Algal Carbon Research Articles

Periplasmic carbonic anhydrase CAH1 contributes to high inorganic carbon affinity in Chlamydomonas reinhardtii.

Carbonic anhydrase (CA), an enzyme conserved across species, is pivotal in the interconversion of inorganic carbon (Ci; CO2 and HCO3-). Compared to the well-studied intracellular CA, the specific role of extracellular CA in photosynthetic organisms is still not well understood. In the green alga Chlamydomonas (Chlamydomonas reinhardtii), carbonic anhydrase 1 (CAH1), located at the periplasmic space, is strongly induced under CO2-limiting conditions by the Myb transcription factor LCR1. While the lcr1 mutant shows decreased Ci-affinity, the detailed mechanisms behind this phenomenon are yet to be elucidated. In this study, we aimed to unravel the LCR1-dependent genes essential for maintaining high Ci-affinity. To achieve this, we identified a total of 12 LCR1-dependent inducible genes under CO2-limiting conditions, focusing specifically on the most prominent ones - CAH1, LCI1, LCI6, and Cre10.g426800. We then created mutants of these genes using the CRISPR-Cas9 system, all from the same parental strain, and compared their Ci-affinity. Contrary to earlier findings that reported no reduction in Ci-affinity in the cah1 mutant, our cah1-1 mutant exhibited a decrease in Ci-affinity under high HCO3-/CO2-ratio conditions. Additionally, when we treated wild-type cells with a CA inhibitor with low membrane permeability, a similar reduction in Ci-affinity was observed. Moreover, the addition of exogenous CA to the cah1 mutant rescued the decreased Ci-affinity. These results, highlighting the crucial function of the periplasmic CAH1 in maintaining high Ci-affinity in Chlamydomonas cells, provide insights into the functions of periplasmic CA in algal carbon assimilation.

Seasonal patterns of phytoplankton photoacclimation in a dimictic oligotrophic lake over 5 yr: Implications for chlorophyll as an estimate of biomass

AbstractChlorophyll a is commonly used as a surrogate for algal biomass in lakes and oceans even though phytoplankton can readily adjust intracellular chlorophyll concentration to changes in the environment through a cellular process termed photoacclimation. Marine studies have documented fluctuations in cellular chlorophyll to year‐round changes in light intensity and nutrients using the chlorophyll : carbon ratio to estimate cellular pigment density. However, similar freshwater studies are almost exclusively limited to chlorophyll : carbon ratios at the summertime deep chlorophyll maximum (DCM) depth in less productive water. This study expands direct estimates of freshwater photoacclimation to all seasons of the year utilizing optically derived estimates of algal carbon and chlorophyll fluorescence from high‐frequency (daily) data. We describe patterns of photoacclimation at daily, seasonal, and interannual time scales over a 5‐yr period. We show that increases in chlorophyll density at the cellular level not only occurred at the DCM depth during summer stratification but were a dominant and recurring feature when the lake was vertically mixing in fall, winter, and spring. Pigment density within the mixed layer was negatively correlated with light level, indicating a photoacclimation driven response to reduced light intensity. Predicting how cellular pigment density is affected by the surrounding environment in a replicated range of lake systems is needed if chlorophyll is to be accurately used as an estimate of algal biomass in freshwaters.

Metagenomic insights into the dynamic degradation of brown algal polysaccharides by kelp-associated microbiota.

