River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons

Inshore massive corals often display bright luminescent lines that have been linked to river flood plumes into coastal catchments and hence have the potential to provide a long-term record of hinterland precipitation. Coral luminescence is thought to result from the incorporation of soil-derived humic acids transported to the reef during major flood events. Corals far from terrestrial sources generally only exhibit dull relatively broad luminescence bands, which are attributed to seasonal changes in coral density. We therefore tested the hypothesis that spectral ratios rather than conventional luminescence intensity provide a quantitative proxy record of river runoff without the confounding effects of seasonal density changes. For this purpose, we have developed a new, rapid spectral luminescence scanning (SLS) technique that splits emission intensities into red, green and blue domains (RGB) for entire cores with an unprecedented linear resolution of 71.4 μm. Since humic acids have longer emission wavelength than the coral aragonite, normalisation of spectral emissions should yield a sensitive optical humic acid/aragonite ratio for humic acid runoff, i.e., G/B ratio. Indeed, G/B ratios rather than intensities are well correlated with Ba/Ca, a geochemical coral proxy for sediment runoff, and with rainfall data, as exemplified for coral records from Madagascar. Coral cores also display recent declining trends in luminescence intensity, which are also reported in corals elsewhere. Such trends appear to be associated with a modern decline in skeletal densities. By contrast, G/B spectral ratios not only mark the impact of individual cyclones but also imply that humic acid runoff increased in Madagascar over the past few decades while coral skeletal densities decreased. Consequently, the SLS technique deconvolves the long-term interplay between humic acid incorporation and coral density that have confounded earlier attempts to use luminescence intensities as a proxy for river runoff.     

Measurement of luminescence in coral skeletons

Luminescent lines in skeletons of the massive coral Porites record periods when seawater was significantly diluted by land runoff. Records developed from such lines would be useful in a wide range of areas, including climatology, oceanography, civil engineering, agriculture, water resources and reef management. To realise this enormous potential, we built an instrument for routine, reliable recovery of luminescence information from coral skeletons. Skeletal slices were laid on a table that moved in 0.25 mm steps. The coral skeleton was illuminated with ultra-violet light (UV) at 390 nm and luminescent emissions at 490 nm were recorded. Light at 490 nm was then shone on the same 2 mm diameter point on the skeleton and the reflection of 490 nm light was recorded. Luminescent emissions from a point were then standardised by the reflectivity of that same point.Slices cut from three corals that grew at an inshore reef had many strong luminescent lines. Measurements of luminescence in these colonies were nearly identical, both for multiple tracks across one slice and for tracks across slices from the different corals. There was a clear link with discharge from a nearby river. Slices cut from two corals that grew at a reef 56 km offshore had occasional, weak luminescent lines that were also linked with river discharge. Tracks across these slices were similar but the weak luminescence due to river discharge was partially obscured by weak luminescence associated with the annual density banding pattern that characterises massive coral skeletons. The technique recovered excellent information about skeletal luminescence. However, there is a need to gain better understanding of the link between seawater dilution and luminescence and to develop procedures for data processing before the technique can be used to construct useful proxy environmental records.     

Investigation of luminescent banding in solid coral: the contribution of phosphorescence

This study investigates the nature and components of annual luminescent banding in massive Porites coral skeletons, with a view to refining the technique for using this banding to reconstruct past environmental conditions. Three-dimensional excitation-emission-matrix spectroscopy and optical fibre beam delivery have been used to investigate the luminescence properties of the bright and dull bands of solid coral. Six characteristic excitation/emission peaks have been identified: 280/450–600, 340/450, 370/470, 390/485, 420/505 and 450/530 nm. The first peak corresponds to protein-type fluorescence. The others are characteristic of humic acid luminescence. The difference in luminescence intensity between bright and dull bands has been quantified and characterised spectroscopically. The luminescence of the bright bands is up to 25% more intense than their neighbouring dull bands with the greatest increase in relative intensity in the long wavelength emission region, between 500 and 600 nm. The contribution of long-lived phosphorescence to the total luminescence intensity has been determined by time-resolved measurements on the 100 ms timescale. Both bright and dull bands show long-lived phosphorescence with decay times up to 1.5 s. This phosphorescence accounts for about 10% of the total luminescence intensity of bright bands. The difference in phosphorescence intensity between bright and dull bands is substantially greater than the difference in total luminescence intensity: the phosphorescence of bright bands is up to twice as intense as that of dull bands. This suggests that phosphorescence plays an important role in defining luminescent banding in coral. Furthermore, the large observable difference in phosphorescence between bright and dull bands indicates that measurement of phosphorescence profiles across growth bands in corals may prove to be a more sensitive indicator of past environmental conditions than measurements of total luminescence. Received: 18 March 1999 / Accepted: 20 December 1999     

