Large-amplitude internal waves sustain coral health during thermal stress

Ocean warming is a major threat for coral reefs causing widespread coral bleaching and mortality. Potential refugia are thus crucial for coral survival. Exposure to large-amplitude internal waves (LAIW) mitigated heat stress and ensured coral survival and recovery during and after an extreme heat anomaly. The physiological status of two common corals, Porites lutea and Pocillopora meandrina, was monitored in host and symbiont traits, in response to LAIW-exposure throughout the unprecedented 2010 heat anomaly in the Andaman Sea. LAIW-exposed corals of both species survived and recovered, while LAIW-sheltered corals suffered partial and total mortality in P. lutea and P. meandrina, respectively. LAIW are ubiquitous in the tropics and potentially generate coral refuge areas. As thermal stress to corals is expected to increase in a warming ocean, the mechanisms linking coral bleaching to ocean dynamics will be crucial to predict coral survival on a warming planet.     

Interseasonal and interspecies diversities of <Emphasis Type="Italic">Symbiodinium</Emphasis> density and effective photochemical efficiency in five dominant reef coral species from Luhuitou fringing reef,northern South China Sea

Although it is well established that different coral species have different susceptibilities to thermal stress, the reasons behind this variation are still unclear. In this study, 384 samples across five dominant coral species were collected seasonally between September 2013 and August 2014 at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea, and their algal symbiont density and effective photochemical efficiency (Φ _PSII) were measured. The results indicated that both the Symbiodinium density and Φ _PSII of corals were subject to significant interspecies and seasonal variations. Stress-tolerant coral species, including massive Porites lutea and plating Pavona decussata, had higher symbiont densities but lower Φ _PSII compared to the vulnerable branching species of Acropora over the course of all four seasons. Seasonally, coral symbiont densities were the lowest during winter, while during the same period, Φ _PSII of corals was at the highest point. Further analysis suggested that dissolved inorganic nutrients and upwelling in the reef area were probably responsible for the observed seasonal variations in symbiont density. The fact that Porites lutea has the lowest Φ _PSII during all four seasons is likely related to their symbionts’ lower capacity to provide required photosynthates for calcification. These results suggest that a coral’s thermal tolerance is primarily and positively dependent on its symbiont density and is less related to its effective photochemical efficiency.     

Contrasting physiological plasticity in response to environmental stress within different cnidarians and their respective symbionts

Given concerns surrounding coral bleaching and ocean acidification, there is renewed interest in characterizing the physiological differences across the multiple host–algal symbiont combinations commonly found on coral reefs. Elevated temperature and CO₂ were used to compare physiological responses within the scleractinian corals Montipora hirsuta (Symbiodinium C15) and Pocillopora damicornis (Symbiodinium D1), as well as the corallimorph (a non-calcifying anthozoan closely related to scleractinians) Discosoma nummiforme (Symbiodinium C3). Several physiological proxies were affected more by temperature than CO₂, including photochemistry, algal number and cellular chlorophyll a. Marked differences in symbiont number, chlorophyll and volume contributed to distinctive patterns of chlorophyll absorption among these animals. In contrast, carbon fixation either did not change or increased under elevated temperature. Also, the rate of photosynthetically fixed carbon translocated to each host did not change, and the percent of carbon translocated to the host increased in the corallimorph. Comparing all data revealed a significant negative correlation between photosynthetic rate and symbiont density that corroborates previous hypotheses about carbon limitation in these symbioses. The ratio of symbiont-normalized photosynthetic rate relative to the rate of symbiont-normalized carbon translocation (P:T) was compared in these organisms as well as the anemone, Exaiptasia pallida hosting Symbiodinium minutum, and revealed a P:T close to unity (D. nummiforme) to a range of 2.0–4.5, with the lowest carbon translocation in the sea anemone. Major differences in the thermal responses across these organisms provide further evidence of a range of acclimation potential and physiological plasticity that highlights the need for continued study of these symbioses across a larger group of host taxa.     

