primary production Archives - Page 9 of 22

Posts Tagged 'primary production'

Impact of ocean acidification and warming on the productivity of a rock pool community

Published 13 February 2018 Science Closed
Tags: algae, biological response, BRcommunity, laboratory, multiple factors, photosynthesis, primary production, temperature

Highlights

• Fleshy algae drive the response of assemblages.
• The response of coralline algae to global change depend on the season.
• Rock pool assemblages are robust to ocean acidification and warming.

Abstract

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO₂. Increased temperature and pCO₂ have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO₂, in terms of primary production.

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

Published 12 February 2018 Science Closed
Tags: biological response, flow, laboratory, mesocosms, multiple factors, North Atlantic, phanerogams, physiology, primary production, respiration

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.

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

Published 8 February 2018 Science Closed
Tags: abundance, biological response, BRcommunity, growth, laboratory, mesocosms, multiple factors, North Atlantic, otherprocess, phytoplankton, primary production, temperature

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 pH_T (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 (P_P) by 50 % and 160 %, respectively. During the declining phase of the bloom, warming accelerated the loss of diatom cells and negatively affected P_P. 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.

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The Arctic picoeukaryote Micromonas pusilla benefits synergistically from warming and ocean acidification

Published 6 February 2018 Science Closed
Tags: Arctic, biological response, growth, laboratory, multiple factors, phytoplankton, primary production, temperature

In the Arctic Ocean, climate change effects such as warming and ocean acidification (OA) are manifesting faster than in other regions. Yet, we are lacking a mechanistic understanding of the interactive effects of these drivers on Arctic primary producers. In the current study, one of the most abundant species of the Arctic Ocean, the prasinophyte Micromonas pusilla, was exposed to a range of different pCO₂levels at two temperatures representing realistic scenarios for current and future conditions. We observed that warming and OA synergistically increased growth rates at intermediate to high pCO₂ levels. Furthermore, elevated temperatures shifted the pCO₂-optimum of biomass production to higher levels. Based on changes in cellular composition and photophysiology, we hypothesise that the observed synergies can be explained by beneficial effects of warming on carbon fixation in combination with facilitated carbon acquisition under OA. Our findings help to understand the higher abundances of picoeukaryotes such as M. pusilla under OA, as has been observed in many mesocosm studies.

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Effects of CO2 enrichment on benthic primary production and inorganic nitrogen fluxes in two coastal sediments

Published 24 January 2018 Science Closed
Tags: biogeochemistry, biological response, BRcommunity, laboratory, photosynthesis, physiology, primary production, sediment, South Pacific

Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment–seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO_X⁻ (nitrite/nitrate), NH₄⁺ and O₂, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO₂-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO_X⁻ content but the seawater kept at pH 7.9 lost only 18%. Excess CO₂ increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO_X⁻ efflux into influx. The estuarine sand sustained its initial NO_X⁻ influx but, by the end of the incubation, released more NH₄⁺ at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO₂ increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH₄⁺ and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO₂ may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication.

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Greenland tidal pools as hot spots for ecosystem metabolism and calcification

Published 24 January 2018 Science Closed
Tags: biogeochemistry, biological response, BRcommunity, calcification, chemistry, field, North Atlantic, primary production

The hypothesis that Arctic tidal pools provide environmental conditions suitable for calcifiers during summer, thereby potentially providing refugia for calcifiers in an acidifying Arctic Ocean, was tested on the basis of measurements conducted during two midsummers (2014 and 2016) in tidal pools colonised by a community composed of macroalgae and calcifiers in Disko Bay, Greenland (69° N). The tidal pools exhibited steep diurnal variations in temperature from a minimum of about 6 °C during the night to a maximum of almost 18 °C in the afternoon, while the temperature of the surrounding shore water was much lower, typically in the range 3 to 8 °C. O₂ concentrations in the tidal pools were elevated relative to those in the adjacent open waters, by up to 11 mg O₂ L⁻¹, and exhibited heavy super-saturation (up to > 240%) during daytime emersion, reflecting intense and sustained photosynthetic rates of the tidal macroalgae. The intense photosynthetic activity of the seaweeds resulted in the drawdown of pCO₂ concentrations in the pools during the day to levels down to average (±SE) values of 66 ± 18 ppm, and a minimum recorded value of 14.7 ppm, corresponding to pH levels as high as 8.69 ± 0.08, as compared to CO₂ levels of 256 ± 4 and pH levels of 8.14 ± 0.01 in the water flooding the pools during high tide. The corresponding Ω_arag reached 5.04 ± 0.49 in the pools as compared to 1.55 ± 0.02 in the coastal waters flooding the pools. Net calcification averaged 9.6 ± 5.6 μmol C kg⁻¹ h⁻¹ and was strongly and positively correlated with calculated net ecosystem production rates, which averaged 27.5 ± 8.6 μmol C kg⁻¹ h⁻¹. Arctic tidal pools promote intense metabolism, creating conditions suitable for calcification during the Arctic summer, and can, therefore, provide refugia from ocean acidification to vulnerable calcifiers as extended periods of continuous light during summer are conducive to suitable conditions twice a day. Meroplankton larvae are exposed to ocean acidification until they settle in vegetated tidal pools, where they benefit from the protection offered by the “macroalgae-carbonate saturation state” interaction favouring calcification rates.

