Posts Tagged 'nutrients'

Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) dynamics in the surface ocean

Dimethyl sulfide (DMS) is a trace gas produced in the ocean that plays an important role in climate and contributes to the Earths energy balance. DMS is a product of the enzymatic cleavage of dimethyl sulfoniopropionate (DMSP), which is produced by certain phytoplankton species and bacteria. Processes within the DMS/P cycles in the surface ocean are complex and vary with time and space. In the sea surface microlayer (SML), which is the interface between the ocean and the atmosphere, DMS concentration may be altered relative to subsurface water (SSW), by elevated biological activity, light intensity, and gas exchange. The aim of this thesis is to determine the importance of the SML in DMS/P dynamics and air-sea exchange by developing a more robust technique for SML sampling to better understand the dynamics of DMSP and DMS, and comparing their dynamics in the SML and SSW in coastal waters and the open ocean. In addition, the impact of warming and ocean acidification on DMS/P dynamics is investigated to determine how they will be impacted by future climate change.

To characterize DMS dynamics in the SML, a more effective method for sampling trace gases in the SML was developed (Chapter 2). The method is reliant on diffusion through a gas-permeable tube due to the concentration gradient. The floating tube was tested and calibrated under semi-controlled conditions using coastal water, where its reproducibility, accuracy and effectiveness were established. The potential benefits of this new technique for sampling trace gases in the SML include reduced loss of DMS to air. The higher reproducibility and accuracy compared to other techniques confirmed the potential of the floating tube technique for trace gas measurement in the SML.

The method developed in Chapter 2 was applied in sampling of DMS in the SML along a coastal-open ocean gradient (Chapter 3), and in various water masses of the open ocean (Chapter 4). In both chapters, DMSP and DMS dynamics were related to biological, biogeochemical, and physical properties of the SML and SSW. Sampling was conducted over 3 months at three different stations with different degrees of coastal and open water influence around Wellington, New Zealand in Chapter 3. DMSP was significantly enriched in the SML in most sampling events and DMSP and DMS enrichments were influenced by biological production and bacterial consumption. Overall, there was no temporal trends or coastal-offshore gradient in DMS or related biogeochemical variables in the SML. However, DMS concentration, and also DMS to DMSP ratio, were significantly correlated with solar radiation indicating a role for light as a determinant of DMSP and DMS in the SML. In open ocean waters around the Chatham Rise, east of New Zealand, the SML and SSW in water masses of different phytoplankton composition and biomass were sampled (Chapter 4). There was no chlorophyll a enrichment in the SML, and bacterial and DMSP enrichment were only apparent at one station, despite sampling within a phytoplankton bloom. Furthermore, there were no relationships between DMSP and phytoplankton biomass or community composition in the SML, although DMSP was negatively correlated with PAR. DMS was only significantly enriched in the SML at one station. DMS and DMSP concentrations were correlated in both SML and SSW, with the differing slopes attributed to DMS loss in the SML. Daily deck incubations were carried out to quantify DMSP and DMS processes in the SML, including the net effect of light on DMS/P, bacterial consumption of DMS/P and DMS production, and DMS air-sea flux. Air-sea flux was the main pathway with a DMS flux of 1.0-11.0 µmol m-2 d-1 that concurs with climatological predictions for the region. Excluding air-sea emission, biological DMS production was the dominant process in the SML relative to biological consumption and the net effect of light. SML DMS yield was not significantly different to that in the SSW, and consequently processes within the SML do not significantly affect regional DMS emissions.

The impact of ocean acidification and warming on DMSP and DMS concentrations was established for New Zealand coastal waters. Four mesocosm experiments, in which temperature and pH were manipulated to values projected for the years 2100 and 2150, were carried out over three years with the initial phytoplankton community differing in composition and bloom status (Chapter 6:). Temporal changes in DMSP and DMS were established and linked to changes in community composition and biogeochemistry. Results indicate that future warming may have greater influence on DMS production than ocean acidification. The observed reduction in DMSP at warmer temperatures was associated with changes in phytoplankton community, and in particular with a decrease in small flagellates. As nutrient availability also influenced the response this should also be considered in models of future DMS. Although DMS concentration decreased under future conditions of ocean acidification and higher temperature, this decrease was not as significant as reported by other studies.

