Archive for August, 2017



Ecological energetic perspectives on responses of nitrogen-transforming chemolithoautotrophic microbiota to changes in the marine environment

Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere, and hydrosphere constitute the Earth’s biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. The diverse bioenergetic pathways and eco-energetic strategies of the microorganisms are essentially the outcome of biosphere-geosphere interactions over evolutionary times. The biogeochemical cycles are intimately interconnected with energy fluxes across the biosphere and the capacity of the ocean to fix inorganic carbon is generally constrained by the availability of nutrients and energy. The understanding of how microbial eco-energetic processes influence the structure and function of marine ecosystems and how they interact with the changing environment is thus fundamental to a mechanistic and predictive understanding of the marine carbon and nitrogen cycles and the trends in global change. By using major groups of chemolithoautotrophic microorganisms that participate in the marine nitrogen cycle as examples, this article examines their eco-energetic strategies, contributions to carbon cycling, and putative responses to and impacts on the various global change processes associated with global warming, ocean acidification, eutrophication, deoxygenation, and pollution. We conclude that knowledge gaps remain despite decades of tremendous research efforts. The advent of new techniques may bring the dawn to scientific breakthroughs that necessitate the multidisciplinary combination of eco-energetic, biogeochemical and “omics” studies in this field.

Continue reading ‘Ecological energetic perspectives on responses of nitrogen-transforming chemolithoautotrophic microbiota to changes in the marine environment’

The organizing effects of elevated CO2 on competition among estuarine primary producers

Fossil fuel combustion, eutrophication, and upwelling introduce excess CO2 into coastal zones. The extent to which marine autotrophs may benefit from elevated CO2 will be a function of their carbon limitation and, among other factors, competition with other primary producers. Here, we report on experiments performed with North Atlantic species of Ulva and Gracilaria grown in situ or exposed to ambient (~400 µatm) and elevated pCO2 (~2500 µatm) and/or subjected to competition with each other and/or with natural plankton assemblages. Elevated pCO2significantly increased the growth rates of Gracilaria and Ulva and yielded significant declines in tissue δ13C, suggesting that increased growth was associated with increased CO2 use relative to HCO3−. Gracilaria growth was unaffected by competition with plankton or Ulva, while Ulva experienced significantly reduced growth when competing with Gracilaria or plankton. Dinoflagellates experienced significantly increased growth when exposed to elevated pCO2 but significantly slower growth when competing with Gracilaria. Elevated carbon-to-nitrogen ratios among macroalgae suggested that competition for nitrogen also shaped interactions among autotrophs, particularly Ulva. While some estuarine autotrophs benefit from elevated pCO2, the benefit can change when direct competition with other primary producers is considered with Gracilaria outcompeting Ulva and dinoflagellates outcompeting diatoms under elevated pCO2.

Continue reading ‘The organizing effects of elevated CO2 on competition among estuarine primary producers’

Biochemical composition of turbinid snails and its sensitivity to ocean climate change

Information on the biochemical composition of under-utilised species, such as turban snails, is required to establish their nutritional quality, and improve consumer acceptance as a novel food source. Turbo militaris, Lunella undulata and L. torquata are large common gastropod species with overlapping distributions in eastern Australia. The edible foot tissue from these three species was analysed for comparison of their proximate composition, fatty acids and mineral elements. All species were found to have a high protein content and low lipid levels that are rich in polyunsaturated fatty acids (PUFAs), with a favourable ratio of omega–3/omega–6 PUFAs for human consumption. Turban snails also provide a good source of essential elements. To quantify the temporal changes in nutritional properties, L. undulata was collected monthly from the same site, Evans head, NSW from December 2013 to January 2015. Sex, shell sizes and gonadosomatic index (GSI) were recorded in order to investigate if these parameters influence the condition index (CI), meat yield (MY), proximate composition and trace elements of the edible foot tissue. The flesh of L. undulata can be considered nutritious and generally safe for human consumption all year round, but for the purpose of sustainable harvest, the peak spawning should be avoided to allow for successful reproduction. A manipulative experiment to investigate the effects of 38-day exposure to near-future ocean warming and acidification revealed that temperature alone affects the percentages of PUFAs in the foot tissue. Nevertheless, the main nutritional properties of high protein and low lipids dominated by PUFAs were consistently found in the Turbinidae. Toxic heavy metal elements remained well below the maximum allowed under Australia and New Zealand Food Standards. Based on their upper thermal limit, turban snails may be resilient to near-future ocean-warming, but they prefer lower temperatures, which could result in a southward retraction of the distribution of these species in NSW, Australia. Overall, this study shows that turban snails can provide a fisheries resource of similar quality to abalone, but ocean warming may influence the range of the target populations and the quality of lipids, but the product would be otherwise little-affected.

