Posts Tagged 'abundance'

Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO2, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO2 levels (ambient CO2, 400 ppm; elevated CO2, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L−1; medium, 2.0 g FW L−1; high, 4.0 g FW L−1]. Under ambient CO2, the relative growth rate (RGR) was 5.87% d−1, 2.32% d−1 and 1.51% d−1 in low, medium and high densities, and elevated CO2 reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (FV/FM) was higher in low than in high densities, so were the light‐utilized efficiency (α ), saturation irradiance (EK) and maximum relative electron transfer rate (rETRmax). Elevated CO2 enhanced the FV/FM in low density but not in higher densities, as well as the α, EK and rETRmax. In addition, elevated CO2 reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO2‐induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO2‐induced reduction on growth and promotion on photosynthesis indicates that rising CO2 may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.

Continue reading ‘Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China’

Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana: an evaluation of the effects of pH on culture performance in tubular photobioreactors

A priority of the industrial applications of microalgae is the reduction of production costs while maximizing algae biomass productivity. The purpose of this study was to carry out a comprehensive evaluation of the effects of pH control on the production of Nannochloropsis gaditana in tubular photobioreactors under external conditions while considering the environmental, biological, and operational parameters of the process. Experiments were carried out in 3.0 m3 tubular photobioreactors under outdoor conditions. The pH values evaluated were 6.0, 7.0, 8.0, 9.0, and 10.0, which were controlled by injecting pure CO2 on-demand. The results have shown that the ideal pH for microalgal growth was 8.0, with higher values of biomass productivity (Pb) (0.16 g L−1 d−1), and CO2 use efficiency (ECO2) (74.6% w w−1); RCO2/biomass value obtained at this pH (2.42 gCO2 gbiomass−1) was close to the theoretical value, indicating an adequate CO2 supply. At this pH, the system was more stable and required a lower number of CO2 injections than the other treatments. At pH 6.0, there was a decrease in the Pb and ECO2; cultures at pH 10.0 exhibited a lower Pb and photosynthetic efficiency as well. These results imply that controlling the pH at an optimum value allows higher CO2 conversions in biomass to be achieved and contributes to the reduction in costs of the microalgae production process.

Continue reading ‘Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana: an evaluation of the effects of pH on culture performance in tubular photobioreactors’

The ability of fragmented kelp forests to mitigate ocean acidification and the effects of seasonal upwelling on kelp-purple sea urchin interactions

Bull kelp (Nereocystis leutkeana) forests along the coast for northern California have decreased dramatically as a result of a ‘perfect storm’ of multiple environmental stressors. The disappearance of a predatory sea star and subsequent increase in purple sea urchins (Strongylocentrotus purpuratus) and the recurrence of marine heat waves have caused these once diverse ecosystems to be rapidly converted into relative species-depauperate urchin barrens. By examining the interactive effects of both a rapidly changing abiotic environment and the increase in urchin grazing pressure that is affecting this vital ecosystem, we can better understand its ultimate fate and make better-informed decisions to manage and protect it. As once large and persistent kelp forests are converted into fragmented landscapes of small kelp patches, kelp’s ability to take up dissolved inorganic carbon and reduce nearby acidity and increase both dissolved oxygen and bio-available calcium carbonate may be reduced, preventing it from serving as an environmental stress-free ‘oasis’ of reduced environmental stresses for local marine organisms and affecting ecosystem dynamics. In my first chapter, I examined whether small, fragmented kelp patches are able to retain their ability to alter local seawater chemistry to the same extent a large persistent kelp forests that have been studied previously. I found that in the canopies of small kelp patches, multiple parameters of carbonate chemistry fluctuated more than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pCO2 during the day to a similar degree as large, intact kelp forests. These results suggest that small kelp patches could mitigate OA stress during the day and serve as spatial and temporal refugia for canopy-dwelling organisms. I also found that the benthic environment in kelp forests and adjacent urchin barrens is subject to unbuffered decreases in temperature, dissolved oxygen and pH. Thus, in chapter two, I assessed how current-day and future-predicted fluctuations in the duration and magnitude of these upwelling-associated stressors would impact the grazing, growth, and survivorship of purple urchins from kelp forest and urchin barren habitats. With upwelling predicted to increase in both intensity and duration with global climate change, understanding whether urchins from different habitats are differentially affected by upwelling-related stressors will give insight into how current and future stressors may be able to help ‘tip the scales’ and convert the increasing number of urchin barrens back into healthy productive kelp forests. I found condition-dependent susceptibility in urchins to increased magnitude and duration upwelling-related stressors. Grazing and gonadal development in kelp forest urchins was most negatively affected by distant future upwelling conditions, whereas in urchin barren urchins, grazing and survival were sensitive to exposure to upwelling in general, and also to increase in magnitudes of acidity, hypoxia, and temperature across both upwelling and non-upwelling events in the future. These results have important implications for population dynamics of urchins and their interactions with bull kelp, which could strongly affect ecosystem dynamics and transitions between kelp forests and urchin barrens. Taken together, the two chapters my thesis provide valuable insight into the potential resilience of bull kelp, a critical foundation species in northeastern Pacific coastal habitats, in the face of a rapidly changing multi-stressor environment.

