Calcification and photosynthesis in montipora sp. (cnidaria) and corallina officinalis (rhodophyceae)

PhDOver half of the world's calcification is carried out by algae or by organisms which harbour them, such as coccol ithoph ores, foraminiferans, coralline seaweeds and reef-building corals. Calcification acts as a sink for inorganic carbon and although rather little is known about the precise mechanisms of biological CaC03 formation, the process as a whole is thought to be under threat from atmosphericC02 rise. This study examined the response of a reef-building coral, Montipora digitata and a coralline seaweed, Corallina officinalis to the main factors which influence calcification, namely light, dissolved inorganic carbon (DIC), pH, nitrate and calcium. In contrast to the commonly held view, this study demonstrates that both photosynthesis and calcification were carbon limited in seawater. Since the degree of stimulation by DIC in the light was different for each process, and dark calcification also increased with added DIC, it is clear that photosynthesis and calcification are only loosely coupled. Simultaneous pH measurements were made on the surface of the epithelium and at the site of calcification in the coral Galaxea fascicularis using pH microelectrodes, and demonstrated for the first time that pH at the site of calcification is not a simple response to seawater pH. 2 In this study, nitrate inhibition of calcification was shown to be more powerful in the dark than in the light, indicating that daylength may be a more significant factor in coral biology than previously realised. The currently-accepted hypothesis that biological calcification rates are a simple function of seawater CaC03saturation state was tested experimentally. Results from both Corallina officinalis and Montipora digitata reveal that: a) calcification is far more responsive to changes in inorganic carbon than to calcium concentrations; and b) when [C03 2-] is kept constant, increases in [HC03-1 cause dramatic increases in calcification rates, even at reduced pH. All of these data suggest that calcification in M. digitata and C. officinalis is a strongly biologically controlled process, influenced principally by the seawater bicarbonate concentration and pH, but strongly mediated by light and combined nitrogen

Effect of temperature rise and ocean acidification on growth of calcifying tubeworm shells (Spirorbis spirorbis): an in situ benthocosm approach

The calcareous tubeworm Spirorbis spirorbis is a widespread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbis shell growth we carried out four seasonal experiments in the Kiel Outdoor Benthocosms at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbis was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favoured selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification

An improved approach investigating epithelial ion transport in scleractinian corals

Coral epithelia control ion fluxes to the calcification site influencing biomineralization and proxy incorporation. However, data on in vivo characteristics of coral tissue such as permeability, selectivity, and active ion transport are scarce but important for calcification and proxy modeling. To investigate ion permeability and ion fluxes across coral tissues in vivo, we developed an electrophysiological approach for the assessment of active and passive epithelial transport properties. Growing Stylophora pistillata corals in a thin layer over permeable filters allowed ion exchange at the site of skeleton formation for reproducible measurements of electrophysiological properties of coral tissues in a modified Ussing chamber. Compared to former applications, electrical measurements on these coral filter units were dominated by tissue characteristics with minimal influence of skeleton or physical stress. Coral tissues were cation selective. Their overall high electrical resistance characterized them as tight epithelia indicating low paracellular permeability for passive ion diffusion. This includes ions relevant for calcification. A small short-circuit current indicates active charge transport across the entire coral tissue. The present approach is applicable to corals laterally overgrowing substrates. It allows the electrophysiological characterization of coral tissue in vivo in response to environmental conditions. This will improve our knowledge on transepithelial transport relevant for biomineralization in corals

Boron isotope ratio determination in carbonates /via/ LA-MC-ICP-MS using soda-lime glass standards as reference material

A new in situ method using LA-MC-ICP-MS (193 nm excimer laser) for the determination of stable boron isotope ratios (δ11B) in carbonates was developed. Data were acquired via a standard sample standard bracketing procedure typically providing a reproducibility of 0.5‰ (SD) for samples containing 35 ppm of boron. A single ablation interval consumed about 5 µg of sample corresponding to about 0.2 ng of boron. The major finding was the similar instrumental fractionation behaviour of carbonates, soda-lime glass and sea salt with respect to boron isotopes. As no matrix induced offset was detectable between these distinct materials we propose the use of NIST glasses as internal standards for boron isotope ratio measurements via LA-MC-ICP-MS. This finding overcomes the problem of a missing matrix matched carbonate standard for in situ boron isotope studies. As a first application a set of coral samples from a culturing experiment was analysed. δ11B values range from 19.5 to 25‰ depending on the pH of the water used in the particular treatment. This is in good agreement with the results of earlier studies

Data from: Electrophysiological evidence for light-activated cation transport in calcifying corals

Light has been demonstrated to enhance calcification rates in hermatypic coral species. To date, it remains unresolved whether calcifying epithelia change their ion transport activity during illumination, and whether such a process is mediated by the endosymbiotic algae or can be controlled by the coral host itself. Using a modified Ussing chamber in combination with H+ sensitive microelectrode measurements, the present work demonstrates that light triggers the generation of a skeleton positive potential of up to 0.9 mV in the hermatypic coral Stylophora pistillata. This potential is generated by a net flux of cations towards the skeleton and reaches its maximum at blue (450 nm) light. The effects of pharmacological inhibitors for photosynthesis (DCMU) and anion transport (DIDS) were investigated by pH microelectrode measurements in coral tissues demonstrating a rapid decrease in tissue pH under illumination. However, these inhibitors showed no effect on the electrophysiological light response of the coral host. In contrast, metabolic inhibition by cyanide and deoxyglucose reversibly inhibited the light-induced cation flux towards the skeleton. These results suggest that ion transport across coral epithelia is directly triggered by blue light, independent of photosynthetic activity of algal endosymbionts. Measurements of this very specific and quantifiable physiological response can provide parameters to identify photoreception mechanisms and will help to broaden our understanding of the mechanistic link between light stimulation and epithelial ion transport, potentially relevant for calcification in hermatypic corals

New analytical approach in monitoring of CO2 cycle in aquatic ecosystems

The isotopic signatures of carbon (δ13C) and oxygen (δ18O) can be used as a tool to understand pathways, processes and the fate of CO2 molecules in particular in the marine environment. This is because δ13C-values are controlled by species specific metabolic processes of respiration and photosynthesis, while the δ18O-values are affected by the oxygen exchange between the molecules of CO2 and the ambient water. Here we present a new analytical approach to determine δ13C and δ18O changes using a mid-infrared laser (IRIS) absorption spectrometer, Thermo Scientific™ Delta Ray™ IRIS with URI Connect. With IRIS technology, it is possible to record online changes of carbon and oxygen isotopes with time resolutions of seconds,and with this to have a better insight in CO2 fluxes