Alkalinity to calcium flux ratios for corals and coral reef communities: variances between isolated and community conditions

Calcification in reef corals and coral reefs is widely measured using the alkalinity depletion method which is based on the fact that two protons are produced for every mole of CaCO3 precipitated. This assumption was tested by measuring the total alkalinity (TA) flux and Ca2+ flux of isolated components (corals, alga, sediment and plankton) in reference to that of a mixed-community. Experiments were conducted in a flume under natural conditions of sunlight, nutrients, plankton and organic matter. A realistic hydrodynamic regime was provided. Groups of corals were run separately and in conjunction with the other reef components in a mixed-community. The TA flux to Ca2+ flux ratio (ΔTA: ΔCa2+) was consistently higher in the coral-only run (2.06 ± 0.19) than in the mixed-community run (1.60 ± 0.14, p-value = 0.011). The pH was higher and more stable in the mixed-community run (7.94 ± 0.03 vs. 7.52 ± 0.07, p-value = 3 × 10−5). Aragonite saturation state (Ωarag) was also higher in the mixed-community run (2.51 ± 0.2 vs. 1.12 ± 0.14, p-value = 2 × 10−6). The sediment-only run revealed that sediment is the source of TA that can account for the lower ΔTA: ΔCa2+ ratio in the mixed-community run. The macroalgae-only run showed that algae were responsible for the increased pH in the mixed-community run. Corals growing in a mixed-community will experience an environment that is more favorable to calcification (higher daytime pH due to algae photosynthesis, additional TA and inorganic carbon from sediments, higher Ωarag). A paradox is that the alkalinity depletion method will yield a lower net calcification for a mixed-community versus a coral-only community due to TA recycling, even though the corals may be calcifying at a higher rate due to a more optimal environment

Alliance for Coastal Technologies: Advancing Moored pCO2 Instruments in Coastal Waters

The Alliance for Coastal Technologies (ACT) has been established to support innovation and to provide the information required to select the most appropriate tools for studying and monitoring coastal and ocean environments. ACT is a consortium of nationally prominent ocean science and technology institutions and experts who provide credible performance data of these technologies through third-party, objective testing. ACT technology verifications include laboratory and field tests over short- and long-term deployments of commercial technologies in diverse environments to provide unequivocal, unbiased confirmation that technologies meet key performance requirements. ACT demonstrations of new technologies validate the technology concept and help eliminate performance problems before operational introduction. ACT’s most recent demonstration of pCO2 sensors is an example of how ACT advances the evolution of ocean observing technologies, in this case to address the critical issue of ocean acidification, and promotes more informed decision making on technology capabilities and choices

Phosphate metabolism of coral reef flats

Bibliography: leaves 86-90Microfiche.viii, 90 leaves, bound ill., maps 29 cmThe present dogma on coral reef metabolism suggests that there is little exchange of phosphate between the benthic community and the water overlying that community. The reef's nutritional requirements supposedly are met by cycling or retention within the benthic community. I posed the hypothesis that the phosphate needs of the reef producers could be met through exchange with the water column, and that net changes of phosphate in water as it flows over reef communities reflect net metabolic processes. Phosphate uptake experiments were conducted on collections of reef organisms incubated in aquaria. Extensive field sampling was performed. to determine the net changes of phosphate over the Kaneohe Bay barrier reef flat. Carbon, nitrogen, and phosphorus ratios were determined for reef autotrophs. Results of these experiments indicate that the uptake rate of phosphate is proportional to the reactive phosphate concentrations, and that at ambient phosphate concentrations of 0.15 μM the uptake and release of phosphate between the reef benthos and the water column is approximately 0.1% of community dark respiration (mole P uptake/mole O2 respired). The field results demonstrate that the depletion of phosphate over the reef flat may be used to measure net community carbon production if the C:P ratio of the reef autotrophic organisms (approximately 500-650) is used to scale phosphorus uptake to net carbon production. It is reasoned that recycling of phosphorus for a whole reef flat is not tight, and the system can depend primarily on exchange with the water column for its nutrients. The high advective flux of phosphate over most reef flats encourages a large biomass system, whereas the low concentration of phosphate probably influences the growth rate per biomass of most reef primary producers