Marine bacteria play important roles in the degradation and cycling of algal polysaccharides. However, the dynamics of epiphytic bacterial communities and their roles in algal polysaccharide degradation during kelp decay are still unclear. Here, we performed metagenomic analyses to investigate the identities and predicted metabolic abilities of epiphytic bacterial communities during the early and late decay stages of the kelp Saccharina japonica. During kelp decay, the dominant epiphytic bacterial communities shifted from Gammaproteobacteria to Verrucomicrobia and Bacteroidetes. In the early decay stage of S. japonica, epiphytic bacteria primarily targeted kelp-derived labile alginate for degradation, among which the gammaproteobacterial Vibrionaceae (particularly Vibrio) and Psychromonadaceae (particularly Psychromonas), abundant in alginate lyases belonging to the polysaccharide lyase (PL) families PL6, PL7, and PL17, were key alginate degraders. More complex fucoidan was preferred to be degraded in the late decay stage of S. japonica by epiphytic bacteria, predominantly from Verrucomicrobia (particularly Lentimonas), Pirellulaceae of Planctomycetes (particularly Rhodopirellula), Pontiellaceae of Kiritimatiellota, and Flavobacteriaceae of Bacteroidetes, which depended on using glycoside hydrolases (GHs) from the GH29, GH95, and GH141 families and sulfatases from the S1_15, S1_16, S1_17, and S1_25 families to depolymerize fucoidan. The pathways for algal polysaccharide degradation in dominant epiphytic bacterial groups were reconstructed based on analyses of metagenome-assembled genomes. This study sheds light on the roles of different epiphytic bacteria in the degradation of brown algal polysaccharides.IMPORTANCEKelps are important primary producers in coastal marine ecosystems. Polysaccharides, as major components of brown algal biomass, constitute a large fraction of organic carbon in the ocean. However, knowledge of the identities and pathways of epiphytic bacteria involved in the degradation process of brown algal polysaccharides during kelp decay is still elusive. Here, based on metagenomic analyses, the succession of epiphytic bacterial communities and their metabolic potential were investigated during the early and late decay stages of Saccharina japonica. Our study revealed a transition in algal polysaccharide-degrading bacteria during kelp decay, shifting from alginate-degrading Gammaproteobacteria to fucoidan-degrading Verrucomicrobia, Planctomycetes, Kiritimatiellota, and Bacteroidetes. A model for the dynamic degradation of algal cell wall polysaccharides, a complex organic carbon, by epiphytic microbiota during kelp decay was proposed. This study deepens our understanding of the role of epiphytic bacteria in marine algal carbon cycling as well as pathogen control in algal culture.

Year-round utilization of sea ice-associated carbon in Arctic ecosystems

Sea ice primary production is considered a valuable energy source for Arctic marine food webs, yet the extent remains unclear through existing methods. Here we quantify ice algal carbon signatures using unique lipid biomarkers in over 2300 samples from 155 species including invertebrates, fish, seabirds, and marine mammals collected across the Arctic shelves. Ice algal carbon signatures were present within 96% of the organisms investigated, collected year-round from January to December, suggesting continuous utilization of this resource despite its lower proportion to pelagic production. These results emphasize the importance of benthic retention of ice algal carbon that is available to consumers year-round. Finally, we suggest that shifts in the phenology, distribution and biomass of sea ice primary production anticipated with declining seasonal sea ice will disrupt sympagic-pelagic-benthic coupling and consequently the structure and the functioning of the food web which is critical for Indigenous Peoples, commercial fisheries, and global biodiversity.

Combined effects of microplastics and warming enhance algal carbon and nitrogen storage

Algae dominate primary production in groundwater and oceans and play a critical role in global carbon dioxide fixation and climate change but are threatened by ongoing global warming events (such as heatwaves) and increasing microplastic (MP) pollution. However, whether and how ecologically important phytoplankton respond to the combined effects of warming and MPs remain poorly understood. We thus investigated the combined effects of these factors on carbon and nitrogen storage and the mechanisms underlying the alterations in the physiological performance of a model diatom, Phaeodactylum tricornutum, exposed to a warming stressor (25 °C compared with 21 °C) and polystyrene MP acclimation. Although warmer conditions decreased the cell viability, the diatoms subjected to the synergistic effects of MPs and warming showed significant increases in the growth rate (1.10-fold) and nitrogen uptake rate (1.26-fold). Metabolomics and transcriptomic analyses revealed that MPs and warming mainly promoted fatty acid metabolism, the urea cycle, glutamine and glutamate production, and the tricarboxylic acid (TCA) cycle due to an increased level of 2-oxoglutarate, which is the hub of carbon and nitrogen metabolism and accounts for the acquisition and utilization of carbon and nitrogen. Our findings emphasize the nonnegligible effects of MPs and HWs on the algal carbon and nitrogen cycles in waters.

