Posts Tagged 'North Pacific'

Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis

The rapidly intensifying process of ocean acidification (OA) due to anthropogenic CO2 is not only depleting carbonate ions necessary for calcification but also causing acidosis and disrupting internal pH homeostasis in several marine organisms. These negative consequences of OA on marine calcifiers, i.e. oyster species, have been very well documented in recent studies; however, the consequences of reduced or impaired calcification on the end-product, shells or skeletons, still remain one of the major research gaps. Shells produced by marine organisms under OA are expected to show signs of dissolution, disorganized microstructure and reduced mechanical properties. To bridge this knowledge gap and to test the above hypothesis, we investigated the effect of OA on juvenile shells of the commercially important oyster species, Magallana angulata, at ecologically and climatically relevant OA levels (using pH 8.1, 7.8, 7.5, 7.2). In lower pH conditions, a drop of shell hardness and stiffness was revealed by nanoindentation tests, while an evident porous internal microstructure was detected by scanning electron microscopy. Crystallographic orientation, on the other hand, showed no significant difference with decreasing pH using electron back-scattered diffraction (EBSD). These results indicate the porous internal microstructure may be the cause of the reduction in shell hardness and stiffness. The overall decrease of shell density observed from micro-computed tomography analysis indicates the porous internal microstructure may run through the shell, thus inevitably limiting the effectiveness of the shell’s defensive function. This study shows the potential deterioration of oyster shells induced by OA, especially in their early life stage. This knowledge is critical to estimate the survival and production of edible oysters in the future ocean.

Continue reading ‘Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis’

Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO2 rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO2 levels. Under low light conditions, elevated CO2 significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO2 level predicted for the end of the century.

Continue reading ‘Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising’

Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)

A mesocosm experiment was conducted in Wuyuan Bay (Xiamen), China, to investigate the effects of elevated pCO2 on the phytoplankton species Phaeodactylum tricornutum (P. tricornutum), Thalassiosira weissflogii (T. weissflogii) and Emiliania huxleyi (E. huxleyi) and their production ability of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), as well as four halocarbon compounds, bromodichloromethane (CHBrCl2), methyl bromide (CH3Br), dibromomethane (CH2Br2) and iodomethane (CH3I). Over a period of 5 weeks, P. tricornuntum outcompeted T. weissflogii and E. huxleyi, comprising more than 99% of the final biomass. During the logarithmic growth phase (phase I), mean DMS concentration in high pCO2 mesocosms (1000µatm) was 28% lower than that in low pCO2 mesocosms (400µatm). Elevated pCO2 led to a delay in DMSP-consuming bacteria concentrations attached to T. weissflogii and P. tricornutum and finally resulted in the delay of DMS concentration in the high pCO2 treatment. Unlike DMS, the elevated pCO2 did not affect DMSP production ability of T. weissflogii or P. tricornuntum throughout the 5-week culture. A positive relationship was detected between CH3I and T. weissflogii and P. tricornuntum during the experiment, and there was a 40% reduction in mean CH3I concentration in the high pCO2 mesocosms. CHBrCl2, CH3Br, and CH2Br2 concentrations did not increase with elevated chlorophyll a (Chl a) concentrations compared with DMS(P) and CH3I, and there were no major peaks both in the high pCO2 or low pCO2 mesocosms. In addition, no effect of elevated pCO2 was identified for any of the three bromocarbons.

Continue reading ‘Effect of elevated pCO2 on trace gas production during an ocean acidification mesocosm experiment (update)’

Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia

The severity of carbonate chemistry changes from ocean acidification is predicted to increase greatly in the coming decades, with serious consequences for marine species-­ especially those reliant on calcium carbonate for structure and function (Fabry et al. 2008). The Northern California Current Ecosystem off the coast of US West Coast experiences seasonal variations in upwelling and downwelling patterns creating natural episodes of hypoxia and calcite/aragonite undersaturation, exacerbating global trends of increasing ocean acidification and hypoxia (OAH) (Chan et al. 2008) (Gruber et al. 2012). The goal of these experiments was to identify thresholds of tolerance and attempt to quantify a point at which variance in responses to stress collapses. This study focuses on two species: Cancer magister (Dungeness crab) and Haliotis rufescens (red abalone). These species were selected for this study based on their economic and ecological value, as well as their taxonomic differences. Respirometry was used as a proxy for metabolic activity at four different scenarios mimicking preindustrial, upwelling, contemporary upwelling, and distant future conditions by manipulating dissolved oxygen and inorganic carbon (DIC) concentrations. Both species showed a decrease in mean respiration rate as OAH stressors increase, including an effect in contemporary upwelling conditions. These results suggest that current exposure to ocean acidification (OA) and hypoxia do not confer resilience to these stressors for either taxa. In teasing apart the effects of OAH as multiple stressors, it was found that Dungeness crab response was more strongly driven by concentration of dissolved oxygen, while red abalone data suggested a strong interactive effect between OA and hypoxia. Not only did these two different taxa exhibit different responses to a multiple stressors, but the fact that the Dungeness crab were secondarily impacted by acidification could suggest that current management concerns may need to be focus more strongly on deoxygenation.

Continue reading ‘Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia’

Modeling the variability, trends and future changes in ocean acidification in the Humboldt Current System

The largest buffer against climate change is the oceanic sink of anthropogenic CO2. However, this important ecosystem service to humanity leads to the reduction of pH and the saturation state of the biologically relevant calcium carbonate minerals aragonite and calcite  (Ωarag and Ωcalc). This process, known as anthropogenic ocean acidification, is a major marine ecosystem stressor and has negative impacts that range from reduced calcification to changes in population dynamics of important fisheries. Some of the most productive regions of the world, the Eastern Boundary Upwelling Systems (EBUS), are also among the most vulnerable to become undersaturated in the next decades due to the natural occurrence of low pH and Ω values at shallow depths and the projected further uptake of anthropogenic CO2. While extensive research on ocean acidification has been conducted in the California Current upwelling System, little is known about the dynamics of the marine carbonate chemistry in the much more productive Humboldt Current Upwelling System (HumCS), in the west coast of South America. To fill this gap, I used the high resolution Regional Ocean Modelling System (ROMS) and two different ecosystem models to study the progression of ocean acidification in the HumCS and the natural fluctuations superimposed to this anthropogenic perturbation. Results from a preindustrial simulation (year 1870) show that even then, pH and Ωarag values in the HumCS were respectively ⇠ 0.3 and 1 units lower than the preindustrial global average. The simulated evolution of ocean acidification to the end of the century showed that the continuous uptake of anthropogenic CO2 will push the nearshore off Peru to even lower values, from a present-day pH of 7.8 and Ωarag of 1.8 to year-round undersaturated conditions in year 2090 in at least 60 % of the top layer of the water column in the nearshore off Peru. Aragonite undersaturation in the following decades is already a committed change regardless of the amount of carbon emitted to the atmosphere in the future. However, a striking difference arises between following a “high CO2 emissions” scenario (RCP8.5, pCO2 values 840 μatm by year 2090) or a “low CO2 emissions” scenario (RCP2.6, pCO2 values of 428 μatm). In the former, water corrosive to calcite, a less soluble form of calcium carbonate than aragonite, will be found in the first 15 km off Peru and will potentially impact a larger range of calcifying organisms. On the other hand, this can be avoided the RCP2.6 scenario is followed, and strong CO2 mitigation measures are established and executed. In the high CO2 emissions scenario, an overall decrease of 0.9 ± 0.1 units in Ωarag from present day to the end of the century is projected in the nearshore off Peru, and a similar trend in the nearshore off Chile. On top of this long-term trend, natural climate variability off Peru can lead to strong year-to-year variations in the progression of ocean acidification. The largest contribution to Ωarag variability in the HumCS is on the interannual timescale, mainly forced by remotely forced tropical oscillations (e.g. El Ni˜no/Southern Oscillation) but also by local and regional phenomena (e.g., El Ni˜no costero). Analysis from a hindcast simulation for the period of 1979-2016 reveals that under present day conditions, the magnitude of such variability is comparable to the anthropogenic trend. Interannual changes in Ω are mainly driven by variations in the thermocline structure and wind patterns. Off Peru, the deepening of the thermocline associated with warm, El Ni˜no-like events, is translated into an increase in Ωarag in the surface layer of 0.4 units, while a shallower thermocline driven by cold interannual events (e.g., La Ni˜na) leads to a decrease in Ωarag values of 0.3 units. These natural interannual variations account for ⇠ 30 to and 40 % of the magnitude of the expected anthropogenic change, potentially bringing forward of delaying by some decades the pervasive appearance of aragonite undersaturated waters in the surface layer of the most productive EBUS of the Pacific: the Humboldt Current.

