Acid processes in the atmosphere, particularly those caused by anthropogenic acid gases, increase the amount of bioavailable P in dust and hence are predicted to increase microbial biomass and ...primary productivity when supplied to oceanic surface waters. This is likely to be particularly important in the Eastern Mediterranean Sea (EMS), which is P limited during the winter bloom and N&P co-limited for phytoplankton in summer. However, it is not clear how the acid processes acting on Saharan dust will affect the microbial biomass and primary productivity in the EMS. Here, we carried out bioassay manipulations on EMS surface water on which Saharan dust was added as dust (Z), acid treated dust (ZA), dust plus excess N (ZN), and acid treated dust with excess N (ZNA) during springtime (May 2012) and measured bacterioplankton biomass, metabolic, and other relevant chemical and biological parameters. We show that acid treatment of Saharan dust increased the amount of bioavailable P supplied by a factor of ~40 compared to non-acidified dust (18.4 vs. 0.45 nmoles P mg super(-1) dust, respectively). The increase in chlorophyll, primary, and bacterial productivity for treatments Z and ZA were controlled by the amount of N added with the dust while those for treatments ZN and ZNA (in which excessive N was added) were controlled by the amount of P added. These results confirm that the surface waters were N&P co-limited for phytoplankton during springtime. However, total chlorophyll and primary productivity in the acid treated dust additions (ZA and ZNA) were less than predicted from that calculated from the amount of the potentially limiting nutrient added. This biological inhibition was interpreted as being due to labile trace metals being added with the acidified dust. A probable cause for this biological inhibition was the addition of dissolved Al, which forms potentially toxic Al nanoparticles when added to seawater. Thus, the effect of anthropogenic acid processes in the atmosphere, while increasing the flux of bioavailable P from dust to the surface ocean, may also add toxic trace metals such as Al, which moderate the fertilizing effect of the added nutrients.
Thirty-four dinoflagellate cyst taxa were found in surface sediment (0-2 cm) at five stations (60-100-m water depth) in the Gulf of Gemlik, Marmara Sea, during four seasons from August 2011 to May ...2012. Lingulodinium machaerophorum, Operculodinium centrocarpum and Selenopemphix quanta dominated cyst assemblages in the polluted gulf, where nutrient-rich surface water was stratified during most seasons and bottom water was hypoxic. Twelve cyst taxa were incubated and produced motile cells that reproduced and survived 14-15 days. Highest cyst species number (33) occurred in summer; maximum number of cysts (living and empty) per cm
3
wet sediment was in spring, with the annual range from 1520 (fall) to 108,000 (spring). Nine taxa (Brigantedinium simplex, L. machaerophorum, O. centrocarpum, S. quanta, Spiniferites mirabilis, Spiniferites ramosus, cysts of Alexandrium sp., Scrippsiella trifida and S. trochoidea) were found in all seasons at all stations. The harmful dinoflagellates L. machaerophorum and cysts of S. trochoidea and Alexandrium sp. were the most abundant species. The cyst of the toxic species, Cochlodinium sp., is reported for the first time from Turkey. Other HAB species included A. tamarense, Protoceratium reticulatum, Heterocapsa triquetra and Gymnodinium catenatum/nolleri. Relative abundance of potentially toxic dinoflagellates (74%-92% of total cysts cm
−3
) was always higher than nontoxic species, and percentage abundance of cysts cm
−3
produced by autotrophs (19/34 total species) almost always exceeded those of heterotrophs. Although distributions of the resting cyst taxa were significantly influenced by surface temperature, dissolved oxygen and total water depth, surface salinity was the strongest predictor for cyst occurrences.
Notwithstanding the increasing amount of researches on the effect of ocean acidification (OA) on marine ecosystems, no consent has emerged on its consequences on many prokaryote-mediated processes. ...Two mesocosm experiments were performed in coastal Mediterranean areas with different trophic status: the summer oligotrophic Bay of Calvi (BC, Corsica, France) and the winter mesotrophic Bay of Villefranche (BV, France). During these experiments, nine enclosures (∼54 m3) were deployed: 3 unamended controls and 6 elevated CO2, following a gradient up to 1250 μatm. We present results involving free-living viral and prokaryotic standing stocks, bacterial carbon production, abundance of highly active cells (CTC+), and degradation processes (beta-glucosidase, chitinase, leucine-aminopeptidase, lipase and alkaline phosphatase activities).
