Despite the ecological significance of the relationship between reef-building corals and intracel... more Despite the ecological significance of the relationship between reef-building corals and intracellular photosynthetic dinoflagellates of the genus Symbiodinium, very little is known about the molecular mechanisms involved in its establishment. Indeed, microarray-based analyses point to the conclusion that host gene expression is largely or completely unresponsive during the establishment of symbiosis with a competent strain of Symbiodinium. In this study, the use of Illumina RNA-Seq technology allowed detection of a transient period of differential expression involving a small number of genes (1073 transcripts; <3% of the transcriptome) 4 h after the exposure of Acropora digitifera planulae to a competent strain of Symbiodinium (a clade B strain). This phenomenon has not previously been detected as a consequence of both the lower sensitivity of the microarray approaches used and the sampling times used. The results indicate that complex changes occur, including transient suppression of mito-chondrial metabolism and protein synthesis, but are also consistent with the hypothesis that the symbiosome is a phagosome that has undergone early arrest, raising the possibility of common mechanisms in the symbiotic interactions of corals and symbiotic sea anemones with their endosymbionts.
Understanding species differences in demographic strategies is a fundamental goal of ecology. In ... more Understanding species differences in demographic strategies is a fundamental goal of ecology. In scleractinian corals, colony morphology is tightly linked with many demographic traits, such as size-specific growth and morality. Here we test how well morphology predicts the colony size-fecundity relationship in eight species of broadcast-spawning corals. Variation in colony fecundity is greater among morphologies than between species with a similar morphology, demonstrating that colony morphology can be used as a quantitative proxy for demographic strategies. Additionally, we examine the relationship between size-specific colony fecundity and mechanical vulnerability (i.e., vulnerability to colony dislodgment). Interestingly, the relationship between size-specific fecundity and mechanical vulnerability varied among morphologies. For tabular species, the most fecund colonies are the most mechanically vulnerable, while the opposite is true for massive species. For corymbose and digitate colonies, mechanical vulnerability remains relatively constant as fecundity increases. These results reveal strong differences in the demographic tradeoffs among species of different morphologies. Using colony morphology as a quantitative proxy for demographic strategies can help predict coral community dynamics and responses to anthropogenic change.
ABSTRACT Despite a recent expansion in the geographic extent of coral reproductive research, ther... more ABSTRACT Despite a recent expansion in the geographic extent of coral reproductive research, there remain many regions in the Indo-Pacific where knowledge is limited. For example, Lord Howe Island is the southernmost reef system in the world (31° S); however, very little is known of the reproductive biology of the coral fauna. Here, aspects of the reproductive biology and the timing of reproduction for 40 of the approximately 65 species that occur on Lord Howe Island are documented. In December 2010, field assessments of the stage of gamete maturity in Acropora spp. colonies suggested that 5 species spawned in December 2010 and 11 in January 2011. In January 2012, similar sampling suggested that 12 Acropora species spawned in January and 1 in February. In addition, 11 species from 10 genera broadcast spawned gametes from 17:30 to 24:00 h in January 2012, 10 to 12 d after full moon. Goniastrea favulus was inferred to spawn prior to 17:00 h, 6 to 12 d after fullmoon and Porites heronensis released brooded larvae. The reproductive biology of 3 other brooding species was examined using dissections and histology monthly for 1 yr from April 2011. Of these, Seriatopora hystrix contained planulae between November 2011 and March 2012, Stylophora pistillata contained planulae between November 2011 and February 2012. No eggs or planulae were observed in Pocillopora damicornis. In conclusion, the spawning patterns on Lord Howe Island are consistent with other locations in the Indo-Pacific: multi-species synchronous spawning episodes occur after full moons, when water temperatures are relatively high.