Tailoring structure and acidity of ZSM-5 zeolite by algae carbon modification: Promoting effect in the MTO reaction

A biochar obtained from algae (Trachydiscus minutus, TRA) with rich surface functional groups and metal ions was used as a hard template to efficiently synthesize modified ZSM-5 zeolites with high external surface area (ESA) and mild acidity. Compared with pristine ZSM-5, which exhibited an ESA of 121 m2/g, TRA/ZSM-5 modified with algal carbon yielded an ESA of 171 m2/g. In addition, the catalytic lifetime of TRA/ZSM-5 zeolite in the methanol-to-hydrocarbons (MTH) reaction was also greatly improved compared with H-ZSM-5: TRA/ZSM-5 maintained a methanol conversion >95% during 16 h (at 400 °C, WHSV = 8 h−1), whilst H-ZSM-5 could only last for 10 h. After further optimization, the lifespan of TRA/ZSM-5 could be further enhanced to 24 h. Finally, it could be shown that the presence of hydrophilic functional groups and heteroelements were the key parameters to enhance the ESA of the zeolite and reduce its Brønsted acidity.

A multi-trophic marker approach reveals high feeding plasticity in Barents Sea under-ice fauna

Microalgae growing within and attached to the bottom of Arctic sea ice (sympagic algae) can serve as a nutritious food resource for animals inhabiting the sea-ice water interface (under-ice fauna), particularly during the bottom ice-algal bloom in spring. As a consequence, under-ice fauna is likely impacted by sea-ice decline and changes in ice-algal primary production. To investigate this, samples of pelagic (=PPOM) and ice-associated particulate organic matter (=IPOM) and the ice-associated amphipods Apherusa glacialis and Eusirus holmii, and polar cod (Boreogadus saida), collected below ridged sea ice at two locations with pronounced differences in productivity in the northern Barents Sea during May 2021, were assessed for their trophic marker content. Specifically, we investigated the composition of diatom- and dinoflagellate-produced fatty acids (FAs), pelagic and sympagic highly branched isoprenoid (HBI) lipids as well as sterols to determine the animals’ dietary preferences and trophic association to the sea-ice habitat during spring. Relative proportions of FAs differed strongly between PPOM and IPOM, indicating differences in species composition and degradation state between pelagic and sympagic habitats, respectively. FA signatures and sterol content of the consumers largely resembled known diet compositions with a strong reliance on diatom-derived carbon in A. glacialis, a higher degree of carnivory in E. holmii and evidence of Calanus-feeding in polar cod. Sympagic HBIs were detected at either low concentrations or not at all, in both producers and consumers, likely as a result of the very low abundance of their source diatoms. Pronounced trophic marker variability in A. glacialis collected at the highly productive shelf slope station versus the less productive central Arctic Basin station suggests a surprisingly high flexibility in carbon-source composition with a stronger reliance on pelagic food when available versus a higher importance of ice algal carbon when pelagic production is low. Nevertheless and despite the general lack (below detection limit) of sympagic HBIs in our dataset, high ice-algal biomass and elevated proportions of polyunsaturated FAs in IPOM compared to other seasons indicate that ice algae constitute a valuable nutritional carbon source as alternative to pelagic carbon during spring.

