Posts Tagged 'North Atlantic'

Ocean acidification modifies biomolecule composition in organic matter through complex interactions

The main source of marine organic carbon (OC) is autotrophic production, while heterotrophic degradation is its main sink. Increased anthropogenic CO2 release leads to ocean acidification and is expected to alter phytoplankton community composition, primary production rates and bacterial degradation processes in the coming decades with potential consequences for dissolved and particulate OC concentration and composition. Here we investigate effects of increased pCO2 on dissolved and particulate amino acids (AA) and carbohydrates (CHO), in arctic and sub-arctic planktonic communities in two large-scale mesocosm experiments. Dissolved AA concentrations responded to pCO2/pH changes during early bloom phases but did not show many changes after nutrient addition. A clear positive correlation in particulate AA was detected in post-bloom phases. Direct responses in CHO concentrations to changing pCO2/pH were lacking, suggesting that observed changes were rather indirect and dependent on the phytoplankton community composition. The relative composition of AA and CHO did not change as a direct consequence of pCO2 increase. Changes between bloom phases were associated with the prevailing nutrient status. Our results suggest that biomolecule composition will change under future ocean conditions but responses are highly complex, and seem to be dependent on many factors including bloom phase and sampling site.

Continue reading ‘Ocean acidification modifies biomolecule composition in organic matter through complex interactions’

Evaluating the sensor-equipped autonomous surface vehicle C-Worker 4 as a tool for identifying coastal ocean acidification and changes in carbonate chemistry

The interface between land and sea is a key environment for biogeochemical carbon cycling, yet these dynamic environments are traditionally under sampled. Logistical limitations have historically precluded a comprehensive understanding of coastal zone processes, including ocean acidification. Using sensors on autonomous platforms is a promising approach to enhance data collection in these environments. Here, we evaluate the use of an autonomous surface vehicle (ASV), the C-Worker 4 (CW4), equipped with pH and pCO2 sensors and with the capacity to mount additional sensors for up to 10 other parameters, for the collection of high-resolution data in shallow coastal environments. We deployed the CW4 on two occasions in Belizean coastal waters for 2.5 and 4 days, demonstrating its capability for high-resolution spatial mapping of surface coastal biogeochemistry. This enabled the characterisation of small-scale variability and the identification of sources of low pH/high pCO2 waters as well as identifying potential controls on coastal pH. We demonstrated the capabilities of the CW4 in both pre-planned “autonomous” mission mode and remote “manually” operated mode. After documenting platform behaviour, we provide recommendations for further usage, such as the ideal mode of operation for better quality pH data, e.g., using constant speed. The CW4 has a high power supply capacity, which permits the deployment of multiple sensors sampling concurrently, a shallow draught, and is highly controllable and manoeuvrable. This makes it a highly suitable tool for observing and characterising the carbonate system alongside identifying potential drivers and controls in shallow coastal regions.

Continue reading ‘Evaluating the sensor-equipped autonomous surface vehicle C-Worker 4 as a tool for identifying coastal ocean acidification and changes in carbonate chemistry’

DNA damage and oxidative stress responses of mussels Mytilus galloprovincialis to paralytic shellfish toxins under warming and acidification conditions – elucidation on the organ-specificity

