Phototrophic microendoliths bloom during coral “white syndrome”

Following rapid lesion progression of white syndrome in tabular Acropora spp., the white bare skeleton gradually changes to green, a result of endolithic algae blooms (primarily Ostreobium spp.). Endolithic algal biomass and chlorophyll concentration were found to be an order of magnitude higher in the green zone compared with healthy appearing parts of each colony. Chl b to Chl a ratio increased from 1:1.6 in the healthy area to 1:2 and 1:3.5 in the white exposed skeleton and green zones, respectively. These observations together with pulse amplitude modulated (PAM) fluorometry suggest photoacclimation of the endoliths in the green zone. Histopathological microscopy revealed that the endolithic algal filaments penetrate the coral tissue. This study highlights the interaction of endolithic algae with both the skeleton and host tissue. This may have a critical role in the processes that accompany the post-disease state in reef-building corals.     

Isolation of New <Emphasis Type="Italic">Symbiodinium</Emphasis> Strains from Tridacnid Giant Clam (<Emphasis Type="Italic">Tridacna crocea</Emphasis>) and Sea Slug (<Emphasis Type="Italic">Pteraeolidia ianthina</Emphasis>) Using Culture Medium Containing Giant Clam Tissue Homogenate

Recent molecular biological studies have revealed that some photosymbiotic invertebrates dwelling in coral reefs host several genetically different dinoflagellates, Symbiodinium species, as symbionts. However, little is known about the difference in physiologic characteristics among these symbionts living in a single host, because some Symbiodinium strains are difficult to culture in vitro. To isolate some of these Symbiodinium strains, we have developed an agar culture medium plate containing antibiotics and a giant clam tissue homogenate. Using-this medium we isolated two new Symbiodinium strains from two molluscan hosts, Tridacna crocea and Pteraeolidia ianthina, each of which hosted two different Symbiodinium strains belonging to Symbiodinium C and D, respectively. The tissue homogenate was essential for the growth of Symbiodinium D. Although it was not essential for the growth of Symbiodinium C, it did stimulate the initial growth. For the isolation of some Symbiodinium strains, isolation medium containing host homogenate is effective.     

Photobiology of Symbiodinium revisited: bio-physical and bio-optical signatures

Light is often the most abundant resource within the nutrient-poor waters surrounding coral reefs. Consequently, zooxanthellae (Symbiodinium spp.) must continually photoacclimate to optimise productivity and ensure coral success. In situ coral photobiology is becoming dominated by routine assessments using state-of-the-art non-invasive bio-optical or chlorophyll a fluorescence (bio-physical) techniques. Multiple genetic types of Symbiodinium are now known to exist; however, little focus has been given as to how these types differ in terms of characteristics that are observable using these techniques. Therefore, this investigation aimed to revisit and expand upon a pivotal study by Iglesias-Prieto and Trench (1994) by comparing the photoacclimation characteristics of different Symbiodinium types based on their bio-physical (chlorophyll a fluorescence, reaction centre counts) and bio-optical (optical absorption, pigment concentrations) ‘signatures’. Signatures described here are unique to Symbiodinium type and describe phenotypic responses to set conditions, and hence are not suitable to describe taxonomic structure of in hospite Symbiodinium communities. In this study, eight Symbiodinium types from clades and sub-clades (A–B, F) were grown under two PFDs (Photon Flux Density) and examined. The photoacclimation response by Symbiodinium was highly variable between algal types for all bio-physical and for many bio-optical measurements; however, a general preference to modifying reaction centre content over effective antennae-absorption was observed. Certain bio-optically derived patterns, such as light absorption, were independent of algal type and, when considered per photosystem, were matched by reaction centre stoichiometry. Only by better understanding genotypic and phenotypic variability between Symbiodinium types can future studies account for the relative taxonomic and physiological contribution by Symbiodinium to coral acclimation.     

