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1.
《Ecological modelling》2007,200(1-2):225-233
An eco-hydrodynamic (ECOH) model is proposed for Lake Tanganyika to study the plankton productivity. The hydrodynamic sub-model solves the non-linear, reduced-gravity equations in which wind is the dominant forcing. The ecological sub-model for the epilimnion comprises nutrients, primary production, phytoplankton biomass and zooplankton biomass. In the absence of significant terrestrial input of nutrients, the nutrient loss is compensated for by seasonal, wind-driven, turbulent entrainment of nutrient-rich hypolimnion water into the epilimnion, which gives rise to high plankton productivity twice in the year, during the transition between two seasons. Model simulations predict well the seasonal contrasts of the measured physical and ecological parameters. Numerical tests indicate that the half saturation constant for grazing by zooplankton and the fish predation rate on zooplankton affect the zooplankton biomass measurably more than that of phytoplankton biomass. This work has implications for the application of this model to predict the climatological biological productivity of Lake Tanganyika.  相似文献   

2.
The development of the so-called late winter bloom in subtropical water was studied in an oceanic area north of the Canary Islands from January to May 2000. Zooplankton was sampled at short-term intervals (1–4 days) during the bloom (January–March), and biomass, indices of grazing (gut fluorescence) and metabolism (electron transfer system activity, ETS) were measured in four different size fractions (100–200, 200–500, 500–1000 and >1000 µm). During the bloom, ETS activity and gut fluorescence increased before the development of zooplankton biomass. At the end of February, the presence of an impressive cloud of dust formed in the Sahara desert was related to an increase in chlorophyll and small zooplankton a week later. The increments in biomass were the consequence of consumption by zooplankton as inferred from the indices of grazing and metabolism. Estimated grazing from gut fluorescence and gut evacuation rates during the period of study accounted for 55% of the assessed total ingestion from respiration and normal values of assimilation, showing the importance of the non-pigmented food in the diet of zooplankton in these waters. In contrast, the sharp decreases in zooplankton biomass observed during the bloom appeared during the dark period of the moon, the days in which the diel vertical migrants reach the shallower layers, in agreement with previous works in the area. Thus, the development of the late winter bloom in this region is suggested to be driven by the interplay between resource and consumer controls.Communicated by S.A. Poulet, Roscoff  相似文献   

3.
The response of the Baltic Sea spring bloom was studied in mesocosm experiments, where temperatures were elevated up to 6°C above the present-day sea surface temperature of the spring bloom season. Four of the seven experiments were carried out at different light levels (32–202?Wh?m?2 at the start of the experiments) in the different experimental years. In one further experiment, the factors light and temperature were crossed, and in one experiment, the factors density of overwintering zooplankton and temperature were crossed. Overall, there was a slight temporal acceleration of the phytoplankton spring bloom, a decline of peak biomass and a decline of mean cell size with warming. The temperature influence on phytoplankton bloom timing, biomass and size structure was qualitatively highly robust across experiments. The dependence of timing, biomass, and size structure on initial conditions was tested by multiple regression analysis of the y-temperature regressions with the candidate independent variables initial light, initial phytoplankton biomass, initial microzooplankton biomass, and initial mesozooplankton (=copepod) biomass. The bloom timing predicted for mean temperatures (5.28°C) depended on light. The peak biomass showed a strong positive dependence on light and a weaker negative dependence on initial copepod density. Mean phytoplankton cell size predicted for the mean temperature responded positively to light and negatively to copepod density. The anticipated mismatch between phytoplankton supply and food demand by newly hatched copepod nauplii occurred only under the combination of low light and warm temperatures. The analysis presented here confirms earlier conclusions about temperature responses that are based on subsets of our experimental series. However, only the comprehensive analysis across all experiments highlights the importance of the factor light.  相似文献   

4.
Phytoplankton production, standing crop, and loss processes (respiration, sedimentation, grazing by zooplankton, and excretion) were measured on a daily basis during the growth, dormancy and decline of a winter-spring diatom bloom in a large-scale (13 m3) marine mesocosm in 1987. Carbonspecific rates of production and biomass change were highly correlated whereas production and loss rates were unrelated over the experimental period when the significant changes in algal biomass characteristic of phytoplankton blooms were occurring. The observed decline in diatom growth rates was caused by nutrient limitation. Daily phytoplankton production rates calculated from the phytoplankton continuity equation were in excellent agreement with rates independently determined using standard 14C techniques. A carbon budget for the winter bloom indicated that 82.4% of the net daytime primary production was accounted for by measured loss processes, 1.3% was present as standing crop at the end of the experiment, and 16.3% was unexplained. Losses via sedimentation (44.8%) and nighttime phytoplankton respiration (24.1%) predominated, while losses due to zooplankton grazing (10.7%) and nighttime phytoplankton excretion (2.8%) were of lesser importance. A model simulating daily phytoplankton biomass was developed to demonstrate the relative importance of the individual loss processes.  相似文献   

5.
S. L. Smith 《Marine Biology》1978,49(2):125-132
During March and April 1976, a red tide, dominated by the dinoflagellate Gymnodinium splendens Lebour, developed in the vicinity of 15°06'S and 75°31'W off Peru. At the height of the bloom, the euphotic zone was 6 m deep and the chlorophyll a at the surface was 48 g l-1. A daily collection of zooplankton at 09.00 hrs showed large fluctuations of biomass, from 0.2 to 3.84 g dry weight m-2 in a water column of 120m. Copepodids and nauplii dominated the collections. During a period of reduced wind, the adult copepods were a mixture of the species characteristic of the coastal upwelling system and the neritic species associated with more northerly, tropical waters. Nitrogen regeneration by the zooplankton varied with the development of the bloom, the type of zooplankton dominating the experiment, and biomass fluctuations, but never accounted for more than 25% of the nitrogen uptake by phytoplankton.  相似文献   