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Carbonate system parameters of an algal-dominated reef along West Maui

Published 23 January 2018 Science Closed
Tags: algae, biogeochemistry, biological response, BRcommunity, calcification, chemistry, corals, field, North Pacific, primary production, respiration

Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO₂ concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. To constrain the carbonate chemistry system, nutrients and carbonate chemistry were measured along the Kahekili reef flat every 4 h over a 6-d sampling period in March 2016. Abiotic process – primarily SGD fluxes – controlled the carbonate chemistry adjacent to the primary SGD vent site, with nutrient-laden freshwater decreasing pH levels and favoring undersaturated aragonite saturation (Ω_arag) conditions. In contrast, diurnal variability in the carbonate chemistry at other sites along the reef flat was driven by reef community metabolism. Superimposed on the diurnal signal was a transition during the second sampling period to a surplus of total alkalinity (TA) and dissolved inorganic carbon (DIC) compared to ocean end-member TA and DIC measurements. A shift from net community production and calcification to net respiration and carbonate dissolution was identified. This transition occurred during a period of increased SGD-driven nutrient loading, lower wave height, and reduced current speeds. This detailed study of carbon chemistry dynamics highlights the need to incorporate local effects of nearshore oceanographic processes into predictions of coral reef vulnerability and resilience.

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Interaction between elevated CO2 and phytoplankton-derived organic matter under solar radiation on bacterial metabolism from coastal waters

Published 15 January 2018 Science Closed
Tags: abundance, biogeochemistry, biological response, laboratory, North Atlantic, otherprocess, physiology, phytoplankton, primary production, prokaryotes, respiration

Microcosm experiments to assess bacterioplankton response to phytoplankton-derived organic matter obtained under current and future-ocean CO₂ levels were performed. Surface seawater enriched with inorganic nutrients was bubbled for 8 days with air (current CO₂ scenario) or with a 1000 ppm CO₂–air mixture (future CO₂ scenario) under solar radiation. The organic matter produced under the current and future CO₂ scenarios was subsequently used as inoculum. Triplicate 12 L flasks filled with 1.2 µm-filtered natural seawater enriched with the organic matter inocula were incubated in the dark for 8 days under CO₂ conditions simulating current and future CO₂ scenarios to study the bacterial response. The acidification of the media increased bacterial respiration at the beginning of the experiment while the addition of the organic matter produced under future levels of CO₂ was related to changes in bacterial production and abundance. The balance between both, respiration and production, made that the bacteria grown under future CO₂ levels with an addition of non-acidified matter showed the best growth efficiency at the end of the incubation. However cells grown under future scenarios with high CO₂ levels and acidified organic matter additions did not perform differently than those grown under present CO₂ conditions, independently of the addition of acidified or non-acidified organic matter. This study demonstrates that the increase in atmospheric CO₂ concentrations can affect bacterioplankton directly by changes in the respiration rate and indirectly by changes on the organic matter with concomitant effects on bacterial production and abundance.

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Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO2 tolerance in phytoplankton productivity (update)

Published 12 January 2018 Science Closed
Tags: abundance, Antarctic, biogeochemistry, biological response, BRcommunity, laboratory, otherprocess, photosynthesis, physiology, primary production, prokaryotes

High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO₂ levels ranging from ambient (343 µatm) to 1641 µatm in six 650 L minicosms. Productivity assays were performed to identify whether a CO₂ threshold existed that led to a change in primary productivity, bacterial productivity, and the accumulation of chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 µatm. CO₂ levels ≥ 1140 µatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csGPP_¹⁴C), causing significant reductions in gross primary production (GPP_¹⁴C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO₂ on C : N ratios. Over time, the phytoplankton community acclimated to high CO₂ conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO₂ treatments ≥ 953 µatm (days 3–5), yet gross bacterial production (GBP_¹⁴C) remained unchanged and cell-specific bacterial productivity (csBP_¹⁴C) was reduced. Towards the end of the experiment, GBP_¹⁴C and csBP_¹⁴C markedly increased across all treatments regardless of CO₂ availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO₂ uptake. Increases in bacterial abundance under high CO₂ conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration.