Coral Luminescence Identifies the Pacific Decadal Oscillation as a Primary Driver of River Runoff Variability Impacting the Southern Great Barrier Reef

The Pacific Decadal Oscillation (PDO) is a large-scale climatic phenomenon modulating ocean-atmosphere variability on decadal time scales. While precipitation and river flow variability in the Great Barrier Reef (GBR) catchments are sensitive to PDO phases, the extent to which the PDO influences coral reefs is poorly understood. Here, six Porites coral cores were used to produce a composite record of coral luminescence variability (runoff proxy) and identify drivers of terrestrial influence on the Keppel reefs, southern GBR. We found that coral skeletal luminescence effectively captured seasonal, inter-annual and decadal variability of river discharge and rainfall from the Fitzroy River catchment. Most importantly, although the influence of El Niño-Southern Oscillation (ENSO) events was evident in the luminescence records, the variability in the coral luminescence composite record was significantly explained by the PDO. Negative luminescence anomalies (reduced runoff) were associated with El Niño years during positive PDO phases while positive luminescence anomalies (increased runoff) coincided with strong/moderate La Niña years during negative PDO phases. This study provides clear evidence that not only ENSO but also the PDO have significantly affected runoff regimes at the Keppel reefs for at least a century, and suggests that upcoming hydrological disturbances and ecological responses in the southern GBR region will be mediated by the future evolution of these sources of climate variability.     

On the nature and causes of luminescent lines and bands in coral skeletons

Holes pushed into the surface of laboratory grade CaCO₃ powder reproduced visible and measurable luminescence similar to that seen and measured in coral skeletons. Heating such powder to 450 °C for 2 h did not destroy the luminescence although it did destroy luminescence in powdered coral skeleton. The effect in coral skeletal powder was probably due to carbonisation of contained organics because addition of small and increasing amounts of powdered charcoal to laboratory grade CaCO₃ increasingly attenuated luminescence. Luminescent lines and bands in coral skeletons have previously been ascribed to incorporation of humic substances. However, coating laboratory grade powder with humic acid attenuates rather than enhances luminescence. Ultra-violet lamps used to display coral luminescent lines and bands emit significant amounts of violet and blue visible light. Reflection of these visible wavelengths from the surface of laboratory grade CaCO₃ powder obscured luminescence of the powder. Multiple reflections within a hole in the powder resulted in absorption of the short wavelengths of visible light, including violet and blue light that would otherwise mask luminescence, and their re-emission at longer wavelengths. Luminescent bands in offshore corals were associated with the low-density regions of the annual density banding pattern. Luminescent lines in skeletons of inshore corals were in narrow regions of low-density skeleton, probably resulting from altered growth during periods of lowered salinity. Accepted: 20 April 2000     

Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef

Coral core records, combined with measurements of coral community structure, were used to assess the long-term impact of multiple environmental stressors on reef assemblages along an environmental gradient. Multiple proxies (luminescent lines, Ba/Ca, δ¹⁵N) that reflect different environmental conditions (freshwater discharge, sediment delivery to the nearshore, nutrient availability and transformations) were measured in Porites coral cores collected from nearshore reefs at increasing distance from the intensively agricultural region of Mackay (Queensland, Australia). The corals provide a record (1968–2002) of the frequency and intensity of exposure to terrestrial runoff and fertilizer-derived nitrogen and were used to assess how the present-day coral community composition may have been influenced by flood-related disturbance. Reefs closest to the mainland (5–32 km offshore) were characterized by low hard coral cover (≤10%), with no significant differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 μmol mol⁻¹; mean ± SD) in the most inshore corals (Round Top Island; 5 km offshore) indicated chronic, sub-annual exposure to freshwater and resuspended terrestrial sediment that may have historically prevented reef formation. By contrast, corals from Keswick Island (32 km offshore) indicated episodic, high-magnitude exposure to Pioneer River discharge during extreme flood events (e.g., 1974, 1991), with strongly luminescent lines and substantially enriched coral skeletal δ¹⁵N (12–14‰). The reef assemblages at Keswick and St. Bees islands were categorically different from all other locations, with high fleshy macroalgal cover (80.1 ± 7.2% and 62.7 ± 7.1%, respective mean ± SE) overgrowing dead reef matrix. Coral records from Scawfell Island (51 km offshore) indicated little exposure to Pioneer catchment influence: all locations from Scawfell and further offshore had total hard and soft coral cover comparable to largely undisturbed nearshore to middle shelf reefs of the southern Great Barrier Reef.     

