Books by O. Hoegh-guldberg
Papers by O. Hoegh-guldberg
Journal of Experimental Marine Biology and Ecology, 2012
ABSTRACT This study experimentally investigated the effect of an early summer short-term summer t... more ABSTRACT This study experimentally investigated the effect of an early summer short-term summer thermal anomaly in November on Heron Reef (Great Barrier Reef), on the performance of the coral–algal symbiosis during a subsequent, thermally induced bleaching event (defined by loss of symbionts) in February 2009. Fragments of the reef flat coral, Acropora millepora, exposed to the two heating events lost 78% of their symbionts and showed a 64% decline in dark adapted quantum yield (Fv/Fm) to values less than 0.25. Whereas corals that were only heated in the second event lost 57% symbionts and displayed a 75% decline in Fv/Fm to values less than 0.2. Coral in both pre-stressed and non pre-stressed treatments at 34 °C had net photosynthetic rates significantly less than zero (Pnet max < 0), suggesting that daytime O2 respiration rates were significantly greater than rates of O2 evolution through photosynthesis. Increases in the daily light field and/or increases in temperature led to the observation of dark-adapted xanthophyll de-epoxidation suggesting that the potential for non-photochemical quenching is maintained into the dark (after 1 h dark adaption). Pre-stressed corals were also found to have de-epoxidation ratios three times greater than non pre-stressed corals at 34 °C and xanthophyll pool to Chl a, much greater than non pre-stressed corals. Combined, these results indicate that symbionts in pre-stressed corals have a greater ability to dump incoming light energy as heat. We conclude that whilst differences were observed between pre-stressed and non pre-stressed populations in measurements of photosynthetic productivity, photosynthetic pigments and areal protein, thermal bleaching as defined by symbiont loss did not vary between treatments.
Marine Biology, 2001
The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in ... more The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in KwaZulu-Natal, South Africa, was examined using allozyme electrophoresis. The six separate reefs lie within two dierent reef complexes. Twenty-two enzymes were screened on ®ve buer systems, but only ®ve polymorphic loci (Gpi-1, Gdh-1, Lgg-2, Lpp-1, Est-1) could be consistently resolved. No signi®cant dierences in allelic frequencies were detected among the six sites. All local collections were genotypically diverse, with evidence of only very limited clonal replication at each site. Indeed, the ratio of observed to expected genotypic diversity (mean Go:Ge=0.640.05 SD), the ratio of observed number of genotypes to the number of individuals (mean Ng:N=0.650.04 SE), and deviations from the Hardy± Weinberg equilibrium indicate that sexual reproduction plays a major role in the maintenance of the populations. No genetic dierentiation was found either within (FSR=0.0260.003 SE) or between (FRT=0.000 0.001 SE) reef complexes. The homogeneity of the gene frequencies across the six reefs strongly supports the assumption that the KwaZulu-Natal reef complexes are highly connected by gene¯ow (Nem=44). The reefs in the southern and central reef complexes along the northern Maputaland coastline can therefore be considered part of a single population.
Journal of Experimental Biology, 2009
SUMMARY The larvae of most coral species spend some time in the plankton, floating just below the... more SUMMARY The larvae of most coral species spend some time in the plankton, floating just below the surface and hence exposed to high levels of ultraviolet radiation (UVR). The high levels of UVR are potentially stressful and damaging to DNA and other cellular components, such as proteins, reducing survivorship. Consequently, mechanisms to either shade (prevent) or repair damage potentially play an important role. In this study, the role of photoreactivation in the survival of coral planulae was examined. Photoreactivation is a light-stimulated response to UV-damaged DNA in which photolyase proteins repair damaged DNA. Photoreactivation rates, as well as the localization of photolyase, were explored in planulae under conditions where photoreactivation was or was not inhibited. The results indicate that photoreactivation is the main DNA repair pathway in coral planulae, repairing UV-induced DNA damage swiftly (K=1.75 h–1 and a half-life of repair of 23 min), with no evidence of any lig...