Continue reading ‘The ability of fragmented kelp forests to mitigate ocean acidification and the effects of seasonal upwelling on kelp-purple sea urchin interactions’

Effects of ocean acidification on Antarctic microbial communities

Antarctic waters are amongst the most vulnerable in the world to ocean acidification due to their cold temperatures, naturally low levels of calcium carbonate and upwelling that brings deep CO2-rich waters to the surface. A meta-analysis demonstrated groups of Antarctic marine biota in waters south of 60!S have a range of tolerances to ocean acidification. Invertebrates and phytoplankton showed negative effects above 500 μatm and 1000 μatm CO2 respectively, while bacteria appear tolerant to elevated CO2. Phytoplankton studied as part of a natural microbial community were found to be more
sensitive than those studied as a single species in culture. This highlights the importance of community and ecosystem level studies, which incorporate the interaction and competition among species and trophic levels, to accurately assess the effects of ocean acidification on the Antarctic ecosystem.

Antarctic marine microbes (comprising phytoplankton, protozoa and bacteria) drive ocean productivity, nutrient cycling and mediate trophodynamics and the biological pump. While they appear vulnerable to changes in ocean chemistry, little is known about the nature and magnitude of their responses to ocean acidification, especially for natural communities. To address this lack of information, a six level, dose-response ocean acidification experiment was conducted in Prydz Bay, East Antarctica, using 650 L incubation tanks (minicosms). The minicosms were filled with Antarctic nearshore water and adjusted to a gradient of carbon dioxide (CO2) from 343 to 1641 μatm. Microscopy
and phylogenetic marker gene sequence analysis found the microbial community
composition altered at CO2 levels above approximately 1000 μatm. The CO2-
induced responses of microeukaryotes (>20 μm) and nanoeukaryotes (2 to 20 μm) were taxon-specific. For diatoms the response of taxa was related to cell size with micro-sized diatoms (>20 μm) increasing in abundance with moderate CO2 (506 to 634 μatm), while above this level their abundance declined. In contrast, nano-size diatoms (<20 μm) tolerated elevated CO2. Like large diatoms, Phaeocystis antarctica increased in abundance between 343 to 634 μatm CO2 but fell at higher levels. 18S and 16S rDNA sequencing showed that picoeukaryotic and prokaryotic composition was unaffected by CO2, despite having higher abundances at CO2 levels !634 μatm. This was likely due to the lower abundance of heterotrophic nanoflagellates at CO2 levels exceeding 953 μatm, which reduced the top-down control of their pico- and nanoplanktonic prey. As a result of the differences in the tolerance of individual taxa/size categories, CO2 caused a
significant change in the microbial community structure to one dominated by nano-sized diatoms, picoeukaryotes and prokaryotes.

Based on the CO2-induced changes in the microbial community, modelling was performed to investigate the future effects of different levels of elevated CO2 on the structure and function of microbial communities in Antarctic coastal systems. These models indicate CO2 levels predicted toward the end of the century under a “business as usual scenario” elicit changes in microbial composition, significantly altering trophodynamic pathways, reducing energy transfer to higher trophic levels and favouring respiration of carbon within the microbial loop. Such responses would alter elemental cycles, jeopardise the productivity that underpins the wealth and diversity of life for which Antarctica is renowned. In addition, it would reduce carbon sequestration in coastal Antarctic waters thereby having a positive feedback on global climate change.

Continue reading ‘Effects of ocean acidification on Antarctic microbial communities’

Abalone populations are most sensitive to environmental stress effects on adult individuals

Marine organisms are exposed to stressors associated with climate change throughout their life cycle, but a majority of studies focus on responses in single life stages, typically early ones. Here, we examined how negative impacts from stressors associated with climate change, ocean acidification, and pollution can act across multiple life stages to influence long-term population dynamics and decrease resilience to mass mortality events. We used a continuous-size-structured density-dependent model for abalone (Haliotis spp.), calcifying mollusks that support valuable fisheries, to explore the sensitivity of stock abundance and annual catch to potential changes in growth, survival, and fecundity across the organism’s lifespan. Our model predicts that decreased recruitment from lowered fertilization success or larval survival has small negative impacts on the population, and that stock size and fishery performance are much more sensitive to changes in parameters that affect the size or survival of adults. Sensitivity to impacts on subadults and juveniles is also important for the population, though less so than for adults. Importantly, likelihood of recovery following mortality events showed more pronounced sensitivity to most possible parameter impacts, greater than the effects on equilibrium density or catch. Our results suggest that future experiments on environmental stressors should focus on multiple life stages to capture effects on population structure and dynamics, particularly for species with size-dependent fecundity.

