Algal Detritus Research Articles

Metagenomic analysis of carbohydrate-active enzymes and their contribution to marine sediment biodiversity

Marine sediments constitute the world’s most substantial long-term carbon repository. The microorganisms dwelling in these sediments mediate the transformation of fixed oceanic carbon, but their contribution to the carbon cycle is not fully understood. Previous culture-independent investigations into sedimentary microorganisms have underscored the significance of carbohydrates in the carbon cycle. In this study, we employ a metagenomic methodology to investigate the distribution and abundance of carbohydrate-active enzymes (CAZymes) in 37 marine sediments sites. These sediments exhibit varying oxygen availability and were isolated in diverse regions worldwide. Our comparative analysis is based on the metabolic potential for oxygen utilisation, derived from genes present in both oxic and anoxic environments. We found that extracellular CAZyme modules targeting the degradation of plant and algal detritus, necromass, and host glycans were abundant across all metagenomic samples. The analysis of these results indicates that the oxic/anoxic conditions not only influence the taxonomic composition of the microbial communities, but also affect the occurrence of CAZyme modules involved in the transformation of necromass, algae and plant detritus. To gain insight into the sediment microbial taxa, we reconstructed metagenome assembled genomes (MAG) and examined the presence of primary extracellular carbohydrate active enzyme (CAZyme) modules. Our findings reveal that the primary CAZyme modules and the CAZyme gene clusters discovered in our metagenomes were prevalent in the Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria classes. We compared those MAGs to organisms from the same taxonomic classes found in soil, and we found that they were similar in its CAZyme repertoire, but the soil MAG contained a more abundant and diverse CAZyme content. Furthermore, the data indicate that abundant classes in our metagenomic samples, namely Alphaproteobacteria, Bacteroidia and Gammaproteobacteria, play a pivotal role in carbohydrate transformation within the initial few metres of the sediments.

Meiofaunal assemblages associated with macroalgal detritus decomposition

A field-based experiment was performed on a detritus-loaded area of the east coast of Dadaepo Beach, South Korea, to investigate the decomposition rates of different types of algal detritus and their associated meiofaunal assemblages. Red (Grateloupia spp.), green (Ulva spp.), and brown (Undaria pinnatifida) algae were selected to investigate how the diversity of decaying algal detritus affects the degradation rate and associated meiofaunal assemblages. Samples were collected 10 times at 7-day intervals for 70 days. Organic matter weight loss was fastest in red algae and slowest in green algae. Meiofaunal density was greater in green algae than in red and brown algae. The most dominant phylum was Nematoda (81.4%), followed by Oligochaeta (8.8%) and Copepoda (8.4%), in all algal detritus types. Consistent positive relationship between diversity and decay rate and negative relationship between density and decay rate were identified over the experiment period. These results indicate that each of three types of macroalgal detritus provide diverse nutrients encouraging different meiofaunal community compositions.

Photochemical Release of Dissolved Organic Nitrogen from Algal Detritus and Sediment Particles in Lake Taihu, China

Solar irradiation in aquatic systems can induce the conversion of substances from the solid to the dissolved phase (photodissolution). Yet, the photochemical release of dissolved organic nitrogen (DON) from internal particles in lakes remains largely unknown. In this study, suspensions of algal detritus and sediment particles from a shallow eutrophic lake were exposed to simulated solar irradiation, and the release and compositional changes of dissolved organic matter were explored by measuring their UV–Visible absorption spectroscopy and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The photochemical release of inorganic nitrogen during the incubations was also investigated. Results showed that light irradiation induced stronger dissolved organic carbon and DON production in the algal detritus suspensions, with release rates of 1.17 mg C L−1 h−1 and 0.14 mg N L−1 h−1, respectively, at an algal detritus concentration of 0.1 dry g L−1. Light irradiation also induced compositional changes of DON in both algal and sediment suspensions. A larger number of DON molecules with lower molecular weight were continuously released in the algal suspensions, e.g., the total number of DON formulas increased from 1349 to 4135 during an 8 h irradiation. In contrast, upon irradiation of sediment suspensions, DON showed decreased molecular diversity and increased aromaticity. The photochemical release of ammonium (photoammonification) was also higher in the algal suspensions with a rate of 0.015 mg N L−1 h−1, which may contribute to the eutrophication of the lake. This study provides new molecular insights into the photochemical release of DON from typical internal particles in eutrophic lakes.