Proceedings of the National Academy of Sciences, 2008
Coral bleaching has been identified as one of the major contributors to coral reef decline, and t... more Coral bleaching has been identified as one of the major contributors to coral reef decline, and the occurrence of different symbionts determined by broad genetic groupings (clades A–H) is commonly used to explain thermal responses of reef-building corals. By using Stylophora pistillata as a model, we monitored individual tagged colonies in situ over a two-year period and show that fine level genetic variability within clade C is correlated to differences in bleaching susceptibility. Based on denaturing gradient gel electrophoresis of the internal transcribed spacer region 2, visual bleaching assessments, symbiont densities, host protein, and pulse amplitude modulated fluorometry, we show that subcladal types C78 and C8/a are more thermally tolerant than C79 and C35/a, which suffered significant bleaching and postbleaching mortality. Although additional symbiont types were detected during bleaching in colonies harboring types C79 and C35/a, all colonies reverted back to their origina...
Proceedings of the National Academy of Sciences, 2008
Ocean acidification represents a key threat to coral reefs by reducing the calcification rate of ... more Ocean acidification represents a key threat to coral reefs by reducing the calcification rate of framework builders. In addition, acidification is likely to affect the relationship between corals and their symbiotic dinoflagellates and the productivity of this association. However, little is known about how acidification impacts on the physiology of reef builders and how acidification interacts with warming. Here, we report on an 8-week study that compared bleaching, productivity, and calcification responses of crustose coralline algae (CCA) and branching ( Acropora ) and massive ( Porites ) coral species in response to acidification and warming. Using a 30-tank experimental system, we manipulated CO 2 levels to simulate doubling and three- to fourfold increases [Intergovernmental Panel on Climate Change (IPCC) projection categories IV and VI] relative to present-day levels under cool and warm scenarios. Results indicated that high CO 2 is a bleaching agent for corals and CCA under ...
PLoS ONE, 2011
Outbreaks of coral disease have increased worldwide over the last few decades. Despite this, rema... more Outbreaks of coral disease have increased worldwide over the last few decades. Despite this, remarkably little is known about the ecology of disease in the Indo-Pacific Region. Here we report the spatiotemporal dynamics of a coral disease termed 'Acroporid white syndrome' observed to affect tabular corals of the genus Acropora on the southern Great Barrier Reef. The syndrome is characterised by rapid tissue loss initiating in the basal margins of colonies, and manifests as a distinct lesion boundary between apparently healthy tissue and exposed white skeleton. Surveys of eight sites around Heron Reef in 2004 revealed a mean prevalence of 8.160.9%, affecting the three common species (Acropora cytherea, A. hyacinthus, A. clathrata) and nine other tabular Acropora spp. While all sizes of colonies were affected, white syndrome disproportionately affected larger colonies of tabular Acroporids (.80 cm). The prevalence of white syndrome was strongly related to the abundance of tabular Acroporids within transects, yet the incidence of the syndrome appears unaffected by proximity to other colonies, suggesting that while white syndrome is density dependant, it does not exhibit a strongly aggregated spatial pattern consistent with previous coral disease outbreaks. Acroporid white syndrome was not transmitted by either direct contact in the field or by mucus in aquaria experiments. Monitoring of affected colonies revealed highly variable rates of tissue loss ranging from 0 to 1146 cm 22 week 21 , amongst the highest documented for a coral disease. Contrary to previous links between temperature and coral disease, rates of tissue loss in affected colonies increased threefold during the winter months. Given the lack of spatial pattern and non-infectious nature of Acroporid white syndrome, further studies are needed to determine causal factors and longer-term implications of disease outbreaks on the Great Barrier Reef.