Commonly affected by changes in climate and environmental conditions, coastal areas are very dynamic environments where shellfish play an important ecological role. In this study, the oxidative stress and genotoxic responses of mussels (Mytilus galloprovincialis) exposed to paralytic shellfish toxin (PST) – producing dinoflagellates Gymnodinium catenatum were evaluated under i) current conditions (CC: 19 °C; pH 8.0), ii) warming (W: 24 °C; pH 8.0), iii) acidification (A:19 °C; pH 7.6) and iv) combined effect of warming and acidification (WA: 24 °C; pH 7.6). Mussels were fed with G. catenatum for 5 days, and to a non-toxic diet during the following 10 days. A battery of oxidative stress biomarkers and comet assay was performed at the peak of toxin accumulation and at the end of the post-exposure phase. Under CC, gills and hepatopancreas displayed different responses/vulnerabilities and mechanisms to cope with PST. While gills presented a tendency for lipid peroxidation (LPO) and genetic damage (expressed by the Genetic Damage Indicator – GDI), hepatopancreas seems to better cope with the toxins, as no LPO was observed. However, the mechanisms involved in hepatopancreas protection were not enough to maintain DNA integrity. The absence of LPO, and the antioxidant system low responsiveness, suggests DNA damage was not oxidative. When exposed to toxic algae under W, toxin-modulated antioxidant responses were observed in both gills and hepatopancreas. Simultaneous exposure to the stressors highlighted gills susceptibility with a synergistic interaction increasing DNA damage. Exposure to toxic algae under A led to genotoxicity potentiation in both organs. The combined effect of WA did not cause relevant interactions in gills antioxidant responses, but stressors interactions impacted LPO and GDI. Antioxidant responses and LPO pointed out to be modulated by the environmental conditions in hepatopancreas, while GDI results support the dominance of toxin-triggered process. Overall, these results reveal that simultaneous exposure to warming, acidification and PSTs impairs mussel DNA integrity, compromising the genetic information due to the synergetic effects. Finally, this study highlights the increasing ecological risk of harmful algal blooms to Mytilus galloprovinciallis populations.

Continue reading ‘DNA damage and oxidative stress responses of mussels Mytilus galloprovincialis to paralytic shellfish toxins under warming and acidification conditions – elucidation on the organ-specificity’

Resilience of the temperate coral Oculina arbuscula to ocean acidification extends to the physiological level

Both juvenile and adult life stages of the temperate scleractinian coral Oculina arbuscula are resilient to the effects of moderate ocean acidification (OA) in contrast to many tropical corals in which growth and calcification rates are suppressed. Here, potential mechanisms of resilience to OA related to photosynthetic physiology and inorganic carbon processing were studied in adult O. arbuscula colonies. After exposing colonies to ambient and elevated carbon dioxide (CO2) treatments for 7 weeks, photosynthetic performance was characterized using photosynthesis versus irradiance experiments, chlorophyll fluorescence kinetics, and algal pigment content. Inorganic carbon-processing capabilities were assessed by measurement of internal and external carbonic anhydrase activity of the coral host, internal carbonic anhydrase activity of symbiotic algae, and the reliance of photosynthesis on external carbonic anhydrase. Photosynthetic physiology was unaffected by OA ruling out the possibility that resilience was mediated by increased photosynthetic energy supply. Carbonic anhydrase activities were maintained at elevated CO2 suggesting no major rearrangements of the inorganic carbon-processing machinery, but this could be a sign of resilience since tropical corals often down-regulate carbonic anhydrases at high CO2. The general lack of effect of ocean acidification on these physiological traits suggests other characteristics, such as maintenance of calcifying fluid pH and ability to acquire energy from heterotrophy, may be more important for the resilience of O. arbuscula to OA.

Continue reading ‘Resilience of the temperate coral Oculina arbuscula to ocean acidification extends to the physiological level’

Impact of temperature increase and acidification on growth and the reproductive potential of the clam Ruditapes philippinarum using DEB

Highlights

  • A simulation model based on DEB theory was parameterized for the Manila clam.
  • The pH forecast in 2100 will limit the growth of Manila clam.
  • The temperature forecast in 2100 enhances the reproductive potential of Manila clam.

Abstract

We built a simulation model based on Dynamic Energy Budget theory (DEB) to assess the growth and reproductive potential of the Manila clam Ruditapes philippinarum under different temperature and pH conditions, based on environmental values forecasted for the end of the 21st c. under climate change scenarios. The parameters of the DEB model were calibrated with the results of seasonal growth experiments under two levels of temperature (ambient and plus 2–3 °C) and three levels of pH (8.1 used as control and 7.7 and 7.3 representing acidification). The results showed that R. philippinarum is expected to have moderate growth in length or individual body mass (ultimate length and body weight would be larger than current values by 2–3%) when taking into account only the effect of temperature increase. However, acidification is likely to have a deleterious effect on growth, with a decrease of 2–5% length or body weight under the pH value of 7.7 forecasted for the end of the 21st c, or 10–15% under a more extreme scenario (pH = 7.3). However, the aggregated reproductive potential, integrated along a lifetime of 10 years, is likely to increase by 30% with temperature increase. Decreasing pH would impact negatively on reproductive potential, but in all simulations under warmer conditions, reproductive potential values were higher than current, suggesting that temperature increase would compensate losses due to acidification. The results are discussed in relation to their possible impact on aquaculture and fisheries of this important commercial bivalve.

