Bleaching Patterns Research Articles

Changes in Caribbean coral disease prevalence after the 2005 bleaching event

Bleaching events and disease epizootics have increased during the past decades, suggesting a positive link between these 2 causes in producing coral mortality. However, studies to test this hypothesis, integrating a broad range of hierarchical spatial scales from habitats to distant localities, have not been conducted in the Caribbean. In this study, we examined links between bleaching intensity and disease prevalence collected from 6 countries, 2 reef sites for each country, and 3 habitats within each reef site (N = 6 x 2 x 3 = 36 site-habitat combinations) during the peak of bleaching in 2005 and a year after, in 2006. Patterns of disease prevalence and bleaching were significantly correlated (Rho = 0.58, p = 0.04). Higher variability in disease prevalence after bleaching occurred among habitats at each particular reef site, with a significant increase in prevalence recorded in 4 of the 10 site-habitats where bleaching was intense and a non-significant increase in disease prevalence in 18 out of the 26 site-habitats where bleaching was low to moderate. A significant linear correlation was found (r = 0.89, p = 0.008) between bleaching and the prevalence of 2 virulent diseases (yellow band disease and white plague) affecting the Montastraea species complex. Results of this study suggest that if bleaching events become more intense and frequent, disease-related mortality of Caribbean coral reef builders could increase, with uncertain effects on coral reef resilience.

The effect of species and colony size on the bleaching response of reef-building corals in the Florida Keys during the 2005 mass bleaching event

Understanding the variation in coral bleaching response is necessary for making accurate predictions of population changes and the future state of reefs in a climate of increasing thermal stress events. Individual coral colonies, belonging to inshore patch reef communities of the Florida Keys, were followed through the 2005 mass bleaching event. Overall, coral bleaching patterns followed an index of accumulated thermal stress more closely than in situ temperature measurements. Eight coral species (Colpophyllia natans, Diploria strigosa, Montastraea cavernosa, M. faveolata, Porites astreoides, P. porites, Siderastrea siderea, and Stephanocoenia intersepta), representing >90% of the coral colonies studied, experienced intense levels of bleaching, but responses varied. Bleaching differed significantly among species: Colpophyllia natans and Diploria strigosa were most susceptible to thermal stress, while Stephanocoenia intersepta was the most tolerant. For colonies of C. natans, M. faveolata, and S. siderea, larger colonies experienced more extensive bleaching than smaller colonies. The inshore patch reef communities of the Florida Keys have historically been dominated by large colonies of Montastraea sp. and Colpophyllia natans. These results provide evidence that colony-level differences can affect bleaching susceptibility in this habitat and suggest that the impact of future thermal stress events may be biased toward larger colonies of dominant reef-building species. Predicted increases in the frequency of mass bleaching and subsequent mortality may therefore result in significant structural shifts of these ecologically important communities.

Improved water quality can ameliorate effects of climate change on corals

The threats of wide-scale coral bleaching and reef demise associated with anthropogenic climate change are widely known. Moreover, rates of genetic adaptation and/or changes in the coral-zooxanthella partnerships are considered unlikely to be sufficiently fast for corals to acquire increased physiological resistance to increasing sea temperatures and declining pH. However, it has been suggested that coral reef resilience to climate change may be improved by good local management of coral reefs, including management of water quality. Here, using major data sets from the Great Barrier Reef (GBR), Australia, we investigate geographic patterns of coral bleaching in 1998 and 2002 and outline a synergism between heat stress and nutrient flux as a major causative mechanism for those patterns. The study provides the first concrete evidence for the oft-expressed belief that improved coral reef management will increase the regional-scale survival prospects of coral reefs to global climate change.

