Posts Tagged 'calcification'

Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance

While seawater acidification induced by elevated CO2 is known to impact coccolithophores, the effects in combination with decreased salinity caused by sea ice melting and/or hydrological events have not been documented. Here we show the combined effects of seawater acidification and reduced salinity on growth, photosynthesis and calcification of Emiliania huxleyi grown at 2 CO2 concentrations (low CO2 LC: 400 μatm; high CO2 HC: 1000 μatm) and 3 levels of salinity (25, 30 and 35 ‰). A decrease of salinity from 35 to 25‰ increased growth rate, cell size and effective photochemical efficiency under both LC or HC. Calcification rates were relatively insensitive to combined effects of salinity and OA treatment but were highest under 3 5‰ and HC conditions, with higher ratios of calcification to photosynthesis (C : P) in the cells grown under 35 ‰ compared with those grown at 25 ‰. In addition, elevated dissolved inorganic carbon (DIC) concentration at the salinity of 35 ‰ stimulated its calcification. In contrast, photosynthetic carbon fixation increased almost linearly with decreasing salinity, regardless of the pCO2 treatments. When subjected to short-term exposure to high light, the low-salinity-grown cells showed the highest photochemical effective quantum yield with the highest repair rate, though HC treatment enhanced PSII damage rate. Our results suggest Emiliania huxleyi can tolerate low salinity plus acidification conditions by up-regulating its photosynthetic performance together with a relatively insensitive calcification response, which may help it better adapt to future ocean global environmental changes, especially in the coastal areas of high latitudes.

Continue reading ‘Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance’

Ecological and physiological constraints of deep-sea corals in a changing environment

Deep-water or cold-water corals are abundant and highly diverse, greatly increase habitat heterogeneity and species richness, thereby forming one of the most significant ecosystems in the deep sea. Despite this remote location, they are not removed from the different anthropogenic disturbances that commonly impact their shallow-water counterparts. The global decrease in seawater pH due to increases in atmospheric CO2 are changing the chemical properties of the seawater, decreasing the concentration of carbonate ions that are important elements for different physiological and ecological processes. Predictive models forecast a shoaling of the carbonate saturation in the water column due to OA, and suggest that cold-water corals are at high risk, since large areas of suitable habitat will experience suboptimal conditions by the end of the century. The main objective of this study was to explore the fate of the deep-water coral community in time of environmental change. To better understand the impact of climate change this study focused in two of the most important elements of dee-sea coral habitat, the reef forming coral Lophelia pertusa and the octocoral community, particularly the gorgonian Callogorgia delta. By means of controlled experiments, I examined the effects of long and short-term exposures to seawater simulating future scenarios of ocean acidification on calcification and feeding efficiency. Finally In order to understand how the environment influences the community assembly, and ultimately how species cope with particular ecological filters, I integrated different aspects of biology such functional diversity and ecology into a more evolutionary context in the face of changing environment. My results suggest that I) deep-water corals responds negatively to future OA by lowering the calcification rates, II) not all individuals respond in the same way to OA with high intra-specific variability providing a potential for adaptation in the longterm III) there is a disruption in the balance between accretion and dissolution that in the long term can shift from net accretion to net dissolution, and IV) there is an evolutionary implication for certain morphological features in the coral community that can give an advantage under stresfull conditions. Nevertheless, the suboptimal conditions that deepwater corals will experience by the end of the century could potentially threaten their persistence, with potentially negative consequences for the future stability of this already fragile ecosystem.

Continue reading ‘Ecological and physiological constraints of deep-sea corals in a changing environment’

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

The processes that occur at the micro‐scale site of calcification are fundamental to understanding the response of coral growth in a changing world. However, our mechanistic understanding of chemical processes driving calcification is still evolving. Here, we report the results of a long‐term in situ study of coral calcification rates, photo‐physiology, and calcifying fluid (cf) carbonate chemistry (using boron isotopes, elemental systematics, and Raman spectroscopy) for seven species (four genera) of symbiotic corals growing in their natural environments at tropical, subtropical, and temperate locations in Western Australia (latitudinal range of ~11°). We find that changes in net coral calcification rates are primarily driven by pHcf and carbonate ion concentration []cf in conjunction with temperature and DICcf. Coral pHcf varies with latitudinal and seasonal changes in temperature and works together with the seasonally varying DICcf to optimize []cf at species‐dependent levels. Our results indicate that corals shift their pHcf to adapt and/or acclimatize to their localized thermal regimes. This biological response is likely to have critical implications for predicting the future of coral reefs under CO2‐driven warming and acidification.

