Different pathways of nitrogen and phosphorus regeneration mediated by extracellular enzymes in temperate lakes under various trophic state

Several Italian and Chinese temperate lakes with soluble reactive phosphorus concentrations &lt; 0.015 mg L-1 were studied to estimate nitrogen and phosphorus regeneration mediated by microbial decomposition and possible different mechanisms driven by prevailing oligo- or eutrophic conditions. Leucine aminopeptidase (LAP), beta-glucosidase (GLU) and alkaline phosphatase (AP), algal, and bacterial biomass were related to trophic and environmental variables. In the eutrophic lakes, high algal and particulate organic carbon concentrations stimulated bacterial respiration (&gt; 20 mu g C L-1 h(-1)) and could favor the release of inorganic phosphorus. High extracellular enzyme activities and phosphorus solubilizing bacteria abundance in sediments accelerated nutrient regeneration. In these conditions, the positive GLU-AP relationship suggested the coupling of carbon and phosphorus regeneration; an efficient phosphorus regeneration and high nitrogen levels (up to 0.067 and 0.059 mg L-1 NH4 and NO3 in Italy; 0.631 and 1.496 mg L-1 NH4 and NO3 in China) led to chlorophyll a peaks of 14.9 and 258.4 mu g L-1 in Italy and China, respectively, and a typical algal composition. Conversely, in the oligo-mesotrophic lakes, very low nitrogen levels (in Italy, 0.001 and 0.005 mg L-1 NH4 and NO3, respectively, versus 0.053 and 0.371 mg L-1 in China) induced high LAP, while low phosphorus (33.6 and 46.3 mu g L-1 total P in Italy and China, respectively) led to high AP. In these lakes, nitrogen and phosphorus regeneration were coupled, as shown by positive LAP-AP relationship; however, the nutrient demand could not be completely met without the supply from sediments, due to low enzymatic activity and phosphorus solubilizing bacteria found in this compartment.</p

Prokaryotic abundance and heterotrophic metabolism in the deep Mediterranean Sea

A synthesis of field data carried out in the Mediterranean Sea are presented, aimed at contributing to the knowledge of three prokaryotic-mediated processes and their implications on the Carbon cycle. The distribution of exoenzymatic activities, secondary production and respiration rates was studied together with the prokaryotic abundances. Particular attention was paid to the meso- and bathypelagic layers which play an important role in the Mediterranean carbon cycle. The study is noteworthy because of its large spatial scale spanning the entire Mediterranean Sea over 4 years. In addition, two Atlantic stations in front of the Gibraltar Strait were investigated. The longitudinal distribution of prokaryotic activities and abundance along the MED showed different trends along the depthlayers. In particular, higher exoenzymatic rates were detected in the Eastern basin compared to the Western one; carbon respiration rate showed patterns variable with the sampling periods in the epipelagic and bathypelagic layers, while a consistent Westwards decreasing trend at the mesopelagic layers occurred. Specific enzyme activities per cell showed high values in the deepest layers for leucine aminopeptidase. Comparison with Carbon respiration rate data collected before the 2000s showed changing patterns of microbial heterotrophic processes in the Mediterranean Sea

Trophic and Microbial Patterns in the Ross Sea Area (Antarctica): Spatial Variability during the Summer Season

In open regions of the Ross Sea, the role of the microbial community in the turnover of organic matter has scarcely been investigated; indeed, very little is known on how microbial distribution and functional diversity respond to environmental conditions and hydrographic structures. During the austral summer of 2017, two pelagic areas of the Ross Sea [the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya (A area), and the continental Shelf Break area near Cape Adare (C area)] were studied at selected depths [surface, Deep Chlorophyll Maximum (DCM), Circumpolar Deep Water (CDW), deep waters]. Trophic properties [nutrient concentrations, particulate (POC), dissolved organic carbon (DOC) and its optically significant fraction (CDOM) were measured, together with the main hydrological variables. Microbial community abundance [total prokaryotes, living, dead, and actively respiring fraction, high- and low nucleic acid cells (HNA and LNA), picoand nano-eukaryotes, culturable heterotrophic bacteria], composition, and metabolism (as whole community and as isolated bacteria) were also assessed. Through a multidisciplinary dataset, this study highlighted the variable response of microbial abundance, diversity, and metabolism of the microbial community to the changing local environmental conditions of the Ross Sea. Different forces, such as organic matter inputs (mostly of detrital nature) released from the Drygalski glacier in the A area, and a coastal-to-offshore gradient in the C area, coexisted within this extreme ecosystem. This resulted in a significant spatial segregation of the edaphic parameters, and of the microbial community distribution and metabolic activity patterns