The experiments revealed clear differences in the response of the two prokaryotic communities to CO2 manipulation. Only abundances of heterotrophic prokaryotes, viruses and lipase activity were not affected by CO2 manipulation at both locations. On the contrary, the percent of CTC+ was positively correlated to CO2 only in BC, concomitantly to a bulk reduction of 3H-leucine uptake. The other tested parameters showed a different response at the two sites suggesting that the trophic regime of the systems plays a fundamental role on the effect of OA on prokaryotes through indirect modifications of the available substrate.
Modified degradation rates may affect considerably the export of organic matter to the seafloor and thus ecosystem functioning within the water column. Our results highlight the need to further analyse the consequences of OA in oligotrophic ecosystems with particular focus on dissolved organic matter.
•Different trophic regimes revealed diverse effects of ocean acidification on prokaryotes.•Ocean acidification and organic substrates were responsible for metabolic alterations.•Viral and prokaryotic abundances were not affected by increased CO2 levels.
The frequency of lytically infected and lysogenic cells (FLIC and FLC, respectively) was estimated during an in situ mesocosm experiment studying the impact of ocean acidification on the plankton ...community of a low nutrient low chlorophyll (LNLC) system in the north-western Mediterranean Sea (Bay of Villefranche, France) in February/March 2013. No direct effect of elevated partial pressure of CO2 (pCO2) on viral replication cycles could be detected. FLC variability was negatively correlated to heterotrophic bacterial and net community production as well as the ambient bacterial abundance, confirming that lysogeny is a prevailing life strategy under unfavourable-for-the-hosts conditions. Further, the phytoplankton community, assessed by chlorophyll a concentration and the release of >0.4 μm transparent exopolymeric particles, was correlated with the occurrence of lysogeny, indicating a possible link between photosynthetic processes and bacterial growth. Higher FLC was found occasionally at the highest pCO2-treated mesocosm in parallel to subtle differences in the phytoplankton community. This observation suggests that elevated pCO2 could lead to short-term alterations in lysogenic dynamics coupled to phytoplankton-derived processes. Correlation of FLIC with any environmental parameter could have been obscured by the sampling time or the synchronization of lysis to microbial processes not assessed in this experiment. Furthermore, alterations in microbial and viral assemblage composition and gene expression could be a confounding factor. Viral-induced modifications in organic matter flow affect bacterial growth and could interact with ocean acidification with unpredictable ecological consequences.
•No direct effect of elevated pCO2 on viral replication cycles could be detected.•Lysogeny was dependent on system productivity, as well as on phytoplankton dynamics.•Lysis was not related to any of the measured environmental parameters.•Mild differences in lysogeny in the most perturbed mesocosm were occasionally found, along with different phytoplankton dynamics.
This study examines mussel accumulation capacity in relation to metal concentrations in the marine environment as well as mussel food availability in the coastal marine environment. Field data ...obtained from mussel-farms facing different natural and/or human derived pressures (Thermaikos gulf receiving river discharges and Elefsis bay receiving industrial effluents). Cd, Cr, Cu, Fe, Mn, Ni and Zn concentration in mussels and seawater (particulate phase) chlorophyll α, particulate organic carbon and suspended particulate matter (SPM), seawater temperature and salinity were measured. Median mussel metal concentrations measured as μg g−1 dw were 0.62 for Cd, 5.6 for Cu, 2.8 for Cr, 5.0 for Ni, 129 for Zn, 311 for Fe and 12.4 for Mn. The corresponding concentrations in SPM expressed as μg L−1 were 0.004 for Cd, 0.33 for Cu, 1.14 for Cr, 0.31 for Ni, 3.60 for Zn, 46.0 for Fe and 1.63 for Mn. Mussel metal concentrations were higher at the industrial site. Metals in the seawater particulate phase were higher in the estuary front, which was attributed to higher SPM levels from river discharges. Due to the limited nutritional value of the SPM in the industrial area, mussels were exposed to elevated metal load by both the anthropogenic activities and the slower and more effective digestion of their potential food in order to optimize available organic matter exploitation from restricted and low nutrition value food.