FRAP and Photoconversion in Multiple Arbitrary Regions of Interest Using a Programmable Array Microscope (PAM)

Photomanipulation (photobleaching, photoactivation, or photoconversion) is an essential tool in fluorescence microscopy. Fluorescence recovery after photobleaching (FRAP) is commonly used for the determination of lateral diffusion constants of membrane proteins, and can be conveniently implemented in confocal laser scanning microscopy (CLSM). Such determinations provide important information on molecular dynamics in live cells. However, the CLSM platform is inherently limited for FRAP because of its inflexible raster (spot) scanning format. We have implemented FRAP and photoconversion protocols using a programmable array microscope (PAM). The bleaching or photoconversion patterns are arbitrary in number and shape, dynamic, and adjustable to and by the sample characteristics. We have used multi-spot PAM-FRAP to measure the lateral diffusion of the erbB3 (HER3) receptor tyrosine kinase labeled by fusion with mCitrine on untreated cells and after treatment with reagents that perturb the cytoskeleton or plasma membrane or activate coexpressed erbB1 (HER1, the EGF receptor EGFR). We also explored the versatility of the PAM for photoconversion in arbitrary regions of interest, in cells expressing erbB3 fused with the fluorescent protein dronpa.

Reef structure regulates small-scale spatial variation in coral bleaching

Coral bleaching is often characterized by high spatial variation across reef systems. Using a field survey and manipulative experiment, we tested whether the physical structure of coral reefs modifies environmental conditions that, in turn, influence spatial variation in bleaching in 3 scleractinian corals, Pocillopora verrucosa, Acropora elseyi, and Porites rus. Corals inhabit mainly the hard-bottom seafloor, or dead or partially dead coral heads ('bommies'). Bommies (0.10 to 3.0 m tall) position corals at different water depths and expose them to differences in light, temperature, hydrodynamics, and sedimentation, factors that can influence patterns of bleaching. We conducted our study in association with a 14 d warming event that caused bleaching in lagoons of Moorea, French Polynesia. Bleaching in naturally occurring colonies of Pocillopora spp. and Acopora spp. was greater on the seafloor (0 m tall) than on short (0.35 to 0.40 m tall) and tall bommies (1.0 to 1.2 m tall). Bleaching in P. verrucosa and A. elseyi transplanted to reef structures in the experiment generally decreased with increasing reef height (seafloor > short bommies > tall bommies). P. rus did not bleach under any conditions observed. Regression analyses revealed that reef structure controlled current speed and sedimentation at the microhabitat scale (from centimeters to meters), and that these factors regulated bleaching and mortality in P. verrucosa and A. elseyi. Our results imply that the physical structure of shallow water reef habitat influences the performance of coral colonies by modifying environmental stress, and that accounting for this structure is important in managing coral reef systems.

DESICCATION PROTECTION AND DISRUPTION: A TRADE-OFF FOR AN INTERTIDAL MARINE ALGA(1).

For marine algae, the benefits of drying out are often overshadowed by the stresses involved. Here we used laboratory and field experiments to examine both the costs and benefits of desiccation in the intertidal turf alga Endocladia muricata (Endlichter) J. Agardh. Laboratory experiments showed that when Endocladia is dry, photosynthesis stops, but thermotolerance increases to the point that the alga is protected from heat-induced mortality. Drying rates measured in a wind tunnel, combined with tidal data and measured wave splash, indicate that a substantial fraction of the year is spent "drying out" (∼30% of the total time available for photosynthesis). During these periods, the rate of drying determines how much time is spent hydrated and potentially engaged in photosynthesis, but also vulnerable to high temperatures. Turf algae such as Endocladia dry from the edge of a clump inward. Consequently, the clump center remains hydrated longer than the clump edge. The resulting regionalization of a clump results in notable patterns of frond mortality ("fairy rings," and zoned patterns of frond bleaching) within the Endocladia zone.