Phosphate uptake by a coral reef flat : a measurement of the Stanton number

International audienceThe mass-transfer-limited equation for nutrient uptake is m = St×Ub×Cb, where St is the Stanton number, which is a physical descriptor of the bottom; Ub is water velocity, and Cb the bulk water nutrient concentration. We measured St in the field by using phosphate uptake across a 300m wide mixed coral-algal reef flat in Reunion Island. Phosphate concentrations and current velocities were measured at six stations evenly distributed along a cross-shore transect. We used peristaltic pumps to get integrated water samples for 4-6 hr over the rising tide, to smooth the variability created by complex current trajectories. The gradient (k) of the natural logarithm of phosphate concentration, versus distance along the transect, was (43±6)*10-4 m -1. Water velocities were measured in the middle of the transect, using an acoustic Doppler current profiler. Depth-averaged cross-reef horizontal velocity (Ux) was 0.042±0.011 m.s-1. To account for oscillatory flows, we measured Urms (0.102±0.030 m.s -1), using dissolution of plaster forms at the six stations. k was multiplied by the mean water depth, and Ux/Urms, giving the reef flat Stanton number. St was (19±4)*10-4, which is consistent with published values for coral communities in flumes, given the low water velocities and high 3-dimensional relief of the reef. This corroborates the idea that phosphate uptake by reef flats operates very near a mass-transfer limit

Nutrient loading affects the relationship between coral calcification and aragonite saturation state

International audienceOral presentation about Nutrient loading affects the relationship between coral calcification and aragonite saturation stat

Buffer Capacity, Ecosystem Feedbacks, and Seawater Chemistry under Global Change

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Rising carbonate dissolution due to bioeroding microflora under climate change - an overlooked buffer process?

International audienceSince the industrial era, the atmospheric partial pressure of CO2 (pCO2) has been rising. Consequently, the world’s ocean is getting warmer and acidified. By the end of the century, IPCC models in the worst case scenario predict an increase of sea surface temperature of 4°C and a decrease of seawater pH estimated at 0.3-0.4 pH-units. As a consequence, the saturation state of surface seawater (Ω) with respect to calcium carbonate minerals (CaCO3) will also decrease. All these climatic factors are expected to affect calcification and dissolution processes, putting for instance in jeopardy coral reef ecosystems which are entirely made of carbonates. Among those processes, biogenic dissolution of carbonates due to bioeroding microflora (or euendoliths), which comprise cyanobacteria, algae and fungi, has been the most overlooked process and is currently not taken into account in biogeochemical models. So far, rates of biogenic dissolution were estimated by quantifying the volume of calcium carbonate removed by bioeroding filaments using microscopy observations. Although those rates are significant (up to 1.1 kg CaCO3 dissolved per m2 per year in coral reefs), the question is how much alkalinity bioeroding microflora are able to release in the ocean, and how they are influenced by climate change (pH and temperature). In addition, all experiments recently carried out which highlighted the positive effects of ocean warming and acidification on biogenic dissolution, were realized under controlled conditions (mesocosms) in tropical regions over short periods of time (2-3 months). The long term dynamics of the process of biogenic dissolution under natural conditions remains poorly known. Here we present results of five experiments carried out in tropical (Hawaii, New Caledonia reefs) and temperate regions (Ischia in Italy) at different time scales (a few hours up to 4 years), to show that (1) the amount of alkalinity produced by bioeroding microflora is significant (as high as 71 mequiv m-2 d-1 which converts to a CaCO3 dissolution rate of 1.3 kg m-2 y-1 under constant light conditions in tropical regions), (2) biogenic dissolution can occur under various saturation states (0.8 2 (by 50% to 250% depending on conditions) as long as the saturation state is above 1 (otherwise carbonate dissolution due to chemical conditions limits euendolith development and thus, biogenic dissolution), and (3) biogenic dissolution is more efficient (x2.7) when new carbonate substrates become available for colonization by microboring communities in the summer season (higher temperature, light intensities, etc…) than in the winter season in tropical regions as colonization by the main agents of biogenic dissolution is faster in summer than in winter. These results suggest that at least in coral reef systems, global warming and ocean acidification will most probably stimulate the process of carbonate bioegenic dissolution due to microboring flora, accelerating the transition from a net coral reef accretion towards net coral reef dissolution. We estimate that today, at ambient temperature and pH in coral reef ecosystems, at most 20% of produced carbonates are dissolved by bioeroding microflora. By 2100, these organisms may be responsible for the dissolution of up to 70% of reef carbonates that are expected to be produced. If all dissolution processes are taken into account, i.e. chemical dissolution driven by water chemistry and bacteria metabolic activity, biogenic dissolution by bioeroding flora and biogenic dissolution by macroborers (such as boring sponges), reef carbonate budget may become negative much earlier than 2100. The capacity of carbonate biogenic dissolution due to bioeroding flora in buffering seawater remains however, unknown and needs to be investigated in order to better understand carbon biogeochemical cycles and to improve predictions of the fate of carbonate coastal systems

