Posts Tagged 'laboratory'

Ocean acidification increases the toxic effects of TiO2 nanoparticles on the marine microalga Chlorella vulgaris


  • Ocean acidification enhanced growth inhibition of algal cells caused by TiO2 NPs.
  • Ocean acidification increased oxidative damage of TiO2 NPs on Chlorella vulgaris.
  • Elevated internalization of NPs contributed to enhanced toxicity of TiO2 NPs.
  • Slighter aggregation and more suspended NPs in acidified seawater were detected.


Concerns about the environmental effects of engineered nanoparticles (NPs) on marine ecosystems are increasing. Meanwhile, ocean acidification (OA) has become a global environmental problem. However, the combined effects of NPs and OA on marine organisms are still not well understood. In this study, we investigated the effects of OA (pH values of 7.77 and 7.47) on the bioavailability and toxicity of TiO2 NPs to the marine microalga Chlorella vulgaris. The results showed that OA enhanced the growth inhibition of algal cells caused by TiO2 NPs. We observed synergistic interactive effects of pH and TiO2 NPs on oxidative stress, indicating that OA significantly increased the oxidative damage of TiO2 NPs on the algal cells. Importantly, the elevated toxicity of TiO2 NPs associated with OA could be explained by the enhanced internalization of NPs in algal cells, which was attributed to the slighter aggregation and more suspended particles in acidified seawater. Overall, these findings provide useful information on marine environmental risk assessments of NPs under near future OA conditions.

Continue reading ‘Ocean acidification increases the toxic effects of TiO2 nanoparticles on the marine microalga Chlorella vulgaris’

Biological responses of the marine diatom Chaetoceros socialis to changing environmental conditions: a laboratory experiment

Diatoms constitute a major group of phytoplankton, accounting for ~20% of the world’s primary production. It has been shown that iron (Fe) can be the limiting factor for phytoplankton growth, in particular, in the HNLC (High Nutrient Low Chlorophyll) regions. Iron plays thus an essential role in governing the marine primary productivity and the efficiency of biological carbon pump. Oceanic systems are undergoing continuous modifications at varying rates and magnitudes as a result of changing climate. The objective of our research is to evaluate how changing environmental conditions (dust deposition, ocean warming and acidification) can affect marine Fe biogeochemistry and diatom growth. Laboratory culture experiments using a marine diatom Chaetoceros socialis were conducted at two temperatures (13°C and 18°C) and under two pCO2 (carbon dioxide partial pressure) (400 μatm and 800 μatm) conditions. The present study clearly highlights the effect of ocean acidification on enhancing the release of Fe upon dust deposition. Our results also confirm that being a potential source of Fe, dust provides in addition a readily utilizable source of macronutrients such as dissolved phosphate (PO4) and silicate (DSi). However, elevated atmospheric CO2 concentrations may also have an adverse impact on diatom growth, causing a decrease in cell size and possible further changes in phytoplankton composition. Meanwhile, ocean warming may lead to the reduction of diatom production and cell size, inducing poleward shifts in the biogeographic distribution of diatoms. The changing climate has thus a significant implication for ocean phytoplankton growth, cell size and primary productivity, phytoplankton distribution and community composition, and carbon (C), nitrogen (N), phosphorus (P), silicon (Si) and Fe biogeochemical cycles in various ways.

Continue reading ‘Biological responses of the marine diatom Chaetoceros socialis to changing environmental conditions: a laboratory experiment’

Effects of CO2-driven acidification of seawater on the calcification process in the calcareous hydrozoan Millepora alcicornis (Linnaeus, 1758)

