Posts Tagged 'phytoplankton'

Ocean acidification has little effect on the biochemical composition of the coccolithophore Emiliania huxleyi

Owing to the hierarchical organization of biology, from genomes over transcriptomes and proteomes down to metabolomes, there is continuous debate about the extent to which data and interpretations derived from one level, e.g. the transcriptome, are in agreement with other levels, e.g. the metabolome. Here, we tested the effect of ocean acidification (OA; 400 vs. 1000 μatm CO2) and its modulation by light intensity (50 vs. 300 μmol photons m-2 s-1) on the biomass composition (represented by 75 key metabolites) of diploid and haploid life-cycle stages of the coccolithophore Emiliania huxleyi (RCC1216 and RCC1217) and compared these data with interpretations from previous physiological and gene expression screenings. The metabolite patterns showed minor responses to OA in both life-cycle stages. Whereas previous gene expression analyses suggested that the observed increased biomass buildup derived from lipid and carbohydrate storage, this dataset suggests that OA slightly increases overall biomass of cells, but does not significantly alter their metabolite composition. Generally, light was shown to be a more dominant driver of metabolite composition than OA, increasing the relative abundances of amino acids, mannitol and storage lipids, and shifting pigment contents to accommodate increased irradiance levels. The diploid stage was shown to contain vastly more osmolytes and mannitol than the haploid stage, which in turn had a higher relative content of amino acids, especially aromatic ones. Besides the differences between the investigated cell types and the general effects on biomass buildup, our analyses indicate that OA imposes only negligible effects on E. huxleyi´s biomass composition.

Continue reading ‘Ocean acidification has little effect on the biochemical composition of the coccolithophore Emiliania huxleyi’

Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions.

Continue reading ‘Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels’

Calcite dissolution rates in seawater: lab vs. in-situ measurements and inhibition by organic matter

Highlights

• Calcite dissolution in lab and in-situ exhibits the same dissolution mechanisms.

• In-situ dissolution rates are likely inhibited by dissolved organic carbon.

• Orthophosphate has no effect on seawater calcite dissolution rates from pH 5.5 to 7.5.

• Previous in-situ dissolution rates fall between bounds established by our measurements.

• Rate measurements suggest need to reevaluate marine carbonate system equilibria.

Abstract

Ocean acidification from fossil fuel burning is lowering the mean global ocean saturation state (Ω = ), thus increasing the thermodynamic driving force for calcium carbonate minerals to dissolve. This dissolution process will eventually neutralize the input of anthropogenic CO2, but the relationship between Ω and calcite dissolution rates in seawater is still debated. Recent advances have also revealed that spectrophotometric measurements of seawater pHs, and therefore in-situ Ωs, are systematically lower than pHs/Ωs calculated from measurements of alkalinity (Alk) and total dissolved inorganic carbon (DIC). The calcite saturation horizon, defined as the depth in the water column where Ω = 1, therefore shifts by ~5–10% depending on the parameters used to calculate Ω. The “true” saturation horizon remains unknown. To resolve these issues, we developed a new in-situ reactor and measured dissolution rates of 13C-labeled inorganic calcite at four stations across a transect of the North Pacific Ocean. In-situ saturation was calculated using both Alk-DIC (Ω(Alk, DIC)) and Alk-pH (Ω(Alk, pH)) pairs. We compare in-situ dissolution rates with rates measured in filtered, poisoned, UV-treated seawater at 5 and 21 °C under laboratory conditions. We observe in-situ dissolution above Ω(Alk, DIC) = 1, but not above Ω(Alk, pH) = 1. We emphasize that marine carbonate system equilibria should be reevaluated and that care should be taken when using proxies calibrated to historical Ω(Alk, DIC). Our results further demonstrate that calcite dissolution rates are slower in-situ than in the lab by a factor of ~4, but that they each possess similar reaction orders (n) when fit to the empirical Rate = k(1-Ω)n equation. The reaction orders are n < 1 for 0.8 < Ω < 1 and n = 4.7 for 0 < Ω < 0.8, with the kink in rates at Ωcrit = 0.8 being consistent with a mechanistic transition from step edge retreat to homogenous etch pit formation. We reconcile the offset between lab and in-situ rates by dissolving calcite in the presence of elevated orthophosphate (20 μm) and dissolved organic carbon (DOC) concentrations, where DOC is in the form of oxalic acid (20 μm), gallic acid (20 μm), and d-glucose (100 μm). We find that soluble reactive phosphate has no effect on calcite dissolution rates from pH 5.5–7.5, but the addition of DOC in the form of d-glucose and oxalic acid slows laboratory dissolution rates to match in-situ observations, potentially by inhibiting the retreat rate of steps on the calcite surface. Our lab and in-situ rate data form an envelope around previous in-situ dissolution measurements and may be considered outer bounds for dissolution rates in low/high DOC waters. The lower bound (high DOC) is most realistic for particles formed in, and sinking out of, surface waters, and is described by R(mol cm-2 s-1) = 10–14.3±0.2(1-Ω)0.11±0.1 for 0.8 < Ω < 1, and R(mol cm-2 s-1) = 10–10.8±0.4(1-Ω)4.7±0.7 for 0 < Ω < 0.8. These rate equations are derived from in-situ measurements and may be readily implemented into marine geochemical models to describe water column calcite dissolution.

