Blue Haslea species are marine benthic pennate diatoms able to synthesize a blue-green water-soluble pigment, like marennine produced by H. ostrearia Simonsen. New species of Haslea synthetizing blue ...pigments were recently described (H. karadagensis, H. nusantara, H. provincialis and H. silbo). Their marennine-like pigments have allelopathic, antioxidative, antiviral and antibacterial properties, which have been demonstrated in laboratory conditions. Marennine is also responsible for the greening of oysters, for example, in the Marennes Oléron area (France), a phenomenon that has economical and patrimonial values. While blue Haslea spp. blooms have been episodically observed in natural environments (e.g., France, Croatia, USA), their dynamics have only been investigated in oyster ponds. This work is the first description of blue Haslea spp. benthic blooms that develop in open environments on the periphyton, covering turf and some macroalgae-like Padina. Different sites were monitored in the Mediterranean Sea (Corsica, France and Croatia) and two different blue Haslea species involved in these blooms were identified: H. ostrearia and H. provincialis. A non-blue Haslea species was also occasionally encountered. The benthic blooms of blue Haslea followed the phytoplankton spring bloom and occurred in shallow calm waters, possibly indicating a prominent role of light to initiate the blooms. In the absence of very strong winds and water currents that can possibly disaggregate the blue biofilm, the end of blooms coincided with the warming of the upper water masses, which might be profitable for other microorganisms and ultimately lead to a shift in the biofilm community.
Marine surface microlayer (SML) is a large and extreme marine environment with an important role in biogeochemical cycling and climate regulation. We explored the seasonal structure and abundance of ...bacterial assemblages in SML (bacterioneuston) and underlying water layer (ULW) (bacterioplankton) in eutrophic marine Rogoznica Lake and more oligotrophic coastal area of the adjacent Adriatic Sea. SML and ULW in each site were similar in pH, salinity, dissolved oxygen, oxygen saturation, and temperature. Rogoznica Lake was colder in winter and warmer in summer compared to the Adriatic Sea. Regarding nutrients, SML and ULW were notably different environments. SML was consistently enriched in nitrate, nitrite, orthophosphate, and total organic carbon than ULW in both investigated environments. Except in spring in Rogoznica Lake, bacterial abundance in SML was also significantly higher (
p
< 0.05) than in ULW. Both layers and sites show prominent seasonal variability. High-throughput 16S rRNA gene sequencing of DNA and cDNA revealed a considerable difference in bacterial assemblage structure, although study sites were < 200 m apart. Heterotrophs were predominant in both layers with pronounced spatial and temporal structural differences, except in autumn in Rogoznica Lake when, autotrophs became the dominant fraction under oxygen-deprived conditions. All these variations were driven by in situ conditions, the most important ones being total organic carbon and temperature (and additionally dissolved oxygen in Rogoznica Lake). This is especially important in terms of ongoing eutrophication, warming and deoxygenation, noticed not only in the Adriatic Sea and Rogoznica Lake but globally as well. Therefore, further structural and physiological changes in bacterioneuston and bacterioplankton assemblages can be expected.
This report presents the first record of Tripos rotundatus (Jørgensen) Gómez in the Adriatic Sea. The species was found in a net sample in the 50 – 100 m depth layer, taken on July 2021 off the ...southern coast of the Adriatic Sea. The species T. rotundatus was probably previously misidentified as the morphologically similar species T. digitatus (Schütt) Gómez.
Hypoxic and anoxic niches of meromictic lakes are important sites for studying the microbial ecology of conditions resembling ancient Earth. The expansion and increasing global distribution of such ...environments also means that information about them serves to understand future phenomena. In this study, a long-term chemical dataset (1996–2015) was explored together with seasonal (in 2015) information on the diversity and abundance of bacterial and archaeal communities residing in the chemocline, monimolimnion and surface sediment of the marine meromictic Rogoznica Lake. The results of quantitative PCR assays, and high-throughput sequencing, targeting 16S rRNA genes and transcripts, revealed a clear vertical structure of the microbial community with Gammaproteobacteria (Halochromatium) and cyanobacteria (Synechococcus spp.) dominating the chemocline, Deltaproteobacteria and Bacteroidetes dominating the monimolimnion, and significantly more abundant archaeal populations in the surface sediment, most of which affiliated to Nanoarchaeota. Seasonal changes in the community structure and abundance were not pronounced. Diversity in Rogoznica Lake was found to be high, presumably as a consequence of stable environmental conditions accompanied by high dissolved carbon and nutrient concentrations. Long-term data indicated that Rogoznica Lake exhibited climate changes that could alter its physico-chemical features and, consequently, induce structural and physiological changes within its microbial community.
