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.

Properties of seawater and particulate matter from a FRRF instrument, operating in a flow-through mode on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous measurements made with a FRRF instrument, operating in a flow-through mode during the 2009-2012 part of the expedition. It operates by exciting chlorophyll fluorescence using a series of short flashes of controlled energy and time intervals (Kolber et al, 1998). The fluorescence transients produced by this excitation signal were analysed in real-time to provide estimates of abundance of photosynthetic pigments, the photosynthetic yields (Fv/Fm), the functional absorption cross section (a proxy for efficiency of photosynthetic energy acquisition), the kinetics of photosynthetic electron transport between Photosystem II and Photosystem I, and the size of the PQ pool. These parameters were measured at excitation wavelength of 445 nm, 470nm, 505 nm, and 535 nm, allowing to assess the presence and the photosynthetic performance of different phytoplankton taxa based on the spectral composition of their light harvesting pigments. The FRRF-derived photosynthetic characteristics were used to calculate the initial slope, the half saturation, and the maximum level of Photosynthesis vs Irradiance relationship. FRRF data were acquired continuously, at 1-minute time intervals.

Properties of seawater and particulate matter from a WETLabs ALFA hyperspectral laser spectrofluorometer mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous measurements made with an Aquatic Laser Fluorescence Analyzer (ALFA) (Chekalyuk et al., 2014), connected in-line to the TARA flow through system during 2013. The ALFA instrument provides dual-wavelength excitation (405 and 514 nm) of laser-stimulated emission (LSE) for spectral and temporal analysis. It offers in vivo fluorescence assessments of phytoplankton pigments, biomass, photosynthetic yield (Fv/Fm), phycobiliprotein (PBP)-containing phytoplankton groups, and chromophoric dissolved organic matter (CDOM) (Chekalyuk and Hafez, 2008; 2013A). Spectral deconvolution (SDC) is used to assess the overlapped spectral bands of aquatic fluorescence constituents and water Raman scattering (R). The Fv/Fm measurements are spectrally corrected for non-chlorophyll fluorescence background produced by CDOM and other constituents (Chekalyuk and Hafez, 2008). The sensor was cleaned weakly following the manufacturer recommended protocol.

Differing responses of three Southern Ocean Emiliania huxleyi ecotypes to changing seawater carbonate chemistry

The invasion of anthropogenic carbon dioxide into the surface ocean is altering seawater carbonate speciation, a process commonly called ocean acidification. The high latitude waters of the Southern Ocean are one of the primary and most severely affected regions. Coccolithophores are an important phytoplankton group, responsible for the majority of pelagic calcium carbonate production in the world's oceans, with a distribution that ranges from tropical to polar waters. Emiliania huxleyi is numerically the most abundant coccolithophore species and appears in several different ecotypes. We tested the effects of ocean acidification on 3 carefully selected E. huxleyi ecotypes isolated from the Southern Ocean. Their responses were measured in terms of growth, photosynthesis, calcification, cellular geometry, and stoichiometry. The 3 ecotypes exhibited differing sensitivities in regards to seawater carbonate chemistry when cultured at the same temperature (14°C) and continuous light (110 µmol photons/m2/s). Under future ocean acidification scenarios, particulate inorganic to organic carbon ratios (PIC:POC) decreased by 38-44, 47-51 and 71-98% in morphotype A 'over-calcified' (A o/c), A and B/C, respectively. All ecotypes reduced their rate of calcification, but the cold-water adapted ecotype (morphotype B/C) was by far the most sensitive, and almost ceased calcification at partial pressure of carbon dioxide ( pCO2) levels above 1000 µatm. We recommend that future surveys for E. huxleyi cells in the Southern Ocean should include the capability of recognising 'naked cells' by molecular and microscopic tools. The distinct differences in the physiological responses of these 3 dominant Southern Ocean coccolithophore ecotypes are likely to have consequences for future coccolithophore community structures and thereby the Southern Ocean carbon cycle.