals inhabit environments where they are frequently exposed to high levels of solar radiation, and analysis of the Acropora genome data indicates that the coral host can independently carry out de novo synthesis of mycosporine-like amino acids, which are potent ultraviolet-protective compounds. In addition, the coral innate immunity repertoire is notably more complex than that of the sea anemone, indicating that some of these genes may have roles in symbiosis or coloniality. A number of genes with putative roles in calcification were identified, and several of these are restricted to corals. The coral genome provides a platform for understanding the molecular basis of symbiosis and responses to environmental changes.     

涠洲岛珊瑚礁特点、演变及保护与修复对策的思考

涠洲岛珊瑚礁最早形成于约7 000年前的末次海侵,是中国大陆沿海成礁珊瑚分布最北缘的典型边缘珊瑚礁（Marginal Coral Reefs）,与区域内其他珊瑚礁缺少生态关联,其特征不同于热带珊瑚礁,即块状珊瑚占优势。20多年来,涠洲岛珊瑚礁持续退化,枝状珊瑚大量死亡,石珊瑚盖度急剧降低,反映珊瑚礁良好状况的指标生物如鹦嘴鱼、蝴蝶鱼等的数量大幅减少。近10年来,珊瑚虽未出现异常死亡现象,但珊瑚自然修复不明显,表明珊瑚补充不足。功能性植食性鱼类的缺乏,显示珊瑚礁恢复力不足。涠洲岛珊瑚礁国家级海洋公园的建立,体现了保护涠洲岛珊瑚礁的政治意愿。只有恢复鹦嘴鱼等功能性植食性鱼类的数量,才能恢复和增强珊瑚礁固有恢复力,进而促进涠洲岛珊瑚礁的自然恢复。人为修复可采取移植珊瑚断枝的方式,并以实现生态、经济和社会增益为目标,构建能应对人为干预且能持续演化的珊瑚礁。     

Twenty-five years of change in scleractinian coral communities of Daya Bay （northern South China Sea） and its response to the 2008 AD extreme cold climate event

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Nino-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit （-30℃） at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes （i.e., currently cooler sea surface temperatures） will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes （i.e., currently warmer sea surface temperatures）. Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay （22°31′--22°50′N）, northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006--2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years （i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008）. Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 （13 January-13 February）. During the 2008 cold event, the lowest air temperature reaches only 6.6℃, and the mean sea surface temperature for February fall to 〈 14℃, including six continuous days at 12.3℃. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold （-13℃） that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before （August 2007） and after （late February 2008） the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming.     

Estimate of carbonate production by scleractinian corals at Luhuitou fringing reef, Sanya, China

Carbonate production by scleractinian corals not only maintains coral reef growth, but also represents an important source of atmospheric carbon dioxide. In this paper the carbonate production by scler-actinian corals at Luhuitou fringing reef, Sanya, Hainan Island, China, is investigated with an ecological census-based method. Averaged carbonate production is 1.16 ± 0.55 kg·m-2·a-1 and 3.52 ± 1.32 kg·m-2·a-1 on the reef flat and reef slope, respectively, depending on the composition and distribution of cor...     

涠洲岛珊瑚礁生态环境条件初步研究

分析涠洲岛沿岸与珊瑚礁发育关系密切的水温、水深、光照、波浪、海流、潮汐、pH值、盐度、溶解氧、磷酸盐、基岩基底、珊瑚礁块基底、珊瑚砂砾基底、虫黄藻、褐藻等生态环境条件,探讨这些生态变化条件的变化规律,及其对珊瑚生长、发育的影响。     

一个大陆坡环礁—南海华光珊瑚环礁的沉积相模式及其演化趋势

华光珊瑚环礁是一典型的大陆坡环礁,区别于大洋环礁和大陆架环礁。其发育既受全球板块运动,又受海面升降运动的控制。现代环礁的结构是在冰期时形成的先成台地之上复盖着一薄层的全新世礁相沉积。东亚季风的作用使礁形成各向相似的沉积相带。环礁礁冠与泻湖宽度之比可作为现代环礁成熟度的定量标志。华光环礁目前尚处于幼年期。     

Permanent El Niño during the Pliocene warm period not supported by coral evidence

The El Ni?o/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Ni?o state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean. This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change, ENSO variability--and related global climate teleconnections-could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial. Here we show that permanent El Ni?o conditions did not exist during the PWP. Our spectral analysis of the δ(18)O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ(18)O events in the fossil corals closely resemble the decreases in δ(18)O seen in the live coral during El Ni?o events. Prior research advocating a permanent El Ni?o state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.     