Coral community responses to declining water quality: Whitsunday Islands,Great Barrier Reef,Australia

A five-year period (2002–2006) of below-median rainfall followed by a six-year period (2007–2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll-a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February–April), while TSS was elevated for four months, extending into the dry season (March–June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes.     

Historical mortality in massive<Emphasis Type="Italic"> Porites</Emphasis> from the central Great Barrier Reef,Australia: evidence for past environmental stress?

>Two hiatuses in coral skeleton growth, associated tissue death and subsequent regrowth, were discovered while dating eight multi-century Porites coral cores collected from the central Great Barrier Reef (GBR), Australia. Cross-dating of characteristic annual luminescent lines visible in the coral core slices under UV-light (Hendy et al. 2003) accurately dated the two events to 1782–85 and 1817 a.d.. Die-off scars were observed in only one core for each event. X-radiographs and photographs taken under UV-light show the pattern of regrowth and the period taken by the coral to recover. Bioerosion, predominately by boring sponges ( Cliona spp.), of the exposed coral surface following the 1782–85 event caused a hiatus of up to 14 years' growth, with the coral taking 7–8 years to reclaim the whole surface contained within the 9-cm-diameter core. Contemporary historical and proxy-climate records indicate that El Niño climatic conditions occurred at the time of both growth discontinuities. Intense luminescence observed in corals growing continuously during the 1817 event suggests that low salinity from river runoff was a contributing factor, analogous environmental conditions to those that were associated with the 1998 bleaching event in the GBR.     

Satellite‐derived estimates of forest leaf area index in southwest Western Australia are not tightly coupled to interannual variations in rainfall: implications for groundwater decline in a drying climate

There is increasing concern that widespread forest decline could occur in regions of the world where droughts are predicted to increase in frequency and severity as a result of climate change. The average annual leaf area index (LAI) is an indicator of canopy cover and the difference between the annual maximum and minimum LAI is an indicator of annual leaf turnover. In this study, we analyzed satellite‐derived estimates of monthly LAI across forested coastal catchments of southwest Western Australia over a 12 year period (2000–2011) that included the driest year on record for the last 60 years. We observed that over the 12 year study period, the spatial pattern of average annual satellite‐derived LAI values was linearly related to mean annual rainfall. However, interannual changes to LAI in response to changes in annual rainfall were far less than expected from the long‐term LAI‐rainfall trend. This buffered response was investigated using a physiological growth model and attributed to availability of deep soil moisture and/or groundwater storage. The maintenance of high LAIs may be linked to a long‐term decline in areal average underground water storage and diminished summer flows, with an emerging trend toward more ephemeral flow regimes.     

Environmental Records from Great Barrier Reef Corals: Inshore versus Offshore Drivers

The biogenic structures of stationary organisms can be effective recorders of environmental fluctuations. These proxy records of environmental change are preserved as geochemical signals in the carbonate skeletons of scleractinian corals and are useful for reconstructions of temporal and spatial fluctuations in the physical and chemical environments of coral reef ecosystems, including The Great Barrier Reef (GBR). We compared multi-year monitoring of water temperature and dissolved elements with analyses of chemical proxies recorded in Porites coral skeletons to identify the divergent mechanisms driving environmental variation at inshore versus offshore reefs. At inshore reefs, water Ba/Ca increased with the onset of monsoonal rains each year, indicating a dominant control of flooding on inshore ambient chemistry. Inshore multi-decadal records of coral Ba/Ca were also highly periodic in response to flood-driven pulses of terrigenous material. In contrast, an offshore reef at the edge of the continental shelf was subject to annual upwelling of waters that were presumed to be richer in Ba during summer months. Regular pulses of deep cold water were delivered to the reef as indicated by in situ temperature loggers and coral Ba/Ca. Our results indicate that although much of the GBR is subject to periodic environmental fluctuations, the mechanisms driving variation depend on proximity to the coast. Inshore reefs are primarily influenced by variable freshwater delivery and terrigenous erosion of catchments, while offshore reefs are dominated by seasonal and inter-annual variations in oceanographic conditions that influence the propensity for upwelling. The careful choice of sites can help distinguish between the various factors that promote Ba uptake in corals and therefore increase the utility of corals as monitors of spatial and temporal variation in environmental conditions.     