The effect of phosphate (P), nitrate (N), and organic carbon (C, glucose) enrichment on heterotrophic bacterial production was examined along two longitudinal transects covering the whole ...Mediterranean Sea during June and September 1999. During these cruises, integrated bacterial production ranged from 11 to 349 mgC m-2d-1for the 0-150 m layer. P was found to stimulate bacterial production (BP) in 13 out of 18 experiments, in the eastern and in the western Mediterranean Sea. Organic carbon stimulation of bacterial production was observed at two stations in the Alboran Sea, where the highest bacterial production was recorded (216 and 349 mg C m-2d-1) and in the Sicily Strait. Maximum rates of alkaline phosphatase (AP) increased from the Alboran to the Levantine Sea whereas AP turnover time decreased. Moreover, alkaline phosphatase activity was not systematically reduced following additions of P. In cases of P limitation, however, the alkaline phosphatase activity to bacterial production ratio was severely reduced in the P and NPC enrichments. Generally, the addition of the limiting factor-whether P or C-had a synchronous stimulating effect on bacterial production and ectoaminopeptidase activity and induced a decline in the amino acid respiration percentage. At two selected stations in the eastern and northwestern Mediterranean, response to enrichment was tested on vertical profiles. Bacteria shifted from P to C limitation at a depth where soluble reactive phosphorus was still undetectable, but corresponding to a strong increase in alkaline phosphatase turnover time. Our results showed that values of AP turnover time lower than 100 h corresponded to situations of P limitation of bacterial production.
The impact of viral lysis and grazing by flagellates on bacterioplankton production was assessed during a mesocosm experiment in the Eastern Mediterranean Sea, in response to Saharan dust (SD) vs. ...mixed aerosols (A) addition. The results highlight a positive effect on bacterial abundance, production and growth rate (~1.2, ~2.4 and ~1.9 –fold higher than the controls) in both SD and A, which was also confirmed by the increased portion of high DNA content bacteria (up to 48% of the bacterial community). Lytic viral production and the portion of bacterial production lost due to viral lysis were lower in SD and A after dust addition than in the controls (0.33 ± 0.17 x106 virus-like particles mL-1 h-1 and 6 ± 4%, respectively). Potential ingestion rate of bacteria by flagellates increased upon dust enrichment, but did not differ between mesocosms. Larger predators possibly down regulated flagellate abundance, and the calculated portion of bacterial production lost due to flagellate grazing was probably an artifact. Higher frequency of lysogenic cells in A compared to SD and the controls four days after dust addition may reflect faster phosphorus limitation in A, due to receiving less dissolved inorganic phosphorus and more dissolved inorganic nitrogen than SD.
Vertical distribution, standing stocks, size-class structure, community structure, mixotrophy and cell content of ciliate assemblages were studied at 9 stations along a transect in the Mediterranean ...Sea in June 1999. The aim of the study was to relate the trophic conditions in the Mediterranean to the ciliate community structure and the grazing impact of ciliates. The vertical distribution was more or less uniform in the Eastern Basin but presented an extended upper layer with higher density and a maximum at 50 to 75 m in the Western Basin. The integrated abundance (11.2 to 26.9 x 10 super(6) cells m super(-2)) and biomass (41.5 to 84.8 mg C m super(-2)) decreased by a factor of 2 from west to east. A total of 55 tintinnid species were identified. Aloricates < 30 mu m represented 62 % of integrated abundance and 16 % of biomass. Mixotrophs made up 17 % of integrated abundance and 18 % of biomass. From west to east, there was no evident change in the structure of the ciliate community with respect to (1) aloricate size-classes, (2) mixotroph size-classes, (3) contribution of mixotrophs to total abundance. The cell content of all ciliates was examined for Synechococcus and photosynthetic algae under epifluorescence inverted microscopy. Tintinnids contained similar quantities of algae and Synechococcus (1.04 plus or minus 0.59 algae tintinnid super(-1), 0.94 plus or minus 0.87 Synechococcus tintinnid super(-1)) and the same was true for aloricates. Based on cell content, it was estimated that (1) the ingestion rate for tintinnids was: 0.61 photosynthetic algae h super(-1) and 0.41 Synechococcus h super(-1) and for aloricates: 0.14 photosynthetic algae h super(-1) and 0.13 Synechococcus h super(-1); (2) tintinnids ingested significantly more prey than aloricates by a factor of 5; and (3) ciliates consumed 26 % of primary production in the Western, 41 % in the Central and 70 % in the Eastern Basin.
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.
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