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1.
Despite the fact that marine viruses have been increasingly investigated in the last decade, knowledge on virus abundance, biomass and distribution in mesopelagic and bathypelagic waters is limited. We report here the results of a large-spatial-scale study (covering more than 3000 km) on the virioplankton distribution in epi-, meso- and bathypelagic waters in 19 areas of the Mediterranean Sea, from the Alboran Sea and Western Mediterranean, to the Tyrrhenian Sea, Sicily Channel and Ionian Sea. Integrated viral abundance in epipelagic waters was significantly higher than in deep-sea waters (on average, 2.4 vs. 0.5×1012 viruses m−3). However, abundance of viruses in the deep-Mediterranean waters was the highest reported so far for deep seas worldwide (7.0 and 3.1×1011 viruses m−3 in mesopelagic and bathypelagic waters, respectively) and their biomass accounted for 13–18% of total prokaryotic C biomass. The significant relationship between viral abundance and prokaryotic abundance and production in deep waters suggests that also deep-sea viruses are closely dependent on the abundance and metabolism of their hosts. Moreover, virus to prokaryote (and nucleoid-containing cell (NuCC)) abundance ratio increased with increasing depths suggesting that deep waters may represent optimal environments for viral survival or proliferation. Overall, our results indicate that deep waters may represent a significant reservoir of viruses and open new perspectives for future investigations of viral impact on the functioning of meso-bathypelagic ecosystems.  相似文献   

2.
This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth >1000 m). Abundance, production and respiration of prokaryotes reflect supplies of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further testing on the validity of conversion factors. Archaea, especially marine Crenarchaeota Group I, are abundant in deep waters where they can fix dissolved inorganic carbon. Viruses appear to be important in the microbial loop in deep waters, displaying remarkably high virus to prokaryote abundance ratios in some oceanic regions. Sequencing of 18S rRNA genes revealed a tremendous diversity of small-sized protists in bathypelagic waters. Abundances of heterotrophic nanoflagellates (HNF) and ciliates decrease with depth more steeply than prokaryotes; nonetheless, data indicated that HNF consumed half of prokaryote production in the bathypelagic zone. Aggregates are important habitats for deep-water microbes, which produce more extracellular enzymes (on a per-cell basis) than surface communities. The theory of marine gel formation provides a framework to unravel complex interactions between microbes and organic polymers. Recent data on the effects of hydrostatic pressure on microbial activities indicate that bathypelagic microbial activity is generally higher under in situ pressure conditions than at atmospheric pressures. High-throughput sequencing of 16S rRNA genes revealed a remarkable diversity of Bacteria in the bathypelagic ocean. Metagenomics and comparative genomics of piezophiles reveal not only the high diversity of deep sea microbes but also specific functional attributes of these piezophilic microbes, interpreted as an adaptation to the deep water environment. Taken together, the data compiled on bathypelagic microbes indicate that, despite high-pressure and low-temperature conditions, microbes in the bathypelagic ocean dynamically interact with complex mixtures of organic matter, responding to changes in the ocean’s biogeochemical state.  相似文献   

3.
Studies in epipelagic waters report higher heterotrophic microbial biomass in the productive high latitudes than in the oligotrophic low latitudes; however, biogeographical data are scarce in the deep ocean. To examine the hypothesis that the observed latitudinal differences in heterotrophic microbial biomass in the epipelagic zone also occur at depth, abundance and biomass of heterotrophic prokaryotes, nanoflagellates (HNF), and ciliates were determined at depths of 5–5000 m in the central Pacific between August and September of 2005. Heterotrophic microbial biomass increased from the tropical to the subarctic region over the full water column, with latitudinal differences in prokaryotic biomass increasing from 2.3-fold in the epipelagic zone to 4.4-fold in the bathypelagic zone. However, the latitudinal difference in HNF and ciliate biomass decreased with depth. In the mesopelagic zone, the vertical attenuation rate of prokaryotic abundance, which was calculated as the linear regression slope of log-log plot of abundance versus depth, ranged from –0.55 to –1.26 and was more pronounced (steeper slope) in the lower latitudes. In contrast, the vertical attenuation rate of HNF in the mesopelagic zone (–1.06 to –1.27) did not differ with latitude. In the subarctic, the attenuation rate of HNF was 1.7 times steeper than for prokaryotes. These results suggest the accumulation of prokaryotes in the deep subarctic Pacific, possibly due to low grazing pressure. Although the vertical attenuation rate of ciliates was steepest in the bathypelagic zone, HNF abundance did not further decrease at depths below 1000 m, except for at 2000 m where HNF was lowest across the study area. Ciliate abundance ranged 0.3–0.8 cells l–1 at 4000 m, and were below the detection limit (<0.1 cells l –1) at 5000 m. To our knowledge, this study presents the first data for ciliates below 2000 m.  相似文献   