<Emphasis Type="Italic">Symbiodinium</Emphasis> associations with diseased and healthy scleractinian corals

Despite recent advances in identifying the causative agents of disease in corals and understanding the impact of epizootics on reef communities, little is known regarding the interactions among diseases, corals, and their dinoflagellate endosymbionts (Symbiodinium spp.). Since the genotypes of both corals and their resident Symbiodinium contribute to colony-level phenotypes, such as thermotolerance, symbiont genotypes might also contribute to the resistance or susceptibility of coral colonies to disease. To explore this, Symbiodinium were identified using the internal transcribed spacer-2 region of ribosomal DNA from diseased and healthy tissues within individual coral colonies infected with black band disease (BB), dark spot syndrome (DSS), white plague disease (WP), or yellow blotch disease (YB) in the Florida Keys (USA) and the US Virgin Islands. Most of the diseased colonies sampled contained B1, B5a, or C1 (depending on host species), while apparently healthy colonies of the same coral species frequently hosted these types and/or additional symbiont diversity. No potentially “parasitic” Symbiodinium types, uniquely associated with diseased coral tissue, were detected. Within most individual colonies, the same dominant Symbiodinium type was detected in diseased and visually healthy tissues. These data indicate that specific Symbiodinium types are not correlated with the infected tissues of diseased colonies and that DSS and WP onset do not trigger symbiont shuffling within infected tissues. However, few diseased colonies contained clade D symbionts suggesting a negative correlation between hosting Symbiodinium clade D and disease incidence in scleractinian corals. Understanding the influence of Symbiodinium diversity on colony phenotypes may play a critical role in predicting disease resistance and susceptibility in scleractinian corals.     

The distribution of <Emphasis Type="Italic">Symbiodinium</Emphasis> diversity within individual host foraminifera

While one-to-one specificity between reef-dwelling hosts and symbiotic dinoflagellates of the genus Symbiodinium may occur, detailed examination of some hosts reveals that they contain multiple symbiont types. Individuals of the foraminifer Amphisorus hemprichii living in Papua New Guinea contained mixed communities of Symbiodinium dominated by symbiont types in clades C and F. Moreover, the types showed a distinct pattern in their distribution across the radius of the foraminifer, with clade F Symbiodinium more prevalent in the center of the host cell. The mixed community of symbionts and their pattern of distribution within the foraminifer is likely the result of processes happening both inside the foraminifer and in its external environment. Persistent mixed symbiont communities in foraminifera may be stabilized through benefits conferred by maintaining multiple symbiont lineages for symbiont shuffling. Alternatively they may be stabilized through a heterogeneous internal host environment, partitioning of symbiont functional roles or limitation of symbiont reproduction by the host. Six factors generally determine the presence of any particular symbiont type within a foraminifer: mode of transmission, availability from the environment, recognition by the host, regulation by the host, competition between lineages, and fitness of the holobiont. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Metabolic recovery of the Antarctic liverwort <Emphasis Type="Italic">Cephaloziella varians</Emphasis> during spring snowmelt

We measured the responses of pigments and chlorophyll a fluorescence parameters of the Antarctic leafy liverwort Cephaloziella varians to snowmelt during austral spring 2005 at Rothera Point on the western Antarctic Peninsula. Although no changes to the concentrations of UV-B photoprotective pigments were detected during snowmelt, chlorophyll and carotenoid concentrations and maximum photosystem (PS)II yield (F _v /F _m) were respectively 88, 60 and 144% higher in the tissues of the liverwort that had recently emerged from snow than in those under a 10 cm depth of snow. A laboratory experiment similarly showed that effective PSII yield increased rapidly within the first 45 min after plants sampled from under snow were removed to an illuminated growth cabinet. The pigmentation and PSII yields of plants during snowmelt were also compared with those of plants in January, during the middle of the growing season at Rothera Point. During snowmelt, plants had lower F _v /F _m values, chlorophyll a/b ratios and concentrations of UV-B photoprotective pigments and carotenoids than during mid-season, suggesting that although there is some recovery of PSII activity and increases in concentrations of photosynthetic pigments during snowmelt, the metabolism of C. varians is restricted during this period.     

