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1.
Gulati  R. D. 《Hydrobiologia》1990,(1):99-118
Structure and grazing activities of crustacean zooplankton were compared in five lakes undergoing manipulation with several unmanipulated eutrophic (shallow) and mesotrophic (deep) lakes in The Netherlands. The biomanipulated lakes had lesser number of species and their abundance, both of rotifers and crustaceans, and had much larger mean animal size (3–11 μg C ind.−1) than in the unmanipulated eutrophic lakes (0.65 μG C ind.−1). WhereasD. hyalina (=D. galeata) andD. cucullata generally co-occurred in the unmanipulated lakes, in the manipulated lakes bothD. hyalina and other large-bodied daphnids,D. magna,D. pulex (=D. pulicaria), were the important grazers. In the biomanipulated lakes an increase in the individual crustacean size and of zooplankton mass were reflected in a decrease in seston concentration, higher Secchi-disc depth and a marked decrease in the share in phytoplankton biovolume of cyanobacteria. Biomass relationship between seston (150 μm) and zooplankton indicated a Monod type relationship, with an initial part of the curve in which the zooplankton responds linearly to the seston increase up to aboutca. 2 mg C l−1, followed by a saturation of zooplankton mass (0.39 mg C l−1) at 3–4 mg C l−1 seston, and an inhibitory effect on zooplankton mass at seston levels>4 mg C l−1. This latter is related to predominance in the seston of cyanobacteria. In the biomanipulated lakes, the zooplankton grazing rates often exceeded 100% d−1, during the spring, and food levels generally dropped to <0.5 mg C l−1. The computed specific clearance rate (SCR) of zooplankton of 1.9 l mg−1 Zoop C is well within the range of SCR values (1.7–2.2 l mg−1 Zoop C) from deep and mesotrophic waters, but about an order of magnitude higher than in the eutrophic lakes, with the food levels 10-fold higher. For 25% d−1 clearance of lake seston between 35 and 60 ind. l−1 are needed in the biomanipulated lakes against 1200–1300 ind. l−1 in eutrophic lakes. Similarly, about 10 to 15 times more crustacean grazers are required to eliminate the daily primary production in the eutrophic lakes than in the biomanipulated lakes. These numbers are inversely related to the differences in animal size. The corresponding biomass values of zooplankton needed to clear the daily primary production in the eutrophic waters were 0.1–0.2 mg C l−1 in the biomanipulated lakes, but about 0.45 mg C l−1 in the unmanipulated eutrophic waters. Only if the water was kept persistently clear by zooplankton was there a balanced seston budget between the inputvia primary production and elimination by zooplankton. Mostly, however, the input exceeded the assimilatory removal by zooplankton, such that the estimated seston loss could be attributed to sedimentation and mineralization.  相似文献   

2.
The primary production of phytoplankton in Lake Vechten   总被引:6,自引:6,他引:0  
The primary production of the phytoplankton of Lake Vechten (The Netherlands) (area, 4.7 ha; mean depth, 6 m), an unpolluted and stratified sandpit was investigated from 1969 to 1980 (except in 1971, 1975 and 1976) by the in situ 14C-technique. Other data collected include: solar radiation, transparency, oxygen and thermal structure. In winter and spring diatoms, Cryptophyceae and Chlorococcales were important algal groups, while in summer Dinophyceae and Chrysophyceae were important. The chlorophyll-a concentration was compared to the cellular biovolumes (= fresh weight) of the most abundant phytoplankton species. The primary production maxima occurred in winter, spring and during the summer stratification. The vertical profiles of photosynthesis exhibit light inhibition at surface to a maximum of 4 m. The maximum of zooplankton grazing in May–June caused a sharp decrease in the phytoplankton biomass and seston concentration accompanied by the highest transparency (clear water phase).The values for cellular C-fixation range from 10 to 1307 mg C · M–2 · day–1 (annual mean of 280 mg C · m–2 · day–1). High dark fixation (up to 100%) was encountered in the metalimnion and hypolimnion from July to October together with peaks of 14C-fixation due to a crowding of phytoplankton and phototrophic anoxic bacteria. Extracellular excretion by phytoplankton, investigated in 1977 to 1979, was 15% of the annual mean of the total C-fixation. The photosynthetic efficiency, turnover rates, and activity coefficients were low, particularly in the summer months when Ceratium hirundinella was predominant. The seasonal variations were controlled mainly by solar radiation and probably phosphate, the former being more important in the non-stratification period and the latter during the stratification period.  相似文献   

