Silicoflagellate abundance, vertical distribution and morphology were studied during spring (March 2014) at three sampling stations located in the Northeast Aegean Sea adjacent to the Dardanelles ...Strait and characterized by a variable influx of cold, low-salinity Black Sea water. The silicoflagellate assemblage was dominated by Dictyocha stapedia and Stephanocha speculum with minor contribution of D. aculeata and Octactis pulchra. While specimens of D. stapedia were represented by the typical morphologies described in other areas of the Mediterranean Sea, populations of S. speculum displayed peculiar characters: they were large, predominantly 7-sided, with a small apical ring as well as apical ring spines, concave basal ring sides and non-rotated apical structure. Some of these features have been described for S. speculum at high latitudes, but the combined characters make these specimens slightly different from the high latitude populations. Similar morphologies have been observed in the western Black Sea, thus we can infer that the peculiar specimens detected in the Northeast Aegean are associated with the influx of Black Sea water masses.
L’abondance, la distribution vertical et la morphologie de silicoflagellés ont été étudiés au cours du printemps (mars 2014) à trois stations d’échantillonnage situées dans la Mer Egée du Nord-Est à proximité du détroit des Dardanelles et caractérisés par un afflux variable d’eau froide à faible salinité de la Mer Noire. L’assemblage de silicoflagellates était dominé par Dictyocha stapedia et Stephanocha speculum avec une contribution mineure de D. aculeata et Octactis pulchra. Bien que des spécimens de D. stapedia étaient représentés par les morphologies typiques décrites dans d’autres zones de la Mer Méditerranée, les populations de S. speculum montré des caractéristiques particuliers: ils étaient grands, très souvent avec 7 côtés, avec un petit anneau apical et avec des épines sur l’anneau apical, les côtés concaves de l’anneau de base et la structure apicale non-tournée. Certaines de ces caractéristiques ont été décrites pour S. speculum dans les hautes latitudes, mais les caractéristiques combinées rendent ces spécimens légèrement différents des populations des hautes latitudes. Des morphologies similaires ont été observées dans la Mer Noire de l’Ouest, de sorte que nous pouvons en déduire que les spécimens particuliers détectés dans la Mer Egée du Nord-Est sont associés à l’afflux de masses d’eau de la Mer Noire.
The release of silver nanoparticles (AgNPs) is expected to rise in the near future, with possible negative effects on aquatic life and enhancement of microbial resistance against AgNPs. However, a ...realistic evaluation of the toxicity of AgNPs to the marine ecosystem is currently missing. Therefore, we designed a mesocosm experiment to assess the impact of AgNP exposure on natural microbial plankton community dynamics in a coastal marine site at environmentally relevant concentrations. We monitored changes in the composition of the planktonic community, from viruses to protists. Further, we analyzed the concentration and properties of AgNPs for the total time of exposure. We found that the addition of AgNPs even at a low dose affected the plankton communities. Specifically, the growth of
Synechococcus
was inhibited and bacterial community composition significantly changed. Additionally, the amount of a lysogeny-related gene increased and viral auxiliary metabolic genes that are involved in cyanobacterial photosynthesis decreased, revealing a damaged photosynthetic potential after AgNP exposure. Microbial plankton was significantly affected due to both increased dissolved silver ions and decreased AgNP size. Our results highlight that the release of AgNPs alters the functioning of the marine food web by hampering important viral and bacterial processes.
Numerous specimens of coccolithophore combination coccospheres in water samples collected from the North Aegean and Tyrrhenian (Mediterranean Sea) have been photographed using the scanning electron ...microscope. As a consequence a series of taxonomic revisions are proposed, in which the names of the heterococcolithophores and holococcolithophores involved in the same life-cycle are synonymized. This has resulted in synonymizing the genus Coronosphaera with Syracosphaera and establishing one new combination; Syracosphaera arethusae (Kamptner 1941) comb. nov.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this study, we investigate the strength and efficiency of carbon sequestration in the Southern European Seas (SES), by analyzing the export of POC at three deep sites located in the Western ...Mediterranean Sea (WMED), the Eastern Mediterranean Sea (EMED) and the Black Sea (BS). We combine estimations of satellite and algorithm-generated primary production data, calculated POC fluxes out of the euphotic layer and POC fluxes measured by sediment traps at the mesopelagic and bathypelagic layers during a one year period, with an ultimate goal to obtain a better understanding of the functioning of the biological pump in the SES.
Annual particulate primary production based on satellite estimations (SeaWiFS) at the three sites, averages 205, 145 and 225gCm−2y−1 at the WMED, EMED and BS, respectively. According to our findings, the fraction of primary production that is exported out of the euphotic zone in the SES ranges between 4.2% and 11.4%, while the fraction reaching the mesopelagic layer (1000–1400m depth) ranges between 0.6% and 1.8%. Finally, the fraction of primary production exported at the bathypelagic layer (2000–2800m depth) is found to be 0.6%, 0.3% and 1.4% in the WMED, EMED and BS, respectively. The role of various processes responsible for the replenishment of surface waters with nutrients, giving rise to productivity episodes and organic carbon export to depth at the three SES sites is considered.
