scholarly journals Lack of P-limitation of phytoplankton and heterotrophic prokaryotes in surface waters of three anticyclonic eddies in the stratified Mediterranean Sea

2011 ◽  
Vol 8 (2) ◽  
pp. 525-538 ◽  
Author(s):  
T. Tanaka ◽  
T. F. Thingstad ◽  
U. Christaki ◽  
J. Colombet ◽  
V. Cornet-Barthaux ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
Ammonium Phosphate ◽  
Turnover Time ◽  
General Notion ◽  
Western Basin ◽  
P Limitation ◽  
Levantine Basin ◽  
Heterotrophic Prokaryotes ◽  
Anticyclonic Eddies

Abstract. We investigated the identity of the limiting nutrient of the pelagic microbial food web in the Mediterranean Sea using nutrient manipulated microcosms during summer 2008. Experiments were carried out with surface waters at the center of anticyclonic eddies in the Western Basin, the Ionian Basin, and the Levantine Basin. In situ, the ratio of N to P was always higher in both dissolved and particulate organic fractions compared to the Redfield ratio, suggesting a relative P-starvation. In each experiment, four different treatments in triplicates (addition of ammonium, phosphate, a combination of both, and the unamended control) were employed and chemical and biological parameters monitored throughout a 3–4 day incubation. Temporal changes of turnover time of phosphate and ATP, and alkaline phosphatase activity during the incubation suggested that the phytoplankton and heterotrophic prokaryotes (Hprok) communities were not P-limited at the sites. Furthermore, statistical comparison among treatments at the end of the incubation did not support a hypothesis of P-limitation at the three study sites. In contrast, primary production was consistently limited by N, and Hprok growth was not limited by N nor P in the Western Basin, but N-limited in the Ionian Basin, and N and P co-limited in the Levantine Basin. Our results demonstrated the gap between biogeochemical features (an apparent P-starved status) and biological responses (no apparent P-limitation). We question the general notion that Mediterranean surface waters are limited by P alone during the stratified period.

scholarly journals N-limited or N and P co-limited indications in the surface waters of three Mediterranean basins

2010 ◽  
Vol 7 (6) ◽  
pp. 8143-8176 ◽  
Author(s):  
T. Tanaka ◽  
T. F. Thingstad ◽  
U. Christaki ◽  
J. Colombet ◽  
V. Cornet-Barthaux ◽  
...  
Keyword(s):  
Surface Waters ◽  
Ammonium Phosphate ◽  
Turnover Time ◽  
General Notion ◽  
Biological Parameters ◽  
Western Basin ◽  
P Limitation ◽  
Levantine Basin ◽  
Limiting Nutrient ◽  
Set Up

Abstract. The limiting nutrient for the pelagic microbial food web in the Mediterranean Sea was investigated in the nutrient manipulated microcosms during summer 2008. Surface waters were collected into 12 carboys at a center of anticyclonic eddy at the Western Basin, the Ionian Basin, and the Levantine Basin, respectively. As compared to the Redfield ratio, the ratio of N to P in the collected waters was always smaller in the dissolved inorganic fraction but higher in both dissolved and particulate organic fractions. Four different treatments in triplicates (addition of ammonium, phosphate, a combination of both, and the unamended control) were set up for the carboys. Responses of chemical and biological parameters in these different treatments were measured during the incubation (3–4 days). Temporal changes of turnover time of phosphate and ATP, and alkaline phosphatase activity during the incubation suggested that the phytoplankton and heterotrophic prokaryotes (Hprok) communities were not purely P-limited at any studied stations. Statistical comparison between the treatments for a given parameter measured at the end of the incubation did not find pure P-limitation in any chemical and biological parameters at three study sites. Primary production was consistently limited by N, and Hprok growth was not limited by N nor P in the Western Basin, but N-limited in the Ionian Basin, and N and P co-limited in the Levantine Basin. Our results demonstrated the gap between biogeochemical features and biological responses in terms of the limiting nutrient. We question the general notion that Mediterranean surface waters are limited by P alone during the stratified period.

scholarly journals Integrated survey of elemental stoichiometry (C, N, P) from the Western to Eastern Mediterranean Sea

2010 ◽  
Vol 7 (5) ◽  
pp. 7315-7358 ◽  
Author(s):  
M. Pujo-Pay ◽  
P. Conan ◽  
L. Oriol ◽  
V. Cornet-Barthaux ◽  
C. Falco ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Surface Waters ◽  
Eastern Mediterranean ◽  
Vertical Gradient ◽  
Western Basin ◽  
P Limitation ◽  
Severe Deficiency ◽  
Elemental Stoichiometry ◽  
Redfield Ratios