The results in this thesis contribute to a better understanding of DMSP and DMS dynamics in the surface ocean. The floating tube method developed to sample DMS in the SML, will permit the study of DMS in the SML in various oceanic regions with improved accuracy. This technique may also have potential for measuring other trace gases in the SML. Application of this technique in coastal and open ocean waters demonstrated differences in DMS dynamics in the SML between these regions. DMS enrichment in the SML was rarely found, and DMS enrichment does not affect DMS air-sea flux significantly. Biological and biogeochemical variables and DMS/P process rates need to be established to further understanding of DMS/P dynamics in the SML and near surface water. Finally, results suggest that impacts of future climate change on DMS emissions may not be as significant as reported elsewhere, but that phytoplankton community composition plays a role and must be considered in future scenario models to better predict future DMS emissions. 

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The potential of kelp Saccharina japonica in shielding Pacific oyster Crassostrea gigas from elevated seawater pCO2 stress

Ocean acidification (OA) caused by elevated atmospheric CO2 concentration is predicted to have negative impacts on marine bivalves in aquaculture. However, to date, most of our knowledge is derived from short-term laboratory-based experiments, which are difficult to scale to real-world production. Therefore, field experiments, such as this study, are critical for improving ecological relevance. Due to the ability of seaweed to absorb dissolved carbon dioxide from the surrounding seawater through photosynthesis, seaweed has gained theoretical attention as a potential partner of bivalves in integrated aquaculture to help mitigate the adverse effects of OA. Consequently, this study investigates the impact of elevated pCO2 on the physiological responses of the Pacific oyster Crassostrea gigas in the presence and absence of kelp (Saccharina japonica) using in situ mesocosms. For 30 days, mesocosms were exposed to six treatments, consisting of two pCO2 treatments (500 and 900 μatm) combined with three biotic treatments (oyster alone, kelp alone, and integrated kelp and oyster aquaculture). Results showed that the clearance rate (CR) and scope for growth (SfG) of C. gigas were significantly reduced by elevated pCO2, whereas respiration rates (MO2) and ammonium excretion rates (ER) were significantly increased. However, food absorption efficiency (AE) was not significantly affected by elevated pCO2. The presence of S. japonica changed the daytime pHNBS of experimental units by ~0.16 units in the elevated pCO2 treatment. As a consequence, CR and SfG significantly increased and MO2 and ER decreased compared to C. gigas exposed to elevated pCO2 without S. japonica. These findings indicate that the presence of S. japonica in integrated aquaculture may help shield C. gigas from the negative effects of elevated seawater pCO2.

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Caribbean king crab larvae and juveniles show tolerance to ocean acidification and ocean warming

Coastal habitats are experiencing decreases in seawater pH and increases in temperature due to anthropogenic climate change. The Caribbean king crab, Maguimithrax spinosissimus, plays a vital role on Western Atlantic reefs by grazing macroalgae that competes for space with coral recruits. Therefore, identifying its tolerance to anthropogenic stressors is critically needed if this species is to be considered as a potential restoration management strategy in coral reef environments. We examined the effects of temperature (control: 28 °C and elevated: 31 °C) and pH (control: 8.0 and reduced pH: 7.7) on the king crab’s larval and early juvenile survival, molt-stage duration, and morphology in a fully crossed laboratory experiment. Survival to the megalopal stage was reduced (13.5% lower) in the combined reduced pH and elevated temperature treatment relative to the control. First-stage (J1) juveniles delayed molting by 1.5 days in the reduced pH treatment, while second-stage (J2) crabs molted 3 days earlier when exposed to elevated temperature. Juvenile morphology did not differ among treatments. These results suggests that juvenile king crabs are tolerant to changes associated with climate change. Given the important role of the king crab as a grazer of macroalgae, its tolerance to climate stressors suggests that it could benefit restoration efforts aimed at making coral reefs more resilient to increasingly warm and acidic oceans into the future.

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The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord


In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100–2,300 µm), (2) live fjord zooplankton plus krill (>7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals ‘lost’ 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

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Marine macrophytes as carbon sinks: comparison between seagrasses and the non-native alga Halimeda incrassata in the Western Mediterranean (Mallorca)

Seagrass species play a critical role in the mitigation of climate change by acting as valuable carbon sinks and storage sites. Another important ecosystem service of this coastal vegetation is nutrient removal. However, coastal ecosystems are under increasing pressure of global warming and associated establishment of invasive species. To elucidate the respective contributions of seagrass species Posidonia oceanica and Cymodocea nodosa and the non-native macroalga Halimeda incrassata as primary producers and nutrient sinks in coastal habitats we conducted in-situ incubations in the North-western Mediterranean Sea. Measured metabolic activity and nutrient removal as well as calcification rates in these habitats over a 24 h period in spring and summer confirmed that the endemic seagrass P. oceanica represents a valuable ecosystem with high O2 production and considerable carbon capture. The documented regression of P. oceanica meadows with higher temperatures and decline in autotrophy as measured here causes concern for the continuity of ecosystem services rendered by this habitat throughout the Mediterranean Sea with progressing climate warming. In contrast, the enhanced performance of C. nodosa and the calcifying alga H. incrassata with increasing temperatures, under expected rates of future warming is uncertain to mitigate loss of productivity in case of a potential shift in marine vegetation. This could ultimately lead to a decline in ecosystem services, decreased carbon storage and mitigation of climate change. Furthermore, this study provides a first estimate for the growth rate of H. incrassata in the Mediterranean Sea, supporting evidence for the mechanism of its rapid extension.