Zooxanthellae Harvested by Ciliates Associated with Brown Band Syndrome of Corals Remain Photosynthetically Competent

Brown band syndrome is a new coral affliction characterized by a local accumulation of yet-unidentified ciliates migrating as a band along the branches of coral colonies. In the current study, morphologically intact zooxanthellae (= Symbiodinium) were observed in great numbers inside the ciliates (>50 dinoflagellates per ciliate). Microscale oxygen measurements and variable chlorophyll a fluorescence analysis along with microscopic observations demonstrated that zooxanthellae within the ciliates are photosynthetically competent and do not become compromised during the progression of the brown band zone. Zooxanthellae showed similar trends in light acclimation in a comparison of rapid light curve and steady-state light curve measures of variable chlorophyll a fluorescence. Extended light exposure of steady-state light curves resulted in higher quantum yields of photosystem II. The brown band tissue exhibited higher photosynthetically active radiation absorptivity, indicating more efficient light absorption due to a higher density of zooxanthellae in the ciliate-dominated zone. This caused relatively higher gross photosynthesis rates in the zone with zooxanthella-containing ciliates compared to healthy coral tissue. The observation of photosynthetically active intracellular zooxanthellae in the ciliates suggests that the latter can benefit from photosynthates produced by ingested zooxanthellae and from photosynthetic oxygen production that alleviates diffusion limitation of oxic respiration in the densely populated brown band tissue. It remains to be shown whether the zooxanthellae form a stable symbiotic association with the ciliate or are engulfed incidentally during grazing on coral tissue and then maintained as active inside the ciliate for a period before being digested and replaced by new zooxanthellae.     

Juvenile corals can acquire more carbon from high-performance algal symbionts

Algal endosymbionts of the genus Symbiodinium play a key role in the nutrition of reef building corals and strongly affect the thermal tolerance and growth rate of the animal host. This study reports that ¹⁴C photosynthate incorporation into juvenile coral tissues was doubled in Acropora millepora harbouring Symbiodinium C1 compared with juveniles from common parentage harbouring Symbiodinium D in a laboratory experiment. Rapid light curves performed on the same corals revealed that the relative electron transport rate of photosystem II (rETR_MAX) was 87% greater in Symbiodinium C1 than in Symbiodinium D in hospite. The greater relative electron transport through photosystem II of Symbiodinium C1 is positively correlated with increased carbon delivery to the host under the applied experimental conditions (r ² = 0.91). This may translate into a competitive advantage for juveniles harbouring Symbiodinium C1 under certain field conditions, since rapid early growth typically limits mortality. Both symbiont types exhibited severe reductions in ¹⁴C incorporation during a 10-h exposure to the electron transport blocking herbicide diuron (DCMU), confirming the link between electron transport through PSII and photosynthate incorporation within the host tissue. These findings advance the current understanding of symbiotic relationships between corals and their symbionts, providing evidence that enhanced growth rates of juvenile corals may result from greater translocation of photosynthates from Symbiodinium C1. Communicated by Biology Editor Dr. Ruth Gates     

Nucleotide sequence of two cDNAs encoding fucoxanthin chlorophyll a/c proteins in the diatom Odontella sinensis

Two cDNA clones encoding fucoxanthin chlorophyll a/c-binding proteins (FCP) in the diatom Odontella sinensis have been cloned and sequenced. The derived amino acid sequences of both clones are identical, comparison of the corresponding nucleic acids reveals differences only in the third codon position, suggesting a recent gene duplication. The derived proteins are similar to the chlorophyll a/b-binding proteins of higher plants. The presequences for plastid import resemble signal sequences for cotranslational import rather than transit peptides of higher plants. They are very similar to the presequences of FCP proteins in the diatom Phaeodactylum, but different from the presequences of the -subunit of CF₀CF₁ of Odontella and the peridinin chlorophyll a binding proteins (PCP) of the dinoflagellate Symbiodinium.Abbreviations CAB chlorophyll a/b-binding protein - FCP fucoxanthin chlorophyll a/c-binding protein - fcp the respective FCP genes - LHC light-harvesting complex - PCP peridinin chlorophyll a-binding protein - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate     

One-year survey of a single Micronesian reef reveals extraordinarily rich diversity of <Emphasis Type="Italic">Symbiodinium</Emphasis> types in soritid foraminifera

