Andrew T. Revill

The effects of varying CO2 concentration on lipid composition and carbon isotope fractionation in Emiliania huxleyi.

We have measured the stable carbon isotopic composition of bulk organic matter (POC), alkenones, sterols, fatty acids, and phytol in the coccolithophorid Emiliania huxleyi grown in dilute batch cultures over a wide range of CO2 concentrations (1.1–53.5 μmol L−1). The carbon isotope fractionation of POC (ePOC) varied by ca. 7‰ and was positively correlated with aqueous CO2 concentration [CO2aq]. While this result confirms general trends observed for the same alga grown in nitrogen-limited chemostat cultures, considerable differences were obtained in absolute values of ePOC and in the slope of the relationship of ePOC with growth rate and [CO2aq]. Also, a significantly greater offset was obtained between the δ13C of alkenones and bulk organic matter in this study compared with previous work (5.4, cf. 3.8‰). This suggests that the magnitude of the isotope offset may depend on growth conditions. Relative to POC, individual fatty acids were depleted in 13C by 2.3‰ to 4.1‰, phytol was depleted in 13C by 1.9‰, and the major sterol 24-methylcholesta-5,22E-dien-3β-ol was depleted in 13C by 8.5‰. This large spread of δ13C values for different lipid classes in the same alga indicates the need for caution in organic geochemical studies when assigning different sources to lipids that might have δ13C values differing by just a few ‰. Increases in [CO2aq] led to dramatic increases in the alkenone contents per cell and as a proportion of organic carbon, but there was no systematic effect on values of U37k′ used for reconstructions of paleo sea surface temperature.

Archaeal ammonia oxidizers and nirS -type denitrifiers dominate sediment nitrifying and denitrifying populations in a subtropical macrotidal estuary

Nitrification and denitrification are key steps in nitrogen (N) cycling. The coupling of these processes, which affects the flow of N in ecosystems, requires close interaction of nitrifying and denitrifying microorganisms, both spatially and temporally. The diversity, temporal and spatial variations in the microbial communities affecting these processes was examined, in relation to N cycling, across 12 sites in the Fitzroy river estuary, which is a turbid subtropical estuary in central Queensland. The estuary is a major source of nutrients discharged to the Great Barrier Reef near-shore zone. Measurement of nitrogen fluxes showed an active denitrifying community during all sampling months. Archaeal ammonia monooxygenase (amoA of AOA, functional marker for nitrification) was significantly more abundant than Betaproteobacterial (β-AOB) amoA. Nitrite reductase genes, functional markers for denitrification, were dominated by nirS and not nirK types at all sites during the year. AOA communities were dominated by the soil/sediment cluster of Crenarchaeota, with sequences found in estuarine sediment, marine and terrestrial environments, whereas nirS sequences were significantly more diverse (where operational taxonomic units were defined at both the threshold of 5% and 15% sequence similarity) and were closely related to sequences originating from estuarine sediments. Terminal-restriction fragment length polymorphism (T-RFLP) analysis revealed that AOA population compositions varied spatially along the estuary, whereas nirS populations changed temporally. Statistical analysis of individual T-RF dominance suggested that salinity and C:N were associated with the community succession of AOA, whereas the nirS-type denitrifier communities were related to salinity and chlorophyll-α in the Fitzroy river estuary.

The effects of nitrogen and water on mineralisation of hydrocarbons in diesel-contaminated terrestrial Antarctic soils

Bioremediation of petroleum-contaminated soil in the Antarctic will be logistically and technically difficult and will cost more than similar treatment in temperate regions or the Arctic because of the remote location and unfavourable environmental conditions. To optimise nutrient amendments for the remediation of a long-term hydrocarbon-contaminated site at Old Casey Station in Antarctica, we investigated the effects of nitrogen (and phosphorus) amendments on microbial mineralisation using radiometric microcosm experiments and gas chromatography. Hydrocarbon mineralisation at nine different inorganic nitrogen concentrations (ranging from 85 to over 27,000 mg N kg-soil-H2O−1) was monitored over 95-day incubation at 10 °C. Total 14C-octadecane mineralisation increased with increasing nutrient concentration peaking in the range 1000–1600 mg N kg-soil-H2O−1. The microcosms with the lowest and highest concentrations of N had extended lag phases of over 12.5 days prior to significant mineralisation. Gas chromatographic analysis of the aliphatic components of Special Antarctic Blend (SAB) diesel in the contaminated soil showed good agreement with the 14C-octadecane mineralisation outcomes. Ratios of n-C17/pristane and n-C18/phytane indicated that low nutrient concentrations rather than water were the main limiting factor for biodegradation of hydrocarbons in the soil collected from Old Casey Station when incubated at 10 °C. However, because the soils from this site are characterised by low water holding capacities, it would be difficult to maintain optimal nutrient concentrations during full-scale treatment, and thus the use of a controlled release nutrient is being considered as a nutrient source in the bioremediation of SAB-contaminated Antarctic soils.

