Posts Tagged 'mesocosms'

Do increasing CO2 concentration impacted on changing phytoplankton assemblages?

The effect of seawater pCO2 concentration of 280, 380, 550, 650, 750 and 1000 ppm on the changing of phytoplankton assemblage was determined through a mesocosm experiment at the Barrang Lompo Island. The experiment was run for 48 and 96 hours without nutrient enrichment. The aim of the study is to examine the effect of the increasing CO2 concentration on the changing phytoplankton assemblages. The result showed that Bacillariophyceae has been the most important algal group accounting for 74.5% for 48 hours of incubation period. Moreover, Diatomaceae was the most dominant algal group for 96 hours of the incubation period, accounting for 50.9%. There was no clear trend of Shannon diversity (H’) and the evenness values between CO2 concentration and incubation period. There was a clear grouping of species assemblages between the incubation periods. ANOSIM result showed that there is no significant difference in species assemblage among CO2 treatments. On the other hand, a significant difference in species assemblage between incubation periods between CO2 concentration treatments was observed. The three taxa that are most responsible for the dissimilarity were Rhizosolenia fragilissima (10.1%), Gyrosigma acuminatum (9.3%), and Biddulphia sinensis (9.2%).
Continue reading ‘Do increasing CO2 concentration impacted on changing phytoplankton assemblages?’

Rapid evolution of highly variable competitive abilities in a key phytoplankton species

Climate change challenges plankton communities, but evolutionary adaptation could mitigate the potential impacts. Here, we tested with the phytoplankton species Emiliania huxleyi whether adaptation to a stressor under laboratory conditions leads to equivalent fitness gains in a more natural environment. We found that fitness advantages that had evolved under laboratory conditions were masked by pleiotropic effects in natural plankton communities. Moreover, new genotypes with highly variable competitive abilities evolved on timescales significantly shorter than climate change.

Continue reading ‘Rapid evolution of highly variable competitive abilities in a key phytoplankton species’

Effects of ocean acidification and hydrodynamic conditions on carbon metabolism and dissolved organic carbon (DOC) fluxes in seagrass populations

Global change has been acknowledged as one of the main threats to the biosphere and its provision of ecosystem services, especially in marine ecosystems. Seagrasses play a critical ecological role in coastal ecosystems, but their responses to ocean acidification (OA) and climate change are not well understood. There have been previous studies focused on the effects of OA, but the outcome of interactions with co-factors predicted to alter during climate change still needs to be addressed. For example, the impact of higher CO2 and different hydrodynamic regimes on seagrass performance remains unknown. We studied the effects of OA under different current velocities on productivity of the seagrass Zostera noltei, using changes in dissolved oxygen as a proxy for the seagrass carbon metabolism, and release of dissolved organic carbon (DOC) in a four-week experiment using an open-water outdoor mesocosm. Under current pH conditions, increasing current velocity had a positive effect on productivity, but this depended on shoot density. However, this positive effect of current velocity disappeared under OA conditions. OA conditions led to a significant increase in gross production rate and respiration, suggesting that Z. noltei is carbon-limited under the current inorganic carbon concentration of seawater. In addition, an increase in non-structural carbohydrates was found, which may lead to better growing conditions and higher resilience in seagrasses subjected to environmental stress. Regarding DOC flux, a direct and positive relationship was found between current velocity and DOC release, both under current pH and OA conditions. We conclude that OA and high current velocity may lead to favourable growth scenarios for Z. noltei populations, increasing their productivity, non-structural carbohydrate concentrations and DOC release. Our results add new dimensions to predictions on how seagrass ecosystems will respond to climate change, with important implications for the resilience and conservation of these threatened ecosystems.

Continue reading ‘Effects of ocean acidification and hydrodynamic conditions on carbon metabolism and dissolved organic carbon (DOC) fluxes in seagrass populations’

Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi

We exposed a natural phytoplankton community to combined present (390 µatm, low carbon [LC]) and future CO2 levels predicted for the year 2100 (900 µatm, high carbon [HC]), and ambient (4.5 nM, -DFB [desferoxamine B]) and high (12 nM, +DFB) dissolved iron (dFe) levels, for 25 d in mesocosms. We report on the physiological response of the community dominated by the coccolithophore Emiliania huxleyi. The community structure shifted on Day 10, leading to 2 different phases (1 and 2), i.e. before and after Day 10, respectively. We focussed on the massive bloom of E. huxleyi that developed in Phase 2, in the LC+DFB treatment. In high dFe conditions, pigments and photosynthetic parameters increased compared to the control (LC-DFB). Cell death was only detected during the community shift (Days 10-12) and mostly increased in the presence of high CO2. The accumulation of reactive oxygen species (ROS) decreased under high dFe, pointing to an efficient, rather than a stressed, metabolism. DNA lesions, caused by excess irradiance, were minimised under high Fe. E. huxleyi is known for its low Fe requirements for growth. However, we demonstrate that Fe is essential to E. huxleyi for DNA repair and ROS management, and to maintain optimal functioning of the photosynthetic machinery, with implications for carbon cycling and future ecosystem functioning.