Bacteria are not the primary cause of bleaching in the Mediterranean coral Oculina patagonica

Coral bleaching occurs when the endosymbiosis between corals and their symbionts disintegrates during stress. Mass coral bleaching events have increased over the past 20 years and are directly correlated with periods of warm sea temperatures. However, some hypotheses have suggested that reef-building corals bleach due to infection by bacterial pathogens. The 'Bacterial Bleaching' hypothesis is based on laboratory studies of the Mediterranean invading coral, Oculina patagonica, and has further generated conclusions such as the coral probiotic hypothesis and coral hologenome theory of evolution. We aimed to investigate the natural microbial ecology of O. patagonica during the annual bleaching using fluorescence in situ hybridization to map bacterial populations within the coral tissue layers, and found that the coral bleaches on the temperate rocky reefs of the Israeli coastline without the presence of Vibrio shiloi or bacterial penetration of its tissue layers. Bacterial communities were found associated with the endolithic layer of bleached coral regions, and a community dominance shift from an apparent cyanobacterial-dominated endolithic layer to an algal-dominated layer was found in bleached coral samples. While bacterial communities certainly play important roles in coral stasis and health, we suggest environmental stressors, such as those documented with reef-building corals, are the primary triggers leading to bleaching of O. patagonica and suggest that bacterial involvement in patterns of bleaching is that of opportunistic colonization.

EFFECTS OF CLIMATE AND SEAWATER TEMPERATURE VARIATION ON CORAL BLEACHING AND MORTALITY

Coral bleaching due to thermal and environmental stress threatens coral reefs and possibly people who rely on their resources. Here we explore patterns of coral bleaching and mortality in East Africa in 1998 and 2005 in a region where the equatorial current and the island effect of Madagascar interact to create different thermal and physicochemical environments. A variety of temperature statistics were calculated, and their relationships with the degree-heating months (DHM), a good predictor of coral bleaching, determined. Changes in coral cover were analyzed from 29 sites that span >1000 km of coastline from Kenya to the Comoros Islands. Temperature patterns are influenced by the island effect, and there are three main temperature environments based on the rise in temperature over 52 years, measures of temperature variation, and DHM. Offshore sites north of Madagascar that included the Comoros had low temperature rises, low DHM, high standard deviations (SD), and the lowest relative coral mortality. Coastal sites in Kenya had moderate temperature rises, the lowest temperature SD, high DHM, and the highest relative coral mortality. Coastal sites in the south had the highest temperature rises, moderate SD and DHM, and low relative coral mortality. Consequently, the rate of temperature rise was less important than background variation, as reflected by SD and kurtosis measures of sea surface water temperature (SST), in predicting coral survival across 1998. Coral bleaching responses to a warm-water anomaly in 2005 were also negatively related to temperature variation, but positively correlated with the speed of water flow. Separating these effects is difficult; however, both factors will be associated with current environments on the opposite sides of reefs and islands. Reefs in current shadows may represent refugia where corals acclimate and adapt to environmental variation, which better prepares them for rising temperature and anomalies, even though these sites are likely to experience the fastest rates of temperature rise. We suggest that these sites are a conservation priority and should be targeted for management and further ecological research in order to understand acclimation, adaptation, and resilience to climate change.

Role of three-dimensional bleach distribution in confocal and two-photon fluorescence recovery after photobleaching experiments

The quantitative analysis of fluorescence perturbation experiments such as fluorescence recovery after photobleaching (FRAP) requires suitable analytical models to be developed. When diffusion in 3D environments is considered, the description of the initial condition produced by the perturbation (i.e., the photobleaching of a selected region in FRAP) represents a crucial aspect. Though it is widely known that bleaching profiles approximations can lead to errors in quantitative FRAP measurements, a detailed analysis of the sources and the effects of these approximations has never been conducted until now. In this study, we measured the experimental 3D bleaching distributions obtained in conventional and two-photon excitation schemes and analyzed the deviations from the ideal cases usually adopted in FRAP experiments. In addition, we considered the non-first-order effects generated by the high energy pulses usually delivered in FRAP experiments. These data have been used for finite-element simulations mimicking FRAP experiments on free diffusing molecules and compared with FRAP model curves based on the ideal bleach distributions. The results show that two-photon excitation more closely fits ideal bleaching patterns even in the event of fluorescence saturation, achieving estimations of diffusion coefficients within 20% accuracy of the correct value.