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry in the whole Mediterranean Sea during the summer 2008. During this strong stratified period, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were investigated along a 3000 km transect (BOUM cruise) crossing the Western and Eastern Mediterranean basins. The partitioning of chemical C, N and P species among all these mineral and organic pools has been analysed to produce a detailed spatial and vertical extended examination of the elemental stoichiometry. Surface Mediterranean waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, concomitantly to the gradual deepening of the thermocline and nutriclines. We used threshold in oxygen concentration to discriminate the water column in three layers; surface (Biogenic Layer BL), intermediate (Mineralization Layer ML), and deep layer (DL) and to propose a schematic representation of biogeochemical fluxes between the different compartments and to compare the functioning of the two basins. The stoichiometry revealed a clear longitudinal and vertical gradient in the mineral fraction with a P-depletion evidenced on both dimension. As a consequence of the severe deficiency in phosphorus, the C:N:P ratios in all pools within the BL largely exceed the Redfield ratios. Despite these gradients, the deep estimated fluxes in the mineral compartment tend towards the canonical Redfield values in both basins. A change in particulate matter composition has been evidenced by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. More surprisingly, a decrease in N relative to P with depth was encountered in the whole Mediterranean Sea. We suggest that there was a more rapid recycling of N than P in intermediate waters (below BL) and a complete use of DOP in surface waters. DOC accumulated in surface waters according to the oligotrophic status but this was not the case for nitrogen nor phosphorus. Our data clearly showed a noticeable stability of the DOC:DON ratio (12–13) in the whole Mediterranean Sea, contradicting the fact that N is recycled faster than C in the DOM but in agreement with a P limitation of bacterial activity. Finally, comparisons between these elemental distributions and ratios along the West-East Mediterranean gradient of trophic status provide new insights for identifying and understanding fundamental interactions between marine biogeochemistry and ecosystems, which will help to predict the impacts of environmental climate changes on the Mediterranean marine ecosystems. Indeed, the outflowing through the various Mediterranean straits have been shown to be changing, the functioning of the BL ecosystem could be impacted, not only by changes in nutrients surface sources but also by changes in deep nutrients one.

scholarly journals Integrated survey of elemental stoichiometry (C, N, P) from the western to eastern Mediterranean Sea

2011 ◽  
Vol 8 (4) ◽  
pp. 883-899 ◽  
Author(s):  
M. Pujo-Pay ◽  
P. Conan ◽  
L. Oriol ◽  
V. Cornet-Barthaux ◽  
C. Falco ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Eastern Mediterranean ◽  
Western Basin ◽  
Nutrient Sources ◽  
P Limitation ◽  
Elemental Stoichiometry ◽  
Deep Layers ◽  
Redfield Ratios ◽  
The Mediterranean

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry along an East-West transect of 3000 km across the Mediterranean Sea during summer 2008 (BOUM cruise). During this period of strong stratification, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were examined to produce a detailed spatial and vertically extended description of the elemental stoichiometry of the Mediterranean Sea. Surface waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, with the phosphacline deepening to a greater extent than that for corresponding nitracline and thermocline depths. We used the minimum oxygen concentration through the water column in combination with 2 fixed concentrations of dissolved oxygen to distinguish an intermediate layer (Mineralization Layer; ML) from surface (Biogenic Layer; BL), and deep layers (DL). Whilst each layer was represented by different water masses, this approach allowed us to propose a schematic box-plot representation of the biogeochemical functioning of the two Mediterranean basins. Despite the increasing oligotrophic nature and the degree of P-depletion along the West to East gradient strong similarities were encountered between eastern and western ecosystems. Within the BL, the C:N:P ratios in all pools largely exceeded the Redfield ratios, but surprisingly, the nitrate vs. phosphate ratios in the ML and DL tended towards the canonical Redfield values in both basins. A change in particulate matter composition has been identified by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. Our data showed a noticeable stability of the DOC:DON ratio (12–13) throughout the Mediterranean Sea. This is in good agreement with a P-limitation of microbial activities but in contradiction of the accepted concept that N is recycled faster than C. The western and eastern basins had similar or close biological functioning. Differences come from variability in the allochtonous nutrient sources in terms of quantity and quality, and to the specific hydrodynamic features of the Mediterranean basins.

scholarly journals Springtime contribution of dinitrogen fixation to primary production across the Mediterranean Sea

2013 ◽  
Vol 10 (1) ◽  
pp. 1-26 ◽  
Author(s):  
E. Rahav ◽  
B. Herut ◽  
A. Levi ◽  
M. R. Mulholland ◽  
I. Berman-Frank
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
N2 Fixation ◽  
Eastern Mediterranean ◽  
Dominant Role ◽  
Early Spring ◽  
Strait Of Gibraltar ◽  
Western Basin ◽  
Eastern Basin ◽  
The Mediterranean