The taxonomic composition and structure of a marine epilithic diatom community were sampled from the bottom of the two sites at monthly intervals from January to December 2011 in the small ...semi-enclosed oligotrophic Neum Bay in Bosnia and Herzegovina (Middle Adriatic). Altogether, 264 diatom taxa (species and infraspecific taxa) within 69 genera were identified. Among them, 149 and 203 taxa occurred in samples from the shallow (0.5 m depth) and deep (8 m depth) sites, respectively. The monthly distribution of most of the diatoms was irregular and high numbers of sporadic taxa were found. SIMPER analysis indicated that the difference between shallow and deep sites could be largely attributed to the frequently recorded diatom taxa and those with high percentage abundances. They were Halamphora coffeiformis, Caloneis excentrica, Cocconeis scutellum var. scutellum, Licmophora flabellata, Licmophora gracilis, Licmophora sp., Navicula abunda, Rhabdonema adriaticum, and Striatella unipunctata. Canonical Correspondence Analysis (CCA) showed that temperature, oxygen saturation (O2/O2′), silicate concentration (SiO4), and salinity were the most important factors influencing diatom community structure in the bay.
The initial colonization of bacteria and diatoms on a immersed artificial substrate and the development of diatom assemblages in relation to physico-chemical parameters were investigated on a weekly ...basis at one station in the marine Lake Mrtvo More, South Croatia, from April to October 2016. According to TRIX trophic index, lake showed different trophic character: (i) oligotrophic (at the beginning and the end of the study), (ii) mesotrophic (the end of June to mid-July), (iii)
eutrophic (the end of July to mid-September). Heterotrophic bacteria increased to peak abundances (69,268 cells cm–2) at the beginning of June when the diatoms abundances start to increase. The lake has high diatom species richness (285 diatom taxa within 72 genera), with the highest species diversity index in August. Among diatoms, adnate were the primary colonizers, particularly Cocconeis dirupta W.Gregory var. flexella (Janisch and Rabenhorst) Grunow and Cocconeis scutellum Ehrenberg var. scutellum, while motile taxa joined the fouling communities from July to September. This study showed close relationship
between diatom species composition and changes of physico-chemical parameters, particularly the nutrient concentrations.
Bacteria are the most important microorganisms in the world oceans, accounting for up to 75% of the total biomass. They are responsible for fundamental biogeochemical processes and therefore often ...used as ecological indicators. In this study, bacteria were quantified by flow cytometry and their diversity assessed by High Throughput Sequencing (HTS) in the southern Adriatic Sea. The most abundant bacterial groups were also quantified by qPCR. The samples were collected from the surface to the seabed over a total of 16 different depths at four stations during the late winter BIOTA (BIO-Tracing Adriatic water masses) cruise conducted in March 2016. The investigated area showed unusual water mass properties and was characterized by a shallow mixed layer, which differed from the usual winter convection conditions, typical of middle-altitude ecosystems and important for the seasonal picoplankton dynamics of this area. Heterotrophic bacteria were separated into HNA (relative High Nucleic Acid content) and LNA (Low Nucleic Acid content) subpopulations with abundances up to 1.8 × 105 and 8.8 × 105 cells mL−1, respectively. HNA dominated at offshore stations reaching their maximum at depths below the euphotic zone. The bacterial community was dominated by Alphaproteobacteria, accounting for >40% of the total sequence reads and were mainly represented by the SAR11 clade (90.84%), followed by Marinimicrobia (18% of the total sequence reads), mainly represented by clade SAR406 (8.44%). Distinctive bacterial groups were found in the euphotic layer (Bacteroidetes and Actinobacteria) and aphotic layer samples (Deltaproteobacteria, Marinimicrobia, Chloroflexi, Acidobacteria and Planctomycetes). Results of the qPCR analyses further confirmed HTS results with highest abundances obtained for Alphaproteobacteria, followed by Gammaproteobacteria and Bacteroidetes. The adopted multiple approach, combining different molecular tools, critically supported by optics and flow cytometry, reveal changes in the bacterial assemblages during the unusual thermohaline conditions observed in 2016 in the southern Adriatic Sea.
•Multilayer approach provided in depth characterization of microbial community.•In winter 2016 a 200 m mixed overlaid stratified waters were formed.•Euphotic and aphotic layer harbor distinctive bacterial communities•Communities distribution was affected by the absence of the deep-water convection.•α-Proteobacteria and γ-proteobacteria represented dominant bacterial populations.