Seasonal variations of macrozoobenthic community trophic structure in the waters adjacent to the seaweed beds of Dalian Island in the North Yellow Sea.

To investigate the effects of algal detritus export on the trophic structure of macrozoobenthic community in the adjacent benthic habitat during the bloom and decline of macroalgae, we collected macrozoobenthos from the adjacent sea area of Dalian Island in the North Yellow Sea in May (the algal bloom period) and August (the algal decay period) of 2020. We quantifyied the seasonal changes in the trophic structure of macrozoobenthic community by using carbon and nitrogen stable isotope techniques. Results showed that δ13C and δ15N values of macrozoo-benthos in May ranged from -23.14‰ to -14.24‰, 6.21‰ to 12.90‰, respectively, and -22.36‰ to -14.13‰, 5.33‰ to 12.00‰, respectively in August. Results of PERMANOVA analysis showed that δ13C values of macrozoobenthos differed significantly between the two months, while δ15N values were not significantly different. Based on the Euclidean distance, the macrozoobenthic communities in both months could be classified into five trophic functional groups. The trophic levels of macrozoobenthos ranged from 2.00 (Nitidotellina minuta) to 3.97 (Glycera onomichiensis) in May and from 2.00 (N. minuta) to 3.96 (G. onomichiensis) in August. The δ13C range, δ15N range, mean centroid distance, total area and corrected standard ellipse areas which represented community trophic structure indices in August were higher than those in May. Our results indicated that the trophic diversity level and trophic niche width of the macrozoobenthic community in the adjacent sea area of the seaweed bed were higher in the algal decline season.

Iron and Manganese Oxidation States, Bonding Environments, and Mobility in the Mining-Impacted Sediments of Coeur d’Alene Lake, Idaho: Core Experiments

The mobility of a metal in mining-impacted sediments is determined by the environmental conditions that influence the metal’s oxidation state and bonding environment. Coeur d’Alene Lake, USA, has been impacted by legacy mining practices that allowed the hydrologic transport of mining waste to the lakebed, resulting in substantial amounts of redox-sensitive Fe and Mn along with Ag, As, Cd, Cu, Hg, Pb, Sb, and Zn. Future lake conditions may include algal blooms and additional algal detritus at the sediment–water interface, which may alter Fe and Mn forms that can influence their, and other metal(loid)s, mobility during seasonal anoxia. Cores of the lakebed sediments were exposed to anoxic and anoxic + algal detritus conditions for 8 weeks. Sediment samples were collected biweekly for analysis of Fe and Mn oxidation states and bonding environments by synchrotron-based X-ray absorption spectroscopy. Over the 8-week period and at a location 12.5 cm deep in the sediments, anoxic and anoxic + algae conditions produced limited changes in Fe and Mn oxidation states and bonding environments. At a location 2.5 cm below the sediment–water interface, the anoxic condition promoted a relatively stable environment in which Fe and Mn oxidation states and bonding environments did not vary greatly during the experiment. At the 2.5 cm depth, the anoxic + algae condition substantially altered the Mn oxidation state distribution and bonding environment, but this condition did not strongly influence the Fe oxidation state distribution or bonding environment. The anoxic + algae condition increased the presence of Mn3+, produced Mn4+ at select times, altered the Mn bonding environment, and temporarily increased the release of Mn into porewater. The algae influence on sediment and porewater Mn likely occurred because of the increased formation of organo-Mn complexes produced during algae-enhanced enzymatic processes. The lack of influence of algal detritus on sediment and porewater Fe and the formation of soluble organo-Mn complexes may limit the potential increase in the mobility of other metal(loid)s with future lake conditions.