Water flow influences the distribution of photosynthetic efficiency within colonies of the scleractinian coral Montastrea annularis (Ellis and Solander, 1786); implications for coral bleaching

Recent studies have determined that water flow may perform a number of roles during and following episodes of coral reef bleaching. Increased water flow has the potential to improve the capacity of some scleractinian corals to cope with high concentrations of oxygen in the boundary layer that are photosynthetically derived, and coral reef damage is often at its highest in areas where flow is restricted. Conversely, water motion has been shown to increase metabolic rate (both photosynthesis and respiration) and such flow-modulated metabolism may affect bleaching patterns asymmetrically within a coral colony. To broaden these earlier studies and to further examine the effects of flow on photosynthetic efficiency, we tested to determine whether or not corals would exhibit a spatially asymmetric distribution of photosynthetic efficiency related to velocity gradients (degree of mixing) across the coral colony. We conducted experiments from the NOAA underwater habitat Aquarius on colonies of Montastrea annularis (Ellis and Solander, 1786) with controlled exposures to increased flow ( ca. 40 cm s − 1 , 1 cm above coral surface) and temperature ( ca. 2 °C above ambient) using in situ flow chambers. We measured photosynthetic efficiency as a light-adapted quantum yield ( F v′ / F m′) using Pulse Amplitude Modulation (PAM) fluorometry to examine the short-term (daily) and medium term (≥ 9 days) response of patches of polyps within coral colonies. M. annularis colonies developed and sustained a significant spatially asymmetric pattern of photosynthetic yield across the entire coral surface, with the upstream side of the colonies exhibiting reduced quantum yield. The mechanism producing this pattern is unclear; we speculate that increased flow may lead to increased photosynthesis by upstream polyps through bicarbonate delivery accentuated by the Q 10 effect. Local down-regulation of the photosynthetic response (decreased quantum yield) might then occur to keep tissue oxygen concentrations within tolerable limits.

Opposing forces of aerosol cooling and El Nino drive coral bleaching on Caribbean reefs.

Bleaching of corals as a result of elevated sea surface temperatures (SST) is rapidly becoming a primary source of stress for reefs globally; the scale and extent of this threat will depend on how the drivers of SST interact to influence bleaching patterns. We demonstrate how the opposing forces of the El Niño-Southern Oscillation (ENSO) and levels of atmospheric aerosols drive regional-scale patterns of coral bleaching across the Caribbean. When aerosol levels are low, bleaching is largely determined by El Niño strength, but high aerosol levels mitigate the effects of a severe El Niño. High aerosol levels, resulting principally from recent volcanic activity, have thus protected Caribbean reefs from more frequent widespread bleaching events but cannot be relied on to provide similar protection in the future.

Aerial exposure influences bleaching patterns

[Extract]On the 17th December 2005 Acropora millepora and other reef flat corals at Heron Island (23.44S, 151.91E) were found to have bleached on the west-north-west face of aerially exposed branches (Fig. 1). Visual surveys on the 15th and 16th had not detected any bleaching signs. In the preceding 3 days, water temperatures reached a maximum of 32.0 C on the 15th December and exceeded 31.0 C for only 2.5 h. Past studies suggest this alone is not sufficient to cause bleaching. Analysis of wind speed and direction for the morning of the 17th showed that the low tide at 03:00 hours coincided with 4 h of high winds from the west-north-west. Peak gusts (57 km h)1) were within the highest 2.5% of all reading from the previous 6 years. Analysis of the red absorbing photosynthetic pigments (absorptivity) and dark-adapted fluorescent yield (Ralph et al. 2005) demonstrated a 65% loss of photosynthetic pigments and a 40% decrease in yield on the west-north-west face of exposed corals (Fig. 2) compared to the eastern side.