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Nutrient alteration drives the impacts of seawater acidification on the bloom-forming dinoflagellate Karenia mikimotoi

Seawater acidification and nutrient alteration are two dominant environmental factors in coastal environments that influence the dynamics and succession of marine microalgae. However, the impacts of their combination have seldom been recorded. A simulated experimental system was set up to mimic the effects of elevated acidification on a bloom-forming dinoflagellate, Karenia mikimotoi, exposed to different nutrient conditions, and the possible mechanism was discussed. The results showed that acidification at different pH levels of 7.6 or 7.4 significantly influenced microalgal growth (p<0.05) compared with the control at pH 8.0. Mitochondria, the key sites of aerobic respiration and energy production, were impaired in a pH-dependent manner, and a simultaneous alteration of reactive oxygen species (ROS) production occurred. Cytochrome c oxidase (COX) and citrate synthase (CS), two mitochondrial metabolism-related enzymes, were actively induced with acidification exposure, suggesting the involvement of the mitochondrial pathway in coping with acidification. Moreover, different nutrient statuses indicated by various N:P ratios of 7:1 (N limitation) and 52:1 (P limitation) dramatically altered the impacts of acidification compared with those exposed to an N:P ratio of 17:1 (control), microalgal growth at pH 7.4 was obviously accelerated with the elevation of the nutrient ratio compared to that at pH 8.1 (p<0.05), and nutrient limitations seemed beneficial for growth in acidifying conditions. The production of alkaline phosphatase (AP) and acid phosphatase (AcP), an effective index indicating the microalgal growth status, significantly increased at the same time (p<0.05), which further supported this speculation. However, nitrate reductase (NR) was slightly inhibited. Hemolytic toxin production showed an obvious increase as the N:P ratio increased when exposed to acidification. Taken together, mitochondrial metabolism was suspected to be involved in the process of coping with acidification, and nutrient alterations, especially P limitation, could effectively alleviate the negative impacts induced by acidification. The obtained results might be a possible explanation for the competitive fitness of K. mikimotoi during bloom development.

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The brown algae Saccharina japonica and Sargassum horneri exhibit species-specific responses to synergistic stress of ocean acidification and eutrophication

Ocean acidification and eutrophication are two important environmental stressors. They inevitably impact marine macroalgae, and hence the coastal ecosystem of China. Saccharina japonica, as the main culture species in China, is suffering the harmful golden tide caused by Sargassum horneri. However, it remains unclear whether the detrimental effects of S. horneri on S. japonica cultivation become more severe in future acidified and eutrophic scenario. In this study, we respectively investigated the effects of pCO2 (400 µatm and 1000 µatm) and nutrients (non-enriched and enriched seawater) on the growth, photosynthesis, respiration, chlorophyll contents, and tissue nitrogen of S. japonica and S. horneri. Results indicated that enrichment of nutrients contributed S. horneri to utilize HCO3. The carbon acquisition pathway shifted from HCO3 to CO2 in S. japonica, while S. horneri remained using HCO3 regulated by nutrient enrichment. S. horneri exhibited better photosynthetic traits than S. japonica, with a higher level of net photosynthetic rate and chlorophyll contents at elevated pCO2 and enriched nutrients. Tissue nitrogen also accumulated richly in the thalli of S. horneri under higher pCO2 and nutrients. Significant enhancement in growth was only detected in S. horneri under synergistic stress. Together, S. horneri showed competitive dominance in current study. These findings suggest that increasing risk of golden tide in acidified and eutrophic ocean can most likely result in great damage to S. japonica cultivation.

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Elevated CO2 accelerated the bloom of three Ulva species after one life cycle culture

Human activities and the resulting global climate change have profound effects on ecosystems, and economic and social systems, including those dependent on the ocean. Increasing concentrations of atmospheric CO2 have led to gradual changes in the marine carbonate system. It is well known that environmental changes determine the composition and abundance of algal populations. In the present study, we evaluated the growth, photosynthesis, nutrient uptake rates, tissue C and N content, nitrate reductase activity, and nitrate transporter gene expression of Ulva proliferaUlva linza, and Ulva compressa exposed to 400, 1000, and 2000 ppm CO2 levels after one life cycle culture. Elevated CO2 promoted the rapid propagation of three Ulva species, which can result in the formation of a green tide. This was due to enhanced photosynthetic and respiration efficiency, reductions in energy requirements for biosynthesis and metabolism for maintaining external pH, and promotion of NO3 uptake by increased NO3 gene expression level and NO3 reductase activity.