Use of \u3cem\u3eIn Situ\u3c/em\u3e and Airborne Reflectance for Scaling-Up Spectral Discrimination of Coral Reef Macroalgae from Species to Communities

In principle, a priori knowledge of organism-scale spectral signatures for key ecological end-members is a basic requirement for identifying coral reef benthic communities using hyperspectral remotely-sensed imagery. Spectral signatures of end-members are now relatively well known for predominant reef taxa (coral, algae) and for the background of the living communities (e.g. sediments). What remains unclear is whether the criteria for spectral discrimination between endmembers at the millimeter or centimeter scale remain valid when attempting to process images at several meters resolution. In other words, is it possible to scale-up spectral criteria of identification from species/organisms to communities? We address this issue with in situ and \u27compact airborne spectrometer imager\u27 (CASI) hyperspectral measurements of the tropical marine flora of 2 South Pacific Ocean coral reefs. Targets were the dominant algal species and communities encountered in the shallow (0 to 3 m) barrier and fringing reefs of Moorea Island and the outer margin of the rim of Rangiroa Atoll (French Polynesia). Stepwise wavelength selection and linear discriminant analysis highlighted the key non-redundant wavelengths necessary to achieve good separation between the predefined ecological groups. Comparison of the wavelengths identified from in situ and airborne measurements allowed definition of a subset of common wavelengths that were robust to changes in spatial scale and still provided excellent discrimination and classification accuracy between the ecological groups. These results suggest that continuous spectral signatures acquired in situ at the centimeter scale can be used to select key discrete wavelengths for remote-sensing observations of communities at the meter scale despite the spatial heterogeneity in benthic cover and the resulting spectral mixing

Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef

The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21st century. This increase will reduce the concentration of CO32− of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage. Using the large 2650 m3 coral reef mesocosm at the BIOSPHERE‐2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcification of coral reef organisms at the community scale. Our experimental design was to obtain a long (3.8 years) time series of the net calcification of the complete system and all relevant physical and chemical variables (temperature, salinity, light, nutrients, Ca2+,pCO2, TCO2, and total alkalinity). Periodic additions of NaHCO3, Na2CO3, and/or CaCl2 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcification in response to our manipulations of the saturation state. We show that the net community calcification rate responds to manipulations in the concentrations of both Ca2+ and CO32− and that the rate is well described as a linear function of the ion concentration product, [Ca2+]0.69[CO32−]. This suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcification on coral reefs at the ecosystem level. We compare the sensitivity of calcification to short‐term (days) and long‐term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification between the years 1880 and 2065 A.D. based on our long‐term results is 40%. Previous small‐scale, short‐term organismal studies predicted a calcification reduction of 14‐30%. This much longer, community‐scale study suggests that the impact on coral reefs may be greater than previously suspected. In the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses

Performance Demonstration Statement for Sunburst Sensors SAMI-CO2

The plant glutathione peroxidase (GPX) family consists of multiple isoenzymes with distinct subcellular locations which exhibit different tissue-specific expression patterns and environmental stress responses. Contrary to most of their counterparts in animal cells, plant GPXs contain cysteine instead of selenocysteine in their active site and while some of them have both glutathione peroxidase and thioredoxin peroxidase functions, the thioredoxin regenerating system is much more efficient in vitro than the glutathione system. At present, the function of these enzymes in plants is not completely understood. The occurrence of thiol-dependent activities of plant GPX isoenzymes suggests that - besides detoxification of H2O2 and organic hydroperoxides - they may be involved in regulation of the cellular redox homeostasis by maintaining the thiol/disulfide or NADPH/NADP+ balance. GPXs may represent a link existing between the glutathione- and the thioredoxin-based system. The various thiol buffers, including Trx, can affect a number of redox reactions in the cells most probably via modulation of thiol status. It is still required to identify the in vivo reductant for particular GPX isoenzymes and partners that GPXs interact with specifically. Recent evidence suggests that plant GPXs does not only protect cells from stress induced oxidative damage but they can be implicated in plant growth and development. Following a more general introduction, this study summarizes present knowledge on plant GPXs, highlighting the results on gene expression analysis, regulation and signaling of Arabidopsis thaliana GPXs and also suggests some perspectives for future research