Recent molecular studies of symbiotic dinoflagellates (genus Symbiodinium) from a wide array of invertebrate hosts have revealed exceptional fine-scale symbiont diversity whose distribution among hosts, regions and environments exhibits significant biogeographic, ecological and evolutionary patterns. Here, similar molecular approaches using the internal transcribed spacer-2 (ITS-2) region were applied to investigate cryptic diversity in Symbiodinium inhabiting soritid foraminifera. Approximately 1,000 soritid specimens were collected and examined during a 12-month period over a 40 m depth gradient from a single reef in Guam, Micronesia. Out of 61 ITS-2 types distinguished, 46 were novel. Most types found are specific for soritid hosts, except for three types (C1, C15 and C19) that are common in metazoan hosts. The distribution of these symbionts was compared with the phylotype of their foraminiferal hosts, based on soritid small subunit ribosomal DNA sequences, and three new phylotypes of soritid hosts were identified based on these sequences. Phylogenetic analyses of 645 host-symbiont pairings revealed that most Symbiodinium types associated specifically with a particular foraminiferal host genus or species, and that the genetic diversity of these symbiont types was positively correlated with the genetic diversity found within each of the three host genera. Compared to previous molecular studies of Symbiodinium from other locations worldwide, the diversity reported here is exceptional and suggests that Micronesian coral reefs are home to a remarkably large Symbiodinium assemblage.     

Acquisition of symbiotic dinoflagellates (Symbiodinium) by juveniles of the coral Acropora longicyathus

Scleractinian corals may acquire Symbiodinium from their parents (vertically) or from the environment (horizontally). In the present study, adult colonies of the coral Acropora longicyathus from One Tree Island (OTI) on the southern Great Barrier Reef (Australia) acquired two distinct varieties of symbiotic dinoflagellates (Symbiodinium) from the environment. Adult colonies had either Symbiodinium from clade C (86.7%) or clade A (5.3%), or a mixture of both clades A and C (8.0% of all colonies). In contrast, all 10-day-old juveniles were associated with Symbiodinium from clade A, while 83-day-old colonies contained clades A, C and D even though they were growing at the same location. Symbiodinium from clade A were dominant in both 10- and 83-day-old juveniles (99 and 97% of all recruits, respectively), while clade D was also found in 31% of 83-day-old juveniles. Experimental manipulation also revealed that parental association (with clade A or C), or the location within the OTI reef, did not influence which clade of symbiont was acquired by juvenile corals. The differences between the genetic identity of populations of Symbiodinium resident in juveniles and adult A. longicyathus suggest that ontogenetic changes in the symbiosis may occur during the development of scleractinian corals. Whether or not these changes are due to host selective processes or differences in the physical environment associated with juvenile versus adult colonies remains to be determined.     

Vectored introductions of marine endosymbiotic dinoflagellates into Hawaii

Endosymbiotic dinoflagellates belonging to the genus Symbiodinium associate with a diverse range of marine invertebrate hosts and also exist free-living in the ocean. The genus is divided into eight lineages (clades A–H), which contain multiple subclade types that show geographic and host specificity. It is commonly known that free-living dinoflagellates can and have been introduced to new geographic locations, primarily through shipping ballast water. In this study we sequenced the ITS2 region of Symbiodinium found in symbiosis with the coral Acropora cytherea in the Northwestern Hawaiian Islands Marine National Monument and from shipping ballast water. Identification of an unusual symbiont in Acropora cytherea and an analysis of the distribution of this symbiont suggests an introduction to Hawaii vectored by the scyphozoan host, Cassiopea sp. Symbiodinium were also detected in shipping ballast water. This work confirms that marine invertebrate endosymbionts can be introduced to new geographic locations vectored by animal hosts or the ballast water of ships.     