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Moderate nutrient concentrations are not detrimental to corals under future ocean conditions

Under predicted future ocean conditions, reefs exposed to elevated nutrients will simultaneously experience ocean acidification and elevated temperature. We evaluated if moderate nutrients mitigate, minimize, or exacerbate negative effects of predicted future ocean conditions on coral physiology. For 30 days, Acropora millepora and Turbinaria reniformis were exposed to a fully factorial experiment of eight treatments including two seawater temperatures (26.4 °C and 29.8 °C), pCO2 levels (401 μatm pCO2 and 760 μatm pCO2), and nutrient concentrations (ambient: 0.40 μmol L−1 NO3 and 0.22 μmol L−1 PO43−, and moderate: 3.56 μmol L−1 NO3 and 0.31 μmol L−1 PO43−). Added nitrate was taken up by the algal endosymbionts and transferred to the coral hosts in both species, though to a much higher degree in A. millepora. When exposed to elevated temperature, elevated pCO2, or both, effects observed for chlorophyll a, calcification, biomass, and energy reserves were not compounded by the moderate nutrient concentrations in either species. Moderate nutrients enabled A. millepora to continue to meet daily metabolic demand via photosynthesis under predicted future ocean conditions and T. reniformis to greatly exceed daily metabolic demand via photosynthesis and heterotrophy. Our results suggest that balanced moderate nutrients are not detrimental to corals under predicted future ocean conditions and may even provide some benefits.

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Physiology, niche characteristics and extreme events: current and future habitat suitability of a rhodolith-forming species in the Southwestern Atlantic

Highlights

  • Global climate change and local stressors are the main threats to reef-building organisms and habitats they build, such as rhodolith beds.
  • Through an experimental essay and ecological niche modelling, we were able to determine the environmental factors that determine the distribution and affect the physiology of an important rhodolith-forming species in the southwestern Atlantic.
  • Our results raise the possibility of some rhodolith-forming species being resilient to future environmental change based on our current understanding of their distributions, a perspective that will need to be further explored by future studies.
  • This information is helpful in informing policies for the conservation of priority areas, aiding the preservation of marine biodiversity in the South Atlantic.

Abstract

Given the ecological and biogeochemical importance of rhodolith beds, it is necessary to investigate how future environmental conditions will affect these organisms. We investigated the impacts of increased nutrient concentrations, acidification, and marine heatwaves on the performance of the rhodolith-forming species Lithothamnion crispatum in a short-term experiment, including the recovery of individuals after stressor removal. Furthermore, we developed an ecological niche model to establish which environmental conditions determine its current distribution along the Brazilian coast and to project responses to future climate scenarios. Although L. crispatum suffered a reduction in photosynthetic performance when exposed to stressors, they returned to pre-experiment values following the return of individuals to control conditions. The model showed that the most important variables in explaining the current distribution of L. crispatum on the Brazilian coast were maximum nitrate and temperature. In future ocean conditions, the model predicted a range expansion of habitat suitability for this species of approximately 58.5% under RCP 8.5. Physiological responses to experimental future environmental conditions corroborated model predictions of the expansion of this species’ habitat suitability in the future. This study, therefore, demonstrates the benefits of applying combined approaches to examine potential species responses to climate-change drivers from multiple angles.

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Viral-mediated microbe mortality modulated by ocean acidification and eutrophication: consequences for the carbon fluxes through the microbial food web

