Flexibility in algal endosymbioses shapes growth in reef corals

The relation between corals and their algal endosymbionts has been a key to the success of scleractinian (stony) corals as modern reef-builders, but little is known about early stages in the establishment of the symbiosis. Here, we show that initial uptake of zooxanthellae by juvenile corals during natural infection is nonspecific (a potentially adaptive trait); the association is flexible and characterized by a change in (dominant) zooxanthella strains over time; and growth rates of experimentally infected coral holobionts are partly contingent on the zooxanthella strain harbored, with clade C-infected juveniles growing two to three times as fast as those infected with clade D.     

Glycerol excretion by symbiotic algae from corals and tridacna and its control by the host

Zooxanthellae isolated from reef corals and Tridacna crocea incorporate labeled carbon dioxide photosynthetically. In the presence of some component of the host tissue, up to 40 percent of the labeled algal photosynthate is liberated primarily as glycerol. Excretion of glycerol by the algae in situ and its control and utilization by the host may represent a mechanism by which zooxanthellae contribute to produtctivity of coral reefs.     

Discovery of symbiotic nitrogen-fixing cyanobacteria in corals

Colonies of the Caribbean coral Montastraea cavernosa exhibit a solar-stimulated orange-red fluorescence that is spectrally similar to a variety of fluorescent proteins expressed by corals. The source of this fluorescence is phycoerythrin in unicellular, nonheterocystis, symbiotic cyanobacteria within the host cells of the coral. The cyanobacteria coexist with the symbiotic dinoflagellates (zooxanthellae) of the coral and express the nitrogen-fixing enzyme nitrogenase. The presence of this prokaryotic symbiont in a nitrogen-limited zooxanthellate coral suggests that nitrogen fixation may be an important source of this limiting element for the symbiotic association.     

苯并[a]芘胁迫对3种石珊瑚虫黄藻密度及叶绿素a含量的影响

苯并[a]芘[Benzo(a)pyrene,BaP]是一种在环境中广泛存在的有毒的环境污染物,珊瑚是构成珊瑚礁生态系统的基石,具有重要的价值.本研究以南海3种典型的造礁石珊瑚:鹿角杯型珊瑚(Pocilloporadamicornis)、指状蔷薇珊瑚(Montipora digitata)和美丽鹿角珊瑚(Acropora...     

The effect of algal symbionts on the accuracy of Sr/Ca paleotemperatures from coral

The strontium-to-calcium ratio (Sr/Ca) of reef coral skeleton is commonly used as a paleothermometer to estimate sea surface temperatures (SSTs) at crucial times in Earth's climate history. However, these estimates are disputed, because uptake of Sr into coral skeleton is thought to be affected by algal symbionts (zooxanthellae) living in the host tissue. Here, we show that significant distortion of the Sr/Ca temperature record in coral skeleton occurs in the presence of algal symbionts. Seasonally resolved Sr/Ca in coral without symbionts reflects local SSTs with a temperature sensitivity equivalent to that of laboratory aragonite precipitated at equilibrium and the nighttime skeletal deposits of symbiotic reef corals. However, up to 65% of the Sr/Ca variability in symbiotic skeleton is related to symbiont activity and does not reflect water temperature.     

长砗磲（Tridacna maxima）个体大小与虫黄藻数量的相关性研究

[目的]分析长砗磲个体大小与虫黄藻数量的关系。[方法]以采自海南东瑁洲岛的28只长砗磲为试材,用SAS统计软件对长砗磲体内的虫黄藻数量和叶绿素a含量与壳长和干重进行相关性分析。[结果]长砗磲体内的虫黄藻总数随着长砗磲壳长和干重的增加均呈对数增长,与壳长的相关系数为0.967 2（P〈0.01）,与干重的相关系数为0.934 0（P〈0.01）,二者均表现极显著相关性。长砗磲体内的总叶绿素a含量随着壳长的增长而增加,其相关系数为0.936 7（P〈0.01）,二者亦具有极显著相关性,但单个虫黄藻细胞内叶绿素含量不随长砗磲个体的增大而增加,而是保持了1个恒定值2.5（±0.32,n=28）pg/cell。[结论]长砗磲通过增加体内虫黄藻的数量来增加光合作用产物的总量,以满足自身生存与生长的需要。     

The dynamics of zooxanthellae populations: A long-term study in the field

Coral bleaching characterized by the expulsion of symbiotic algae (zooxanthellae) is an increasing problem worldwide. Global warming has been implicated as one cause, but the phenomenon cannot be fully comprehended without an understanding of the variability of zooxanthellae populations in field conditions. Results from a 6-year field study are presented, providing evidence of density regulation but also of large variability in the zooxanthellae population with regular episodes of very low densities. These bleaching events are likely to be part of a constant variability in zooxanthellae density caused by environmental fluctuations superimposed on a strong seasonal cycle in abundance.     

