Porites Lobata Research Articles

Development of microsatellite markers from four Hawaiian corals: Acropora cytherea, Fungia scutaria, Montipora capitata and Porites lobata

Comprehensive population genetic studies of coral communities are comparatively rare, because of the scarcity of population genetic markers. The Hawaiian archipelago offers a unique perspective into understanding the population genetic structuring of this ecologically important group of organisms. Here we report the development of microsatellite marker libraries from holobiont extracts of four corals: Acropora cytherea (n = 50), Fungia scutaria (n = 118), Montipora capitata (n = 140) and Porites lobata (n = 149). Blast searches indicate that these libraries contain microsatellites from both the coral host and Symbiodinium endosymbionts from each coral. In addition, we also present redesigned primers for the nuclear coding region (atpsβ) for use in M. capitata. We report testing and optimization for seven of these microsatellites from A. cytherea, and eight microsatellites and the atpsβ locus from M. capitata. Using 25 individuals per species collected from each French Frigate Shoals (FF) and Johnston Atoll (JO), the number of alleles per locus ranged from 2 to 9. Expected heterozygosities ranged from 0.38 to 0.85 and 0.08 to 0.87 for A. cytherea and M. capitata, respectively. We expect that these libraries will be a valuable resource and provide additional useful microsatellite markers for both the coral host and zooxanthellae.

Effects of frequent fish predation on corals in Hawaii

The abundance of lesions from fish bites on corals was quantified at nine shallow reefs in the main Hawaiian Islands. There were on average 117 bite scars m−2 on Pocillopora meandrina tissue from the barred filefish Cantherhines dumerilii, 69 bites m−2 on Porites compressa tissue, and 4 bites m−2 on Porites lobata tissue from the spotted puffer Arothron meleagris. Across sites, the frequency of A. meleagris bites on P. compressa per unit area of living coral cover declined exponentially with increasing coral cover. P. compressa nubbins in two size classes (1–2 cm and 4–5 cm) were transplanted onto six study reefs. Nubbins in the small size class were entirely removed by bites from A. meleagris, while nubbins ≥4 cm were only partially consumed, leaving them able to recover. At sites with abundant P. compressa, predation had little effect on transplanted nubbins; at sites where P. compressa comprised less than 5% of living cover, all nubbins were preyed upon. A. meleagris bite lesions on P. compressa were monitored through time and fully recovered in 42 ± 4 days. A model of the risk of over-predation (a second predation event before the first is healed) decreased exponentially with increasing coral cover and increased linearly with increasing lesion healing time. The increased risk of over-predation at low coral cover could indicate an Allee effect limiting the recovery of coral populations if coral cover is substantially reduced by natural or anthropogenic disturbances.

Antibacterial chemical defenses in Hawaiian corals provide possible protection from disease

Diseases of marine organisms, and corals in particular, have been reported with increas- ing frequency over the past 3 decades. Although little is known about resistance to disease in corals, a potential mechanism of defense is the production of antimicrobial compounds that protect corals from microbial pathogens. We assessed the antibacterial activity of crude aqueous extracts from 3 common Hawaiian reef corals, Montipora capitata, Porites lobata, and Pocillopora meandrina, against 9 strains of bacteria. The bacteria selected included known coral pathogens, potential marine pathogens found in human waste, and bacteria previously identified from the surfaces of Hawaiian corals. Extracts from all 3 coral species exhibited high levels of antibacterial activity. Overall, 54.3% of assays resulted in bacterial growth inhibition. In addition, 9.9% of extracts stimulated the growth of certain bacteria. Although levels of overall antibacterial activity did not differ significantly among coral species (ranging from 40.7% of assays for P. meandrina to 63.0% of assays for M. capitata), the 3 species exhibited a high degree of selectivity as demonstrated by significant variability in their effects toward specific bacteria. Extracts also exhibited intraspecific variability, both within and between sites, and significant site-by-species interactions were observed against 6 of 9 bacterial strains. In M. capitata, healthy corals had significantly higher levels of antibacterial activity than those affected by Montipora White Syndrome, and affected tissues had significantly higher levels of antibacterial activity than unaffected tissues. Variability in antibacterial activity of Hawaiian corals may, in part, explain differential susceptibility to disease at the colony, species, or population level.

