Production of Dimethyl Sulphide (DMS) by Scleractinian Coral during Aerial Exposure – Effect of Temperature and Light

In this thesis I investigated how rates of DMS production in three Scleractinian corals were affected by both aerial exposure and different light and temperature regimes. Coral specimens were acclimated over a 1 month period prior to data collection. Gas samples were collected from corals both prior to and during emersion in a hermetically sealed vial system and DMS was content measured via gas chromatography. Major differences in DMS production during emersion were observed between species; Acropora inermis production increased significantly upon exposure (from ~20 to ~600 nmol/h/cm2) with Turbinaria reniformis also increasing but to a lesser degree. No significant increase was observed in Porites cylindrica. Prolonged acclimation to low light (~20 µmol photons/m²/s) resulted in a general decrease in DMS production in A. inermis and Turbinaria reniformis compared to control (~200 µmol photons/m²/s). The most dramatic effect was observed in T. reniformis where production was very low and in some cases not detected. The effect of temperature on DMS production was dependent on species and light, with either an increase, decrease or no measurable effect being observed. However the magnitude of this effect was smaller compared to other factors. Although interspecific differences in symbiont density, chlorophyll content and total DMSP were observed, no measurable effect of acclimation to light and temperature was recorded, suggesting that intraspecific differences in DMS production were not driven by changes in Symbiodinium physiology. The results of this study show that coral reefs exposed regularly at low tide can potentially act as significant contributors to the local DMS-flux. However, interspecific differences in response, as well as the effects of environmental factors, make predicting habitat-wide DMS production challenging. Further investigation into the mechanisms behind these responses is warranted to support potential reef-wide shifts in DMS production

Quantifying coral morphology

Funding: John Templeton Foundation (60501), Australian Research Council (FT110100609), Leverhulme Trust.Coral morphology has important implications across scales, from differences in physiology, to the environments they are found, through to their role as ecosystem engineers. However, quantifying morphology across taxa is difficult, and so morphological variation is typically captured via coarse growth form categories (e.g. arborescent and massive). In this study, we develop an approach for quantifying coral morphology by identifying continuous three-dimensional shape variables. To do so, we contrast six variables estimated from 152 laser scans of coral colonies that ranged across seven growth form categories and three orders of magnitude of size. We found that 88% of the variation in shape was captured by two principal components. The main component was variation in volume compactness (cf. convexity), and the second component was a trade-off between surface complexity and top-heaviness. Variation in volume compactness also limited variation along the second axis, where surface complexity and top-heaviness ranged more freely when compactness was low. Traditional growth form categories occupied distinct regions within this morphospace; however, these regions overlapped due to scaling of shape variables with colony size. Nonetheless, with four of the shape variables we were able to predict traditional growth form categories with 70 to 95% accuracy, suggesting that the continuous variables captured most of the qualitative variations implied by these growth forms. Distilling coral morphology into continuous variables that capture shape variation will allow for better tests of the mechanisms that govern coral biology, ecology and ecosystem services such as reef building and provision of habitat.Publisher PDFPeer reviewe

Cumulative effects of cyclones and bleaching on coral cover and species richness at Lizard Island

Funding was provided by the Australian Council Centre of Excellence for Coral Reef Studies (COE140100020) and the John Templeton Foundation (M.D., J.S.M. grant #60501 'Putting the Extended Evolutionary Synthesis to the Test’).Coral reefs are being subjected to an increase in the frequency and intensity of disturbance, such as bleaching and cyclones, and it is important to document the effects of such disturbance on reef coral assemblages. Between March 2014 and May 2017, the reefs of Lizard Island in the northern section of the Great Barrier Reef were affected by 4 consecutive disturbances: severe tropical cyclones Ita and Nathan in 2014 and 2015, and mass bleaching events in 2016 and 2017. Loss of coral cover following the cyclones was patchy and dependent on the direction of the waves generated. In contrast, loss of cover following bleaching was much more uniform. Overall, coral cover declined 5-fold from 36% pre-cyclone Ita to 7% post-bleaching in 2017, while mean species richness dropped from 10 to 4 species per transect. The spatial scale and magnitude of the loss of coral cover in the region suggests that it will be many years before these reefs recover.PostprintPeer reviewe

Contrasting patterns of changes in abundance following a bleaching event between juvenile and adult scleractinian corals

Funding was provided by the Australian Research Council Centre of Excellence for Coral Reef Studies (CE140100020) and the Templeton Foundation (Grant #60501, ‘Putting the Extended Evolutionary Synthesis to the Test’). MD is grateful to the Scottish Funding Council (MASTS, grant reference HR09011) and the European Research Council (grant BioTIME). The study was partially supported by Australian Research Council grants DP1093448 and FT110100609.Coral bleaching events have caused extensive mortality on reefs around the world. Juvenile corals are generally less affected by bleaching than their conspecific adults and therefore have the potential to buffer population declines and seed recovery. Here, we use juvenile and adult abundance data at 20 sites encircling Lizard Island, Great Barrier Reef, before and after the 2016 bleaching event to quantify: (1) correlates of changes in juvenile abundance following a bleaching event; (2) differences in susceptibility to extreme thermal stress between juveniles and adults. Declines in juvenile abundance were lower at sites closer to the 20-m-depth contour and higher for Acropora and Pocillopora juveniles than for other taxa. Juveniles of Acropora and Goniastrea were less susceptible to bleaching than adults, but the opposite was true for Pocillopora spp. and taxa in the family Merulinidae. Our results indicate that the potential of the juvenile life stage to act as a buffer during bleaching events is taxon-dependent.PostprintPeer reviewe