In this study, we focus on the interactive dynamics between physico-chemical processes and picoplankton distribution in order to advance our current understanding of the roles of various parameters ...in regulating picoplankton community structure in highly dynamic marine system such as the South Adriatic Sea. The research was carried out between October 2011 and September 2012 along the transect in the northern part of the South Adriatic Pit. The deep water convection occurred in the southern Adriatic during February 2012, with vertical mixing reaching the depth of 500 m. The picoplankton community was highly affected by this mixing event, whilst its compartments each responded differently. During deep water convection low nucleic acid heterotrophic bacteria (LNA HB) and Synechococcus had their lowest abundances (4 × 105 cell ml−1 and 8 × 102 cell ml−1, respectively), picoeucaryotes had their highest abundances (104 cell ml−1), while Prochlorococcus was absent from the area, most likely due to intense cooling and vertical mixing. In March 2012 Eastern Adriatic Current (EAC) brought warm and saline water with more nutrients, which resulted in the proliferation of high nucleic acid heterotrophic bacteria (HNA HB), having maximal abundance (4 × 105 cell ml−1). The re-establishment of Levantine Intermediate Water (LIW) intrusion after the deep water convection resulted in the re-appearance of Prochlorococcus and maximal abundances of Synechococcus (4 × 104 cell ml−1) in May 2012. The distribution of picoheterotrophs was mainly explained by the season, while the distribution of picophytoplankton was explained by the depth. Aside from nutrients, salinity was an important parameter, affecting particularly Prochlorococcus. The re-appearance of Prochlorococcus in the southern Adriatic during the period of LIW intrusion, together with their correlation with salinity, indicates their potential association with LIW. The relationship between Prochloroccocus distribution and physico-chemical environmental parameters provides an important insight into the ecological roles and niche preferences of this group.
•The picoplankton community was highly affected by deep water convection event, whilst its compartments each responded differently.•The distribution of picoheterotrophs was mainly explained by the season, while the distribution of picophytoplankton was explained by the depth.•The re-appearance of Prochlorococcus in the southern Adriatic during the LIW intrusion, indicates its potential association with LIW.
Phytoplankton community structure and dynamics were investigated in the open southern Adriatic Sea during two winter-spring seasons (2016 and 2017) under different oceanographic and meteorological ...conditions. The principal environmental factor was a pronounced inflow of the Levantine Intermediate Water into the Adriatic, favoured by the cyclonic circulation of the Northern Ionian Gyre. As a consequence, high salinity values of about 38.8–38.9, were registered. Fifteen research cruises were undertaken in the same sampling area situated in the northern part of the Southern Adriatic Pit (SAP) with a maximum depth of 1200 m. Two specific circumstances were encountered: (i) high abundances of phytoplankton in the deep layer associated with strong downward flow in 2016, and (ii) an intense surface phytoplankton bloom in March 2017. This particular event occurred following the strong vertical convective mixing, which increased nutrient availability in the euphotic layer. High in situ Chl-a concentrations (max. 1.65 mg m−3) and phytoplankton abundances higher than 105 cells L−1 are not common in the habitually oligotrophic open southern Adriatic Sea, and this study attempts to determine the driving force of that phenomenon. The phytoplankton community in SAP involved nanoflagellates and diatoms as the most abundant taxonomic groups during the March 2017 bloom. Presence of some coastal phytoplankton taxa suggests the influx of coastal water masses and transport of species either longitudinally, from the northern to the Southern Adriatic in concomitance of the Northern Adriatic Dense Water spreading, or transversal as a response to the strong mesoscale activity in the study region, comprising intense shelf - open sea interaction.
•Local climatic and environmental variations modified thermohaline properties.•Deep water convection is important processes driving primary productivity.•Winter-spring diatom bloom did not show a regular pattern among years.•Phytoplankton community can be a good indicator of convective downward flow.
The South Adriatic (SA) is an entry point for water masses originating from the Ionian Sea (IS) and a place of dense water formation for the eastern Mediterranean deep circulation cell. Water masses, ...entering the SA in larger amount during the winter, show decadal variability explained by different circulating regimes (cyclonic and anticyclonic) in the IS, referred to as “Bimodal Oscillating System” (BiOS). Sampling station was situated in the South Adriatic Pit (SAP) with depth of 1200m. Micro- and nano-phytoplankton abundances, community structure, chlorophyll a concentrations, physical and chemical properties are presented in the winter and spring months for five consecutive years (2009–2013) during different circulating regimes of BiOS. Vertical convective mixing was regularly observed in winter except in 2011 which had effect on nutrient availability and consequently on biomass of primary producers. Effect of strong vertical mixing in February 2012 resulted with exceptionally high phytoplankton abundance and chlorophyll a concentrations in March of 2012. Strong convective mixing resulted in higher diatom abundances, comparing to winter when mixing did not occur. No such bloom was observed during investigated spring.
•Major factor controlling phytoplankton abundance and biomass is deep winter convection.•Winter convection happened during anticyclonic and cyclonic years.•Strong convective mixing resulted in higher diatom abundances.•No bloom was observed during spring investigations.•Regional meteorology and different water masses influence on winter production.
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