Fighting ocean acidification with underwater forests

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A California sea lion in a kelp forest. (Reinhard Dirscherl/ullstein bild via Getty Images.)

As the ocean’s pH drops, scientists are studying whether kelp and seagrass can create refuges to could help marine life survive acidifying waters.

As the sun crept above the horizon on a recent April morning, Anna George, an environmental science student at the University of California, Los Angeles, and two peers climbed into an idling zodiac and cruised into Santa Monica Bay off the Southern California coast. Cutting the engine when they reached a patch of kelp, its floating brown-green ribbons visible at the surface, they dipped in an instrument to measure the dissolved carbon dioxide the water contained.

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Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development

Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH  =  7.8, pCO2  =  643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of  >  3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs’ key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond. Continue reading ‘Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development’

The spatial and temporal variability of air-sea CO2 fluxes and the effect of net coral reef calcification in the Indonesian Seas: a numerical sensitivity study

A numerical model system was developed and applied to simulate air-sea fluxes of CO2 and coral reef calcification in the Indonesian Seas and adjacent ocean basin for the period 1960–2014 on a fine resolution grid (ca. 11 km) in order to study their response to rising sea water temperatures and CO2 concentrations in the atmosphere. Results were analyzed for different sub-regions on the Sunda Shelf (Gulf of Thailand, Malacca Strait, Java Sea) and show realistic and different levels, signs and pronounced temporal variability in air-sea CO2 flux. The Gulf of Thailand changes from an atmospheric CO2 sink during the boreal winter to a CO2 source in summer due to higher water temperatures, while other sub-regions as well as the entire averaged Sunda Shelf act as a continuous source of CO2 for the atmosphere. However, increasing atmospheric CO2 concentrations weakened this source function during the simulation period. In 2007, the model simulations showed even a first flux inversion, in course of which the Java Sea took up CO2. The simulated trends suggest that the entire Sunda Shelf will turn into a permanent sink for atmospheric CO2 within the next 30–35 years if current trends remain constant. Considering the period between 2010 and 2014, coral reef calcification enhanced the average CO2 emission of the Sunda Shelf by more than 10% from 15 to 17 Tg C yr−1 due to lowering the pH and increasing the partial pressure of CO2 in surface water. During the entire period of simulation, net reef calcification decreased although increasing seawater temperature mitigated effects of reduced CO2 emission and the resulting decrease of the pH values on reef calcification. Our realistic simulation results already without consideration of any biological processes suggest that biological processes taking up and releasing CO2 are currently well balanced in these tropical regions. However, the counteracting effects of climate change on the reef calcification, on other biological processes and the carbonate system need to be investigated in more detail. SST increased by about 0.6°C during the last 55 years, while SSS decreased by about 0.7 psu.

Continue reading ‘The spatial and temporal variability of air-sea CO2 fluxes and the effect of net coral reef calcification in the Indonesian Seas: a numerical sensitivity study’

Sex differences in oxidative stress responses of tropical topshells (Trochus histrio) to increased temperature and high pCO2

Highlights

• Sex differences in oxidative stress of topshells were investigated under climate change.
• Males undergo cellular damage under high pCO2, counter-balanced by increased temperature.
• Heat shock response was thermo- and sex-regulated, most predominant in males.
• Catalase and GSTs activities were maximum under high temperature and hypercapnia.
• Sexes have distinct physiological strategies to cope oxidative stress, more efficient in females.

Abstract

Given scarcity of knowledge on gender ecophysiological responses of tropical marine organisms to global climate change, the major aim of this research was to investigate potential sex differences in oxidative status of topshell Trochus histrio, after a combined exposure to increased temperature and pCO2. Lipid peroxidation, heat-shock response and antioxidant enzymatic activities were evaluated. Lipid peroxidation varied differently between sexes, with males undergoing cellular damage under high pCO2, which was elevated temperature-counteracted. Heat shock response was thermo- and sex-regulated, with males exhibiting significantly higher heat shock proteins production than females. Catalase activity increased with temperature and was exacerbated in combination with hypercapnia, being highest in females, while glutathione S-transferases activity peaked in males. These results clearly support the existence of distinct physiological strategies to cope oxidative stress between sexes, apparently more efficient in females, and also reinforce for the need of encompassing sex as meaningful variable in future biomarker studies.

