Archive for the 'Science' Category

Calcium carbonate (CaCO3) sediment dissolution under elevated concentrations of carbon dioxide (CO2) and nitrate (NO3−)

Ocean acidification (OA), attributed to the sequestration of atmospheric carbon dioxide (CO2) into the surface ocean, and coastal eutrophication, attributed in part to land-use change and terrestrial runoff of fertilizers, have received recent attention in an experimental framework examining the effects of each on coral reef net ecosystem calcification (Gnet). However, OA and eutrophication in conjunction have yet to receive attention from the perspective of coral reef sediment dissolution. To address this omission, CO2 and nitrate (NO3−) addition experiments were performed in Mo’orea, French Polynesia. Incubation chambers were used to measure sediment Gnet during the day and night under three different [NO3−] (0, 9.8, and 19.7 μM) that were nested within four separate constructed coral reef communities maintained at different PCO2 levels (417, 721, 1030, and 1333 μatm, respectively). PCO2 negatively affected sediment Gnetduring the day and night, resulting in a shift to diel net dissolution at a PCO2 of 1030 μatm. Elevated NO3− alone, and the combination of NO3− and PCO2, both negatively affected sediment Gnet at night. However, the response of Gnet to NO3− was less clear during the day, where diurnal sediment Gnet was enhanced under the combined treatment of elevated NO3− and PCO2, resulting in no net effect of NO3− on sediment Gnet on diel timescales. Overall, these results show that ocean acidification represents a greater threat to the balance of calcification and dissolution in Mo’orea’s back reef sediment communities than the potential impact of NO3− enrichment on relatively short timescales.

Continue reading ‘Calcium carbonate (CaCO3) sediment dissolution under elevated concentrations of carbon dioxide (CO2) and nitrate (NO3−)’

Effects of acidified seawater on calcification, photosynthetic efficiencies and the recovery processes from strong light exposure in the coral Stylophora pistillata

The aim of this study was to investigate whether coral photosynthetic efficiencies and recovery processes are affected by CO2-driven ocean acidification in symbiont photosynthesis and coral calcification. We investigated the effects of five CO2 partial pressure (pCO2) levels in adjusted seawater ranging from 300 μatm (pre-industrial) to 800 μatm (near-future) and strong and weak light intensity on maximum photosynthetic efficiency and calcification of a branching coral, Stylophora pistillata, as this species has often been used in rearing experiments to investigate the effects of acidified seawater on calcification and photosynthetic algae of corals. We found that, the photosynthetic efficiencies and recovery patterns under different light conditions did not differ among pCO2 treatments. Furthermore, calcification of S. pistillata was not affected by acidified seawater under weak or strong light conditions. Our results indicate that the photosynthetic efficiency and calcification of S. pistillata are insensitive to changes in ocean acidity.

Continue reading ‘Effects of acidified seawater on calcification, photosynthetic efficiencies and the recovery processes from strong light exposure in the coral Stylophora pistillata’

Calcifying response and recovery potential of the brown alga Padina pavonica under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification (OA), which affects calcifying organisms. Recent studies have shown that Padina pavonica investigated along a natural pCO2 gradient seems to acclimate to OA by reducing calcified structures and changing mineralogy from aragonite to calcium sulphate salts. The aim of the present study was to study the potential for acclimation of P. pavonica to OA along the same gradient and in aquaria under controlled conditions. P. pavonica was cross-transplanted for one week from a normal pH site (median value: pHTS = 8.1; pCO2 = 361 μatm) to a low pH site (median value: pHTS = 7.4; pCO2 = 1025 μatm) and vice versa. Results showed that this calcifying alga did survive under acute environmental pHTS changes but its calcification was significantly reduced. P. pavonica decalcified and changed mineralogy at pHTS = 7.4, but once brought back at pHTS = 8.1 it partially recovered the aragonite loss while preserving the calcium sulphate minerals that formed under low pHTS. These results suggest that P. pavonica could be used as a bio-indicator for monitoring OA, as well as localized anthropogenic acidity fluctuations.

Continue reading ‘Calcifying response and recovery potential of the brown alga Padina pavonica under ocean acidification’

Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification

The effects of ultraviolet radiation (UVR) under future expected conditions of acidification and increase in nutrient inputs were studied on a post-bloom phytoplankton and bacterioplankton community of Patagonian coastal waters. We performed an experiment using microcosms where two environmental conditions were mimicked using a cluster approach: present (ambient nutrients and pH) and future (increased nutrients and acidification), and acclimating the samples for five days to two radiation treatments (full solar radiation [+UVR] and exclusion of UVR [–UVR]). We evaluated the short-term (hours) sensitivity of the community to solar UVR through chlorophyll afluorescence parameters (e.g. the effective photochemical quantum yield of PSII [ΦPSII]) at the beginning, at the mid-point and at the end of the acclimation period. Primary production and heterotrophic bacterial production (HBP) were determined, and biological weighting functions were calculated, at the beginning and at the end of the acclimation period. Mid-term effects (days) were evaluated as changes in taxonomic composition, growth rates and size structure of the community. Although the UVR-induced inhibition on ΦPSII decreased in both clusters, samples remained sensitive to UVR after the 5 days of acclimation. Also, under the future conditions, there was, in general, an increase in the phytoplankton carbon incorporation rates along the experiment as compared to the present conditions. Bacterioplankton sensitivity to UVR changed along the experiment from inhibition to enhancement of HBP, and future environmental conditions stimulated bacterial growth, probably due to indirect effects caused by phytoplankton. Those changes in the microbial loop functioning and structure under future global change conditions might have important consequences for the carbon pump and thus for the carbon sequestration and trophodynamics of Patagonian coastal waters.

Continue reading ‘Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification’

Decreased pH and increased temperatures affect young-of-the-year red king crab (Paralithodes camtschaticus)

The red king crab (Paralithodes camtschaticus) is a high-latitude commercially important species with a complex life-history cycle which encompasses a wide variety of conditions and habitats. High-latitude waters, including those around Alaska where red king crab live, are predicted to have increased ocean acidification and temperatures in comparison to other areas. The interaction of ocean acidification and increased temperature has not been examined for any life history stage of red king crab. To determine the effects of near-future ocean acidification and warming temperature on young-of-the-year red king crab survival, growth, and morphology, we conducted a long-term (184 d) fully crossed experiment with two pHs and three temperatures: ambient pH (∼7.99), pH 7.8, ambient temperature, ambient +2 °C, and ambient +4 °C, for a total of six treatments. Mortality increased with exposure to reduced pH and higher temperatures, but a clear trend in the interactive effects of the stressors was not observed. A synergetic effect on mortality was observed in the pH 7.8 and ambient +4 °C temperature treatment. This treatment also had the lowest survival with only 3% surviving to the end of the experiment. However, an antagonistic effect on mortality was observed in the pH 7.8 and ambient +2 °C treatment. Lower pH and warmer temperatures affected intermoult duration, only temperature affected percent increase in size, but carapace length was not affected. Decreased pH and increased temperature had no effect on morphology. The results of this study combined with other studies show that decreased pH and warming has profound negative effects on red king crab. Unless the species is able to adapt or acclimate to changing climate conditions, red king crabs populations may decrease in the upcoming decades due to ocean acidification and rising temperatures.

Continue reading ‘Decreased pH and increased temperatures affect young-of-the-year red king crab (Paralithodes camtschaticus)’

Intraspecific variations in responses to ocean acidification in two branching coral species

Ocean acidification is widely recognised to have a negative impact on marine calcifying organisms by reducing calcifications, but controversy remains over whether such organisms could cope with ocean acidification within a range of phenotypic plasticity and/or adapt to future acidifying ocean. We performed a laboratory rearing experiment using clonal fragments of the common branching corals Montipora digitata and Porites cylindrica under control and acidified seawater (lower pH) conditions (approximately 400 and 900 μatm pCO2, respectively) and evaluated the intraspecific variations in their responses to ocean acidification. Intra- and interspecific variations in calcification and photosynthetic efficiency were evident according to both pCO2 conditions and colony, indicating that responses to acidification may be individually variable at the colony level. Our results suggest that some corals may cope with ocean acidification within their present genotypic composition by adaptation through phenotypic plasticity, while others may be placed under selective pressures resulting in population alteration.

Continue reading ‘Intraspecific variations in responses to ocean acidification in two branching coral species’

Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish

Ocean acidification threatens marine ecosystems by altering ocean chemistry and calcification processes in marine organisms. This study investigated the effects of predicted future CO2 levels, under varying temperature levels, on otolith development (size and shape) and chemistry, with the latter aimed at developing a chemical tracer of environmental pCO2. Juvenile barramundi (Lates calcarifer), a diadromous fish species, were reared in ambient (pCO2: 640 μatm; pH: 7.9) and elevated (pCO2: 1490 μatm; pH: 7.5) pCO2 treatments representing current and projected coastal systems crossed with three temperature levels (26 °C, 30 °C and 34 °C) for 42 days. Otolith shape and size parameters (length, width, perimeter and area) were measured and element concentrations (Na, Mg, Sr, Ba, Li, Mn and B) were quantified using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS). There was an interactive effect of elevated pCO2 and temperature on otolith shape and perimeter, whereas otolith chemistry did not vary among treatments. This study demonstrates that combined elevated pCO2 and temperature can affect the development of important internal structures in diadromous fish, but also suggests that otolith elemental chemistry was not a suitable tracer for pCO2 histories in fish. Future climate change conditions affect an important auditory and balance organ; consequently, rising CO2 levels may interfere with sensory function.

Continue reading ‘Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish’


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Ocean acidification in the IPCC AR5 WG II

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