•POC fluxes were monitored during 1-year (Sept 2007 - Sept 2008) at three deep sites in the Mediterranean and Black Seas (SES).•Less than 2.0% and 1.4% of the carbon produced via PP is exported below 1000m and 2000m, respectively, in the SES.•Different physical and biogeochemical settings affect the seasonality of the POC export in the three contrasting sites.
The short-time scale evolution of plankton carbon partitioning and downward flux in the modified Black Sea water (BSW) mass entering the northeast Aegean Sea was studied using a Lagrangian approach ...(6–10 April 2008). The free-drifting sediment trap positioned at the bottom of the BSW layer and the control drifter, followed the same path within the anticyclone that circulates the BSW in the area. Ζooplankton biomass increased (from 159 to 292 mg C m−2), as did faecal pellet production (from 5 to 8 mg C m−2 day−1), whereas a generally decreasing trend was displayed by particulate organic carbon (POC) (from 2099 to 1440 mg C m−2), net primary production and biomass of plankton cells >5 µm (from 32 to 11 mg C m−2 day−1 and from 153 to 124 mg C m−2, respectively). At the same time, the organic carbon flux increased (from 131 to 311 mg C m−2 day−1), due to the contribution of zooplankton detritus (from 30 to 165 mg C m−2 day−1). Normalized biomass-size spectra slopes suggest an elevated grazing pressure upon microplankton cells and a non-steady-state ecosystem. Moreover, both the overall shallow slope values and their high correlation to organic carbon flux indicate an increased efficiency of energy transfer to higher trophic levels.
This study presents the species composition of living coccolithophore communities in the Aegean Sea (northeastern Mediterranean), investigating their spatial and temporal variations in various ...environmental conditions from mesotrophic to ultra- oligotrophic regions. Coccolithophores of the photic zone in the Aegean Sea are relatively diverse (65 heterococcolithophores and 34 holococcolithophores) and dominated mostly by Emiliania huxleyi, Syracosphaera spp., Rhabdosphaeraceae and holococcolithophores. Hierarchical classification using R-mode cluster analysis distinguished five coccolithophore groups: Group Ia (Emiliania huxleyi, Syracosphaera molischii and Syracosphaera ossa) prevails in the high cell density and low diversity assemblages during the winter and early spring, when low temperatures and high nutrient concentrations are prevailing. Particularly in the north Aegean, E. huxleyi is dominating the upper photic zone being affected by the Black Sea Water inflow and the associated control on the water column stratification. Group Ib (Florisphaera profunda, Algirosphaera robusta, Syracosphaera anthos and Syracosphaera lamina) becomes important in the lower photic zone, making up the typical deep assemblages, whereas Group Ic (mainly Helicosphaera carteri and Gephyrocapsa oceanica) implies an opportunistic behavior in distinctly polluted neritic regions. Group IIa (Rhabdosphaera clavigera, Syracosphaera protrudens, Syracosphaera halldalii and numerous holococcolithophores) dominates the late spring-early autumn low cell density and high diversity assemblages, mainly in the thermally-stratified south Aegean and/or shallow, coastal environments with normal/ oligotrophic conditions, while Group IIb (Umbellosphaera tenuis and Syracosphaera pulchra) dominates the coccolithophore assemblages mainly during the early autumn in the north Aegean, thus reflecting the influence of Levantine Intermediate Water masses in the middle-lower photic zone. Our results suggest that abundance and variability in Aegean Sea coccolithophore assemblages are primarily controlled by surface water circulation and the associated water column stratification,with the sea temperature gradient affecting species composition.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The release of silver nanoparticles (AgNPs) is expected to rise in the near future, with possible negative effects on aquatic life and enhancement of microbial resistance against AgNPs. However, a ...realistic evaluation of the toxicity of AgNPs to the marine ecosystem is currently missing. Therefore, we designed a mesocosm experiment to assess the impact of AgNP exposure on natural microbial plankton community dynamics in a coastal marine site at environmentally relevant concentrations. We monitored changes in the composition of the planktonic community, from viruses to protists. Further, we analyzed the concentration and properties of AgNPs for the total time of exposure. We found that the addition of AgNPs even at a low dose affected the plankton communities. Specifically, the growth of
Synechococcus
was inhibited and bacterial community composition significantly changed. Additionally, the amount of a lysogeny-related gene increased and viral auxiliary metabolic genes that are involved in cyanobacterial photosynthesis decreased, revealing a damaged photosynthetic potential after AgNP exposure. Microbial plankton was significantly affected due to both increased dissolved silver ions and decreased AgNP size. Our results highlight that the release of AgNPs alters the functioning of the marine food web by hampering important viral and bacterial processes.