Continue reading ‘Biochemical composition of turbinid snails and its sensitivity to ocean climate change’

Global and local disturbances interact to modify seagrass palatability

Global change, such as warming and ocean acidification, and local anthropogenic disturbances, such as eutrophication, can have profound impacts on marine organisms. However, we are far from being able to predict the outcome of multiple interacting disturbances on seagrass communities. Herbivores are key in determining plant community structure and the transfer of energy up the food web. Global and local disturbances may alter the ecological role of herbivory by modifying leaf palatability (i.e. leaf traits) and consequently, the feeding patterns of herbivores. This study evaluates the main and interactive effects of factors related to global change (i.e. elevated temperature, lower pH levels and associated ocean acidification) and local disturbance (i.e. eutrophication through ammonium enrichment) on a broad spectrum of leaf traits using the temperate seagrass Cymodocea nodosa, including structural, nutritional, biomechanical and chemical traits. The effect of these traits on the consumption rates of the generalist herbivore Paracentrotus lividus (purple sea urchin) is evaluated. The three disturbances of warming, low pH level and eutrophication, alone and in combination, increased the consumption rate of seagrass by modifying all leaf traits. Leaf nutritional quality, measured as nitrogen content, was positively correlated to consumption rate. In contrast, a negative correlation was found between feeding decisions by sea urchins and structural, biomechanical and chemical leaf traits. In addition, a notable accomplishment of this work is the identification of phenolic compounds not previously reported for C. nodosa. Our results suggest that global and local disturbances may trigger a major shift in the herbivory of seagrass communities, with important implications for the resilience of seagrass ecosystems.

Continue reading ‘Global and local disturbances interact to modify seagrass palatability’

Boron isotope sensitivity to seawater pH change in a species of Neogoniolithon coralline red alga

The increase in atmospheric carbon dioxide (CO2) observed since the industrial revolution has reduced surface ocean pH by ∼0.1 pH units, with further change in the oceanic system predicted in the coming decades. Calcareous organisms can be negatively affected by extreme changes in seawater pH (pHsw) such as this due to the associated changes in the oceanic carbonate system. The boron isotopic composition (δ11B) of biogenic carbonates has been previously used to monitor pH at the calcification site (pHcf) in scleractinian corals, providing mechanistic insights into coral biomineralisation and the impact of variable pHsw on this process. Motivated by these investigations, this study examines the δ11B of the high-Mg calcite skeleton of the coralline red alga Neogoniolithon sp. to constrain pHcf, and investigates how this taxon’s pHcf is impacted by ocean acidification. δ11B was measured in multiple algal replicates (n = 4 to 5) cultured at four different pCO2 scenarios – averaging (± 1σ) 409 (± 6), 606 (± 7), 903 (± 12) and 2856 (± 54) μatm, corresponding to average pHsw (± 1σ) of 8.19 (± 0.03), 8.05 (± 0.06), 7.91 (± 0.03) and 7.49 (± 0.02) respectively. Results show that skeletal δ11B is elevated relative to the δ11B of seawater borate at all pHsw treatments by up to 18 ‰. Although substantial variability in δ11B exists between replicate samples cultured at a given pHsw (smallest range = 2.32 ‰ at pHsw 8.19, largest range = 6.08 ‰ at pHsw 7.91), strong correlations are identified between δ11B and pHsw (R2 = 0.72, p < 0.0001, n = 16) and between δ11B and B/Ca (R2 = 0.72, p < 0.0001, n = 16). Assuming that skeletal δ11B reflects pHcf as previously observed for scleractinian corals, the average pHcf across all experiments was 1.20 pH units (0.79 to 1.56) higher than pHsw, with the magnitude of this offset varying parabolically with decreasing pHsw, with a maximum difference between pHsw and pHcf at a pHsw of 7.91. Observed relationships between pHsw and calcification rate, and between pHsw and pHcf, suggest that coralline algae exhibit some resilience to moderate ocean acidification via increase of pHcf relative to pHsw in a similar manner to scleractinian corals. However, these results also indicate that pHcf cannot be sufficiently increased by algae exposed to a larger reduction in pHsw, adversely impacting calcification rates of coralline red algae.