Continue reading ‘Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia’

Seawater temperature and buffering capacity modulate coral calcifying pH

Scleractinian corals promote the precipitation of their carbonate skeleton by elevating the pH and dissolved inorganic carbon (DIC) concentration of their calcifying fluid above that of seawater. The fact corals actively regulate their calcifying fluid chemistry implies the potential for acclimation to ocean acidification. However, the extent to which corals can adjust their regulation mechanism in the face of decreasing ocean pH has not been rigorously tested. Here I present a numerical model simulating pH and DIC up-regulation by corals, and use it to determine the relative importance of physiological regulation versus seawater conditions in controlling coral calcifying fluid chemistry. I show that external seawater temperature and buffering capacity exert the first-order control on the extent of pH elevation in the calcifying fluid and explain most of the observed inter- and intra-species variability. Conversely, physiological regulation, represented by the interplay between enzymatic proton pumping, carbon influx and the exchange of calcifying fluid with external seawater, contributes to some variability but remain relatively constant as seawater conditions change. The model quantitatively reproduces variations of calcifying fluid pH in natural Porites colonies, and predicts an average 0.16 unit decrease in Porites calcifying fluid pH, i.e., ~43% increase in H+ concentration, by the end of this century as a combined result of projected ocean warming and acidification, highlighting the susceptibility of coral calcification to future changes in ocean conditions. In addition, my findings support the development of coral-based seawater pH proxies, but suggest the influences of physicochemical and biological factors other than seawater pH must be considered.

Continue reading ‘Seawater temperature and buffering capacity modulate coral calcifying pH’

Evaluation of autonomously measured alkalinity, pH, and pCO2 variability on a coral reef

Currently, our understanding of alkalinity (AT) variability in highly dynamic
environments such as coral reefs is limited by the dearth of AT measurements. In order to better characterize these environments, high temporal resolution AT data are needed. This work employed the newly developed Submersible Autonomous Moored Instrument for Alkalinity (SAMI-alk), a fully autonomous in situ AT analyzer, to study seawater AT variability. The main goals of this research were to evaluate the utility of combining the SAMI-alk data with currently available in situ measurements of pH and partial pressure of carbon dioxide (pCO2) to characterize the inorganic carbon cycle, and to measure AT variability and determine what drives it on a coral reef. Autonomous AT and pH sensors (SAMI-alk and SAMI-pH) were deployed along with existing pCO2 (MAPCO2) and pH (SeaFET) sensors in Kanoehe Bay, HI from June 4 – 21, 2013. The results show that the pH – AT combination can provide important information about autonomously measured in situ data quality, and that it can be used to fully characterize the inorganic CO2 system in seawater. The SAMI-alk data were also used to examine AT variability and thereby calcification rates on coral reefs in Kaneohe Bay. AT varied by more than 100 µmol kg-1 on a diel basis due to CaCO3 production and dissolution. Dissolved inorganic carbon (DIC), calculated from the pH – AT sensor pair, varied by more than 200 µmol kg-1 , due primarily to biological metabolism on the reef. Reef calcification and metabolism dramatically alter the seawater chemistry from the open ocean source water and drive the large diel changes in all measured inorganic carbon parameters (i.e. aragonite saturation state (Ωarag), pH, pCO2, AT, DIC). This data set demonstrates the value of a high-quality in situ AT analyzer in a coral reef environment; making it possible to determine combined CO2 system variability with unprecedented temporal resolution. These data show that NEC can be consistently sustained (net CaCO3 production) until a threshold level of net respiration (NEP) is reached, around -50 (mmol m-2 h-1), which corresponds to an AT : DIC ratio of about 1:1.

Continue reading ‘Evaluation of autonomously measured alkalinity, pH, and pCO2 variability on a coral reef’

Diurnally fluctuating pCO2 modifies the physiological responses of coral recruits under ocean acidification

Diurnal pCO2 fluctuations have the potential to modulate the biological impact of ocean acidification (OA) on reef calcifiers, yet little is known about the physiological and biochemical responses of scleractinian corals to fluctuating carbonate chemistry under OA. Here, we exposed newly settled Pocillopora damicornis for 7 days to ambient pCO2, steady and elevated pCO2 (stable OA) and diurnally fluctuating pCO2 under future OA scenario (fluctuating OA). We measured the photo-physiology, growth (lateral growth, budding and calcification), oxidative stress and activities of carbonic anhydrase (CA), Ca-ATPase and Mg-ATPase. Results showed that while OA enhanced the photochemical performance of in hospite symbionts, it also increased catalase activity and lipid peroxidation. Furthermore, both OA treatments altered the activities of host and symbiont CA, suggesting functional changes in the uptake of dissolved inorganic carbon (DIC) for photosynthesis and calcification. Most importantly, only the fluctuating OA treatment resulted in a slight drop in calcification with concurrent up-regulation of Ca-ATPase and Mg-ATPase, implying increased energy expenditure on calcification. Consequently, asexual budding rates decreased by 50% under fluctuating OA. These results suggest that diel pCO2 oscillations could modify the physiological responses and potentially alter the energy budget of coral recruits under future OA, and that fluctuating OA is more energetically expensive for the maintenance of coral recruits than stable OA.

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Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers

This thesis investigates the drivers of coral reef ecosystem metabolism and the abilities of the different methodologies and analytical approaches to accurately represent reef dynamics. It encompassed tracing natural nutrient additions through bird guano into a coral cay. Developing a new, automated system for measuring carbonate chemistry for coral reef metabolism and the effects of mass coral bleaching on ecosystem functioning were quantified. Overall, it showed that natural nutrient additions and bleaching differentially affect coral reef metabolism and that subtle differences in analytical methods, sampling approaches, and data interpretation techniques can cause significant variation in metabolic estimates.

Continue reading ‘Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers’

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Ocean acidification in the IPCC AR5 WG II

OUP book