Coral skeletons: storage and recovery of environmental information

Understanding the nature and causes of past global change is a key to understanding what may happen in the future. The discovery, nearly 25 years ago, of annual density bands in skeletons of long-lived, massive corals promised high-resolution proxy climate records for tropical oceans. The tropics are regions of major importance to the global climate system and they are poorly represented by high-resolution proxy climate records such as tree rings, ice cores and historical documents. In this review we examine the principles and procedures underlying routine recovery and interpretation of information from proxy environmental recorders. We summarize an extensive literature which indicates that coral skeletons are excellent archives for considerable and diverse environmental information. We show that this potential has not been fully realized, largely because corals seemed to yield inconsistent, sometimes conflicting, information. We discuss ways in which much of this confusion is resolved by new understanding of coral skeletal growth mechanisms. We also examine several records which indicate that corals can meet requirements for reconstruction of useful, reliable environmental information.     

Fluorescent and skeletal density banding in Porites lutea from Papua New Guinea and Indonesia

Shallow water Porites lutea corals were collected along two transects normal to mainland shorelines, parallel to gradients in water quality: one, 7 km long, near Motupore Island in South Papua New Guinea, the other, 70 km long, from Jakarta Bay along the Pulau Seribu chain in the Java Sea. The corals were slabbed and studies were made of skeletal density bands as revealed by X-ray photography and fluorescent bands as revealed by ultraviolet light. Water quality measurements and rain-fall data were assembled for the two areas and related to skeletal banding patterns. For both areas, with increasing distance form mainland there is a decrease in overall brightness of fluorescence in corals and an increase in the contrast between bright and dull fluorescent bands. Fluorescence is bright, but seasonal banding is obscure in corals within about 2 km of stream mouths at Motopure and about 5 km of the coast in Jakarta Bay; this suggests that, despite low freshwater run-off during dry seasons, there are sufficient organic compounds which cause fluorescence in coral skeletons, to swamp seasonal effects. During the wet seasons, deluges of freshwater consequent on mainland rainfall of greater than about 150 mm/ month extend at least 7 km offshore in the Motupore area and perhaps tens of kilometres into Java Sea, giving distinctive bright and dull fluorescent banding in off-shore corals. The fluorescent banding pattern within corals on the Motupore reefs is similar in most corals along the transect and it correlates well with the Port Moresby monthly rainfall data. This relationship suggests that the same body (or bodies) of freshwater affect all reefs of the area during the wet season. The fluorescent banding in Java Sea corals does not show a precise correlation with either mainland or island monthly rainfall data; indeed the pattern of fluorescent banding on Pulau Seribu can only be matched in corals from reefs less than about 25 km apart. This suggests that in this area discrete water bodies carrying the relevant organic acids for coral fluorescence affect the fringing reefs on the chain of islands. Comparisons of fluorescent and density banding have revealed that for these areas, in general, periods of high freshwater run-off are times of deposition of less dense skeleton in Porites lutea corals.     

Modelling the acclimation capacity of coral reefs to a warming ocean

The symbiotic relationship between corals and photosynthetic algae is the foundation of coral reef ecosystems. This relationship breaks down, leading to coral death, when sea temperature exceeds the thermal tolerance of the coral-algae complex. While acclimation via phenotypic plasticity at the organismal level is an important mechanism for corals to cope with global warming, community-based shifts in response to acclimating capacities may give valuable indications about the future of corals at a regional scale. Reliable regional-scale predictions, however, are hampered by uncertainties on the speed with which coral communities will be able to acclimate. Here we present a trait-based, acclimation dynamics model, which we use in combination with observational data, to provide a first, crude estimate of the speed of coral acclimation at the community level and to investigate the effects of different global warming scenarios on three iconic reef ecosystems of the tropics: Great Barrier Reef, South East Asia, and Caribbean. The model predicts that coral acclimation may confer some level of protection by delaying the decline of some reefs such as the Great Barrier Reef. However, the current rates of acclimation will not be sufficient to rescue corals from global warming. Based on our estimates of coral acclimation capacities, the model results suggest substantial declines in coral abundances in all three regions, ranging from 12% to 55%, depending on the region and on the climate change scenario considered. Our results highlight the importance and urgency of precise assessments and quantitative estimates, for example through laboratory experiments, of the natural acclimation capacity of corals and of the speed with which corals may be able to acclimate to global warming.     

