Maria Saggiomo

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 Bacillus sp. isolated from sediments of the Sarno River mouth, Gulf of Naples (Italy) produces a biofilm biosorbing Pb(II)

A Pb-resistant bacterial strain (named hereinafter Pb15) has been isolated from highly polluted marine sediments at the Sarno River mouth, Italy, using an enrichment culture to which Pb(II) 0.48mmoll(-1) were added. 16S rRNA gene sequencing (Sanger) allowed assignment of the isolate to the genus Bacillus, with Bacillus pumilus as the closest species. The isolate is resistant to Pb(II) with a minimum inhibitory concentration (MIC) of 4.8mmoll(-1) and is also resistant to Cd(II) and Mn(II) with MIC of 2.22mmoll(-1) and 18.20mmoll(-1), respectively. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that Pb inoculated in the growth medium is absorbed by the bacterial cells at removal efficiencies of 31.02% and 28.21% in the presence of 0.48mmoll(-1) or 1.20mmoll(-1) Pb(II), respectively. Strain Pb15 forms a brown and compact biofilm when grown in presence of Pb(II). Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS) confirm that the biofilm contains Pb, suggesting an active biosorption of this metal by the bacterial cells, sequestering 14% of inoculated Pb as evidenced by microscopic analyses. Altogether, these observations support evidence that strain Pb15 has potentials for being used in bioremediation of its native polluted sediments, with engineering solutions to be found in order to eliminate the adsorbed Pb before replacement of sediments in situ.

Trophic Characterization of the Pelagic Ecosystem in Vlora Bay (Albania)

Abstract Phytoplankton assemblages were studied to characterize the trophic status of the semienclosed Vlora Bay (Albania) and to evaluate the influence of terrestrial inputs on its pelagic ecosystem. The study was carried out as part of the European Project CISM (INTERREG IIIA Italy–Albania) and conducted during two oceanographic cruises (spring 2007, winter 2008). The size-fractionated chlorophyll a concentrations, primary production rates, and the chemotaxonomic composition (high-performance liquid chromatography) of the phytoplankton assemblages were measured. The spatial variability of primary production rates and chlorophyll a concentrations both showed a pronounced E-W gradient in the surface layer, with the highest values along the eastern coast. In spring, a deep chlorophyll maximum was observed in the central western part of the bay, whereas in winter a homogeneous vertical distribution was observed. The phytoplankton assemblages were quite similar in both seasons and were dominated by the picophytoplankton fraction (≈46% and 53% in spring and in winter, respectively). Haptophytes and pelagophytes were the major phytoplankton groups, and accounted, respectively, for 50% and 15% in spring, and 40% and 25% in winter. The results showed that Vlora Bay was characterized by generally oligotrophic conditions and that the influence of the southern Adriatic open waters was negligible. The trophic characteristics of the pelagic ecosystem of the bay were essentially driven by terrestrial inputs.

Gorgonian disease outbreak in the Gulf of Naples: pathology reveals cyanobacterial infection linked to elevated sea temperatures.

In recent years, mass mortality events of benthic invertebrates in the Mediterranean Sea have been documented to coincide with the increased seawater temperatures associated with global climate change. Following a disease outbreak in gorgonians during the summer seasons of 2008 and 2009 in the Gulf of Naples (Tyrrhenian Sea), we conducted gross and microscopic analyses of healthy and diseased specimens of Eunicella cavolinii and E. singularis using both light and electron microscopy (SEM). Macroscopically, diseased colonies exhibited evident tissue thinning, and dead colonies showed a complete loss of polyps and coenenchyme, exposing their skeletons to settlement by fouling organisms. Histopathology revealed chronic inflammatory lesions at the polyp and axial level, characterized by amoebocyte infiltration of tissue accompanied by new apposition of melanin/gorgonin sheets. We interpreted this response as a defense against different kinds of pathogens-identified as mainly a heterogeneous consortium of filamentous cyanobacteria-and which gradually led to enlargement and hardening of the coral axis, which resembled a wood-like structure at the final stage of the disease. These processes elicited the formation of multiple inflammatory nodules and capsules, some of which were macroscopically visible. A parallel 16S rRNA and ITS analysis of the diseased tissue identified Synechococcus, Arthrospira and other uncultured cyanobacteria grouped within the Oscillatoriales. These results suggest that a cyanobacterial consortium is involved in the pathogenesis of the inflammatory disease leading to the mortality of Gorgoniaceae in the area. Finally, there were anomalously high temperatures (up to 25°C) between 10 and 20 m depth during the sampling period, particularly in June 2009. This supports the hypothesis that the coral skeleton may serve as a reservoir for the pathogens in cooler seasons, with warmer conditions leading to pathogen reactivation and recurring mortality events.