涠洲岛珊瑚岸礁的沉积特征

涠洲岛珊瑚岸礁发育根基于火山岩,除了冬、春的低温影响外,环境因素是适合于珊瑚生长的。在岸礁区有两个沉积带:珊瑚生成带和火山岩海底礁坪。陆地的有机废物移到海底而珊瑚移到陆地,但在水能和环境的影响下,它们形成混合沉积,这种沉积主要分布在岸礁的平面和海滩底部。由于属于岸礁形成早期,涠洲岛约从3100年前就一直不断生长,涠洲岛的海滩岩石位于高于海平面5米的位置。     

涠洲岛西局部造礁石珊瑚盖度和大小频率分布

本研究通过分析珊瑚大小频率分布,探讨涠洲岛西局部造礁石珊瑚群落结构特点和种群动态,以了解珊瑚的生活史和所经历的变化。所分析的珊瑚大小数据来自2021年2月24-26日开展的涠洲岛西珊瑚礁的造礁石珊瑚样带调查,利用对数转换将珊瑚大小变换为珊瑚迭代,然后作直方图对珊瑚大小频率分布加以分析。分析结果表明,片状的牡丹珊瑚属Pavona和块状的滨珊瑚属Porites、角蜂巢珊瑚属Favites、盘星珊瑚属Dipsastraea等在涠洲岛西局部珊瑚群落中占优势(珊瑚面积和珊瑚个数)。对数转换的大小频率分布呈正态分布,偏斜不明显,变异系数小于0.5,表明这些珊瑚目前处于正常的自然补充、生长和死亡过程。涠洲岛西局部造礁石珊瑚盖度降低,主要是因为个体大的枝状珊瑚锐减。     

Fluorescent pigments in corals are photoprotective

All reef-forming corals depend on the photosynthesis performed by their algal symbiont, and such corals are therefore restricted to the photic zone. The intensity of light in this zone declines over several orders of magnitude--from high and damaging levels at the surface to extreme shade conditions at the lower limit. The ability of corals to tolerate this range implies effective mechanisms for light acclimation and adaptation. Here we show that the fluorescent pigments (FPs) of corals provide a photobiological system for regulating the light environment of coral host tissue. Previous studies have suggested that under low light, FPs may enhance light availability. We now report that in excessive sunlight FPs are photoprotective; they achieve this by dissipating excess energy at wavelengths of low photosynthetic activity, as well as by reflecting of visible and infrared light by FP-containing chromatophores. We also show that FPs enhance the resistance to mass bleaching of corals during periods of heat stress, which has implications for the effect of environmental stress on the diversity of reef-building corals, such as enhanced survival of a broad range of corals allowing maintenance of habitat diversity.     

Interspecies and spatial diversity in the symbiotic zooxanthellae density in corals from northern South China Sea and its relationship to coral reef bleaching