Algal carbon assimilation by Senegalese sole (Solea senegalensis) from a compound diet including 13C-enriched Ulva ohnoi meal

The incorporation of macroalgae in formulated fish diets is an important goal for fish farming sustainability that is under current development. While several studies have evaluated the effects of algae on growth or functional aspects in fish, the fraction of algae biomass that is effectively incorporated into their tissues has not yet been assessed. This is a key issue to understand the potential that macroalgae may have to replace conventional food resources whose availability is limited. In present study, a compound feed that included the green seaweed Ulva ohnoi enriched in the stable 13C isotope (δ13C = 1235‰) was used to determine its nutritional contribution in a carnivorous fish species such as Senegalese sole (Solea senegalensis). Under isotopic equilibrium with the diet, the negative discrimination factor found for algal 13C, both under natural isotope abundance (Δ13C = −11.1167‰), and for algae that were isotopically enriched (Δ13C = −684.58‰) suggested that certain algal constituents were selectively digested. Fitting 13C uptake kinetics in sole tissues over time determined that 37.05 ± 2.01% and 36.35 ± 2.76% of the algal carbon was incorporated into muscle and liver, respectively. The metabolic contribution of 13C to isotope turnover was 21.7% in muscle and 64.9% in liver. The isotopic enrichment of the algae resulted in more stable C assimilation estimates compared to those obtained from food sources with natural isotope abundance. In general, variability of results was less affected by lipid extraction when 13C-enriched alga was used, thus achieving less dependence for a sample pre-treatment whose application is under debate. In the non-lipid fraction of muscle and liver, C assimilation was estimated at 24.1% and 29.0%, respectively. In the lipid fraction, assimilation estimates above 100% in both tissues were consistent with a strong lipid routing effect and also with metabolic processes that incorporate C of non-lipid origin into new lipid compounds. Results obtained in this study suggest that U. ohnoi represents a good dietary source of proteins and lipids for sole, while carbohydrates do not appear to be used.

Uncertainty analysis and stochastic studies of techno-economics of algal carbon sequestration at Indian coal powered plants

Formidable increase in atmospheric carbon dioxide (CO2) levels and the economic and environmental unfeasibility of the existing industrial carbon capture technologies have diverted the focus towards microalgae which can trap CO2, grow and, are processed into value-added products. Despite the enormous potential, the real-time adoption of algae-based industrial carbon capture is still lacking due to the uncertain economics and resource feasibility. Most studies done so far have analysed the economical aspect of microalgal carbon sequestration under varying concentrations of CO2 and not the percentage of emitted flue gas to be captured. To provide a better insight into the magnitude of scalability of microalgae-based industrial carbon capture the present study aims to evaluate the economic feasibility of capturing 1%, 10%, and 100% of the emitted industrial flue gas. Economic feasibility concerning the product to be harnessed and the uncertainties and risks linked with the input and output cost variables were analysed Algal productivity data obtained from the site-specific biophysical model was used as the input for techno-economic analysis and process simulation in SuperPro Designer® to produce 1 metric tonne of algal biomass as functional unit. Economic analysis revealed the decline in operating costs with decrease in the load of the emitted flue gas. 10% of the emitted flue gas capture scenario was considered favourable in terms of the 75% gross profit margin and lowest payback time (0.93 years). Capture of 1% of the emitted flue gas, reduced the operating expenditure, but, revenues generated are not sufficient enough for the process feasibility. Further, algal biorefinery scenarios were considered more feasible than a single product exploration. Uncertainty analysis showed 75% chances for profitability with variation in operating and capital expenses along with alteration in revenues. Such studies aid in real-time implementation of algae-based industrial carbon capture technologies.

Viral lysis modifies seasonal phytoplankton dynamics and carbon flow in the Southern Ocean

Phytoplankton form the base of marine food webs and are a primary means for carbon export in the Southern Ocean, a key area for global pCO2 drawdown. Viral lysis and grazing have very different effects on microbial community dynamics and carbon export, yet, very little is known about the relative magnitude and ecological impact of viral lysis on natural phytoplankton communities, especially in Antarctic waters. Here, we report on the temporal dynamics and relative importance of viral lysis rates, in comparison to grazing, for Antarctic nano- and pico-sized phytoplankton of varied taxonomy and size over a full productive season. Our results show that viral lysis was a major loss factor throughout the season, responsible for roughly half (58%) of seasonal phytoplankton carbon losses. Viral lysis appeared critically important for explaining temporal dynamics and for obtaining a complete seasonal mass balance of Antarctic phytoplankton. Group-specific responses indicated a negative correlation between grazing and viral losses in Phaeocystis and picoeukaryotes, while for other phytoplankton groups losses were more evenly spread throughout the season. Cryptophyte mortality was dominated by viral lysis, whereas small diatoms were mostly grazed. Larger diatoms dominated algal carbon flow and a single ‘lysis event’ directed >100% of daily carbon production away from higher trophic levels. This study highlights the need to consider viral lysis of key Antarctic phytoplankton for a better understanding of microbial community interactions and more accurate predictions of organic matter flux in this climate-sensitive region.

