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  • 1
    ISSN: 1432-0975
    Keywords: Key words Flow cytometry ; Chlorophyll ; Fiji ; Primary production ; Nutrient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  Phytoplankton biomass, community structure and productivity of the Great Astrolabe lagoon and surrounding ocean were studied using measurements of chlorophyll concentration and carbon uptake. The contribution of picophytoplankton to biomass, productivity and community structure was estimated by size fractionation, 14C-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll 〈3 μm. Consequently, the percentage contribution to chl a〈3 μm from each picoplankton group could be calculated using regression estimated values of ψ i (fg chl a per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m-3 with 45% of phytoplankton 〈3 μm. Primary production reached 1.3 g C m-2 day-1 with 53% due to phytoplankton 〈3 μm. Synechococcus was the most abundant group at all stations, followed by Prochlorococcus and picoeukaryotes. At all stations, Prochlorococcus represented less than 4% of the chl a 〈3 μm, Synechococcus between 85 and 95%, and Picoeukaryotes between 5 and 10%. In the upper 40 m of surrounding oceanic waters, phytoplankton biomass was dominated by the 〉3 μm size fraction. In deeper water, the 〈1 μm size fraction dominated. Prochlorococcus was the most abundant picoplankton group and their contributions to the chlorophyll a〈3 μm were close to that of the picoeukaryotes (50% each).
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  • 2
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Dissolved, particulate and sedimentary lipid compounds were analyzed in samples collected in May 1988 at three sites in the lagoon of the closed atoll of Takapoto (Tuamotu archipelago, French Polynesia). The study provides background information dealing with water quality and the nature and concentration of lipids. Non-aromatic hydrocarbons and fatty acids were isolated from lipids and analyzed by gas chromatography/mass spectrometry. Non-aromatic hydrocarbon concentrations did not exceed 1000 ng l-1 in water, and 2300 ng g-1 in surface sediments and are among the lowest encountered in pristine marine environments. No noticeable petroleum pollution was evidenced in the lagoon. Nevertheless, traces of petroleum-derived compounds were detected at the central site for both surface and deep water. Total fatty acid concentrations varied in the range 6.3–14.4 μg l-1 for the particulate phase and in the range 0.5–3.2 μg l-1 for the dissolved phase. The molecular fingerprints of fatty acids and hydrocarbons evidenced a predominant algal, and to a lesser extent microbial, origin of the organic matter present in water and sediments. Mono- and polyunsaturated fatty acids, which are essential components for animal metabolism, were identified in noticeable amounts in suspended matter (1.8–4.6 μg l-1), and at highly variable levels in the dissolved phase (0.08–1.21 μg l-1).
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  • 3
    ISSN: 1573-5117
    Keywords: Patagonic Coast ; phytoplankton assemblage ; particulate matter ; synecologic study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phytoplankton assemblage and seston composition of the San José's gulf (Argentine, 42° ϕ S) were studied during a period of two years. Cell counts, chlorophyll, particulate nitrogen and particulate carbon determination were made. Phytoplankton synecology was studied using principal component analysis.
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  • 4
    ISSN: 1573-5117
    Keywords: Patagonic Coast ; nutritive reserve ; limiting factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Physical and chemical characteristics of the Gulf San Jose (42°ϕ. S.) were studied during two annual cycles. The results indicate a possibility for high primary productivity.
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  • 5
    ISSN: 1573-5117
    Keywords: Patagonic Coast ; annual production ; turn over time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Annual primary production was estimated from two years data. The results indicate a high primary productivity and a short turn over time for nitrogen.
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  • 6
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The standing stock and taxonomic composition of zooplankton (〉200 μm) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals 〉200 μm comprised 50% of the total biomass of all organisms from 35 to 〉2000 μm. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K 2, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K 2 values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of 14C uptake during April 1985 and April 1986, respectively. Ingestion of animals 〉35μm was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean.
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nutrient concentrations were measured in the lagoon and surrounding oceanic waters of Tikehau Atoll (Tuamotu Archipelago, French Polynesia) from 1984 to 1987. The “atoll-mass effect” alters the nutrient profiles: turbulent vertical mixing of the waters along the deeper slopes of the atoll induces nitrogen and phosphorus enrichment of the surface layer. Nutrient concentrations varied with year and month of sampling; except for ammonium, inorganic nutrient levels were lower inside the lagoon than in the surrounding oceanic waters. Nitrogen, phosphorus and silica budgets were calculated by mean differences in nutrient concentrations recorded between lagoon and oceanic surface waters and by the waterexchange rate through the passage linking the lagoon and oceanic waters and the reef-flat spillways. Particulate and dissolved organic nitrogen and ammonium are exported from the lagoon to the open ocean through the westward passage. The nitrogen budget is not balanced by the nitrate input from oceanic waters and the organic nitrogen and ammonium output from lagoonal waters. Nitrogen fixation would appear to constitute another source of nitrogen for lagoonal waters. The phosphorus budget is largely balanced by phosphate input from the oceanic waters and organic phosphorus output from the lagoon waters. The oceanic waters became impoverished in silicate during their crossing of the atoll reef edge and their residence in the lagoon. The atoll constitutes a source of nitrogen for the surrounding oceanic waters.
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  • 8
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Suspended particulate matter was comprehensively investigated from 6 to 17 April 1986 in the lagoon of Tikehau atoll (15°00′S; 148°10′W). Dry weight (DW), particulate organic carbon (POC), adenosine triphosphate (ATP), and chlorophyll a were measured for five size-classes (0.2 to 0.8 μm, 0.8 to 3 μm, 3 to 35 μm, 35 to 200 μm, and 200 to 2000 μm). Taxa were identified and counted for the whole plankton (both autotrophic and heterotrophic). Particles 〈3 μm accounted for 81% of the total POC (192 mg m-3), and detritus comprised 82% of the total POM. Phytoplankton (cyanobacteria plus algae) accounted for 35% of the living carbon, 75% of which consisted of heterotrophic bacteria and cyanobacteria. The zooplankton biomass was composed of 31% nano-, 26% micro-, and 43% mesoplankton.
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