Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi, 2008

Ocean acidification in response to rising atmospheric CO2 partial pressures is widely expected to reduce calcification by marine organisms. From the mid-Mesozoic, coccolithophores have been major calcium carbonate producers in the world's oceans, today accounting for about a third of the total marine CaCO3 production. Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.

Seawater carbonate chemistry, particulate organic particles, nutrients and species data during experiments with diatoms, 2006

We examine the effects of seawater pCO2 concentration of 25, 41, and 76 kPa (250, 400, and 750 matm) on the growth rate of a natural assemblage of mixed phytoplankton obtained from a carefully controlled, 14-d mesocosm experiment. Throughout the experiment period, in all enclosures, two phytoplankton taxa (microflagellates and cryptomonads) and two diatom species (Skeletonema costatum and Nitzschia spp.) account for approximately 90% of the phytoplankton community. During the nutrient-replete period from day 9 to day 14 populations of Skeletonema costatum and Nitzschia spp. increased substantially; however, only Skeletonema costatum showed an increase in growth rate with increasing seawater pCO2. Not all diatom species in Korean coastal waters are sensitive to seawater pCO2 under nutrient-replete conditions.

Seawater carbonate chemistry and calcification at Anse des Cuivres, NW Mediterranean, 2004

The community metabolism of a shallow infralittoral ecosystem dominated by the calcareous macroalgae Corallina elongata was investigated in Marseilles (NW Mediterranean), by monitoring hourly changes of seawater pH and total alkalinity over 6 d in February 2000. Fair weather conditions prevailed over the study period as indicated by oceanographic (temperature, salinity, and current velocity and direction) and meteorological variables, which validated the standing water hypothesis. This temperate ecosystem exhibited high community gross primary production (GPP = 519 ± 106 mmol C m-2 d-1, n = 6) and also supported high rates of community respiration (R). As a result, the system was slightly autotrophic (net community production, NCP = 20 mmol C m-2 d-1), with a GPP/R ratio of 1.06. NCP exhibited circadian variations with 2- to 3-fold changes in community respiration, both in the light and in the dark. Rates of net community calcification also exhibited circadian variations, with positive rates (up to 24 mmol CaCO3 m-2 h-1) for irradiance values >300 W m-2 (about 1380 µmol photon m-2 s-1). Below this irradiance threshold, net community dissolution prevailed. Daily net calcification (G) was on average 8 mmol CaCO3 m-2 d-1. CO2 fluxes generated by primary production, respiration, and calcification suggest that the study site was a potential atmospheric CO2 sink of 15 mmol CO2 m-2 d-1 at the time of measurement.

Seawater carbonate chemistry, photosynthesis, respiration and calcification during experiments with scleractinian 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, growth rate and Emiliania huxleyi (strain AC481) biological processes during experiments, 2010

The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppmV CO2, 380 ppmV CO2 and 750 ppmV CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13 °C and 18 °C) during the exponential growth phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that cellular production rate of Particulate Organic Carbon (POC) increased from the present to the future CO2 treatments at 13 °C. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cellular production rate of Particulate Inorganic Carbon (PIC) as well as a lower PIC:POC ratio at future CO2 levels and at 18 °C. Coccosphere-sized particles showed a size reduction with both increasing temperature and CO2concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effects of pCO2 and temperature were observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming.

Seawater carbonate chemistry and processes during experiments with seaurchins Hemicentrotus pulcherrimus and Echinometra mathaei, 2004

Increased carbon dioxide (CO2) concentration in the atmosphere will change the balance of the components of carbonate chemistry and reduce the pH at the ocean surface. Here, we report the effects of increased CO2 concentration on the early development of the sea urchins Hemicentrotus pulcherrimus and Echinometra mathaei. We examined the fertilization, early cleavage, and pluteus larval stage to evaluate the impact of elevated CO2 concentration on fertilization rate, cleavage rate, developmental speed, and pluteus larval morphology. Furthermore, we compared the effects of CO2 and HCl at the same pH in an attempt to elucidate any differences between the two. We found that fertilization rate, cleavage rate, developmental speed, and pluteus larval size all tended to decrease with increasing CO2 concentration. Furthermore, CO2-seawater had a more severe effect than HCl-seawater on the fertilization rate. By contrast, the effects on cleavage rate, developmental speed, and pluteus larval morphology were similar for CO2- and HCl-seawater. Our results suggest that both decreased pH and altered carbonate chemistry affect the early development and life history of marine animals, implying that increased seawater CO2 concentration will seriously alter marine ecosystems. The effects of CO2 itself on marine organisms therefore requires further clarification.