3.
Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l–1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33m) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind–1.d–1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l–1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 gC.ind–1.d–1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg–1 body C.d–1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production.  相似文献   

4.
Summary Unidirectional 22Na+ and 36Cl fluxes were determined in short-circuited, stripped rumen mucosa from sheep by using the Ussing chamber technique. In both CO2/HCO 3 -containing and CO2/HCO 3 -free solutions, replacement of gluconate by short-chain fatty acids (SCFA, 39 mM) significantly enhanced mucosal-toserosal Na+ absorption without affecting the Cl transport in the same direction. Short-chain fatty acid stimulation of Na+ transport was at least partly independent of Cl and could almost completely be abolished by 1 mM mucosal amiloride, while stimulation of Na+ transport was enhanced by lowering the mucosal pH from 7.3 to 6.5. Similar to the SCFA action, raising the PCO2 in the mucosal bathing solution led to an increase in the amiloride-sensitive mucosal-to-serosal Na+ flux. Along with its effect on sodium transport, raising the PCO2 also stimulated chloride transport. The results are best explained by a model in which undissociated SCFA and/or CO2 permeate the cell membrane and produce a raise in intracellular H+ concentration. This stimulates an apical Na+/H+ exchange, leading to increased Na+ transport. The stimulatory effect of CO2 on Cl transport is probably mediated by a Cl/HCO 3 exchange mechanism in the apical membrane. Binding of SCFA anions to that exchange as described for the rat distal colon (Binder and Mehta 1989) probably does not play a major role in the rumen.Abbreviations DIDS 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid - G t transepithelial conductance (mS·cm-2) - HSCFA undissociated short-chain fatty acids - J ms mucosal-to-serosal flux (Eq · cm-2 · h-1) - J net net flux (Eq · cm-2 · h-1) - J sm serosal-to-mucosal flux (Eq · cm-2 · h-1) - PD transepithelial potential difference (mV) - SCFA dissociated short-chain fatty acids - SCFA short-chain fatty acids  相似文献   

5.
Feeding of Euchlanis dilatata lucksiana, a brachionid rotifer isolated from the Loosdrecht Lakes (The Netherlands), was examined in the laboratory using 14C-labelled food. The gut-filling time at a food concentration of 9.6 µg C ml–1 was about 15 minutes. Animals which were fed on 3 size fractions of the lake seston (< 7 µm, 7–15 µm, and 15–33 µm) showed a clear preference (Jacobs' selectivity index) for the largest size fraction. This fraction was composed predominantly of filamentous cyanobacteria. For animals weighing 0.37–0.49 µm C ind.–1 the daily ration (daily food consumption per unit body weight × 100) ranged from 50 to 100% at food levels of 2 mg C l–1 and below, but increased to 150–250% at food concentrations of 5 mg C l–1 and above. The assimilation efficiency was 100% up to 5 mg C l–1 of food, but decreased to about 80% at higher food levels.  相似文献   

6.
The suspension feeding of Bithynia tentaculata was tested in laboratory experiments. The animals were fed in 1-1 aerated glass beakers, and filtration rates were calculated from changes in cell concentrations during the 6-h experiment. Temperature influenced the filtering rate, with minimum values of 5ml · ind–1 · h–1 at 5° C and maxima of 17.2 ml · ind–1 · h–1 at 18° C. Three food species of different size, motility and cell surface characteristics (Chlamydomonas reinhardii, Chlorella vulgaris and Chlorogonium elongatum) did not affect filtration rates. Suspension feeding increased with increasing food concentrations up to 12 nl · ml–1, above which feeding rate was kept constant by lowering the filtering rates. Even the smallest animals tested (<4 mm body length) were found to be feeding on suspended food at a rate of 2.7 ml · ind–1 · h–1, and increasing rates up to 8.4 ml were found in the 6–7 mm size class. All size classes of Bithynia showed a circannual fluctuation of their filtration rates. The ecological consequences of Bithynia's ability to switch between two feeding modes, grazing and suspension feeding, are discussed.  相似文献   

