Showing papers in "Journal of Plankton Research in 1995"

An estimate of global primary production in the ocean from satellite radiometer data

Abstract: An estimate of global net primary production in the ocean has been computed from the monthly mean near-surface chlorophyll fields for 1979-1986 obtained by the Nimbus 7 CZCS radiometer. Our model required information about the subsurface distribution of chlorophyll, the parameters of the photosynthesis-light relationship, the sun angle and cloudiness. The computations were partitioned among 57 biogeochemical provinces that were specified from regional oceanography and by examination of the chlorophyll fields. Making different assumptions about the overestimation of chlorophyll by the CZCS in turbid coastal areas, the global net primary production from phytoplankton is given as 45-50 Gt C year"1. This may be compared with current published estimates for land plants of 45-68 Gt C year"' and for coastal vegetation of 1.9 Gt C year"1.

Remote sensing of chlorophyll in Lake Kinneret using highspectral-resolution radiometer and Landsat TM: spectral features of reflectance and algorithm development

Abstract: High-resolution reflectance spectra in the range of 400-850 nm were obtained from Lake Kinneret during a period when dense populations of the dinoflagellate Peridinium gatunense dominated the phytoplankton. Chlorophyll (ChI) concentrations ranged from 5.1 to 185 mg mand from 2.4 to 187.5 mg m-3 in the samples of two independent experiments. The most prominent features of the reflectance spectra were: (i) a wide minimum from 400 to 500 nm; (ii) a maximum at 550-570 nm, which did not surpass 3% in samples with high ChI concentration (>20 mg m-3), indicating a strong absorption by pigments in the green range of the spectrum; (iii) a minimum at 676 nm; this was ~ 1 % and was almost insensitive to variation in ChI concentration >10 mg m-3; (iv) a maximum reflectance showed near 700 nm; its magnitude and position were highly dependent on chlorophyll concentration. Highspectral-resolution data were used as a guideline for selection of the most suitable spectral bands for chlorophyll remote sensing. Models were devised, based on the calculation of the integrated area above the baseline from 670 to 850 nm and the reflectance maximal height within this range. Some algorithms already used in previous studies were tested and showed a plausible degree of accuracy when applied to the current data base. However, novel models devised in this study improved substantially the accuracy of ChI estimation by remotely sensed data, by reducing the estimation error from >11 to 6.5 mg m-• Those models were validated by an independent data set where ChI concentration ranged over two orders of magnitude. The use of three relatively narrow spectral bands was sufficient for ChI mapping in Lake Kinneret. Therefore, a relatively simple sensor, measuring only a few bands will be employed in future applications for ChI monitoring in inland waters. Radiometric data were also used to simulate radiances in the channels of TM Landsat and to find the algorithm for ChI assessment. The ratio of channel 4 to channel 3 was used and enabled ChI estimation with an error of <15 mg m-• This algorithm was employed to map ChI in the entire area of Lake Kinneret with 10 gradations.

Early warning of toxic dinoflagellate blooms of Gymnodinium catenatum in southern Tasmanian waters

Abstract: Blooms of the toxic dinoflagellate Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) in the Derwent and Huon estuaries of southern Tasmania, Australia, are predictable, annually recurrent events in the period January to June (late summer to early winter). However, their spatial distribution, duration and magnitude exhibit significant interannual variability. High shellfish toxicities in 1986, 1991 and 1993 (>8000 μ.g paralytic shellfish poisoning per 100 g shellfish meat) also coincided with the greatest spatial extent of shellfish toxicity (up to 35 shellfish farms closed for periods up to 6 months). An exploratory analysis of the results of a shellfish toxin monitoring programme conducted from 1986 to 1994, and of available hydrological and meteorological data for the region, indicates that a significant G.catenatum bloom in Tasmanian waters can only develop within a permissive seasonal water temperature window (>14°C at the time of bloom initiation) requiring a rainfall event as a trigger (Huon River discharge, measured at Frying Pan Creek, must exceed 100 000 megalitres over a 3-week period) and a calm stable water column for sustained development (windspeed <5 m s-1 for periods of 5 days or more). Once established, dinoflagellate populations are subject to disturbance by turbulence caused by high windstress; this explains the incidence in some years of multiple shellfish toxicity peaks. In winter months declining water temperatures (<10°C) and increasing windstress are responsible for the termination of seasonal dinoflagellate blooms. © 1995 Oxford University Press.