<Emphasis Type="Italic">Euphyllia paradivisa</Emphasis>, a successful mesophotic coral in the northern Gulf of Eilat/Aqaba,Red Sea

Mesophotic coral ecosystems (MCEs) host a thriving community of biota that has remained virtually unexplored. Here we report for the first time on a large population of the endangered coral species Euphyllia paradivisa from the MCEs of the Gulf of Eilat/Aqaba (GOE/A), Red Sea. The mesophotic zone in some parts of the study site harbors a specialized coral community predominantly comprising E. paradivisa (73 % of the total coral cover), distributed from 36 to 72 m depth. Here we sought to elucidate the strict distribution but high abundance of E. paradivisa in the MCEs at the GOE/A. We present 4 yr of observations and experiments that provide insight into the physiological plasticity of E. paradivisa: its low mortality rates at high light intensities, high competitive abilities, successful symbiont adaptation to the shallow-water environment, and tolerance to bleaching conditions or survival during prolonged bleaching. Despite its ability to survive under high irradiance in shallow water, E. paradivisa is not found in the shallow reef of the GOE/A. We suggest several factors that may explain the high abundance and exclusivity of E. paradivisa in the MCE: its heterotrophic capabilities; its high competition abilities; the possibility of it finding a deep-reef refuge there from fish predation; and its concomitant adaptation to this environment.     

Can heterotrophic uptake of dissolved organic carbon and zooplankton mitigate carbon budget deficits in annually bleached corals?

Annual coral bleaching events due to increasing sea surface temperatures are predicted to occur globally by the mid-century and as early as 2025 in the Caribbean, and severely impact coral reefs. We hypothesize that heterotrophic carbon (C) in the form of zooplankton and dissolved organic carbon (DOC) is a significant source of C to bleached corals. Thus, the ability to utilize multiple pools of fixed carbon and/or increase the amount of fixed carbon acquired from one or more pools of fixed carbon (defined here as heterotrophic plasticity) could underlie coral acclimatization and persistence under future ocean-warming scenarios. Here, three species of Caribbean coral—Porites divaricata, P. astreoides, and Orbicella faveolata—were experimentally bleached for 2.5 weeks in two successive years and allowed to recover in the field. Zooplankton feeding was assessed after single and repeat bleaching, while DOC fluxes and the contribution of DOC to the total C budget were determined after single bleaching, 11 months on the reef, and repeat bleaching. Zooplankton was a large C source for P. astreoides, but only following single bleaching. DOC was a source of C for single-bleached corals and accounted for 11–36 % of daily metabolic demand (CHAR_DOC), but represented a net loss of C in repeat-bleached corals. In repeat-bleached corals, DOC loss exacerbated the negative C budgets in all three species. Thus, the capacity for heterotrophic plasticity in corals is compromised under annual bleaching, and heterotrophic uptake of DOC and zooplankton does not mitigate C budget deficits in annually bleached corals. Overall, these findings suggest that some Caribbean corals may be more susceptible to repeat bleaching than to single bleaching due to a lack of heterotrophic plasticity, and coral persistence under increasing bleaching frequency may ultimately depend on other factors such as energy reserves and symbiont shuffling.     

The reproductive biology and early life ecology of a common Caribbean brain coral, <Emphasis Type="Italic">Diploria labyrinthiformis</Emphasis> (Scleractinia: Faviinae)

