Ocean annual phytoplankton carbon and new production,and annual export production estimated with empirical equations and CZCS data

Empirical equations are parameterized for use with chlorophyll a, derived from satellite ocean colour data, to calculate phytoplankton carbon production, phytoplankton new production, and export production. For environments in a high variance (HV) pigment statistical class, annual phytoplankton particulate organic carbon production (AIP) is linearly related to annual average in situ chlorophyll a within the near‐surface layer. Linear relations were also obtained between AIP and annual new nitrogen production, and between AIP and particulate organic carbon annually exported from the euphotic zone for environments in that class. We found no relation between AIP and C_SFC, or between the annual production variables, for oceanic environments characterized by low pigment variance (LV). Ratios of export production to AIP, called e, and new production to nitrogen annually used in phytoplankton production, called f, are widely used to express marine food web processes. The trends of these ratios with AIP differ between HV and LV environments. This is a result of differences in the coupling between nitrogen and carbon transfer in pelagic food webs, which contain different organism size classes in HV compared to LV environments. We applied the empirical equations to CZCS data to estimate global new and export production. The HV environments are responsible for about 40% of global ocean annual phytoplankton carbon production and 70% of global ocean annual new and export production.     

Modelling enteric bacteria survival in aquatic systems

We measured the uptake of carbon and inorganic nitrogen in nutrient-enriched water samples during 15-days incubation in summer in Lake Nakanuma, Japan. We calculated daily variations in neutral sugars and amino acids of the phytoplankton and estimated the efficiency of the increases in sugars and amino acids relative to photosynthetic activities. Only a small portion of carbon incorporated via photosynthesis was used for synthesis of sugars and amino acids during the incubation periods. The percentage increase in neutral sugars plus amino acids compared to photosynthetic rates ranged from 3.7 to 26.9% with an average of 12.8%. These findings suggest that large amounts of photosynthates were not used for the synthesis of cell components of phytoplankton and were lost through processes such as excretion and respiration.     

The role of plankton biomass in controlling fluctuations of suspended matter in Lake Constance

The concentrations of particulate matter, expressed as dry weight (DW), particulate organic (POM), and inorganic material were measured at regular intervals in Lake Constance between February 1980 and December 1982. Maximum particle concentrations were recorded for the euphotic zone in summer (7 mg l⁻¹), while minima occurred during the early summer and in winter. Annual mean concentrations of DW within the entire water column varied between 0.6 and 0.7 mg l⁻¹. In the euphotic zone nearly 70% of DW is organic material. The inorganic particles originate either from phytoplankton (diatomaceous silicon, biogenic decalcification) or from the tributaries. Although phytoplankton biomass only comprises a relatively small proportion (i.e. 30% at maximum) of organic matter, it is the primary source of POM. Therefore, seasonal variations in phytoplankton control epilimnetic concentrations of POM in Lake Constance. Inorganic material comprises smaller proportions of suspended matter. Seasonal variations are related predominantly to fluctuations in biomass and therefore particulate inorganic matter is suggested to originate mainly from autochthonous sources. At the sampling station concentrations of inorganic particles supported by the main tributary, the Alpenrhein, only occasionally vary concomitantly with runoff.     

Urea degradation by picophytoplankton in the euphotic zone of Lake Biwa

The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0 μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton cells and of liberation of CO₂ into water) measured by radiocarbon urea were 8 and 17 μmol urea m⁻³ day⁻¹ in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m⁻³ day⁻¹, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded into two phases, carbon incorporation and CO₂ liberation, whereas in the dark it was degraded only into the CO₂ liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa. Received: June 25, 1998 / Accepted: February 10, 1999     

Phosphatase activity and its rôle in the mineralization of organic phosphorus in coastal sea water

Alkaline phosphatase activity in sea-water samples taken from Tokyo, Sagami, and Suruga Bays in Japan was measured by a sensitive fluorometric method. There is a relationship between the phosphatase activity and bacterial biomasses in these three bays. The phosphatase-producing bacteria accounted for 40, 46, and 41% of heterotrophic bacteria in Tokyo, Sagami and Suruga Bays, respectively. Significant amounts of phosphatase-hydrolysable organic phosphorus were found in the euphotic zones of these bays and this organic phosphorus fraction accounted for 19 and 50% of organic phosphorus in Tokyo and Sagami Bays, respectively. Phosphatase-hydrolysable organic phosphorus was decomposed completely in the euphotic zone suggesting that this organic fraction is re-cycled in the primary production of the bays. Decomposition of natural organic phosphorus by enzymes was followed by measuring the release of inorganic orthophosphate from samples saturated with chloroform. Release of inorganic phosphorus proceeds rapidly for 2 or 3 days followed by a slow release. Enzymes present in the samples contributed to the decomposition of 50% of the organic phosphorus and the phosphatase enzyme was responsible for the decomposition of one-third of the hydrolysable organic phosphorus in the samples. Potential phosphatase activity in the samples was found to be indicative of the extent and rate of decomposition of organic phosphorus in coastal waters.     

