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This manuscript was improved by constructive comments from the Responsible Editor and 2 anonymous reviewers. This study was supported by the Endeavour International and JCU Postgraduate Research Scholarship to K.M.Q., the Australian Research Council grant, through the ARC Centre of Excellence for Coral Reef Studies, to B.L.W., and by funding from the Australian Institute of Marine Science to L.K.B.

Black band disease (BBD) is a virulent coral disease, and although its microbiology has been studied extensively, the aetiology of BBD remains poorly understood. Here we used aquaria and field experiments to determine if feeding on BBD lesions by corallivorous fishes influences disease progression rates. Although selective predation on lesions was observed in both controlled laboratory experiments and field-based observations, we found no evidence that fish feeding either reduced or enhanced progression rates of BBD. Variability in disease progression rates in the field was explained by variation among coral colonies (24.46%) and among sample days (37.77%) rather than by predation treatment (

Disease outbreaks are implicated in coral reef degradation worldwide, but little is known about the role of viruses in coral health. In this study, transmission electron microscopy (TEM) was employed in parallel with flow cytometry to compare viral communities associated with visually healthy and white syndrome (WS)-infected tissues of the coral Acropora hyacinthus at Lizard Island on Australia's northern Great Barrier Reef. Viral community shifts were observed on WS-infected corals that were characterized by higher abundance, smaller size and distinct morphology of virus-like particles (VLPs) on disease lesions relative to healthy tissues. Coral tissues displaying WS contained 65% more VLPs, with 87% of these falling in the sub-100 nm size range, compared to only 7% from healthy tissues. While the observed viral community shifts are not necessarily indicative of disease causation, they may provide diagnostic criteria to discriminate between distinct, but macroscopically similar, WS and WS-like coral diseases. Furthermore, these results highlight the need to incorporate virology in investigations of coral health and disease.

The impact of a mass bleaching event on temporal and spatial population genetic struc- ture in 4 scleractinian coral species in the Acropora aspera group was studied around the Palm Islands in the central Great Barrier Reef. Species status of sympatric populations of 2 of the 4 species, A. millepora and A. spathulata, was confirmed by the population genetic data; these species have recently been separated based on morphological and breeding characters. Spatial analyses of popu- lation samples from 2004 detected differences in the level of gene flow among locations. No signifi- cant genetic differentiation was inferred between conspecific populations at Orpheus and Pelorus Islands, which are both located in the northern part of the island group and separated by ~1000 m. In contrast, all populations at Fantome Island were genetically differentiated, despite this island being located only 11 km south. Sampling of A. millepora and A. pulchra in the year prior to the 1998 mass bleaching event enabled a temporal comparison across this event. The genetic composition of these populations changed between 1997 and 2004, but patterns of genetic differentiation among locations were similar in 1997 and 2004. Extensive mortality of these species following the 1998 bleaching event did not cause an apparent reduction in genetic diversity and identical multi-locus genotypes were encountered in both temporal samples, suggesting that re-growth of surviving genotypes con- tributed to the recovery of these populations. Comparisons among the 4 study species revealed lower genetic diversity in A. papillare, consistent with its low abundance throughout its distributional range.

Reef-building corals are threatened by increasing sea surface temperatures resulting from global climate change. Whether corals can adapt to increasing temperatures over the course of generations will depend in part on heritable variation in thermal physiology and dispersal potential, which may serve as the raw material for natural selection. To investigate whether such variation exists in coral populations, and build a framework for identifying the coral-specific genetic factors involved, we performed controlled crosses between 3 genetically distinct colonies of the branching coral Acropora millepora. We compared the families of larvae (which in this species naturally lack symbionts) for several physiological traits, and observed between-family differences in nearly every case. Using larvae cultured at standard and elevated temperatures, we measured the developmental decrease in protein content and the expression of candidate heat response genes. We used an in vivo assay for mitochondrial enzyme activity to evaluate the metabolic response to temperature changes in individual larvae. We also compared the responsiveness of larvae from different families to a nat- ural settlement cue to gain insights into long-range dispersal potential. Partitioning the components of total phenotypic variance confirmed the existence of additive genetic effects for settlement rates and βγ-crystallin expression, while variance in mitochondrial Q10 and the expression of actin and Hsp16 were driven by non-additive effects. The phenotypic variance observed among the small num- ber of families analyzed here suggests the existence of considerable heritable variation in natural coral populations, which supports the possibility of effective adaptive responses to climate change.