Despite the fact that most of the severe demographic bottlenecks in coral populations occur during their earliest life stages, information on the reproductive biology and early life history traits of many coral species is limited and often inferred from adult traits only. This study reports on several atypical aspects of the reproductive biology and early life ecology of the grooved brain coral, Diploria labyrinthiformis (Linnaeus, 1758), a conspicuous reef-building species on Caribbean reefs. The timing of gamete release of D. labyrinthiformis was monitored in Curaçao over eight consecutive months, and embryogenesis, planulae behavior, and settlement rates were observed and quantified. We further studied growth and symbiont acquisition in juvenile D. labyrinthiformis for 3.5 yr and compared settler survival under ambient and nutrient-enriched conditions in situ. Notably, D. labyrinthiformis reproduced during daylight hours in six consecutive monthly spawning events between May and September 2013, with a peak in June. This is the largest number of reproductive events per year ever observed in a broadcast-spawning Caribbean coral species. In settlement experiments, D. labyrinthiformis planulae swam to the bottom of culture containers 13 h after spawning and rapidly settled when provided with settlement cues (42% within 14 h). After 5 months, the survival and growth rates of settled juveniles were 3.7 and 1.9 times higher, respectively, for settlers that acquired zooxanthellae within 1 month after settlement, compared to those that acquired symbionts later on. Nutrient enrichment increased settler survival fourfold, but only for settlers that had acquired symbionts within 1 month after settlement. With at least six reproductive events per year, a short planktonic larval phase, high settlement rates, and a positive response to nutrient enrichment, the broadcast-spawning species D. labyrinthiformis displays a range of reproductive and early life-history traits that are more often associated with brooding coral species, illustrating that classical divisions of coral species by reproductive mode alone do not always reflect the true biology and ecology of their earliest life stages.     

Skeletal dissolution kinetics and mechanical tests in response to morphology among coral genera

Ocean acidification is widely accepted as a primary threat to coral reef populations. Negative physiological effects include decreased calcification rates, heightened metabolic energy expenditure, and increased dissolution of coral skeletons. However, studies on the dissolution of coral skeletons structures under ocean acidification conditions and their implications on sediments remain scarce. In this work, we examined skeletal dissolution kinetics from four of the most representative hermatypic corals of the Eastern Pacific coasts (Pocillopora, Porites, Pavona, and Psammocora). Samples were treated with a highly acidic solution for defined periods of time, and measurements of dissolved calcium ([Ca⁺²]) were used to evaluate the kinetics of coral skeleton dissolution. All genera tests except Porites showed a zero reaction rate. Porites exhibited a first-order reaction and a faster reaction rate than other genera. Compression strength tests and skeletal density did not correlate with reaction rate. Pavona showed greater structural strength. Porites were the most susceptible to acidic dissolution compared to other genera tested due to their morphology, i.e., possession of the largest surface area, suggesting a high vulnerability under low-pH conditions. The hierarchical response in dissolution kinetics among coral genera tested suggests that the most soluble coral might act as a buffer under ocean acidification conditions.     

The combined effects of blue light and dilution rate on lipid class and fatty acid composition of <Emphasis Type="Italic">Tisochrysis lutea</Emphasis>

The lipid class and the fatty acid compositions of microalgae highly influence bivalve larval and post-larval development. Light is an essential environmental factor for microalgal culture, and quantity and quality of light may induce changes in the biochemical composition of the algae. The objective of this study was to investigate the effect of light spectrum (blue vs. white light) on lipid class and fatty acid compositions of Tisochrysis lutea cultured in a chemostat. Two different dilution rates (D) were assayed for each light spectrum: 0.2 and 0.7 day^?1. Triacylglycerol (TAG), sterol, and hydrocarbon (HC) content increased sharply at low D. The proportion of alkenones was significantly reduced under blue light. Polyunsaturated fatty acids (PUFA), and particularly n-3 PUFA, content in phospholipids (PL) increased under blue light compared to white light at low D. Thus, blue light raised 22:6(n-3) levels in total lipids of T. lutea at low D. The cultivation of T. lutea in a chemostat at low D under blue light may improve nutritional value as feed for bivalve larvae by modifying the PUFA profile, especially increasing 22:6(n-3).     

