Seawater carbonate chemistry and encrusting algal communities during 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 processes during experiments with cyanobacterium Nodularia spumigena, 2009

The surface ocean absorbs large quantities of the CO2 emitted to the atmosphere from human activities. As this CO2 dissolves in seawater, it reacts to form carbonic acid. While this phenomenon, called ocean acidification, has been found to adversely affect many calcifying organisms, some photosynthetic organisms appear to benefit from increasing [CO2]. Among these is the cyanobacterium Trichodesmium, a predominant diazotroph (nitrogen-fixing) in large parts of the oligotrophic oceans, which responded with increased carbon and nitrogen fixation at elevated pCO2. With the mechanism underlying this CO2 stimulation still unknown, the question arises whether this is a common response of diazotrophic cyanobacteria. In this study we therefore investigate the physiological response of Nodularia spumigena, a heterocystous bloom-forming diazotroph of the Baltic Sea, to CO2-induced changes in seawater carbonate chemistry. N. spumigena reacted to seawater acidification/carbonation with reduced cell division rates and nitrogen fixation rates, accompanied by significant changes in carbon and phosphorus quota and elemental composition of the formed biomass. Possible explanations for the contrasting physiological responses of Nodularia compared to Trichodesmium may be found in the different ecological strategies of non-heterocystous (Trichodesmium) and heterocystous (Nodularia) cyanobacteria.

Seawater carbonate chemistry and calcification during tropical reef studies at Moorea (French Polynesia), 1997

Community metabolism and air-sea carbon dioxide (CO2) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskál (Børgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight/m**2. Community gross production (Pg), respiration (R), and net calcification (G) were measured in an open-top enclosure. Pg and R were respectively 248 and 240 mmol Co2/m**2/d, and there was a slight net dissolution of CaCO3 (0.8 mmol/m**2/d). This site was a sink for atmospheric CO2 (10 ± 4 mmol CO2/m**2/d), and the analysis of data from the literature suggests that this is a general feature of algal-dominated reefs. Measurement of air-sea CO2 fluxes in open water close to the enclosure demonstrated that changes in small-scale hydrodynamics can lead to misleading conclusions. Net CO2 evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a C02 source) to the study site.

Seawater carbonate chemistry and community calcification during Shiraha coral reef (Ishigaki Island, Japan) studies, 1995

Only about half of all the CO_2 that has been produced by the burning of fossil fuels now remains in the atmosphere. The CO_2 "missing" from the atmosphere is the subject of an important debate. It was thought that the great majority of the missing CO_2 has invaded the ocean, for this system naturally acts as a giant chemical regulator of the atmosphere. Although it is clear that ocean processes have a major role in the regulation of the carbon dioxide content of the atmosphere through air-sea exchange processes, recent studies of the oceanic carbon cycle and air-sea interaction indicate that oceanic carbon is in a quasi-steady state via the system of biological and physical processes in the ocean interior. It is difficult to determine whether the ocean has the capacity to take up the increasing air-born CO_2 released by human activities over the past five or six decades. To understand this enigma, we need a better understanding of the natural variability of the oceanic carbon cycle.

Seawater carbonate chemistry and carbon allocation, growth and morphology of the coccolithophore Emiliania huxleyi (calcifying strain CCMP 371) during experiments, 2011