Anthropogenic carbon emissions are causing changes in seawater carbonate chemistry including a decline in the pH of the oceans. While its aftermath for calcifying microbes has been widely studied, the effect of ocean acidification (OA) on marine viruses and their microbial hosts is controversial, and even more in combination with another anthropogenic stressor, i.e., human-induced nutrient loads. In this study, two mesocosm acidification experiments with Mediterranean waters from different seasons revealed distinct effects of OA on viruses and viral-mediated prokaryotic mortality depending on the trophic state and the successional stage of the plankton community. In the winter bloom situation, low fluorescence viruses, the most abundant virus-like particle (VLP) subpopulation comprising mostly bacteriophages, were negatively affected by lowered pH with nutrient addition, while the bacterial host abundance was stimulated. High fluorescence viruses, containing cyanophages, were stimulated by OA regardless of the nutrient conditions, while cyanobacteria of the genus Synechococcus were negatively affected by OA. Moreover, the abundance of very high fluorescence viruses infecting small haptophytes tended to be lower under acidification while their putative hosts’ abundance was enhanced, suggesting a direct and negative effect of OA on viral–host interactions. In the oligotrophic summer situation, we found a stimulating effect of OA on total viral abundance and the viral populations, suggesting a cascading effect of the elevated pCO2 stimulating autotrophic and heterotrophic production. In winter, viral lysis accounted for 30 ± 16% of the loss of bacterial standing stock per day (VMMBSS) under increased pCO2 compared to 53 ± 35% in the control treatments, without effects of nutrient additions while in summer, OA had no significant effects on VMMBSS (35 ± 20% and 38 ± 5% per day in the OA and control treatments, respectively). We found that phage production and resulting organic carbon release rates significantly reduced under OA in the nutrient replete winter situation, but it was also observed that high nutrient loads lowered the negative effect of OA on viral lysis, suggesting an antagonistic interplay between these two major global ocean stressors in the Anthropocene. In summer, however, viral-mediated carbon release rates were lower and not affected by lowered pH. Eutrophication consistently stimulated viral production regardless of the season or initial conditions. Given the relevant role of viruses for marine carbon cycling and the biological carbon pump, these two anthropogenic stressors may modulate carbon fluxes through their effect on viruses at the base of the pelagic food web in a future global change scenario.

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Effects of extra feeding combined with ocean acidification and increased temperature on the carbon isotope values (δ13C) in the mussel shell

Highlights

  • Ocean acidification, OA, increased metabolic carbon uptake in mussel shell calcite.
  • Additive effects of increased temperature and extra feeding on carbon uptake.
  • Mussels alter their biomineralisation pathways relating to food carbon uptake.
  • Metabolic carbon uptake is 7–11% higher in the shell aragonite compared to calcite.
  • Molluscs with different composites may alter biomineralisation under OA.

Abstract

Ocean acidification (OA) and global warming present future challenges for shell producing organisms such as mussels through reduction in the carbonate available to produce shells in these and other valuable aquaculture species. Molluscs control their shell growth through biomineralisation, but the response of the mechanisms behind biomineralisation to OA conditions are relatively unknown. It is unclear how much carbon is taken into the shell from the environment compared to the uptake through the food source. Shell production is energetically costly to molluscs and metabolic processes and energetic partitioning may affect their ability to perform the underlying mechanisms of biomineralisation under OA. It is possible that additional food consumption might alleviate some impacts caused by acidification. We assessed the ability of extra feeding to alter the impacts of OA and increased temperatures on adult Mytilus edulis. Carbon isotopes (δ13C) were used to examine the change in biomineralisation pathway in mussels. OA did not alter the δ13C directly in separate analyses of the shell calcite and aragonite layers, mantle tissue and extrapallial fluid. However, ambient treatments with increased temperatures altered the mussel biomineralisation pathway in the shell calcite using CO32− instead of HCO3 as the main source of carbon. The proportion of metabolic carbon uptake into the mussel shell calcite layer increased under OA, with additive effects when exposed to increased temperatures and extra feeding. The proportion of metabolic carbon uptake is higher (7%–11%) in the shell aragonite layer compared to calcite, under ambient treatments. OA initially reduced the metabolic carbon uptake into the shell aragonite, but after a period of 4-months with extra feeding, the mussels were able to adjust their metabolic carbon uptake to a level experienced under ambient treatments. This indicates that an abundance of food resources may enable changes in mussel biomineralisation pathways to compensate for any decrease in seawater inorganic carbon associated with OA. The impact of OA on phytoplankton varies from species to species, changing the structure of the community which could provide sufficient food resources to maintain metabolic carbon uptake for mussel shell growth. This study of δ13C isotopic values has identified changes in biomineralisation pathway relating to the mussel metabolic carbon uptake from their food source, with varying results for the aragonite and calcite shell polymorphs. The implications of these findings suggest that some bivalve species with different shell composites may cope better under OA than others, demanding further study into species-specific biomineralisation pathways.