7.
Seasonal cycle of the microbial plankton in Crooked Lake,Antarctica   总被引:3,自引:0,他引:3  
Summary Changes in the abundance of the components of the microbial plankton between July 1990 and March 1991 in Crooked Lake, one of the largest and deepest freshwater lakes in Antarctica, are described. Chlorophyll a concentration is low (0.2–0.4g·1–1) and there is no discernable spring increase. The phytoplankton is largely dominated by flagellates. Bacterioplankton exhibits a seasonal pattern of abundance ranging from 1.0 × 108·1–1 in July to 3.25 × 108·1–1 in September. Changes in bacterial abundance probably relate to temperature and grazing by heterotrophic and mixotrophic flagellates. Total flagellated protozoan concentrations ranged between 25–136 × 102·l–1. Autotrophic and heterotrophic flagellate abundances were coupled and peaks in their abundance oscillated with peaks in bacterioplankton concentration. Four species of ciliated protozoa, dominated by oligotrichs, particularly the plastidic Strombidium, inhabit the lake. The plankton is characterised by the presence of floes which act as loci for bacteria, flagellates and amoebae and feeding sites for the ciliates and the two sparce metazoan components of the plankton. Crooked Lake is extremely oligotrophic but nonetheless supports a plankton community with a low species diversity and simple trophodynamics.  相似文献   

8.
Phosphorus and nitrogen excretion rates by zooplankton communities from two eutrophic and shallow Dutch lakes were measured in laboratory. The variations in excretion rates in the lakes (May–October) were caused mainly by fluctuation in zooplankton biomass. Mean summer excretion rates (June–September) were 2.4 and 0.9 µg PO4P·1–1·d–1 in Lake Loosdercht and Lake Breukeleveen, respectively. This difference between the lakes was caused mainly by the lower zooplankton biomass in Lake Breukeleveen. The excretion of 2.4 µg PO4P·1–1·d compared with the calculated P-demand of phytoplankton of 8.0 µg PO4P·1–1·d–1 is substantial in the summer (June–September) and far more important than the external P-supply of 0.4 µg P·1–1·d–1 and sediment release of 0.5 µg P·1–1·d–1. Both temperature and composition of zooplankton affected the weight specific excretion rates of the zooplankton community. The weight specific community excretion rates of P and N increased with temperature (exponential model); 1–8 g PO4P·mg–1 zooplankton-C·d–1 and 5–42 µg NH3N·mg–1 zooplankton-C·d–1 (10°C–20°C).  相似文献   

9.
Isolated posterior gills (no. 7) of shore crabsCarcinus maenas acclimated to brackish water of a salinity of 10 S were bathed and perfused with 50% sea water (200 mmol·l-1 Na+), and the internal perfusate collected during subsequent periods of 5 min. During a single passage through the gill the pH of the perfusion medium decreased from ca. 8.1 to ca. 7.7, a result implying that the gill possesses structures which recognize unphysiologically high pH values in the haemolymph and regulates them down to physiological values of ca. 7.7. The calculated apparent proton fluxes from the epithelial cells into the haemolymph space amounted to 17.9 mol·g fw-1·h-1, a value of only 3.8% of net Na+ fluxes observed under comparable conditions. When 0.1 mmol·l-1 KCN, an inhibitor of mitochondrial cytochrome oxidase, or 5 mmol·l-1 ouabain, a specific inhibitor of Na+/K+-ATPase were applied in the internal perfusate, down-regulation of pH was no longer observed and the gill was completely depolarized, i.e. transepithelial potential differences dropped from-7.8 to 0 mV (haemolymph space negative to bath). Regulation of pH was completely inhibited by antagonists of carbonic anhydrase (0.1 mmol·l-1 acetazolamide or 0.01 mmol·l-1 ethoxyzolamide) applied in the perfusate. Inhibitors of Na+/H+ exchange, 0.1 mmol·l-1 amiloride applied in the external bathing medium or in the internal perfusate, and symmetrical 0.01 mmol·l-1 5-(N-ethyl-N-isopropyl)amiloride, as well as inhibitors of Cl-/HCO3 - exchange and Na+/HCO3 - cotransport, 0.5 mmol·l-1 4,4-diisothiocyanatostilbene-2,2-disulphonate or 0.3 mmol·l-1 4-acetamido-4-isothiocyanatostilbene 2,2-disulphonate applied on both sides of the gill, and inhibitors of H+-ATPase, 0.05 mmol·l-1 N-ethylmaleimide and 0.1 mmol·l-1 N,N-dicyclohexylcarbodiimide —applied on both sides of the gill — did not alter the acidification of the perfusate observed in controls. Using artificial salines buffered to pH 8.1 with 0.75 mmol·l-1 tris (hydroxymethyl) aminomethane instead of 2 mmol·l-1 HCO3 -, apparent proton fluxes were reduced to 11% of controls, a result suggesting that pH regulation by crab gills needs the presence of HCO3 -. The findings obtained suggest that pH regulation by crab gills depends on the oxidative metabolism of the intact branchial epithelium and that carbonic anhydrase plays a central role in this process. Na+/H+ exchange, anion exchange or cotransport and active proton secretion seem not to be involved. While unimpaired active ion uptake is a prerequisite for pH regulation, ion transport itself is independent of it.Abbreviations acetazolamide (N-[sulphamoyl-1, 3, 4-thiadiazol-2-yl]-acetamide) - amiloride 3,5-diamino-6-chloropyrazinoyl-guanidine - CA carbonic anhydrase - DBI dextrane-bound inhibitor thiadiazolesulphonamide - DCCD N N dicyclohexylcarbodiimide - DIDS 4,4-diisothiocyanato-stilbene-2,2-disulphonate - EIPA 5-(N-ethyl-N-isopropyl) amiloride - ethoxyzolamide 6-ethoxy-2-benzothiazole-sulphonamide - fw fresh weight - J H + apparent proton flux - NEM N-ethylmaleimide - PD transepithelial potential difference - PEG-STZ polyethylene-glycol-thiadiazolesulphonamide - STTS 4-acetamido-4-isothiocyanatostibene 2,2-disulphonate - SW sea water - TRIS tris(hydroxymethyl)aminomethane  相似文献   