Fish communities critically depend on forest subsidies in small neotropical streams with high biodiversity value

AbstractTrophic support of species‐rich tropical fish communities remains uncertain in small forest streams where dense and constant canopy cover strongly limits the solar radiation available to aquatic producers. We sampled >1300 fish from 80 species in 14 remote headwater streams during the dry season in French Guiana. Carbon and nitrogen stable isotope analyses and mixing models were run to estimate the trophic position (TP) of each species and its dependence on terrestrial organic carbon sources. Matching patterns were found between nitrogen stable isotope ratios and the literature on diets of species at the base and top of the food web. Nearly 60% of the species fed exclusively on animal prey (mean TP >3), including piscivorous and parasitic fish species. Phylogenetic analysis revealed that TP were distributed broadly along the phylogeny and changed gradually within lineages. Carbon stable isotope ratios differed strongly between herbivores that fed on aquatic primary producers and those that fed on terrestrial plants along banksides. Terrestrial carbon was dominant in nearly 90% of species, and most of them depended more or less exclusively on terrestrial carbon. Ancestral state reconstructions indicated that only a few lineages showed local changes toward the consumption of algal carbon. We conclude that fish in neotropical headwater streams shaded by a dense tree canopy depend strongly on terrestrial subsidies. Changes in this aquatic‐terrestrial linkage would have major consequences for the remarkable fish biodiversity in these streams.Abstract in French is available with online material.

Corrigendum to: Carbon sources supporting Australia's most widely distributed freshwater fish, Nematalosa erebi (Günther) (Clupeidae: Dorosomatinae)

Both brown (detrital-based) and green (algal-based) food pathways support freshwater food webs, although the importance of either source may vary within species, regions and different phases of the flow regime. The bony bream (Nematalosa erebi Clupeidae: Dorosomatinae) is one of Australia's most widely distributed freshwater fish species and is a key component of freshwater food webs, especially in northern Australia. We sought to better define the feeding habits of this species, previously classified as a detritivore, algivore or zooplanktivore (or combinations thereof), by undertaking meta-analyses of published accounts based on stomach content analysis and 13C and 15N stable isotope analysis. Stomach content analysis clearly indicated that detritus was the dominant food item, although benthic algae could be an important dietary component in some habitats (inland river flood plains) and during the wet season. Zooplankton were important for small fish (i.e. juveniles 13C enriched, indicating the latter source was not the dominant contributor to the biomass of this species. However, using site-specific data and a regression approach, a significant relationship was revealed between algal carbon and that of large fish, suggesting that carbon derived from benthic algae contributed ~20% of the carbon of adult bony bream. Zooplankton contributed a similar amount. Zooplankton provided the majority of carbon for small fish. We contend that detritus derived from terrestrial vegetation is the likely remaining carbon source for large bony bream, and this interpretation was supported by the outcomes of multiple regression analyses. Although previous studies of aquatic food webs in northern Australia have emphasised the importance of high-quality algal basal resources, this study indicates that terrestrial sources may be important for some species and demonstrates the need to better consider the circumstances that cause biota to switch between different food sources.