Many symbiotic marine invertebrates acquire free-living Symbiodinium from the envi- ronment. Abun... more Many symbiotic marine invertebrates acquire free-living Symbiodinium from the envi- ronment. Abundance and diversity of free-living Symbiodinium could influence recovery from bleaching, resilience, and the long-term adaptation of host organisms. Although free-living Symbio- dinium have been detected in the water column and substrates of coral reefs, their diversity and availability to the hosts are poorly understood. Tank experiments were conducted
Journal of Experimental Marine Biology and Ecology, 2013
ABSTRACT We tested the effects of pCO2 on Seriatopora caliendrum recruits over the first 5.3 d of... more ABSTRACT We tested the effects of pCO2 on Seriatopora caliendrum recruits over the first 5.3 d of post-settlement existence. In March 2011, 11–20 larvae were settled in glass vials (3.2 mL) and incubated at 24.0 °C and ~ 250 μmol quanta m− 2 s− 1 while supplied with seawater (at 1.4 mL s− 1) equilibrated with 51.6 Pa pCO2 (ambient) or 86.4 Pa pCO2. At 51.6 Pa pCO2, mean respiration 7 h post-settlement was 0.056 ± 0.007 nmol O2 recruit− 1 min− 1, but rose quickly to 0.095 ± 0.007 nmol O2 recruit− 1 min− 1 at 3.3 d post-settlement, and thereafter declined to 0.075 ± 0.002 nmol O2 recruit− 1 min− 1 at 5.3 d post-settlement (all ± SE). Elevated pCO2 depressed respiration of recruits by 19% after 3.3 d and 12% overall (i.e., integrated over 5.3 d), and while it had no effect on corallite area, elevated pCO2 was associated with weaker adhesion to the glass settlement surface and lower protein biomass. The unique costs of settlement and metamorphosis for S. caliendrum over 5.3 d are estimated to be 257 mJ recruit− 1 at 51.6 Pa pCO2, which is less than the energy content of the larvae and recruits.
Despite the ecological significance of the relationship between reef-building corals and intracel... more Despite the ecological significance of the relationship between reef-building corals and intracellular photosynthetic dinoflagellates of the genus Symbiodinium, very little is known about the molecular mechanisms involved in its establishment. Indeed, microarray-based analyses point to the conclusion that host gene expression is largely or completely unresponsive during the establishment of symbiosis with a competent strain of Symbiodinium. In this study, the use of Illumina RNA-Seq technology allowed detection of a transient period of differential expression involving a small number of genes (1073 transcripts; <3% of the transcriptome) 4 h after the exposure of Acropora digitifera planulae to a competent strain of Symbiodinium (a clade B strain). This phenomenon has not previously been detected as a consequence of both the lower sensitivity of the microarray approaches used and the sampling times used. The results indicate that complex changes occur, including transient suppression of mito-chondrial metabolism and protein synthesis, but are also consistent with the hypothesis that the symbiosome is a phagosome that has undergone early arrest, raising the possibility of common mechanisms in the symbiotic interactions of corals and symbiotic sea anemones with their endosymbionts.
Understanding species differences in demographic strategies is a fundamental goal of ecology. In ... more Understanding species differences in demographic strategies is a fundamental goal of ecology. In scleractinian corals, colony morphology is tightly linked with many demographic traits, such as size-specific growth and morality. Here we test how well morphology predicts the colony size-fecundity relationship in eight species of broadcast-spawning corals. Variation in colony fecundity is greater among morphologies than between species with a similar morphology, demonstrating that colony morphology can be used as a quantitative proxy for demographic strategies. Additionally, we examine the relationship between size-specific colony fecundity and mechanical vulnerability (i.e., vulnerability to colony dislodgment). Interestingly, the relationship between size-specific fecundity and mechanical vulnerability varied among morphologies. For tabular species, the most fecund colonies are the most mechanically vulnerable, while the opposite is true for massive species. For corymbose and digitate colonies, mechanical vulnerability remains relatively constant as fecundity increases. These results reveal strong differences in the demographic tradeoffs among species of different morphologies. Using colony morphology as a quantitative proxy for demographic strategies can help predict coral community dynamics and responses to anthropogenic change.
ABSTRACT Despite a recent expansion in the geographic extent of coral reproductive research, ther... more ABSTRACT Despite a recent expansion in the geographic extent of coral reproductive research, there remain many regions in the Indo-Pacific where knowledge is limited. For example, Lord Howe Island is the southernmost reef system in the world (31° S); however, very little is known of the reproductive biology of the coral fauna. Here, aspects of the reproductive biology and the timing of reproduction for 40 of the approximately 65 species that occur on Lord Howe Island are documented. In December 2010, field assessments of the stage of gamete maturity in Acropora spp. colonies suggested that 5 species spawned in December 2010 and 11 in January 2011. In January 2012, similar sampling suggested that 12 Acropora species spawned in January and 1 in February. In addition, 11 species from 10 genera broadcast spawned gametes from 17:30 to 24:00 h in January 2012, 10 to 12 d after full moon. Goniastrea favulus was inferred to spawn prior to 17:00 h, 6 to 12 d after fullmoon and Porites heronensis released brooded larvae. The reproductive biology of 3 other brooding species was examined using dissections and histology monthly for 1 yr from April 2011. Of these, Seriatopora hystrix contained planulae between November 2011 and March 2012, Stylophora pistillata contained planulae between November 2011 and February 2012. No eggs or planulae were observed in Pocillopora damicornis. In conclusion, the spawning patterns on Lord Howe Island are consistent with other locations in the Indo-Pacific: multi-species synchronous spawning episodes occur after full moons, when water temperatures are relatively high.