The shift from macrophytic to algal particulate organic matter favours dissimilatory nitrate reduction to ammonium over denitrification in a eutrophic lake

Abstract In eutrophic lakes, the shift from a macrophyte‐dominated state to an algae‐dominated state changes the particulate organic matter (POM) sources, which in turn alters organic matter quality that is released and that sinks to the benthos. However, the influences of this shift on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are unclear in eutrophic lakes. Here, we elucidated how various POM sources influenced these nitrate reduction pathways in a eutrophic lake. The lake sediments from August were incubated under algae, macrophyte, and soil treatments in aquarium tanks. Potential denitrification and DNRA rates and related functional gene abundances were measured periodically. Meanwhile, the n‐alkanes composition of POM and fluorescence excitation‐emission matrices of dissolved organic matter were measured before and during incubations, respectively, to aid in the analysis of the potential mechanisms by which organic matter quality affect nitrate reduction. The results indicated that algal detritus was more labile and decomposed faster than other POM, coupled with higher DNRA rates and nrfA gene abundances. Macrophyte treatments resulted in nitrate accumulation and the increase of gene abundances related to denitrification, but no increase in denitrification rates was observed. In soil treatments, nitrate reduction processes were not significantly influenced by the addition of POM. Overall, compared with other sources, algae‐derived POM can produce high‐quality organic carbon, low dissolved oxygen and nitrate concentrations, which is more conducive to DNRA than denitrification. A loss of macrophytes and increase in algal biomass will induce changes in autochthonous POM quality and potentially drive nitrogen recycling in eutrophic lakes.

The influence of the composition of algal detritus on nematode assemblages

A field-based experiment was conducted on a detritus-loaded beach from the south coast of the British Isles (Poole Harbour) to investigate the decay rates of different combinations of algal detritus and their associated nematode assemblages. Ten algal mixture treatment combinations (monocultures with all possible 2 or 3 mixed algal treatments) of three different species of green (Chlorophyta), brown (Phaeophyta), and red (Rhodophyta) algae were used to determine how the diversity of decaying algal detritus affects the associated nematode assemblage composition and structure. Our results indicated that nematode density, diversity, and assemblage composition differed significantly among the different algal treatments. The nematode densities and genera richness were significantly higher in the mixed algal treatments compared to those in the algal monoculture treatments. The loss of seaweed dry weight varied significantly among the algal detritus treatments with which included brown algae tending to decay at a slower rate than others. These results indicate different type of macroalgae detritus could offer different nutrient input and that encourage different dominant nematode species and composition.

Sulfur Species, Bonding Environment, and Metal Mobilization in Mining-Impacted Lake Sediments: Column Experiments Replicating Seasonal Anoxia and Deposition of Algal Detritus

The oxidation state of sulfur [S] is a primary control on mobility of metals in sediments impacted by legacy mining practices. Coeur d’Alene Lake of northern Idaho, USA, has been impacted by upstream legacy mining practices that deposited an estimated 75 Mt of metal(loid)- and S-rich sediments into the lake. Future lake conditions are expected to include algal blooms, which may alter S and metal remobilization during the seasonal euxinic environment. Cores of the lake sediments were exposed to anoxic and anoxic + algal detritus conditions for eight weeks at 4.5 °C through introduction of a N2 atmosphere and addition of algal detritus. At a location 2.5 cm below the sediment-water interface, anoxic conditions promoted a shift in S species to continually larger concentrations of reduced species and an associated shift in the bonding environment reflective of increased S–metal bonds. Anoxic + algal detritus conditions suppressed the increasing trend of reduced S species and induced greater release of Mn compared to the anoxic-only conditions but did not appear to enhance the release of As, Cd, or Fe. The addition of algal detritus to the sediment-water interface of these Fe- and S-rich sediments enhanced mobilization of Mn likely because of dissimilatory metal reduction where the anaerobic oxidation of the algal detritus stimulated Mn reduction. Results of the study indicate that future metal release from the lake sediments will be altered with the likely deposition of algal detritus, but the effect may not enhance the release of acutely toxic metals, such as As or Cd, or substantially impact Fe cycling in the sediments.

Trash Dance: Anthropogenic Litter and Organic Matter Co-Accumulate on Urban Beaches

Anthropogenic litter (i.e., trash, AL) on beaches has negative ecological and economic impacts. Beach AL is likely moved together with coarse particulate organic matter (CPOM, algae, leaves), but no previous studies have assessed AL and CPOM co-distribution. We measured AL and CPOM on four urban beaches in Chicago, Illinois, USA, along two transect types (pier-adjacent, non-pier adjacent) in which each has three habitats (upland, beach, strand line). As expected, AL and CPOM density were positively related across all transects. AL and CPOM were significantly higher adjacent to piers, and variable among habitats. Wood, leaves, and smoking-related AL were most abundant in beach and upland zones while glass and algal detritus were abundant at the strandline. Overall, AL and CPOM show ‘patchy’ distribution attributed to wind and wave movement toward accumulation sites. Beach CPOM is a hot spot of biological activity (e.g., microbes, invertebrates, birds). Therefore, mixing of AL and CPOM suggests organisms may be more likely to encounter AL in mixed accumulations. Efforts to reduce the abundance and biological impacts of beach AL will benefit from emphasizing organic matter accumulation sites.