Diversity of the Most Commonly Reported Facultative Symbionts in Two Closely-Related Aphids with Different Host Ranges

Richness and abundance of facultative symbionts vary strongly with aphid species and genotype, symbiont strain, host plant, biogeography, and a number of abiotic factors. Despite indications that aphids in the same ecological niche show similar levels of facultative symbiont richness, existing reports do not consider the potential role of host plants on aphid microbial community. Little is known about how oligophagy and polyphagy may be influenced by secondary symbiont distribution, mainly because studies on secondary symbiont diversity are biased towards polyphagous aphids from the Northern Hemisphere. Here, we demonstrate the richness and abundance of the most common aphid-associated facultative symbionts in two tropical aphid species, the oligophagous Aphis (Toxoptera) citricidus (Kirkaldy) (Hemiptera: Aphididae) and the polyphagous Aphis aurantii (Boyer de Fonscolombe) (Hemiptera: Aphididae). Aphis citricidus is restricted to Citrus sp. host plants and closely related genera, whereas A. aurantii successfully exploits a wide variety of host plants from different families. Both were collected in the same ecological niche and our data basically indicated the same richness of secondary symbionts, but the abundance at which secondary symbionts occurred was very distinct between the two species. Spiroplasma was the most abundant facultative symbiont associated with A. citricidus and A. aurantii in the ecological niche studied. Single and multiple secondary symbiont infections were observed, but diversity of multiple infections was particularly high in A. citricidus. We discuss our findings and suggest hypotheses to explain causes and consequences of the differences in secondary symbiont diversity observed between these two aphid species.     

Nutritional symbionts of a putative vector, <Emphasis Type="Italic">Xyleborus bispinatus</Emphasis>, of the laurel wilt pathogen of avocado, <Emphasis Type="Italic">Raffaelea lauricola</Emphasis>

Ambrosia beetles subsist on fungal symbionts that they carry to, and cultivate in, their natal galleries. These symbionts are usually saprobes, but some are phytopathogens. Very few ambrosial symbioses have been studied closely, and little is known about roles that phytopathogenic symbionts play in the life cycles of these beetles. One of the latter symbionts, Raffaelea lauricola, causes laurel wilt of avocado, Persea americana, but its original ambrosia beetle partner, Xyleborus glabratus, plays an uncertain role in this pathosystem. We examined the response of a putative, alternative vector of R. lauricola, Xyleborus bispinatus, to artificial diets of R. lauricola and other ambrosia fungi. Newly eclosed, unfertilized females of X. bispinatus were reared in no-choice assays on one of five different symbionts or no symbiont. Xyleborus bispinatus developed successfully on R. lauricola, R. arxii, R. subalba and R. subfusca, all of which had been previously recovered from field-collected females of X. bispinatus. However, no development was observed in the absence of a symbiont or on another symbiont, Ambrosiella roeperi, recovered from another ambrosia beetle, Xylosandrus crassiusculus. In the no-choice assays, mycangia of foundress females of X. bispinatus harbored significant colony-forming units of, and natal galleries that they produced were colonized with, the respective Raffaelea symbionts; with each of these fungi, reproduction, fecundity and survival of the beetle were positively impacted. However, no fungus was recovered from, and reproduction did not occur on, the A. roeperi and no symbiont diets. These results highlight the flexible nature of the ambrosial symbiosis, which for X. bispinatus includes a fungus with which it has no evolutionary history. Although the “primary” symbiont of the neotropical X. bispinatus is unclear, it is not the Asian R. lauricola.     

Genetic diversity of free-living <Emphasis Type="Italic">Symbiodinium</Emphasis> in the Caribbean: the importance of habitats and seasons