Continue reading ‘Modeling the variability, trends and future changes in ocean acidification in the Humboldt Current System’

Bioeconomic analysis of the impact of ocean acidification associated with low recruitment of Isostichopus badionotus and implications for adaptive fishery management in the north of the Yucatan Peninsula, Mexico

The impact that ocean acidification (OA) could generate in the fisheries of Isostichopus badionotus at the north of the Yucatan Peninsulta, Mexico, was analysed by reducing the value of a parameter of the Beverton-Holt recruitment function, in accordance with the acidification scenarios of the Intergovermental Panel Panel on Climate Change (IPCC). The behaviour of the stock and the resulting fishery were analysed in a bioeconomic model structured by age, taking into account different market prices and fishing efforts. The results were compared in decision matrices that used the MiniMax and MaxMin criteria to determine the management strategy that best reduced the impact of  acidification. The largest stock reduction occurred during the first years of exploitation (B10>B15/BO) and all the variables that were considered did stabilize with time, reaching bioeconomic equilibrium. The worst scenario for not considering acidification occurred with low market prices, while the increase in price decreased the exploitation rate. The recruitment reduction determined the maximum effort that should have been applied; under such conditions it is recommended to operate an effort of 137 boats, considering the best market price.

Continue reading ‘Bioeconomic analysis of the impact of ocean acidification associated with low recruitment of Isostichopus badionotus and implications for adaptive fishery management in the north of the Yucatan Peninsula, Mexico’

Modelling the mechanisms and drivers of the spatiotemporal variability of pCO2 and air-sea CO2 fluxes in the Northern Humboldt Current System

Highlights

• Air-sea CO2 fluxes follow the upwelling intensity throughout the year.
• Circulation is the dominant mechanism driving variability in the nearshore area.
• Biology and solubility effects partially damp upwelling-driven pCO2 variability.
• High coastal pCO2 values are due to a spatiotemporal decoupling between circulation and biology.
pCO2 is more sensitive to changes in dissolved inorganic carbon and temperature.

Abstract

We use a coupled physical-biogeochemical model to investigate the drivers and mechanisms responsible for the spatiotemporal variability of the partial pressure of carbon dioxide in seawater (pCO2) and associated air-sea CO2 fluxes in the Northern Humboldt Current System (NHCS). Simulated pCO2 is in good agreement with available observations with an average absolute error of, approximately, 24 μatm. The highly productive upwelling region, 300 km from the shore and between 5°S-17°S, is shown to be a strong CO2 source with an averaged flux of 5.60  ±  2.94 mol C m−2 yr−1, which represents an integrated carbon flux of 0.028  ±  0.015 Pg C yr−1 . Through a series of model experiments we show that the high pCO2 is primarily the result of coastal upwelling, which is incompletely compensated by biology. Specifically, the supply of dissolved inorganic carbon (DIC)-rich waters to the surface pushes pCO2 up to levels around 1100 μatm. Even though biological production is high, it reduces pCO2 only by about 300 μatm. We show that this relatively low degree of biological compensation, which implies an inefficient biological pump in the nearshore domain, results from a spatiotemporal decoupling between the counteracting effects of biological production and the transport and mixing of DIC. The contribution of the outgassing and the processes affecting CO2 solubility, associated with the seasonal cycle of heating and cooling, are minor. Across the whole domain, the balance of mechanisms is similar, but with smaller amplitudes. We demonstrate that seawater pCO2 is more sensitive to changes in DIC and sea surface temperature, while alkalinity plays a minor role.

Continue reading ‘Modelling the mechanisms and drivers of the spatiotemporal variability of pCO2 and air-sea CO2 fluxes in the Northern Humboldt Current System’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,123,853 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book