Continue reading ‘Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO2 tolerance in phytoplankton productivity (update)’

Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation

Published 11 January 2018 Science Closed
Tags: abundance, adaptation, biogeochemistry, biological response, BRcommunity, community composition, communitymodeling, laboratory, mesocosms, modeling, mortality, multiple factors, otherprocess, physiology, primary production, South Pacific, temperature

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems worldwide. However, most of these projections are based on ecological proxies or experiments on single species or simplified food webs. How energy fluxes are likely to change in marine food webs in response to future climates remains unclear, hampering forecasts of ecosystem functioning. Using a sophisticated mesocosm experiment, we model energy flows through a species-rich multilevel food web, with live habitats, natural abiotic variability, and the potential for intra- and intergenerational adaptation. We show experimentally that the combined stress of acidification and warming reduced energy flows from the first trophic level (primary producers and detritus) to the second (herbivores), and from the second to the third trophic level (carnivores). Warming in isolation also reduced the energy flow from herbivores to carnivores, the efficiency of energy transfer from primary producers and detritus to herbivores and detritivores, and the living biomass of detritivores, herbivores, and carnivores. Whilst warming and acidification jointly boosted primary producer biomass through an expansion of cyanobacteria, this biomass was converted to detritus rather than to biomass at higher trophic levels—i.e., production was constrained to the base of the food web. In contrast, ocean acidification affected the food web positively by enhancing trophic flow from detritus and primary producers to herbivores, and by increasing the biomass of carnivores. Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer–consumer dynamics, both of which have important implications for the structuring of benthic communities.

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Diatom performance in a future ocean: interactions between nitrogen limitation, temperature, and CO2-induced seawater acidification

Published 10 January 2018 Science Closed
Tags: biological response, growth, laboratory, morphology, multiple factors, nutrients, photosynthesis, phytoplankton, primary production, temperature

Phytoplankton cells living in the surface waters of oceans are experiencing alterations in environmental conditions associated with global change. Given their importance in global primary productivity, it is of considerable concern to know how these organisms will perform physiologically under the changing levels of pH, temperatures, and nutrients predicted for future oceanic ecosystems. Here we show that the model diatom, Thalassiosira pseudonana, when grown at different temperatures (20 or 24 °C), pCO₂ (400 or 1000 µatm), and nitrate concentrations (2.5 or 102.5 µmol l⁻¹), displayed contrasting performance in its physiology. Elevated pCO₂ (and hence seawater acidification) under the nitrate-limited conditions led to decreases in specific growth rate, cell size, pigment content, photochemical quantum yield of PSII, and photosynthetic carbon fixation. Furthermore, increasing the temperature exacerbated the negative effects of the seawater acidification associated with elevated pCO₂ on specific growth rate and chlorophyll content under the N-limited conditions. These results imply that a reduced upward transport of nutrients due to enhanced stratification associated with ocean warming might act synergistically to reduce growth and carbon fixation by diatoms under progressive ocean acidification, with important ramifications for ocean productivity and the strength of the biological CO₂ pump.

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Taking the metabolic pulse of the world’s coral reefs

Published 10 January 2018 Science Closed
Tags: biogeochemistry, biological response, calcification, chemistry, corals, dissolution, field, Indian, North Atlantic, North Pacific, physiology, primary production, Red Sea, South Pacific

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO₃) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.

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Increased CO2 and iron availability effects on carbon assimilation and calcification on the formation of Emiliania huxleyi blooms in a coastal phytoplankton community

Published 8 January 2018 Science Closed
Tags: abundance, biogeochemistry, biological response, BRcommunity, mesocosms, metals, multiple factors, otherprocess, phytoplankton, primary production

Highlights

• Increased dFe enhanced carbon fixation promoting a bloom of Emiliania huxleyi.
• High CO₂ decreased carbon production during a bloom of Emiliania huxleyi.
• Carbon uptake was unaffected by CO₂ and Fe availability in a bloom of Emiliania huxleyi.