Many symbiotic marine invertebrates acquire free-living Symbiodinium from the envi- ronment. Abun... more Many symbiotic marine invertebrates acquire free-living Symbiodinium from the envi- ronment. Abundance and diversity of free-living Symbiodinium could influence recovery from bleaching, resilience, and the long-term adaptation of host organisms. Although free-living Symbio- dinium have been detected in the water column and substrates of coral reefs, their diversity and availability to the hosts are poorly understood. Tank experiments were conducted
Journal of Experimental Marine Biology and Ecology, 2013
ABSTRACT We tested the effects of pCO2 on Seriatopora caliendrum recruits over the first 5.3 d of... more ABSTRACT We tested the effects of pCO2 on Seriatopora caliendrum recruits over the first 5.3 d of post-settlement existence. In March 2011, 11–20 larvae were settled in glass vials (3.2 mL) and incubated at 24.0 °C and ~ 250 μmol quanta m− 2 s− 1 while supplied with seawater (at 1.4 mL s− 1) equilibrated with 51.6 Pa pCO2 (ambient) or 86.4 Pa pCO2. At 51.6 Pa pCO2, mean respiration 7 h post-settlement was 0.056 ± 0.007 nmol O2 recruit− 1 min− 1, but rose quickly to 0.095 ± 0.007 nmol O2 recruit− 1 min− 1 at 3.3 d post-settlement, and thereafter declined to 0.075 ± 0.002 nmol O2 recruit− 1 min− 1 at 5.3 d post-settlement (all ± SE). Elevated pCO2 depressed respiration of recruits by 19% after 3.3 d and 12% overall (i.e., integrated over 5.3 d), and while it had no effect on corallite area, elevated pCO2 was associated with weaker adhesion to the glass settlement surface and lower protein biomass. The unique costs of settlement and metamorphosis for S. caliendrum over 5.3 d are estimated to be 257 mJ recruit− 1 at 51.6 Pa pCO2, which is less than the energy content of the larvae and recruits.
Coral reefs were considered as the product of a mutualistic relationship between the corals and a... more Coral reefs were considered as the product of a mutualistic relationship between the corals and algae of the genus Symbiodinium. However, recent research has demonstrated that corals lives in close associations with large, diverse and specific populationsof other microorganisms collectively referred to as the coral holobiont. Symbiodinium belongs to a group of protists called alveolates and recently it has been established that a number of other related alveolates are also intimately associated with corals including: the newly discovered algal species Chromera. Currently, there is a great deal of interest in Chromera because it is thought to be the missing link between the photosynthetic dinoflagellates and the non-photosynthetic apicomplexans. Interestingly, all the members of the Apicomplexa are, so far, identified as parasitic organisms. Although the literature implies that Chromerais a coral symbiont, this hypothesis has not been rigorously tested; its close relationship to apicomplexans suggests that it might be a facultative parasite. The research project aims to establish the nature of the relationship between Chromera and corals by investigating its impact on coral health/fitness using molecular-based approaches. Gene expression levels will be compared in A.digitiferalarvae exposed to Chromera with larvae exposed to a compatible Symbiodinium strain (as a positive control), using the Illumina RNA seq technology. Stress and immune challenges have distinct transcriptomic signatures, as does the normal Symbiodinium infection process. Hence analysis of the transcriptomic impact of Chromera infection should shed some light on the nature of the association of this organism with coral.
Since the discovery of Chromera velia, a novel microalga in 2008 during a study of Australian cor... more Since the discovery of Chromera velia, a novel microalga in 2008 during a study of Australian coral symbionts, great interest in this new algal species has developed. C. velia is an important organism being considered to sit phylogenetically between the photosynthetic dinoflagellate algae and the parasitic Apicomplexa. C. velia has been detected and isolated from different scleractinian corals in Australia including corals of the Great Barrier Reef. However little is known about the ecology and genetics of this microorganism. The study aims to use next generation sequencing technology (Illumina RNAseq) to generate a reference transcriptome assembly of C. velia isolated from Montipora digitata at the GBR. Differential gene expression in altered experimental treatments is investigating the diversity and dynamics of C. velia transcripts (mRNAs). Cultures were subjected to heat shock, heat stress, cold shock, cold stress, and darkness with control cultures grown under normal conditions, cultures grown under mixotrophic condition and cultures containing motile/immotile stages. Analysis of the transcriptome of C. velia will provide genomic insight into this novel chromerid alga through identifying genes involved in various physiological and metabolic processes as investigated under different experimental conditions.
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