Variability in the bottom-up (BU) and top-down (TD) regulation of bacteria was analysed on trophic and temporal (seasonal and inter-annual) scales in the middle Adriatic Sea during 1997-2006 using 3 ...empirical models. The analyses showed the tendency for bacteria to be TD controlled in oligotrophic open sea stations, and BU controlled in more eutrophic coastal stations. However, temporal variability in BU and TD controls was much stronger, with periods of both strong BU and strong TD controls being observed at all studied stations, independently of their trophic status. Decomposition of the time series was performed to identify seasonal and inter-annual changes in the relative importance of the BU and TD controls of bacteria. At all stations, BU control dominated during colder periods of the year, whereas TD control dominated during warmer periods. Nonseasonal fluctuations in the relative importance of BU and TD controls of bacteria pointed to a few periods when one or the other type of control was very strong. These periods coincided with some specific meteorological and hydrographic conditions - the strong influence of North Adriatic Dense Water in 1997, the strong Levantine Intermediate Water ingression in 2004, and the extremely warm winter and the Po River runoff in 2000-2001.
To understand the activity of marine viruses, experiments on viral production, viral decay and the percentage of lytic and lysogenic bacterial cells among the total number of bacterial cells were ...carried out seasonally at two stations in the Adriatic Sea with different trophic conditions. Additionally, we are providing an insight on the enrichment with dissolved and particulate organic matter by viral lysis in the studied area. Viral production was higher at the coastal station than at the open-sea station. Viral decay rates were also higher at the coastal sea station than at the open-sea station, and accounted for approximately 40% of viral production at both investigated stations. The percentage of lysogenic infection was lower than that of lytical infection, which indicates the prevalence of the lytic cycle at both stations. Viruses had a significant influence on bacterial mortality through high daily removal of the bacterial standing stock at the coastal and open-sea station. The viruses contributed to the restoration of dissolved organic carbon, nitrogen and phosphorus in the microbial loop by lysing the bacterial cells at the studied stations. All the above suggest that viruses are important in the microbial food web and an important factor in the control of bacterial populations within the study area.
The Mediterranean Sea (including the Adriatic Sea) has been identified as a ‘hotspot’ for climate change, with the prediction of the increase in water temperature of 2–4°C over the next few decades. ...Being mainly oligotrophic, and strongly phosphorus limited, the Adriatic Sea is characterized by the important role of the microbial food web in production and transfer of biomass and energy towards higher trophic levels. We hypothesized that predicted 3°C temperature rise in the near future might cause an increase of bacterial production and bacterial losses to grazers, which could significantly enlarge the trophic base for metazoans. This empirical study is based on a combined ‘space-for-time substitution’ analysis (which is performed on 3583 data sets) and on an experimental approach (36 in situ grazing experiments performed at different temperatures). It showed that the predicted 3°C temperature increase (which is a result of global warming) in the near future could cause a significant increase in bacterial growth at temperatures lower than 16°C (during the colder winter-spring period, as well as in the deeper layers).
The effect of temperature on bacterial growth could be additionally doubled in conditions without phosphorus limitation. Furthermore, a 3°C increase in temperature could double the grazing on bacteria by heterotrophic nanoflagellate (HNF) and ciliate predators and it could increase the proportion of bacterial production transferred to the metazoan food web by 42%. Therefore, it is expected that global warming may further strengthen the role of the microbial food web in a carbon cycle in the Adriatic Sea.
•Temperature effect on bacterial growth is more significant at lower temperatures.•Availability of phosphorus doubled temperature effect on bacterial growth.•Bacterial carbon flux towards metazoan food web increases with temperature.•Global warming could strengthen the role of microbial food web in a carbon cycle.