Implications of climate change for potamodromous fishes

There is little understanding of how climate change will impact potamodromous freshwater fishes. Since the mid 1970s, a decline in annual rainfall in south‐western Australia (a globally recognized biodiversity hotspot) has resulted in the rivers of the region undergoing severe reductions in surface flows (ca. 50%). There is universal agreement amongst Global Climate Models that rainfall will continue to decline in this region. Limited data are available on the movement patterns of the endemic freshwater fishes of south‐western Australia or on the relationship between their life histories and hydrology. We used this region as a model to determine how dramatic hydrological change may impact potamodromous freshwater fishes. Migration patterns of fishes in the largest river in south‐western Australia were quantified over a 4 year period and were related to a number of key environmental variables including discharge, temperature, pH, conductivity and dissolved oxygen. Most of the endemic freshwater fishes were potamodromous, displaying lateral seasonal spawning migrations from the main channel into tributaries, and there were significant temporal differences in movement patterns between species. Using a model averaging approach, amount of discharge was clearly the best predictor of upstream and downstream movement for most species. Given past and projected reductions in surface flow and groundwater, the findings have major implications for future recruitment rates and population viabilities of potamodromous fishes. Freshwater ecosystems in drying climatic regions can only be managed effectively if such hydro‐ecological relationships are considered. Proactive management and addressing existing anthropogenic stressors on aquatic ecosystems associated with the development of surface and groundwater resources and land use is required to increase the resistance and resilience of potamodromous fishes to ongoing flow reductions.     

Effects of past and projected river discharge variability on freshwater production in an anadromous fish

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On the nature and causes of luminescent lines and bands in coral skeletons: II. Contribution of skeletal crystals

Slices cut from skeletons of massive Porites display two types of luminescence when illuminated by ultra-violet (UV) light: (1) faint luminescent banding associated with the annual skeletal density banding pattern and (2) narrow lines of strong luminescence associated with monsoonal runoff of fresh water from nearby land. Barnes and Taylor [Barnes, D.J. Taylor, R.B. 2001a. On the nature and causes of luminescent lines and bands in coral skeletons. Coral Reefs 19, 221-230] showed how larger skeletal holes could give rise to increased luminescence—thus accounting for the link between skeletal density banding and faint luminescent banding. Work described here tests the notion that strongly luminescent lines are also regions of lower skeletal density. Experiments involving real and artificial coral skeletons indicated that likely changes in hole size in real skeletons cannot account for the amount of luminescence associated with luminescent lines. Larger particles (< 50 μm) of powdered skeleton from cut from luminescent lines were more luminescent than similar particles cut from adjacent less luminescent skeleton. However, very small particles (< 3 μm) from the two regions of skeleton showed no difference in luminescence. Since skeletal crystals would have been largely destroyed by powdering skeleton to very small particle sizes, most of the luminescence of strongly luminescent lines is probably associated with changed crystal size and packing, with changed crystal chemistry, or with a combination of these possibilities.     

Coral reproduction in the world��s warmest reefs: southern Persian Gulf (Dubai, United Arab Emirates)

Despite extensive research on coral reproduction from numerous geographic locations, there remains limited knowledge within the Persian Gulf. Given that corals in the Persian Gulf exist in one of the most stressful environments for reef corals, with annual variations in sea surface temperature (SST) of 12°C and maximum summer mean SSTs of 36°C, understanding coral reproductive biology in the Gulf may provide clues as to how corals may cope with global warming. In this study, we examined six locally common coral species on two shallow reef sites in Dubai, United Arab Emirates (UAE), in 2008 and 2009 to investigate the patterns of reproduction, in particular the timing and synchrony of spawning. In total, 71% colonies in April 2008 and 63% colonies in April 2009 contained mature oocytes. However, the presence of mature gametes in May indicated that spawning was potentially split between April and May in all species. These results demonstrate that coral reproduction patterns within this region are highly seasonal and that multi-species spawning synchrony is highly probable. Acropora downingi, Cyphastrea microphthalma and Platygyra daedalea were all hermaphroditic broadcast spawners with a single annual gametogenic cycle. Furthermore, fecundity and mature oocyte sizes were comparable to those in other regions. We conclude that the reproductive biology of corals in the southern Persian Gulf is similar to other regions, indicating that these species have adapted to the extreme environmental conditions in the southern Persian Gulf.     