Continue reading ‘Sex differences in oxidative stress responses of tropical topshells (Trochus histrio) to increased temperature and high pCO2’

Behavioural responses of Antarctic krill (Euphausia superba) to CO2-induced ocean acidification: would krill really notice?

The Southern Ocean is expected to be significantly affected by future ocean acidification. Antarctic krill (Euphausia superba) is the key species of the Southern Ocean ecosystem. Understanding their behavioural responses to acidification is critical for assessing the impacts of ocean acidification on the ecosystem. Adult Antarctic krill reared in different holding tanks with various CO2 levels for 6 months prior to the experiments were tested for their behavioural responses to different carbon dioxide partial pressures (pCO2) (400, 1000, 1500, 2000, and 4000 μatm pCO2) in a two-channel flume. The time krill occupied either of the flume channels (with high or ambient CO2 levels) was highly variable in all tests. In most cases no significant preference to either side of the flume was found. The krill did not display any systematic discrimination to the sea water with different CO2 levels regardless of the CO2 levels that krill were acclimated for in the 6 months prior to the experiment. Poor ability to discriminate high CO2 waters may have an important implication to their life history in the future as ocean acidification rapidly progresses in parts of Southern Ocean.

Continue reading ‘Behavioural responses of Antarctic krill (Euphausia superba) to CO2-induced ocean acidification: would krill really notice?’

An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result

The amount of carbon dioxide (CO2) in the atmosphere has increased in the past 60 years and the technology of carbon capture and storage (CCS) has recently been extensively studied. One of the strategies of CCS is to directly inject a high dissolved inorganic carbon (DIC) concentration (or high partial pressure of carbon dioxide, pCO2) solution into the ocean. However, the carbonate dynamics and air-sea gas exchange are usually neglected in a CCS strategy. This study assesses the effect of a DIC-solution injection by using a simple two end-member model to simulate the variation of pH, DIC, total alkalinity (TA) and pCO2 between the river and sea mixing process for the Danshuei River estuary and Hoping River in Taiwan. We observed that the DIC-solution injection can contribute to ocean acidification and can also lead the pCO2 value to change from being undersaturated to oversaturated (with respect to the atmospheric CO2 level). Our model result also showed that the maximum Revelle factors (Δ[CO2]/[CO2])/(Δ[DIC]/[DIC]) among varied pH values (6–9) and DIC concentrations (0.5–3.5 mmol kg−1) were between pH 8.3 and 8.5 in fresh water and were between 7.3 and 7.5 in waters with a salinity of 35, reflecting the changing efficiency of dissolving CO2 gas into the DIC solution and the varying stability of this desired DIC solution. Finally, we suggest this uncoupled Revelle factor between fresh and salty water should be considered in the (anthropogenic) carbonate chemical weathering on a decade to century scale.

Continue reading ‘An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result’

Inorganic carbon and pH dependency of Trichodesmium’s photosynthetic rates

We established the relationship between photosynthetic carbon fixation rates and pH, CO2 and HCO3 concentrations in the diazotroph Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measured in TRIS-buffered ASW medium where the absolute and relative concentrations of CO2, pH and HCO3 were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (< 0 to ~ 5 mM) at constant pH, so ratios of CO2 and HCO3 remained relatively constant. Second, we varied pH (~ 8.54 to 7.52) at constant TIC, so CO2 increased whilst HCO3 declined. We found that 14C-assimilation could be described by the same function of CO2 for both approaches but showed different dependencies on HCO3 when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of Trichodesmium’s CCM showed carboxylation rates are modulated by HCO3 and pH. The decrease in Ci assimilation at low CO2, when TIC was varied, is due to HCO3 uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO3 and CO2 leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.

Continue reading ‘Inorganic carbon and pH dependency of Trichodesmium’s photosynthetic rates’


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Ocean acidification in the IPCC AR5 WG II

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