This paper addresses the dynamics of the prokaryotic picoplankton community in the coastal and open sea areas of the central Adriatic and in the coastal area of the southern Adriatic. This involved ...the study, from January to December 2005, of bacteria (total number of non-pigmented bacteria; high nucleic acid content (HNA) bacteria; low nucleic acid content (LNA) bacteria), cyanobacteria (Synechococcus and Prochlorococcus) and heterotrophic nanoflagellates. During the warmer seasons, in the mainly oligotrophic area under investigation into the Adriatic Sea, bacterial densities and bacterial production have shown an increase in values and domination of the LNA group of the bacterial population. In contrast, in those areas influenced by karstic rivers, the domination of HNA bacteria in total abundance of non-pigmented bacteria and high values of bacterial production was estimated throughout the investigated period. Our results show the importance of both HNA and LNA bacterial groups in the total bacterial activity throughout the investigated area. The biomass of bacteria was mostly predominant in the prokaryotic community, while within the autotrophic community Synechococcus biomass mostly predominated. During the warmer seasons, an increase in autotrophic biomass was observed in relation to non-pigmented biomass. The importance of predation in controlling bacteria by heterotrophic nanoflagellates was pronounced during the warmer period and in the coastal areas.
La abundancia, biomasa volumen y la diversidad morfológica bacteriana fueron estudiadas en sedimentos recogidos del este del mar Adriático (bahía de Kastela) con el objeto de investigar su relación ...con los cambios de diferentes parámetros ambientales. Para establecer los cambios de los parámetros investigados a escala temporal y entre capas de sedimentos, las muestras de sedimento fueron recogidas mensualmente durante 2002, con un corer de pistón desde la superficie del sedimento hasta la profundidad de 10 cm. La concentración de materia orgánica, pigmentos cloroplastídicos equivalentes (CPE), clorofila a (chl a) y feopigmentos (PHAEO) fueron utilizados como indicadores de la concentración de sustrato en el sedimento. La profundidad del sedimento era un factor significativo en la influencia de la distribución del número de bacterias, biomasa y volumen. Las propiedades granulométricas del sedimento no tenían efecto sobre la distribución de bacterias. La abundancia, la biomasa y el volumen bacteriano estaban fuertemente relacionadas con los indicadores de sustrato en ambas escalas. La acumulación de la materia orgánica lábil en las capas más profundas también tenían un gran efecto sobre el tamaño y la estructura bacteriana. Una alta cantidad de materia orgánica y baja proporción de la fracción orgánica lábil (CPE; chl a y PHAEO) indica que estos ambientes actúan como sumideros para la acumulación de material detrítico.
Bacterial abundance, biomass, volume and morphological diversity were studied in sediments collected in the eastern Adriatic Sea (Kastela Bay) in order to investigate their relationship with changes in environmental parameters. To asses the changes in the investigated parameters on a temporal scale and between sediment layers, the sediment samples were collected monthly in 2002 with a piston corer from the sediment surface to a depth of 10 cm. The concentrations of organic matter (OM), chloroplastic pigment equivalents (CPE), chlorophyll a (chl a) and phaeopigments (PHAEO) were used as indicators of substrate concentrations in sediments. Sediment depth was a significant factor influencing the distribution of bacterial abundance, biomass and volume. Granulometric properties of the sediment had no effect on the distribution of bacteria. Bacterial abundance, biomass and volume were strongly related to the indicators of substrate concentrations on both scales. The accumulation of labile OM in deeper layers also had a profound effect on the size and structure of bacteria. High amounts of OM and the low proportion of labile organic fraction (CPE; chl a and PHAEO) indicate that this environment acts as a sink for accumulation of detrital material.