Coccolithophores are unicellular phytoplankton that produce calcium carbonate coccoliths as an exoskeleton. Emiliania huxleyi, the most abundant coccolithophore in the world's ocean, plays a major role in the global carbon cycle by regulating the exchange of CO2 across the ocean-atmosphere interface through photosynthesis and calcium carbonate precipitation. As CO2 concentration is rising in the atmosphere, the ocean is acidifying and ammonium (NH4) concentration of future ocean water is expected to rise. The latter is attributed to increasing anthropogenic nitrogen (N) deposition, increasing rates of cyanobacterial N2 fixation due to warmer and more stratified oceans, and decreased rates of nitrification due to ocean acidification. Thus future global climate change will cause oceanic phytoplankton to experience changes in multiple environmental parameters including CO2, pH, temperature and nitrogen source. This study reports on the combined effect of elevated pCO2 and increased NH4 to nitrate (NO3) ratio (NH4/NO3) on E. huxleyi, maintained in continuous cultures for more than 200 generations under two pCO2 levels and two different N sources. Here we show that NH4 assimilation under N-replete conditions depresses calcification at both low and high pCO2, alters coccolith morphology, and increases primary production. We observed that N source and pCO2 synergistically drive growth rates, cell size and the ratio of inorganic to organic carbon. These responses to N source suggest that, compared to increasing CO2 alone, a greater disruption of the organic carbon pump could be expected in response to the combined effect of increased NH4/NO3 ratio and CO2 level in the future acidified ocean. Additional experiments conducted under lower nutrient conditions are needed prior to extrapolating our findings to the global oceans. Nonetheless, our results emphasize the need to assess combined effects of multiple environmental parameters on phytoplankton biology in order to develop accurate predictions of phytoplankton responses to ocean acidification.

Seawater carbonate chemistry and length, weight, survival rate, metabolic rate of coral reef fish Amphiprion melanopus in a laboratory experiment

Carbon dioxide concentrations in the surface ocean are increasing owing to rising CO2 concentrations in the atmosphere. Higher CO2 levels are predicted to affect essential physiological processes of many aquatic organisms, leading to widespread impacts on marine diversity and ecosystem function, especially when combined with the effects of global warming. Yet the ability for marine species to adjust to increasing CO2 levels over many generations is an unresolved issue. Here we show that ocean conditions projected for the end of the century (approximately 1,000 µatm CO2 and a temperature rise of 1.5-3.0 °C) cause an increase in metabolic rate and decreases in length, weight, condition and survival of juvenile fish. However, these effects are absent or reversed when parents also experience high CO2 concentrations. Our results show that non-genetic parental effects can dramatically alter the response of marine organisms to increasing CO2 and demonstrate that some species have more capacity to acclimate to ocean acidification than previously thought.

Seawater carbonate chemistry and biological parameters during experiments with white sea bass Atractoscion nobilis, 2009

A large fraction of the carbon dioxide added to the atmosphere by human activity enters the sea, causing ocean acidification. We show that otoliths (aragonite ear bones) of young fish grown under high CO2 (low pH) conditions are larger than normal, contrary to expectation. We hypothesize that CO2 moves freely through the epithelium around the otoliths in young fish, accelerating otolith growth while the local pH is controlled. This is the converse of the effect commonly reported for structural biominerals.

Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi (PML B93/11A)

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments. This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange. The present rise in atmospheric CO2 levels causes significant changes in surface ocean pH and carbonate chemistry. Such changes have been shown to slow down calcification in corals and coralline macroalgae, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica . This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.

Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi (TW1), 2003

Precipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange of CO2 at the ocean-atmosphere interface. Previous experiments have demonstrated that, under nutrient-sufficient conditions, doubling the partial pressure of CO2 (pCO2) in seawater-a likely scenario for the end of the century-can significantly decrease both the rate of calcification by coccolithophorids and the ratio of inorganic to organic carbon production. The present work investigates the effects of high pCO2 on calcification by the coccolithophore Emiliania huxleyi (Strain TW1) grown under nitrogen-limiting conditions, a situation that can also prevail in the ocean. Nitrogen limitation was achieved in NO3-limited continuous cultures renewed at the rate of 0.5 d-1 and exposed to a saturating light level. pCO2 was increased from 400 to 700 ppm and controlled by bubbling CO2-rich or CO2-free air into the cultures. The pCO2 shift has a rapid effect on cell physiology that occurs within 2 cell divisions subsequent to the perturbation. Net calcification rate (C) decreased by 25% and, in contrast to previous studies with N-replete cultures, gross community production (GCP) and dark community respiration (DCR) also decreased. These results suggest that increasing pCO2 has no noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited.