Continue reading ‘Impact of temperature increase and acidification on growth and the reproductive potential of the clam Ruditapes philippinarum using DEB’

Efeitos neurotóxicos do crack-cocaína combinado a cenários de acidificação oceânica no mexilhão marinho Perna perna (in Portuguese)

The oceans are undergoing physical and biogeochemical changes in response to the increasing atmospheric CO2 load and increased ocean uptake, such as surface warming, reduced oxygen and a reduction in calcium carbonate and pH saturation levels. Changes in the pH and chemical composition of seawater can modify the speciation of contaminants, interfering with their bioavailability and toxicity. The present study aimed to evaluate the sublethal effect of the illicit drug crack-cocaine at different concentrations (0.5; 5; 50 µg / L) combined with ocean acidification by CO2 at pH values of 8.1; 7.5; 7.0; 6.5 and 6.0. For this purpose, an analysis of the biomarker of neurotoxic effect acetylcholinesterase (AChe) was performed on mussels Perna perna. The inhibition of AChe after exposure to crack at pH 7.5, 7.0 and 6.5 was preliminarily observed, demonstrating a combined effect of crack-cocaine and pH reduction, which can be observed in future scenarios of acidification in coastal zones contaminated by illicit drugs.

Continue reading ‘Efeitos neurotóxicos do crack-cocaína combinado a cenários de acidificação oceânica no mexilhão marinho Perna perna (in Portuguese)’

Irradiance, photosynthesis and elevated pCO2 effects on net calcification in tropical reef macroalgae

Highlights

  • Most species from high-light environments are not able to calcifying under OA at night
  • Low-light species may be more susceptible to OA compared to high-light
  • Some species exhibit light-triggered calcification independent of photosystem II
  • Photosystem II independent calcification not sustained under OA

Abstract


Calcifying tropical macroalgae produce sediment, build three-dimensional habitats, and provide substrate for invertebrate larvae on reefs. Thus, lower calcification rates under declining pH and increasing ocean pCO2, or ocean acidification, is a concern. In the present study, calcification rates were examined experimentally under predicted end-of-the-century seawater pCO2 (1116 μatm) and pH (7.67) compared to ambient controls (pCO2 409 μatm; pH 8.04). Nine reef macroalgae with diverse calcification locations, calcium carbonate structure, photophysiology, and site-specific irradiance were examined under light and dark conditions. Species included five from a high light patch reef on the Florida Keys Reef Tract (FKRT) and four species from low light reef walls on Little Cayman Island (LCI). Experiments on FKRT and LCI species were conducted at 500 and 50 μmol photons m−2 s−1 in situ irradiance, respectively. Calcification rates independent of photosystem-II (PSII) were also investigated for FKRT species. The most consistent negative effect of elevated pCO2 on calcification rates in the tropical macroalgae examined occurred in the dark. Most species (89%) had net calcification rates of zero or net dissolution in the dark at low pH. Species from the FKRT that sustained positive net calcification rates in the light at low pH also maintained ~30% of their net calcification rates without PSII at ambient pH. However, calcification rates in the light independent of PSII were not sustained at low pH. Regardless of these low pH effects, most FKRT species daily net calcification rates, integrating light/dark rates over a 24h period, were not significantly different between low and ambient pH. This was due to a 10-fold lower dark, compared to light, calcification rate, and a strong correspondence between calcification and photosynthetic rates. Interestingly, low-light species sustained calcification rates on par with high-light species without high rates of photosynthesis. Low-light species’ morphology and physiology that promote high calcification rates at ambient pH, may increase their vulnerability to low pH. Our data indicate that the negative effect of elevated pCO2 and low pH on tropical macroalgae at the organismal level is their impact on dark net calcification, probably enhanced dissolution. However, elevated pCO2 and low pH effects on macroalgae daily calcification rates are greatest in species with lower net calcification rates in the light. Thus, macroalgae able to maintain high calcification rates in the light (high and low irradiance) at low pH, and/or sustain strong biotic control with high [H+] in the bulk seawater, are expected to dominate under global change.