回头岸礁区4 种造礁珊瑚中可培养细菌的多样性

采用稀释涂布平板法,分离三亚鹿回头岸礁区4种造礁珊瑚及其周围海水中的细菌,并基于16S r RNA基因序列进行了系统发育分析,从而探讨造礁珊瑚中可培养细菌的物种多样性。从澄黄滨珊瑚(Porites lutea)、鹿角珊瑚(Acropora sp.)、盔形珊瑚(Galaxea sp.)、扁脑珊瑚(Platygyra sp.)样品中分别分离获得细菌60、61、54、20株,从珊瑚周边海水中分离获得细菌31株。16S r RNA基因序列分析表明,珊瑚来源的细菌分布于放线菌门(Actinobacteria)、α-变形菌纲(Alphaproteobacteria)、γ-变形菌纲(Gammaproteobacteria)、厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)。在属级水平上对4种珊瑚及海水来源细菌群落组成分析,发现在4种珊瑚中均有分布的属有3个,为Brachybacterium、Microbacterium和Ruegeria,珊瑚来源细菌类群有一定差异。同时发现4种珊瑚来源细菌与海水来源细菌类群差异较大。在分离的菌株中,有7株菌与已有效描述的细菌物种典型菌株的全长16S r RNA基因相似性低于97%,代表着潜在新属或新种。试验结果表明,三亚鹿回头岸礁区珊瑚中存在较为丰富的细菌多样性,并潜藏较多的新物种资源。     

Paleoceanography of coral reefs in the hawaiian-emperor chain

The fossil record of shallow marine organisms in the Hawaiian Archipelago and Emperor seamount chain indicates that reef corals were absent during the first half of the Tertiary. Their appearance during the early Oligocene, 34 million years ago, is associated with several paleoceanographic events that appear to have combined to intensify gradually gyral surface currents in the north Pacific. This association suggests that corals were absent in the early Tertiary because of isolation of the Hawaiian Archipelago from the Indo-West Pacific (IWP), the center of reef coral abundance and diversity in the Pacific. Today, the number of species of reef corals in Hawaii is less than 10 percent of the number of species in the IWP. Since their initial colonization, reef corals have been present continuously in the Hawaiian Archipelago, although not without taxonomic change. Episodes of extinction and recolonization are the most likely cause of change in species composition. Recolonization from the IWP may also explain the low rate of endemism (about 20 percent) in the present-day coral fauna.     

不同方法提取珊瑚总蛋白质的比较

以海南省近岸海域的鼻形鹿角珊瑚(Acropora nasuta)和箭排孔珊瑚(Seriatopora hystrix)2种硬珊瑚为研究对象,比较了TRIzol试剂提取法和BP-酚提取法在珊瑚蛋白质提取量、双向蛋白点数量和分布上的差异。结果表明,BP-酚抽提法的蛋白质得率相对较高。通过1-DE及2-DE电泳比较分析发现,2种方法获得的蛋白样品存在较大差异。BP-酚抽提法能够获得更多蛋白条带和点数,并且具有较少的拖尾现象。在低相对分子质量蛋白的提取方面,TRIzol试剂提取法具有优势;在高相对分子质量的提取方面,BP-酚抽法具有明显优势。研究结果有望为硬珊瑚的蛋白质组学研究奠定一定的基础。     

Do corals lie about their age? Some demographic consequences of partial mortality, fission, and fusion

Population dynamics of corals and other colonial animals are complicated by their modular construction and growth. Partial colony mortality, colony fission, and colony fusion distort any simple relationship between size and age among reef corals.     

Sea anemone with zooxanthellae: simultaneous contraction and expansion in response to changing light intensity

Under increasing intensity of light, the normal tentacles of Lebrunea contract whereas the pseudotentacles expand; in decreasing light the reverse is true. This behavior may be correlated with greater numbers of zooxanthellae in the pseudotentacles. Simultaneous but opposite response of parts suggests adaptations toward photosynthesis by day and predation by night.     