6.
Zooplankton species composition and biomass were investigated during the spring of 1984 in three areas west of Ireland. In general, biomass of the gelatinous zooplankters [Salpa fusiformis (Cuvier) forma gregata and solitaria, Cymbulia sp., Euclio sp.; max. 360 mg Cm-3] exceeded that of other zooplankton namely copepods (max. 70 mg C m-3). Feeding by salps in the upper layers of all areas during the observed diatom spring bloom resulted in sedimentation of diatom-rich salp fecal pellets. This process ended the diatom spring bloom prior to nutrient depletion in surface waters and, thus, prior to mass sedimentation of algal cells.Publication No. 17 of the SFB 313 at Kiel University  相似文献   

7.
Zooplankton represents a key contributor to the ocean biological pump through its consumption of sinking and suspended carbon. A specific and highly sensitive method to evaluate zooplankton carbon requirement from the sinking flux is through the estimation of the activity of the electron transport system. The present study was carried out from samplings in 2006, and it was focused on the spatial 200–0?m zooplankton carbon demand across 24 sampling stations, along the Mediterranean Sea, from the island of Crete to the Strait of Gibraltar. Its potential day/night variability was evaluated. The zooplankton composition, abundance and biomass were investigated. The carbon demand per unit zooplankton biomass indicates geographical and diel differences among the sampling stations. A higher mean carbon demand was seen for the western Mediterranean with respect to the eastern Mediterranean, which can be justified through the observed ratio of gelatinous:crustacean taxa and the water temperatures recorded. Higher carbon demand was measured in samples collected during the dark hours. The relation to the presence and abundance of actively migrating euphausiids and copepods was discussed. A comparison with data from another of our study carried out in the same study area but in another seasonal period was done.  相似文献   

8.
Viable heterotrophic microorganisms were enumerated to be 3.7±7.3 bacterial cells per microbial clump during summer in the euphotic zone of Saanich Inlet, British Columbia, Canada. Large microbial aggregates were observed, especially after the phytoplankton bloom, when the phytoplankton biomass formed about 1/2 the total suspended organic matter in the sea. The cell number per microbial clump was minimal when the phytoplankton fraction in the total suspended organic matter was almost 0 (i.e., before the phytoplankton bloom), and again when the phytoplankton bloom occurred. The size of the microbial clumps is discussed, particularly in reference to the food chain in the sea.The work was carried out at the Fisheries Research Board of Canada, Biological Station, Nanaimo, during the tenure of a National Research Council Post-doctoral fellowship.  相似文献   

9.
Analysing long-term diatom data from the German Bight and observational climate data for the period 1962–2005, we found a close connection of the inter-annual variation of the timing of the spring bloom with the boreal winter atmospheric circulation. We examined the fact that high diatom counts of the spring bloom tended to occur later when the atmospheric circulation was characterized by winter blocking over Scandinavia. The associated pattern in the sea level pressure showed a pressure dipole with two centres located over the Azores and Norway and was tilted compared to the North Atlantic Oscillation. The bloom was earlier when the cyclonic circulation over Scandinavia allowed an increased inflow of Atlantic water into the North Sea which is associated with clearer, more marine water, and warmer conditions. The bloom was later when a more continental atmospheric flow from the east was detected. At Helgoland Roads, it seems that under turbid water conditions (=?low light) zooplankton grazing can affect the timing of the phytoplankton bloom negatively. Warmer water temperatures will facilitate this. Under clear water conditions, light will be the main governing factor with regard to the timing of the spring bloom. These different water conditions are shown here to be mainly related to large-scale weather patterns. We found that the mean diatom bloom could be predicted from the sea level pressure one to three months in advance. Using historical pressure data, we derived a proxy for the timing of the spring bloom over the last centuries, showing an increased number of late (proxy-) blooms during the eighteenth century when the climate was considerably colder than today. We argue that these variations are important for the interpretation of inter-annual to centennial variations of biological processes. This is of particular interest when considering future scenarios, as well to considerations on past and future effects on the primary production and food webs.  相似文献   

10.
Two oceanographic cruises were carried out in the northern Adriatic Sea, from June, 1996 to February, 1997. Samples were collected using a BIONESS electronic multinet (204 samples on 54 stations) along inshore-offshore sections. Zooplankton abundance and biomass were estimated in relation to the variability of temperature, salinity and fluorescence. Spatial and vertical distribution patterns of the most important zooplankton groups were studied. During June, in the northern area, abundance and biomass of 2787 - 1735 r ind m and 29.3 - 26.7 r mg r m, respectively, were reported. The zooplankton community was constituted essentially by copepods and cladocerans. In the southern area, instead, an abundance of 4698 - 5978 r ind r m and a dry weight of 25.4 - 15.3 r mg r m were observed, with a reverse dominance ratio between these groups. In February, in the northern area the zooplankton community (1380 - 595 r ind r m and 19.6 - 9.9 r mg r m) was mainly constituted by copepods, larvae of invertebrates, appendicularians and cladocerans; in the southern area zooplankton average abundance was 969 - 493 r ind r m and 9.9 - 3.2 r mg r m being copepods, cladocerans, appendicularians and larvae of invertebrates. The zooplankton spatial distribution, in this period, did not show the classic inshore-offshore gradient. Spatial distribution and biomass values of zooplankton, in the northern Adriatic Sea, were strongly influenced by hydrological characteristics, allowed up to formulate a preliminary model about distribution, along the water column, of the different associations of species assemblages with regard to different water masses in the neritic system.  相似文献   

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