Seawater carbonate chemistry during 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 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 processes during an experiment with coral reef, 2000

The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21st century. This increase will reduce the concentration of [CO3]2- of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage. Using the large 2650 m3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcification of coral reef organisms at the community scale. Our experimental design was to obtain a long (3.8 years) time series of the net calcification of the complete system and all relevant physical and chemical variables (temperature, salinity, light, nutrients, Ca2+,pCO2, TCO2, and total alkalinity). Periodic additions of NaHCO3, Na2CO3, and/or CaCl2 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcification in response to our manipulations of the saturation state. We show that the net community calcification rate responds to manipulations in the concentrations of both Ca2+ and [CO3]2- and that the rate is well described as a linear function of the ion concentration product, [Ca2+]0.69[[CO3]2-]. This suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcification on coral reefs at the ecosystem level. We compare the sensitivity of calcification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification between the years 1880 and 2065 A.D. based on our long-term results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. In the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.

Seawater carbonate chemistry, thickness and carbonate elemental composition of the test of juvenile sea urchins in a laboratory experiment

Continuous anthropogenic CO2 emissions to the atmosphere and uptake by the oceans will cause a reduction of seawater pH and saturation state (Omega) of CaCO3 minerals from which marine calcifiers build their shells and skeletons. Sea urchins use the most soluble form of calcium carbonate, high-magnesium calcite, to build their skeleton, spines and grazing apparatus. In order to highlight the effects of increased pCO2 on the test thickness and carbonate elemental composition of juvenile sea urchins and potential differences in their responses linked to the diet, we performed a laboratory experiment on juvenile Paracentrotus lividus, grazing on calcifying (Corallina elongata) and non-calcifying (Cystoseira amentacea, Dictyota dichotoma) macroalgae, under different pH (corresponding to pCO2 values of 390, 550, 750 and 1000 µatm). Results highlighted the importance of the diet in determining sea urchin size irrespectively of the pCO2 level, and the relevance of macroalgal diet in modulating urchin Mg/Ca ratio. The present study provides relevant clues both in terms of the mechanism of mineral incorporation and in terms of bottom-up processes (algal diet) affecting top-down ones (fish predation) in rocky subtidal communities

Seawater carbonate chemistry and accumulation of radiotracers in squid, Loligo vulgaris during experiments, 2011

The anthropogenic release of carbon dioxide (CO2) into the atmosphere leads to an increase in the CO2 partial pressure (pCO2) in the ocean, which may reach 950 ?atm by the end of the 21st century. The resulting hypercapnia (high pCO2) and decreasing pH ("ocean acidification") are expected to have appreciable effects on water-breathing organisms, especially on their early-life stages. For organisms like squid that lay their eggs in coastal areas where the embryo and then paralarva are also exposed to metal contamination, there is a need for information on how ocean acidification may influence trace element bioaccumulation during their development. In this study, we investigated the effects of enhanced levels of pCO2 (380, 850 and 1500 ?atm corresponding to pHT of 8.1, 7.85 and 7.60) on the accumulation of dissolved 110mAg, 109Cd, 57Co, 203Hg, 54Mn and 65Zn radiotracers in the whole egg strand and in the different compartments of the egg of Loligo vulgaris during the embryonic development and also in hatchlings during their first days of paralarval life. Retention properties of the eggshell for 110mAg, 203Hg and 65Zn were affected by the pCO2 treatments. In the embryo, increasing seawater pCO2 enhanced the uptake of both 110mAg and 65Zn while 203Hg showed a minimum concentration factor (CF) at the intermediate pCO2. 65Zn incorporation in statoliths also increased with increasing pCO2. Conversely, uptake of 109Cd and 54Mn in the embryo decreased as a function of increasing pCO2. Only the accumulation of 57Co in embryos was not affected by increasing pCO2. In paralarvae, the CF of 110mAg increased with increasing pCO2, whereas the 57Co CF was reduced at the highest pCO2 and 203Hg showed a maximal uptake rate at the intermediate pCO2. 54Mn and 65Zn accumulation in paralarvae were not significantly modified by hypercapnic conditions. Our results suggest a combined effect of pH on the adsorption and protective properties of the eggshell and of hypercapnia on the metabolism of embryo and paralarvae, both causing changes to the accumulation of metals in the tissues of L. vulgaris.