Characterization of odorants in contrasting ecotypes of Lake Taihu: algae-dominated versus macrophyte-dominated zones

Globally, odorant incidents are occurring at an increasing frequency, magnitude, and duration under the dual influences of eutrophication and climate change. However, the contribution of multiple ecotypes to odorant production in the complicated and dynamic lake ecosystems remains unclear. In this study, the odorants and environmental conditions in algae-dominated zones (ADZs) and macrophyte-dominated zones (MDZs) in Lake Taihu were identified and characterized. Results showed that the ADZs were characterized by an abundance of pigments and nutrients and low DO levels, while the MDZs were featured as high TOC/TN ratios and high DO levels. Most odorants in ADZs and several in MDZs exceeded the odorant threshold content. The dominant odorants were dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), β-ionone and β-cyclocitral in ADZs, which were associated with the accumulation and decomposition of algal detritus. For MDZs, the dominant odorants were 2-methylisoborneol (2-MIB) and geosmin, which were at least partially attributed to the massive addition of bait in a traditional aquaculture area. In addition, the odorant concentration in the water of ADZs was approximately 3 to 21 times higher than that in MDZs, while in the benthic sediment, the odorant concentration in ADZs was approximately 2 to 3 orders of magnitude higher than in MDZs. This study highlights the production and accumulation of nuisance odorants in the benthic sediment of ADZs, indicating a risk of diffusion from the sediment to the water column. This was supported by the correlation of odorants in the water column with that in the sediment. The results of this study will be helpful for the management of different ecotypes suffering from nuisance odorants problems.

Benthic carbon fixation and cycling in diffuse hydrothermal and background sediments in the Bransfield Strait, Antarctica

Abstract. Sedimented hydrothermal vents are likely to be widespread compared to hard substrate hot vents. They host chemosynthetic microbial communities which fix inorganic carbon (C) at the seafloor, as well as a wide range of macroinfauna, including vent-obligate and background non-vent taxa. There are no previous direct observations of carbon cycling at a sedimented hydrothermal vent. We conducted 13C isotope tracing experiments at three sedimented sites in the Bransfield Strait, Antarctica, which showed different degrees of hydrothermalism. Two experimental treatments were applied, with 13C added as either algal detritus (photosynthetic C), or as bicarbonate (substrate for benthic C fixation). Algal 13C was taken up by both bacteria and metazoan macrofaunal, but its dominant fate was respiration, as observed at deeper and more food-limited sites elsewhere. Rates of 13C uptake and respiration suggested that the diffuse hydrothermal site was not the hot spot of benthic C cycling that we hypothesised it would be. Fixation of inorganic C into bacterial biomass was observed at all sites, and was measurable at two out of three sites. At all sites, newly fixed C was transferred to metazoan macrofauna. Fixation rates were relatively low compared with similar experiments elsewhere; thus, C fixed at the seafloor was a minor C source for the benthic ecosystem. However, as the greatest amount of benthic C fixation occurred at the “Off Vent” (non-hydrothermal) site (0.077±0.034 mg C m−2 fixed during 60 h), we suggest that benthic fixation of inorganic C is more widespread than previously thought, and warrants further study.

Observation of a high abundance aggregation of the deep-sea urchin Chaetodiadema pallidum A. Agassiz and H.L. Clark, 1907 on the Northwestern Hawaiian Island Mokumanamana

AUV images of deep-sea megafauna on the seamount Mokumanamana in the Northwestern Hawaiian Islands revealed a large aggregation of the diadematoid urchin Chaetodiadema pallidum. This species had not been previously recorded on this seamount, but was known from other locations in the Hawaiian Archipelago. A total of 11,360 individuals were counted by eye from 1,369 seafloor images along the 200, 250, and 300 m depth contours on the west side of Mokumanamana. To estimate the full population size, Inverse Distance Weighting and Empirical Bayesian Kriging interpolation calculated a total population size of between 139,552 and 144,063 individuals. These estimates are 1-2 orders of magnitude greater than any previous estimates of urchin aggregation abundances. Little biological data exists for this species; thus, it is difficult to know if this is a spawning aggregation, a feeding front, a type of “schooling” behavior, or some combination thereof, but a food source did seem to be present in the form of mesophotic green algal detritus.