Abstract

In the present work, we exposed a natural phytoplankton community to either present (390-μatm, LC) or future CO₂ levels predicted for year-2100 (900-μatm, HC) combined with ambient (4.5 nmol L⁻¹, −DFB) or high (12 nmol L⁻¹, +DFB) dissolved iron (dFe) levels, during 25 days by using mesocosms. We report on changes in carbon assimilation processes (acquisition, fixation, and calcification) of the phytoplankton community due to increased dissolved CO₂ and dFe and to the interaction of both factors. The isotopic disequilibrium assay results showed that inorganic carbon (C_i) acquisition by the community was unaffected by CO₂ and Fe availability. The main C_i source for photosynthesis was HCO₃⁻ and external carbonic anhydrase activity was only detected at the beginning of the experiment, suggesting a relevant role for HCO₃⁻ transporters in the phytoplankton community developed in all treatments. However, there was a significant effect of both factors on particulate organic carbon (POC) content, particulate calcium production and carbon fixation rates. Increased dFe at LC conditions led to the highest values of carbon fixation and POC of all treatments, promoting a massive Emiliania huxleyi bloom. This response was not observed in the HC treatments. The latter indicates a negative impact of increased CO₂ on the formation of E. huxleyi blooms, in agreement with the observed significant reduction in calcium production under HC. Our results suggest that ocean acidification can decrease primary production under iron-replete conditions in E. huxleyi blooming areas, affecting the biological carbon pump in coastal ecosystems.

Continue reading ‘Increased CO2 and iron availability effects on carbon assimilation and calcification on the formation of Emiliania huxleyi blooms in a coastal phytoplankton community’

Species interactions can shift the response of a maerl bed community to ocean acidification and warming (update)

Published 1 December 2017 Science Closed
Tags: abundance, algae, biological response, BRcommunity, calcification, dissolution, echinoderms, laboratory, mesocosms, mollusks, multiple factors, North Atlantic, otherprocess, physiology, primary production, respiration, temperature

Predicted ocean acidification and warming are likely to have major implications for marine organisms, especially marine calcifiers. However, little information is available on the response of marine benthic communities as a whole to predicted changes. Here, we experimentally examined the combined effects of temperature and partial pressure of carbon dioxide (pCO₂) increases on the response of maerl bed assemblages, composed of living and dead thalli of the free-living coralline alga Lithothamnion corallioides, epiphytic fleshy algae, and grazer species. Two 3-month experiments were performed in the winter and summer seasons in mesocosms with four different combinations of pCO₂ (ambient and high pCO₂) and temperature (ambient and +3 °C). The response of maerl assemblages was assessed using metabolic measurements at the species and assemblage scales. This study suggests that seasonal variability represents an important driver influencing the magnitude and the direction of species and community response to climate change. Gross primary production and respiration of assemblages was enhanced by high pCO₂ conditions in the summer. This positive effect was attributed to the increase in epiphyte biomass, which benefited from higher CO₂ concentrations for growth and primary production. Conversely, high pCO₂ drastically decreased the calcification rates in assemblages. This response can be attributed to the decline in calcification rates of living L. corallioides due to acidification and increased dissolution of dead L. corallioides. Future changes in pCO₂ and temperature are likely to promote the development of non-calcifying algae to the detriment of the engineer species L. corallioides. The development of fleshy algae may be modulated by the ability of grazers to regulate epiphyte growth. However, our results suggest that predicted changes will negatively affect the metabolism of grazers and potentially their ability to control epiphyte abundance. We show here that the effects of pCO₂ and temperature on maerl bed communities were weakened when these factors were combined. This underlines the importance of examining multi-factorial approaches and community-level processes, which integrate species interactions, to better understand the impact of global change on marine ecosystems.

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Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer

Published 21 November 2017 Science Closed
Tags: abundance, Antarctic, biological response, BRcommunity, laboratory, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, primary production, prokaryotes

Highlights

• Elevated CO₂ decreased primary productivity and gross primary production.
• Elevated CO₂ decreased bacterial productivity but increased bacterial production.
• Increased bacterial production was associated with reduced grazing pressure.
• Elevated CO₂ decreased net community production when nitrate was available.
• Under nitrate limitation net community production responses to CO₂ were suppressed.

