Posts Tagged 'protists'

Sensitivity of planktic foraminiferal test bulk density to ocean acidification

The anthropogenic CO2 accumulating in the ocean is lowering seawater carbonate ion concentration and may reduce calcification rates of marine calcareous organisms. Several proxies based on test weights of planktic foraminifera have been used to evaluate the impact of ocean acidification on these organisms. Unfortunately, because of the absence of a method to evaluate the bulk density of a test, the impact of seawater carbonate chemistry on test calcification is still not fully understood. In this study, we measured bulk densities of living Globigerina bulloides (planktic foraminifera) tests with an X-ray micro-computed tomography (XMCT) scanner and compared them with ambient seawater characteristics. Results demonstrated that test bulk densities were controlled by ambient seawater carbonate ion concentrations and that changes of test bulk densities were accompanied by changes in micron to submicron scale porosity of internal ultrastructure. These results suggest that alteration of the bulk density of foraminiferal tests due to acidification of ambient seawater can be directly observed by XMCT scanning. A useful metric of calcification intensity would therefore be physical measurements of test densities with XMCT.

Continue reading ‘Sensitivity of planktic foraminiferal test bulk density to ocean acidification’

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’

Seagrass Posidonia oceanica diel pH fluctuations reduce the mortality of epiphytic forams under experimental ocean acidification

Highlights

• Forams epiphyte of Posidonia oceanica are resistant to ocean acidification scenarios.

• Seagrasses may provide “refugia” from ocean acidification to associated biota.

• There is an urgent need to incorporate pH fluctuations in the experimental designs.

Abstract

It is hypothesized that pH fluctuations produced by seagrasses metabolism may confer marine calcifiers resistance to ocean acidification. Here, we tested this thesis by comparing the net population growth rate (NPGR) of a foraminifer species (Rosalina sp.) epiphytic of Mediterranean seagrass (Posidonia oceanica) to average current and projected pH scenarios under either stable conditions or diel fluctuations in pH of 0.3 units; variations similar to that experienced in their habitat. No significant differences were found in NPGRs between the fluctuating and stable pH treatments at current pH levels. NPGRs in treatments where pH fluctuated did not present significant differences to the treatment with high and stable pH conditions. In contrast, foraminifers exposed to stable low pH regimes experienced a steep decline in NPGR. These results suggest that diel pH fluctuations generated by P. oceanica photosynthetic activity could confer resistance to ocean acidification to Rosalina sp.

Continue reading ‘Seagrass Posidonia oceanica diel pH fluctuations reduce the mortality of epiphytic forams under experimental ocean acidification’

Experimental validation of planktic foraminifera fragmentation index as a proxy for end-cretaceous ocean acidification

The final ~50 ky of the Maastrichtian leading up to the Cretaceous-Tertiary boundary mass extinction at Bidart (France) show records of poor carbonate preservation, the final ~25 ky being critical. This event has been proposed as evidence for ocean acidification immediately preceding the mass extinction. High planktic foraminifera test fragmentation index, anomalously low bulk-rock magnetic susceptibility and peak mercury content in this same interval link this crisis interval to peak Deccan volcanism in India. New results provide experimental validation for fragmentation index as an authentic proxy of end-Cretaceous ocean acidification event. Pristine Cretaceous planktic foraminifera morphotypes were exposed to buffers of pH 8.0, 7.5, 7.0 and 6.5 for 15 days each and their preservation state was quantified as a function of time. The critical variables affecting test vulnerability and taphonomy are morphology, pH and time of exposure. Thin-walled fragile biserial species(60%) such as Heterohelix globulosa and H. planata are the most susceptible to dissolution, followed by simple coiled forms such as Rugoglobigerina (19%) sp. and Hedbergella sp(6.4%). The globotruncanids(12%) appear to be least susceptible to chemical and physical damage. Tests exposed to low pH conditions clearly show a higher vulnerability to fragmentation. These results indicate a strong influence of chemical and physical taphonomy on planktic foraminifera census data with serious palaeoenvironmental implications. Results also indicate that an overestimation of the abundance of environmentally sensitive Cretaceous species (e.g. globotruncanids) due to taphonomic preservation bias could result in underestimation of the degree/nature of faunal crisis and tempo of extinctions in the pre-extinction acidification interval.