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Producción de CO2 metabólico en el mar Mediterráneo: Un caso de estudio para estimar el balance de carbono en el mar

A synthesis of published metabolic CO2 production rates determined in the water column of the Eastern Mediterranean Sea from 1993 to 1999 is reported with the aim of furnishing an overall picture of the remineralization processes occurring in the basin. The trends of the remineralization are also interpreted with respect to the so-called Eastern Mediterranean Transient (EMT) event. This study augments the sparse data set of respiration measurements, from oceanographic surveys, and highlights the tight coupling between biological processes and circulation patterns. In the photic zone, the rates decreased from West to East as well as from North to South. In the aphotic zone, the C remineralization trend followed the traditional routes of intermediate and deep waters in the Eastern Mediterranean Basin, and underwent the important modifications into the depths as a consequence of the EMT impact.Se realiza una síntesis de los datos publicados de tasas de producción metabólica en la columna de agua en el mar Mediterráneo Oriental desde 1993 a 1999, con el fin de proporcionar una imagen general de los procesos de remineralización que tienen lugar en la cuenca. Las tendencias de la remineralización se interpretan asimismo en relación con el llamado evento Transitorio del Mediterráneo Oriental (EMT). Este estudio aumenta los escasos conjuntos de datos de mediciones de respiración procedentes de campañas oceanográficas y destaca el estrecho acoplamiento entre procesos biológicos y pautas de circulación. En la zona fótica, las tasas decrecen de oeste a este así como de norte a sur. En la zona afótica, la tendencia de la remineralización de C siguió las rutas tradicionales de aguas intermedias y profundas en la cuenca oriental del Mediterráneo, y experimentó las importantes modificaciones en aguas profundas como consecuencia del impacto del EMT

Morphology and LPS content for the estimation of marine bacterioplankton biomass in the Ionian Sea

Fue estudiada la comunidad bacteriana del Mar Jónico mediante el análisis directo en epifluorescencia (recuentos, morfometría y biovolumen celular) y la determinación del contenido de lipopolisacáridos (LPS). Los microorganismos fueron agrupados en cinco morfotipos: cocos, bacilos, cocobacilos, vibriones y espirilos. La columna de agua se encontró dominada por formas cocoideas (39-73%); las formas bacilares y cocobacilares representaron morfotipos uniformemente distribuidos mientras la presencia de vibriones resultó ser muy variable y los espirilos prácticamente ausentes por debajo de los 100 m de profundidad. Los contenidos de LPS fueron encontrados estrechamente correlacionados con los recuentos celulares (P< 0,01; n=88; r=68) y sin relación significativa alguna con los biovolúmenes totales de las muestras. El contenido medio de LPS por ?m3 celular resultó ser de 3,11 (??1,35) ng en las muestras provenientes de la zona fótica y de 0,96 (??0,37) ng en las muestras provenientes de la zona afótica. El contenido medio de C por célula calculado a partir del contenido medio de LPS resultó ser de 23 fg C célula-1 siendo similar al calculado a partir del volumen celular (19 fg C célula-1); las biomasas celulares calculadas a partir de ambos parámetros (LPS y volumen celular) resultaron estar significativamente correlacionadas (P< 0,01; n=95; r=0,59). Del análisis de nuestros resultados surge que el contenido medio de 20 fg C célula-1 (Lee and Furhman, 1987), utilizado ampliamente en la determinación de la biomasa bacteriana marina, podría ser utilizado en línea de máxima también en el Mar Jónico. No obstante, la amplia variabilidad morfológica-dimensional de las células bacterianas observadas, frecuentemente en una misma columna de agua, cuestionan firmemente el empleo de un único factor de conversión en el estudio de todos los ecosistemas marinos. En consecuencia, resulta esencial el análisis de la biomasa bacteriana en cada ambiente en particular para lograr una visión más precisa de los flujos de los principales bioelementos en el ecosistema

Dynamics of microbial biomass and respiratory activity during late summer in a site of Arctic Kongsfjorden