Feces as food: The nutritional value of urchin feces and implications for benthic food webs

Algal subsidies are important to basal consumers of the deep benthos where there is little to no primary productivity. Algal detritus such as pieces of kelp that sink into deep habitats can be an important direct nutritional subsidy, but sea urchin feces may provide an additional, indirect energetic link from shallow-water macroalgae to benthic community members that are too small to handle and consume large detritus directly. Urchins digest macroalgae inefficiently, creating the potential for two key trophic consequences to the benthic food webs they live in. First, urchins act as marine ‘shredders’ creating smaller detrital particles from larger drift; second, the poor digestion may enable microbes to enrich the food value of both the digesta within the urchin guts, and the egesta (feces) after it leaves the gut. We quantified the relative nutritional value of algae and of feces of red and green sea urchins (Mesocentrotus franciscanus and Strongylocentrotus droebachiensis) fed on monodiets of various algae in laboratory experiments. We then conducted feeding experiments with an epibenthic copepod (Tigriopus californicus) to evaluate consequences to a model consumer of different diets including feces. We also quantified assimilation efficiencies of red urchins fed a diet of bull kelp (Nereocystis luetkeana). In many cases, key indicators of nutritional value (especially calories and protein content) of algal material increased after being consumed and egested by urchins, and urchin feces “aged” in seawater generally became even more calorie-rich. Benthic copepods raised on diets of urchin feces derived from kelp had faster population growth than those raised on chopped fresh kelp tissue. It is likely that microbiota inside urchin guts are driving these counterintuitive results. The creation of nutritious feces could add to the importance of urchins as a link to benthic communities that rely heavily on detritus for their success.

Adsorptive removal of polycyclic aromatic hydrocarbons by detritus of green tide algae deposited in coastal sediment

Rare information is available on the adsorptive removal of polycyclic aromatic hydrocarbons (PAHs) in the presence of algal detritus deposited in the coastal sediment during the outbreak of the green tide. The adsorptive removal of typical PAHs by Ulva prolifera (U. prolifera) detritus was firstly investigated since the algal detritus was of great importance for the biogeochemical cycle of coastal contaminants. The results showed that equilibrium adsorptive capacities of naphthalene, phenanthrene and benzo[a] pyrene on the U. prolifera detritus were 1.27, 1.97, and 2.49 mg kg−1, respectively, at the initial concentration of 10 μg L−1. The in situ monitoring using laser confocal scanning microscopy confirmed the adsorptive removal of PAHs by U. prolifera detritus. The adsorption of these PAHs was highly pH-dependent. The increase in salinity led to the increase in naphthalene removal rate, while the salinity showed scarce influence on the removal of phenanthrene and benzo[a] pyrene. There was a good linear relationship (R2 ≥ 0.9892) between the removal efficiency of PAHs and the initial concentration of PAHs. Slow desorption kinetics and low desorption rate (<16%) indicated that the adsorptive removal of PAHs could be benign to the environment. These findings demonstrated that the occurrence of green tide could provide a new natural remediation approach for contamination of PAHs through the adsorptive removal by the detritus of green tidal algae deposited in the coastal sediment.

Carbon processing by the benthic ecosystem and benthic C fixation in methane-rich sediments on the South Georgia margin

AbstractAs bottom water warms, destabilisation of gas hydrates may increase the extent of methane-rich sediments. The authors present an assessment of organic carbon processing by the benthic community in methane-rich sediments, including one of the first investigations of inorganic C fixation in a non-hydrothermal vent setting. This topic was previously poorly studied, and there is much need to fill the gaps in knowledge of such ecosystems. The authors hypothesized that benthic C fixation would occur, and that a high biomass macrofaunal community would play a substantial role in organic C cycling. Experiments were conducted at a 257 m deep site off South Georgia. Sediment cores were amended with13C and15N labelled algal detritus, or13C labelled bicarbonate solution. In the bicarbonate experiment, labelling of bacteria-specific phospholipid fatty acids provided direct evidence of benthic C fixation, with transfer of fixed C to macrofauna and dissolved organic carbon (DOC). In the algae experiment, macrofauna played an active role in organic carbon cycling. Compared to similar experiments, low temperature supressed the rates of community respiration and macrofaunal C uptake. While benthic C fixation occurred, the biological processing of organic carbon was dominantly controlled by low temperature and high photic zone productivity.