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Impact of increased nutrients and lowered pH on photosynthesis and growth of three marine phytoplankton communities from the coastal South West Atlantic (Patagonia, Argentina)

Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters (Isla Escondida, IE). We exposed samples to two contrasting scenarios: Present (nutrients at in situ levels) vs. Future (with lowered pH and higher nutrients inputs), and determined growth and photosynthetic responses after 2 days of acclimation. Under the Future condition phytoplankton growth was higher in the estuarine site compared to those in PM and IE. This effect was the most pronounced on large diatoms. While the increase of photosynthetic activity was not always observed in the Future scenario, the lower photosynthetic electron requirement for carbon fixation (Φe,C = ETR/PmB) in this scenario compared to the Present, suggests a more effective energy utilization. Long-term experiments were also conducted to assess the responses along a 4 days acclimation period in PU. Diatoms benefited from the Future conditions and had significantly higher growth rates than in the Present. In addition, Φe,C was lower after the acclimation period in the Future scenario, compared to the Present. Our results suggest that the availability, frequency and amount of nutrients play a key role when evaluating the effects of global change on natural phytoplankton communities. The observed changes in diatom growth under the Future scenario in PU and IE and photosynthesis may have implications in the local trophodynamics by bottom up control.

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Photosynthetic responses of Halimeda scabra (Chlorophyta, Bryopsidales) to interactive effects of temperature, pH, and nutrients and its carbon pathways

In this study, we evaluated the interactive effects of temperature, pH, and nutrients on photosynthetic performance in the calcareous tropical macroalga Halimeda scabra. A significant interaction among these factors on gross photosynthesis (Pgross) was found. The highest values of Pgross were reached at the highest temperature, pH, and nutrient enrichment tested and similarly in the control treatment (no added nutrients) at 33 °C at the lowest pH. The Q10 Pgross values confirmed the effect of temperature only under nutrient enrichment scenarios. Besides the above, bicarbonate (HCO3) absorption was assessed by the content of carbon stable isotope (δ13C) in algae tissue and by its incorporation into photosynthetic products, as well as by carbonic anhydrase (CA) inhibitors (Acetazolamide, AZ and Ethoxyzolamide, EZ) assays. The labeling of δ13C revealed this species uses both, CO2 and HCO3 forms of Ci relying on a CO2 Concentration Mechanism (CCM). These results were validated by the EZ-AZ inhibition assays in which photosynthesis inhibition was observed, indicating the action of internal CA, whereas AZ inhibitor did not affect maximum photosynthesis (Pmax). The incorporation of 13C isotope into aspartate in light and dark treatments also confirmed photosynthetic and non-photosynthetic the HCO3uptake.

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Springtime spatial distributions of biogenic sulfur compounds in the Yangtze river estuary and their responses to seawater acidification and dust

The spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) were investigated in the Yangtze River Estuary from 9 to 23 March, 2018. The average concentrations of DMS, dissolved DMSP (DMSPd), particulate DMSP (DMSPp), dissolved DMSO (DMSOd) and particulate DMSO (DMSOp) were 3.00 ± 2.53, 1.75 ± 1.08, 10.89 ± 14.28, 9.80 ± 7.79, and 9.51 ± 8.90 nmol L‐1, respectively. The high DMS and DMSP concentrations occurred mainly in the open sea, exhibiting distribution patterns similar to chlorophyll a (Chl‐a). Due to the release of resuspended sediments, elevated DMSO concentrations were observed in the bottom waters of some stations. The three sulfur compounds were positively correlated with Chl‐a (p < 0.05), suggesting that phytoplankton played an essential role in the production of sulfur compounds. Comparisons with previous research showed that the concentrations of DMS, DMSP, and DMSOp exhibited clear seasonal variability. The average sea‐to‐air flux of DMS was 8.19 ± 12.94 μmol m‐2 d‐1 in the study area, indicating that the estuary and continental shelf sea were significant contributors to the global sulfur cycle. Ship‐based incubation experiments showed that lower pH inhibited the production of the three biogenic sulfur compounds, while the addition of dust promoted their release. Therefore, in the future, the inhibitory effect of seawater acidification on the production of phytoplankton and sulfur compounds might be offset, to some degree, by the input of nutrient‐rich dust.

Continue reading ‘Springtime spatial distributions of biogenic sulfur compounds in the Yangtze river estuary and their responses to seawater acidification and dust’

The dual benefit of ocean acidification for the laminarialean kelp, Saccharina latissima: enhanced growth and reduced herbivory

