Posts Tagged 'phytoplankton'

Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions

Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.

Continue reading ‘Carbonate dissolution by reef microbial borers: a biogeological process producing alkalinity under different pCO2 conditions’

A potential role for epigenetic processes in the acclimation response to elevated pCO2 in the model diatom Phaeodactylum tricornutum

Understanding of the molecular responses underpinning diatom responses to ocean acidification is fundamental for predicting how important primary producers will be shaped by the continuous rise in atmospheric CO2. In this study, we have analyzed global transcriptomic changes of the model diatom Phaeodactylum tricornutum following growth for 15 generations in elevated pCO2 by strand-specific RNA sequencing (ssRNA-seq). Our results indicate that no significant effects of elevated pCO2 and associated carbonate chemistry changes on the physiological performance of the cells were observed after 15 generations whereas the expression of genes encoding histones and other genes involved in chromatin structure were significantly down-regulated, while the expression of transposable elements (TEs) and genes encoding histone acetylation enzymes were significantly up-regulated. Furthermore, we identified a series of long non-protein coding RNAs (lncRNAs) specifically responsive to elevated pCO2, suggesting putative regulatory roles for these largely uncharacterized genome components. Taken together, our integrative analyses reveal that epigenetic elements such as TEs, histone modifications and lncRNAs may have important roles in the acclimation of diatoms to elevated pCO2 over short time scales and thus may influence longer term adaptive processes in response to progressive ocean acidification.

Continue reading ‘A potential role for epigenetic processes in the acclimation response to elevated pCO2 in the model diatom Phaeodactylum tricornutum’

Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses

The composition of phytoplankton communities plays a major role in the efficiency of the biological carbon pump and energy transfer to higher trophic levels. Phytoplankton community composition can be significantly affected by changes in environmental conditions. We investigated the effect of increased pCO2 and light intensity on natural communities from two Southern Ocean water masses, the Subtropical Frontal Zone (STFZ) and Subantarctic Surface Waters (SASW). The community in both experiments shifted to predominately dinoflagellates under high pCO2 and high light and the community composition was significantly different between both treatments at the end of the incubation. In the STFZ assemblage, the combination of increased light and pCO2 had a small positive effect on diatom, coccolithophores and picoeukaryote abundance at the beginning of the experiment while higher pCO2 alone had no or a negative effect. In the SASW assemblage, the combination of increased light and pCO2 had a negative effect on diatom abundance while lower pH/higher pCO2 alone resulted in an increase in diatom counts compared to the control. Coccolithophores grew only in the control treatment. Our results show that there are taxon-specific and locality specific differences in natural phytoplankton community responses to increased light and pCO2 within low nutrient regions.

Continue reading ‘Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses’

Effects of higher CO2 and temperature on exopolymer particle content and physical properties of marine aggregates

We investigated how future ocean conditions, and specifically the interaction between temperature and CO2, might affect marine aggregate formation and physical properties. Initially, mesocosms filled with coastal seawater were subjected to three different treatments of CO2 concentration and temperature: (1) 750 ppm CO2, 16°C, (2) 750 ppm CO2, 20°C, and (3) 390 ppm CO2, 16°C. Diatom-dominated phytoplankton blooms were induced in the mesocosms by addition of nutrients. In aggregates produced in roller tanks using seawater taken from the mesocosms during different stages of the bloom, we measured sinking velocity, size, chlorophyll a, particulate organic carbon and nitrogen, and exopolymer particle content; excess density and mass were calculated from the sinking velocity and size of the aggregates. As has been seen in previous experiments, no discernable differences in overall nutrient uptake, chlorophyll-a concentration, or exopolymer particle concentrations could be related to the acidification treatment in the mesocosms. In addition, in the aggregates formed during the roller tank experiments (RTEs), we observed no statistically significant differences in chemical composition among the treatments during Pre-Bloom, Bloom, and Post-Bloom periods. However, physical characteristics were different and showed a synergistic effect of warmer temperature and higher CO2 during the Pre-Bloom period; at this time, temperature had a larger effect than CO2 on aggregate sinking velocity. In RTEs with warmer and acidified treatment (future conditions), aggregates were larger, heavier, and settled faster than aggregates formed at present-day or only acidified conditions. During the Post-Bloom, however, aggregates formed under present and future conditions had similar physical properties. In acidified tanks at ambient temperature, aggregates were slower, smaller and less dense than those formed at the same temperature but under present CO2 or under warmer and acidified conditions. Thus, the sinking velocity of aggregates formed in acidified tanks at ambient temperature was slower than the other two cases. Our findings point out the potential of ocean acidification and warming to modify physical properties of sinking aggregates but also emphasize the need of future experiments investigating multiple environmental stressors to clarify the importance of each factor.