Ocean acidification is expected to intensify due to increasing levels in the partial pressure of atmospheric CO2 (pCO2). This could negatively affect major calcifying reef organisms. In this study, the effects of different levels of CO2-driven acidification of seawater (control: pH 8.1; moderate: pH 7.8; intermediate: pH 7.5; and severe: pH 7.2) on the net calcification rate and activity of enzymes related to the calcification process (Ca-ATPase and carbonic anhydrase) were evaluated in the calcareous hydrozoan Millepora alcicornis. The experiment was run for 30 d using a marine mesocosm system. Net calcification ratio was significantly reduced in hydrocorals exposed to intermediate seawater acidification for 16 d and to severe seawater acidification for 16 d or 30 d, compared to animals at control conditions. However, only hydrocorals exposed to severe seawater acidification showed lower net calcification rates than those exposed to control conditions for 30 d. In accordance, the activities of enzymes involved in the calcification process markedly increased in hydrocorals exposed to reduced pH. Ca-ATPase seemed to be more sensitive to seawater acidification than carbonic anhydrase as it increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d, while carbonic anhydrase activity was only stimulated under severe seawater acidification. Therefore, our findings clearly show that the hydrocoral M. alcicornis is able to cope, to some extent, with long-term CO2-driven acidification of seawater (pH ≥ 7.5). In addition, they show that Ca-ATPase plays a key role in the maintenance of calcification rate under scenarios of moderate and intermediate levels of seawater acidification. However, the observed increase in Ca-ATPase and carbonic anhydrase activity was not enough to compensate for the effects of CO2-driven reduction in seawater pH on the net calcification rate of the hydrocoral M. alcicornis under a scenario of severe ocean acidification (pH 7.2).

Continue reading ‘Effects of CO2-driven acidification of seawater on the calcification process in the calcareous hydrozoan Millepora alcicornis (Linnaeus, 1758)’

Coral calcification mechanisms facilitate adaptive responses to ocean acidification

Ocean acidification (OA) is a pressing threat to reef-building corals, but it remains poorly understood how coral calcification is inhibited by OA and whether corals could acclimatize and/or adapt to OA. Using a novel geochemical approach, we reconstructed the carbonate chemistry of the calcifying fluid in two coral species using both a pH and dissolved inorganic carbon (DIC) proxy (δ11B and B/Ca, respectively). To address the potential for adaptive responses, both species were collected from two sites spanning a natural gradient in seawater pH and temperature, and then subjected to three pHT levels (8.04, 7.88, 7.71) crossed by two temperatures (control, +1.5°C) for 14 weeks. Corals from the site with naturally lower seawater pH calcified faster and maintained growth better under simulated OA than corals from the higher-pH site. This ability was consistently linked to higher pH yet lower DIC values in the calcifying fluid, suggesting that these differences are the result of long-term acclimatization and/or local adaptation to naturally lower seawater pH. Nevertheless, all corals elevated both pH and DIC significantly over seawater values, even under OA. This implies that high pH upregulation combined with moderate levels of DIC upregulation promote resistance and adaptive responses of coral calcification to OA.

Continue reading ‘Coral calcification mechanisms facilitate adaptive responses to ocean acidification’

Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel

The combined effects of elevated pCO2 and temperature were investigated during an autumn phytoplankton bloom in the Western English Channel (WEC). A full factorial 36-day microcosm experiment was conducted under year 2100 predicted temperature (+4.5 °C) and pCO2 levels (800 μatm). The starting phytoplankton community biomass was 110.2 (±5.7 sd) mg carbon (C) m−3 and was dominated by dinoflagellates (~ 50 %) with smaller contributions from nanophytoplankton (~ 13 %), cryptophytes (~ 11 %)and diatoms (~ 9 %). Over the experimental period total biomass was significantly increased by elevated pCO2 (20-fold increase) and elevated temperature (15-fold increase). In contrast, the combined influence of these two factors had little effect on biomass relative to the ambient control. The phytoplankton community structure shifted from dinoflagellates to nanophytoplankton at the end of the experiment in all treatments. Under elevated pCO2 nanophytoplankton contributed 90% of community biomass and was dominated by Phaeocystis spp., while under elevated temperature nanophytoplankton contributed 85 % of the community biomass and was dominated by smaller nano-flagellates. Under ambient conditions larger nano-flagellates dominated while the smallest nanophytoplankton contribution was observed under combined elevated pCO2 and temperature (~ 40 %). Dinoflagellate biomass declined significantly under the individual influences of elevated pCO2, temperature and ambient conditions. Under the combined effects of elevated pCO2 and temperature, dinoflagellate biomass almost doubled from the starting biomass and there was a 30-fold increase in the harmful algal bloom (HAB) species, Prorocentrum cordatum. Chlorophyll a normalised maximum photosynthetic rates (PBm) increased > 6-fold under elevated pCO2 and > 3-fold under elevated temperature while no effect on PBm was observed when pCO2 and temperature were elevated simultaneously. The results suggest that future increases in temperature and pCO2 do not appear to influence coastal phytoplankton productivity during autumn in the WEC which would have a negative feedback on atmospheric CO2.