Continue reading ‘Irradiance, photosynthesis and elevated pCO2 effects on net calcification in tropical reef macroalgae’

Coastal ocean acidification: dynamics and potential to affect marine mollusks

Coastal marine ecosystems are both ecologically and economically productive, and as human coastal populations expand, these critical habitats have become subject to a suite of anthropogenic stressors. During the past century, the progressive rise in levels of atmospheric carbon dioxide (CO2) entering world oceans has decreased ocean pH and caused ocean acidification. An additional and often overlooked cause of acidification in coastal zones is the production of CO2 via microbial degradation of organic matter. Nutrient loading in coastal ecosystems facilitates enhanced algal productivity and the subsequent decomposition of this algal biomass reduces oxygen levels and can promote hypoxia. The precise temporal and spatial dynamics of acidification and hypoxia as well as their potential effects on resource bivalves are not well described in most coastal waters. Here, to evaluate the status of aquatic acidification in coastal systems, I examine the seasonal, diel, and high-resolution spatiotemporal dynamics of carbonate chemistry and dissolved oxygen (DO) over a six year period in multiple northeast US estuaries and across multiple coastal habitats that host keystone marine species while concurrently quantifying the growth and survival of multiple early life stage suspension feeding bivalves. To assess the potential for acidification in eutrophic estuaries, the levels of DO, pH, the partial pressure of carbon dioxide (pCO2), and the saturation state of aragonite (ΩAr) were iv horizontally and vertically assessed during the onset, peak, and demise of low oxygen conditions in systems across the northeast US including Narragansett Bay (RI), Long Island Sound (CTNY), Jamaica Bay (NY), and Hempstead Bay (NY). Hypoxic waters and/or regions in close proximity to sewage discharge had extremely high levels of pCO2, (> 3,000 µatm), acidic pH (< 7.0), and were undersaturated with respect to aragonite (ΩAr < 1). The close spatial and temporal correspondence between DO and pH and the occurrence of extremes in these conditions in regions with the most intense nutrient loading indicated that they were driven primarily by enhanced microbial respiration relative to physical exchange processes. Next, I quantified the temporal and spatial dynamics of DO, carbonate chemistry, and net ecosystem metabolism (NEM) from spring through fall in multiple, distinct, temperate estuarine habitats: seagrass meadows, salt marshes, an open water estuary, and a shallow water habitat dominated by benthic macroalgae. All habitats displayed clear diurnal patterns of pH and DO, with minimums observed during early morning and maximums observed in the afternoon where diel ranges in pH and DO varied by site. NEM across habitats ranged from net autotrophic (macroalgae and seagrass) to metabolically balanced (open water) and net heterotrophic (salt marsh). Each habitat examined exhibited distinct buffering capacities that varied seasonally and were modulated by adjacent biological activity and variations in total alkalinity (TA) and dissolved inorganic carbon (DIC). I utilized continuous monitoring devices to characterize the diurnal dynamics of DO and carbonate chemistry from spring through fall across two, temperate eutrophic estuaries, western Long Island Sound and Jamaica Bay, NY. Vertical dynamics were resolved using an underway towing profiler and an automated stationary profiling unit. During the study, high rates of respiration in surface and bottom waters (> -0.2 mg O2 L -1 h -1 ) were observed where ephemeral surface water algal blooms caused brief periods of basification and supersaturation of DO that v were succeeded by periods of acidification and hypoxia. Diurnal vertical profiles demonstrated that oxic surface waters saturated with respect to calcium carbonate (aragonite) during the day transitioned to being unsaturated and hypoxic at night. Evidence is presented that, beyond respiration, nitrification of surface water strongly influenced by sewage discharge and oxidation processes in sediments can also contribute to acidification in these estuaries. Finally, the growth and survival of three bivalve species (Argopecten irradians, Crassostrea virginica, Mytilus edulis) were examined in an in-situ CO2 enrichment system deployed in a seagrass meadow and an open water estuary, and across a natural eutrophication gradient in Jamaica Bay, NY. In the seagrass meadow, the growth and survival of C. virginica and A. irradians significantly declined during the late summer in response to CO2 gas injection. During the open water CO2 enrichment experiment, all three species of bivalves exhibited depressed growth within the acidified chambers with no significant difference in mortality between treatments. In Jamaica Bay, dense phytoplankton blooms in the early summer decreased CO2 and increased DO creating spatial refuges for bivalves where growth rates were enhanced, but by the late summer, trends reversed as bivalve growth was depressed at these same locations due to the onset of acidification and hypoxia. Collectively, this dissertation has identified coastal ocean acidification as a symptom of eutrophication that can threaten marine bivalve populations.

