Archive for May, 2014

Bay acidification requires immediate action

It’s no secret that the health of the Chesapeake Bay has been in peril for decades, but ocean acidification poses what may be the greatest threat to the oyster population of the bay. Sadly, for most people this will go unnoticed. It’s not like the obvious environmental threat of trees being cut or land being bulldozed. Damage occurring to oysters and other aquatic species can’t be seen from a casual observation of the surface, but the threat is real. With water covering so much of the earth’s surface it’s easy enough for people to think that our waters can handle whatever we pour into them, but nothing could be further from the truth.

There have been a lot of efforts to protect and restore the Chesapeake Bay. Those efforts are noble. But they’re not enough. It’s beyond time to get serious about doing something. The time for studying is over. It’s time for action.

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Contrasting effects of ocean acidification on tropical fleshy and calcareous algae

Despite the heightened awareness of ocean acidification (OA) effects on marine organisms, few studies empirically juxtapose biological responses to CO2 manipulations across functionally distinct primary producers, particularly benthic algae. Algal responses to OA may vary because increasing CO2 has the potential to fertilize photosynthesis but impair biomineralization. Using a series of repeated experiments on Palmyra Atoll, simulated OA effects were tested across a suite of ecologically important coral reef algae, including five fleshy and six calcareous species. Growth, calcification and photophysiology were measured for each species independently and metrics were combined from each experiment using a meta-analysis to examine overall trends across functional groups categorized as fleshy, upright calcareous, and crustose coralline algae (CCA). The magnitude of the effect of OA on algal growth response varied by species, but the direction was consistent within functional groups. Exposure to OA conditions generally enhanced growth in fleshy macroalgae, reduced net calcification in upright calcareous algae, and caused net dissolution in CCA. Additionally, three of the five fleshy seaweeds tested became reproductive upon exposure to OA conditions. There was no consistent effect of OA on algal photophysiology. Our study provides experimental evidence to support the hypothesis that OA will reduce the ability of calcareous algae to biomineralize. Further, we show that CO2 enrichment either will stimulate population or somatic growth in some species of fleshy macroalgae. Thus, our results suggest that projected OA conditions may favor non-calcifying algae and influence the relative dominance of fleshy macroalgae on reefs, perpetuating or exacerbating existing shifts in reef community structure.

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Research center to monitor acid levels (audio)

Remotely operated vehicles will be plying Prince William Sound and the Gulf of Alaska this summer, measuring acid levels. The float and glider vehicles are the latest technology deployed through a long running monitoring project overseen by University of Alaska Fairbanks Ocean Acidification Research Center Director Jeremy Mathis.

The six-year study has previously relied on measurements taken from fixed buoys, or twice a year from a ship.  The battery and solar powered ROV’s will be at sea for five months, piloted by a technician in Seattle.

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Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

A large scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78° 56.2´ N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance, however no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400-700 nm), and therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.

Continue reading ‘Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels’

Coral calcification under daily oxygen saturation and pH dynamics reveals the important role of oxygen

Coral reefs are essential to many nations, and are currently in global decline. Although climate models predict decreases in seawater pH (∼0.3 units) and oxygen saturation (∼5 percentage points), these are exceeded by the current daily pH and oxygen fluctuations on many reefs (pH 7.8–8.7 and 27–241% O2 saturation). We investigated the effect of oxygen and pH fluctuations on coral calcification in the laboratory using the model species Acropora millepora. Light calcification rates were greatly enhanced (+178%) by increased seawater pH, but only at normoxia; hyperoxia completely negated this positive effect. Dark calcification rates were significantly inhibited (51–75%) at hypoxia, whereas pH had no effect. Our preliminary results suggest that within the current oxygen and pH range, oxygen has substantial control over coral growth, whereas the role of pH is limited. This has implications for reef formation in this era of rapid climate change, which is accompanied by a decrease in seawater oxygen saturation owing to higher water temperatures and coastal eutrophication.

Continue reading ‘Coral calcification under daily oxygen saturation and pH dynamics reveals the important role of oxygen’

Response of benthic foraminifera to ocean acidification and impact on Florida’s carbonate sediment production

Increasing concentrations of atmospheric CO2 are in dynamic equilibrium with the oceans. The absorption of CO2 by seawater causes a decrease in seawater pH and calcite saturation state (SS). This process, termed ocean acidification, exerts deleterious effects on marine calcifiers. Studies of symbiont-bearing large benthic foraminifera (LBF) have reported a generally unfavorable response to increased concentrations of carbon dioxide ([CO2]).

Experiments and analyses were undertaken to examine the effect of increased [CO2] on the growth rate, ultrastructure, stable isotopes of carbon and oxygen, as well as Mg/Ca of the high-Mg miliolid Archaias angulatus and the low-Mg rotalid Amphistegina gibbosa. A CO2-injection culture study was performed at pH 8.0, 7.8 and 7.6, corresponding to CO2 concentrations of approximately 400 ppm, 800 ppm, and 1,300 ppm. After 2, 4, or 6 weeks of treatment, bags containing groups of approximately 20 previously-imaged live specimens were removed and prepared for the aforementioned analyses.