Abstract. Dinitrogen (N2) fixation rates were measured during early spring across the different provinces of Mediterranean Sea surface waters. N2 fixation rates, measured using 15N2 enriched seawater, were lowest in the eastern basin and increased westward with a maximum at the Strait of Gibraltar (0.10 to 2.35 nmol N L−1 d−1, respectively). These rates were 3–7 fold higher than N2 fixation rates measured previously in the Mediterranean Sea during summertime. Moreover, comparisons between N2 fixation rates measured during dark versus natural light incubations (48 h) show higher rates during dark incubations at the eastern Mediterranean stations but lower rates at the western stations. This suggests that heterotrophic diazotrophy has a significant role in the Eastern Mediterranean while autotrophic diazotrophy has a more dominant role in the Western basin.

scholarly journals Deep silicon maxima in the stratified oligotrophic Mediterranean Sea

2010 ◽  
Vol 7 (5) ◽  
pp. 6789-6846 ◽  
Author(s):  
Y. Crombet ◽  
K. Leblanc ◽  
B. Quéguiner ◽  
T. Moutin ◽  
P. Rimmelin ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
Particulate Carbon ◽  
Carbon Export ◽  
Common View ◽  
Centric Diatoms ◽  
Levantine Basin ◽  
The Common ◽  
The Mediterranean ◽  
Marine Productivity

Abstract. The silicon biogeochemical cycle has been studied in the Mediterranean Sea during fall 1999 and summer 2008. The distribution of nutrients, particulate carbon and silicon, fucoxanthin (Fuco) and total chlorophyll-a (Tchl-a) were investigated along an eastward gradient of oligotrophy during two cruises (PROSOPE and BOUM) encompassing the entire Mediterranean Sea during the stratified period. At both seasons, surface waters were depleted in nutrients and the nutriclines gradually deepened towards the East, the phosphacline being the deepest in the easternmost Levantine basin. Following the nutriclines, correlated deep maxima of biogenic silica (DSM), fucoxanthin (DFM) and Tchl-a (DCM) were evidenced during both seasons with maximal concentrations of 0.45 μmol L−1 for BSi, 0.26 μg L−1 for Fuco, and 1.70 μg L−1 for Tchl-a, all measured during summer. Contrary to the DCM which was a persistent feature in the Mediterranean Sea, the DSM and DFMs were observed in discrete areas of the Alboran Sea, the Algero-Provencal basin, the Ionian sea and the Levantine basin, indicating that diatoms were able to grow at depth and dominate the DCM under specific conditions. Diatom assemblages were dominated by Chaetoceros spp., Leptocylindrus spp., Pseudonitzschia spp. and the association between large centric diatoms (Hemiaulus hauckii and Rhizosolenia styliformis) and the cyanobacterium Richelia intracellularis was observed at nearly all sites. The diatom's ability to grow at depth is commonly observed in other oligotrophic regions and could play a major role in ecosystem productivity and carbon export to depth. Contrary to the common view that Si and siliceous phytoplankton are not major components of the Mediterranean biogeochemistry, we suggest here that diatoms, by persisting at depth during the stratified period, could contribute to a large part to the marine productivity and biological pump, as observed in other oligotrophic areas.

scholarly journals Deep silicon maxima in the stratified oligotrophic Mediterranean Sea

2011 ◽  
Vol 8 (2) ◽  
pp. 459-475 ◽  
Author(s):  
Y. Crombet ◽  
K. Leblanc ◽  
B. Quéguiner ◽  
T. Moutin ◽  
P. Rimmelin ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
Late Summer ◽  
Particulate Carbon ◽  
Carbon Export ◽  
Common View ◽  
Levantine Basin ◽  
The Common ◽  
The Mediterranean ◽  
Marine Primary Production

Abstract. The silicon biogeochemical cycle has been studied in the Mediterranean Sea during late summer/early autumn 1999 and summer 2008. The distribution of nutrients, particulate carbon and silicon, fucoxanthin (Fuco), and total chlorophyll-a (TChl-a) were investigated along an eastward gradient of oligotrophy during two cruises (PROSOPE and BOUM) encompassing the entire Mediterranean Sea during the stratified period. At both seasons, surface waters were depleted in nutrients and the nutriclines gradually deepened towards the East, the phosphacline being the deepest in the easternmost Levantine basin. Following the nutriclines, parallel deep maxima of biogenic silica (DSM), fucoxanthin (DFM) and TChl-a (DCM) were evidenced during both seasons with maximal concentrations of 0.45 μmol L−1 for BSi, 0.26 μg L−1 for Fuco, and 1.70 μg L−1 for TChl-a, all measured during summer. Contrary to the DCM which was a persistent feature in the Mediterranean Sea, the DSM and DFMs were observed in discrete areas of the Alboran Sea, the Algero-Provencal basin, the Ionian sea and the Levantine basin, indicating that diatoms were able to grow at depth and dominate the DCM under specific conditions. Diatom assemblages were dominated by Chaetoceros spp., Leptocylindrus spp., Pseudonitzschia spp. and the association between large centric diatoms (Hemiaulus hauckii and Rhizosolenia styliformis) and the cyanobacterium Richelia intracellularis was observed at nearly all sites. The diatom's ability to grow at depth is commonly observed in other oligotrophic regions and could play a major role in ecosystem productivity and carbon export to depth. Contrary to the common view that Si and siliceous phytoplankton are not major components of the Mediterranean biogeochemistry, we suggest here that diatoms, by persisting at depth during the stratified period, could contribute to a large part of the marine primary production as observed in other oligotrophic areas.