Although reef corals are dependent of the dinoflagellate Symbiodinium, the large majority of corals spawn gametes that do not contain their vital symbiont. This suggests the existence of a pool of Symbiodinium in the environment, of which surprisingly little is known. Reefs around Curaçao (Caribbean) were sampled for free-living Symbiodinium at three time periods (summer 2009, summer 2010, and winter 2010) to characterize different habitats (water column, coral rubble, sediment, the macroalgae Halimeda spp., Dictyota spp., and Lobophora variegata, and the seagrass Thalassia testudinum) that could serve as environmental sources of symbionts for corals. We detected the common clades of Symbiodinium that engage in symbiosis with Caribbean coral hosts A, B, and C using Symbiodinium-specific primers of the hypervariable region of the chloroplast 23S ribosomal DNA gene. We also discovered clade G and, for the first time in the Caribbean, the presence of free-living Symbiodinium clades F and H. Additionally, this study expands the habitat range of free-living Symbiodinium as environmental Symbiodinium was detected in T. testudinum seagrass beds. The patterns of association between free-living Symbiodinium types and habitats were shown to be complex. An interesting, strong association was seen between some clade A sequence types and sediment, suggesting that sediment could be a niche where clade A radiated from a free-living ancestor. Other interesting relationships were seen between sequence types of Symbiodinium clade C with Halimeda spp. and clades B and F with T. testudinium. These relationships highlight the importance of some macroalgae and seagrasses in hosting free-living Symbiodinium. Finally, studies spanning beyond a 1-yr cycle are needed to further expand on our results in order to better understand the variation of Symbiodinium in the environment through time. All together, results presented here showed that the great diversity of free-living Symbiodinium has a dynamic distribution across habitats and time.     

Influence of the coral reef assemblages on the spatial distribution of echinoderms in a gradient of human impacts along the tropical Mexican Pacific

Fourteen species of echinoderms and their relationships to the benthic structure of the coral reefs were assessed at 27 sites—with different levels of human disturbances—along the coast of the Mexican Central Pacific. Diadema mexicanum and Phataria unifascialis were the most abundant species. The spatial variation of the echinoderm assemblages showed that D. mexicanum, Eucidaris thouarsii, P. unifascialis, Centrostephanus coronatus, Toxopneustes roseus, Holothuria fuscocinerea, Cucumaria flamma, and Echinometra vanbrunti accounted for the dissimilarities among the sites. The spatial variation among the sites was mainly explained by the cover of the hard corals (Porites, Pocillopora, Pavona, Psammocora), different macroalgae species (turf, encrusting calcareous algae, articulated calcareous algae, fleshy macroalgae), sponges, bryozoans, rocky, coral rubble, sand, soft corals (hydrocorals and octocorals), Tubastrea coccinea coral, Balanus spp., and water depth. The coverage of Porites, Pavona, and Pocillopora corals, soft coral, rock, and Balanos shows a positive relationship with the sampling sites included within the natural protected area with low human disturbances. Contrary, fleshy macroalgae, sponges, and soft coral show a positive relationship with higher disturbance sites. The results presented here show the importance of protecting the structural heterogeneity of coral reef habitats because it is a significant factor for the distribution of echinoderm species and can contribute to the design of conservation programs for the coral reef ecosystem.     

Obligate gut symbiotic association in the sloe bug <Emphasis Type="Italic">Dolycoris baccarum</Emphasis> (Hemiptera: Pentatomidae)

A number of phytophagous stinkbugs are associated with specific bacterial symbionts in their alimentary tracts. The sloe bug Dolycoris baccarum (Linnaeus), a notorious pest of diverse crops, possesses a number of sac-like tissues, called crypts, in a posterior section of the midgut, wherein a specific bacterial symbiont colonizes. Here we characterized the symbiotic bacterium of D. baccarum by histological analysis, molecular phylogeny, and diagnostic PCR with a specific primer set. The cloning and sequencing analyses of bacterial 16S rRNA genes and fluorescent in situ hybridization demonstrated that the sloe bug is associated with a single species of Gammaproteobacteria in the midgut crypts. Molecular phylogenetic analysis strongly suggested that the symbiont should be placed in the genus Pantoea of the Enterobacteriaceae. Diagnostic PCR and egg surface sterilization with formalin indicated the stinkbug vertically transmits the Pantoea symbiont via egg-smearing. The sterilization-produced aposymbiotic nymphs showed high mortality and no insects reached adulthood. In addition, the Pantoea symbiont was uncultivable outside the insect host, indicating an obligate and intimate host-symbiont association.     