4.
Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, Kd, which varies from 0.67 × 105 to 3.38 × 106 ml g−1 for suspended particle concentrations of 2–64 mg l−1. The Kd values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for Kd values of 105, 106 and 107 ml g−1 with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with Kd value 107 ml g−1 and C0 values 16 × 10−6 mg ml−1 and 92 × 10−6 mg ml−1. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.  相似文献   

5.
Current estimates point to a mismatch of particulate organic carbon supply derived from the surface ocean and the microbial organic carbon demand in the meso- and bathypelagic realm. Based on recent findings that chemoautotrophic Crenarchaeota are abundant in the mesopelagic zone, we quantified dissolved inorganic carbon (DIC) fixation in the meso- and bathypelagic North Atlantic and compared it with heterotrophic microbial activity. Measuring 14C-bicarbonate fixation and 3H-leucine incorporation revealed that microbial DIC fixation is substantial in the mesopelagic water masses, ranging from 0.1 to 56.7 μmol C m−3 d−1, and is within the same order of magnitude as heterotrophic microbial activity. Integrated over the dark ocean’s water column, DIC fixation ranged from 1–2.5 mmol C m−2 d−1, indicating that chemoautotrophy in the dark ocean represents a significant source of autochthonously produced ‘new organic carbon’ in the ocean’s interior amounting to about 15–53% of the phytoplankton export production. Hence, chemoautotrophic DIC fixation in the oxygenated meso- and bathypelagic water column of the North Atlantic might substantially contribute to the organic carbon demand of the deep-water microbial food web.  相似文献   

6.
The spatial and temporal patterns in bacterial abundance, biomass, production, nanoflagellate abundance and the loss of bacterial production due to viral lysis were investigated in a temporarily open/closed estuary along the eastern seaboard of southern Africa over the period May 2006 to April 2007. Bacterial abundance, biomass and production ranged between 1.00 × 109 and 4.93 × 109 cells l−1, 32.43 and 108.59 μg C l−1 and 0.01 and 1.99 μg C l−1 h−1, respectively. With a few exceptions there were no significant spatial patterns in the values (P > 0.05). Bacterial abundance, biomass and production, however, demonstrated a distinct temporal pattern with the lowest values consistently recorded during the winter months. Bacterial dynamics showed no effect of mouth opening events. Nanoflagellate and bacterial abundances were significantly correlated to one another (P < 0.05) suggesting a strong predator-prey relationship. The frequency of visibly infected bacterial cells and the number of virus particles within each bacterial cell during the study demonstrated no significant temporal or spatial pattern (P > 0.05) and ranged from 0.5 to 6.1% and 12.0 to 37.5 virus particles per bacterium, respectively. Viral infection and lysis was thus a constant source of bacterial mortality throughout the year. The estimated percentage of bacterial production removed by viral lysis ranged between 7.8 and 88.9% (mean = 30.3%) of the total which suggests that viral lysis represents a very important source of bacterial mortality during the study.  相似文献   