Continue reading ‘Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi’

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

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 2600 L 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 2900 µatm, 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 particulate primary production (PP) by 50 % and 160 %, respectively. During the declining phase of the bloom, warming accelerated the loss of diatom cells and negatively affected PP. Due to the countervailing responses of the plankton community to warming during the two phases of the experiment, the time-integrated primary production was not significantly affected over the full duration of the study. The diatom bloom was paralleled by a gradual decrease in the abundance of photosynthetic picoeukaryotes and followed by a bloom of picocyanobacteria. Increasing pCO2 and warming did not influence the abundance of picoeukaryotes, but warming stimulated picocyanobacteria proliferation. 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’

Effects of sub-seabed CO2 leakage: short- and medium-term responses of benthic macrofaunal assemblages

Highlights

• A significant impact on community structure, abundance and species richness was observed in the short-term exposure.
• Significant impact of on macrofaunal assemblages occur mainly over short time periods.
• Individual taxa showed idiosyncratic responses to acidification.
• This study gives a step forward into the cost-benefit analysis of CCS strategies.

Abstract

The continued rise in atmospheric carbon dioxide (CO2) levels is driving climate change and temperature shifts at a global scale. CO2 Capture and Storage (CCS) technologies have been suggested as a feasible option for reducing CO2 emissions and mitigating their effects. However, before CCS can be employed at an industrial scale, any environmental risks associated with this activity should be identified and quantified. Significant leakage of CO2 from CCS reservoirs and pipelines is considered to be unlikely, however direct and/or indirect effects of CO2 leakage on marine life and ecosystem functioning must be assessed, with particular consideration given to spatial (e.g. distance from the source) and temporal (e.g. duration) scales at which leakage impacts could occur. In the current mesocosm experiment we tested the potential effects of CO2 leakage on macrobenthic assemblages by exposing infaunal sediment communities to different levels of CO2 concentration (400, 1000, 2000, 10,000 and 20,000 ppm CO2), simulating a gradient of distance from a hypothetic leakage, over short-term (a few weeks) and medium-term (several months). A significant impact on community structure, abundance and species richness of macrofauna was observed in the short-term exposure. Individual taxa showed idiosyncratic responses to acidification. We conclude that the main impact of CO2 leakage on macrofaunal assemblages occurs almost exclusively at the higher CO2 concentration and over short time periods, tending to fade and disappear at increasing distance and exposure time. Although under the cautious perspective required by the possible context-dependency of the present findings, this study contributes to the cost-benefit analysis (environmental risk versus the achievement of the intended objectives) of CCS strategies.

Continue reading ‘Effects of sub-seabed CO2 leakage: short- and medium-term responses of benthic macrofaunal assemblages’

Interactive network configuration maintains bacterioplankton community structure under elevated CO2 in a eutrophic coastal mesocosm experiment (update)

There is increasing concern about the effects of ocean acidification on marine biogeochemical and ecological processes and the organisms that drive them, including marine bacteria. Here, we examine the effects of elevated CO2 on the bacterioplankton community during a mesocosm experiment using an artificial phytoplankton community in subtropical, eutrophic coastal waters of Xiamen, southern China. Through sequencing the bacterial 16S rRNA gene V3-V4 region, we found that the bacterioplankton community in this high-nutrient coastal environment was relatively resilient to changes in seawater carbonate chemistry. Based on comparative ecological network analysis, we found that elevated CO2 hardly altered the network structure of high-abundance bacterioplankton taxa but appeared to reassemble the community network of low abundance taxa. This led to relatively high resilience of the whole bacterioplankton community to the elevated CO2 level and associated chemical changes. We also observed that the Flavobacteria group, which plays an important role in the microbial carbon pump, showed higher relative abundance under the elevated CO2 condition during the early stage of the phytoplankton bloom in the mesocosms. Our results provide new insights into how elevated CO2 may influence bacterioplankton community structure.

Continue reading ‘Interactive network configuration maintains bacterioplankton community structure under elevated CO2 in a eutrophic coastal mesocosm experiment (update)’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book