Coral reef bleaching is usually characterized by expulsion of symbiotic zooxanthellae, loss of zooxanthellae pigmentation, or both. We collected 128 samples comprising 39 species of 21 genera of reef-building corals from Luhuitou and Xiaodonghai in Sanya of Hainan Island and Daya Bay of Guangdong Province, respectively, and analyzed the symbiotic zooxanthellae population density. The results show that： （1） the symbiotic zooxanthella density varies from 0.67×10^6 to 8.48×10^6 cell/cm^2, displaying significant interspecies variability, with branch corals usually having relatively less zooxanthellae （ranging from 0.67×10^6 to 2.47×10^6 cell/cm^2） than massive species （from 1.0×10^6 to 8.48×10^6 cell/cm^2）; （2） corals inhabiting within 4 m water depth have higher levels of symbiotic zooxanthellae than those living at the bottom （-7 m depth） of the reef area; （3） there is no discernable difference in the zooxanthellae density between corals from relatively high latitude Daya Bay （-22°N） and those from relatively low latitude Sanya （-18°N） at comparable sea surface temperatures （SST）; （4） in partially-bleached corals, the density of zooxanthellae shows the following order： healthy-looking part〉 semi-bleached part 〉 bleached part. Based on the above results, we suggest that （1） the zooxanthellae density difference between branching and massive coral species is the main cause that branching corals are more vulnerable to bleaching than massive corals. For example, symbiotic zooxanthellae levels are low in branching Acropora and Pocillopora corals and thus these corals are more susceptible to bleaching and mortality; （2） symbiotic zooxanthellae density can also be affected by environmental conditions, such as sediment loads, diving-related turbidity, and aquaculture-related nitrate and phosphate input, and their increase may reduce symbiotic zooxanthellae density in corals.     

Coral community changes in response to a high sedimentation event: A case study in southern Hainan Island

A high sedimentation event caused by dredging and dumping of sediment was recorded on Xiaodonghai Reef in Yulin Bay,southern Hainan Island,China.Significantly high sedimentation and constant light shading were observed during the sediment dumping event(SD Event).Using long-term video transects,we quantified coral community changes and responses to the SD Event between 2008 and 2010.The SD Event caused severe coral mortality on Xiaodonghai Reef at a depth of 6 m,while corals at 3 m were less affected.Total live coral cover at 6 m decreased from 54.3% to 14.8%,and Diploastrea heliopora replaced Galaxea fascicularis as the dominant coral species at 6 and 9 m.The density of juvenile corals also declined after the SD Event,especially for the genera Galaxea and Platygyra.However,the density of juvenile Porites and Pocillopora spp.slightly increased.Monitoring for 11 months after the SD Event indicated no recovery of coral communities on Xiaodonghai Reef.Long-term video transect data also revealed that mean live coral cover dramatically declined,from 30.5% in 2008 to 9% in 2010,while the dominant corals in Yulin Bay shifted to more tolerant coral species,such as massive Porites spp.and D.heliopora.The rapid coral community degradation in Yulin Bay between 2008 and 2010 was probably caused by high sediment deposition resulting from intensive dredging and land-clearing activities.These results highlight the necessity for an integrated watershed management to control sediment deposition on near-shore coral reefs.     

Effects of temperature,hypoxia, ammonia and nitrate on the bleaching among three coral species

Coral bleaching, which is defined as the loss of colour in corals due to the loss of their symbiotic algae (commonly called zooxanthellae) or pigments or both, is occurring globally at increasing rates, and its harm becomes more and more serious during these two decades. The significance of these bleaching events to the health of coral reef ecosystems is extreme, as bleached corals exhibited high mortality, reduced fecundity and productivity and increased susceptibility to diseases. This decreased coral fitness is easily to lead to reef degradation and ultimately to the breakdown of the coral reef ecosystems. Recently, the reasons leading to coral bleaching are thought to be as follows: too high or too low temperature, excess ultraviolet exposure, heavy metal pollution, cyanide poison and seasonal cycle. To date there has been little knowledge of whether mariculture can result in coral bleaching and which substance has the worst effect on corals. And no research was conducted on the effect of hypoxia on corals. To address these questions, effects of tem- perature, hypoxia, ammonia and nitrate on bleaching of three coral species were studied through examination of morphology and the measurement of the number of symbiotic algae of three coral species Acropora nobilis, Palythoa sp. and Alveopora verrilliana. Results showed that increase in temperature and decrease in dissolved oxygen could lead to increasing number of symbiotic algae and more serious bleaching. In addition, the concentration of 0.001 mmol/L ammonia or nitrate could increase significantly the expulsion of the symbiotic algae of the three coral species. Except for Acropora nobilis, the numbers of symbiotic algae of other two corals did not significantly increase with the increasing concentration of ammonia and nitrate. Furthermore, different hosts have different stress susceptibilities on coral bleaching.     