Abstract

Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO₂ at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650 L) were filled with 200 μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12 days at CO₂ concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH¹⁴CO₃ and ¹⁴C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (P_max, mg C mg chl a^− 1 h^− 1) decreased with elevated CO₂, clearly reducing rates of total gross primary production (mg C L^− 1 h^− 1). Rates of cell-specific bacterial productivity (μg C cell^− 1 h^− 1) also decreased under elevated CO₂, yet total bacterial production (μg C L^− 1 h^− 1) and cell abundances increased with CO₂ over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO₂ concentrations > 2 × present day (> 780 ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate + nitrite (NOx) availability. At NOx concentrations < 1.5 μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO₂ responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO₂, thus forming a positive feedback to climate change. NO_X limitation may suppress this OA response but cause a similar decline.

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The impact of elevated CO2 on Prochlorococcus and microbial interactions with ‘helper’ bacterium Alteromonas

Published 2 November 2017 Science Closed
Tags: biological response, BRcommunity, growth, laboratory, molecular biology, mortality, performance, physiology, primary production, prokaryotes

Prochlorococcus is a globally important marine cyanobacterium that lacks the gene catalase and relies on ‘helper’ bacteria such as Alteromonas to remove reactive oxygen species. Increasing atmospheric CO₂ decreases the need for carbon concentrating mechanisms and photorespiration in phytoplankton, potentially altering their metabolism and microbial interactions even when carbon is not limiting growth. Here, Prochlorococcus (VOL4, MIT9312) was co-cultured with Alteromonas (strain EZ55) under ambient (400 p.p.m.) and elevated CO₂ (800 p.p.m.). Under elevated CO₂, Prochlorococcus had a significantly longer lag phase and greater apparent die-offs after transfers suggesting an increase in oxidative stress. Whole-transcriptome analysis of Prochlorococcus revealed decreased expression of the carbon fixation operon, including carboxysome subunits, corresponding with significantly fewer carboxysome structures observed by electron microscopy. Prochlorococcus co-culture responsive gene 1 had significantly increased expression in elevated CO₂, potentially indicating a shift in the microbial interaction. Transcriptome analysis of Alteromonas in co-culture with Prochlorococcus revealed decreased expression of the catalase gene, known to be critical in relieving oxidative stress in Prochlorococcus by removing hydrogen peroxide. The decrease in catalase gene expression was corroborated by a significant ~6-fold decrease in removal rates of hydrogen peroxide from co-cultures. These data suggest Prochlorococcus may be more vulnerable to oxidative stress under elevated CO₂ in part from a decrease in ecosystem services provided by heterotrophs like Alteromonas. This work highlights the importance of considering microbial interactions in the context of a changing ocean.

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The regulation of coralline algal physiology, an in situ study of Corallina officinalis (Corallinales, Rhodophyta) (update)

Published 13 October 2017 Science Closed
Tags: algae, biological response, calcification, chemistry, field, North Atlantic, primary production, respiration

Calcified macroalgae are critical components of marine ecosystems worldwide, but face considerable threat both from climate change (increasing water temperatures) and ocean acidification (decreasing ocean pH and carbonate saturation). It is thus fundamental to constrain the relationships between key abiotic stressors and the physiological processes that govern coralline algal growth and survival. Here we characterize the complex relationships between the abiotic environment of rock pool habitats and the physiology of the geniculate red coralline alga, Corallina officinalis (Corallinales, Rhodophyta). Paired assessment of irradiance, water temperature and carbonate chemistry, with C. officinalis net production (NP), respiration (R) and net calcification (NG) was performed in a south-western UK field site, at multiple temporal scales (seasonal, diurnal and tidal). Strong seasonality was observed in NP and night-time R, with a P_max of 22.35 µmol DIC (g DW)⁻¹ h⁻¹, E_k of 300 µmol photons m⁻² s⁻¹ and R of 3.29 µmol DIC (g DW)⁻¹ h⁻¹ determined across the complete annual cycle. NP showed a significant exponential relationship with irradiance (R² = 0.67), although was temperature dependent given ambient irradiance > E_k for the majority of the annual cycle. Over tidal emersion periods, dynamics in NP highlighted the ability of C. officinalis to acquire inorganic carbon despite significant fluctuations in carbonate chemistry. Across all data, NG was highly predictable (R² = 0.80) by irradiance, water temperature and carbonate chemistry, providing a NG_max of 3.94 µmol CaCO₃ (g DW)⁻¹ h⁻¹ and E_k of 113 µmol photons m⁻² s⁻¹. Light NG showed strong seasonality and significant coupling to NP (R² = 0.65) as opposed to rock pool water carbonate saturation. In contrast, the direction of dark NG (dissolution vs. precipitation) was strongly related to carbonate saturation, mimicking abiotic precipitation dynamics. Data demonstrated that C. officinalis is adapted to both long-term (seasonal) and short-term (tidal) variability in environmental stressors, although the balance between metabolic processes and the external environment may be significantly impacted by future climate change.