7.
We tested the idea that bacterial cells with high nucleic acid content (HNA cells) are the active component of marine bacterioplankton assemblages, while bacteria with low nucleic acid content (LNA cells) are inactive, with a large data set (>1700 discrete samples) based on flow cytometric analysis of bacterioplankton in the Northeast Pacific Ocean off the coast of Oregon and northern California, USA. Samples were collected in the upper 150 m of the water column from the coast to 250 km offshore during 14 cruises from March 2001 to September 2003. During this period, a wide range of trophic states was encountered, from dense diatom blooms (chlorophyll-a concentrations up to 43 μg l−1) at shelf stations during upwelling season (March–September) to lower chlorophyll-a concentrations (0.1–5 μg l−1) during winter (November–February) and at basin stations (>1700 m depth). We found only weakly positive relations of log total bacterial abundance to log chlorophyll-a concentration (as a proxy for availability of organic substrate), and of HNA bacteria as a fraction of total bacteria to log chlorophyll-a. Abundance of HNA and LNA bacteria co-varied positively in all regions, although HNA bacteria were more responsive to high phytoplankton biomass in shelf waters than in slope and basin waters. Since LNA cell abundance in general showed responses similar to those of HNA cell abundance to changes in phytoplankton biomass, our data do not support the hypothesis that HNA cells are the sole active component of marine bacterioplankton.  相似文献   

8.
The distribution and abundance of viable and non-viable (so-called resting eggs) embryos of the calanoid copepod Tortanus forcipatus were determined in the laboratory by the enumeration of nauplii that emerge from sediments collected in Victoria Harbor (Hong Kong). Sediment cores sliced down to a depth of 37 cm showed the highest number of viable resting eggs near the surface layer (0–5 cm). The number of viable eggs sharply decreased with sediment depth, particularly at the inner harbor stations, although diapause eggs remained viable as deep as 25 cm. 210Pb analyses of the sediments indicated that the mean egg age was 4.9 years. The egg mortality of T. forcipatus in the sediments was 0.135 year−1, or 78.22% annual egg survival, calculated by regressing ln (egg density) from sediment age. The range of horizontal distribution of viable resting eggs was 24.25 × 103–58.90 × 103 m−2, with a mean value of 36.8 × 103 m−2 over all stations. The accumulation of viable resting eggs that can persist for an extended period of time provided evidence for the existence of an egg bank of T. forcipatus in the sediments of Victoria Harbor.  相似文献   

9.
Habitat use by the European eel Anguilla anguilla in Irish waters   总被引：2，自引：0，他引：2  
The apparent use of marine and freshwater habitats by European eel Anguilla anguilla was examined by analyzing the strontium (Sr) and calcium (Ca) concentrations in otoliths of the eels collected from Irish coastal and fresh waters. The age and growth of eels were also examined using their otolith annuli. The sizes and ages of the female eels were greater than those of the males. The somatic growth rates ranged from 15 to 62 mm/year, which is typical for Ireland and other European countries. Analyses of Sr:Ca ratios along a life history transect in each otolith showed peaks (maximum more than 25 × 10−3) between the core and elver mark corresponding to the period of their leptocephalus and early glass eel stages in the ocean. Outside the elver mark, the Sr:Ca ratios indicated that eels had remained in different habitats that included freshwater (average Sr:Ca ratios, 0.98–1.78 × 10−3) and areas with relatively high salinities (average Sr:Ca ratios, 6.73–8.89 × 10−3). Some individuals showed clear evidence of shifts from sea to fresh waters. These findings suggest that Irish eels have the same behavioral plasticity regarding whether or not to enter freshwater or remain in marine environments as has been recently documented in this species and several other temperate anguillid species. However, patterns of habitat use in Irish waters were somewhat different than those previously reported for other habitats.  相似文献   

10.
Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of 226Ra and 228Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO2. Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25–2 L water samples containing as little as 20 fg of 226Ra and 0.2–0.4 fg of 228Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in 226Ra and 228Ra compared to the samples further offshore. The high precision radium measurements display a small but significant 226Ra and 228Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of 226Ra and 228Ra through SGD to be 5.2 × 1010 and 21 × 1010 dpm/d respectively. The 226Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, 228Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24–4.5 × 1010 l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 1010 l/d during the study period (1.6 to 29% of the river flow).  相似文献   