Spatio-temporal study of phytoplankton cell viability in a eutrophic reservoir using SYTOX Green nucleic acid stain

Despite the global importance of phytoplankton primary production, the ecological role of cell death as an important loss process in phytoplankton is poorly understood. To assess the significance of cell death in phytoplankton, we studied cell viability of dominant species in the canyon-shaped eutrophic ?ímov Reservoir (Czech Republic) at weekly and biweekly intervals from April to October 2011. Surface samples were taken from the lacustrine zone (near the dam, low nutrient level) and transition zone (near the river inflow, high nutrient level) of the reservoir. Moreover, samples from euphotic depth (1% of surface irradiance) were taken from the lacustrine zone. We used the membrane-impermeant nucleic acid dye SYTOX Green to examine seasonal and spatial differences in phytoplankton cell viability. Three species (diatoms Asterionella formosa, Fragilaria crotonensis, and cyanobacterium Aphanizomenon flos-aquae) were studied in detail. There was no difference in Asterionella cell viability among sampling sites. In the lacustrine zone, Fragilaria and Aphanizomenon exhibited lower viability than in the transition zone. In addition, Aphanizomenon viability was significantly lower at the euphotic depth. Nutrient levels were revealed as a factor influencing Fragilaria viability, while light availability was more important for Aphanizomenon. Our results evidenced that the importance of cell death, in particular phytoplankton taxa, varies both spatially and temporally. Moreover, our study indicates that coexisting taxa may differ in their capacity to cope with different environmental stressors.     

A Compositional and Structural Analysis of Phytoplankton in Lake Khurpatal, (U.P.), India

The phytoplankton community in Lake Khurpatal (Kumaun Himalya), India, was analyzed in relation to physico-chemical variables. Phytoplankton biomass ranged from 2.7 to 20.0 g m⁻³ in the euphotic zone of the lake. Dinoflagellates monopolized the algal community with a mean annual contribution of 94.5 % to the total phytoplankton biomass. The community coefficient used to quantify the seasonal changes in algal population reflected the fact that successional episodes were not very significant, the percentage similarity among the consecutive algal samples ranging from 47.8 to 89.9 %. The phytoplankton community was characterized by low species richness, low equitability and species diversity. Various ecological characteristics of the community are discussed and the phytoplankton biomass is also compared with that of some tropical and temperate lakes.     

The physiological state of the phytoplankton community of three types of lakes as estimated by its adenylate energy charge

Variations in physiological state and biomass of the phytoplankton community were examined in three different types of lakes, namely Lake Barato, Lake Akan, and Lake Shikaribetu. When the physiological state of the phytoplankton community was estimated by its adenylate energy charge (AEC), low biomass and low physiological state co-appeared gradually in the metalimnion and hypolimnion during stratification. The physiological state of the phytoplankton as estimated by its AEC value did not always correspond to its biomass, estimated by chlorophyll-a and ATP in these three lakes. A high physiological state of the community was usually observed in the euphotic zone, but the low AEC value observed in the euphotic zone of Lake Barato was not identified in the euphotic zones of the other lakes. Thus, the relationship between the value of AEC, and biomass of phytoplankton is a complex variable, which is further discussed in this paper.     

The Spatial Variability of the Fluorescent Characteristics of Phytoplankton in the Black Sea

The spatial variability of the photochemical efficiency of phytoplankton photosystem II was analyzed in two contrasting regions of the Black Sea: the western part of the deepwater region and a region influenced by the Danube River discharge. The fluorescence values for open (F₀) and closed (F_m) photosystem II reaction centers in the investigated areas varied by an order of magnitude and correlated closely. The potential photochemical efficiency of phytoplankton photosystem II (F_m ? F₀)/F_m varied from 0.16 to 0.70. Three types of the vertical distribution of this index were found. In the first type, the values increased from the surface to the top of the thermocline and then remained stable down to the bottom of the euphotic zone; in the second type, they increased from the surface to the bottom of the euphotic zone; in shallow areas, they were stable within the euphotic zone. With an increase in light intensity, the phytoplankton photochemical efficiency decreased. The light inhibition of the photosystem II efficiency was more intense in the deeper than in the upper layers of the euphotic zone.     