Archaias angulatus responded to increased [CO2] by reducing test growth rate at 1,300 ppm CO2 (pH 7.6) by 50% (p < 0.01, r2 = 36%), increasing its pore area (F(2,3477) = 103.37, p<0.001), as well as recording increased d18O values (F(2,40) = 3.21, p = 0.51) and Mg/Ca ratios (t(17) = 2.17, p = 0.04). Amphistegina gibbosa responded by increasing the test growth rate at 800 ppm CO2 (pH 7.8) and decreasing test growth slightly at 1,300 ppm CO2 (pH 7.6) (F(3,281) = 9.07, p < 0.001, r2 = 72.4%). There was no significant impact on isotopic or Mg/Ca composition of the test measured. Individuals with higher test growth rates also contained increased amounts of organic material.

West Florida shelf LBF carbonate production attributed to LBF was estimated by combining interpolations of SS calcite at three treatment levels, corresponding to pH 8.1 (400 ppm CO2), pH 7.8 (800 ppm CO2), and pH 7.6 (1,300 ppm CO2), with a map of the carbonate fraction of seafloor sediment. Growth rates for 10 species were estimated in a meta-analysis of culture studies; these rates were used to model the response of miliolids and rotalids to increased [CO2].

In the model, rotalids responded to higher CO2 concentrations by reducing their average adult size by 20% at 800 ppm CO2 and 40% at 1,300 ppm CO2. Miliolids responded by reducing their average adult size by 40% at 800 ppm CO2 and 75% at 1,300 ppm CO2. Modeled LBF carbonate production for the west Florida shelf is 7 Mt at 400 ppm, 4.8 Mt at 800 ppm, and 2.5 Mt at 1,300 ppm. In a high CO2 world, low-Mg rotalids exhibit modest reductions in test growth rates and carbonate production, whereas high-Mg miliolids exhibit major reductions in test growth rates and carbonate production.

Continue reading ‘Response of benthic foraminifera to ocean acidification and impact on Florida’s carbonate sediment production’

Coral-algae metabolism and diurnal changes in the CO2-carbonate system of bulk sea water

Precise measurements were conducted in continuous flow seawater mesocosms located in full sunlight that compared metabolic response of coral, coral-macroalgae and macroalgae systems over a diurnal cycle. Irradiance controlled net photosynthesis (Pnet), which in turn drove net calcification (Gnet), and altered pH. Pnet exerted the dominant control on [CO32−] and aragonite saturation state (Ωarag) over the diel cycle. Dark calcification rate decreased after sunset, reaching zero near midnight followed by an increasing rate that peaked at 03:00 h. Changes in Ωarag and pH lagged behind Gnet throughout the daily cycle by two or more hours. The flux rate Pnet was the primary driver of calcification. Daytime coral metabolism rapidly removes dissolved inorganic carbon (DIC) from the bulk seawater and photosynthesis provides the energy that drives Gnet while increasing the bulk water pH. These relationships result in a correlation between Gnet and Ωarag, with Ωarag as the dependent variable. High rates of H+ efflux continued for several hours following mid-day peak Gnet suggesting that corals have difficulty in shedding waste protons as described by the Proton Flux Hypothesis. DIC flux (uptake) followed Pnet and Gnet and dropped off rapidly following peak Pnet and peak Gnet indicating that corals can cope more effectively with the problem of limited DIC supply compared to the problem of eliminating H+. Over a 24 h period the plot of total alkalinity (AT) versus DIC as well as the plot of Gnet versus Ωarag revealed a circular hysteresis pattern over the diel cycle in the coral and coral-algae mesocosms, but not the macroalgae mesocosm. Presence of macroalgae did not change Gnet of the corals, but altered the relationship between Ωarag and Gnet. Predictive models of how future global changes will effect coral growth that are based on oceanic Ωarag must include the influence of future localized Pnet on Gnet and changes in rate of reef carbonate dissolution. The correlation between Ωarag and Gnet over the diel cycle is simply the response of the CO2-carbonate system to increased pH as photosynthesis shifts the equilibria and increases the [CO32−] relative to the other DIC components of [HCO3−] and [CO2]. Therefore Ωarag closely tracked pH as an effect of changes in Pnet, which also drove changes in Gnet. Measurements of DIC flux and H+ flux are far more useful than concentrations in describing coral metabolism dynamics. Coral reefs are systems that exist in constant disequilibrium with the water column.