The laminarialean kelp, Saccharina latissima, is a common macroalgae along rocky shorelines that is also frequently used in aquaculture. This study examined how ocean acidification may alter the growth of S. latissima as well as grazing on S. latissima by the gastropod, Lacuna vincta. Under elevated nutrients, S. latissima experienced significantly enhanced growth at pCO2 levels >1,200 µatm compared to ambient pCO2 (~400 µatm). Elevated pCO2 (>830 µatm) also significantly reduced herbivory of L. vincta grazing on S. latissima relative to ambient pCO2. There was no difference in grazing of S. latissima previously grown under elevated or ambient pCO2, suggesting lowered herbivory was due to harm to the gastropods rather than alteration of the biochemical composition of the kelp. Decreased herbivory was specifically elicited when L. vincta were exposed to elevated pCO2 in the absence of food for >18 h prior to grazing, with reduced grazing persisting 72 h. Elevated growth of S. latissima and reduced grazing by L. vincta at 1,200 µatm pCO2 combined to increase net growth rates of S. latissima by more than four-fold relative to ambient pCO2L. vincta consumed 70% of daily production by S. latissima under ambient pCO2 but only 38% and 9% at 800 µatm and 1,200 µatm, respectively. Collectively, decreased grazing by L. vincta coupled with enhanced growth of S. latissima under elevated pCO2 demonstrates that increased CO2 associated with climate change and/or coastal processes will dually benefit commercially and ecologically important kelps by both promoting growth and reducing grazing pressure. 

Continue reading ‘The dual benefit of ocean acidification for the laminarialean kelp, Saccharina latissima: enhanced growth and reduced herbivory’

Photosynthesis and calcification of the coccolithophore Emiliania huxleyi are more sensitive to changed levels of light and CO2 under nutrient limitation

Highlights

  • Nutrient limitation reduced the light intensity for cells to achieve the highest rates of photosynthesis and calcification.
  • Nitrate limitation enhanced calcification rate and phosphate limitation reduced photosynthetic rate.
  • Electron transport rate linearly and positively correlated with rates of photosynthesis and calcification.

Abstract

Photophysiological responses of phytoplankton to changing multiple environmental drivers are essential in understanding and predicting ecological consequences of ocean climate changes. In this study, we investigated the combined effects of two CO2 levels (410 and 925 μatm) and five light intensities (80 to 480 μmol photons m−2 s−1) on cellular pigments contents, photosynthesis and calcification of the coccolithophore Emiliania huxleyi grown under nutrient replete and limited conditions, respectively. Our results showed that high light intensity, high CO2 level and nitrate limitation acted synergistically to reduce cellular chlorophyll a and carotenoid contents. Nitrate limitation predominantly enhanced calcification rate; phosphate limitation predominantly reduced photosynthetic carbon fixation rate, with larger extent of the reduction under higher levels of CO2 and light. Reduced availability of both nitrate and phosphate under the elevated CO2 concentration decreased saturating light levels for the cells to achieve the maximal relative electron transport rate (rETRmax). Light-saturating levels for rETRmax were lower than that for photosynthetic and calcification rates under the nutrient limitation. Regardless of the culture conditions, rETR under growth light levels correlated linearly and positively with measured photosynthetic and calcification rates. Our findings imply that E. huxleyi cells acclimated to macro-nutrient limitation and elevated CO2 concentration decreased their light requirement to achieve the maximal electron transport, photosynthetic and calcification rates, indicating a photophysiological strategy to cope with CO2 rise/pH drop in shoaled upper mixing layer above the thermocline where the microalgal cells are exposed to increased levels of light and decreased levels of nutrients.

Continue reading ‘Photosynthesis and calcification of the coccolithophore Emiliania huxleyi are more sensitive to changed levels of light and CO2 under nutrient limitation’

Phosphorus enrichment masked the negative effects of ocean acidification on picophytoplankton and photosynthetic performance in the oligotrophic Indian Ocean

Highlights

  • High pCO2 and P interactively increased the abundances of Syn, Pro and PEuks.
  • Rising pCO2 alone decreased the abundances of Syn, Pro and PEuks.
  • Elevated pCO2 alone facilitated the NPQNSV process significantly.
  • There was a strong coupling of picophytoplankton and the charge separation rates.
  • P enrichment masked the negative effects of OA on picophytoplankton and photosynthesis.

Abstract

Dynamics of picophytoplankton and photosynthesis will be inevitably impacted by changing marine environment, such as ocean acidification and nutrient supply, but related studies are very scarce. Here we cultured the picophytoplankton-dominated surface water of the oligotrophic Eastern Indian Ocean (EIO; R/V Shiyan-3, 20 March to 18 May 2019) at two levels of pCO2 (400 and 1000 ppm) and phosphate (0.05 and 1.50 µM) to investigate the interactive effects of elevated pCO2 and phosphate (P) on the dynamics of picophytoplankton and photosynthetic properties. High pCO2 and P levels interactively increased the abundances of SynechococcusProchlorococcus and picoeukaryotes by 33%, 18%, and 21%, respectively, of which high P level had a major promoting effect. Conversely, rising pCO2 alone decreased their abundances by 9%, 32%, and 46%, respectively. For the photophysiological responses in relation to the combination of high pCO2 and P levels, there was an increase in the maximum (Fv/Fm) and effective (Fq‘/Fm‘) photochemical efficiency, the electron transfer rates (ETRRCII) and the charge separation rates (JVPSII, an indicator of primary production), but a decrease in the non-photochemical quenching (NPQNSV). Elevated pCO2 alone facilitated the NPQNSV process significantly, ultimately leading to reduced light use efficiency (e.g., Fv/Fm, Fq‘/Fm‘ and ETRRCII) and primary production (JVPSII). There was a strong coupling of picophytoplankton and JVPSII, suggesting the EIO primary productivity was potentially controlled by picophytoplankton. Overall, our results indicate that the negative effects caused by ocean acidification may be masked or outweighted by the role that P availability plays in regulating growth and metabolism in this oligotrophic ecosystem.