Continue reading ‘Boron isotope sensitivity to seawater pH change in a species of Neogoniolithon coralline red alga’

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

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

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’

Effect of CO2-induced seawater acidification on growth, photosynthesis and inorganic carbon acquisition of the harmful bloom-forming marine microalga, Karenia mikimotoi

Karenia mikimotoi is a widespread, toxic and non-calcifying dinoflagellate, which can release and produce ichthyotoxins and hemolytic toxins affecting the food web within the area of its bloom. Shifts in the physiological characteristics of K. mikimotoi due to CO2-induced seawater acidification could alter the occurrence, severity and impacts of harmful algal blooms (HABs). Here, we investigated the effects of elevated pCO2 on the physiology of K. mikimotoi. Using semi-continuous cultures under controlled laboratory conditions, growth, photosynthesis and inorganic carbon acquisition were determined over 4–6 week incubations at ambient (390ppmv) and elevated pCO2 levels (1000 ppmv and 2000 ppmv). pH-drift and inhibitor-experiments suggested that K. mikimotoi was capable of acquiring HCO3-, and that the utilization of HCO3-was predominantly mediated by anion-exchange proteins, but that HCO3- dehydration catalyzed by external carbonic anhydrase (CAext) only played a minor role in K. mikimotoi. Even though down-regulated CO2 concentrating mechanisms (CCMs) and enhanced gross photosynthetic O2 evolution were observed under 1000 ppmv CO2 conditions, the saved energy did not stimulate growth of K. mikimotoi under 1000 ppmv CO2, probably due to the increased dark respiration. However, significantly higher growth and photosynthesis [in terms of photosynthetic oxygen evolution, effective quantum Yield (Yield), photosynthetic efficiency (α), light saturation point (Ek) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity] were observed under 2000 ppmv CO2 conditions. Furthermore, elevated pCO2increased the photo-inhibition rate of photosystem II (β) and non-photochemical quenching (NPQ) at high light. We suggest that the energy saved through the down-regulation of CCMs might lead to the additional light stress and photo-damage. Therefore, the response of this species to elevated CO2 conditions will be determined by more than regulation and efficiency of CCMs.

Continue reading ‘Effect of CO2-induced seawater acidification on growth, photosynthesis and inorganic carbon acquisition of the harmful bloom-forming marine microalga, Karenia mikimotoi’

Effects of ocean acidification and contact with the brown alga Stypopodium zonale on the settlement and early survival of the coral Porites astreoides

To evaluate the effects of ocean acidification (OA) and algal presence on the early life-history stages of corals, we conducted an aquarium study that examined the isolated and combined effects of reduced pH (pH 8.10 vs. 7.85) and contact with the alga Stypopodium zonale on the survival, settlement, and post-settlement growth of larvae from the brooding coral Porites astreoides. Two settlement substrates, biofilmed tiles and the crustose coralline alga (CCA) Hydrolithon boergesenii, were initially incubated for 12 d in separate tanks under a factorial combination of low pH and S. zonale contact, and then subjected to a series of settlement assays. Across both substrate types, S. zonale presence significantly reduced coral settlement. Low pH imposed relatively minor effects; however, there was a significant interaction between pH and S. zonale presence for settlement on the CCA substrate, such that low pH exacerbated the negative effects of S. zonale. Post-settlement growth for 2 wk was unaffected by either S. zonale presence or low pH on either substrate. While our results demonstrate that S. zonale contact likely remains a dominant threat to larval survival and settlement, in certain cases, OA may amplify the negative effects of S. zonale presence, highlighting the need to consider multiple factors in studies aimed at assessing the future health of coral reef ecosystems.

Continue reading ‘Effects of ocean acidification and contact with the brown alga Stypopodium zonale on the settlement and early survival of the coral Porites astreoides’

Morphological response of the larvae of Arbacia lixula to near-future ocean warming and acidification

The distribution of the sea urchin Arbacia lixula, a warm affinity species, has been expanding in the Mediterranean Sea. To address questions on potential for future success of this species in the region, the thermotolerance of larval development was investigated in context of regional warming. The larvae were reared in present day spawning period (20 °C) and warming conditions (+4 = 24 and +6 = 26 °C). As the calcifying larvae of sea urchins are vulnerable to stunted growth caused by ocean acidification, the impact of lower pH (−0.3 pH units) on larval development was also investigated in combination with warming. Morphological traits of the larvae, post-oral length arms, overall length of larvae and body length, were affected by increased temperature across pH treatments, indicating that for the larvae of southern Mediterranean population here, 24 °C appears to approximate the optimal temperature for development. A slightly negative effect of pH was evident. Increased temperature ameliorated the stunting effect of acidification on growth. The thermal tolerance of A. lixula development overlaps with projections for warming in the region by 2100 and also indicates that this species has acclimatized or adapted its reproductive biology to the broad environmental conditions of the Mediterranean Sea. Due to the broad thermal range (∼10 °C) of development of A. lixula across its distribution, this species is likely to be a winner in the climate change stakes. The broad thermal tolerance of the larvae is likely to assure population connectivity between Mediterranean sub-basins populations. The continued success of A. lixula can have a strong consequences for the ecological structure of Mediterranean rocky habitat.

Continue reading ‘Morphological response of the larvae of Arbacia lixula to near-future ocean warming and acidification’


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