Zinc stimulation of coastal productivity in low carbon dioxide environments.

Zinc (Zn) is a key micronutrient used by phytoplankton for carbon (C) acquisition, yet there have been few observations of its influence on natural oceanic phytoplankton populations. In this study, we observed Zn limitation of growth in the natural phytoplankton community of Terra Nova Bay, Antarctica, due to low (~220 µatm) pCO2 conditions, in addition to primary iron (Fe) limitation. Shipboard incubation experiments amended with Zn and Fe resulted in significantly higher chlorophyll a content and dissolved inorganic carbon drawdown compared to Fe addition alone. Zn and Fe response proteins detected in incubation and environmental biomass provided independent verification of algal co-stress for these micronutrients. These observations of Zn limitation under low pCO2 conditions demonstrate Zn can influence coastal primary productivity. Yet, as surface ocean pCO2 rises with continued anthropogenic emissions, the occurrence of Zn/C co-limitation will become rarer, impacting the biogeochemical cycling of Zn and other trace metal micronutrients.

Surface Bacterioplankton Community Structure Crossing the Antarctic Circumpolar Current Fronts.

The Antarctic Circumpolar Current (ACC) is the major current in the Southern Ocean, isolating the warm stratified subtropical waters from the more homogeneous cold polar waters. The ACC flows from west to east around Antarctica and generates an overturning circulation by fostering deep-cold water upwelling and the formation of new water masses, thus affecting the Earth's heat balance and the global distribution of carbon. The ACC is characterized by several water mass boundaries or fronts, known as the Subtropical Front (STF), Subantarctic Front (SAF), Polar Front (PF), and South Antarctic Circumpolar Current Front (SACCF), identified by typical physical and chemical properties. While the physical characteristics of these fronts have been characterized, there is still poor information regarding the microbial diversity of this area. Here we present the surface water bacterioplankton community structure based on 16S rRNA sequencing from 13 stations sampled in 2017 between New Zealand to the Ross Sea crossing the ACC Fronts. Our results show a distinct succession in the dominant bacterial phylotypes present in the different water masses and suggest a strong role of sea surface temperatures and the availability of Carbon and Nitrogen in controlling community composition. This work represents an important baseline for future studies on the response of Southern Ocean epipelagic microbial communities to climate change.

Bacterioplankton Diversity and Distribution in Relation to Phytoplankton Community Structure in the Ross Sea Surface Waters.

Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. However, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here, we report data on the bacterial diversity in relation to phytoplankton community structure in the surface waters of the Ross Sea during the Austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay (TNB) coastal waters and the Ross Sea Open Waters (RSOWs), with a dominance of members belonging to the bacterial phyla Bacteroidetes and Proteobacteria. In the TNB coastal area, microbial communities were characterized by a higher abundance of sequences related to heterotrophic bacterial genera such as Polaribacter spp., together with higher phytoplankton biomass and higher relative abundance of diatoms. On the contrary, the phytoplankton biomass in the RSOW were lower, with relatively higher contribution of haptophytes and a higher abundance of sequences related to oligotrophic and mixothrophic bacterial groups like the Oligotrophic Marine Gammaproteobacteria (OMG) group and SAR11. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provide new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters, suggesting that specific rather than random interaction contribute to the organic matter cycling in the Southern Ocean.

Thermo resistant antioxidants from photoautotrophic microorganisms: screening and characterization.

The demand for natural antioxidants to be used in food industry is increasing, as synthetic antioxidants are toxic and have high production costs. Specifically, food processing and preservation require antioxidants resistant to thermal sterilization processes. In this study, twenty-five strains among microalgae and cyanobacteria were screened as antioxidants producers. The species Enallax sp., Synechococcus bigranulatus and Galdieria sulphuraria showed the highest content of chlorophyll a and total carotenoids. In vitro stability and antioxidant activity of the ethanolic extracts were performed. The results revealed that pigments present in the extracts, obtained from the previously mentioned species, were stable at room temperature and exhibited in vitro free radical scavenging potential with IC50 values of 0.099 ± 0.001, 0.048 ± 0.001 and 0.13 ± 0.02 mg mL-1, respectively. Biocompatibility assay showed that the extracts were not toxic on immortalized cell lines. The antioxidant activity was also tested on a cell-based model by measuring intracellular ROS levels after sodium arsenite treatment. Noteworthy, extracts were able to exert the same protective effect, before and after the pasteurization process. Results clearly indicate the feasibility of obtaining biologically active and thermostable antioxidants from microalgae. Green solvents can be used to obtain thermo-resistant antioxidants from cyanobacteria and microalgae which can be used in the food industry. Thus, the substitution of synthetic pigments with natural ones is now practicable.

Phytoplankton Blooms Below the Antarctic Landfast Ice During the Melt Season Between Late Spring and Early Summer.

