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.     

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.     

Coral mucus functions as an energy carrier and particle trap in the reef ecosystem

Zooxanthellae, endosymbiotic algae of reef-building corals, substantially contribute to the high gross primary production of coral reefs, but corals exude up to half of the carbon assimilated by their zooxanthellae as mucus. Here we show that released coral mucus efficiently traps organic matter from the water column and rapidly carries energy and nutrients to the reef lagoon sediment, which acts as a biocatalytic mineralizing filter. In the Great Barrier Reef, the dominant genus of hard corals, Acropora, exudes up to 4.8 litres of mucus per square metre of reef area per day. Between 56% and 80% of this mucus dissolves in the reef water, which is filtered through the lagoon sands. Here, coral mucus is degraded at a turnover rate of at least 7% per hour. Detached undissolved mucus traps suspended particles, increasing its initial organic carbon and nitrogen content by three orders of magnitude within 2 h. Tidal currents concentrate these mucus aggregates into the lagoon, where they rapidly settle. Coral mucus provides light energy harvested by the zooxanthellae and trapped particles to the heterotrophic reef community, thereby establishing a recycling loop that supports benthic life, while reducing loss of energy and nutrients from the reef ecosystem.     

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.     

Heterotrophic plasticity and resilience in bleached corals

Mass coral bleaching events caused by elevated seawater temperatures have resulted in extensive coral mortality throughout the tropics over the past few decades. With continued global warming, bleaching events are predicted to increase in frequency and severity, causing up to 60% coral mortality globally within the next few decades. Although some corals are able to recover and to survive bleaching, the mechanisms underlying such resilience are poorly understood. Here we show that the coral host has a significant role in recovery and resilience. Bleached and recovering Montipora capitata (branching) corals met more than 100% of their daily metabolic energy requirements by markedly increasing their feeding rates and CHAR (per cent contribution of heterotrophically acquired carbon to daily animal respiration), whereas Porites compressa (branching) and Porites lobata (mounding) corals did not. These findings suggest that coral species with high-CHAR capability during bleaching and recovery, irrespective of morphology, will be more resilient to bleaching events over the long term, could become the dominant coral species on reefs, and may help to safeguard affected reefs from potential local and global extinction.     

珊瑚礁相关病毒的研究进展

珊瑚礁被称为海洋中的“热带雨林”,是海洋生态系统中的核心组成部分之一。珊瑚礁病毒包含珊瑚本身感染的病毒和珊瑚共生生物（如藻类、细菌等）感染的病毒,对于珊瑚礁健康与疾病、生长与死亡起着独特而重要的作用,在维持珊瑚礁生态系统的物质循环和能量流动等生态学功能方面起着潜在作用。由于技术的局限以及关注度较低等原因,有关珊瑚礁病毒的研究较少。近年来,随着高通量测序技术的发展,宏转录组和宏基因组逐渐成为研究珊瑚礁病毒多样性及其生态学功能的重要方法之一。本文对国内外相关研究进行总结和归纳,拟为珊瑚礁病毒后续研究提供新的方向和思路,同时指导我国珊瑚礁的保护以及修复。     

Communication arising. Is coral bleaching really adaptive?

From an experiment in which corals are transplanted between two depths on a Panamanian coral reef, Baker infers that bleaching may sometimes help reef corals to survive environmental change. Although Baker's results hint at further mechanisms by which reef-building corals may acclimatize to changing light conditions, we do not consider that the evidence supports his inference.     

涠洲岛园艺式珊瑚苗圃的架设与移植

【目的】探讨涠洲岛不同底质下最适宜的硬珊瑚苗圃架设方法和最佳移植培育种类。【方法】在涠洲岛周边海域砂质、基岩、珊瑚碎屑和礁石等4种不同底质架设固定式(20个)及悬浮式(112个)珊瑚苗圃,移植块状、枝状、叶状等7种硬珊瑚断枝,共2 436个;观测记录苗圃保存情况及珊瑚成活率、珊瑚体积增长率等。【结果】礁石底质海域的苗圃保存程度最高,为70%;其次是珊瑚碎屑海域(北部牛角坑)的苗圃,为57%。铁架式苗圃的平均保存率为63%,是保存程度最好的苗圃形式。经过一年时间的培育,风信子鹿角珊瑚Acropora hyacinthus的成活率为20%~80%,体积增加3.5倍;粗野鹿角珊瑚Acropora humilis成活率为25%~49%,体积增加1.5倍。其他种类珊瑚生长较慢,成活率较低。【结论】铁架式苗圃结构稳固、不易受台风等风暴潮的影响,是涠洲岛最适合的珊瑚苗圃形式。涠洲岛四面环海,珊瑚苗圃应架设在岛屿北部礁石和珊瑚碎屑基底的海域。风信子鹿角珊瑚在一年时间内体积可以增加3倍,且存活率高,是涠洲岛珊瑚礁移植最优先考虑的种类。     

Confronting the coral reef crisis

The worldwide decline of coral reefs calls for an urgent reassessment of current management practices. Confronting large-scale crises requires a major scaling-up of management efforts based on an improved understanding of the ecological processes that underlie reef resilience. Managing for improved resilience, incorporating the role of human activity in shaping ecosystems, provides a basis for coping with uncertainty, future changes and ecological surprises. Here we review the ecological roles of critical functional groups (for both corals and reef fishes) that are fundamental to understanding resilience and avoiding phase shifts from coral dominance to less desirable, degraded ecosystems. We identify striking biogeographic differences in the species richness and composition of functional groups, which highlight the vulnerability of Caribbean reef ecosystems. These findings have profound implications for restoration of degraded reefs, management of fisheries, and the focus on marine protected areas and biodiversity hotspots as priorities for conservation.     