Continue reading ‘Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel’

Nutrient co-limited Trichodesmium as nitrogen source or sink in a future ocean

Nitrogen-fixing (N2) cyanobacteria provide bioavailable nitrogen to vast ocean regions but are in turn limited by iron (Fe) and/or phosphorus (P), which may force them to employ alternative nitrogen acquisition strategies. The adaptive responses of nitrogen-fixers to global-change drivers under nutrient-limited conditions could profoundly alter the current ocean nitrogen and carbon cycles. Here, we show that the globally-important N2-fixer Trichodesmium fundamentally shifts nitrogen metabolism towards organic-nitrogen scavenging following long-term high-CO2 adaptation under iron and/or phosphorus (co)-limitation. Global shifts in transcripts and proteins under high CO2/Fe-limited and/or P-limited conditions include decreases in the N2-fixing nitrogenase enzyme, coupled with major increases in enzymes that oxidize trimethylamine (TMA). TMA is an abundant, biogeochemically-important organic nitrogen compound that supports rapid Trichodesmium growth while inhibiting N2 fixation. In a future high-CO2 ocean, this whole-cell energetic reallocation towards organic nitrogen scavenging and away from N2-fixation may reduce new-nitrogen inputs by Trichodesmium, while simultaneously depleting the scarce fixed-nitrogen supplies of nitrogen-limited open ocean ecosystems.

Continue reading ‘Nutrient co-limited Trichodesmium as nitrogen source or sink in a future ocean’

Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii


  • Global warming increases the photoinactivation rate.
  • Ocean acidification alleviates the effect of global warming on photoinactivation.
  • Global warming does not affect PsbA removal but ocean acidification enhances it.
  • Ocean acidification induces high nonphotochemical quenching.
  • Global warming increases antioxidant systems, but ocean acidification does not


Diatoms, as important contributors to aquatic primary production, are critical to the global carbon cycle. They tend to dominate phytoplankton communities experiencing rapid changes of underwater light. However, little is known regarding how climate change impacts diatoms’ capacity in coping with variable light environments. Here we grew a globally abundant diatom T. weissflogii, under two levels of temperature (18, 24 °C) and pCO2 (400, 1000 μatm), and then treated it with a light challenge to understand the combined effects of ocean warming and acidification on its exploitation of variable light environments. The higher temperature increased the photoinactivation rate at 400 μatm pCO2 and the higher pCO2 alleviated the negative effect of the higher temperature on PSII photoinactivation. Temperature did not affect the PsbA removal rate, but higher pCO2 stimulated PsbA removal. Photoinactivation outran repair, leading to decreased maximum photochemical yield in PSII. The higher pCO2 induced high sustained phase of nonphotochemical quenching when cells were less photoinhibited. The high light exposure induced the activity of both superoxide dismutase (SOD) and catalase (CAT) and the higher temperature stimulated them further, with insignificant effect of pCO2. Our findings suggest that ocean warming, ocean acidification and high light exposure would interact on PSII function and protection, and combination of these three environmental factors would lead to a reduced PSII activity in T. weissflogii. This study provides helpful insight into how climate change variables combined with local stressor impact diatoms’ photosynthetic physiology.

Continue reading ‘Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii’

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Ocean acidification in the IPCC AR5 WG II

OUP book