Prokaryotic and phytoplankton interaction plays a key role in relevant processes such as carbon fluxes and nutrient regeneration (Zaccone et al., 2004). Sinking biogenic particles drive respiration in the ocean and related studies are important to determine the flow of organic matter along the water column (Martin et al., 1987; Karl et al., 1987). However, organic matter collected by sediment traps (Langone et al., 2000) or the studies of the disequilibrium 234Th/238U (Aliani et al., 2004) does not take into account the entire pool of oxidable organic matter, which includes the dissolved organic matter present in the seawater. The study of microbial respiration rates instead fills this gap, since respiration includes oxidation of both dissolved and particulate organic mater, providing an integrated estimate of the carbon utilization in the sea (Azzaro et al., 2006). In this context, a study on an Arctic fjord (Kongsfyorden, Svalbard) was done in late summer 2013, with the purpose of knowing the variability of prokaryotic and phytoplanktonic biomass and of microbial remineralization rates over short time scales in a coastal station (water depth ~105 m), where a mooring (Mooring Dirigibile Italia, MDI: 78° 54 .859'N; 12° 15. 411' E) is positioned. The Kongsfjorden was affected by inflow of Atlantic water as well as glacier melt water runoff (Cottier et al., 2005). The experiment comprised 5 samplings performed during a 7 day period in MDI station. For each sampling, photosynthetically active radiation (PAR), temperature and conductivity (salinity) were recorded along the water column with a PNF-300 profiler and a SeaBird Electronics SBE-911 plus profiler, respectively . Water samples were taken at five different depths (surface, 5, 25, 50 and 100 m) to determine nutrients, particulate organic carbon, prokaryotes and phytoplankton biomass, and community respiration. In addition, prokaryotes sunk with the particulate matter were studied into the sediment trap positioned in the MDI during the period between June and September 2013. The latter assessment allowed us to determine the flow of prokaryotes, conveyed from organic matter sinking, throughout the summer. Due to melting of the glaciers in the surface water of the study site, there were sediment loads which strongly limited light penetration and low irradiance (~0.7% E0+) at 5 meters below the surface. Along the water column the intrusion of the salty and warm Atlantic water was visible in the study site and the warm core was at about 25 m depth. PO4 concentrations ranged between 0.43 (surface) and 1 µM (100 m) and in general the values increased from surface to bottom. NH4, NO2 and NO3 significantly changed along the vertical and with time and varied between 0.39 and 5.05µM, 0.01 and 0.67µM, 0.001 and 4.18µM, respectively. Prokaryotic abundances and cell volumes ranged between 5.6 and 15.9 E+05 cells ml-1 and 0.033 and 0.093 µm3, respectively. These latter parameters showed a peak at 25 m depth in the core of incoming Atlantic water. This evidence was not determined in chlorophyll a (range 0.034-1.102 mg m-3), where the highest values were determined at the surface and 5 m depth. Speculations will be made on the variability of the fluxes of carbon remineralization in the short time scale and the different role played by autotrophic and heterotrophic communities along the water column

Microbial communities and biogeochemistry in an area of <i>Engraulis encrasicolus</i> spawning in the Sicilian Channel