Addressing algal blooms by bio-pumps to reduce greenhouse gas production and emissions with multi-path

The collapse of dense algal blooms is identified as a significant source of methane (CH4) emissions. When flocculation is used for algae removal, algal carbon is often turned into CH4 and carbon dioxide (CO2). Here, we established a “bio-pump” to control algal blooms and reduce greenhouse gas (GHG) emissions by the introduction of submerged macrophytes to the aquatic ecosystem and combination of flocculation and capping. The results suggested that this strategy contributed to an approximately 98% algae removal and sustainably improved dissolved oxygen (DO) in the water and sediment after the 40-day incubation. The aerobic condition at the sediment-water interface and deeper oxygen penetration in the sediment inhibited the abundance of microorganisms related to anaerobic CH4 production, then changed the metabolic pathway and fate of algal carbon. After the 40-day incubation, compared with flocculation-capping treatments, the bio-pump reduced 69.07% CH4 and 77.57% CO2 emissions, which was jointly contributed by the inhibition of anaerobic CH4 production, aerobic oxidation of CH4 and carbon sequestration of submerged macrophytes. This was also demonstrated from the finding of a decrease in methyl coenzyme M reductase (mcrA) gene, an increase in particulate methane monooxygenase (pmoA) gene and the absorption of 13C-labeled from algae biomass by submerged macrophytes at the end of incubation. Therefore, the bio-pump established in the present study can improve DO in algal blooms water and turn algal-derived organic matter into the plant biomass, which supplied a sustainable method for algae removal and GHG reduction.

Challenges and process economics for algal carbon capture with novel integration: Hydrothermal carbonization

A techno-economic analysis (TEA) of the integration of hydrothermal carbonization of waste biomass with an algal bioreactor is presented. Analyses of qualitative data from a two-m3 tubular photobioreactor constructed at Honda R&D Americas in Raymond, Ohio, USA, indicated that microalgal nutrient cost was a key economic challenge. The use of hydrothermal carbonization (HTC) of solid biowastes to provide lower cost nutrients was modeled. The TEA used results of previous work culturing microalgae in HTC process water, along with other data from the Honda algal bioreactor. Assumption for the scope of the analysis included capture of all carbon emissions from the Honda Marysville Auto Plant in Marysville, Ohio and application of a small onsite power plant using HTC solids to provide electricity and additional CO2 for the bioreactor system. Results indicated that HTC integration could decrease total operating costs of the bioreactor system by 17% and carbon capture costs by 11%. Additionally, results indicated the HTC system could contribute nearly 50% of key cost inputs (C, P, N and electricity) and increase EROI from 8.05 to 13.5.

Source and quantity of carbon influence its sequestration in Rostherne Mere (UK) sediment: a novel application of stepped combustion radiocarbon analysis

We explored the roles of phytoplankton production, carbon source, and human activity on carbon accumulation in a eutrophic lake (Rostherne Mere, UK) to understand how changes in nutrient loading, algal community structure and catchment management can influence carbon sequestration in lake sediments. Water samples (dissolved inorganic, organic and particulate carbon) were analysed to investigate contemporary carbon sources. Multiple variables in a 55-cm sediment core, which represents the last ~ 90 years of accumulation, were studied to determine historical production rates of algal communities and carbon sources. Fluctuations in net primary production, inferred from sedimentary diatom abundance and high-performance liquid chromatography (HPLC) pigment methods, were linked to nutrient input from sewage treatment works (STW) in the catchment. Stepped combustion radiocarbon (SCR) measurements established that lake sediment contains between 11% (~ 1929 CE) and 69% (~ 1978 CE) recalcitrant carbon, with changes in carbon character coinciding with peaks in accumulation rate and linked to STW inputs. Catchment disturbance was identified by radiocarbon analysis, and included STW construction in the 1930s, determined using SCR analysis, and recent nearby highway construction, determined by measurements on dissolved organic carbon from the lake and outflow river. The quantity of autochthonous carbon buried was related to diatom biovolume accumulation rate (DBAR) and decreased when diatom accumulation rate and valve size declined, despite an overall increase in net carbon production. HPLC pigment analysis indicated that changes in total C deposition and diatom accumulation were related to proliferation of non-siliceous algae. HPLC results also indicated that dominance of recalcitrant carbon in sediment organic carbon was likely caused by increased deposition rather than preservation factors. The total algal accumulation rate controlled the sediment organic carbon accumulation rate, whereas DBAR was correlated to the proportion of each carbon source buried.

