Posts Tagged 'growth'

Calcification moderates the increased susceptibility to UV radiation of the coccolithophorid Gephryocapsa oceanica grown under elevated CO2 concentration: evidence based on calcified and non‐calcified cells

The physiological performance of calcified and non‐calcified cells of Gephyrocapsa oceanica (NIES‐1318) and their short‐term responses to UV radiation were compared for cultures grown under present‐day (LC, 400 μatm) and high pCO2 (HC, 1000 μatm) conditions. Similar growth rates and Fv / Fm values were observed in both types of cell under LC conditions, indicating that the loss of calcification in the non‐calcified cell did not lead to a competitive disadvantage under such conditions. Detrimental effects of elevated pCO2 were observed in both cell types, with the growth rate of non‐calcified cells decreasing more markedly, which might reflect a negative impact of higher cytoplasmic H+. When exposed to short‐term UV radiation, similar trends in effective quantum yield were observed in both cell types acclimated to LC conditions. Elevated pCO2 and associated seawater chemical changes strongly reduced effective quantum yield in non‐calcified cells but no significant influence was observed in calcified cells. Based on these findings and comparisons with previous studies, we suggest that the negative impact of elevated cytoplasmic H+ would exacerbate the detrimental effects of UV radiation while the possession of calcification attenuated this influence.

Continue reading ‘Calcification moderates the increased susceptibility to UV radiation of the coccolithophorid Gephryocapsa oceanica grown under elevated CO2 concentration: evidence based on calcified and non‐calcified cells’

Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean


• In a future scenario, attenuation by DOM outcompetes its physico-chemical role.
• Global change conditions will favor growth and photosynthesis of nanoplankton.
• Global change favors growth and photosynthesis of nano- as compared to microplankton.


We evaluated the dual role of DOM (i.e., as a source of inorganic nutrients and as an absorber of solar radiation) on a phytoplankton community of the western South Atlantic Ocean. Using a combination of microcosms and a cluster approach, we simulated the future conditions of some variables that are highly influenced by global change in the region. We increased nutrients (i.e., anthropogenic input) and dissolved organic matter (DOM), and we decreased the pH, to assess their combined impact on growth rates (μ), species composition/abundance and size structure, and photosynthesis (considering in this later also the effects of light quality i.e., with and without ultraviolet radiation). We simulated two Future conditions (Fut) where nutrients and pH were similarly manipulated, but in one the physical role of DOM (Futout) was assessed whereas in the other (Futin) the physico-chemical role was evaluated; these conditions were compared with a control (Present condition, Pres). The μ significantly increased in both Fut conditions as compared to the Pres, probably due to the nutrient addition and acidification in the former. The highest μ were observed in the Futout, due to the growth of nanoplanktonic flagellates and diatoms. Cells in the Futin were photosynthetically less efficient as compared to those of the Futout and Pres, but these physiological differences, also between samples with or without solar UVR observed at the beginning of the experiment, decreased with time hinting for an acclimation process. The knowledge of the relative importance of both roles of DOM is especially important for coastal areas that are expected to receive higher inputs and will be more acidified in the future.

Continue reading ‘Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean’

An integrated response of Trichodesmium erythraeum IMS101 growth and photo-physiology to iron, CO2, and light intensity

We have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m−2 s−1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe′) concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe′ concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.

Continue reading ‘An integrated response of Trichodesmium erythraeum IMS101 growth and photo-physiology to iron, CO2, and light intensity’

Bivalves in the face of ocean acidification

Anthropogenic CO2 emissions are leading to a gradual decrease in ocean pH and changes in seawater carbonate chemistry, a process known as ocean acidification (OA). Such changes in oceanic environmental conditions will have negative consequences for marine life and organisms producing calcium carbonate (CaCO3) structures are amongst the most vulnerable due to the additional costs associated with calcification and maintenance of calcified structures under more acidic conditions. As calcifying animals of particular commercial and ecological relevance, bivalve molluscs have frequently been the object of OA research. In this thesis, responses to changes in seawater acidity in commercially important bivalve species were investigated with the aim of understanding their adaptation potential to OA. As the main focus was on blue mussels, the first part of the thesis provided an introduction to blue musselspecies complex in Europe which is characterized by the three species Mytilus edulis, M. galloprovincialis and M. trossulus. An analysis of potential consequences of interspecies hybridization for the aquaculture industry, especially in the context of changing environmental conditions, was provided. Possible positive and negative effects of hybridization were identified, the complexity of the blue mussel-species complex was highlighted and the implications of hybridization for adaptation were discussed. In the following section of the thesis, responses of Mytilus edulis larvae from a Swedish west coast population to elevated seawater acidity were investigated. By exposing larvae to a wide range of seawater acidity, the physiological tolerance threshold for normal shell development was identified and corresponded to pHT (pH on the total scale) ~ 7.8 which approximates the lower extremes of the local pH range naturally experienced by the larvae. This suggests that these mussels are well adapted to their local environment characterized by considerable fluctuations in seawater pH. Additionally, this result allowed selecting an appropriate pH level (pHT ~ 7.5, beyond the present range of natural variability), representing a realistic OA scenario for the investigated population and driving enough biological response to further investigate adaptation potential. This was achieved by measuring genetic variance and heritability of larval fitness-related traits (i.e. size and malformation of shell) through a crossbreeding experimental design and quantitative genetic techniques. Results showed high trait heritability under elevated seawater acidity, an indication of the potential of adapting to OA. Finally, in order to understand what functions and genes may be targeted by natural selection in the context of OA, genes involved in the initial phases of shell formation in Pacific oyster (Crassostrea gigas) larvae were identified. With a genome available, the Pacific oyster was an ideal candidate for this task. The identified genes were attributed to four categories (metabolic genes, transmembrane proteins, shell matrix proteins and protease inhibitors) and are candidates for genes under selection in the context of an acidifying ocean. Altogether the results of this thesis contribute to a better understanding of bivalve adaptation potential to global changes and provide critical information for future work (e.g. investigation of allelespecific associated tolerance to changes in environmental parameters).