The release of silver nanoparticles (AgNPs) is expected to rise in the near future, with possible negative effects on aquatic life and enhancement of microbial resistance against AgNPs.
This work is a study of plankton food web structure and carbon flow in March and September 1997 in the Aegean Sea, area of outflow of Black Sea waters in the Mediterranean Sea. Biomass and production ...of autotrophs were measured by size fraction as well as bacterial biomass and production; furthermore, we studied heterotrophic nanoflagellates (HNAN), ciliates and mesozooplankton biomass, copepod production and grazing impact on phytoplankton. The obtained low values of nutrients and plankton biomass and production confirmed the oligotrophic character of this region. Despite the fact that there was no significant horizontal variability in the spatial distribution of nutrients throughout the study area, the planktonic biomass and production revealed a gradual decrease from the Northeast Aegean (NEA) towards the South Aegean (SA). In the Northeast Aegean, a large part of the fixed carbon was channelled through the microbial food web towards copepods; in contrast there was a low transfer of energy in the South Aegean where the multivorous food web was developed. Throughout the study area, almost 60–70% of autotrophic biomass and primary production was performed by cells <3 μm.
Numerous specimens of coccolithophore combination coccospheres in water samples collected from the North Aegean and Tyrrhenian (Mediterranean Sea) have been photographed using the scanning electron ...microscope.As a consequence a series of taxonomic revisions are proposed, in which the names of the heterococcolithophores and holococcolithophores involved in the same life-cycle are synonymized. This has resulted in synonymizing the genus Coronosphaera with Syracosphaera and establishing one new combination; Syracosphaera arethusae (Kamptner 1941) comb. nov.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
During May 2001 and May 2002, the structure and function of the microbial community within and outside the Cyprus quasi-stationary warm-core eddy in the Levantine Basin of the eastern Mediterranean ...was studied down to the depth of the bathypelagic layer. We present here the detailed description of the microbial food web in one of the most oligotrophic and P-starved marine systems on earth. The isothermal layer was at the depth between 20 and 260/300
m at the core of the eddy, and between 20 and 100/110
m outside. Nitrate and phosphate were found at higher concentration between 100 and 500/800
m outside the eddy compared within the core of the eddy, but the vertical diffusive flux of nitrate and phosphate across the pycnocline was higher within the core of the eddy. There were only minor differences in microbial abundance in the euphotic layers of the two sites. It is suggested that the differences in the areal supply of nutrients to the isothermal layer, between the two sites, resulted in essentially a similar volumetric supply of nutrients to the euphotic layer. This suggests that the results of this study can be applied to describe the microbial food web within the euphotic layer over the larger area of the Levantine Basin, which exhibits ultra-oligotrophic and P-starved conditions. Primary production and abundances of the microbial community were somewhat higher in May 2001 than in May 2002, possibly because of higher nutrient fluxes in the euphotic layer, which are probably the result of deeper winter mixing in 2001, although a later onset of winter mixing or increased dust supply could not be discounted. In the euphotic layer, heterotrophs (bacteria, heterotrophic nanoflagellates (HNF), and ciliates) dominated (60–70%) the microbial carbon biomass. Heterotrophic ciliates were found to be much more abundant in the upper 50
m of the water column, while no consistent pattern was found for bacteria and HNF throughout the euphotic layer. Autotrophs showed a maximum distribution at the deep chlorophyll maximum found between 100 and 130
m. In the euphotic layer, the relationships between biomass and production for phytoplankton and bacteria suggested a higher top-down control on the phytoplankton in the upper ∼50
m and a consistently tight top-down control on the bacterial biomass throughout the euphotic layer. The phosphate addition experiment in the Cyprus Eddy suggests that the close predator–prey relationships within the microbial heterotrophic community were required for the rapid transfer of a limiting element to higher trophic levels without biomass oscillations in the P-fertilized surface mixed layers (0–20
m). The results from the unmodified system in this study suggested that the rapid P transfer mechanisms would function only in the upper ∼50
m, while the element transfer would be based on a predator–prey relationship with more conceivable biomass oscillations in the deeper waters (∼100–160
m) of the euphotic layer. In the Mediterranean Sea, nutrient concentrations, POC export, and integrated chlorophyll and primary production all tend to decrease toward the east. Our results together with a literature survey showed that abundances of the microbial components in the euphotic layer were not consistently lower in the study area than in the northwestern Mediterranean and that abundances of bacteria and HNF found in the mesopelagic and bathypelagic layers of the study area were within the reported ranges and quite similar to those found in the northwestern Mediterranean. This suggests that the oligotrophic status and the low export production are not reflected in the abundance of the microbial components down to the bathypelagic layer of the eastern Mediterranean.
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