Continue reading ‘Experimental validation of planktic foraminifera fragmentation index as a proxy for end-cretaceous ocean acidification’

Quantification of the effects of ocean acidification on benthic foraminifera

The global ocean has experienced an alteration of its seawater chemistry due to the continuing uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere. This ongoing process called Ocean acidification (OA) has reduced seawater pH levels, carbonate ion concentrations (CO₃⁻²) and carbonate saturation state (Ω) with implications for the diversity and functioning of marine life, particularly for marine calcifiers such as foraminifera. The vulnerability of this ubiquitous calcifying group to future high 𝘱CO₂ /low pH scenarios has been assessed naturally and experimentally in the last decades. However, little is known about how benthic foraminifera from coastal environments such as intertidal environments will respond to the effects of OA projected by the end of the century. This research aimed to quantify the effects of OA on a series of biological parameters measured on the benthic foraminifera 𝘌𝘭𝘱𝘩𝘪𝘥𝘪𝘶𝘮 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏𝘢𝘺𝘯𝘦𝘴𝘪𝘯𝘢 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 through a laboratory-based experimental approach where future scenarios of a high CO₂ atmosphere and low seawater pH were explored.
Experimental evidence revealed that survival rates, test weight and size-normalized weight (SNW) of 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 were negatively affected by OA. Whereas 𝘏. 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 was positively affected (i.e. enhanced growth rates) showing a species-specific response to OA at 13°C. However, the combined effect of OA and temperature (15°C) reduced survival and growth rates for 𝘌𝘭𝘱𝘩𝘪𝘥𝘪𝘶𝘮 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏𝘢𝘺𝘯𝘦𝘴𝘪𝘯𝘢 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢. Test morphology (i.e. test surface and feeding ornamentation) of live 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪 and 𝘏. 𝘨𝘦𝘳𝘮𝘢𝘯𝘪𝘤𝘢 were severely affected after 6 weeks by OA, negatively influencing the uptake of 13C-labelled diatoms of 𝘕𝘢𝘷𝘪𝘤𝘶𝘭𝘢 𝘴𝘱., notably for 𝘌. 𝘸𝘪𝘭𝘭𝘪𝘢𝘮𝘴𝘰𝘯𝘪. Test dissolution rates were enhanced by OA and negatively affected foraminiferal morphology of recently dead assemblages with implications for net accumulation and preservation. These results imply that the long-term storage of inorganic carbon and cycling of carbon in coastal benthic ecosystems will be considerably altered by future OA.

Continue reading ‘Quantification of the effects of ocean acidification on benthic foraminifera’

Ocean acidification at a coastal CO2 vent induces expression of stress-related transcripts and transposable elements in the sea anemone Anemonia viridis

Ocean acidification threatens to disrupt interactions between organisms throughout marine ecosystems. The diversity of reef-building organisms decreases as seawater CO2 increases along natural gradients, yet soft-bodied animals, such as sea anemones, are often resilient. We sequenced the polyA-enriched transcriptome of adult sea anemone Anemonia viridis and its dinoflagellate symbiont sampled along a natural CO2 gradient in Italy to assess stress levels in these organisms. We found that about 3.1% of the anemone transcripts, but <1% of the Symbiodinium sp. transcripts were differentially expressed. Processes enriched at high seawater CO2 were linked to cellular stress and inflammation, including significant up-regulation of protective cellular functions and down-regulation of metabolic pathways. Transposable elements were differentially expressed at high seawater CO2, with an extreme up-regulation (> 100-fold) of the BEL-family of long terminal repeat retrotransposons. Seawater acidified by CO2 generated a significant stress reaction in A. viridis, but no bleaching was observed and Symbiodinium sp. appeared to be less affected. These observed changes indicate the mechanisms by which A. viridis acclimate to survive chronic exposure to ocean acidification conditions. We conclude that many organisms that are common in acidified conditions may nevertheless incur costs due to hypercapnia and/or lowered carbonate saturation states.

Continue reading ‘Ocean acidification at a coastal CO2 vent induces expression of stress-related transcripts and transposable elements in the sea anemone Anemonia viridis’

Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio‐calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non‐classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high‐resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio‐calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.

Continue reading ‘Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book