Continue reading ‘Coastal ocean acidification: dynamics and potential to affect marine mollusks’

Development of an autonomous dissolved inorganic carbon sensor for oceanic measurements

Since the industrial revolution the CO2 concentrations in the atmosphere have increased from 280 ppm to over 400 ppm, and each year the oceans take up approximately 25% of the annually emitted anthropogenic CO2. This increase in CO2 in the oceans has had a measure able impact on the marine carbonate system, and the resultant increase in the acidity of the ocean is a potential stressor for a range of ecosystems. In order to fully quantify the marine carbonate system there are four variables that can be measured, these are dissolved inorganic carbon (DIC), pH, total alkalinity and partial pressure of CO2. By measuring two of the four variables the others can be determined. Of these variables DIC is the only one without either an underway or in situ sensor, despite being one half of the preferred pairs for observing the carbonate system. To address this technological gap and increase the measurement coverage there is a clear need for an autonomous sensor capable of making quality measurements while having a robust, small physical size, and low power requirements. Presented here are the results of developmental work that has led to a full ocean depth rated autonomous DIC sensor, based on a microfluidic “Lab On Chip” (LOC) design. The final version of the DIC LOC sensor operates by acidifying < 1 ml of seawater, converting the DIC to CO2, which is diffused across a gas permeable membrane into an acceptor solution. The CO2 reacts with the acceptor resulting in a conductivity drop that is measured using a Capacitively Coupled Contactless Conductivity Detector (C4D). Each measurement takes ~15 minutes and the sensor can be set up to perform calibrations in situ. Laboratory testing demonstrated this system has a precision of < 1 µmol kg-1. The sensor was deployed as part of a large EU project aiming to detect a simulated sub-seabed leak of CO2. Over multiple deployments in the North Sea the sensor collected data used to locate the leak. A number of field tests have established the sensor has a precision of < 10 µmol kg-1. This work has demonstrated that this sensor offers potential to fill the current technological gap and collect data that will enhance understanding of the marine carbonate system.

Continue reading ‘Development of an autonomous dissolved inorganic carbon sensor for oceanic measurements’

ARIOS: a database for ocean acidification assessment in the Iberian upwelling system (1976–2018) (update)

A data product of 17 653 discrete samples from 3343 oceanographic stations combining measurements of pH, alkalinity and other biogeochemical parameters off the northwestern Iberian Peninsula from June 1976 to September 2018 is presented in this study. The oceanography cruises funded by 24 projects were primarily carried out in the Ría de Vigo coastal inlet but also in an area ranging from the Bay of Biscay to the Portuguese coast. The robust seasonal cycles and long-term trends were only calculated along a longitudinal section, gathering data from the coastal and oceanic zone of the Iberian upwelling system. The pH in the surface waters of these separated regions, which were highly variable due to intense photosynthesis and the remineralization of organic matter, showed an interannual acidification ranging from −0.0012 to −0.0039 yr−1 that grew towards the coastline. This result is obtained despite the buffering capacity increasing in the coastal waters further inland as shown by the increase in alkalinity by 1.1±0.7 and 2.6±1.0 µmol kg−1 yr−1 in the inner and outer Ría de Vigo respectively, driven by interannual changes in the surface salinity of 0.0193±0.0056 and 0.0426±0.016 psu yr−1 respectively. The loss of the vertical salinity gradient in the long-term trend in the inner ria was consistent with other significant biogeochemical changes such as a lower oxygen concentration and fertilization of the surface waters. These findings seem to be related to a growing footprint of sediment remineralization of organic matter in the surface layer of a more homogeneous water column.

Continue reading ‘ARIOS: a database for ocean acidification assessment in the Iberian upwelling system (1976–2018) (update)’

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