Hydrocarbon biomarkers, thermal maturity, and depositional setting of tasmanite oil shales from Tasmania, Australia

This study represents the first geological and organic geochemical investigation of samples of tasmanite oil shale representing different thermal maturities from three separate locations in Tasmania, Australia. The most abundant aliphatic hydrocarbon in the immature oil shale from Latrobe is a C19 tricyclic alkane, whereas in the more mature samples from Oonah and Douglas River low molecular weight n-alkanes dominate the extractable hydrocarbon distribution. The aromatic hydrocarbons are predominantly derivatives of tricyclic compounds, with 1,2,8-trimethylphenanthrene increasing in relative abundance with increasing maturity. Geological and geochemical evidence suggests that the sediments were deposited in a marine environment of high latitude with associated cold waters and seasonal seaice. It is proposed that the organism contributing the bulk of the kerogen, Tasmanites, occupied an environmental niche similar to that of modern sea-ice diatoms and that bloom conditions coupled with physical isolation from atmospheric CO2 led to the distinctive “isotopically heavy” δ13C values (−13.5‰ to −11.7‰) for the kerogen. δ13C data from modern sea-ice diatoms (−7‰) supports this hypothesis. Isotopic analysis of n-alkanes in the bitumen (−13.5 to −31‰) suggest a multiple source from bacteria and algae. On the other hand, the n-alkanes generated from closed-system pyrolysis of the kerogen (−15‰) are mainly derived from the preserved Tasmanites biopolymer algaenan. The tricyclic compounds (mean −8‰) both in the bitumen and pyrolysate, have a common precursor. They are consistently enriched in 13C compared with the kerogen and probably have a different source from the n-alkanes. The identification of a location where the maturity of the tasmanite oil shale approaches the “oil window” raises the possibility that it may be a viable petroleum source rock.

Ocean acidification reverses the positive effects of seawater pH fluctuations on growth and photosynthesis of the habitat-forming kelp, Ecklonia radiata

Ocean acidification (OA) is the reduction in seawater pH due to the absorption of human-released CO2 by the world’s oceans. The average surface oceanic pH is predicted to decline by 0.4 units by 2100. However, kelp metabolically modifies seawater pH via photosynthesis and respiration in some temperate coastal systems, resulting in daily pH fluctuations of up to ±0.45 units. It is unknown how these fluctuations in pH influence the growth and physiology of the kelp, or how this might change with OA. In laboratory experiments that mimicked the most extreme pH fluctuations measured within beds of the canopy-forming kelp Ecklonia radiata in Tasmania, the growth and photosynthetic rates of juvenile E. radiata were greater under fluctuating pH (8.4 in the day, 7.8 at night) than in static pH treatments (8.4, 8.1, 7.8). However, pH fluctuations had no effect on growth rates and a negative effect on photosynthesis when the mean pH of each treatment was reduced by 0.3 units. Currently, pH fluctuations have a positive effect on E. radiata but this effect could be reversed in the future under OA, which is likely to impact the future ecological dynamics and productivity of habitats dominated by E. radiata.

Effects of estuarine sediment hypoxia on nitrogen fluxes and ammonia oxidizer gene transcription

The effects of sediment hypoxia, resulting from increased carbon loads or decreased dissolved oxygen (DO), on nitrogen cycling in estuarine environments is poorly understood. The important role played by bacterial and archaeal ammonia oxidizers in the eventual removal of nitrogen from estuarine environments is likely to be strongly affected by hypoxic events. In this study, an analysis of the effects of different levels of sediment hypoxia (5%, 20% and 75% DO) was performed in a microcosm experiment. Changes in the nutrient fluxes related to nitrification at 5% DO were observed after 4 h. Quantification of the key nitrification gene ammonium monooxygenase (amoA) in both DNA and RNA extracts suggests that bacterial amoA transcription was reduced at both of the lower DO concentrations, while changes in DO had no significant effect on archaeal amoA transcription. There was no change in the diversity of expressed archaeal amoA, but significant change in bacterial amoA transcriptional diversity, indicative of low- and high-DO phylotypes. This study suggests that groups of ammonia oxidizers demonstrate differential responses to changes in sediment DO, which may be a significant factor in niche partitioning of different ammonia oxidizer groups.