IMAGING OF OXYGEN DYNAMICS WITHIN THE ENDOLITHIC ALGAL COMMUNITY OF THE MASSIVE CORAL PORITES LOBATA(1).

We used transparent planar oxygen optodes and a luminescence lifetime imaging system to map (at a pixel resolution of <200 μm) the two-dimensional distribution of O2 within the skeleton of a Porites lobata colony. The O2 distribution was closely correlated to the distribution of the predominant endolithic microalga, Ostreobium quekettii Bornet et Flahault that formed a distinct green band inside the skeleton. Oxygen production followed the outline of the Ostreobium band, and photosynthetic O2 production was detected at only 0.2 μmol photons m(-2) · s(-1) , while saturation occurred at ∼37 μmol photons m(-2) · s(-1) . Oxygen levels varied from ∼60% to 0% air saturation in the illuminated section of the coral skeleton in comparison to the darkened section. The O2 production within the Ostreobium band was lower in the region below the upward facing surface of the coral and elevated on the sides. Oxygen consumption in darkness was also greatest within the Ostreobium zone, as well as in the white skeleton zone immediately below the corallites. The rate of O2 depletion was not constant within zones and between zones, showing pronounced heterogeneity in endolithic respiration. When the coral was placed in darkness after a period of illumination, O2 levels declined by 50% within 20 min and approached steady-state after 40-50 min in darkness. Our study demonstrates the use of an important new tool in endolith photobiology and presents the first data of spatially resolved O2 concentration and its correlation to the physical structures and specific zones responsible for O2 production and consumption within the coral skeleton.

Environmental versus Genetic Influences on Growth Rates of the Corals Pocillopora eydouxi and Porites lobata (Anthozoa: Scleractinia)1

Reciprocal transplant experiments of the corals Pocillopora eydouxi Milne Edwards & Haime and Porites lobata Dana were carried out for an 18-month period from September 2004 to March 2006 between two back reef pools on Ofu Island, American Samoa, to test environmental versus genetic effects on skeletal growth rates. Skeletal growth of P. eydouxi showed environmental but not genetic effects, resulting in doubling of growth in Pool 300 compared with Pool 400. There were no environmental or genetic effects on skeletal growth of P. lobata. Pool 300 had more frequent and longer durations of elevated seawater temperatures than Pool 400, characteristics likely to decrease rather than increase skeletal growth. Pool 300 also had higher nutrient levels and flow velocities than Pool 400, characteristics that may increase skeletal growth. However, higher nutrient levels would be expected to increase skeletal growth in both species, but there was no difference between the pools in P. lobata growth. P. eydouxi is much more common in high-energy environments than P. lobata; thus the higher flow velocities in Pool 300 than in Pool 400 may have positively affected skeletal growth of P. eydouxi while not having a detectable effect on P. lobata. The greater skeletal growth of P. eydouxi in Pool 300 occurred despite the presence of clade D zooxanthellae in several source colonies in Pool 300, a genotype known to result in greater heat resistance but slower skeletal growth. Increased skeletal growth rates in higher water motion may provide P. eydouxi a competitive advantage in shallow, high-energy environments where competition for space is intense.

Twenty-five years of change in coral coverage on a hurricane impacted reef in Hawai‘i: the importance of recruitment

Coral coverage was monitored 1981–2005 using a high precision method at four sites near Kahe Point, leeward O‘ahu, Hawai‘i by annually photographing ten 0.66 m2 permanent plots at each site. The study began after a local storm reduced coral coverage in the area by about 50% in 1980 and included two major hurricanes in 1982 and 1992. Repeated measures ANOVA indicate significant differences among sites, time, and site-time interaction with high statistical power. Temporal changes in coral cover varied substantially among the sites, with the most stable coral coverage occurring near a thermal outfall. Although immediate impacts from hurricanes were not substantial, long-term decreases in coral coverage occurred well after the hurricanes. However, no relationships were found between coral cover and offshore wave conditions. Patterns of decline and recovery in coral cover were cyclic on a decadal time scale and significantly correlated with species and site-specific recruitment intervals of 10–12 years for Pocillopora meandrina and 15+ years for Porites lobata. Patterns indicated the potential importance of recruitment as a major factor affecting changes in coral coverage.