11.
The distribution of toxic cyanobacterium Microcystis cf. aeruginosa in the severely polluted Golden Horn Estuary was studied from 1998 to 2000. Microcystis persisted at the upper estuary where the water circulation was poor and values ranged between 2.9 × 104 and 2.7 × 106 cells ml−1 throughout the study. Simultaneously measured physical (salinity, temperature, rainfall and secchi disc) and chemical parameters (nutrients and dissolved oxygen) were evaluated together with Microcystis data. Although the Microcystis blooms generally occur in summer due to the increase in temperature, the blooms were recorded in winter in the present study. The abundance of Microcystis depended on the variations in salinity and both blooms were recorded below S = 2. A moderate partial correlation between Microcystis abundance and salinity was detected in the presence of temperature, dissolved oxygen and precipitation data (r = −0.561, p = 0.002). The M. cf. aeruginosa abundance was low in the summer when the salinity was higher than winter. A remarkable increase in the eukaryotic phytoplankton abundance following the improvements in the water quality of the estuary occurred, whilst the Microcystis abundance remained below bloom level.  相似文献   

12.
A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, KD, decreased from about 120×103 to 10×103 ml g−1, and from about 150×103 to 20×103 ml g−1, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l−1. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds.  相似文献   

13.
The distributions, contamination status and annual sedimentation flux of trace metals in surface sediments of the East China Sea (ECS) were studied. Higher concentrations of the studied metals were generally found in the inner shelf and the concentrations decreased seaward. The sequences of the enrichment factor (EF) of the studied metals are Cu > Mn > Ni > Zn > Pb > Fe. The values of EF suggest that the metals contamination in the middle and outer shelves of the ECS is still minor. The annual sedimentation fluxes of trace metals in the ECS were: Fe, 3.48 × 107 t/y; Mn, 9.07 × 105 t/y; Zn, 1.08 × 105 t/y; Ni, 4.48 × 104 t/y; Pb, 4.32 × 104 t/y and Cu, 3.1 × 104 t/y, respectively. Approximately 55–70% and 10–17% of the sedimentation fluxes of trace metals were deposited in the inner shelf and the Changjiang estuarine zone.  相似文献   

14.
This paper reports the initial results of a study of groundwater and coastal waters of southern Brazil adjacent to a 240 km barrier spit separating the Patos Lagoon, the largest coastal lagoon in South America, from the South Atlantic Ocean. The objective of this research is to assess the chemical alteration of freshwater and freshwater–seawater mixtures advecting through coastal permeable sands, and the influence of the submarine discharge of these fluids (SGD) on the chemistry of coastal waters. Here we focus on dissolved iron in this system and use radium isotopic tracers to quantify SGD and cross-shelf fluxes. Iron concentrations in groundwaters vary between 0.6 and 180 μM. The influence of the submarine discharge of these fluids into the surf zone produces dissolved Fe concentrations as high as several micromolar in coastal surface waters. The offshore gradient of dissolved Fe, coupled with results for Ra isotopes, is used to quantify the SGD flux of dissolved Fe from this coastline. We estimate the SGD flux to be 2 × 106 mol day− 1 and the cross-shelf flux to be 3.2 × 105 mol day− 1. This latter flux is equal to about 10% of the soluble atmospheric Fe flux to the entire South Atlantic Ocean. We speculate on the importance of this previously unrecognized iron input to regional ocean production and on the potential significance of this source to understanding variations in glacial–interglacial ocean production.  相似文献   

15.
The distributions, sources and atmospheric fluxes of nitrous oxide (N2O) in the seawater of Jiaozhou Bay were investigated during four surveys in 2003 to evaluate this area as a source of N2O to the atmosphere. N2O concentrations in both the surface and bottom waters of Jiaozhou Bay showed obvious variability with both seasons and tidal cycles. Atmospheric fluxes of N2O in Jiaozhou Bay showed seasonal and spatial variations, with the highest values occurring in summer and the lowest in winter. The annual emission of N2O from the bay was estimated to be 1.09 × 106–2.23 × 106 mol yr−1. N2O in the water column of Jiaozhou Bay was found to come from several external sources including riverine water, sewage water and groundwater input, among which the riverine input was dominant while the groundwater input was rather limited. The spatial variation in distribution and atmospheric fluxes of N2O in Jiaozhou Bay was influenced by the input of polluted river waters and sewage effluent along the eastern coast, which highlights the effects of human impacts on N2O emission rates.  相似文献   