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Effects of varying pH on the growth and physiology of five marine microphytobenthic diatoms isolated from the Solthörn tidal flat (southern North Sea, Germany)

Diatoms inhabiting intertidal flats are subject to strongly changing environmental conditions, which have a great influence on the oxygen, sulphide and pH gradients in the sediments. In previous studies, variations in pH in the range from 6.5 to 8.5 had only minor effects on the growth of benthic diatoms. In order to determine the physiological responses of marine benthic diatoms to pH changes, cultures of Amphora graeffii, Navicula gregaria, Navicula phyllepta, Nitzschia epithemoides and Pinnularia ambigua (=Biremis ambigua) isolated from the Solthörn tidal flat (lower Saxony, southern North Sea) were used to study the effect on growth rates and biochemical compositions at different pH values (7.25, 7.5, 7.75, 8.0, 8.25, 8.5 and 8.75). During short- (6 h) and long-term exposures (30 d), the composition of free amino acids and the accumulation of polyols, saccharides, quaternary ammonium compounds and β-dimethylsulphoniopropionate (DMSP) were determined. While growth rates of the five tested diatom taxa during short-term exposure to experimental pH were only hardly affected, long-term exposure to experimental pH led to decreasing growth rates in all tested species. Significant differences were found in physiological responses to pH treatments of the species tested. Growth in terms of chlorophyll a and protein contents showed decreasing values also after short-term exposure to experimental pH. Furthermore, at experimental short-term pH treatments, species accumulated higher levels of proline, glycerol, galactose and mannose, while only three out of the five tested taxa also accumulated high amounts of the quaternary ammonium compounds homarine and glycine betaine as well as DMSP. The physiological responses to long-term exposure to experimental pH showed distinct differences in the accumulation of proline, serine, taurine, glycerol and other compatible solutes. In conclusion, significant differences in osmolyte compositions were found in the five diatom species exposed to different pHs, suggesting specific intracellular acclimation processes. These responses provide a possible explanation for the insensitivity to short-term pH variations.

Continue reading ‘Effects of varying pH on the growth and physiology of five marine microphytobenthic diatoms isolated from the Solthörn tidal flat (southern North Sea, Germany)’

Experimental assessment of diazotroph responses to elevated seawater pCO2 in the North Pacific Subtropical Gyre

We examined short-term (24-72 hours) responses of naturally occurring marine N2 fixing microorganisms (termed diazotrophs) to abrupt increases in the partial pressure of carbon dioxide (pCO2) in seawater during 9 incubation experiments conducted between May 2010 and September 2012 at Station ALOHA (22°45’N, 158˚W) in the North Pacific Subtropical Gyre (NPSG). Rates of N2 fixation, nitrogenase (nifH) gene abundances and transcripts of six major groups of cyanobacterial diazotrophs (including both unicellular and filamentous phylotypes), and rates of primary productivity (as measured by 14C-bicarbonate assimilation into plankton biomass) were determined under contemporary (~390 ppm) and elevated pCO2 conditions (~1100 ppm). Quantitative polymerase chain reaction (QPCR) amplification of planktonic nifH genes revealed that unicellular cyanobacteria phylotypes dominated gene abundances during these experiments. In the majority of experiments (7 out of 9), elevated pCO2 did not significantly influence rates of dinitrogen (N2) fixation or primary productivity (two-way ANOVA, P > 0.05). During two experiments, rates of N2 fixation rates and primary productivity were significantly lower (by 79 to 82% and 52 to 72%, respectively) in the elevated pCO2 treatments relative to the ambient controls (two-way ANOVA, P < 0.05). QPCR amplification of nifH genes and gene transcripts revealed that diazotroph abundances and nifH gene expression were largely unchanged by the perturbation of the seawater pCO2. Our results suggest that naturally occurring N2 fixing plankton assemblages in the NPSG are relatively resilient to large, short-term increases in pCO2.

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Precision and accuracy of spectrophotometric pH measurements at environmental conditions in the Baltic Sea

The increasing uptake of anthropogenic CO2 by the oceans has raised an interest in precise and accurate pH measurement in order to assess the impact on the marine CO2-system. Spectrophotometric pH measurements were refined during the last decade yielding a precision and accuracy that cannot be achieved with the conventional potentiometric method. However, until now the method was only tested in oceanic systems with a relative stable and high salinity and a small pH range. This paper describes the first application of such a pH measurement system at conditions in the Baltic Sea which is characterized by a wide salinity and pH range. The performance of the spectrophotometric system at pH values as low as 7.0 (“total” scale) and salinities between 0 and 35 was examined using TRIS-buffer solutions, certified reference materials, and tests of consistency with measurements of other parameters of the marine CO2 system. Using m-cresol purple as indicator dye and a spectrophotometric measurement system designed at Scripps Institution of Oceanography (B. Carter, A. Dickson), a precision better than ±0.001 and an accuracy between ±0.01 and ±0.02 was achieved within the observed pH and salinity ranges in the Baltic Sea. The influence of the indicator dye on the pH of the sample was determined theoretically and is presented as a pH correction term for the different alkalinity regimes in the Baltic Sea. Because of the encouraging tests, the ease of operation and the fact that the measurements refer to the internationally accepted “total” pH scale, it is recommended to use the spectrophotometric method also for pH monitoring and trend detection in the Baltic Sea.

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Ocean acidification in the IPCC AR5 WG II

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