Developmentally regulated localization of endosymbiotic dinoflagellates in different tissue layers of coral larvae

In adult cnidarians, symbiotic dinoflagellate Symbiodinium are usually located in the gastrodermis. However, the onset of this endosymbiotic association and its regulation during larval development are unclear. This study examined the distribution of the Symbiodinium population in tissue layers of planula larvae released from the stony coral Euphyllia glabrescens. Symbiodinium were redistributed from the epidermis to the gastrodermis, at a rate that was fastest during early planulation and then decreased prior to metamorphosis. This process indicates that the endosymbiotic activity of coral tissues is developmentally regulated. During the early larval stage, both the epidermis and gastrodermis contained Symbiodinium; then, as the larvae developed toward metamorphosis, the numbers in the epidermis gradually diminished until they were only found in the gastrodermis. The mechanism of redistribution remains unknown, but may be due to a direct translocation and/or change in the proliferation of symbionts in different tissue layers.     

Physiological acclimation to elevated temperature in a reef-building coral from an upwelling environment

Recent work has found that pocilloporid corals from regions characterized by unstable temperatures, such as those exposed to periodic upwelling, display a remarkable degree of phenotypic plasticity. In order to understand whether important reef builders from these upwelling reefs remain physiologically uncompromised at temperatures they will experience in the coming decades as a result of global climate change, a long-term elevated temperature experiment was conducted with Pocillopora damicornis specimens collected from Houbihu, a small embayment within Nanwan Bay, southern Taiwan that is characterized by 8–9 °C temperature changes during upwelling events. Upon nine months of exposure to nearly 30 °C, all colony (mortality and surface area), polyp (Symbiodinium density and chlorophyll a content), tissue (total thickness), and molecular (gene expression and molecular composition)-level parameters were documented at similar levels between experimental corals and controls incubated at 26.5 °C, suggesting that this species can readily acclimate to elevated temperatures that cause significant degrees of stress, or even bleaching and mortality, in conspecifics of other regions of the Indo-Pacific. However, the gastrodermal tissue layer was relatively thicker in corals of the high temperature treatment sampled after nine months, possibly as an adaptive response to shade Symbiodinium from the higher photosynthetically active radiation levels that they were experiencing at that sampling time. Such shading may have prevented high light and high temperature-induced photoinhibition, and consequent bleaching, in these samples.     

Intra-colonial response to Acroporid “white syndrome” lesions in tabular Acropora spp. (Scleractinia)

‘White syndrome’ is considered to be the most prevalent coral disease on the Great Barrier Reef, characterised by rapid rates of lesion progression and high levels of colony mortality. This study investigated the production and translocation of photoassimilates towards white syndrome lesions (WSLs) and artificially inflicted lesions in healthy and diseased colonies of tabular Acropora spp. to determine the intra-colonial response to white syndrome using ¹⁴C labelling. Translocation of ¹⁴C labelled photoassimilates was preferentially orientated away from active WSLs, with minimal ¹⁴C activity observed in the lesion borders, whilst artificial lesions (ALs) created directly opposite WSL borders showed significantly higher ¹⁴C activity, suggesting active translocation of photoassimilates for tissue regeneration. Transport of photoassimilates in healthy coral colonies was preferentially oriented towards ALs with a higher perimeter–area ratio, although translocation towards WSL boundaries was minimal even though the lesion perimeter was often the width of the colony (>200 cm). We suggest that the preferential orientation of photoassimilates away from WSLs may represent a deliberate strategy by the colony to induce a ‘shutdown reaction’ in order to preserve intra-colonial resources within areas of the colony that are more likely to survive and recover.     

古林箐秋海棠叶斑结构对叶色的影响

该研究以古林箐秋海棠(Begonia gulinqingensis)为材料,通过分析叶片形态特征、上表皮光学特性、组织结构、叶绿素含量及叶绿素荧光参数(F_v/F_m),探讨了叶片色斑的形成原因。结果表明:(1)古林箐秋海棠叶斑发生频率和数量无明显规律,但发生部位相对稳定,叶斑主要发生在正对叶柄的两条主脉之间。(2)斑区有两种光反射模式,点状反射和多角形反射,栅栏组织细胞呈近等轴的圆形,排列疏松,与上表皮细胞间存在空隙;非斑区只有点状反射模式,栅栏组织细胞为漏斗型,排列紧密,与上表皮细胞间不存在空隙。(3)斑区和非斑区叶绿体均有密集的堆积基粒和丰富的类囊体膜,斑区叶绿素a、b及总叶绿素含量仅比非斑区分别低24.9%、25.2%、25.1%。(4)叶绿素荧光参数(F_v/F_m)值斑区为0.793,非斑区为0.790。虽然斑区叶绿素含量比非斑区略低,但叶绿体结构完整,且叶绿素荧光参数与非斑区无显著差异。斑区上表皮与栅栏组织细胞间的空隙可使光线到达绿色组织时发生二次反射,在叶片表皮细胞边缘形成白色多边形光反射使该区域相对周围正常叶片区域偏白,基于上述结果可推测古林箐秋海棠的淡绿色块斑形成与特殊的叶片结构有关。     