Attempts to merge marine food webs and marine biogeochemical research have recently been developed in response to the need to understand how global change will impact marine ecosystems and resources (Salihoglu et al., 2013; Painting, et al., 2013). Among the multiple drivers that influence ecosystem dynamics, Link et al. (2012) focused on three main processes that affect marine fish productivity: biophysical (environmental), exploitative (fisheries), and trophodynamic (species interactions) factors. Previous paper underlined the relationships among microbial parameters and physical and chemical conditions of waters (Zaccone et al., 2012). With the aim of providing an ecosystem approach to fisheries management, the monitoring of biological and environmental variables was carried out in the frame of the Bansic12 cruise performed in the Sicily Channel (Ibleo-Maltese platform) during July 2012. The Sicily Channel is a spawning area of Engraulis encrasicolus (Linnaeus, 1758), a pelagic species of commercial interest (Basilone et al., 2013). As a consequence, fish eggs and larvae together with microbial assemblages (virio-, autotrophic and heterotrophic pico-, nano- and microplankton) were quantified in terms of abundance and biomass (Andrade et al., 2003; Caroppo et al., 2010; Fonda Umani et al., 2010; La Ferla et al., 2012). To give a more comprehensive picture of microbial role in supporting the flux of biogeochemical elements in the study area, rates of microbial metabolic processes (primary and secondary production, enzymatic hydrolysis of dissolved and particulate matter, and community respiration) were also quantified (La Ferla et al., 2005; La Ferla et al., 2010; Caruso et al., 2014). In addition, the hydrology, the trophic parameters and correlated indices were analyzed to contribute to the understanding of plankton communities dynamism (Leonardi et al., 2009). The euphotic layer was characterized by the presence of the typically oligotrophic MAW (Modified Atlantic Water), flowing eastward along the Sicilian coast. Low nutrient concentrations were recorded, particularly regarding the phosphorus, whose values were close to the detection limit. The diffuse oligotrophy of the area was confirmed by high N/P ratios as well as by low Chl-a values. Particulate Organic Carbon (POC) concentrations were low, as well as those of Particulate Nitrogen (PN). Peaks of POC and PN were recorded at the Deep Chlorophyll Maximum (DCM) or below the thermocline (Leonardi et al., 2014). As regards biological parameters, virus counts were low with a mean value of 1.68E+05 ± 7.0E+04 VPL ml-1 and prokaryotic biomass ranged between 24.9 and 113.0 µg C L-1, mainly composed by curved rods and coccobacilli (range size: 0.160 – 0.459 µm3). Low nucleic acid cells (LNA) prevails over high nucleic acid cells (HNA) with a HNA/LNA mean ratio of 0.56, similar to that occurring in surface layer of several pelagic Mediterranean areas (La Ferla et al., 2012). The picophytoplanktonic biomass (range 0.29–26 µg C L-1), was mostly due to the presence of coccoid cyanobacteria, belonging to the genus Synechococcus. Total nanoplankton biomass (range 0.11-1.71 µg C L-1) showed the highest values at the DCM or below the thermocline. Nanoplankton was represented, among the others, by the dinoflagellates Amphidinium carterae and Heterocapsa niei. The coccolithophorid Emiliania huxleyi and flagellates of uncertain taxonomic identification were also abundant. Microphytoplankton abundance ranged between 6.1 and 40.5 E+03 cells L-1, while biomass between 0.28 and 2.43 µg C L-1. Diatoms and dinoflagellates were the main components of the community, composed by 24 and 30 species, respectively. Concerning microzooplankton, eggs, nauplia and metazoan larval stages prevailed in terms of biomass in almost all samples. Heterotrophic dinoflagellates were the second more relevant group while aloricate Ciliates and Tintinnids did not significantly contribute to the total biomass. Biomass maxima were generally observed at the surface or at the DCM, but never exceeded 16.0 µg C L-1. Finally, anchovy eggs and larvae mainly occurred in the 0-10/0-25 m depth intervals, with highest densities of 4.2 eggs m-3 and 2.6 larvae m-3. The rates of production, hydrolysis and degradation activities were quite low, in agreement with the general oligotrophy of the area and in agreement with this findings, picophytoplankton contribution to total production amounted to over than 65%. In terms of metabolic activities, different spatial distributions were observed between the autotrophic and heterotrophic components. In particular, heterotrophic metabolism showed high values in the layer located below the thermocline and above the DCM. Concerning the enzymatic activities, total leucine aminopeptidase activity showed the highest rates, followed by alkaline phosphatase and beta-Glucosidase (Caruso et al., 2014). Distribution of the dissolved enzymatic activities acting on proteins varied widely along the column, accounting for 5 to 90% of the total enzymatic activity and always prevailed on dissolved b-GLU. Total enzymatic activity rates were comparable to those obtained in the oligotrophic zones of Ionian and Mediterranean Sea (Zaccone et al., 2012), while the analysis of the dissolved fraction was the first report for the Mediterranean. In conclusion, the multidisciplinary scientific approach used in this study depicted a complex picture of the study area evidencing a high heterogeneity and dynamism of plankton communities, probably associated to peculiar hydrology of this ecosystem. On the whole, the study area appeared to be characterized by a relatively efficient microbial food web. However, low trophic conditions were stressed by all the biological and biochemical patterns, suggesting an important role of heterotrophic processes in this area in the examined summer period. Consequently, how and how much the microbial web sustains fish reproduction and larval survival need a more comprehensive analysis and will be focused in further research

Prokaryotic abundance and heterotrophic metabolism in the deep Mediterranean Sea

A synthesis of field data carried out in the Mediterranean Sea are presented, aimed at contributing to the knowledge of three prokaryotic-mediated processes and their implications on the Carbon cycle. The distribution of exoenzymatic activities, secondary production and respiration rates was studied together with the prokaryotic abundances. Particular attention was paid to the meso- and bathypelagic layers which play an important role in the Mediterranean carbon cycle. The study is noteworthy because of its large spatial scale spanning the entire Mediterranean Sea over 4 years. In addition, two Atlantic stations in front of the Gibraltar Strait were investigated. The longitudinal distribution of prokaryotic activities and abundance along the MED showed different trends along the depthlayers. In particular, higher exoenzymatic rates were detected in the Eastern basin compared to the Western one; carbon respiration rate showed patterns variable with the sampling periods in the epipelagic and bathypelagic layers, while a consistent Westwards decreasing trend at the mesopelagic layers occurred. Specific enzyme activities per cell showed high values in the deepest layers for leucine aminopeptidase. Comparison with Carbon respiration rate data collected before the 2000s showed changing patterns of microbial heterotrophic processes in the Mediterranean Sea