Photosynthetic pigments of phytoperiphyton in the Sylva River (Middle Ural)

The pigment composition of phytoperiphyton algocenoses on stones and macrophytes (Potamogeton lucens L., P. perfoliatus L., P. gramineus L., P. pectinatus L., Mirophyllum spicatum, Petasites hybridus (L.) Gaertn., Mey. et Sxherb, Nuphar lutea L., and Alisma plantago-aquatica L.) in the submontane Sylva River (Middle Ural) is considered based on the surveys of 2000–2012. The wide variability in the content of plant pigments in phytoperiphyton depends on the season and type of substrate. The maximum values similar for all substrates are observed at the end of summer. The concentrations of Chl a increase during warm low-water years. Chlorophyll a prevails among green pigments in periphyton; the relative concentration of other pigments is lower. The concentration of plant carotenoids in epiphyton is slightly higher compared to epilithon and is comparable to the Chl a level. The trophic state index of the Sylva River may be determined as mesotrophic or weakly eutrophic when the Chl a concentration in phytoperiphyton is used as a marker.     

Nucleotide diversity and phylogenetic relationships among <Emphasis Type="Italic">Gladiolus</Emphasis> cultivars and related taxa of family Iridaceae

The plastid genome regions of two intergenic spacers, psbA–trnH and trnL–trnF, were sequenced to study the nucleotide diversity and phylogenetic relationships among Gladiolus cultivars. Nucleotide diversity of psbA–trnH region was higher than trnL–trnF region of chloroplast. We employed Bayesian, maximum parsimony (MP) and neighbour-joining (NJ) approaches for phylogenetic analysis of Gladiolus and related taxa using combined datasets from chloroplast genome. The psbA–trnH and trnL–trnF intergenic spacers of Gladiolus and related taxa-like Babiana, Chasmanthe, Crocus, Iris, Moraea, Sisyrinchium, Sparaxis and two out group species (Hymenocallis littoralis and Asphodeline lutea) were used in the present investigation. Results showed that subfamily Iridoideae have sister lineage with subfamily Ixioideae and Crocoideae. H. littoralis and A. lutea were separately attached at the base of tree as the diverging Iridaceae relative’s lineage. Present study revealed that psbA–trnH region are useful in addressing questions of phylogenetic relationships among the Gladiolus cultivars, as these intergenic spacers are more variable and have more phylogenetically informative sites than the trnL–trnF spacer, and therefore, are suitable for phylogenetic comparison on a lower taxonomic level. Gladiolus cultivars are extensively used as an ornamental crop and showed high potential in floriculture trade. Gladiolus cultivation still needs to generate new cultivars with stable phenotypes. Moreover, one of the most popular methods for generating new cultivars is hybridization. Hence, information on phylogenetic relationships among cultivars could be useful for hybridization programmes for further improvement of the crop.     

Hybridization as a threat in climate relict <Emphasis Type="Italic">Nuphar pumila</Emphasis> (Nymphaeaceae)

Field studies and conceptual work on hybridization-mediated extinction risk in climate relicts are extremely rare. Nuphar pumila (Nymphaeaceae) is one of the most emblematic climate relicts in Europe with few isolated populations in the Alpine arc. The extent of introgression with related lowland and generalist species Nuphar lutea has never been studied using molecular methods. All biogeographical regions where N. pumila naturally occurs in the neighbourhood of the Alpine arc were sampled and studied using nuclear microsatellite markers. Furthermore, we used forward-in-time simulations and Approximate Bayesian Computation to check whether an introgression scenario fits with the observed admixture patterns and estimated the demographic parameters associated with this process. Our study confirms ongoing hybridization between N. pumila and N. lutea and validates it by the use of population models. More than 40 % of investigated N. pumila individuals were admixed and hybrids were found in over 60 % of studied populations. The introgression is bidirectional and is most likely a result of very recent gene flow. Our work provides strong evidence for rapid extinction risk and demographic swamping between specialized climatic relicts and closely related generalists. The remaining pure populations of N. pumila are rare in the Alpine arc and deserve high conservation priority.     