Visibly healthy corals exhibit variable pigment concentrations and symbiont phenotypes

Understanding the natural variability of photosynthetic pigment ranges and distributions in healthy corals is central to evaluating how useful these measurements are for assessing the health and bleaching status of endosymbiotic reef-building corals. This study examined the photosynthetic pigment variability in visibly healthy Porites lobata and Porites lutea corals from Kaneohe Bay, Hawaii and explored whether pigment variability was related to the genetic identity or phenotypic characteristics of the symbionts. Concentrations of the photosynthetic pigments chlorophyll a, peridinin, chlorophyll c 2 , diadinoxanthin, diatoxanthin, β,β-carotene and dinoxanthin were quantified using high-performance liquid chromatography (HPLC). Pigment concentrations were found to range 1.5–10 fold in colonies of each species at similar depths (0–2, 2–4, 10–15 and 19–21 m). Despite the high pigment variability, pigment ratios for each species were relatively conserved over the 0–21 m depth gradient. The genetic identity of the symbiont communities was examined for each colony using 18S nuclear ribosomal DNA (nrDNA) restriction fragment length polymorphisms. All colonies contained symbionts belonging to clade C. The density and phenotypic characteristics of the symbionts were explored using flow cytometry, and fluorescence and side scatter (cell size) properties revealed phenotypically distinct symbiont subpopulations in every colony. The symbiont subpopulations displayed pigment trends that may be driven by acclimatization to irradiance microenvironments within the host. These results highlight the biological complexity of healthy coral–symbiont associations and the need for future research on pigments and symbiont subpopulation dynamics.

Feeding Preferences of Acanthaster planci (Echinodermata: Asteroidea) under Controlled Conditions of Food Availability

Feeding preferences of the crown-of-thorns sea star, Acanthaster planci (L.), were studied in a series of laboratory-based feeding trials wherein sea stars were provided with equal availability of six different coral species. The order in which corals were consumed was then used to ascertain feeding preferences. Crown-of-thorns sea stars exhibited strong and consistent feeding preferences across replicate feeding trials. The most readily eaten coral species was Acropora hyacinthus, followed by A. gemmifera, A. nasuta, A. formosa, Stylophora pistillata, Montipora undata, and Pocillopora damicornis. Crown-of-thorns sea stars also consumed Goniopora lobata, Fungia fungites, Goniastrea retiformes, and Pavona cactus but only after all Acropora and Montipora (Family Acroporidae) as well as Pocillopora and Stylophora (Family Pocilloporidae) were eaten. The least preferred corals were Favites abidita, Porites lobata, Symphyllia recta, Echinopora horrida, and Porites cylindrica. Of these, P. cylindrica was never eaten in any of the feeding trials in which it was offered. Observed feeding preferences substantiate findings from previous studies, where corals from the families Acroporidae and Pocilloporidae were preferred over all other corals. Further research is required to assess the underlying basis of feeding preferences of A. planci, but this study confirms that these starfish readily distinguish between different corals and have innate preferences for certain species. Still, most corals were eventually consumed, showing that when food is limited (during population outbreaks) A. planci is likely to consume virtually all different coral species, causing extreme devastation to coral reef ecosystems.

