Posts Tagged 'growth'

The requirement for calcification differs between ecologically important coccolithophore species

Summary

  • Coccolithophores are globally distributed unicellular marine algae that are characterized by their covering of calcite coccoliths. Calcification by coccolithophores contributes significantly to global biogeochemical cycles. However, the physiological requirement for calcification remains poorly understood as non‐calcifying strains of some commonly used model species, such as Emiliania huxleyi, grow normally in laboratory culture.
  • To determine whether the requirement for calcification differs between coccolithophore species, we utilized multiple independent methodologies to disrupt calcification in two important species of coccolithophore: E. huxleyi and Coccolithus braarudii. We investigated their physiological response and used time‐lapse imaging to visualize the processes of calcification and cell division in individual cells.
  • Disruption of calcification resulted in major growth defects in C. braarudii, but not in E. huxleyi. We found no evidence that calcification supports photosynthesis in C. braarudii, but showed that an inability to maintain an intact coccosphere results in cell cycle arrest.
  • We found that C. braarudii is very different from E. huxleyi as it exhibits an obligate requirement for calcification. The identification of a growth defect in C. braarudii resulting from disruption of the coccosphere may be important in considering their response to future changes in ocean carbonate chemistry.

 

Continue reading ‘The requirement for calcification differs between ecologically important coccolithophore species’

You better repeat it: complex CO2 × temperature effects in Atlantic Silverside offspring revealed by serial experimentation

Concurrent ocean warming and acidification demand experimental approaches that assess biological sensitivities to combined effects of these potential stressors. Here, we summarize five CO2 × temperature experiments on wild Atlantic silverside, Menidia menidia, offspring that were reared under factorial combinations of CO2 (nominal: 400, 2200, 4000, and 6000 µatm) and temperature (17, 20, 24, and 28 °C) to quantify the temperature-dependence of CO2 effects in early life growth and survival. Across experiments and temperature treatments, we found few significant CO2 effects on response traits. Survival effects were limited to a single experiment, where elevated CO2 exposure reduced embryo survival at 17 and 24 °C. Hatch length displayed CO2 × temperature interactions due largely to reduced hatch size at 24 °C in one experiment but increased length at 28 °C in another. We found no overall influence of CO2 on larval growth or survival to 9, 10, 15 and 13–22 days post-hatch, at 28, 24, 20, and 17 °C, respectively. Importantly, exposure to cooler (17 °C) and warmer (28 °C) than optimal rearing temperatures (24 °C) in this species did not appear to increase CO2 sensitivity. Repeated experimentation documented substantial inter- and intra-experiment variability, highlighting the need for experimental replication to more robustly constrain inherently variable responses. Taken together, these results demonstrate that the early life stages of this ecologically important forage fish appear largely tolerate to even extreme levels of CO2 across a broad thermal regime.

Continue reading ‘You better repeat it: complex CO2 × temperature effects in Atlantic Silverside offspring revealed by serial experimentation’

Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900µatm, at two temperatures (in situ and +5°C; 10°C and 15°C) was monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5°C resulted in a significant increase of the average bacterial production (BP) in all 15°C mesocosms as compared to 10°C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt=particulate+dissolved DMSP) concentrations tracked the development of the bloom although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (<1nmolL−1) increased to reach peak values ranging from 30 to 130nmolL−1 towards the end of the experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66% and 69% at 10°C and 15°C, respectively, over the duration of the experiment. On the other hand, a 5°C warming increased DMS concentrations by an average of 240% as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant positive correlations found between bacterial production rates and concentrations of DMS throughout our experiment point towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver for the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean.

Continue reading ‘Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment’

Experimental assessment of the sensitivity of an estuarine phytoplankton fall bloom to acidification and warming (update)

We investigated the combined effect of ocean acidification and warming on the dynamics of the phytoplankton fall bloom in the Lower St. Lawrence Estuary (LSLE), Canada. Twelve 2600L mesocosms were set to initially cover a wide range of pHT (pH on the total proton scale) from 8.0 to 7.2 corresponding to a range of pCO2 from 440 to 2900µatm, and two temperatures (in situ and +5°C). The 13-day experiment captured the development and decline of a nanophytoplankton bloom dominated by the chain-forming diatom Skeletonema costatum. During the development phase of the bloom, increasing pCO2 influenced neither the magnitude nor the net growth rate of the nanophytoplankton bloom, whereas increasing the temperature by 5°C stimulated the chlorophyll a (Chl a) growth rate and maximal particulate primary production (PP) by 76% and 63%, respectively. During the declining phase of the bloom, warming accelerated the loss of diatom cells, paralleled by a gradual decrease in the abundance of photosynthetic picoeukaryotes and a bloom of picocyanobacteria. Increasing pCO2 and warming did not influence the abundance of picoeukaryotes, while picocyanobacteria abundance was reduced by the increase in pCO2 when combined with warming in the latter phase of the experiment. Over the full duration of the experiment, the time-integrated net primary production was not significantly affected by the pCO2 treatments or warming. Overall, our results suggest that warming, rather than acidification, is more likely to alter phytoplankton autumnal bloom development in the LSLE in the decades to come. Future studies examining a broader gradient of temperatures should be conducted over a larger seasonal window in order to better constrain the potential effect of warming on the development of blooms in the LSLE and its impact on the fate of primary production.

Continue reading ‘Experimental assessment of the sensitivity of an estuarine phytoplankton fall bloom to acidification and warming (update)’

Potential ecotoxicological effects of elevated bicarbonate ion concentrations on marine organisms

Highlights

• Ecotoxicological effects of elevated DIC were evaluated using 10 marine organisms.
• Species-specific toxicity of elevated DIC were found with EC50 of 11–85 mM.
• Mortality for copepod T. japonicus was the most sensitive endpoint for DIC toxicity.
• Tentative criteria of DIC for protecting 80% of marine organisms is 11 mM.