Continue reading ‘Phosphorus enrichment masked the negative effects of ocean acidification on picophytoplankton and photosynthetic performance in the oligotrophic Indian Ocean’

Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica

Coastal ecosystems are prone to multiple anthropogenic and natural stressors including eutrophication, acidification, and invasive species. While the growth of some macroalgae can be promoted by excessive nutrient loading and/or elevated pCO2, responses differ among species and ecosystems. Native to the western Pacific Ocean, the filamentous, turf-forming rhodophyte, Dasysiphonia japonica, appeared in estuaries of the northeastern Atlantic Ocean during the 1980s and the northwestern Atlantic Ocean during the late 2000s. Here, we report on the southernmost expansion of the D. japonica in North America and the effects of elevated nutrients and elevated pCO2 on the growth of D. japonica over an annual cycle in Long Island, New York, USA. Growth limitation of the macroalga varied seasonally. During winter and spring, when water temperatures were < 15 °C, growth was significantly enhanced by elevated pCO2 (p < 0.05). During summer and fall, when the water temperature was 15–24 °C, growth was significantly higher under elevated nutrient treatments (p < 0.05). When temperatures reached 28 °C, the macroalga grew poorly and was unaffected by nutrients or pCO2. The δ13C content of regional populations of D. japonica was −30‰, indicating the macroalga is an obligate CO2-user. This result, coupled with significantly increased growth under elevated pCO2 when temperatures were < 15 °C, indicates this macroalga is carbon-limited during colder months, when in situ pCO2 was significantly lower in Long Island estuaries compared to warmer months when estuaries are enriched in metabolically derived CO2. The δ15N content of this macroalga (9‰) indicated it utilized wastewater-derived N and its N limitation during warmer months coincided with lower concentrations of dissolved inorganic N in the water column. Given the stimulatory effect of nutrients on this macroalga and that eutrophication can promote seasonally elevated pCO2, this study suggests that eutrophic estuaries subject to peak annual temperatures < 28 °C may be particularly vulnerable to future invasions of D. japonica as ocean acidification intensifies. Conversely, nutrient reductions would serve as a management approach that would make coastal regions more resilient to invasions by this macroalga.

Continue reading ‘Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica’

Windows of vulnerability: seasonal mismatches in exposure and resource identity determine ocean acidification’s effect on a primary consumer at high latitude

It is well understood that differences in the cues used by consumers and their resources in fluctuating environments can give rise to trophic mismatches governing the emergent effects of global change. Trophic mismatches caused by changes in consumer energetics during periods of low resource availability have received far less attention, although this may be common for consumers during winter when primary producers are limited by light. Even less is understood about these dynamics in marine ecosystems, where consumers must cope with energetically costly changes in CO2‐driven carbonate chemistry that will be most pronounced in cold temperatures. This may be especially important for calcified marine herbivores, such as the pinto abalone (Haliotis kamschatkana). H. kamschatkana are of high management concern in the North Pacific due to the active recreational fishery and their importance among traditional cultures, and research suggests they may require more energy to maintain their calcified shells and acid/base balance with ocean acidification. Here we use field surveys to demonstrate seasonal mismatches in the exposure of marine consumers to low pH and algal resource identity during winter in a subpolar, marine ecosystem. We then use these data to test how the effects of exposure to seasonally relevant pH conditions on H. kamschatkana are mediated by seasonal resource identity. We find that exposure to projected future winter pH conditions decreases metabolism and growth, and this effect on growth is pronounced when their diet is limited to the algal species available during winter. Our results suggest that increases in the energetic demands of pinto abalone caused by ocean acidification during winter will be exacerbated by seasonal shifts in their resources. These findings have profound implications for other marine consumers and highlight the importance of considering fluctuations in exposure and resources when inferring the emergent effects of global change.

Continue reading ‘Windows of vulnerability: seasonal mismatches in exposure and resource identity determine ocean acidification’s effect on a primary consumer at high latitude’

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