Coral bleaching: thermal adaptation in reef coral symbionts

Many corals bleach as a result of increased seawater temperature, which causes them to lose their vital symbiotic algae (Symbiodinium spp.) - unless these symbioses are able to adapt to global warming, bleaching threatens coral reefs worldwide. Here I show that some corals have adapted to higher temperatures, at least in part, by hosting specifically adapted Symbiodinium. If other coral species can host these or similar Symbiodinium taxa, they might adapt to warmer habitats relatively easily.     

涠洲岛珊瑚礁健康评估

【目的】科学地判断涠洲岛珊瑚礁的现状,并找出造成目前现状的主要原因,为及时采取有效措施以维持涠洲岛珊瑚礁的健康提供有力依据。【方法】根据历年来有关涠洲岛珊瑚礁生长、演变、环境变化与社会发展的研究成果和最新的调查研究资料,采用HRHPI的指标体系法,从生态结构、生态功能、压力及社会经济等几个特征属性对珊瑚礁健康进行评估。【结果】涠洲岛的自然环境仍适合石珊瑚的生存,石珊瑚的种类丰度仍正常;珊瑚礁的覆盖率降低、分布范围缩小、生物多样性下降,尤其在浅海和局部人为影响大的区域,珊瑚死亡率大于补充率。【结论】涠洲岛的珊瑚礁处于衰退中的亚健康状态。过度捕捞、污染、物理损伤（踩踏、抛锚、水下工程等）和大尺度环境变化（如气候异常）等是造成涠洲岛珊瑚礁衰退的主要原因。     

南海深水海山上的新发现

 在国家自然科学基金委重大研究计划“南海深部计划”指导下，于2013-2019年期间，分别运用载人或遥控深潜器，针对南海深海盆中的部分海山开展了4个科学探测航次，在南海首次发现了大面积的高丰度铁锰结核分布区、“南溟”古热液区和惊人的冷水珊瑚生态林。这些发现不仅为深入认识南海不同时空尺度演化的复杂过程及相互作用开辟了新的研究领域，还探索实践了中国海洋高新技术发展与前沿基础科学研究紧密结合并相互促进的高效创新研究模式。     

Conventional taxonomy obscures deep divergence between Pacific and Atlantic corals

Only 17% of 111 reef-building coral genera and none of the 18 coral families with reef-builders are considered endemic to the Atlantic, whereas the corresponding percentages for the Indo-west Pacific are 76% and 39%. These figures depend on the assumption that genera and families spanning the two provinces belong to the same lineages (that is, they are monophyletic). Here we show that this assumption is incorrect on the basis of analyses of mitochondrial and nuclear genes. Pervasive morphological convergence at the family level has obscured the evolutionary distinctiveness of Atlantic corals. Some Atlantic genera conventionally assigned to different families are more closely related to each other than they are to their respective Pacific 'congeners'. Nine of the 27 genera of reef-building Atlantic corals belong to this previously unrecognized lineage, which probably diverged over 34 million years ago. Although Pacific reefs have larger numbers of more narrowly distributed species, and therefore rank higher in biodiversity hotspot analyses, the deep evolutionary distinctiveness of many Atlantic corals should also be considered when setting conservation priorities.     

Sea-level fluctuations during the last glacial cycle

The last glacial cycle was characterized by substantial millennial-scale climate fluctuations, but the extent of any associated changes in global sea level (or, equivalently, ice volume) remains elusive. Highstands of sea level can be reconstructed from dated fossil coral reef terraces, and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios at millennial-scale resolution or higher. Records based on oxygen isotopes, however, contain uncertainties in the range of +/-30 m, or +/-1 degrees C in deep sea temperature. Here we analyse oxygen isotope records from Red Sea sediment cores to reconstruct the history of water residence times in the Red Sea. We then use a hydraulic model of the water exchange between the Red Sea and the world ocean to derive the sill depth-and hence global sea level-over the past 470,000 years (470 kyr). Our reconstruction is accurate to within +/-12 m, and gives a centennial-scale resolution from 70 to 25 kyr before present. We find that sea-level changes of up to 35 m, at rates of up to 2 cm yr(-1), occurred, coincident with abrupt changes in climate.