Abstract

Recently, a novel method for carbon capture and storage has been proposed, which converts gaseous CO2 into aqueous bicarbonate ions (HCO3-), allowing it to be deposited into the ocean. This alkalinization method could be used to dispose large amounts of CO2 without acidifying seawater pH, but there is no information on the potential adverse effects of consequently elevated HCO3- concentrations on marine organisms. In this study, we evaluated the ecotoxicological effects of elevated concentrations of dissolved inorganic carbon (DIC) (max 193 mM) on 10 marine organisms. We found species-specific ecotoxicological effects of elevated DIC on marine organisms, with EC50-DIC (causing 50% inhibition) of 11-85 mM. The tentative criteria for protecting 80% of individuals of marine organisms are suggested to be pH 7.8 and 11 mM DIC, based on acidification data previously documented and alkalinization data newly obtained from this study. Overall, the results of this study are useful for providing baseline information on ecotoxicological effects of elevated DIC on marine organisms. More complementary studies are needed on the alkalinization method to determine DIC effects on seawater chemistry and marine organisms.

Continue reading ‘Potential ecotoxicological effects of elevated bicarbonate ion concentrations on marine organisms’

Calcification of an estuarine coccolithophore increases with ocean acidification when subjected to diurnally fluctuating carbonate chemistry

Ocean acidification has the capacity to impact future coccolithophore growth, photosynthesis, and calcification, but experimental culture work with coccolithophores has produced seemingly contradictory results and has focused on open-ocean species. We investigated the influence of pCO2 (between 250 and 750 µatm) on the growth, photosynthetic, and calcification rates of the estuarine coccolithophore Pleurochrysis carterae using a CO2 manipulation system that allowed for natural carbonate chemistry variability, representing the highly variable carbonate chemistry of coastal and estuarine waters. We further considered the influence of pCO2 on dark calcification. Increased pCO2 conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO2 concentrations of 750 µatm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO2 conditions in both light and dark incubations. This trend of increased calcification at higher pCO2 conditions fits into a recently developed substrate-inhibitor concept, which demonstrates a calcification optima concept that broadly fits the experimental results of many studies on the impact of increased pCO2 on coccolithophore calcification.

Continue reading ‘Calcification of an estuarine coccolithophore increases with ocean acidification when subjected to diurnally fluctuating carbonate chemistry’

Environmental and nutrient controls of marine nitrogen fixation

Highlights

• Fe, P and dust additions could stimulate N2 fixation of Trichodesmium.
• Novel nutrient acquisition strategies have been discovered for Trichodesmium.
• Fe could be the ultimate limiting factor for N2 fixation.
• Ocean acidification may be beneficial for N2 fixation of Trichodesmium.
• Ocean warming may not play an important role in N2 fixation of Trichodesmium.

Abstract

Biological dinitrogen (N2) fixation by diazotrophic cyanobacteria has great biogeochemical implications in nitrogen (N) cycling in the ocean as this process represents the major source of new N input to the oceans, thereby controlling the marine primary productivity. Numerous factors can affect the extent of N2 fixation. A better understanding of the major environmental and nutrient factors governing this process is highly required. Iron (Fe) and/or phosphorus (P) are thought to be limiting factors in most oceanic regions. Special attention has been given in the present study to evaluate the effects of mineral dust deposition which is believed to stimulate N2 fixation as it increases the availability of both Fe and P. Through three laboratory bioassays (+Fe, +P, +Dust) via incubation experiments performed on Trichodesmium IMS101, we found that each addition of Fe, P or desert dust could stimulate the growth and N2 fixation of Trichodesmium IMS101. Several adaptive nutrient utilization strategies were observed, such as a Fe luxury uptake mechanism, a P-sparing effect and colony formation. In addition, during a field study using natural phytoplankton assemblages from the temperate Northeast Atlantic Ocean the critical role of dissolved Fe (DFe) was again highlighted by the remarkably enhanced N2 fixation rate observed after the addition of DFe under low temperature and P-depleted conditions. At the time of our study no Trichodesmium filaments were found in the studied region, the diazotrophic community was dominated by unicellular cyanobacteria symbiont (prymnesiophyte-UCYN-A1) and heterotrophic diazotrophs, therefore demonstrating that DFe could as well be the ultimate factor limiting N2 fixation of these smaller diazotrophs. Recently, the effects of ongoing climate change (ocean warming and acidification) on N2 fixation drew much attention, but various studies led to controversial conclusions. Semi-continuous dilution growth experiments were conducted on Trichodesmium IMS101 under present-day and future high pCO2 (400 and 800 µatm, respectively) and warming seawater (24 and 28 °C) conditions. The results indicate that higher pCO2 and therefore ocean acidification may be beneficial for Trichodesmium growth and N2 fixation. However, our observations suggest that Fe or P limitation in oligotrophic seawaters may offset the stimulation induced on Trichodesmium IMS101 resulting from ocean acidification. In contrast, ocean warming may not play an important role in Trichodesmium growth and N2 fixation with a 4 °C increase from 24 °C to 28 °C. Nevertheless, ocean warming is predicted to cause a shift in the geographical distribution of Trichodesmium species toward higher latitudes, extending its niche to subtropical ocean regions and potentially reducing its coverage in tropical ocean basins.

Continue reading ‘Environmental and nutrient controls of marine nitrogen fixation’


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