Escape performance of temperate king scallop, Pecten maximus under ocean warming and acidification

Among bivalves, scallops are exceptional due to their capacity to escape from predators by swimming which is provided by rapid and strong claps that are produced by the phasic muscle interspersed with tonic muscle contractions. Based on the concept of oxygen and capacity-limited thermal tolerance, the following hypothesis was tested: ocean warming and acidification (OWA) would induce disturbances in aerobic metabolic scope and extracellular acid-case status and impair swimming performance in temperate scallops. Following long-term incubation under near-future OWA scenarios [20 vs. 10 °C (control) and 0.112 kPa CO2 (hypercapnia) vs. 0.040 kPa CO2 (normocapnic control)], the clapping performance and metabolic rates (MR) were measured in resting (RMR) and fatigued (maximum MR) king scallops, Pecten maximus, from Roscoff, France. Exposure to OA, either alone or combined with warming, left MR and swimming parameters such as the total number of claps and clapping forces virtually unchanged. Only the duration of the escape response was affected by OA which caused earlier exhaustion in hyper- than in normocapnic scallops at 10 °C. While maximum MR was unaffected, warm exposure increased RMR in both normocapnic and hypercapnic P. maximus resulting in similar Q 10 values of ~2.2. The increased costs of maintenance and the observation of strongly reduced haemolymph PO2 levels indicate that at 20 °C scallops have reached the upper thermal pejus range with unbalanced capacities for aerobic energy metabolism. As a consequence, warming to 20 °C decreased mean phasic force during escape performance until fatigue. The observed prolonged recovery time in warm incubated scallops might be a consequence of elevated metabolic costs at reduced oxygen availability in the warmth.

Reefs shift from net accretion to net erosion along a natural environmental gradient

Coral reefs persist in an accretion-erosion balance and ocean acidification resulting from anthropogenic CO2 emissions threatens to shift this balance in favor of net reef erosion. Corals and calcifying algae, largely responsible for reef accretion, are vulnerable to environmental changes associated with ocean acidification, but the direct effects of lower pH on reef erosion has received less attention, particularly in the context of known drivers of bioerosion and natural variability. This study examines the balance between reef accretion and erosion along a well-characterized natural environmental gradient in Kane'ohe Bay, Hawai'i using experimental blocks of coral skeleton. Comparing before and after micro-computed tomography (µCT) scans to quantify net accretion and erosion, we show that, at the small spatial scale of this study (tens of meters), pH was a better predictor of the accretion-erosion balance than environmental drivers suggested by prior studies, including resource availability, temperature, distance from shore, or depth. In addition, this study highlights the fine-scale variation of pH in coastal systems and the importance of microhabitat variation for reef accretion and erosion processes. We demonstrate significant changes in both the mean and variance of pH on the order of meters, providing a local perspective on global increases in pCO2. Our findings suggest that increases in reef erosion, combined with expected decreases in calcification, will accelerate the shift of coral reefs to an erosion-dominated system in a high-CO2 world. This shift will make reefs increasingly susceptible to storm damage and sea-level rise, threatening the maintenance of the ecosystem services that coral reefs provide.

The nitrogen costs of photosynthesis in a diatom under current and future pCO2

With each cellular generation, oxygenic photoautotrophs must accumulate abundant protein complexes that mediate light capture, photosynthetic electron transport and carbon fixation. In addition to this net synthesis, oxygenic photoautotrophs must counter the light-dependent photoinactivation of Photosystem II (PSII), using metabolically expensive proteolysis, disassembly, resynthesis and re-assembly of protein subunits. We used growth rates, elemental analyses and protein quantitations to estimate the nitrogen (N) metabolism costs to both accumulate the photosynthetic system and to maintain PSII function in the diatom Thalassiosira pseudonana, growing at two pCO2 levels across a range of light levels. The photosynthetic system contains c. 15-25% of total cellular N. Under low growth light, N (re)cycling through PSII repair is only c. 1% of the cellular N assimilation rate. As growth light increases to inhibitory levels, N metabolite cycling through PSII repair increases to c. 14% of the cellular N assimilation rate. Cells growing under the assumed future 750 ppmv pCO2 show higher growth rates under optimal light, coinciding with a lowered N metabolic cost to maintain photosynthesis, but then suffer greater photoinhibition of growth under excess light, coincident with rising costs to maintain photosynthesis. We predict this quantitative trait response to light will vary across taxa.

Seawater carbonate chemistry, primary production, biomass and calcification of plankton and bacteria, 2009

Production (abundance and biomass) and net calcification rates of the coccolithophorid Pleurochrysis carterae under different partial pressures of CO2 (pCO2) were examined using short (15, 24 and 39 h), long (7 d) and dark (7 d) incubation experiments. Short incubations were conducted at ambient, 500 and 820 ppm pCO2 levels in natural seawater that was enriched with nutrients and inoculated with P. carterae. Long incubations were conducted at ambient and 1200 ppm pCO2 levels in natural seawater (0.2 µm filtered as well as unfiltered) that was enriched with nutrients and inoculated with P. carterae. Dark incubations were conducted at ambient and 1200 ppm pCO2 in unfiltered seawater that was inoculated with P. carterae. The abundance and biomass of coccolithophorids increased with pCO2 and time. The abundance and biomass of most noncalcifying phytoplankton also increased, and were hardly affected by CO2 inputs. Net calcification rates were negative in short incubations during the pre-bloom phase regardless of pCO2 levels, indicating dissolution of calcium carbonate. Further, the negative values of net calcification in short incubations became less negative with time. Net calcification rates were positive in long incubations during blooms regardless of pCO2 level, and the rate of calcification increased with pCO2. Our results show that P. carterae may adapt to increased (~1200 ppm) pCO2 level with time, and such increase has little effect on the ecology of noncalcifying groups and hence in ecosystem dynamics. In dark incubations, net calcification rates were negative, with the magnitude being dependent on pCO2 levels.