Alteration of normal cellular profiles in the scleractinian coral (Pocillopora damicornis) following laboratory exposure to fuel oil

Petroleum contamination from oil spills is a continuing threat to our ocean's fragile ecosystems. Herein, we explored the effects of the water-soluble fraction of crude oil on a stony coral, Pocillopora damicornis (Linneaeus 1758). We developed methods for exposing corals to various concentrations of crude oil and for assessing the potential molecular responses of the corals. Corals were exposed to water-accommodated fraction solutions, and appropriate cellular biomarkers were quantified. When compared to the "healthy" control specimens, exposed corals exhibited shifts in biomarker concentrations that were indicative of a shift from homeostasis. Significant changes were seen in cytochrome P450 1-class, cytochrome P450 2-class, glutathione-S-transferase-pi, and cnidarian multixenobiotic resistance protein- biomarkers, which are involved the cellular response to, and manipulation and excretion of, toxic compounds, including polycyclic aromatic hydrocarbons. A shift in biomarkers necessary for porphyrin production (e.g., protoporphyrinogen oxidase IX and ferrochelatase) and porphyrin destruction (e.g., heme oxygenase-1 and invertebrate neuroglobin homologue) illustrates only one of the cellular protective mechanisms. The response to oxidative stress was evaluated through measurements of copper/zinc superoxide dismutase-1 and DNA glycosylase MutY homologue-1 concentrations. Likewise, changes in heat shock protein 70 and small heat shock proteins indicated an adjustment in the cellular production of proteins. Finally, the results of this laboratory study were nearly identical to what we observed previously among corals of a different species, Porites lobata, exposed to an oil spill in the field after the grounding of the Merchant Vessel Kyowa Violet.

Cellular physiological effects of the MV Kyowa violet fuel‐oil spill on the hard coral, Porites lobata

The grounding of the Merchant Vessel (MV) Kyowa Violet on a coral reef near Yap, Federated States of Micronesia, in December 2002 resulted in the release of an estimated 55,000 to 80,000 gallons of intermediate fuel oil grade 180. The immediate impact was the widespread coating of mangroves and the intertidal zone along more than 8 km of coastline. Of greater concern, however, was the partitioning of the fuel oil in the water column, leading to chronic exposure of organisms in the ecosystem for a considerable period after the initial event. Herein, we report on our examination of one coral species, Porites lobata, nearly three months after the initial exposure. We investigated whether changes in cellular physiology were consistent with the pathological profile that results from the interaction of corals with polycyclic aromatic hydrocarbons, the principal constituent of fuel oil. Specifically, we document, to our knowledge for the first time, changes in the cellular physiological condition of an exposed coral population affected by a fuel-oil spill. We also provide evidence that the observed changes are consistent with a recent exposure to fuel oil, as evidenced by the presence of characteristic cellular lesions attributed to polycyclic aromatic hydrocarbons. Finally, our data support a model for a mechanistic relationship between the cellular pathological profile of the coral and a recent petroleum exposure, such as the MV Kyowa Violet fuel oil spill.

Reef recovery 20 years after the 1982–1983 El Niño massive mortality

For over 20 years the El Nino-Southern Oscillation (ENSO) has caused damage to the coral reefs of the eastern Pacific and other regions. In the mid-1980s scientists estimated that coral cover was reduced by 50–100% in several countries across the region. Almost 20 years (2002) after the 1982–1983 event, we assessed the recovery of the virtually destroyed reefs at Cocos Island (Costa Rica), previously evaluated in 1987 and reported to have less than 4% live coral cover. We observed up to fivefold increase in live coral cover which varied among reefs surveyed in 1987 and 2002. Most new recruits and adults belonged to the main reef building species from pre-1982 ENSO, Porites lobata, suggesting that a disturbance as outstanding as El Nino was not sufficient to change the role or composition of the dominant species, contrary to phase shifts reported for the Caribbean. During the 1990s, new species were observed growing on the reefs. Notably, Leptoseris scabra, considered to be rare in the entire Pacific, was commonly found in the area. Recovery may have begun with the sexual and asexual recruits of the few surviving colonies of P. lobata and Pavona spp. and with long distance transport of larvae from remote reefs. We found an overall 23% live coral cover by 2002 and with one reef above 58% indicating that Cocos Island coral reefs are recovering.