Resilience of benthic ecosystem C-cycling to future changes in dissolved oxygen availability

In marine sediments, the availability, cycling and burial of organic carbon (OC), the size and composition of the faunal community, and the availability of dissolved oxygen (DO) are closely coupled. In light of expected expansions in marine hypoxia and of oxygen minimum zones (OMZs) in particular, it is now necessary to de-convolve DO from the frequently co-varying factors OC concentration and faunal biomass, in order to understand the effect of changing dissolved oxygen (DO) concentrations on the magnitude and pattern of biological processing of organic carbon (OC). This is especially important on the continental slope, a significant location for C cycling and burial.In this study, stable isotope tracer experiments were conducted at three sites with contrasting ambient DO concentrations of 0.5, 2.8 and 21.2 μM (at depths of 530m, 812m and 1140m respectively) on the Indian continental margin. Experiments were conducted both at ambient DO concentrations, and also, for the first time, under manipulated DO concentrations both 5% above and below ambient. The 13C label was added as algal detritus, and traced through the processes of respiration, and uptake into bacterial biomass, and into metazoans and foraminifera.Total C biological processing under ambient DO conditions was similar across all three sites, suggesting that benthic communities are well adapted to local conditions, such that OC processing is optimised even at severely hypoxic sites.DO manipulation produced changes in the pattern of OC processing by the benthic community. Oxygen manipulations in both directions resulted in decreases in total community respiration, except at the most hypoxic site. Bacterial uptake, in contrast, increased in response to all DO manipulations. Faunal 13C uptake tended to increase with increased DO. At the most hypoxic site (0.5 μM) this was attributable to increased foraminiferal activity, whereas at the most oxygenated site (21.2 μM) it was the metazoans that showed increased biomass-specific 13C uptake. Similarly, decreases in DO tended to reduce faunal 13C uptake, with metazoans disproportionately affected where they were already living at the lower end of their DO tolerance (i.e. 2.8 μM). Thus, the taxa most affected by DO manipulation depended on antecedent DO conditions. The total capacity of the benthic community to process freshly deposited OC (i.e. respiration plus uptake by bacterial and different fauna) increased following upwards manipulation of DO at the 0.5 μM site, but was not adversely affected by downwards manipulation of DO. Thus, results suggest that benthic communities possess some functional resilience, and that future expansion of marine hypoxia, while impacting benthic ecosystem structure, may not have as marked an effect on biological C processing.

Late Holocene oceanographic and climatic variability recorded by the Perseverance Drift, northwestern Weddell Sea, based on benthic foraminifera and diatoms

Abstract The Perseverance Drift, located in the Joinville-D' Urville Trough, northwestern Weddell Sea, records changes in ocean and sea ice conditions throughout the middle to late Holocene, with a record extending back to ca. 3400 yr BP. The 2562-cm composite record collected from a water depth of 806 m, documents the uppermost section of the 90-m thick sediment drift. Spring-blooming diatoms (Chaetoceros subg. Hyalochaete) are abundant through the sedimentary record. The greater proportion of Chaetoceros vegetative valves compared to resting spores indicates that the marine environment is highly productive, and nutrients generally are not limiting. Epiphytic diatoms, dominated by Cocconeis spp., are observed throughout JKC36, suggesting transport of algal detritus from shallower regions to the benthos. Three foraminiferal assemblages (FAs): Miliammina spp., Globocassidulina spp., and Paratrochammina bartami/Paratrochammina lepida/Portatrochammina antarctica characterize the benthic foraminiferal fauna and reflect affinities with water masses circulating across the Perseverance Drift and tolerance to corrosive bottom waters. The interval 3400–1800 yr BP is marked by high abundances of Globocassidulina spp., indicating incursions of Weddell Sea Transitional Water over the drift site. This interval implies a period of “freshening” of the water column, coinciding with an open-marine or seasonally open-marine environment during the middle-to-late Holocene Climatic Optimum. The interval 1800 yr BP to the present displays characteristics of slightly colder conditions, as indicated by the absence of the calcareous Globocassidulina spp. FA, and the pronounced presence of agglutinated P. bartami/P. lepida/P. antarctica FA, along with other agglutinated species that are indicative of the presence of sea ice. Therefore, this interval is interpreted to represent the onset of Neoglaciation at the northeastern tip of the Antarctic Peninsula. The consistent presence of Miliammina spp. FA corroborates that the sedimentary record represents a productive, open-marine setting with seasonally variable sea ice extent. The Drift is a unique geologic archive that provides an excellent target for future coring based on the preservation of abundant carbonate material for radiocarbon dating and the potential to develop a multi-proxy data set that could offer a robust understanding of the Holocene depositional and paleoclimatic conditions of the northwestern Weddell Sea.