The impact of ocean acidification and warming on the skeletal mechanical properties of the sea urchin Paracentrotus lividus from laboratory and field observations

Increased atmospheric CO2 concentration is leading to changes in the carbonate chemistry and the temperature of the ocean. The impact of these processes on marine organisms will depend on their ability to cope with those changes, particularly the maintenance of calcium carbonate structures. Both a laboratory experiment (long-term exposure to decreased pH and increased temperature) and collections of individuals from natural environments characterized by low pH levels (individuals from intertidal pools and around a CO2 seep) were here coupled to comprehensively study the impact of near-future conditions of pH and temperature on the mechanical properties of the skeleton of the euechinoid sea urchin Paracentrotus lividus. To assess skeletal mechanical properties, we characterized the fracture force, Young's modulus, second moment of area, material nanohardness, and specific Young's modulus of sea urchin test plates. None of these parameters were significantly affected by low pH and/or increased temperature in the laboratory experiment and by low pH only in the individuals chronically exposed to lowered pH from the CO2 seeps. In tidal pools, the fracture force was higher and the Young's modulus lower in ambital plates of individuals from the rock pool characterized by the largest pH variations but also a dominance of calcifying algae, which might explain some of the variation. Thus, decreases of pH to levels expected for 2100 did not directly alter the mechanical properties of the test of P. lividus. Since the maintenance of test integrity is a question of survival for sea urchins and since weakened tests would increase the sea urchins' risk of predation, our findings indicate that the decreasing seawater pH and increasing seawater temperature expected for the end of the century should not represent an immediate threat to sea urchins vulnerability

Seawater carbonate chemistry and calcification rate in flume experiment

Ocean acidification (OA) poses a severe threat to tropical coral reefs, yet much of what is know about these effects comes from individual corals and algae incubated in isolation under high pCO2. Studies of similar effects on coral reef communities are scarce. To investigate the response of coral reef communities to OA, we used large outdoor flumes in which communities composed of calcified algae, corals, and sediment were combined to match the percentage cover of benthic communities in the shallow back reef of Moorea, French Polynesia. Reef communities in the flumes were exposed to ambient (400 ?atm) and high pCO2 (1300 ?atm) for 8 weeks, and calcification rates measured for the constructed communities including the sediments. Community calcification was reduced by 59% under high pCO2, with sediment dissolution explaining ~ 50% of this decrease; net calcification of corals and calcified algae remained positive but was reduced by 29% under elevated pCO2. These results show that, despite the capacity of coral reef calcifiers to maintain positive net accretion of calcium carbonate under OA conditions, reef communities might transition to net dissolution as pCO2 increases, particularly at night, due to enhanced sediment dissolution.

Synergistic effects of pCO2 and iron availability on nutrient consumption ratio of the Bering Sea phytoplankton community

Little is known concerning the effect of CO2 on phytoplankton ecophysiological processes under nutrient and trace element-limited conditions, because most CO2 manipulation experiments have been conducted under elements-replete conditions. To investigate the effects of CO2 and iron availability on phytoplankton ecophysiology, we conducted an experiment in September 2009 using a phytoplankton community in the iron limited, high-nutrient, low-chlorophyll (HNLC) region of the Bering Sea basin . Carbonate chemistry was controlled by the bubbling of the several levels of CO2 concentration (180, 380, 600, and 1000 ppm) controlled air, and two iron conditions were established, one with and one without the addition of inorganic iron. We demonstrated that in the iron-limited control conditions, the specific growth rate and the maximum photochemical quantum efficiency (Fv/Fm) of photosystem (PS) II decreased with increasing CO2 levels, suggesting a further decrease in iron bioavailability under the high-CO2 conditions. In addition, biogenic silica to particulate nitrogen and biogenic silica to particulate organic carbon ratios increased from 2.65 to 3.75 and 0.39 to 0.50, respectively, with an increase in the CO2 level in the iron-limited controls. By contrast, the specific growth rate, Fv/Fm values and elemental compositions in the iron-added treatments did not change in response to the CO2 variations, indicating that the addition of iron canceled out the effect of the modulation of iron bioavailability due to the change in carbonate chemistry. Our results suggest that high-CO2 conditions can alter the biogeochemical cycling of nutrients through decreasing iron bioavailability in the iron-limited HNLC regions in the future.