Investigating fragment size for culturing reef-building corals ( Porites lobata and P. compressa) in ex situ nurseries

Culturing small propagules of coral has the potential for high yield with low environmental impact, provided that mortality is low. This study investigated the size-specific mortality and growth of minute fragments (as small as 5 polyps) of two of the most abundant reef-building corals in Hawaii ( Porites lobata and P. compressa). Two ex situ nursery systems differing in cost, design complexity, and labor intensity were compared. The first nursery experiment lasted for four months in a large tank with high water motion/surge and extensive manual cleaning to remove competitive algae. The corals were then transferred to a simple low-flow tank containing sea urchins ( Tripneustes gratilla) and reduced cleaning, where they were grown for six more months (Nursery II). ‘Nursery I’ resulted in 92% of P. lobata and 73% of P. compressa fragments surviving and nearly doubling in area, in spite of a brief infestation by a nudibranch ( Phestilla sibogae) that primarily fed on larger P. compressa fragments. There was a significant positive relationship between fragment size and growth rate, and survivorship was significantly different between donor colonies (genets), but there was no evidence of size-specific mortality. ‘Nursery II’ on the other hand had clear size-specific mortality and higher urchin damage for smaller fragments, resulting in moderate survivorship (78% for P. lobata and 76% for P. compressa), and only a slight increase in the total area covered by coral tissue. Fragments larger than 3 cm 2 were undamaged and had the highest survival and growth rates. This study illustrates how size-specific mortality can be reduced by ex situ nursery conditions.

Heterotrophic plasticity and resilience in bleached corals

Mass coral bleaching events caused by elevated seawater temperatures have resulted in extensive coral mortality throughout the tropics over the past few decades. With continued global warming, bleaching events are predicted to increase in frequency and severity, causing up to 60% coral mortality globally within the next few decades. Although some corals are able to recover and to survive bleaching, the mechanisms underlying such resilience are poorly understood. Here we show that the coral host has a significant role in recovery and resilience. Bleached and recovering Montipora capitata (branching) corals met more than 100% of their daily metabolic energy requirements by markedly increasing their feeding rates and CHAR (per cent contribution of heterotrophically acquired carbon to daily animal respiration), whereas Porites compressa (branching) and Porites lobata (mounding) corals did not. These findings suggest that coral species with high-CHAR capability during bleaching and recovery, irrespective of morphology, will be more resilient to bleaching events over the long term, could become the dominant coral species on reefs, and may help to safeguard affected reefs from potential local and global extinction.

Depth limit for reef building corals in the Au’au Channel, S.E. Hawaii

In this paper, the relationship between reef building (accretion) and depth in an optimal inter-island channel environment in Hawaii is analyzed. For accretion, the growth rate of Porites lobata is used as a proxy for the reef community, because it is the most abundant and dominant species of reef building coral in Hawaii. Optimal growth of P. lobata occurs at a depth of 6 m, below which both growth rate and abundance decrease with increasing depth. A lower depth limit for this species is found at about 80–100 m, yet reef accretion ceases at ~50 m depth. Below 50 m, rates of bio-erosion of colony holdfasts equal or exceed the growth of basal attachments, causing colonies to detach from the bottom. Continued bio-erosion further erodes and dislodges colonies leading to their breakdown and ultimately to the formation of coralline rubble and sand. Thus, within this channel environment in Hawaii, a threshold for reef building exists at ~ 50 m depth, where coral accretion is interrupted by bio-erosion. Conceptually viewed, this depth horizon is analogous to a vertical Darwin Point, although quite narrow in space and time. More importantly, it explains the history of reef morphology in the Au’au Channel where a chronological hiatus exists at a depth near 50 m. This hiatus separates shallower modern growth (about 100 years or less) from the deeper reef which is all due to accretion during the early Holocene or Pleistocene epochs.

Strontium in coral aragonite: 3. Sr coordination and geochemistry in relation to skeletal architecture