Mineral distribution in contact-metamorphosed siliceous dolomite at Ubehebe Peak, California, based on airborne imaging spectrometer data

Visible and near-infrared reflectance spectra of minerals in the CaO-MgO-SiO 2 -H 2 O-CO 2 system and airborne imaging spectrometer data with a spatial resolution of 3.6 m were used to map the distribution of dolomite, calcite, tremolite, serpentine, brucite, and related minerals in the Ubehebe Peak contact aureole. The results are entirely consistent with previously mapped isograds, but the high-spatial-resolution imagery offers a more accurate representation of the complex distribution of metamorphic minerals, and serves to highlight critical relationships between mineralogy and controlling factors such as stratigraphy, structure, and fluid infiltration. Rocks in the aureole are predominantly quartz-poor dolomite and limestone, and these are classified as pure dolomite or calcite, accordingly. Tremolite and serpentine (after forsterite) are largely restricted to stratigraphic units that contain siliceous dolomite, quartzite, or chert. In one area, however, tremolite and serpentine delineate a zone of retrograde hydration attributed to fluid flow along a fault. Wall rocks within 200 m of the contact and inliers of marble in the pluton contain brucite (after periclase), which documents sites of focused infiltration of H 2 O-rich fluid. In addition, the imagery reveals local metasomatic zones, marked by grossular-rich skarn and epidote alteration of the adjacent quartz monzonite, as well as large-scale patterns of bleaching, interpreted to define the maximum extent of fluid flow. The degree of bleaching and the intensity of plastic deformation are closely coupled; both effects increase abruptly at the forsterite isograd, which appears to represent a fundamental discontinuity with respect to chemical, physical, and mechanical processes in the aureole.

A comparison of the 1998 and 2002 coral bleaching events on the Great Barrier Reef: spatial correlation, patterns, and predictions

Detailed mapping of coral bleaching events provides an opportunity to examine spatial patterns in bleaching over scales of 10 s to 1,000 s of km and the spatial correlation between sea surface temperature (SST) and bleaching. We present data for two large-scale (2,000 km) bleaching events on the Great Barrier Reef (GBR): one from 1998 and another from 2002, both mapped by aerial survey methods. We examined a wide range of satellite-derived SST variables to determine which one best correlated with the observed bleaching patterns. We found that the maximum SST occurring over any 3-day period (max3d) during the bleaching season predicted bleaching better than anomaly-based SST variables and that short averaging periods (3–6 days) predicted bleaching better than longer averaging periods. Short periods of high temperature are therefore highly stressful to corals and result in highly predictable bleaching patterns. Max3d SST predicted the presence/absence of bleaching with an accuracy of 73.2%. Large-scale (GBR-wide) spatial patterns of bleaching were similar between 1998 and 2002 with more inshore reefs bleached compared to offshore reefs. Spatial change in patterns of bleaching occurred at scales of ~10 s km, indicating that reefs bleach (or not) in spatial clusters, possibly due to local weather patterns, oceanographic conditions, or both. Approximately 42% of reefs bleached to some extent in 1998 with ~18% strongly bleached, while in 2002, ~54% of reefs bleached to some extent with ~18% strongly bleached. These statistics and the fact that nearly twice as many offshore reefs bleached in 2002 compared to 1998 (41 vs. 21%, respectively) makes the 2002 event the worst bleaching event on record for the GBR. Modeling of the relationship between bleaching and max3d SST indicates that a 1 °C increase would increase the bleaching occurrence of reefs from 50% (approximate occurrence in 1998 and 2002) to 82%, while a 2 °C increase would increase the occurrence to 97% and a 3 °C increase to 100%. These results suggest that coral reefs are profoundly sensitive to even modest increases in temperature and, in the absence of acclimatization/adaptation, are likely to suffer large declines under mid-range International Panel for Climate Change predictions by 2050.

