Posts Tagged 'North Atlantic'

Trends of ocean acidification and pCO2 in the northern North Sea, 2003‐2015

For continental shelf regions, the long‐term trend in sea surface carbon dioxide (CO2) partial pressure (pCO2) and rates of ocean acidification are not accurately known. Here, we investigate the decadal trend of observed wintertime pCO2 as well as computed wintertime pH and aragonite saturation state (Ωar) in the northern North Sea, using the first decade long monthly underway data from a Voluntary Observing Ship (VOS) covering the period 2004‐2015. We also evaluate how seawater CO2 chemistry, in response to physical and biological processes, drives variations in the above parameters on seasonal and interannual timescales. In the northern North Sea, pCO2, pH, and Ωar are subject to strong seasonal variations with mean wintertime values of 375±11 μatm, 8.17±0.01, and 1.96±0.05. Dissolved Inorganic Carbon (DIC) is found to be the primary driver of both seasonal and interannual changes while total alkalinity (TA) and sea surface temperature (SST) have secondary effects that reduce the changes produced by DIC. Average interannual variations during winter are around 3%, 0.1% and 2% for pCO2, pH, and Ωar, respectively, and slightly larger in the eastern part of the study area (Skagerrak region) than in the western part (North Atlantic Water (NAW) region). Statistically significant long‐term trends were found only in the NAW region with mean annual rates of 2.39±0.58 μatm yr‐1, ‐0.0024±0.001 yr‐1, and ‐0.010±0.003 yr‐1for pCO2, pH and Ωar, respectively. The drivers of the observed trends as well as reasons for the lack of statistically significant trends in the Skagerrak region are discussed.

Continue reading ‘Trends of ocean acidification and pCO2 in the northern North Sea, 2003‐2015’

The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine

In the next 80 years, sea surface temperatures are expected to increase by 1.5o to 2oC and ocean pH is expected to drop by 0.06 to 0.32 units, with exacerbated effects seen in coastal waters. Temperature increase has already forced organisms to shift their range polewards and ocean acidification has negatively affected calcifying organisms. Interactive effects, only more recently studied, vary depending on phylum and life cycle stage. This study examined both the upper thermal tolerance and interactive effect of temperature and acidification on the heart rate of five cold-water species of nudibranchs (Aeolidia papillosa, Cuthona gymnota, Dendronotus frondosus, Flabellina verrucosa, and Onchidoris bilamellata) and one species of sacoglossan (Placida dendritica) from the Gulf of Maine. Thermal tolerance was determined by recording heart rate for each organism starting at 4oC and increasing the temperature by increments of 4oC until the organism’s heartbeat slowed or ceased. For interactive effects, pH levels used were pH 8 (control) and pH 7 at temperatures: 4o, 8o (control), 12o, and 16oC. Upper thermal tolerance limits ranged from 16o to 20oC for the nudibranchs and 24oC for the sacoglossan. The combined effects of increasing temperature and lower pH were neutral, negatively additive, and antagonistic. Only F. verrucosa exhibited an interactive effect, with higher temperature and lower pH leading to decreased heart rate. Although no interactive effect was demonstrated in C. xgymnota, D. frondosus, and O. bilamellata, lower pH slowed heart rates across all temperatures. Subsequently, the relationship between temperature and growth rates was examined in D. frondosus and F. verrucosa. The nudibranchs were reared for eight weeks at 4o, 10o, or 16oC and growth was measured weekly. The ideal temperature for growth appeared to be 10oC, whereas 16oC was lethal. Additionally, an unsuccessful attempt was made to culture A. papillosa, but the number of embryos per egg capsule and larval growth rates were examined. Size of adult sea slug positively impacted the number of embryos per egg capsule, with embryos increasing in length by 50% over the first week and 10% over subsequent weeks. With an interactive effect only seen in one species and upper temperatures being lethal if held constant for a month, temperature appears to be the greatest threat to survival. What is happening to these sea slugs in the GOM is likely happening to other snails and marine invertebrates throughout the ocean. Knowing how organisms will react to the projected changes can help inform future policies and practices.