A molecular genetic classification of zooxanthellae and the evolution of animal-algal symbioses

Zooxanthellae are unicellular algae that occur as endosymbionts in many hundreds of marine invertebrate species. Because zooxanthellae have traditionally been difficult to classify, little is known about the natural history of these symbioses. Zooxanthellae were isolated from 131 individuals in 22 host taxa and characterized by the use of restriction fragment length polymorphisms (RFLPs) in nuclear genes that encode small ribosomal subunit RNA (ssRNA). Six algal RFLPs, distributed host species specifically, were detected. Individual hosts contained one algal RFLP. Zooxanthella phylogenetic relationships were estimated from 22 algal ssRNA sequences-one from each host species. Closely related algae were found in dissimilar hosts, suggesting that animal and algal lineages have maintained a flexible evolutionary relation with each other.     

Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals

The development of mass spectrometric techniques for determination of (230)Th abundance has made it possible to reduce analytical errors in (238)U-(234)U-(230)Th dating of corals even with very small samples. Samples of 6 x 10(8) atoms of (230)Th can be measured to an accuracy of +/-3 percent (2sigma) and 3 x 10(10) atoms of (230)Th can be measured to an accuracy of +/-0.2 percent. The time range over which useful age data on corals can be obtained now ranges from about 50 to about 500,000 years. For young corals, this approach may be preferable to (14)C dating. The precision with which the age of a coral can now be determined should make it possible to critically test the Milankovitch hypothesis concerning Pleistocene climate fluctuations. Analyses of a number of corals that grew during the last interglacial period yield ages of 122,000 to 130,000 years. The ages coincide with, or slightly postdate, the summer solar insolation high at 65 degrees N latitude which occurred 128,000 years ago. This supports the idea that changes in Pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth's orbit and rotation axis.     

PALEOCLIMATE: A Causality Problem for Milankovitch

According to the Milankovitch theory, changes in the incident solar radiation, called insolation, in the Northern Hemisphere provide the driving force for global glacial cycles. In their Perspective, Karner and Muller discuss recent studies of corals from around the world that shed doubt on the applicability of the theory to the termination of the penultimate glaciation. The authors argue that a fresh, unbiased look at the data is warranted.     

Chitin in sea anemone shells

Chitin, which is widely distributed among life forms, is well documented in the coelenterate class Hydrozoa and is contained in one member of class Scyphozoa. In class Anthozoa, hard corals synthesize it but soft corals do not. Chitin was identified by infrared spectrophotometry in the trochoid shell of the actinian Stylobates. It constitutes 1.7 percent of the shell by weight, the rest probably being protein. The ability of sea anemones to synthesize chitin is there by confirmed.     

Herbivory in asymbiotic soft corals

A zooxanthellae-free soft coral from the Red Sea feeds almost exclusively on phytoplankton, a mode of nutrition so far unknown for corals. Herbivory was also found in three other azooxanthellate soft corals. In tropical oligotrophic waters, phytoplankton biomass density may be an order of magnitude higher than that of zooplankton. Use of this resource allows these azooxanthellate cnidarians to be highly productive in flow-exposed oligotrophic reef waters.     

One-third of reef-building corals face elevated extinction risk from climate change and local impacts

The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.     

Coral community reproductive patterns: red sea versus the great barrier reef

In contrast to many corals of the Great Barrier Reef, Australia, which are synchronous multispecific spawners, the abundant coral species in the northern Red Sea, Israel, exhibit temporal reproductive isolation. Spawning dates of 12 of the 13 Red Sea species followed lunar periodicity and were consistent throughout 3 years of study. Spawning periods of all species occurred in different seasons, different months, or different lunar phases within the same month. The high abundance of the corals studied at Eilat may be due in part to the advantages gained through not having overlapping spawning periods and settlement times.     

A Cretaceous scleractinian coral with a calcitic skeleton

It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well-preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (about 70 million years ago), has preserved skeletal structural features identical to those observed in present-day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite is primary and did not form from the diagenetic alteration of aragonite. This result implies that corals, like other groups of marine, calcium carbonate-producing organisms, can form skeletons of different carbonate polymorphs.