Continue reading ‘Abalone populations are most sensitive to environmental stress effects on adult individuals’

Response of phytoplankton assemblages from naturally acidic coastal ecosystems to elevated pCO2

The interplay of coastal oceanographic processes usually results in partial pressures of CO2 (pCO2) higher than expected from the equilibrium with the atmosphere and even higher than those expected by the end of the century. Although this is a well-known situation, the natural variability of seawater chemistry at the locations from which tested organisms or communities originate is seldom considered in ocean acidification experiments. In this work, we aimed to evaluate the role of the carbonate chemistry dynamics in shaping the response of coastal phytoplankton communities to increased pCO2 levels. The study was conducted at two coastal ecosystems off Chile, the Valdivia River estuary and the coastal upwelling ecosystem in the Arauco Gulf. We characterized the seasonal variability (winter/summer) of the hydrographic conditions, the carbonate system parameters, and the phytoplankton community structure at both sites. The results showed that carbonate chemistry dynamics in the estuary were mainly related to seasonal changes in freshwater discharges, with acidic and corrosive conditions dominating in winter. In the Arauco Gulf, these conditions were observed in summer, mainly associated with the upwelling of cold and high pCO2 (>1,000 μatm) waters. Diatoms dominated the phytoplankton communities at both sites, yet the one in Valdivia was more diverse. Only certain phytoplankton groups in this latter ecosystem showed a significant correlations with the carbonate system parameters. When the impact of elevated pCO2 levels was investigated by pCO2 manipulation experiments, we did not observe any significant effect on the biomass of either of the two communities. Changes in the phytoplankton species composition and abundance during the incubations were related to other factors, such as competition and growth phases. Our findings highlight the importance of the natural variability of coastal ecosystems and the potential for local adaptation in determining responses of coastal phytoplankton communities to increased pCO2 levels.

Continue reading ‘Response of phytoplankton assemblages from naturally acidic coastal ecosystems to elevated pCO2’

Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove


•Combined occurrence of hypoxia, acidification and nutrients increased biofilm bacterial diversity and richness

•Elevated nutrients, and depleted oxygen and pH levels resulted in different bacterial community composition

•Higher abundance of Flavobacteriales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales

•Suggests the identities of bacterial groups affected under the ocean trend of pollution, deoxygenation and acidification


Anthropogenic nutrient enrichment results in hypoxia, ocean acidification and elevated nutrients (HOAN) in coastal environments throughout the world. Here, we examined the composition of biofilm bacterial communities from a nutrient-excessive fish farm with low dissolved oxygen (DO) and pH levels using 16S rRNA gene sequencing. HOAN was accompanied by higher bacterial diversity and richness, and resulted in an altered community composition than the control site. HOAN resulted in more Flavobacteriales, Rhizobiales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales. Photobacterium sp. and Vibrio sp. were mostly found to be exclusive to HOAN conditions, suggesting that HOAN could possibly proliferate the presence of these potential pathogens. Our study suggests the complexity of bacterial communities to hypoxia and acidification in response to increased nutrient loads, along with identities of nutrient, oxygen and pH-susceptible bacterial groups that are most likely affected under this ocean trend.

Continue reading ‘Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove’

Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH

Ocean acidification (OA) is impairing the construction of coral reefs while simultaneously accelerating their breakdown. The metabolism of different reef organism assemblages alters seawater pH in different ways, possibly buffering or exacerbating OA impacts. In spite of this, field data relating benthic community structure and seawater pH are sparse. We collected pH time-series data snapshots at 10 m depth from 28 different reefs (n = 13 lagoon, n = 15 fore reef) across 22 Pacific islands, spanning 31° latitude and 90° longitude. Coincident with all deployments, we measured percent cover of the benthic community. On fore reefs, high coral cover (CC) negatively correlated with mean and minimum pH, but positively correlated with pH variability. Conversely, pH minima were positively correlated to coverage of coralline and turf algae. Benthic cover did not correlate with pH in lagoonal reefs. From 0%–100% CC, mean pH and aragonite saturation state (Ωarag ) declined −0.081 and −0.51, respectively, while declines in minimum values were greater (Δmin pH = −0.164, Δmin Ωarag = −0.96). Based upon previously published relationships, the mean pH decline from 0%–100% CC would depress coral calcification 7.7%–18.0% and increase biologically-mediated dissolution 13.5%–27.9%, with pH minima depressing dark coral calcification 14.4%–35.2% and increasing biologically-mediated dissolution 31.0%–62.2%. This spatially expansive dataset provides evidence that coral reefs with the highest coral cover may experience the lowest and most extreme pH values with OA.