Continue reading ‘The effects of climate change on the heart rates & growth of sea slugs in the Gulf of Maine’

Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics

The Dutch coastal zone is a region of the North Sea with a marked interannual and long‐term abiotic and phytoplankton variability. To investigate the relationship between abiotic variability and phytoplankton composition, two routine water monitoring data sets (1991–2005) were examined. Multivariate statistics revealed two significant partitions in the data. The first consisted of interannual abiotic fluctuations that were correlated to Rhine discharge that affected the abundance of summer and autumn diatom species. The second partition was caused by a shift in the abiotic data from 1998 to 1999 that was followed by a shift in phytoplankton composition from 1999 to 2000. Important factors in the abiotic shift were decreases in suspended matter (SPM) and phosphate (DIP) concentrations, as well as in pH. The decrease in SPM was caused by a reduction in wind speed. The increase in water column daily irradiance from the decrease in SPM led to increases in the abundance of winter–spring species, notably the prymnesiophyte Phaeocystis globosa. Because wind speed is related to the North Atlantic Oscillation (NAO) index it was possible to correlate NAO index and P. globosa abundance. Only five abiotic variables representing interannual and long‐term variability, including Rhine discharge and NAO index, were needed to model the observed partitions in phytoplankton composition. It was concluded that interannual variability in the coastal phytoplankton composition was related to year‐to‐year changes in river discharge while the long‐term shift was caused by an alternating large‐scale meteorological phenomenon.

Continue reading ‘Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics’

Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)

Ocean acidification and ocean warming (OAW) are simultaneously occurring and could pose ecological challenges to marine life, particularly early life stages of fish that, although they are internal calcifiers, may have poorly developed acid-base regulation. This study assessed the effect of projected OAW on key fitness traits (growth, development and swimming ability) in European sea bass (Dicentrarchus labrax) larvae and juveniles. Starting at 2 days post-hatch (dph), larvae were exposed to one of three levels of PCO2 (650, 1150, 1700 μatm; pH 8.0, 7.8, 7.6) at either a cold (15°C) or warm (20°C) temperature. Growth rate, development stage and critical swimming speed (Ucrit) were repeatedly measured as sea bass grew from 0.6 to ~10.0 (cold) or ~14.0 (warm) cm body length. Exposure to different levels of PCO2 had no significant effect on growth, development or Ucrit of larvae and juveniles. At the warmer temperature, larvae displayed faster growth and deeper bodies. Notochord flexion occurred at 0.8 and 1.2 cm and metamorphosis was completed at an age of ~45 and ~60 days post-hatch for sea bass in the warm and cold treatments, respectively. Swimming performance increased rapidly with larval development but better swimmers were observed in the cold treatment, reflecting a potential trade-off between fast grow and swimming ability. A comparison of the results of this and other studies on marine fish indicates that the effects of OAW on the growth, development and swimming ability of early life stages are species-specific and that generalizing the impacts of climate-driven warming or ocean acidification is not warranted.

Continue reading ‘Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax)’

Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod

Highlights

• Prolonged exposures to high pCO2 can severely affect Phorcus sauciatus shell.

• No effects of high pCO2 were found on size-frequency or population density of P. sauciatus.

• Shells from reduced pH sites exhibited a higher shell aspect ratio and greater percentages of shell dissolution and break.

• Shells from high pCO2 areas exhibited changes in mechanical strength.

• Similar desiccation tolerance was found among contrasting environment populations.