Dependence of phytoplankton assimilation quotients on light and nitrogen source: implications for oceanic primary productivity

Photosynthetic production of oxygen by phytoplankton assemblagedominated by Peridinium in Lake Kinneret, Israel, generallyexceeds the molar equivalent rate of carbon assimilation. Carbonassimilation occurs only if oxygenic photosynthesis exceedsa light-dependent threshold. Assimilation quotients (mol C molO₂^–1) are a variable function of irradiance, and typicallyonly about one-half of the photoreductant produced during oxygenicphotosynthesis is used for reduction of carbon dioxide. Mostof the residual oxygenic photoreductant probably is used forlight-dependent reduction of nitrate, which competes with carbondioxide for oxygenic photoreductant. Nitrate is an importantsource of nitrogen for this algal assemblage, and light-dependentnitrate reduction probably is much larger than carbon dioxidereduction at lowest irradiances in the euphotic zone. Oxygenproduction also may be much larger than carbon assimilationat low light levels in other environments where oxidized formsof nitrogen are important nitrogenous nutrients for phytoplankton,as in the lower euphotic zone of the sea, where low rates ofcarbon assimilation by phytoplankton have been thought to beinconsistent with the amount of oxygen that accumulates duringsummer.     

Bacterial response to seasonal changes in primary production and phytoplankton biomass in Lake Constance

Parameters characterizing bacterial biomass and metabolic activityare compared with phytoplankton biomass and daily primary productionrates throughout the year. Between late March (before the onsetof the phytoplankton spring bloom) and mid-July (diatom maximum),bacterial degradation of organic matter was more closely relatedto phytoplankton productivity than during the rest of the year.Bacterial production (as estimated by amino acid net uptake)was significantly correlated with concentrations of chlorophyll and pheopigments. However, bacterial production was correlatedless closely with primary production and only weakly with bacterialbiomass. Bacterial biomass was also only weakly correlated withprimary production but significantly with pheopigments. Numbersof active bacteria as estimated by autoradiography covariedclosely with bacterial production and cell numbers. Wheneverbacterial production was low, enhanced proportions of aminoacids were respired. Oxygen consumption measurements showedthat the size fraction <3 µm contributed 25–75%to total respiration. On average, bacterial biomass comprised11 % of paniculate organic matter and roughly equalled phytoplanktonbiomass. During the growing season, bacterial production inthe uppermost 20 m comprised about 20% of phytoplankton productionwith large seasonal fluctuations. A tentative carbon budgetof the euphotic zone including primary production, zooplanktongrazing, bacterial production and sedimentation is presented. ¹Present address: Institute of Marine Resources A-018, ScrippsInstitution of Oceanography, University of California, San Diego,La Jolla, CA 92093, USA     

Ecophysiological and Trophic Implications of Light-Stimulated Amino Acid Utilization in Marine Picoplankton

By using microautoradiography, light-stimulated utilization of dissolved amino acids for natural marine phytoplankton assemblages was demonstrated. The <2-μm-size (diameter) picoplankton, known to be a dominant fraction of marine primary production, revealed a widespread capability for this process. Autofluorescent (chlorophyll a-containing) picoplankton and some larger phytoplankton from diverse oceanic locations, as well as isolates of the representative cyanobacterial picoplankton Synechococcus spp. (WH7803, WH8101), showed light-stimulated incorporation of amino acids at trace concentrations. Dark-mediated amino acid utilization was dominated by nonfluorescent bacterial populations. Among autofluorescent picoplankton, light-stimulated exceeded dark-mediated amino acid incorporation by 5 to 75%; light-stimulated amino acid incorporation was only partially blocked by the photosystem II inhibitor 3(3,4-dichloro-phenyl)-1,1-dimethy-lurea (2 × 10^-5 M), suggesting a photoheterotrophic incorporation mechanism. Parallel light versus dark incubations with glucose and mannitol indicated a lack of light-stimulated utilization of these nonnitrogenous compounds. Since marine primary production is frequently nitrogen limited, light-mediated auxotrophic utilization of amino acids and possibly other dissolved organic nitrogen (DON) constituents may represent exploitation of the relatively large DON pool in the face of dissolved inorganic nitrogen depletion. This process (i) increases the efficiency of DON retention at the base of oceanic food webs and (ii) may in part be responsible for relatively high rates of picoplankton production under conditions of chronic dissolved inorganic nitrogen limitation. Picoplanktonic recycling of organic matter via this process has important ramifications with respect to trophic transfer via the “microbial loop.”     