The dynamics of the prokaryotic picoplankton community were studied at six stations of three embayments in Boka Kotorska Bay from January 2010 to January 2011. The abundance ofnon-pigmented bacteria, ...high nucleic acid content (HNA) bacteria, low nucleic acid content (LNA) bacteria, bacterial production and heterotrophic nanoflagellates was determined, as well as the chlorophyll a, physical and chemical factors of the water column. It seems that freshwater input has the ability to control bacterial abundance as well as the proportion of HNA cells in bacterial community and thus the abundance of HNF cells. During the warmer seasons, in the investigated area, which is mainly oligotrophic, we found an increase in values and domination of the LNA group in the bacterial population. The dominance of the HNA group was found only during the colder seasons. Weak coupling between bacteria and HNF suggests that predation (top down control) is not dominant in controling of bacterial abundance in studied area.Original Abstract: Raspodjela i aktivnost prokariotskog pikoplanktona u crnogorskom dijelu juznog Jadrana je studirana na sest postaja Bokokotorskog zaljeva u razdoblju od sijecnja 2010. do sijecnja 2011. Istrazivana je brojnost nepigmentiranih bakterija, udjeli bakterija s visokim (HNA) i niskim (LNA) sadrzajem nukleinskih kiselina, bakterijska proizvodnja, heterotrofni nanoflagelati (HNF) te klorofil a i fizikalno kemijski cimbenici. Utvrdeno je da unos slatke vode u istrazivano podrucje ima utjecaja na bakterijsku brojnost, na udjele HNA I LNA grupa bakterija kao i na brojnost HNF-a. U toplijem razdoblju godine u istrazivanom je podrucju utvrden porast i prevladavanje LNA bakterija dok je prevladavanje HNA bakterija utvrdeno u hladnijem dijelu godine. Slaba povezanost izmedu bakterija i HNF ukazuje da predacija nije prevladavajuci mehanizam kontrole bakterijske abundancije u istrazivanom podrucju.
Being filter-feeding organisms, bivalves present a potential health hazard to consumers due to pathogens which may be present in the marine environment. The simultaneous effect of temperature and ...salinity on the rate of concentration of indicator microorganism Escherichia coli (EC) in mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) was studied in experimental conditions with different concentrations of EC in seawater. The experiments were carried out in 3000 L tanks and were performed within the natural range of temperature (12 degree C, 18 degree C and 24 degree C) and salinity (37 psu and 32 psu) and within the common range of EC concentration in the coastal Adriatic Sea. In order to determine the influence of temperature and salinity on the rate of concentration of EC in bivalves, we used short-time experiments confined by the periods of linear increase of concentration of EC in bivalves which lasted between 1 and 3 hrs. The results clearly showed that the rate of EC concentration in mussels and oysters depended on the concentration of EC in the surrounding seawater and on the rate of filtration of seawater by bivalves highly controlled by temperature and salinity. Moreover, the effect of temperature and salinity on concentration rate affected one another regardless the concentration of EC in tanks. The rate of EC concentration was significantly higher in mussels than in oysters. In mussels, variations in salinity had more effect than variations in temperature in bringing about changes of the concentration rate, whereas in oysters the result was reversed. Furthermore, in mussels, temperature had stronger effect in changing concentration rate at salinity of 37 psu than at salinity of 32 psu, whereas in oysters the result was the opposite.
Seasonal variations in abundance and carbon biomass of ciliated protozoa and micrometazoa were studied from May 1998 to November 1999 in the eutrophicated area of Kaštela Bay (Middle Adriatic Sea). ...Ciliates showed peaks in spring and autumn, primarily due to changes in the abundance and biomass of tintinnines, which participated in total ciliate abundance and biomass with 40.48 and 60.02%, respectively. The highest tintinnine density was 4,278 ind. l⁻¹, while their average biomass varied from 0.611 to 26.557 μgC l⁻¹ . Maximal average density and biomass of non-loricates were 1,430 ind. l⁻¹ and 3.925 μgC l⁻¹, respectively. The micrometazoa community was dominated by copepod nauplii, especially during the summer and autumn. The copepod biomass ranged between 3.47 and 26.75 μgC l⁻¹ . High abundance and biomass values of the investigated zooplankton groups point to an important role of these organisms in the secondary production in the Bay, indicating that they may be (1) a crucial factor in controlling the populations of nano-/pico-phytoplankton and heterotrophic nanoflagellates, and (2) a significant prey for larger micrometazoans.