Abstract

Volcanic CO2 vents are useful environments for investigating the biological responses of marine organisms to changing ocean conditions (Ocean acidification, OA). Marine shelled molluscs are highly sensitive to changes in seawater carbonate chemistry. In this study, we investigated the effects of reduced pH on the intertidal gastropod, Phorcus sauciatus, in a volcanic CO2 vent off La Palma Island (Canary Islands, North East Atlantic Ocean), a location with a natural pH gradient ranging from 7.0 to 8.2 over the tidal cycles. Density and size-frequency distribution, shell morphology, shell integrity, fracture resistance, and desiccation tolerance were evaluated between populations from control and CO2 vent sites. We found no effects of reduced pH on population parameters or desiccation tolerance across the pH gradient, but significant differences in shell morphology, shell integrity, and fracture resistance were detected. Individuals from the CO2 vent site exhibited a higher shell aspect ratio, greater percentages of shell dissolution and break, and compromised shell strength than those from the control site. Our results highlight that long-term exposure to high pCO2 can negatively affect the shell features of P. sauciatus but may not have a significant effect on population performance. Moreover, we suggest that loss of shell properties could lead to changes in predator-prey interactions.

Continue reading ‘Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod’

Impacts of ocean acidification on intertidal benthic foraminiferal growth and calcification

Foraminifera are expected to be particularly susceptible to future changes in ocean carbonate chemistry as a function of increased atmospheric CO2. Studies in an experimental recirculating seawater system were performed with a dominant benthic foraminiferal species collected from intertidal mudflats. We investigated the experimental impacts of ocean acidification on survival, growth/calcification, morphology and the biometric features of a calcareous species Elphidium williamsoni. Foraminifera were exposed for 6 weeks to four different pH treatments that replicated future scenarios of a high CO2 atmosphere resulting in lower seawater pH. Results revealed that declining seawater pH caused a decline in foraminiferal survival rate and growth/calcification (mainly through test weight reduction). Scanning electron microscopy image analysis of live specimens at the end of the experimental period show changes in foraminiferal morphology with clear signs of corrosion and cracking on the test surface, septal bridges, sutures and feeding structures of specimens exposed to the lowest pH conditions. These findings suggest that the morphological changes observed in shell feeding structures may serve to alter: (1) foraminiferal feeding efficiency and their long-term ecological competitiveness, (2) the energy transferred within the benthic food web with a subsequent shift in benthic community structures and (3) carbon cycling and total CaCO3 production, both highly significant processes in coastal waters. These experimental results open-up the possibility of modelling future impacts of ocean acidification on both calcification and dissolution in benthic foraminifera within mid-latitude intertidal environments, with potential implications for understanding the changing marine carbon cycle.

Continue reading ‘Impacts of ocean acidification on intertidal benthic foraminiferal growth and calcification’

Recommended priorities for research on ecological impacts of ocean and coastal acidification in the U.S. Mid-Atlantic

The estuaries and continental shelf system of the United States Mid-Atlantic are subject to ocean acidification driven by atmospheric CO2, and coastal acidification caused by nearshore and land-sea interactions that include biological, chemical, and physical processes. These processes include freshwater and nutrient input from rivers and groundwater; tidally-driven outwelling of nutrients, inorganic carbon, alkalinity; high productivity and respiration; and hypoxia. Hence, these complex dynamic systems exhibit substantial daily, seasonal, and interannual variability that is not well captured by current acidification research on Mid-Atlantic organisms and ecosystems. We present recommendations for research priorities that target better understanding of the ecological impacts of acidification in the U. S. Mid-Atlantic region. Suggested priorities are: 1) Determining the impact of multiple stressors on our resource species as well as the magnitude of acidification; 2) Filling information gaps on major taxa and regionally important species in different life stages to improve understanding of their response to variable temporal scales and sources of acidification; 3) Improving experimental approaches to incorporate realistic environmental variability and gradients, include interactions with other environmental stressors, increase transferability to other systems or organisms, and evaluate community and ecosystem response; 4) Determining the capacity of important species to acclimate or adapt to changing ocean conditions; 5) Considering multi-disciplinary, ecosystem-level research that examines acidification impacts on biodiversity and biotic interactions; and 6) Connecting potential acidification-induced ecological impacts to ecosystem services and the economy. These recommendations, while developed for the Mid-Atlantic, can be applicable to other regions will help align research towards knowledge of potential larger-scale ecological and economic impacts.

Continue reading ‘Recommended priorities for research on ecological impacts of ocean and coastal acidification in the U.S. Mid-Atlantic’


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Ocean acidification in the IPCC AR5 WG II

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