Effect of environmental conditions and skeletal ultrastructure on the Li isotopic composition of scleractinian corals

The lithium isotope compositions (Li-7/Li-6) and Li/Ca ratios of shallow-water and deep-sea corals (Porites lutea, Cladocora caespitosa, Lophelia pertusa and Desmophyllum cristagalli) were measured using a Cameca ims 1270 ion microprobe. The two C. caespitosa samples were grown under controlled conditions at CO2 partial pressures (pCO(2)) of 416 +/- 29 mu atm and 729 +/- 30 mu atm, respectively. In situ analyses show that all samples are isotopically homogeneous (within analytical precision, +/- 1.1 parts per thousand, 1 sigma) and display significantly lower delta Li-7 values relative to seawater. indicating a significant isotope fractionation during aragonite formation. In contrast to all other elements analysed so far, there is no relationship between the Li isotopic compositions and the skeletal ultrastructure. However, Li/Ca does show variation correlated with ultrastructure, albeit with significant differences between species. This implies that the bio mineralization mechanisms, which are supposed to be different for the different skeletal components, do not influence the Li isotopic composition in corals. In particular, the model of Rayleigh fractionation in a semi-enclosed calcifying fluid is incompatible with the homogeneity of the Li isotope compositions at the micrometer scale We also. show that changes in pCO(2) (and pH) do not significantly affect the Li isotope signature. Nevertheless, a small but significant and systematic difference in Li isotopic composition is observed between deep-sea azooxanthellate and shallow-water zooxanthellate corals. The lack of dependence on pH and pCO(2) and on skeletal ultrastructure indicates that the U isotopic signature of corals could be used as a proxy for reconstructing the paleo-delta Li-7 of seawater and, potentially, for deconvolving past continental weathering rates. (C) 2009 Elsevier B.V. All rights reserved.

Morphology, microstructure, crystallography, and chemistry of distinct CaCO3 deposits formed by early recruits of the scleractinian coral Pocillopora damicornis

Duncan Alexander, Melany Melissa Gilis, Anders Meibom, Jaroslaw Hubert Stolarski

Scleractinian corals begin their biomineralization process shortly after larval settlement with the formation of calcium carbonate (CaCO3) structures at the interface between the larval tissues and the substrate. The newly settled larvae exert variable degrees of control over this skeleton formation, providing an opportunity to study a range of biocarbonate structures, some of which are transient and not observed in adult coral skeletons. Here we present a morphological, structural, crystallographic, and chemical comparison between two types of aragonite deposits observed during the skeletal development of 2-days old recruits of Pocillopora damicornis: (1) Primary septum and (2) Abundant, dumbbell-like structures, quasi-randomly distributed between initial deposits of the basal plate and not present in adult coralsAt the mesoscale level, initial septa structures are formed by superimposed fan-shaped fasciculi consisting of bundles of fibers, as also observed in adult corals. This organization is not observed in the dumbbell-like structures. However, at the ultrastructural level there is great similarity between septa and dumbbell components. Both are composed of

Wiley-Blackwell2015

Physiological and isotopic responses of scleractinian corals to ocean acidification

Maoz Fine, Anders Meibom

Uptake of anthropogenic CO2 by the oceans is altering seawater chemistry with potentially serious consequences for coral reef ecosystems due to the reduction of seawater pH and aragonite saturation state (Omega(arag)) The objectives of this long-term study were to investigate the viability of two ecologically important reef-building coral species, massive Ponies sp. and Stylophora pistillata, exposed to high pCO(2) (or low pH) conditions and to observe possible changes in physiologically related parameters as well as skeletal isotopic composition. Fragments of Ponies sp. and S. pistillata were kept for 6-14 months under controlled aquarium conditions characterized by normal and elevated pCO(2) conditions, corresponding to pH(T) values of 8.09, 7.49, and 7.19, respectively. In contrast with shorter, and therefore more transient experiments, the long experimental time-scale achieved in this study ensures complete equilibration and steady state with the experimental environment and guarantees that the data provide insights into viable and stably growing corals. During the experiments, all coral fragments survived and added new skeleton, even at seawater Omega(arag) < 1, implying that the coral skeleton is formed by mechanisms under strong biological control. Measurements of boron (B), carbon (C), and oxygen (O) isotopic composition of skeleton, C isotopic composition of coral tissue and symbiont zooxanthellae, along with physiological data (such as skeletal growth, tissue biomass, zooxanthellae cell density, and chlorophyll concentration) allow for a direct comparison with corals living under normal conditions and sampled simultaneously. Skeletal growth and zooxanthellae density were found to decrease, whereas coral tissue biomass (measured as protein concentration) and zooxanthellae chlorophyll concentrations increased under high pCO(2) (low pH) conditions. Both species showed similar trends of delta B-11 depletion and delta O-18 enrichment under reduced pH, whereas the delta C-13 results imply species-specific metabolic response to high pCO(2) conditions. The skeletal delta B-11 values plot above seawater delta B-11 vs. pH borate fractionation curves calculated using either the theoretically derived alpha(B) value of 1.0194 (Kakihana et al. (1977) Bull. Chem. Soc. Jpn. 50, 158) or the empirical alpha(B) value of 1.0272 (Klochko et al. (2006) EPSL 248, 261). However, the effective alpha(B) must be greater than 1.0200 in order to yield calculated coral skeletal delta B-11 values for pH conditions where Omega(arag) >= 1. The delta B-11 vs. pH offset from the seawater delta B-11 vs. pH fractionation curves suggests a change in the ratio of skeletal material laid down during dark and light calcification and/or an internal pH regulation, presumably controlled by ion-transport enzymes. Finally, seawater pH significantly influences skeletal delta C-13 and delta O-18. This must be taken into consideration when reconstructing paleo-environmental conditions from coral skeletons. (C) 2010 Elsevier Ltd. All rights reserved.

2010

Pulsed 86Sr-labeling and NanoSIMS imaging to study coral biomineralization at ultra-structural length scales

Isabelle Domart-Coulon, Anders Meibom, Jaroslaw Hubert Stolarski

A method to label marine biocarbonates is developed based on a concentration enrichment of a minor stable isotope of a trace element that is a natural component of seawater, resulting in the formation of biocarbonate with corresponding isotopic enrichments. This biocarbonate is subsequently imaged with a NanoSIMS ion microprobe to visualize the locations of the isotopic marker on sub-micrometric length scales, permitting resolution of all ultra-structural details. In this study, a scleractinian coral, Pocillopora damicornis, was labeled 3 times with Sr-86-enhanced seawater for a period of 48 h with 5 days under normal seawater conditions separating each labeling event. Two non-specific cellular stress biomarkers, glutathione-S-transferase activity and porphyrin concentration plus carbonic anhydrase, an enzymatic marker involved in the physiology of carbonate biomineralization, as well as unchanged levels of zooxanthellae photosynthesis efficiency indicate that coral physiological processes are not affected by the Sr-86-enhancement. NanoSIMS images of the Sr-86/Ca-44 ratio in skeleton formed during the experiment allow for a determination of the average extension rate of the two major ultra-structural components of the coral skeleton: Rapid Accretion Deposits are found to form on average about 4.5 times faster than Thickening Deposits. The method opens up new horizons in the study of biocarbonate formation because it holds the potential to observe growth of calcareous structures such as skeletons, shells, tests, spines formed by a wide range of organisms under essentially unperturbed physiological conditions.

Springer-Verlag2012

Physiological and isotopic responses of scleractinian corals to ocean acidification

Maoz Fine, Anders Meibom

2010