Microcystin-LR Degradation Following Copper-Based Algaecide Exposures

When copper-based algaecides are used in aquatic systems to decrease cyanobacteria densities, endotoxin fate is a concern, due to the potential for human health and ecological risks. Pulse exposures of algaecides can result in episodic low dissolved oxygen (DO) concentrations (< 2 mg L−1), due to oxygen consumed via microbial oxidation of algal detritus. Research objectives of this study were to determine the influence of declining DO levels on microcystin-LR (MC-LR) degradation and changes in resident bacterial assemblages. It was hypothesized that cyanobacteria cell densities would be positively correlated with rates and extents of DO decline based on the oxygen required for bacteria to degrade cyanobacteria detritus following exposure to copper-based algaecides. In addition, it was hypothesized that total MC-LR concentrations would increase proportionally with increasing cyanobacteria cell densities. Mesocosm experiments were conducted in a pond in Anderson, SC, that frequently experiences cyanobacteria blooms. Three densities of a cyanobacteria assemblage were exposed to a copper ethanolamine algaecide. DO and total MC-LR concentrations were measured with time following algaecide exposures to determine rates and extents of declines. As anticipated, DO concentrations had the highest rate of decline in the highest cell density treatment, followed by medium and low cell densities. MC-LR degradation occurred at similar rates (half-lives 1 to 1.9 days) among cell densities. Acinetobacter and Aeromonas were dominant in treatments following copper exposures. The relationship between cyanobacteria densities and MC-LR half-lives demonstrates the benefits of managing cyanobacteria in early growth stages to minimize MC concentrations.

The releasing characteristics of carbon, nitrogen and phosphorus from sediment under the influence of different densities of algal detritus

The releasing characteristics of carbon, nitrogen and phosphorus from sediment under the influence of different densities of algal detritus

Predicted microbial secretomes and their target substrates in marine sediment.

Scientific drilling has identified a biosphere in marine sediments 1 , which contain many uncultivated microbial groups known only by their DNA sequences 2-4 . Recycling of organic matter in sediments is an important component of biogeochemical cycles because marine sediments are critical forlong-term carbon storage 5 . Turnover of carbon is hypothesized to be driven by the secretion of enzymes by microbial organisms 5-7 , which act to break down macromolecules into constitutive monomers that can be transported into cells. As such, the nature of the microbial secretome often influences the function of a community 6 . However, the microbial groups involved in this process and the biochemistry theyencode is poorly understood. Here, we show that expressed genes from 5 to 159 meters below the seafloor 8 (mbsf) encode numerous candidate peptidases and carbohydrate-active enzymes ('CAZymes') 9 targeted for secretion. The majority (90-99%) were assigned to Bacteria, of which 12% shared the highest sequence similarity with candidate phyla 10,11 . The remaining putatively secreted proteins shared highest sequence similarity with archaeal and fungal enzymes, which peak in two redox transition zones 12 . In the shallower redox zone at 30 mbsf, 20% of the transcripts encoding putative secreted peptidases were assigned to lineages 7,13,14 of uncultivated Archaea. The target compounds of the predicted secreted proteome show a preference for necromass in the form of microbial cell envelopes as well as plankton and algal detritus. The predicted fungal secreted proteome encodes CAZymes not present in the predicted bacterial or archaeal secreted proteomes, indicating that fungi putatively play a minimal but specialized role in subseafloor carbohydrate recycling.