Autunmal sedimentation of Microcystis spp. as result of an increase in carbohydrate ballast at reduced temperature

Abstract: Autumnal sedimentation of the Microcystis population was studied in Lake Nieuwe Meer (Amsterdam, The Netherlands). In summer, Microcystis formed a high percentage of the total phytoplankton in the water column, but a low percentage in sedimentation traps. The reverse was found during September and October, with a high percentage in the sedimentation traps, but a low percentage in the water column. The decrease in the numbers of Microcystis colonies coincided with a decrease in water temperature. In experiments with a strain of Microcystis, isolated from Lake Nieuwe Meer, the percentage of total colonies that were sinking increased in a few days to 100% after a shift from 20 degrees C to 15.3, 13.0 or 10.5 degrees C. The gas-vesicle volume in the cells remained constant during the incubations. Sinking of the colonies resulted from an increased glycogen content. Calculation of carbon (C) flows during the first 2 days of the incubation at reduced temperature showed that the glycogen accumulation was the result of a much lower rate of protein synthesis during the light period at the lower temperatures. Although the photosynthetic rate itself decreased at reduced temperature, it resulted in more fixed CO2 being stored as glucose. Because the respiratory rate also decreased (with an almost similar decrease to that of photosynthesis), glycogen accumulated at lower temperatures. It was calculated that after an incubation period of similar to 1 week at reduced temperature, the rate of photosynthesis had decreased by 10.1% of the value at 20 degrees C per 1 degrees C, while the rate of respiration had decreased only 1.8%. It is proposed that there is a feedback mechanism in which an increasing concentration of glycogen inhibits photosynthesis and stimulates respiration.

The relationship between community respiration and ETS activity in the ocean

Abstract: Abstrad. We have studied the relationship between community respiration ( R ) and enzymatic activity of the electron transport system (ETS) in upper ocean microbial communities (<225 pm) from different oceanic regions. In al1 except one of the regions, R and ETS were significantly positive correlated. This supports the hypothesis that ETS can be widely used to estimate plankton respiration in natural rnarine communities (Packard,T.T., Adv. Aquat. Microbiol., 3,207-261.1985). A regression equation was obtained between al1 the R and ETS data studied. to derive respiration from ETS activity. Thk equation yields a mean error in the prediction of 534%. similar to the errors obtained applying the equations at each area, but lower than the error obtained when using the mean R:ETS ratio to determine respiration (545%). Our results suggest that the use of the ETS-R algorithm, along with rneasurements of ETS activity in seawater, facilitates the estimation of seawater respiratory oxygen consumption on the mesoscale. This means that by using this approach one could extend our knowledge of oceanic respiration over large temporal and spatialscales, and begin to userespiration, not only productivity, in addressing carbon balance problems in the upper ocean.

Intermittency in the plankton: a multifractal analysis of zooplankton biomass variability

Abstract: We present the first evidence that variability in zooplankton biomass can be characterized as a multifractal An hourly tune series of vertically integrated acoustic biomass measurements, taken from a fixed mooring on the Atlantic coastline, provided the data for our analysis Two measures of variability were analyzed: the first difference squared and the squared difference from the mean When integrated over time, these quantities provide estimates of biomass variability The distribution in time of these measures of variability is highly intermittent We show that such intermittency is well described by the scaling properties of multifractals In zooplankton ecology, potential applications of this analysis include comparing plankton variability distributions to those of passive scalars and environmental variables, quantifying spatial or temporal heterogeneity in intermittent quantities, and determining scales over which similar processes are operating

A comparison of whole-community and ecosystem approaches (biomass size distributions, food web analysis, network analysis, simulation models) to study the structure, function and regulation of pelagic food webs

Abstract: A step-by-step procedure for investigating the structure, function and regulation of pelagic communities as an entirety is suggested which proceeds along gradients of increasing requirements for data and knowledge, and of growing understanding of ecosystem functioning. It comprises methodologies based on biomass size distributions, followed by food web analysis, network analysis and dynamic simulation models. The different approaches are compared with respect to data requirements, theoretical foundations, operational problems, time and computational effort, and the different types of information they provide on food web structure and dynamics. These ideas are illustrated with data from Lake Constance. Biomass size distributions provide a structural and energetic food web analysis based only on measurements of abundances and body sizes, and a few general assumptions mainly on size relationships of metabolic activities and trophodynamics. Food web analysis considers binary webs depicting qualitatively trophic links between species or trophic guilds and provides profound information about the food web structure. Mass-balanced flow diagrams (trophic webs) take into account the magnitude of flows between living and non-living compartments, and provide comprehensive descriptions of fluxes and cycling of matter and the trophic food web structure when evaluated by network analysis. These three static approaches are contrasted with tactical dynamic simulation models depicting interaction webs and representing unique possibilities of studying the dynamic nature, spatio-temporal organization, direct and indirect cause-effect relationships, and impact of physical forcing. However, these capabilities are only achievable on the expenditure of a very large research effort.