Utilization of Organic Nitrogen Sources by Two Phytoplankton Species and a Bacterial Isolate in Pure and Mixed Cultures

Algal production of dissolved organic carbon and the regeneration of nutrients from dissolved organic carbon by bacteria are important aspects of nutrient cycling in the sea, especially when inorganic nitrogen is limiting. Dissolved free amino acids are a major carbon source for bacteria and can be used by phytoplankton as a nitrogen source. We examined the interactions between the phytoplankton species Emiliania huxleyi and Thalassiosira pseudonana and a bacterial isolate from the North Sea. The organisms were cultured with eight different amino acids and a protein as the only nitrogen sources, in pure and mixed cultures. Of the two algae, only E. huxleyi was able to grow on amino acids. The bacterium MD1 used all substrates supplied, except serine. During growth of MD1 in pure culture, ammonium accumulated in the medium. Contrary to the expectation, the percentage of ammonium regenerated from the amino acids taken up showed no correlation with the substrate C/N ratio. In mixed culture, the algae grew well in those cultures in which the bacteria grew well. The bacterial yields (cell number) were also higher in mixed culture than in pure culture. In the cultures of MD1 and T. pseudonana, the increase in bacterial yield (number of cells) over that of the pure culture was comparable to the bacterial yield in mixed culture on a mineral medium. This result suggests that T. pseudonana excreted a more-or-less-constant amount of carbon. The bacterial yields in mixed cultures with E. huxleyi showed a smaller and less consistent difference than those of the pure cultures of MD1. It is possible that the ability of E. huxleyi to use amino acids influenced the bacterial yield. The results suggest that interactions between algae and bacteria influence the regeneration of nitrogen from organic carbon and that this influence differs from one species to another.     

Spatial and Temporal Variations in Bacterial Macromolecule Labeling with [methyl-H]Thymidine in a Hypertrophic Lake

The incorporation of [methyl-H]thymidine into three macromolecular fractions, designated as DNA, RNA, and protein, by bacteria from Hartbeespoort Dam, South Africa, was measured over 1 year by acid-base hydrolysis procedures. Samples were collected at 10 m, which was at least 5 m beneath the euphotic zone. On four occasions, samples were concurrently collected at the surface. Approximately 80% of the label was incorporated into bacterial DNA in surface samples. At 10 m, total incorporation of label into bacterial macromolecules was correlated to bacterial utilization of glucose (r = 0.913, n = 13, P < 0.001). The labeling of DNA, which ranged between 0 and 78% of total macromolecule incorporation, was inversely related to glucose uptake (r = -0.823), total thymidine incorporation (r = -0.737), and euphotic zone algal production (r = -0.732, n = 13, P < 0.005). With decreased DNA labeling, increasing proportions of label were found in the RNA fraction and proteins. Enzymatic digestion followed by chromatographic separation of macromolecule fragments indicated that DNA and proteins were labeled while RNA was not. The RNA fraction may represent labeled lipids or other macromolecules or both. The data demonstrated a close coupling between phytoplankton production and heterotrophic bacterial activity in this hypertrophic lake but also confirmed the need for the routine extraction and purification of DNA during [methyl-H]thymidine studies of aquatic bacterial production.     

Primary production studies on a new reservior; Bighorn Lake-Yellowtail Dam,Montana, U.S.A. *

A definite algal succession pattern was established for all 3 years of study. Volume-based phytoplankton density and chlorophyll concentration decreased down-reservoir. However, the depth of the euphotic zone increased down-reservoir as silt settled out. Consequently, the euphotic zone standing crops were greatest mid-reservoir. Insufficient light penetration was established as the principal limiting factor to primary production in the upper end of the reservoir. Decreased primary production in the lower end of the reservoir did not appear to be due to nutrient limitation. Comparison of sampling periods common to all years of the study showed that estimated net primary production increased 84% in 1970 over 1968.     

