Seawater carbonate chemistry and expression of hsp70, hsp90 and hsf1 in the reef coral Acropora digitifera during experiments, 2012

Ocean acidification is an ongoing threat for marine organisms due to the increasing atmospheric CO2 concentration. Seawater acidification has a serious impact on physiologic processes in marine organisms at all life stages. On the other hand, potential tolerance to external pH changes has been reported in coral larvae. Information about the possible mechanisms underlying such tolerance responses, however, is scarce. In the present study, we examined the effects of acidified seawater on the larvae of Acropora digitifera at the molecular level. We targeted two heat shock proteins, Hsp70 and Hsp90, and a heat shock transcription factor, Hsf1, because of their importance in stress responses and in early life developmental stages. Coral larvae were maintained under the ambient and elevated CO2 conditions that are expected to occur within next 100 years, and then we evaluated the expression of hsps and hsf1 by quantitative real-time polymerase chain reaction (PCR). Expression levels of these molecules significantly differed among target genes, but they did not change significantly between CO2conditions. These findings indicate that the expression of hsps is not changed due to external pH changes, and suggest that tolerance to acidified seawater in coral larvae may not be related to hsp expression.

Seawater carbonate chemistry and calcification rate during experiments with coral Stylophora pistillata, 2003

We show here that CO2 partial pressure (pCO2) and temperature significantly interact on coral physiology. The effects of increased pCO2 and temperature on photosynthesis, respiration and calcification rates were investigated in the scleractinian coral Stylophora pistillata. Cuttings were exposed to temperatures of 25°C or 28°C and to pCO2 values of ca. 460 or 760 muatm for 5 weeks. The contents of chlorophyll c2 and protein remained constant throughout the experiment, while the chlorophyll a content was significantly affected by temperature, and was higher under the 'high-temperature-high-pCO2' condition. The cell-specific density was higher at 'high pCO2' than at 'normal pCO2' (1.7 vs. 1.4). The net photosynthesis normalized per unit protein was affected by both temperature and pCO2, whereas respiration was not affected by the treatments. Calcification decreased by 50% when temperature and pCO2 were both elevated. Calcification under normal temperature did not change in response to an increased pCO2. This is not in agreement with numerous published papers that describe a negative relationship between marine calcification and CO2. The confounding effect of temperature has the potential to explain a large portion of the variability of the relationship between calcification and pCO2 reported in the literature, and warrants a re-evaluation of the projected decrease of marine calcification by the year 2100.

Seawater carbonate chemistry and encrusting algal communities duirng a mesocosm experiment, 2007

Owing to anthropogenic emissions, atmospheric concentrations of carbon dioxide could almost double between 2006 and 2100 according to business-as-usual carbon dioxide emission scenarios. Because the ocean absorbs carbon dioxide from the atmosphere, increasing atmospheric carbon dioxide concentrations will lead to increasing dissolved inorganic carbon and carbon dioxide in surface ocean waters, and hence acidification and lower carbonate saturation states. As a consequence, it has been suggested that marine calcifying organisms, for example corals, coralline algae, molluscs and foraminifera, will have difficulties producing their skeletons and shells at current rates, with potentially severe implications for marine ecosystems, including coral reefs. Here we report a seven-week experiment exploring the effects of ocean acidification on crustose coralline algae, a cosmopolitan group of calcifying algae that is ecologically important in most shallowwater habitats. Six outdoor mesocosms were continuously supplied with sea water from the adjacent reef and manipulated to simulate conditions of either ambient or elevated seawater carbon dioxide concentrations. The recruitment rate and growth of crustose coralline algae were severely inhibited in the elevated carbon dioxide mesocosms. Our findings suggest that ocean acidification due to human activities could cause significant change to benthic community structure in shallow-warm-water carbonate ecosystems.

Seawater carbonate chemistry and biological processes during experiments with phytoplankton Emiliania huxleyi (CS369), 2009

Increasing atmospheric CO2 concentration affects calcification in most planktonic calcifiers. Both reduced or stimulated calcification under high CO2 have been reported in the widespread coccolithophore Emiliania huxleyi. This might affect the response of cells to photosynthetically active radiation (PAR; 400-700 nm) and ultraviolet radiation (UVR; 280-400 nm) by altering the thickness of the coccolith layer. Here we show that in the absence of UVR, the calcification rates in E. huxleyi decrease under lowered pH levels (pHNBS of 7.9 and 7.6; pCO2 of 81 and 178 Pa or 804 and 1759 ppmv, respectively) leading to thinned coccolith layers, whereas photosynthetic carbon fixation was slightly enhanced at pH 7.9 but remained unaffected at pH 7.6. Exposure to UVR (UV-A 19.5 W m**-2, UV-B 0.67 W m**-2) in addition to PAR (88.5 W m**-2), however, results in significant inhibition of both photosynthesis and calcification, and these rates are further inhibited with increasing acidification. The combined effects of UVR and seawater acidification resulted in the inhibition of calcification rates by 96% and 99% and that of photosynthesis by 6% and 15%, at pH 7.9 and 7.6, respectively. This differential inhibition of calcification and photosynthesis leads to significant reduction of the ratio of calcification to photosynthesis. Seawater acidification enhanced the transmission of harmful UVR by about 26% through a reduction of the coccolith layer of 31%. Our data indicate that the effect of a high-CO2 and low-pH ocean on E. huxleyi (because of reduced calcification associated with changes in the carbonate system) enhances the detrimental effects of UVR on the main pelagic calcifier.