Carbon sources supporting Australia's most widely distributed freshwater fish, Nematalosa erebi (Günther) (Clupeidae: Dorosomatinae)

Both brown (detrital-based) and green (algal-based) food pathways support freshwater food webs, although the importance of either source may vary within species, regions and different phases of the flow regime. The bony bream (Nematalosa erebi Clupeidae: Dorosomatinae) is one of Australia’s most widely distributed freshwater fish species and is a key component of freshwater food webs, especially in northern Australia. We sought to better define the feeding habits of this species, previously classified as a detritivore, algivore or zooplanktivore (or combinations thereof), by undertaking meta-analyses of published accounts based on stomach content analysis and 13C and 15N stable isotope analysis. Stomach content analysis clearly indicated that detritus was the dominant food item, although benthic algae could be an important dietary component in some habitats (inland river flood plains) and during the wet season. Zooplankton were important for small fish (i.e. juveniles <100mm in length). When data were pooled across a large number of locations, stable isotope analysis indicated that detritus derived from terrestrial vegetation was better aligned isotopically with values for both adult and juvenile bony bream, whereas algae were comparatively 13C enriched, indicating the latter source was not the dominant contributor to the biomass of this species. However, using site-specific data and a regression approach, a significant relationship was revealed between algal carbon and that of large fish, suggesting that carbon derived from benthic algae contributed ~20% of the carbon of adult bony bream. Zooplankton contributed a similar amount. Zooplankton provided the majority of carbon for small fish. We contend that detritus derived from terrestrial vegetation is the likely remaining carbon source for large bony bream, and this interpretation was supported by the outcomes of multiple regression analyses. Although previous studies of aquatic food webs in northern Australia have emphasised the importance of high-quality algal basal resources, this study indicates that terrestrial sources may be important for some species and demonstrates the need to better consider the circumstances that cause biota to switch between different food sources.

Refining the alkenone-pCO2 method II: Towards resolving the physiological parameter ‘b’

Haptophyte algal biomarkers called alkenones are widely used to reconstruct atmospheric CO2 in Earth’s Cenozoic history. This method is based on the notion that the algal carbon isotope fractionation during photosynthesis, as represented by εp37:2, is a function of seawater CO2 concentration and algal physiology. Constraining the algal physiological parameter, known as the ‘b’ term, is the key for successful applications of the alkenone-CO2 method. Using sensitivity analyses, we show that the growth rate (μ), cell size (r), and membrane permeability (P) are the most important variables to determine b. For all life on Earth, body size is a key factor that regulates metabolic rates. Exploiting the interdependence between phytoplankton cell size and growth rate, and specifically, the r – μ relationship for coccolithophores, we show that the length of fossil coccoliths (Lcoccolith) produced by ancient alkenone-synthesizers can be used to estimate r and therefore μ. Combining our new Lcoccolith data and published εp37:2 from the South China Sea Site MD01-2392, existing results from ODP Site 925, and ice core CO2, we determined the cell membrane permeability (P = 5.09 × 10−5 m s−1) for the Pleistocene community employing a bootstrap resampling technique. These new methods of constraining r, μ and P, combined with proxy-derived temperature (T), led us to rebuild b as a variable for each sample individually, which is subsequently used for alkenone-CO2 calculations. Application of this approach established pCO2 of the last 3 glacial-interglacial cycles, which turns out to be comparable with the ice core data in both the amplitude of changes and absolute values. It also reconciles the published Eocene – Oligocene alkenone-CO2 data which showed large geographical differences, with the new estimates much more consistent among different sites, and in line with other proxy-based results and ice sheet model predictions.

Preferential retention of algal carbon in benthic invertebrates: Stable isotope and fatty acid evidence from an outdoor flume experiment.