16.
Seawater samples were collected for microbial analyses between 55 and 235 m depth across the Arctic Ocean during the SCICEX 97 expedition (03 September–02 October 1997) using a nuclear submarine as a research platform. Abundances of prokaryotes (range 0.043–0.47×109 dm−3) and viruses (range 0.68–11×109 dm−3) were correlated (r=0.66, n=150) with an average virus:prokaryote ratio of 26 (range 5–70). Biomass of prokaryotes integrated from 55 to 235 m ranged from 0.27 to 0.85 g C m−2 exceeding that of phytoplankton (0.005–0.2 g C m−2) or viruses (0.02–0.05 g C m−2) over the same depth range by an order of magnitude on average. Using transmission electron microscopy (TEM), we estimated that 0.5% of the prokaryote community on average (range 0–1.4%) was visibly infected with viruses, which suggests that very little of prokaryotic secondary production was lost due to viral lysis. Intracellular viruses ranged from 5 to >200/cell, with an average apparent burst size of 45±38 (mean±s.d.; n=45). TEM also revealed the presence of putative metal-precipitating bacteria in 8 of 13 samples, which averaged 0.3% of the total prokaryote community (range 0–1%). If these prokaryotes are accessible to protistan grazers, the Fe and Mn associated with their capsules might be an important source of trace metals to the planktonic food web. After combining our abundance and mortality data with data from the literature, we conclude that the biomass of prokaryoplankton exceeds that of phytoplankton when averaged over the upper 250 m of the central Arctic Ocean and that the fate of this biomass is poorly understood.  相似文献   

17.
The Fram Strait is very important with regard to heat and mass exchange in the Arctic Ocean, and the large quantities of heat carried north by the West Spitsbergen Current (WSC) influence the climate in the Arctic region as a whole. A large volume of water and ice is transported through Fram Strait, with net water transport of 1.7–3.2 Sv southward in the East Greenland Current and a volume ice flux in the range of 0.06–0.11 Sv. The mean annual ice flux is about 866,000 km2 yr−1. The Kongsfjorden–Krossfjorden fjord system on the coast of Spitsbergen, or at the eastern extreme of Fram Strait, is mainly affected by the northbound transport of water in the WSC. Mixing processes on the shelf result in Transformed Atlantic Water in the fjords, and the advection of Atlantic water also carries boreal fauna into the fjords. The phytoplankton production is about 80 g C m−2 yr−1 in Fram Strait, and has been estimated both below and above this for Kongsfjorden. The zooplankton fauna is diverse, but dominated in terms of biomass by calanoid copepods, particularly Calanus glacialis and C. finmarchicus. Other important copepods include C. hyperboreus, Metridia longa and the smaller, more numerous Pseudocalanus (P. minutus and P. acuspes), Microcalanus (M. pusillus and M. pygmaeus) and Oithona similis. The most important species of other taxa appear to be the amphipods Themisto libellula and T. abyssorum, the euphausiids Thysanoessa inermis and T. longicaudata and the chaetognaths Sagitta elegans and Eukrohnia hamata. A comparison between the open ocean of Fram Strait and the restricted fjord system of Kongsfjorden–Krossfjorden can be made within limitations. The same species tend to dominate, but the Fram Strait zooplankton fauna differs by the presence of meso- and bathypelagic copepods. The seasonal and inter-annual variation in zooplankton is described for Kongsfjorden based on the record during July 1996–2002. The ice macrofauna is much less diverse, consisting of a handful of amphipod species and the polar cod. The ice-associated biomass transport of ice-amphipods was calculated, based on the ice area transport, at about 3.55 × 106 ton wet weight per year or about 4.2 × 105 t C yr−1. This represents a large energy input to the Greenland Sea, but also a drain on the core population residing in the multi-year pack ice (MYI) in the Arctic Ocean. A continuous habitat loss of MYI due to climate warming will likely reduce dramatically the sympagic food source. The pelagic and sympagic food web structures were revealed by stable isotopes. The carbon sources of particulate organic matter (POM), being Ice-POM and Pelagic-POM, revealed different isotopic signals in the organisms of the food web, and also provided information about the sympagic–pelagic and pelagic–benthic couplings. The marine food web and energy pathways were further determined by fatty acid trophic markers, which to a large extent supported the stable isotope picture of the marine food web, although some discrepancies were noted, particularly with regard to predator–prey relationships of ctenophores and pteropods.  相似文献   