10.
The dorsal skin of the leech Hirudo medicinalis was used for electrophysiological measurements performed in Ussing chambers. The leech skin is a tight epithelium (transepithelial resistance = 10.5±0.5 k· cm-2) with an initial short-circuit current of 29.0±2.9 A·cm-2. Removal of Na+ from the apical bath medium reduced short-circuit current about 55%. Ouabain (50mol·l-1) added to the basolateral solution, depressed the short-circuit current completely. The Na+ current saturated at a concentration of 90 mmol Na+·l-1 in the apical solution (K M=11.2±1.8 mmol·l-1). Amiloride (100 mol·l-1) on the apical side inhibited ca. 40% of the Na+ current and indicated the presence of Na+ channels. The dependence of Na+ current on the amiloride concentration followed Michaclis-Menten kinetics (K i=2.9±0.4 mol·l-1). The amiloride analogue benzamil had a higher affinity to the Na+ channel (K i=0.7±0.2 mol·l-1). Thus, Na+ channels in leech integument are less sensitive to amiloride than channels known from vertebrate epithelia. With 20 mmol Na+·l-1 in the mucosal solution the tissue showed an optimum amiloride-inhibitable current, and the amiloride-sensitive current under this condition was 86.8±2.3% of total short-circuit current. Higher Na+ concentrations lead to a decrease in amiloride-blockade short-circuit current. Sitmulation of the tissue with cyclic adenosine monophosphate (100 mol·l-1) and isobutylmethylxanthine (1 mmol·l-1) nearly doubled short-circuit current and increased amiloride-sensitive Na+ currents by 50%. By current fluctuation analysis we estimated single Na+ channel current (2.7±0.9 pA) and Na+ channel density (3.6±0.6 channels·m-2) under control conditions. After cyclic adenosine monophosphate stimulation Na+ channel density increased to 5.4±1.1 channels·m-2, whereas single Na+ channel current showed no significant change (1.9±0.2 pA). These data present a detailed investigation of an invertebrate epithelial Na+ channel, and show the similarities and differences to vertebrate Na+ channels. Whereas the channel properties are different from the classical vertebrate Na+ channel, the regulation by cyclic adenosine monophosphate seems similar. Stimulation of Na+ uptake by cyclic adenosine monophosphate is mediated by an increasing number of Na+ channels.Abbreviations slope of the background noise component - ADH antidiuretic hormone - cAMP cyclic adenosine monophosphate - f frequency - f c coner frequency of the Lorentzian noise component - Hepes N-hydroxyethylpiperazine-N-ethanesulphonic acid - BMX isobutyl-methylxanthine - i Na single Na+ channel current - I Na max, maximal inhibitable Na+ current - I SC short circuit current - K i half maximal blocker concentration - K M Michaelis constandard error of the mean - S (f) power density of the Lorentzian noise component - S 0 plateau value of the Lorentzian noise component - TMA tetramethylammonium - Trizma TRIS-hydroxymethyl-amino-methane - V max maximal reaction velocity - V T transepithelial potential - K half maximal blocker concentration  相似文献   

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