According to the River Continuum Concept, headwater streams are richer in allochthonous (e.g. terrestrial leaves) than autochthonous (e.g. algae) sources of organic matter for consumers. However, compared to algae, leaf litter is of lower food quality, particularly ω‐3 polyunsaturated fatty acids (n‐3 PUFA), and would constrain the somatic growth, maintenance, and reproduction of stream invertebrates. It may be thus assumed that shredders, such as Gammarus, receive lower quality diets than grazers, e.g. Ecdyonurus, that typically feed on algae.The objective of this study was to assess the provision of dietary PUFA from leaf litter and algae to the shredder Gammarus and the grazer Ecdyonurus. Three different diets (algae, terrestrial leaves, and an algae–leaf litter mix) were supplied to these macroinvertebrates in a flume experiment for 2 weeks. To differentiate how diet sources were retained in these consumers, algae were isotopically labelled with 13C.Both consumers became enriched with 13C in all treatments, demonstrating that both assimilated algae. For Gammarus, n‐3 PUFA increased, whereas n‐6 PUFA stayed constant. By contrast, the n‐3 PUFA content of Ecdyonurus decreased as a consequence of declining algal supply.Results from compound‐specific stable isotope analysis provided evidence that the long‐chain n‐3 PUFA eicosapentaenoic acid (EPA) in both consumers was more enriched in 13C than the short‐chain n‐3 PUFA α‐linolenic acid, suggesting that EPA was taken up directly from algae and not from heterotrophic biofilms on leaf litter. Both consumers depended on algae as their carbon and EPA source and retained their EPA from high‐quality algae.

One-pot synthesis of magnetic algal carbon/sulfidated nanoscale zerovalent iron composites for removal of bromated disinfection by-product

Magnetic algal carbon supported flower-like sulfidated nanoscale zerovalent iron (S-nZVI/AC) composite was firstly synthesized through one-pot method and used for removing bromate. More than 98% of bromate was efficiently removed within 48 min. Compared with the individual S-nZVI treatment, the removal rate constant of the S-nZVI/AC composite treatment was almost doubled. The removal rate constant of bromate increased three times when the S/Fe ratio increased from 0 to 0.3. According to the synergistic effect between the algal carbon and S-nZVI on the bromate removal, the introduction of carbon and sulfide-modification of nZVI were efficient modification approaches for enhancing the removal of bromated using S-nZVI/AC composite. The removal efficiency of bromate increased sharply to more than 98% when the composite dose increased from 0 to 40 mg L−1. The removal rate constant increased linearly from 0.08 to 0.31 min−1 when the initial concentration increased from 50 to 200 μg L−1. The removal efficiency of the bromate still maintained at high level (>85%) after 5 recycles of the S-nZVI/AC composite. Bromate was readily removed under neutral or slight acidic conditions. The bromate removal rate constant increased from 0.10 to 0.27 min−1 when the temperature increased from 15 to 35 °C. The bromate removal rate constant increased almost 4 times when the ionic strength increased from 0 to 3 g L−1. This study demonstrates that S-nZVI/AC composite synthesized through one-pot method is a promising water purification material for efficient removal of bromated disinfection by-product.

Macroalgae Derived Fungi Have High Abilities to Degrade Algal Polymers.

Marine fungi associated with macroalgae are an ecologically important group that have a strong potential for industrial applications. In this study, twenty-two marine fungi isolated from the brown seaweed Fucus sp. were examined for their abilities to produce algal and plant biomass degrading enzymes. Growth of these isolates on brown and green algal biomass revealed a good growth, but no preference for any specific algae. Based on the analysis of enzymatic activities, macroalgae derived fungi were able to produce algae specific and (hemi-)cellulose degrading enzymes both on algal and plant biomass. However, the production of algae specific activities was lower than the production of cellulases and xylanases. These data revealed the presence of different enzymatic approaches for the degradation of algal biomass by macroalgae derived fungi. In addition, the results of the present study indicate our poor understanding of the enzymes involved in algal biomass degradation and the mechanisms of algal carbon source utilization by marine derived fungi.