Journal of Experimental Marine Biology and Ecology, 2008
Thermal stress causes the coral-dinoflagellate symbiosis to disassociate and the coral tissues to... more Thermal stress causes the coral-dinoflagellate symbiosis to disassociate and the coral tissues to whiten. The onset and occurrence of this coral bleaching is primarily defined via the dinoflagellate responses. Here we demonstrate that thermal stress responses occur in the coral host tissues in the days before the onset of coral bleaching. The observed sequence of thermal responses includes reductions in thickness of coral tissue layers and apoptosis of the cells prior to reductions in symbiont density. In the days before the onset of coral bleaching the outer coral tissue layer (epithelium) thickness reduces and apoptosis occurs within the gastrodermis. Two days following this, coinciding with an initial reduction of symbiont density (by approximately 25%), gastrodermal thickness decreased and apoptosis of host cells was identified in the epithelium. This was eventually followed by large reduction in symbiont density (by approximately 50%) consistent with coral bleaching. Both pro-apoptotic and anti-apoptotic genes are identified in the reef building coral Acropora aspera, demonstrating the necessary pathways are present for fine control of host apoptosis. Our study shows that defining periods of host stress based on the responses defined by dinoflagellate symbiont underestimates the importance of early cellular events and the cellular complexity of coral host.
Coral Reefs, 2008
Coral larvae acquire populations of the symbiotic dinoXagellate Symbiodinium from the external en... more Coral larvae acquire populations of the symbiotic dinoXagellate Symbiodinium from the external environment (horizontal acquisition) or inherit their symbionts from the parent colony (maternal or vertical acquisition). The eVect of the symbiont acquisition strategy on Symbiodinium-host associations has not been fully resolved. Previous studies have provided mixed results, probably due to factors such as low sample replication of Symbiodinium from a single coral host, biogeographic diVerences in Symbiodinium diversity, and the presence of some apparently host-speciWc symbiont lineages in coral with either symbiont acquisition strategies. This study set out to assess the eVect of the symbiont acquisition strategy by sampling Symbiodinium from 10 coral species (Wve with a horizontal and Wve with a vertical symbiont acquisition strategy) across two adjacent reefs in the southern Great Barrier Reef. Symbiodinium diversity was assessed using singlestranded conformational polymorphism of partial nuclear large subunit rDNA and denaturing gradient gel electrophoresis of the internal transcribed spacer 2 region. The Symbiodinium population in hosts with a vertical symbiont acquisition strategy partitioned according to coral species, while hosts with a horizontal symbiont acquisition strategy shared a common symbiont type across the two reef environments. Comparative analysis of existing data from the southern Great Barrier Reef found that the majority of corals with a vertical symbiont acquisition strategy associated with distinct species-or genus-speciWc Symbiodinium lineages, but some could also associate with symbiont types that were more commonly found in hosts with a horizontal symbiont acquisition strategy.
Aquatic Biology, 2010
White syndrome (WS) is a collective term for coral diseases that cause acute tissue loss, resulti... more White syndrome (WS) is a collective term for coral diseases that cause acute tissue loss, resulting in apparently healthy tissue bordering on exposed skeleton. In this study, the microenvironmental condition and tissue structure of WS-affected tabular acroporid corals were assessed by O 2 microelectrodes and histological techniques. The high spatial resolution of the microelectrode measurements enabled an evaluation of the extent of physiological changes at, and 2 cm away from, the WS border. Respiration of the coral host was decreased on the skeleton-tissue border but was comparable to that of healthy corals only 2 cm away from the border. Histological data, however, showed a decrease in mesogloea thickness on and 2 cm away from the WS border, which correlates with a previously observed allocation of photoassimilates away from the WS border. We suggest that there are colony-wide negative effects of WS which affect only the host physiology and, as disparate etiologies are evident in WS, these must be distinguished through the utilization of a multiple tool approach.
Pacific Studies Series ( …, 2010
Nature Reviews Microbiology, 2007
The Journal of experimental biology, 1995
Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by th... more Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by the problems of small size and the scarcity of suitable measurement techniques. In this study, coulometric respirometry (a new technique for the study of marine embryos and larvae) was used to explore several issues associated with the rate of energy use during embryonic and larval development of marine invertebrates from three phyla. Coulometric respirometry measures rates of oxygen consumption under normoxic conditions by electrochemically replacing the oxygen consumed by organisms during an experiment. This technique is based on the assumption that all electrons consumed by the anodic reactions result in the production of oxygen. We verify this assumption using direct measurements of oxygen production and show that the technique is sensitive enough (1 nmol O2 h-1) to quantify the oxygen consumption of a single individual swimming freely in a relatively large volume (2 ml). Continuous me...
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Books by O. Hoegh-guldberg
Papers by O. Hoegh-guldberg