Climate change and coral reefs: different effects in two high-latitude areas (Arabian Gulf, South Africa)

The findings in this paper show that Arabian Gulf (Abu Dhabi, Dubai, Sharjah) corals have already been measurably affected by climate change and further negative impacts are expected. Corals in South Africa have been only weakly impacted and are expected to persist in this likely refuge. The Arabian Gulf has recently experienced high-frequency recurrences of temperature-related bleaching (1996, 1998, 2002). First evidence may suggest that bleaching patterns in corals changed due to phenotypic adaptation after two strong bleaching events in rapid succession, because Acropora, which during the 1996 and 1998 events always bleached first and suffered heaviest mortality, bleached less than all other corals in 2002 at Sir Abu Nuair and recovered at Jebel Ali and Ras Hasyan. In South Africa, reef corals largely escaped the mass mortalities observed across the tropics in the late 1990s, although bleaching has also increased since 1999. These reefs are protected by local small-scale upwelling events in summer that, if they occur at the right time, keep temperatures below bleaching levels. Both areas, the Arabian Gulf and South Africa, have rich coral faunas but little to no recent reef-framework production. It is possible that many reefs worldwide may have similar dynamics in the future, if the changed climate (recurrence of temperature anomalies, changes in aragonite saturation state, etc.) suppresses sustained reef building at least temporarily. Global climate models predict the possibility of significant environmental changes, including increases in atmospheric temperature, sea-surface temperature (SST), and sea level. Monsoon and El Nino Southeastern Oscillation (ENSO) patterns might change, but climate models are not conclusive. Sea-level rise by up to 0.88 m is expected to be a problem in some low-lying areas, like the southern Arabian Gulf. Ocean aragonite saturation state is predicted to fall throughout the ocean but may not change reef dynamics in the two study areas.

Choosing the appropriate spatial resolution for monitoring coral bleaching events using remote sensing

Bleached corals provide a strong optical signal that suggests that remote sensing investigations of major bleaching events are feasible using airborne or satellite sensors. However, patchy coral cover, varying intensities of bleaching, and water depths are likely to limit the application of remote sensing techniques in monitoring and mapping coral bleaching. Today, satellite multispectral sensors routinely provide images of reefs from 4 m (Ikonos) to 30 m resolution (Landsat); however, the adequacy of these sensors for monitoring and mapping bleaching events remains unclear. To clarify these issues, scanned aerial photographs acquired during the 1998 bleaching event over the Great Barrier Reef (Australia) were analyzed at various spatial resolutions, from 10 cm to 5 m. We found that the accuracy of mapping bleaching is highly sensitive to spatial resolution. Highest accuracy was obtained at 10 cm resolution for detection of totally bleached colonies. At 1 m resolution, as much as 50% of the 10-cm resolution signal is lost, though the spatial patterns remain correctly described. Partially bleached (pale) corals are difficult to detect even in aerial surveys, leading to an underestimation of overall bleaching levels (total and partial bleaching) in aerial photos compared to in-situ surveys. If data volume and processing time are limiting factors, local variance analysis suggests that the optimal resolution necessary to capture spatial patterns of bleaching is in the range 40–80 cm.

Slow photochemical transformations of single dye molecules in polymer environment at room temperature