Antarctic regions are known to be mainly dominated by diatoms in the water column under sea ice. In this study, we report for the first time two distinct phytoplankton blooms dominated by nanoflagellates (<15 µm) under the landfast ice in Terra Nova Bay during the late spring-early summer 2015/2016. The taxa included the pelagic Bolidophyceae Pentalamina corona, the Chrysophyceae Ochromonas spp. and the Chlorophyceae Chlamydomonas spp., typically found in fresh waters, and the Prymnesiophyceae Phaeocystis antarctica usually observed dominating in polynya areas. These species represented from 40% to 91% of the total phytoplankton community, a percentage contrasting with the prevalence of diatoms found previously. The dominance of nanoflagellates, rather than diatoms, during late spring and early summer may have important implications for trophic relationships in Antarctic waters and the presence of typical freshwater species could indicate a great input of continental waters related to environmental changes.

Use of an immobilised thermostable α-CA (SspCA) for enhancing the metabolic efficiency of the freshwater green microalga Chlorella sorokiniana.

There is significant interest in increasing the microalgal efficiency for producing high-quality products that are commonly used as food additives in nutraceuticals. Some natural substances that can be extracted from algae include lipids, carbohydrates, proteins, carotenoids, long-chain polyunsaturated fatty acids, and vitamins. Generally, microalgal photoautotrophic growth can be maximised by optimising CO2 biofixation, and by adding sodium bicarbonate and specific bacteria to the microalgal culture. Recently, to enhance CO2 biofixation, a thermostable carbonic anhydrase (SspCA) encoded by the genome of the bacterium Sulfurihydrogenibium yellowstonense has been heterologously expressed and immobilised on the surfaces of bacteria. Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous metalloenzymes, which catalyse the physiologically reversible reaction of carbon dioxide hydration to bicarbonate and protons: CO2 + H2O ⇄ HCO3- + H+. Herein, we demonstrate for the first time that the fragments of bacterial membranes containing immobilised SspCA (M-SspCA) on their surfaces can be doped into the microalgal culture of the green unicellular alga, Chlorella sorokiniana, to significantly enhance the biomass, photosynthetic activity, carotenoids production, and CA activity by this alga. These results are of biotechnological interest because C. sorokiniana is widely used in many different areas, including photosynthesis research, human pharmaceutical production, aquaculture-based food production, and wastewater treatment.

Phaeocystis antarctica unusual summer bloom in stratified antarctic coastal waters (Terra Nova Bay, Ross Sea).

This study focuses on the potential explanations for a Phaeocystis antarctica summer bloom occurred in stratified waters of Terra Nova Bay (TNB) - which is part of the Antarctic Special Protected Area (n.161) in the Ross Sea - trough a multi-parameter correlative approach. Many previous studies have highlighted that water column stratification typically favors diatom dominance compared to the colonial haptophyte P. antarctica, in the Ross Sea, and this correlation has often been used to explain the historic dominance of diatoms in TNB. To explore the spatial and temporal progression of P. antarctica bloom in coastal waters, four stations were sampled three times each between December 31, 2009 and January 13, 2010. Taxonomic and pigment composition of phytoplankton communities, macro-nutrient concentrations and various different indices, all indicated the relative dominance of P. antarctica. Cell abundances revealed that P. antarctica contributed 79% of total cell counts in the upper 25 m and 93% in the lower photic zone. Similarly, a strong correlation was observed between Chl-a and the Hex:Fuco pigment ratio, corroborating the microscopic analyses. Recent studies have shown that iron can trigger colonial P. antarctica blooms. Based on the Hex:Chl-c3 proxy for iron limitation in P. antarctica, we hypothesize that anomalously higher iron fluxes were responsible for the unusual bloom of colonial P. antarctica observed in TNB.

Austral Summer Bloom of Loricate Choanoflagellates in the Central Ross Sea Polynya.

A bloom of loricate choanoflagellates was recorded for the first time in the Ross Sea polynya during the austral summer 2017. Both individual cells and uncommon large-size colonies (200 µm length) represent the 42-55% of the total plankton community (i.e. specimens from 5 to 150 µm length). Choanoflagellates serve as a link between low and mid trophic levels since they prey on bacteria and in turn are ingested by zooplankton. This twofold role and the unusual abundance recorded in the Antarctic ecosystem may have relevant but still unknown effects on food web structure and dynamics in that area.

Distribution and enrichment of trace metals in surface marine sediments in the Gulf of Pozzuoli and off the coast of the brownfield metallurgical site of Ilva of Bagnoli (Campania, Italy).