scholarly journals Vertical partitioning of phosphate uptake among picoplankton groups in the low Pi Mediterranean Sea

2015 ◽  
Vol 12 (4) ◽  
pp. 1237-1247 ◽  
Author(s):  
A. Talarmin ◽  
F. Van Wambeke ◽  
P. Lebaron ◽  
T. Moutin
Keyword(s):  
Mediterranean Sea ◽  
Cell Sorting ◽  
Soluble Reactive Phosphorus ◽  
Euphotic Zone ◽  
Western Basin ◽  
Uptake Kinetic ◽  
Pi Turnover ◽  
Uptake Rates ◽  
Heterotrophic Prokaryotes ◽  
Reactive Phosphorus

Abstract. Microbial transformations are key processes in marine phosphorus cycling. In this study, we investigated the contribution of phototrophic and heterotrophic groups to phosphate (Pi) uptake fluxes in the euphotic zone of the low-Pi Mediterranean Sea and estimated Pi uptake kinetic characteristics. Surface soluble reactive phosphorus (SRP) concentrations were in the range of 6–80 nmol L−1 across the transect, and the community Pi turnover times, assessed using radiolabeled orthophosphate incubations, were longer in the western basin, where the highest bulk and cellular rates were measured. Using live cell sorting, four vertical profiles of Pi uptake rates were established for heterotrophic prokaryotes (Hprok), phototrophic picoeukaryotes (Pic) and Prochlorococcus (Proc) and Synechococcus (Syn) cyanobacteria. Hprok cells contributed up to 82% of total Pi uptake fluxes in the superficial euphotic zone, through constantly high abundances (2.7–10.2 × 105 cells mL−1) but variable cellular rates (6.6 ± 9.3 amol P cell−1 h−1). Cyanobacteria achieved most of the Pi uptake (up to 62%) around the deep chlorophyll maximum depth, through high abundances (up to 1.4 × 105 Proc cells mL−1) and high cellular uptake rates (up to 40 and 402 amol P cell−1 h−1, respectively for Proc and Syn cells). At saturating concentrations, maximum cellular rates up to 132 amol P cell−1 h−1 were measured for Syn at station (St.) C, which was 5 and 60 times higher than Proc and Hprok, respectively. Pi uptake capabilities of the different groups likely contribute to their vertical distribution in the low Pi Mediterranean Sea, possibly along with other energy limitations.

scholarly journals Ecology of aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea

2011 ◽  
Vol 8 (4) ◽  
pp. 973-985 ◽  
Author(s):  
D. Lamy ◽  
C. Jeanthon ◽  
M. T. Cottrell ◽  
D. L. Kirchman ◽  
F. Van Wambeke ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Bacterial Growth ◽  
Growth Response ◽  
Anoxygenic Phototrophic Bacteria ◽  
Carbon Limitation ◽  
Organic Substrates ◽  
Western Basin ◽  
Eastern Basin ◽  
Nutrient Additions ◽  
The Mediterranean

Abstract. Aerobic anoxygenic phototrophic (AAP) bacteria are photoheterotrophic prokaryotes able to use both light and organic substrates for energy production. They are widely distributed in coastal and oceanic environments and may contribute significantly to the carbon cycle in the upper ocean. To better understand questions regarding links between the ecology of these photoheterotrophic bacteria and the trophic status of water masses, we examined their horizontal and vertical distribution and the effects of nutrient additions on their growth along an oligotrophic gradient in the Mediterranean Sea. Concentrations of bacteriochlorophyll-a (BChl-a) and AAP bacterial abundance decreased from the western to the eastern basin of the Mediterranean Sea and were linked with concentrations of chlorophyll-a, nutrient and dissolved organic carbon. Inorganic nutrient and glucose additions to surface seawater samples along the oligotrophic gradient revealed that AAP bacteria were nitrogen- and carbon-limited in the ultraoligotrophic eastern basin. The intensity of the AAP bacterial growth response generally differed from that of the total bacterial growth response. BChl-a quota of AAP bacterial communities was significantly higher in the eastern basin than in the western basin, suggesting that reliance on phototrophy varied along the oligotrophic gradient and that nutrient and/or carbon limitation favors BChl-a synthesis.

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