Wide-field epi-fluorescence microscopic images of single dye molecules in thin films have been studied with 1 s time resolution using a CCD camera. The fluorophores at a concentration of 10 −7 M were doped in a 12 nm thin polystyrene film layered by spin coating on a surface of fused silica. Terrylene, N, N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide and a heterocyclic derivative of the latter were chosen as dyes. The solvents, polymers and the quartz surface were purified carefully in order to get rid of uncontrolled fluorescence. The time dependence of fluorescence intensity for about 100 molecules in each sample has been followed at an excitation intensity of 500 W cm −2. Both the constant or one-step bleaching patterns of fluorescence intensity were found to be rather an exception than a rule for many systems. Most of the molecules exhibit multiple on–off switching, fluctuating or creeping behavior. The population shelving on the T 1 level and the rotational diffusion of the transition dipole cannot serve as universal explanation of such fluorescence intensity dynamics. The fluctuations depend on the composition of the gas atmosphere (air, N 2 or neat O 2), and the presence of electron donors ( N, N, N′N′-tetramethyl- p-phenylenediamine) or acceptors (C 2Cl 6). It has to be surmised that additional phenomena, such as photoisomerisation may be involved in the blinking effect if it persists in nitrogen atmosphere.

Bleaching patterns in reef corals.

Coral reefs are under threat from the effects of bleaching, in which symbiotic algae or their photosynthetic pigments are destroyed by increased sea temperatures and solar radiation1,2. Here we show that the bleaching susceptibility of Goniastrea aspera, a shallow-water Indo-Pacific coral, can be predicted from its history of exposure to solar radiation, demonstrating how experience can shape coral bleaching patterns.

Light‐induced pigment degradation in leaves and ripening fruits studied in situ with reflectance spectroscopy

Pigment breakdown mediated by activated oxygen species is a consequence and a general symptom of oxidative stress and injury to plants. We have attempted to estimate the patterns of pigment bleaching and follow pigment susceptibility to irradiation as related to the process of senescence/ripening. Light‐induced pigment breakdown was studied in situ in the leaves of a shade‐requiring plant, wax flower (Hoya carnosa R. Br.), as well as in apple (Malus domestica Borlh. cv. Zhigulevskoe) and lemon (Citrus limon Burm. cv. Pavlovsky) fruits, using reflectance spectroscopy. It was found that the sensitivity of plant pigments to photobleaching increases as ripening progresses in lemon fruit. Kinetic analysis showed that in all systems a rapid breakdown of the pigment occurs after a lag‐phase. The signature analysis revealed a common pattern of chlorophyll and carotenoid changes, but degradation of the individual pigments was found to be inhomogeneous. Both in lemon and apple fruits a decrease in reflectance in the band of carotenoid absorption preceded pigment photodestruction. In the fruits, the bulk of chlorophyll b and the long‐wavelength chlorophyll a forms were degraded at early stages of the process whereas the breakdown of both chlorophylls in H. carnosa leaves was more synchronous. Prolonged irradiation induced bleaching of the main chlorophyll a band with maximum at 678 nm in the difference spectra, as well as carotenoids. Some features of reflectance spectra in the bands of chlorophyll and carotenoid absorption were found to be suitable for the differentiation of photo‐induced pigment breakdown from the transformation of the pigments taking place during senescence.

Landscape ecology of algal symbionts creates variation in episodes of coral bleaching.

Reef-building corals are obligate, mutualistic symbioses of heterotrophic animals and phototrophic dinoflagellates (Symbiodinium spp.). Contrary to the earlier, widely accepted belief that corals harbour only one symbiont, we found that the ecologically dominant Caribbean corals Montastraea annularis and M. faveolata can act as hosts to dynamic, multi-species communities of Symbiodinium. Composition of these communities follows gradients of environmental irradiance, implying that physiological acclimatization is not the only mechanism by which corals cope with environmental heterogeneity. The importance of this diversity was underlined by analysis of a natural episode of coral bleaching. Patterns of bleaching could be explained by the preferential elimination of a symbiont associated with low irradiance from the brightest parts of its distribution. Comparative analyses of symbionts before and after bleaching from the same corals supported this interpretation, and suggested that some corals were protected from bleaching by hosting an additional symbiont that is more tolerant of high irradiance and temperature. This 'natural experiment' suggests that temporal and spatial variability can favour the coexistence of diverse symbionts within a host, despite the potential for destabilizing competition among them.