Use of the coral Sr palaeothermometer assumes that the Sr in coral skeletons is substituted randomly for Ca in the aragonite structure. The presence of Sr in additional phases e.g., strontianite, or the non random distribution of Sr across metal sites in aragonite, would complicate the Sr/Ca-sea surface temperature relationship. We have used Sr K-edge microEXAFS (extended X-ray absorption fine structure) to determine the structural state of Sr across selected microvolumes of four coral skeletons ( Porites lobata, Acropora palmata, Pavona clavus, and Montastrea annularis). We used a 5 × 3 μm beam to analyse specific areas of the coral skeletal architecture, i.e., centres of calcification, fasciculi, and dissepiments. All EXAFS analyses refine, within error, to an ideally substituted Sr in aragonite, and we found no evidence of strontianite or partly ordered structural states. Anisotropy in the first shell responses results from the fact that the analysed microvolumes are not necessarily averaged for the responses of all crystal orientations in the aragonite. Although secondary ion mass spectrometry confirmed that Sr/Ca composition can vary substantially between skeletal components, we find no evidence for any contrast in Sr structural state. Sr heterogeneity may result from kinetic effects, reflecting complex disequilibrium processes during crystal precipitation, or biological effects, resulting from variations in the composition of the calcifying fluid which are biologically mediated.

Coral communities and reefs of Ballena Marine National Park, Pacific coast of Costa Rica

The coral communities and reefs at Ballena Marine National Park, on the southern Pacific coast of Costa Rica, were studied using three 10-m long transects per site, parallel to the coast, with 1-m2 quadrants. A total of 15 species of corals (11 hermatypic and 4 ahermatypic) were found, which when added to previous reports for the park makes a total of 18 species. Porites lobata showed the highest coral cover (36.5 ± 3.7%) and was the only species present at all sites. The other coral species had low coverage (&lt;10%) and were observed in a few places. Dead coral had a cover of 1.8 ± 0.6% and the percent of bleached coral (0.7 ± 0.2%) was due to P. lobata at only one site. This park and Caño Island have the highest number of coral species (18 species) in the southern region of Costa Rica, but they differ in composition. The low diversity and low coral covr in the park is attributed to the impact of the El Niño phenomenon in recent years, to sedimentation and to the dilution of waters during the rainy season. We suggest that a long-term monitoring program of this ecosystem is needed to determine future management and conservation strategies.

Oxygen consumption rate of the corals Goniastrea aspera, Porites lobata, and Pavona frondifera under red soil stress in the Ryukyu Islands, Okinawa, Japan

Effects of short-term sedimentation on common coastal coral species, Goniastrea aspera, Porites lobata and Pavona frondifera, from the reef flat southeast of the Ryukyu Islands, Okinawa, Japan were investigated in laboratory experiments using oxygen uptake respirometers. The O2 consumption rate was significantly different among species and between sediment treatments (20 and 200mg l-1 red soil suspension, P<0.05). In dark experiments, Goniastrea showed higher respiration rates (0.020±0.002ml O2 cm-2h-1) than did Pavona (0.017±0.003mL O2 cm-2h-1) and Porites (0.010±0.001ml O2 cm-2h-1). In light experiments, Goniastrea also showed higher O2 consumption rates (0.021±0.003ml O2 cm-2h-1) than did Porites (0.010±0.004ml O2 cm-2h-1) and Pavona (0.007±0.001ml O2 cm-2h-1). Zooxanthellae densities were 6.53±0.13, 3.12±0.05, and 4.37±0.07 (×106cells cm-2; mean±SE, n=8) in Goniastrea, Porites, and Pavona, respectively. Coral respiration rate increased proportionally with zooxanthellae density in Goniastrea and Pavona. High zooxanthellae density may increase the O2 production that contributes to colony respiration; however, in Porites, the relationship between zooxanthellae density and coral respiration rate was not clear. The massive corals, Goniastrea and Porites, are more resistant to sediment stress than is the plate-like coral, Pavona. Goniastrea showed high tolerance and adaptation to stress conditions in all experiments, at all times (12h), with similar trends in both dark and light conditions. Porites was affected only within the first 3h under light conditions, while Pavona was the most affected species. These results help us to understand coral damage caused by red soil sedimentation, as well as coral mortality and potential shifts in community structure related to prolonged or repeated elevated levels of sedimentation on coastal reefs.