The cumulative impact of annual coral bleaching can turn some coral species winners into losers

Mass coral bleaching events caused by elevated seawater temperatures result in extensive coral loss throughout the tropics, and are projected to increase in frequency and severity. If bleaching becomes an annual event later in this century, more than 90% of coral reefs worldwide may be at risk of long‐term degradation. While corals can recover from single isolated bleaching and can acclimate to recurring bleaching events that are separated by multiple years, it is currently unknown if and how they will survive and possibly acclimatize to annual coral bleaching. Here, we demonstrate for the first time that annual coral bleaching can dramatically alter thermal tolerance in Caribbean corals. We found that high coral energy reserves and changes in the dominant algal endosymbiont type (Symbiodinium spp.) facilitated rapid acclimation in Porites divaricata, whereas low energy reserves and a lack of algal phenotypic plasticity significantly increased susceptibility in Porites astreoides to bleaching the following year. Phenotypic plasticity in the dominant endosymbiont type of Orbicella faveolata did not prevent repeat bleaching, but may have facilitated rapid recovery. Thus, coral holobiont response to an isolated single bleaching event is not an accurate predictor of its response to bleaching the following year. Rather, the cumulative impact of annual coral bleaching can turn some coral species ‘winners’ into ‘losers’, and can also facilitate acclimation and turn some coral species ‘losers’ into ‘winners’. Overall, these findings indicate that cumulative impact of annual coral bleaching could result in some species becoming increasingly susceptible to bleaching and face a long‐term decline, while phenotypically plastic coral species will acclimatize and persist. Thus, annual coral bleaching and recovery could contribute to the selective loss of coral diversity as well as the overall decline of coral reefs in the Caribbean.     

Effects of juvenile coral-feeding butterflyfishes on host corals

Corals provide critical settlement habitat for a wide range of coral reef fishes, particularly corallivorous butterflyfishes, which not only settle directly into live corals but also use this coral as an exclusive food source. This study examines the consequences of chronic predation by juvenile coral-feeding butterflyfishes on their specific host corals. Juvenile butterflyfishes had high levels of site fidelity for host corals with 88% (38/43) of small (<30 mm) juveniles of Chaetodon plebeius feeding exclusively from a single host colony. This highly concentrated predation had negative effects on the condition of these colonies, with tissue biomass declining with increasing predation intensity. Declines were consistent across both field observations and a controlled experiment. Coral tissue biomass declined by 26.7, 44.5 and 53.4% in low, medium and high predation intensity treatments. Similarly, a 41.7% difference in coral tissue biomass was observed between colonies that were naturally inhabited by juvenile butterflyfish compared to uninhabited control colonies. Total lipid content of host corals declined by 29–38% across all treatments including controls and was not related to predation intensity; rather, this decline coincided with the mass spawning of corals and the loss of lipid-rich eggs. Although the speed at which lost coral tissue is regenerated and the long-term consequences for growth and reproduction remain unknown, our findings indicate that predation by juvenile butterflyfishes represents a chronic stress to these coral colonies and will have negative energetic consequences for the corals used as settlement habitat.     

Potential role of viruses in white plague coral disease

White plague (WP)-like diseases of tropical corals are implicated in reef decline worldwide, although their etiological cause is generally unknown. Studies thus far have focused on bacterial or eukaryotic pathogens as the source of these diseases; no studies have examined the role of viruses. Using a combination of transmission electron microscopy (TEM) and 454 pyrosequencing, we compared 24 viral metagenomes generated from Montastraea annularis corals showing signs of WP-like disease and/or bleaching, control conspecific corals, and adjacent seawater. TEM was used for visual inspection of diseased coral tissue. No bacteria were visually identified within diseased coral tissues, but viral particles and sequence similarities to eukaryotic circular Rep-encoding single-stranded DNA viruses and their associated satellites (SCSDVs) were abundant in WP diseased tissues. In contrast, sequence similarities to SCSDVs were not found in any healthy coral tissues, suggesting SCSDVs might have a role in WP disease. Furthermore, Herpesviridae gene signatures dominated healthy tissues, corroborating reports that herpes-like viruses infect all corals. Nucleocytoplasmic large DNA virus (NCLDV) sequences, similar to those recently identified in cultures of Symbiodinium (the algal symbionts of corals), were most common in bleached corals. This finding further implicates that these NCLDV viruses may have a role in bleaching, as suggested in previous studies. This study determined that a specific group of viruses is associated with diseased Caribbean corals and highlights the potential for viral disease in regional coral reef decline.