The coral holobiont consists of the host and its microbial partners, including the dinoflagellate endosymbiont Symbiodinium and bacteria living both on and within coral tissues. Although genetically different, Symbiodinium types have been shown to differentially affect the physiology of the coral host; their effects on the bacterial partners in the association are unknown. The present study compares profiles of the bacterial communities associated with juvenile corals of Acropora millepora and A. tenuis that had been experimentally infected with 2 different clades of Symbiodinium, Clade C1 and D, to investigate possible interactions between bacterial and Symbiodinium communities. Three culture-independent 16S rRNA gene profiling methods (clone library construction, terminal restriction length polymorphism and denaturing gradient gel electrophoresis) revealed no discernible pattern in bacterial communities on 9 mo old juvenile corals containing different clades of zooxanthellae, suggesting that coral-associated bacteria are not linked to Symbiodinium types in hospite in early ontogeny. In contrast to bacterial profiles of adult corals, bacterial communities associated with juvenile corals were highly variable, indicating that bacterial associates are not conserved in these early stages. When 12 mo old juveniles were sampled again in summer, bacterial communities associated with A. tenuis hosting Clade D Symbiodinium were dominated by sequences affiliating with Vibrio species, indicating that corals harbouring this symbiont may be more susceptible to temperature stress, allowing growth of opportunistic microbial community members possibly detrimental to coral health.

Recovery of degraded reefs is dependent on the settlement of coral larvae into habitats typically dominated by benthic algae, so that benthic algae may play pivotal roles in coral settlement and reef recovery. Here we demonstrate that waterborne influences of macroalgae could affect coral settlement before larvae contact reef substrata and that such effects vary between macroalgae. We tested for waterborne effects of algae on both pre-settlement behaviour and settlement of larvae of the coral Acropora millepora onto live fragments of the crustose coralline alga Hydrolithon reinboldii. Treatments comprised seawater collected from aquaria that had previously contained 1 of 3 macroalgae common on degraded reefs. The foliose brown macroalga, Lobophora variegata, enhanced coral settlement by 40% relative to substratum control treatments. In contrast, the filamentous green macroalga Chlorodesmis fastigiata ('turtle weed'), hindered coral settlement by delaying settlement of larvae, although final settlement was similar to that in control treatments. Padina sp., a foliose brown macroalga closely related to L. variegata, reduced coral settlement by 30% compared with substratum controls. The demonstration of waterborne effects suggests that macroalgae can influence coral settlement before larvae reach reef substrata, even on a crustose coralline alga known to induce settlement, and even where the immediate settlement location is free of macroalgal cover. These results demonstrate the complexity in the mechanisms underlying the effects that over-abundant macroalgal growth may have on reef recovery. These effects have critical implications for the ecological resilience of coral reefs, especially as climate change increases the frequency and severity of disturbances to reefs.

The photosystem II (PSII) herbicide diuron is commonly used within catchments that drain into the Great Barrier Reef lagoon, where it potentially reduces photosynthesis in Symbiodinium, the dinoflagellate symbiont associated with reef corals. Here we examine the importance of energy (carbohydrates) derived from photosynthesis to the gametogenesis of corals following long-term, experimental exposures to diuron. Two broadcast spawning corals, Acropora tenuis and A. valida, and a brooding coral, Pocillopora damicornis, were exposed to 0 (controls), 1.0 (low) and 10 (moderate) µg l–1 diuron treatments for 2 to 3 mo prior to spawning or planulation. Diuron caused photoinhibition in each species, with pulse amplitude modulation (PAM) fluorometery recording consistent declines in effective quantum yields of 20% at 1.0 µg l–1 and 75% at 10 µg l–1 diuron compared to control corals. A. valida and P. damicornis were both sensitive to chronic diuron-induced photoinhibition, becoming severely bleached (loss of Symbiodinium spp. and/or reductions in light-harvesting pigments), especially at 10 µg l–1 diuron. At this moderate concentration, A. valida sustained both partial and full colony mortality. A. tenuis was more resistant to these concentrations of diuron, and neither bleached nor sustained partial mortality in any of the treatments. We found 2.5- to 5-fold reductions in total lipid content (coral tissue, oocytes and planulae) for the 3 species in the presence of diuron, indicating significant use of storage lipid to meet nutritional demands under conditions of chronic photoinhibition. Polyp fecundity was reduced by 6-fold in A. valida and both A. valida and P. damicornis were unable to spawn or planulate following long-term exposures to 10 µg l–1 diuron. This is the first study to investigate the sub-lethal effects of chronic herbicide-induced photoinhibition on symbiotic corals and provides evidence of a link between reduced energy acquisition due to PSII photoinhibition and reduced reproductive output in zooxanthellate corals.