Carbon and oxygen isotopic composition of a Guam coral and their relationships to environmental variables in the western Pacific

We examine the high-resolution (∼32 samples/year) carbon and oxygen isotopic composition (δ 13 C coral and δ 18 O coral ) in a coral core ( Porites lobata ) from Double Reef, Guam over the years 1980–2000. The δ 13 C coral shows clear seasonal variations with mean seasonal amplitude of 1.89‰, which roughly corresponds with seasonal variations in solar radiation. The seasonal amplitude of δ 18 O coral variations are small (0.23–0.57‰), but they are significantly correlated with sea surface temperature (SST) and salinity (SSS). The δ 18 O coral and SST are more strongly correlated during El Niño/Southern Oscillation (ENSO) warm phases ( r =−0.81, p <0.01) than during non-ENSO phases ( r =−0.65, p <0.01) and ENSO cool phases ( r =−0.48, p <0.01). These different relationships are due to differences in winter SST and in seawater δ 18 O (δ 18 O sw ) during ENSO warm phases (<27 °C and higher values of δ 18 O sw ) compared with cool phases (>28 °C and lower values of δ 18 O sw ) at Guam. These differences in oceanic parameters result from movements of the Western Pacific Warm Pool (WPWP) during the different phases of ENSO. Anomalies in δ 18 O sw , inferred from the δ 18 O coral and instrumental SST, are consistent with SSS anomalies for the years 1980–2000. These δ 18 O sw anomalies may reflect changes in SSS and evaporation–precipitation due to movements of the WPWP. This detailed analysis of a coral from Guam suggests that it may contain an excellent archive of past ENSO events.

Carbon and oxygen isotopic composition of a Guam coral and their relationships to environmental variables in the western Pacific

We examine the high-resolution (∼32 samples/year) carbon and oxygen isotopic composition (δ 13C coral and δ 18O coral) in a coral core ( Porites lobata) from Double Reef, Guam over the years 1980–2000. The δ 13C coral shows clear seasonal variations with mean seasonal amplitude of 1.89‰, which roughly corresponds with seasonal variations in solar radiation. The seasonal amplitude of δ 18O coral variations are small (0.23–0.57‰), but they are significantly correlated with sea surface temperature (SST) and salinity (SSS). The δ 18O coral and SST are more strongly correlated during El Niño/Southern Oscillation (ENSO) warm phases ( r=−0.81, p<0.01) than during non-ENSO phases ( r=−0.65, p<0.01) and ENSO cool phases ( r=−0.48, p<0.01). These different relationships are due to differences in winter SST and in seawater δ 18O (δ 18O sw) during ENSO warm phases (<27 °C and higher values of δ 18O sw) compared with cool phases (>28 °C and lower values of δ 18O sw) at Guam. These differences in oceanic parameters result from movements of the Western Pacific Warm Pool (WPWP) during the different phases of ENSO. Anomalies in δ 18O sw, inferred from the δ 18O coral and instrumental SST, are consistent with SSS anomalies for the years 1980–2000. These δ 18O sw anomalies may reflect changes in SSS and evaporation–precipitation due to movements of the WPWP. This detailed analysis of a coral from Guam suggests that it may contain an excellent archive of past ENSO events.

Strontium in coral aragonite: 2. Sr coordination and the long-term stability of coral environmental records

We have used X-ray Diffraction (XRD) and Sr K-edge Extended X-ray Absorption Fine Structure (EXAFS) to determine the structural state of Sr in a suite of coral aragonite samples. Our samples encompassed a selection of coral species ( Porites lobata, Porites lutea, Pocillopora eydouxi, Montastrea annularis, Pavona gigantea and Pavona clavus) including some commonly used for palaeoenvironmental reconstruction. Aragonite was the only carbonate observed by XRD. We refined the isolated EXAFS against structural models for Sr in aragonite and two-phase strontianite/aragonite mixes. Our data are indistinguishable from Sr ideally substituted in aragonite and strontianite was present below detection levels (estimated at <5% of Sr present). Comparisons of recent and ancient coral aragonite show no sign of exsolution, either by spinodal decomposition or by the direct nucleation of strontianite domains. Published diffusion rates of Sr in ionic solids support the view that exsolution would occur prohibitively slowly. Coral aragonites are metastable materials with slow diffusion kinetics that have the potential to encode environments over timescales of millions of years.