18.
Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg−1), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg−1) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg−1). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×103 cells ml−1, Synechococcus in the frontal zone with >15×103 cells ml−1, and picoeukaryotes in the upwelling region with >8×103 cells ml−1. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field.  相似文献   

19.
A total of 219 deep-sea fishes belonging to five families were examined for the parasite fauna and stomach contents. The demersal fish Macrourus berglax, bathypelagic Bathylagus euryops, and mesopelagic Argentina silus, Borostomias antarcticus, Chauliodus sloani, and Lampanyctus macdonaldi were caught at 243–708 m trawling depth in the Greenland and the Irminger Sea in 2002. A total of 21 different parasite species, six Digenea, one Monogenea, two Cestoda, seven Nematoda, one Acanthocephala, and four Crustacea, were found. The parasite diversity in the meso- and bathypelagic environment was less diverse in comparison to the benthal. Macrourus berglax had the highest diversity (20 species), usually carrying 4–10 different parasite species (mean 7.1), whereas Bathylagus euryops harbored up to three and Argentina silus, Borostomias antarcticus, Chauliodus sloani and Lampanyctus macdonaldi each up to two species. Most Digenea, Cestoda, Nematoda, Acanthocephala, and Crustacea are known from a wide host range. Several of the encountered parasites occurred at a very low prevalence (<10%), indicating that the studied deep-sea fishes are most probably not instrumental to complete the parasite life cycles in the area of investigation. It is suggested that the lack of nutrients in the meso- and bathypelagial limits the abundance of potential first intermediate hosts of nematodes and cestodes, resulting in low infestation rates even of widely distributed, non-specific species. In contrast, the higher biomass in the benthic deep-sea environment increases the availability of potential intermediate hosts, such as molluscs for the digeneans, resulting in increased parasite diversity. Because many deep-sea fish have a generalistic feeding behavior, the observed different parasite diversity reflects a different depth range of the fish and not necessarily a specific fish feeding ecology.  相似文献   

20.
The organic matter released by the marine phytoplankton species Dunaliella tertiolecta and its physico-chemical interaction with cadmium and copper ions were studied by electrochemical methods (differential pulse anodic stripping voltammetry (DPASV) and a.c. polarography). The interactions with cadmium and copper were studied at the model interface (mercury electrodesolution) and in the bulk phase by measuring the complexing ability of the released organic material.The axenic cultures were grown on different growth media, without and with trace metals and chelators. Culture media were analyzed 10 days after inoculation, containing 5 × 105−1.2 × 106 cells cm−3 when untreated or after separation of cells by gentle centrifugation.It was found that the content and type of the released surface-active material and complexing ligands depend on the initial composition of the growth media. In all cases, strong interaction of excreted organic substances with copper in the bulk phase and with cadmium at the model interface were observed.A rather high value of the complexing capacity, 9.5 × 10−7 mol Cu2+ dm−3, was found in the culture grown on medium without trace metals and chelators (medium I) whereas the surface activity of this culture was not high (0.2 mg dm−3 equivalent to Triton-X-100). Higher contents of surface-active material (0.8 and 1.0 mg dm−3) were found in cultures grown in media with trace metals and without chelators (II and III), accompanied by a high content of complexing ligands (5.8 × 10−7 and 9.5 × 10−7 mol Cu2+ dm−3). However, if the complexing capacity is calculated per cell the values obtained for cultures grown in media II and III (0.79 × 10−15 and 0.98 × 10−15 mol Cu2+ dm−3) are lower than for cultures grown on medium I (1.8 × 10−15 mol Cu2− dm−3). The exceptional adsorption effects and the copper complexing capacity for medium 1, and the presence of cells with degenerative symptoms can be ascribed to stressed growth conditions, and, particularly, to deficiency of metals. A qualitatively similar behaviour has been observed in natural samples of estuarine waters, indicating the existence of stressed conditions during the mixing of fresh and saline waters.  相似文献   

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