Nucleotide sequence of a cDNA clone encoding the precursor of the peridinin-chlorophyll a-binding protein from the dinoflagellate Symbiodinium sp.

mRNA from the dinoflagellate Symbiodinium sp. isolated from the staghorn coral Acropora formosa was used for the construction of cDNA libraries. A cDNA clone was identified which encoded the precursor of peridinin-chlorophyll a-binding protein (PCP), including a 52 amino acid transit peptide and the 313 amino acid mature protein. The deduced amino acid sequence clearly contains an internal duplication, implying that amongst dinoflagellates the M _r 35 000 form of PCP has arisen by duplication and fusion of genes encoding the M _r 15 000 form. This is the first reported sequence of a dinoflagellate light-harvesting protein. The anatomy of the mature protein and the transit peptide are discussed.Abbreviations PCP peridinin-chlorophyll a-binding protein; cab, chlorophyll a/b-binding protein - LHC light-harvesting complex - FCP fucoxanthin-chlorophyll a/c-binding protein     

Growth and pigment composition in the red alga <Emphasis Type="Italic">Halymenia floresii</Emphasis> cultured under different light qualities

Halymenia floresii is an edible species consumed in some Asian markets. In the Yucatan peninsula coast of Mexico, H. floresii dominates rocky substrata between 3 and 40 m where it grows up to 50 cm high. After analyzing the seasonal pattern of pigment content on H. floresii, we evaluate if and how the spectral composition of light affects growth and pigment dynamics under laboratory cultivation. Unialgal cultures were exposed to white, blue, red and green light in a 3-week experiment. Green light resulted in the highest algal growth rates. Synthesis of chlorophyll a, α-carotene and lutein, but not of β-carotene, was induced by white or green light. Phycocyanin synthesis was stimulated by blue light and phycoerythrin synthesis by blue or red light. Light quality treatments may be used to manipulate pigment composition in Halymenia floresii cultures.     

High genetic differentiation and cross-shelf patterns of genetic diversity among Great Barrier Reef populations of Symbiodinium

The resilience of Symbiodinium harboured by corals is dependent on the genetic diversity and extent of connectivity among reef populations. This study presents genetic analyses of Great Barrier Reef (GBR) populations of clade C Symbiodinium hosted by the alcyonacean coral, Sinularia flexibilis. Allelic variation at four newly developed microsatellite loci demonstrated that Symbiodinium populations are genetically differentiated at all spatial scales from 16 to 1,360 km (pairwise Φ_ST = 0.01–0.47, mean = 0.22); the only exception being two neighbouring populations in the Cairns region separated by 17 km. This indicates that gene flow is restricted for Symbiodinium C hosted by S. flexibilis on the GBR. Patterns of population structure reflect longshore circulation patterns and limited cross-shelf mixing, suggesting that passive transport by currents is the primary mechanism of dispersal in Symbiodinium types that are acquired horizontally. There was no correlation between the genetic structure of Symbiodinium populations and their host S. flexibilis, most likely because different factors affect the dispersal and recruitment of each partner in the symbiosis. The genetic diversity of these Symbiodinium reef populations is on average 1.5 times lower on inshore reefs than on offshore reefs. Lower inshore diversity may reflect the impact of recent bleaching events on Sinularia assemblages, which have been more widespread and severe on inshore reefs, but may also have been shaped by historical sea level fluctuations or recent migration patterns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Communicated by Biology Editor Dr. Ruth Gates.