Continue reading ‘Bivalves in the face of ocean acidification’

Will temperature and salinity changes exacerbate the effects of seawater acidification on the marine microalga Phaeodactylum tricornutum?


• Combined effects of pH, temperature and salinity were studied on a marine diatom.
• A novel CO2 injection system was used for performing microalgae toxicity test.
• Synergistic effects were found on cell viability, cell size and autofluorescence.
• Results are useful to address the potential impact of climate change.

To evaluate the effects related to the combination of potential future changes in pH, temperature and salinity on microalgae, a laboratory experiment was performed using the marine diatom Phaeodactylum tricornutum. Populations of this species were exposed during 48 h to a three-factor experimental design (3 × 2 × 2) with two artificial pH values (6, 7.4), two levels of temperature (23 °C, 28 °C), two levels of salinity (34 psu, 40 psu) and a control (pH 8, Temp 23 °C, Sal 34 psu). The effects on growth, cell viability, metabolic activity, and inherent cell properties (size, complexity and autofluorescence) of P. tricornutum were studied using flow cytometry. The results showed adverse effects on cultures exposed to pH 6 and high temperature and salinity, being the inherent cell properties the most sensitive response. Also, linked effects of these parameters resulted on cell viability and cell size decrease and an increase of cell autofluorescence. The conclusions obtained from this work are useful to address the potential effects of climate change (in terms of changes on pH, salinity and temperature) in microalgae.

Continue reading ‘Will temperature and salinity changes exacerbate the effects of seawater acidification on the marine microalga Phaeodactylum tricornutum?’

Predictable ecological response to rising CO2 of a community of marine phytoplankton

Rising atmospheric CO2 and ocean acidification are fundamentally altering conditions for life of all marine organisms, including phytoplankton. Differences in CO2 related physiology between major phytoplankton taxa lead to differences in their ability to take up and utilize CO2. These differences may cause predictable shifts in the composition of marine phytoplankton communities in response to rising atmospheric CO2. We report an experiment in which seven species of marine phytoplankton, belonging to four major taxonomic groups (cyanobacteria, chlorophytes, diatoms, and coccolithophores), were grown at both ambient (500 μatm) and future (1,000 μatm) CO2 levels. These phytoplankton were grown as individual species, as cultures of pairs of species and as a community assemblage of all seven species in two culture regimes (high‐nitrogen batch cultures and lower‐nitrogen semicontinuous cultures, although not under nitrogen limitation). All phytoplankton species tested in this study increased their growth rates under elevated CO2 independent of the culture regime. We also find that, despite species‐specific variation in growth response to high CO2, the identity of major taxonomic groups provides a good prediction of changes in population growth and competitive ability under high CO2. The CO2‐induced growth response is a good predictor of CO2‐induced changes in competition (R2 > .93) and community composition (R2 > .73). This study suggests that it may be possible to infer how marine phytoplankton communities respond to rising CO2 levels from the knowledge of the physiology of major taxonomic groups, but that these predictions may require further characterization of these traits across a diversity of growth conditions. These findings must be validated in the context of limitation by other nutrients. Also, in natural communities of phytoplankton, numerous other factors that may all respond to changes in CO2, including nitrogen fixation, grazing, and variation in the limiting resource will likely complicate this prediction.

Continue reading ‘Predictable ecological response to rising CO2 of a community of marine phytoplankton’

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In 6 of 7 experiments, exposure to elevated pCO2 levels (~ 1,700 µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions (p < 0.05) whereas rates were significantly higher in the presence of Ulva in all experiments (p < 0.05). In many cases, the co-exposure elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification only treatment (p < 0.05). Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates (p < 0.05). Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Continue reading ‘The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve’

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Ocean acidification in the IPCC AR5 WG II

OUP book