Susceptibility and Response of Human Blood Monocyte Subsets to Primary Dengue Virus Infection

Human blood monocytes play a central role in dengue infections and form the majority of virus infected cells in the blood. Human blood monocytes are heterogeneous and divided into CD16− and CD16+ subsets. Monocyte subsets play distinct roles during disease, but it is not currently known if monocyte subsets differentially contribute to dengue protection and pathogenesis. Here, we compared the susceptibility and response of the human CD16− and CD16+ blood monocyte subsets to primary dengue virus in vitro. We found that both monocyte subsets were equally susceptible to dengue virus (DENV2 NGC), and capable of supporting the initial production of new infective virus particles. Both monocyte subsets produced anti-viral factors, including IFN-α, CXCL10 and TRAIL. However, CD16+ monocytes were the major producers of inflammatory cytokines and chemokines in response to dengue virus, including IL-1β, TNF-α, IL-6, CCL2, 3 and 4. The susceptibility of both monocyte subsets to infection was increased after IL-4 treatment, but this increase was more profound for the CD16+ monocyte subset, particularly at early time points after virus exposure. These findings reveal the differential role that monocyte subsets might play during dengue disease

Disparity between projected geographic ranges of rare species: a case study of Echinomorpha nishihirai (Scleractinia)

Rare and cryptic species can be easily missed during ecological surveys of coral communities. This study reveals a disparity in the reported geographic range of a rare species, Echinomorpha nishihirai, between three different sources; none of which are wholly consistent with the available published occurrence records. Discrepancies in the species ranges reported in two comprehensive online databases are greater for rare, compared with common, coral species, suggesting a need for a more cautious treatment of rare species in biogeographic studies

A decline in bleaching suggests that depth can provide a refuge from global warming in most coral taxa

Coral reefs are under increasing threat from increasing warm temperature stress. Coral bleaching is caused by a combination of heat and light anomalies and therefore fewer corals should bleach in areas where either heat or light anomalies are ameliorated, such as in turbid waters or at depth. Here, we explore the overall response of the coral assemblage and of 16 individual taxa to a thermal anomaly along a depth gradient during the 2016 mass bleaching event at sites on the outer shelf of the northern Great Barrier Reef. Across all taxa, there was a curvilinear decline in the percentage of colonies bleached with depth that was consistent among sites and reflected the attenuation of light in the ocean. The percentage of colonies bleached was also higher on reefs with higher levels of temperature stress. In 10 taxa, including the abundant and ecologically significant Acropora, Pocillopora and Porites, the percentage of colonies bleached declined with depth. In 4 taxa, the percentage of colonies bleached peaked at intermediate depth. In 2 taxa, there was no effect of depth because bleaching was uniformly low. These data suggest that deeper areas of reef can provide a refuge from mass bleaching for many colonies of most taxa

Savviness of prey to introduced predators

The prey naivety hypothesis posits that prey are vulnerable to introduced predators because many generations in slow gradual coevolution are needed for appropriate avoidance responses to develop. It predicts that prey will be more responsive to native than introduced predators and less responsive to introduced predators that differ substantially from native predators and from those newly established. To test these predictions, we conducted a global meta-analysis of studies that measured the wariness responses of small mammals to the scent of sympatric mammalian mesopredators. We identified 26 studies that met our selection criteria. These studies comprised 134 experiments reporting on the responses of 36 small mammal species to the scent of six introduced mesopredators and 12 native mesopredators. For each introduced mesopredator, we measured their phylogenetic and functional distance to local native mesopredators and the number of years sympatric with their prey. We used predator and prey body mass as a measure of predation risk. Globally, small mammals were similarly wary of the scent of native and introduced mesopredators; phylogenetic and functional distance between introduced mesopredators and closest native mesopredators had no effect on wariness; and wariness was unrelated to the number of prey generations, or years, since first contact with introduced mesopredators. Small mammal wariness was associated with predator-prey body mass ratio, regardless of the nativity. The one thing animals do not seem to recognize is whether their predators are native.</p

Coral settlement and recruitment are negatively related to reef fish trait diversity

The process of coral recruitment is crucial to the functioning of coral reef ecosystems and recovery of coral assemblages following disturbances. Fishes can be key mediators of this process by removing benthic competitors like algae, but their foraging impacts are capable of being facilitative or harmful to coral recruits depending on species traits. Reef fish assemblages are highly diverse in foraging strategies, and the relationship between this diversity with coral settlement and recruitment success remains poorly understood. Here, we investigate how foraging trait diversity of reef fish assemblages covaries with coral settlement and recruitment success across multiple sites at Lizard Island, Great Barrier Reef. Using a multi-model inference approach incorporating six metrics of fish assemblage foraging diversity (foraging rates, trait richness, trait evenness, trait divergence, herbivore abundance, and sessile invertivore abundance), we found that herbivore abundance was positively related to both coral settlement and recruitment success. However, the correlation with herbivore abundance was not as strong in comparison with foraging trait diversity metrics. Coral settlement and recruitment exhibited a negative relationship with foraging trait diversity, especially with trait divergence and richness in settlement. Our findings provide further evidence that fish play a role in making benthic habitats more conducive for coral settlement and recruitment. Because of their ability to shape the reef benthos, the variation of fish biodiversity is likely to contribute to spatially uneven patterns of coral recruitment and reef recovery