Impact of UV radiation on the production patterns and composition of dissolved free and combined amino acids in marine phytoplankton

Using the ¹³C tracer technique in conjunction with gas chromatographic-massspectro-metric (GC-MS) techniques, we examined the patternsof synthesis and the composition of dissolved free and combinedamino acids within phytoplankton photosynthesizing in the presenceand absence of natural solar ultraviolet radiation (UVR). Atlevels that still permitted the uptake of carbon assimilationinto the cells, UVR caused a marked decline in the overall rateof carbon incorporated into amino acids and a reduction in thepool size of total cellular amino acids (TCAA). In contrast,absolute concentrations of amino acids within the intracellulardissolved free amino acid (INDFAA) pool (measured using an aminoacid analyzer) were higher in the presence of UVR. An examinationof the production patterns and composition of amino acids constitutingthe INDFAA and TCAA pools revealed a marked diminution in thesynthesis and accumulation of alanine and valine in the presenceof UVR. On the other hand, the rates of synthesis and concentrationsof glutamic acid (glutamic acid + glutamine) in the INDFAA andTCAA pools of phytoplankton were higher in samples exposed toUVR. These changes are discussed with reference to the knowneffects of UVR on nitrogen and carbon assimilation within phytoplankton.     

Correlation Between Urea and Other Chemical and Biological Parameters in Waters of Lake Suwa,Japan

The vertical profiles of chemical and biological parameters, including urea concentration, have been measured periodically since February of 1977 at a central station in Lake Suwa, which is one of the typical eutrophic lakes in Japan. The seasonal trend in the standing stock of urea in the central water column, together with the ratio of urea versus total inorganic nitrogen in the euphotic zone from 12 March, 1977 to 25 July, 1978, are presented. The possible importance of bacterial decomposition of dead phytoplankton as a urea source in natural waters is demonstrated by this study. At times, a highly significant correlation between the vertical profile of urea and vertical distributions of other chemical and biological parameters which were also measured was found. An apparent in situ utilization of urea by phytoplankton is suggested on the basis of vertical profiles of urea and other chemical and biological parameters.     

Survival strategies of some species of the phytoplankton community in the Barra Bonita Reservoir (São Paulo,Brazil)

The dynamics of the phytoplankton community in the Barra Bonita Reservoir (S?o Paulo, Brazil) were studied through daily sampling in the field (integrated samples from the euphotic zone) and microcosm experiments, for two short periods: the winter of 1993 (June 30 to July 10) and the summer of 1994 (January 24 to February 2). The goal of the study was to evaluate and compare the variations in the composition of isolated phytoplankton community which occur over short periods of time. Three series were separated into Erlenmeyer flasks for each study period, with samples from the euphotic zone divided into three portions: total, smaller than 64 μm, and smaller than 20 μm. All of the Erlenmeyer flasks were inclubated in situ at the sampling station. The maximum period of incubation was 10 d. Variations of the community in the euphotic zone were characterised by high diversity and a community in a state of non-equilibrium in winter, without the predominance of any species. In the summer, the community presented a low diversity and a state of equilibrium, with the predominance of Microcystis aeruginosa. The microcosm experiments showed that the confinement of the community in the Erlenmeyer flasks, and therefore in isolation from the physical variability of the ecosystem, especially in relation to the mixing patterns, stimulated the return of the community to the initial phases of succession with the predominance of small species and those which grow rapidly (r-selective or C-strategist). This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of a cyanobacterial bloom in a hypereutrophic reservoir,Lake Chivero,Zimbabwe

Blooming and non-blooming periods between 2004 and 2006 in a hypereutrophic reservoir, where cyanobacterial blooms have previously been reported to be permanent, presented an opportunity to characterise factors that may favour cyanobacterial dominance. As a bloom developed in May 2004, a shift to dominance by Microcystis aeruginosa, similar to competitive exclusion, was observed. The period of M. aeruginosa dominance was characterised by the lowest Secchi depth and euphotic zone depth readings, and a decline of non-buoyant species because of competitive exclusion by M. aeruginosa, which reduced light availability in the water column. After the bloom collapsed, the euphotic zone depth increased, followed by the establishment of a Cryptomonas–Cyclotella phytoplankton assemblage. Cyanobacterial dominance within the phytoplankton assemblage was favoured by an extended stratification and was limited by nitrogen (mainly ammonium) availability. Other taxa were limited by light availability, as shown by their decline when M. aeruginosa dominated. The period of extended stratification, an increase in ammonium concentration and a decrease in nitrate concentration promoted dominance by M. aeruginosa.