Inorganic carbon physiology underpins macroalgal responses to elevated CO2

Beneficial effects of CO2 on photosynthetic organisms will be a key driver of ecosystem change under ocean acidification. Predicting the responses of macroalgal species to ocean acidification is complex, but we demonstrate that the response of assemblages to elevated CO2 are correlated with inorganic carbon physiology. We assessed abundance patterns and a proxy for CO2:HCO3− use (δ13C values) of macroalgae along a gradient of CO2 at a volcanic seep, and examined how shifts in species abundance at other Mediterranean seeps are related to macroalgal inorganic carbon physiology. Five macroalgal species capable of using both HCO3− and CO2 had greater CO2 use as concentrations increased. These species (and one unable to use HCO3−) increased in abundance with elevated CO2 whereas obligate calcifying species, and non-calcareous macroalgae whose CO2 use did not increase consistently with concentration, declined in abundance. Physiological groupings provide a mechanistic understanding that will aid us in determining which species will benefit from ocean acidification and why.

Sources of nutrients driving production in the Gulf of Carpentaria, Australia: a shallow tropical shelf system

The tropical Gulf of Carpentaria, Australia, has recently been identified as one of the world’s least impacted marine areas, presenting a unique opportunity to understand the nutrient drivers of productivity. The present study examined the nitrogen (N) sources and transformations in this pristine area and the role of N in fuelling primary productivity, principally based on summer data. The N budget estimates on a whole-of-Gulf basis suggest that river N inputs are unlikely to be major contributors to primary productivity. In the deeper waters of the Gulf, beyond the coastal boundary current, the main source of N is estimated to be N fixation by cyanobacteria, principally the abundant genus Trichodesmium. The present study measured high N fixation rates and depleted δ15N–N ratios in the particulate matter in the water column during a summer bloom. During summer, bottom N concentrations increased and δ15N–N ratios were depleted, suggesting that benthic mineralisation is occurring. It is therefore likely that detrital material from N-rich Trichodesmium is an important contributor to benthic processes. During winter, wind-driven mixing results in N from the bottom waters reaching the euphotic zone, and fuelling primary productivity. Therefore, Trichodesmium has an important direct and indirect role in contributing to primary productivity in this pristine tropical ecosystem.

A biochemical approach for identifying plastics exposure in live wildlife

Summary Plastic pollution is a long-standing ubiquitous issue. Global use of plastics is continuing to rise, and there is increasing interest in understanding the prevalence and risk associated with exposure of wildlife to plastics, particularly in the marine environment. In order To facilitate an assessment of ingestion of plastics in seabird populations, we developed a minimally invasive tool that allows for detection of exposure to plastics. Using a simple swabbing technique in which the waxy preen oil is expressed from the uropygial gland of birds, we successfully tested for the presence of three common plasticizers: dimethyl, dibutyl and diethylhexyl phthalate [dimethyl phthalate, dibutyl phthalate and bis(2-ethylhexyl)-phthalate, respectively]. These plasticizers are prevalent in the manufacturing of plastic end-user items which often end up in the marine environment. Using gas chromatography–mass spectrometry and protocols to reduce background contamination, we were confidently able to detect targeted plasticizers at low levels. The method described has broad applicability for detecting plastics exposure in wildlife at individual, population and species levels. Furthermore, the approach can be readily modified as needed to survey for plastics exposure in taxa other than seabirds. Applying the simple, minimally invasive approach we describe here is particularly appealing for detecting plastics exposure at population and species levels, it shows promise for quantification and it has no observed detrimental impacts to wildlife.

Transcriptomic, lipid, and histological profiles suggest changes in health in fish from a pesticide hot spot

Barramundi (Lates calcarifer) were collected at the beginning (1st sampling) and end (2nd sampling) of the wet season from Sandy Creek, an agriculturally impacted catchment in the Mackay Whitsundays region of the Great Barrier Reef catchment area, and from Repulse Creek, located approximately 100 km north in Conway National Park, to assess the impacts of pesticide exposure. Gill and liver histology, lipid class composition in muscle, and the hepatic transcriptome were examined. The first sample of Repulse Creek fish showed little tissue damage and low transcript levels of xenobiotic metabolism enzymes. Sandy Creek fish showed altered transcriptomic patterns, including those that regulate lipid metabolism, xenobiotic metabolism, and immune response; gross histological alterations including lipidosis; and differences in some lipid classes. The second sampling of Repulse Creek fish showed similar alterations in hepatic transcriptome and tissue structure as fish from Sandy Creek. These changes may indicate a decrease in health of pesticide exposed fish.