Continue reading ‘Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH’

External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease

Brown Ring Disease (BRD) is an infection of the Manila clam Ruditapes philippinarum due to the pathogen Vibrio tapetis . During BRD, clams are facing immunodepression and shell biomineralization alteration. In this paper, we studied the role of pH on the growth of the pathogen and formulated hypothesis on the establishment of BRD by V. tapetis .

Methods and Results
In this study, we monitored the evolution of pH during the growth of V. tapetis in a range of pH and temperatures. We also measured the pH of Manila clam hemolymph and extrapallial fluids during infection by V. tapetis . We highlighted that V. tapetis modulates the external pH during its growth, to a value of 7.70. During the development of BRD, V. tapetis also influences extrapallial fluids and hemolymph pH in vitro in the first hours of exposure and in vivo after 3 days of infection.

Our experiments have shown a close interaction between V. tapetis CECT4600, a pathogen of Manila clam that induces BRD, and the pH of different compartments of the animals during infection. These results indicate that that the bacterium, through a direct mechanism or as a consequence of physiological changes encountered in the animal during infection, is able to interfere with the pH of Manila clam fluids. This pH modification might promote the infection process or at least create an imbalance within the animal, that would favor its persistence. This last hypothesis should be tested in future experiment.

Significance and Impact of Study
This study is the first observation of pH modifications in the context of BRD and might orient future research on the fine mechanisms of pH modulation associated to BRD.

Continue reading ‘External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease’

Metabolic responses of subtropical microplankton after a simulated deep-water upwelling event suggest a possible dominance of mixotrophy under increasing CO2 levels

In the autumn of 2014, nine large mesocosms were deployed in the oligotrophic subtropical North-Atlantic coastal waters off Gran Canaria (Spain). Their deployment was designed to address the acidification effects of CO2 levels from 400 to 1,400 μatm, on a plankton community experiencing upwelling of nutrient-rich deep water. Among other parameters, chlorophyll a (chl-a), potential respiration (Φ), and biomass in terms of particulate protein (B) were measured in the microplankton community (0.7–50.0 μm) during an oligotrophic phase (Phase I), a phytoplankton-bloom phase (Phase II), and a post-bloom phase (Phase III). Here, we explore the use of the Φ/chl-a ratio in monitoring shifts in the microplankton community composition and its metabolism. Φ/chl-a values below 2.5 μL O2 h−1 (μg chl-a)−1 indicated a community dominated by photoautotrophs. When Φ/chl-a ranged higher, between 2.5 and 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a mixed community of phytoplankton, microzooplankton and heterotrophic prokaryotes. When Φ/chl-a rose above 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a community where microzooplankton proliferated (>10.0 μL O2 h−1 (μg chl-a)−1), because heterotrophic dinoflagellates bloomed. The first derivative of B, as a function of time (dB/dt), indicates the rate of protein build-up when positive and the rate of protein loss, when negative. It revealed that the maximum increase in particulate protein (biomass) occurred between 1 and 2 days before the chl-a peak. A day after this peak, the trough revealed the maximum net biomass loss. This analysis did not detect significant changes in particulate protein, neither in Phase I nor in Phase III. Integral analysis of Φ, chl-a and B, over the duration of each phase, for each mesocosm, reflected a positive relationship between Φ and pCO2 during Phase II [α = 230·10−5 μL O2 h−1 L−1 (μatm CO2)−1 (phase-day)−1, R2 = 0.30] and between chl-a and pCO2 during Phase III [α = 100·10−5 μg chl-a L−1 (μ atmCO2)−1 (phase-day)−1, R2 = 0.84]. At the end of Phase II, a harmful algal species (HAS), Vicicitus globosus, bloomed in the high pCO2 mesocosms. In these mesocosms, microzooplankton did not proliferate, and chl-a retention time in the water column increased. In these V. globosus-disrupted communities, the Φ/chl-a ratio [4.1 ± 1.5 μL O2 h−1 (μg chl-a)−1] was more similar to the Φ/chl-a ratio in a mixed plankton community than to a photoautotroph-dominated one.

Continue reading ‘Metabolic responses of subtropical microplankton after a simulated deep-water upwelling event suggest a possible dominance of mixotrophy under increasing CO2 levels’

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Ocean acidification in the IPCC AR5 WG II

OUP book