Continue reading ‘The regulation of coralline algal physiology, an in situ study of Corallina officinalis (Corallinales, Rhodophyta) (update)’

Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification

Published 7 September 2017 Science Closed
Tags: adaptation, biogeochemistry, biological response, calcification, field, laboratory, morphology, otherprocess, phytoplankton, primary production, South Pacific

Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxleyi exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxleyi populations in the naturally acidified upwelling waters of the Eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally overcalcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxleyi populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hypercalcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO₂ (400 µatm vs. 1200 µatm), the overcalcified morphotypes showed the same growth inhibition (−29.1 ± 6.3 %) as moderately calcified morphotypes isolated from non-acidified water (−30.7 ± 8.8 %). Under OA conditions, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC/POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. OA affected coccolith morphology equally or more strongly in overcalcified strains compared to moderately calcified strains. OA conditions appear not to directly select for exceptionally overcalcified morphotypes over other morphotypes directly, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turn-over and large population sizes, do not necessarily exhibit adaptations to naturally high CO₂ upwellings, and this ubiquitous coccolithophore may be near a limit of its capacity to adapt to ongoing ocean acidification.
Continue reading ‘Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification’

CO2 fixation stability by Sulfurovum lithotrophicum 42BKTT depending on pH and ionic strength conditions

Published 25 August 2017 Science Closed
Tags: biological response, growth, laboratory, morphology, multiple factors, nutrients, primary production, prokaryotes

The dissolution of CO2, a greenhouse gas most responsible for global warming, in seawater lowers its pH and increases its ionic strength. Sulfurovum lithotrophicum42BKTT, a deep-sea chemolithotrophic bacterium, can fix high concentration CO2. In this study, we investigated the effect of pH and ionic strength variation of seawater on CO2fixation by this bacterium. For a stable and continuous fixation of high concentration CO2by S. lithotrophicum 42BKTT, the pH and ionic strength of the seawater-based medium should be 6.1–6.8 and <0.8 M, respectively. The deviation of pH and ionic strength from these ranges was indicated by the appearance of lengthened and fattened cells whose length and diameter increased by 70–90%. These results imply that the harmful effect of dissolved CO2 on marine ecosystem is due to the increase in ionic strength and decrease in pH of seawater.

Continue reading ‘CO2 fixation stability by Sulfurovum lithotrophicum 42BKTT depending on pH and ionic strength conditions’

Interactive effects of elevated temperature and CO2 on nitrate, urea, and dissolved inorganic carbon uptake by a coastal California, USA, microbial community

Published 24 August 2017 Science Closed
Tags: abundance, biological response, BRcommunity, laboratory, multiple factors, otherprocess, physiology, primary production, prokaryotes, temperature

Average global temperatures and carbon dioxide (CO2) levels are expected to increase in the coming decades. Implications for ocean ecosystems include shifts in microbial community structure and subsequent modifications to nutrient pathways. Studying how predicted future temperature and CO2 conditions will impact the biogeochemistry of the ocean is important because of the ocean’s role in regulating global climate. We determined how elevated temperature and CO2 affect uptake rates of nitrate, urea, and dissolved inorganic carbon (DIC) by 2 size classes (0.7-5.0 and >5.0 µm) of a microbial assemblage collected from coastal California, USA. This microbial community was incubated for 10 d using an ecostat continuous culture system that supplied the microorganisms with either nitrate or urea as the dominant nitrogen source. Biomass parameters, nutrient concentrations, and uptake rates were measured throughout the experiment. In all treatments, urea uptake rates were greater than nitrate, and larger microorganisms had higher uptake rates than smaller microorganisms. Uptake rates of urea and DIC within both size fractions were higher at elevated temperature, and uptake rates of nitrate by smaller microorganisms increased with elevated CO2. These findings suggest that the rate at which nutrients cycle in temperate coastal waters will increase as temperature and CO2 levels rise and that the effect will vary between nitrogen substrates and different microorganisms.

Continue reading ‘Interactive effects of elevated temperature and CO2 on nitrate, urea, and dissolved inorganic carbon uptake by a coastal California, USA, microbial community’

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