Continue reading ‘Effects of higher CO2 and temperature on exopolymer particle content and physical properties of marine aggregates’

Phytoplankton responses to ocean climate change drivers: interaction of ocean warming, ocean acidification and UV exposure

Aquatic primary producers constitute only 1% of the global biomass, but their production equals that of all terrestrial ecosystems taken together (cf. Chapter 3, this volume). They take up a large fraction of anthropogenically emitted CO2, thereby mitigating climate change.

Continue reading ‘Phytoplankton responses to ocean climate change drivers: interaction of ocean warming, ocean acidification and UV exposure’

Climate change effects on copepod physiology and trophic transfer

Increased anthropogenic carbon dioxide (CO2) emissions have led to an increasingly acidified ocean and higher average global sea surface temperatures. This alteration of abiotic conditions is directly affecting aquatic organisms through physiological stress and indirectly through reductions in trophic transfer efficiency. Less efficient trophic transfer at the base of the food web would reduce the overall energy available to support higher trophic levels and could be detrimental to the dependent ecosystem. Estuarine ecosystems are subject to harmful algal blooms (HABs). They are also characterized by low species diversity, which lowers ecosystem resilience to environmental perturbations. This results in a system where changes in phytoplankton and their consumers can dramatically impact the health of the local community. Increased temperature and pCO2 are predicted to change nutritional adequacy and/or toxicity of some HAB species and their copepod consumers. Interactions between Karlodinium veneficum, a HAB species present in the Delaware Inland Bays, and its consumer Acartia tonsa, a locally-dominant copepod, were used to assess direct changes to physiology and/or indirect changes to trophic transfer. Acartia tonsa, toxic prey K. veneficum, and non-toxic prey Storeatula major were grown in multi-generational laboratory cultures at both ambient conditions (25 °C/400 ppm pCO2) and those predicted for year 2100 (29 °C/ 1000 ppm pCO2). Physiological changes were assessed using grazing, respirometry, egg production, and egg hatching success. Grazing experiments indicated there was not a direct toxic effect of the prey on A. tonsa. Respiration rates did not change significantly at higher temperature and pCO2 values, indicating physiological compensation. Egg production did not significantly differ between treatments, but a significant reduction in egg hatching success was found when A. tonsa were fed exclusively K. veneficum. Significant reduction of egg production and hatching also occurred as a result of higher temperature and pCO2. Significant reductions in efficiency of carbon transfer from prey to consumer offspring were found when A. tonsa ingested K. veneficum, and when A. tonsa ingested S. major at elevated temperature and pCO2. In summary, A. tonsa acclimated to the elevated pCO2 and temperature conditions, but changes in resource partitioning led to a lowered transfer of carbon to their offspring. Ingestion of K. veneficum also led to a lowered trophic transfer efficiency, irrespective of temperature and pCO2 level. This indicates that both HABs and increased temperature and pCO2 from climate change have the potential to alter ecosystem dynamics by reducing trophic transfer efficiency at the base of the food chain.

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The effect of pH on the acute toxicity of phenanthrene in a marine microalgae Chlorella salina

Phenanthrene is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) found in continental shelf environment of China and is on the EPA’s Priority Pollutant list. In this study, the effects of phenanthrene on marine algal growth rate were determined after 96-h exposure at pH 6.0, 7.0, 8.0, 9.0, and 10.0 in seawater of salinity 35. Two measuring techniques to assess growth inhibition were also compared using prompt fluorescence and microscopic cell count. The results showed that the toxicity of phenanthrene increased significantly (p < 0.05) with decreasing pH, with the nominal concentration required to inhibit growth rate by 50%, EC50, decreasing from 1.893 to 0.237 mg L−1 as pH decreased from 9.0 to 6.0, with a decrease higher than 55% from 10.0 to 9.0. In addition, the nominal EC50 values calculated in this study were at the same range of some environmental concentrations of phenanthrene close to areas of crude oil exploration. Based on the two measuring techniques, the results showed that cell count and fluorescence measurement were significantly different (p < 0.05), and the nominal EC50 values calculated with cell count measurement were significantly higher than fluorescence measurement at pH 8.0, 9.0 and 10.0. In conclusion, the present studies confirmed that acidification of seawater could affect the toxicity of phenanthrene to this species of microalgae, and which encouraged further studies involving responses of marine organisms to ocean acidification.

Continue reading ‘The effect of pH on the acute toxicity of phenanthrene in a marine microalgae Chlorella salina’


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