Two direct heterotrophic bacterioplankton counting methods, epifluorescence microscopy (EM) and flow cytometry (FCM) were compared using samples collected in two geographically different oceanic ...regions, the Adriatic Sea and the English Channel. A statistically significant correlation was found between results obtained by these two methods for samples collected in the Adriatic Sea (r =0.61, n =919, P <0.001) and in the English Channel (r =0.64, n =33, P <0.001). Samples from the Adriatic Sea showed on average 1.16 times higher values obtained by flow cytometry than values estimated by epifluorescence microscopy, while samples from the English Channel showed on average a 0.74 ratio between flow cytometry and epifluorescence microscopy counts. The overall coefficient of variation for epifluorescence microscopy data for samples from the Adriatic Sea and the English Channel was 15.91% and 12.89%, respectively. The flow cytometry method had lower overall coefficient of variation value; for samples collected in the Adriatic Sea it was 3.64%, while for samples collected in the English Channel it was 1.88%.Original Abstract: Dvije direktne metode za brojanje heterotrofnog bakterioplanktona, epifluorescentna mikroskopija (EM) i protocna citometrija (FCM), usporedjene su koristeci uzorke sakupljene s dva zemljopisno razlicita morska podrucja, Jadranskog mora i Engleskog kanala. Izmedju dvije direktne metode brojanja u uzorcima iz Jadranskog mora (r = 0.61, n = 919, P <0.001) i Engleskog kanala (r = 0.64, n = 33, P <0.001) pronadjena je statisticki znacajna korelacija. U Jadranskom je moru metoda protocne citometrije davala u prosjeku neznatno nize rezultate u odnosu na metodu epifluorescentne mikroskopije, dok je u Engleskom kanalu broj heterotrofnih bakterija dobiven metodom epifluorescentne mikroskopije bio u prosjeku nesto veci u odnosu na protocnu citometriju. Medjutim, srednji koeficijent varijacije rezultata dobivenih epifluorescentnim mikroskopom za podrucje Jadrana iznosio je 15.91%, za podrucje Engleskog kanala 12.89%, dok je protocna citometrija rezultirala nizim koeficijentima varijacije te je za uzorke iz Jadrana iznosila 3.64%, a za uzorke sakupljene u Engleskom kanalu svega 1.88%. Navedeni rezultati predstavljaju doprinos sagledavanju metode protocne citometrije kao brze, sigurnije i preciznije za brojenje bakterioplanktona u morskom okolisu.
Temporal and spatial patterns of bacteria and heterotrophic nanoflagellates (HNF) were studied monthly from January 1997 to December 1998 in the middle Adriatic Sea. Bacterial and HNF relationships ...with phytoplankton biomass and temperature were analyzed to examine how the relative importance of bottom-up and top-down factors may shift over seasons and locations. For the coastal area, an inconsistent relationship between bacterial abundance and chlorophyll a and a stronger relationship between bacterial abundance and bacterial production suggest that other substrates than those of phytoplankton origin are important for bacteria. The analysis of simultaneous effects of temperature and bacterial production on bacterial abundance showed that the effect of temperature obscured the effects of bacterial production, suggesting that bacterial growth itself is highly temperature-dependent. The relationship between HNF abundance and bacterial abundance was slightly improved by the inclusion of in situ temperature, bacterial production or both parameters, as additional independent variables. About 60% of the variability in HNF abundance can be explained by bacterial abundance, bacterial production and temperature. In the open sea, tight coupling of bacterial abundance with chlorophyll a concentrations implied that phytoplankton-derived substrates have a dominant role in controlling bacterial abundance. During the colder months, bacterial abundance was high enough to support higher HNF abundance than observed, suggesting that predation exerted a minor depressing influence on bacterial abundance during that period. During the spring-summer period, HNF controlled bacterial standing stocks by direct cropping of bacterial production.
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