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...     

Ecological consequences of major hydrodynamic disturbances on coral reefs

A recent tsunami and an apparent increase in the frequency of severe tropical storms underscore the need to understand and predict the ecological consequences of major hydrodynamic disturbances. Reef corals provide the habitat structure that sustains the high biodiversity of tropical reefs, and thus provide the foundation for the ecosystem goods and services that are critical to many tropical societies. Here we integrate predictions from oceanographic models with engineering theory, to predict the dislodgement of benthic reef corals during hydrodynamic disturbances. This generalizes earlier work, by incorporating colonies of any shape and by explicitly examining the effects of hydrodynamic gradients on coral assemblage structure. A field test shows that this model accurately predicts changes in the mechanical vulnerability of coral colonies, and thus their size and shape, with distance from the reef crest. This work provides a general framework for understanding and predicting the effects of hydrodynamic disturbances on coral reef communities; such disturbances have a major role in determining species zonation and coexistence on coral reefs, and are critical determinants of how coral assemblages will respond to changes in the frequency and intensity of tropical storms associated with a changing climate.     

Coral cover as a proxy of disturbance:A case study of the biodiversity of the hermatypic corals in Yongxing Island, Xisha Islands in the South China Sea

The Yongxing Island is the biggest island of Xisha Islands in the middle part of the South China Sea. It occupies 1.8 square kilometers of land area and has permanent residence on it. There are only a few papers on the coral community of the Xisha Islands, reporting the species composition, structure and zonations of the hermatypic coral community in 1970s. The present study describes the hermatypic coral community based on the quadrat survey after almost 30 years in Yongxing Island in August 2002. It was the first time to present the percent cover data of live corals of Yongxing Island via a systematic scheme of quantitative quadrat sampling. The average total percent cover of the live coral is 68.4%. We found the total percent cover (TPC) could be an idea proxy of the overall disturbance regime impinging on the coral community. TPC can be used as an integrated measure of disturbance to coral reef. Using this surrogate, the best fit relation between TPC of the live corals and species richness, species diversity, or the species evenness is the unimodal second-order polymorphic parabola equation. This result is expected by the intermediate disturbance hypothesis (IDH). From the fitted parabola equations, we calculated the best TPCs corresponding to the maximal species richness, the highest species diversity, or the most evenness respectively. They are surprisingly stabilized between 55% and 58%. Coralcover is the basic parameter widely available for most observation, research or monitoring programs. The good qualitative characteristics of percent cover provide powerful tool for the experimental, theoretical and modeling studies of coral reef in response to the disturbance.     

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。     

珊瑚礁隐居生物的研究现状和展望

珊瑚礁隐居生物是栖息于珊瑚礁隐匿空间中的后生动物群体，其群落的生物量巨大，在珊瑚礁生物多样性的构成中占据大多数，且在珊瑚礁营养动力学上有着不可或缺的作用。然而，目前国际国内对珊瑚礁生态系统的生物多样性的关注多集中在鱼类及甲壳类、棘皮动物等礁栖或底栖动物上，对珊瑚礁隐居生物的关注度不足，隐居生物的生物多样性构成不甚清楚，有些类别甚至从未被描述。本文结合国内外文献综述了珊瑚礁隐居生物的研究现状，并对基于珊瑚礁自动监测装置(Autonomous Reef Monitoring Structures, ARMS)的隐居生物研究进行了展望。     

世界珊瑚礁现状和威胁研究进展

鉴于珊瑚礁巨大的价值和面临全球气候变化严峻的威胁,珊瑚礁退化和发展前景一直是珊瑚礁研究的最中心议题。人类活动和气候变化已经导致珊瑚礁全球性衰退损失40%~50%。1998年全球珊瑚礁严重白化和2015—2017年延时最长全球珊瑚礁白化事件,一再证实全球变暖已经成为珊瑚礁可持续发展的主要威胁,现在扭转导致海洋水温升高的全球变暖的趋势是保护珊瑚礁的唯一希望。由科学家和慈善机构发起的2011年XL Catlin海景调查和2017年50礁倡议成为珊瑚礁管理保护的创新举措。但仍然需要更多的人认识珊瑚礁,热爱珊瑚礁,研究珊瑚礁,保护珊瑚礁。     

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。     

Mangroves enhance the biomass of coral reef fish communities in the Caribbean

Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs.     

贵州布寨泥盆纪生物礁的古生物学和古生态学特征

贵州布寨泥盆纪生物礁发育在独山组的鸡泡段和鸡窝寨段,大部分是骨架礁,主要由层孔虫和床板珊瑚构成。部分是障积礁,主要由枝状床板珊瑚和藻类构成。在礁组合中可识别出4个生物群落和一个生物组合,各生物群落和生物组合发育于各自互不相同的环境。根据生物群落和生物组合的生态分析及与邻区礁组合的生物群落对比,认为布寨礁发育在环境条件较为稳定的浅海,海水的温度、含盐度、清洁度、深度和水动力条件都比较适合造礁生物生长。图2,参9。     

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。