Continue reading ‘Calcite dissolution rates in seawater: lab vs. in-situ measurements and inhibition by organic matter’

Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis

Ocean acidification (O.A.) influences the ecology of oceans and it may impact plant-animal interactions at various levels. Seagrass meadows located at acidified vents in the Bay of Naples (Italy) are considered an open window to forecast the effects of global-changes on aquatic communities. Epiphytic diatoms of the genus Cocconeis are abundant in seagrass meadows, including acidified environments, where they play key ecological roles. A still-unknown apoptogenic compound produced by Cocconeis triggers the suicide of the androgenic gland of Hippolyte inermis Leach 1816, a protandric hermaphroditic shrimp distributed in P. oceanica meadows located both at normal pH and in acidified vents. Feeding on Cocconeis sp. was proven important for the stability of the shrimp’s natural populations. Since O.A. affects the physiology of diatoms, we investigated if, in future scenarios of O.A., Cocconeis scutellum parva will still produce an effect on shrimp’s physiology. Cell densities of Cocconeis scutellum parva cultivated in custom-designed photobioreactors at two pH conditions (pH 7.7 and 8.2) were compared. In addition, we determined the effects of the ingestion of diatoms on the process of sex reversal of H. inermis and we calculated the % female on the total of mature individuals-1 (F/mat). We observed significant differences in cell densities of C. scutellum parva at the two pH conditions. In fact, the highest cell densities (148,808 ±13,935 cells. mm-2) was obtained at day 13 (pH 7.7) and it is higher than the highest cell densities (38,066 (±4,166) cells. mm-2, day 13) produced at pH 8.2. Diatoms cultured at acidified conditions changed their metabolism. In fact, diatoms grown in acidified conditions produced in H. inermis a proportion of females (F/mat 36.3 ±5.9%) significantly lower than diatoms produced at normal pH (68.5 ±2.8), and it was not significantly different from that elicited by negative controls (31.7 ±5.6%).

Continue reading ‘Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis’

Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates

High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNF), nano- and picophytoplankton, and prokaryotes in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥ 634 μatm, HNF abundance was reduced, coinciding with significantly increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNF. Nanophytoplankton abundance was significantly elevated in the 634 and 953 μatm treatments, suggesting that moderate increases in CO2 may stimulate growth. Changes in predator-prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean. Based on these results, it is likely that the phytoplankton community composition in these waters will shift to communities dominated by prokaryotes, nano- and picophytoplankton. This may intensify organic matter recycling in surface waters, leading to a decline in carbon flux, as well as a reducing the quality and quantity of food available to higher trophic organisms.

Continue reading ‘Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates’

Local drivers of the seasonal carbonate cycle across four contrasting coastal systems

Highlights

• This dataset illustrates how local carbonate chemistry can vary widely along short lengths of coastline due to local drivers, particularly bedrock geology.

• Results highlight which season is most/least favourable for calcifying species and how this relates to their lifecycle.

• The dataset identified a number of key issues when addressing indicators of ecosystem vulnerability (calcium in omega calculations and SIR-).

• Results illustrate that we must understand both regional and local conditions in order to estimate future ocean acidification conditions and potential impacts on local ecosystems and shellfish aquaculture.

Abstract

Four contrasting coastal systems in Ireland, each with shellfish production activities, were studied to provide a first evaluation of the spatial and seasonal influences on the local carbonate system. The study sites included; (1) a coastal system with sandstone bedrock and minimal freshwater sources, (2) an estuarine system with a catchment limestone bedrock, (3) an estuarine system with a catchment granite bedrock, and (4) a karst groundwater-fed estuary. The type of bedrock was the dominant control on regional carbonate chemistry, where the calcium carbonate catchment bedrock was a strong source of both dissolved inorganic carbon and total alkalinity input in the two limestone regions, which are supersaturated with respect to atmospheric CO2 throughout the year. Primary production played an important role in the non-limestone regions, where both systems were CO2-undersaturated during productive months. Minimum aragonite saturation () was observed at all sites during winter when productivity is lowest; surface winter is 2 in the inner estuary. The substrate-to-inhibitor ratio (SIR), an alternative indicator of ecosystem vulnerability to acidification, was positively correlated to in all systems, however with more variability in the two limestone regions. Results highlight challenges of assessing local ecosystem vulnerability to future acidification and the importance of understanding the local spatio-temporal biogeochemistry.

Continue reading ‘Local drivers of the seasonal carbonate cycle across four contrasting coastal systems’

Physiological responses of a coccolithophore to multiple environmental drivers

Highlights
• Coccolithophores were more stressful in the higher solar UV irradiance exposures.

• The cells increased their functional antennae sizes under the future ocean conditions.

• Coccolithophores photosynthesized more in the high CO2 and warming ocean.

• Synergistical or antagonistic interactions were observed among multiple drivers.

Abstract
Ocean acidification is known to affect primary producers differentially in terms of species and environmental conditions, with controversial results obtained under different experimental setups. In this work we examined the physiological performances of the coccolithophore Gephyrocapsa oceanica that had been acclimated to 1000 μatm CO2 for ~400 generations, and then exposed to multiple drivers, light intensity, light fluctuating frequency, temperature and UV radiation. Here, we show that increasing light intensity resulted in higher non-photochemical quenching and the effective absorption cross-section of PSII. The effective photochemical efficiency (Fv′/Fm′) decreased with increased levels of light, which was counterbalanced by fluctuating light regimes. The greenhouse condition acts synergistically with decreasing fluctuating light frequency to increase the Fv′/Fm′ and photosynthetic carbon fixation rate. Our data suggest that the coccolithophorid would be more stressed with increased exposures to solar UV irradiances, though its photosynthetic carbon fixation could be enhanced under the greenhouse condition.

Continue reading ‘Physiological responses of a coccolithophore to multiple environmental drivers’


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Ocean acidification in the IPCC AR5 WG II

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