The distribution of metals in surface sediments of Gulf of Pozzuoli (GoP), embedding the former second Italian largest integrated steelworks of Bagnoli, was studied based on sediment dispersal, quality guidelines (SQGs) and quantitative pollution indices of the respective metals. As, Cd, Hg, Pb, Zn largely exceeded the limits. Hg had a mean of 5.8mg/kg, twentyfold higher the rule, accumulating primarily near Bagnoli site. The mean effective range quotient, m-ERM-Q, revealed a high potential for negative biological effects especially in the area nearby the Bagnoli site. The enrichment factor (EF) values were outstandingly high, >1.5 with values which were often ≥100. The geoaccumulation index, Igeo, was very critical for Cr, Cu, Hg and Ni, showing an Igeo in the range of strongly polluted (45). The principal component analysis (PCA) and Pearson's correlation matrix (CM), excluded significant contribution from weathering products.

Characterization and source apportionment of polycyclic aromatic hydrocarbons (pahs) in the sediments of gulf of Pozzuoli (Campania, Italy).

Most of the literature reports on the impact of the former Bagnoli brownfield on the pollution of Bagnoli Bay, embedded in the Gulf of Pozzuoli (GoP). Thus, we studied concentrations, types and sources of sixteen PAHs (EPA) in sediments at 22 sites along 5 transects covering the entire area of GoP. Outstanding levels of PAHs were found, varying from 7.1µgg-1 to 2.5 E+3µgg-1. Sediments collected at sites far away from Bagnoli were found to be polluted to a similar extent than those facing the brownfield site, with values>100µgg-1. Total PAHs levels in the sediments of GoP were higher by thirty-eleven thousand fold than those reported by other studies from various marine sites in the world. Transit axes of fine and very fine sands and diagnostic indexes revealed a common pyrolytic PAHs pollution spreading from the Bagnoli plant to all GoP.

Phytoplankton blooms during austral summer in the Ross Sea, Antarctica: Driving factors and trophic implications.

During the austral summer of 2014, an oceanographic cruise was conducted in the Ross Sea in the framework of the RoME (Ross Sea Mesoscale Experiment) Project. Forty-three hydrological stations were sampled within three different areas: the northern Ross Sea (RoME 1), Terra Nova Bay (RoME 2), and the southern Ross Sea (RoME 3). The ecological and photophysiological characteristics of the phytoplankton were investigated (i.e., size structure, functional groups, PSII maximum quantum efficiency, photoprotective pigments), as related to hydrographic and chemical features. The aim was to identify the mechanisms that modulate phytoplankton blooms, and consequently, the fate of organic materials produced by the blooms. The observed biomass standing stocks were very high (e.g., integrated chlorophyll-a up to 371 mg m-2 in the top 100 m). Large differences in phytoplankton community composition, relative contribution of functional groups and photosynthetic parameters were observed among the three subsystems. The diatoms (in different physiological status) were the dominant taxa in RoME 1 and RoME 3; in RoME 1, a post-bloom phase was identified, whereas in RoME 3, an active phytoplankton bloom occurred. In RoME 2, diatoms co-occurred with Phaeocystis antarctica, but were vertically segregated by the upper mixed layer, with senescent diatoms dominating in the upper layer, and P. antarctica blooming in the deeper layer. The dominance of the phytoplankton micro-fraction over the whole area and the high Chl-a suggested the prevalence of non-grazed large cells, independent of the distribution of the two functional groups. These data emphasise the occurrence of significant temporal changes in the phytoplankton biomass in the Ross Sea during austral summer. The mechanisms that drive such changes and the fate of the carbon production are probably related to the variations in the limiting factors induced by the concurrent hydrological modifications to the Ross Sea, and they remain to be fully clarified. The comparison of conditions observed during summer 2014 and those reported for previous years reveal considerably different ecological assets that might be the result of current climate change. This suggests that further changes can be expected in the future, even at larger oceanic scales.

A multidisciplinary approach for the characterization of the coastal marine ecosystems of Monte Di Procida (Campania, Italy).

A multidisciplinary survey was carried out on the quality of water and sediments of a coastal protected marine area, embedded between the inputs from Bagnoli steel plant to the south and a sewage plant, Volturno River and Regi Lagni channel to the north. The study integrated chemical-sedimentological data with biological and ecotoxicological analyses to assess anthropogenic pressures and natural variability. Data reveal marked differences in anthropogenic pollution between southeastern and northwestern zone, with the north affected by both inorganic and organic flows and the south influenced by levels of As, Pb and Zn in the sediments above law limits, deriving from inputs of the Bagnoli brownfield site. Meiobenthic data revealed at south higher relative abundance of sensitive species to pollution and environmental stress to the south, i.e. Lobatula lobatula and Rosalina bradyi, whereas to the north relative abundance of stress tolerant Quinqueloculina lata, Quinqueloculina pygmaea and Cribroelphidium cuvilleri were determined.