Use of lipids for chemotaxonomy of octocorals (Cnidaria: <Emphasis Type="Italic">Alcyonaria</Emphasis>)

The relationship between taxonomic position and the lipid composition of octocorals from coastal waters of Vietnam was investigated. The principal component analysis of the total fatty acid (FA) composition of 64 coral specimens showed that total FAs are markers at the family level. A good distinction was obtained between antipatarians, gorgonians, and alcyonarians. Azooxanthellate corals of the genus Dendronephthya formed a separate group. The alcyonarian genera Sinularia, Lobophytum, and Sarcophyton were distinguished only by the composition of polyunsaturated FAs. The taxon-specific composition of FAs in octocorals is likely to be determined by differences in the nutrition of food sources, symbiont composition, and the enzymatic activity of FA biosynthesis.     

The distribution of intra-genomically variable dinoflagellate symbionts at Lord Howe Island,Australia

The symbiotic dinoflagellates of corals and other marine invertebrates (Symbiodinium) are essential to the development of shallow-water coral reefs. This genus contains considerable genetic diversity and a corresponding range of physiological and ecological traits. Most genetic variation arises through the accumulation of somatic mutations that arise during asexual reproduction. Yet growing evidence suggests that occasional sexual reproductive events also occur within, and perhaps between, Symbiodinium lineages, further contributing to the pool of genetic variation available for evolutionary adaptation. Intra-genomic variation can therefore arise from both sexual and asexual reproductive processes, making it difficult to discern its underlying causes and consequences. We used quantitative PCR targeting the ITS2 locus to estimate proportions of genetically homogeneous symbionts and intra-genomically variable Symbiodinium (IGV Symbiodinium) in the reef-building coral Pocillopora damicornis at Lord Howe Island, Australia. We then sampled colonies through time and at a variety of spatial scales to find out whether the distribution of these symbionts followed patterns consistent with niche partitioning. Estimated ratios of homogeneous to IGV Symbiodinium varied between colonies within sites (metres to tens of metres) and between sites separated by hundreds to thousands of metres, but remained stable within colonies through time. Symbiont ratios followed a temperature gradient, with the local thermal maximum emerging as a negative predictor for the estimated proportional abundance of IGV Symbiodinium. While this pattern may result from fine-scale spatial population structure, it is consistent with an increased susceptibility to thermal stress, suggesting that the evolutionary processes that generate IGV (such as inter-lineage recombination and the accumulation of somatic mutations at the ITS2 locus) may have important implications for the fitness of the symbiont and that of the coral host.     

<Emphasis Type="Italic">Megaviridae</Emphasis>-like particles associated with <Emphasis Type="Italic">Symbiodinium</Emphasis> spp. from the endemic coral <Emphasis Type="Italic">Mussismilia braziliensis</Emphasis>

Coral reefs are one of the most dynamic and productive marine ecosystems. The coral holobiont consists of the coral animal and a variety of associated microorganisms that include symbiotic dinoflagellates of the genus Symbiodinium, bacteria, archaea, fungi and viruses. The interactions among these components are crucial for coral health and, consequently, to the coral reef resilience to disturbance. Environmental stressors such as elevated temperature, high irradiance and ultraviolet (UV) radiation can lead to the breakdown of the coral-Symbiodinium symbiosis in a phenomenon known as “coral bleaching”. The present study provides evidence for virus-like particles (VLPs) induced in UV-irradiated Symbiodinium spp. cultures (clades A and C) that were isolated from the coral Mussismilia braziliensis, suggesting a latent viral infection in these strains. Scanning and transmission electron microscopy images of the UV stressed cultures revealed the presence of giant (ca. 450 nm) and small (ca. 40 nm) VLPs. Morphological features link the giant VLPs to the family Megaviridae. Symbiodinium spp. Megaviridae giant viruses and other associated viruses may represent dynamic forces driving and influencing health of the coral holobiont.