Mesoscale variability related to iron speciation in a coastal Ross Sea area (Antarctica) during summer 2014

ABSTRACT Dissolved iron (Fe) distribution and speciation was determined in water samples (0–200 m) collected in a coastal area near Terra Nova Bay during the austral summer of 2014. Nutrients, dissolved oxygen, chlorophyll-a, phytoplankton composition and prokaryotic biomass distribution were investigated in combination with measurements of the physical properties of the water columns and its dynamics. The dFe value was above the limiting growth concentration, ranging from 0.52 to 4.51 nM, and it showed a spatial variability with a horizontal length scale of about 10 km, according to the variability of the water column physical properties and to iron sources. The organic ligands (L) maintained the concentrations of dFe at levels much higher than the inorganic solubility of Fe, keeping it available for phytoplankton and the log K’FeL values found (from 22.1 to 23.6) highlighted the presence of complexes of differing stabilities.

Distribution, community composition and potential metabolic activity of bacterioplankton in an urbanized Mediterranean Sea coastal zone

ABSTRACT Bacterioplankton are fundamental components of marine ecosystems and influence the entire biosphere by contributing to the global biogeochemical cycles of key elements. Yet, there is a significant gap in knowledge about their diversity and specific activities, as well as environmental factors that shape their community composition and function. Here, the distribution and diversity of surface bacterioplankton along the coastline of the Gulf of Naples (GON; Italy) were investigated using flow cytometry coupled with high-throughput sequencing of the 16S rRNA gene. Heterotrophic bacteria numerically dominated the bacterioplankton and comprised mainly Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes. Distinct communities occupied river-influenced, coastal, and offshore sites, as indicated by Bray-Curtis dissimilarity, distance metric (UniFrac), linear discriminant analysis effect size (LEfSe), and multivariate analyses. The heterogeneity in diversity and community composition was mainly due to salinity and changes in environmental conditions across sites, as defined by nutrient and chlorophyll a concentrations. Bacterioplankton communities were composed of a few dominant taxa and a large proportion (92%) of rare taxa (here defined as operational taxonomic units [OTUs] accounting for <0.1% of the total sequence abundance), the majority of which were unique to each site. The relationship between 16S rRNA and the 16S rRNA gene, i.e., between potential metabolic activity and abundance, was positive for the whole community. However, analysis of individual OTUs revealed high rRNA-to-rRNA gene ratios for most (71.6% ± 16.7%) of the rare taxa, suggesting that these low-abundance organisms were potentially active and hence might be playing an important role in ecosystem diversity and functioning in the GON. IMPORTANCE The study of bacterioplankton in coastal zones is of critical importance, considering that these areas are highly productive and anthropogenically impacted. Their richness and evenness, as well as their potential activity, are very important to assess ecosystem health and functioning. Here, we investigated bacterial distribution, community composition, and potential metabolic activity in the GON, which is an ideal test site due to its heterogeneous environment characterized by a complex hydrodynamics and terrestrial inputs of varied quantities and quality. Our study demonstrates that bacterioplankton communities in this region are highly diverse and strongly regulated by a combination of different environmental factors leading to their heterogeneous distribution, with the rare taxa contributing to a major proportion of diversity and shifts in community composition and potentially holding a key role in ecosystem functioning.