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1.
Experiments were conducted to study the distribution of three selectedpolychlorinated biphenyl (PCB) congeners within the microbial food web attwo different nutrient levels; control and nutrient enriched. The objectivewas to quantify the uptake of PCBs through grazing by protozoa. The 14C-PCBs tested were 4-chlorobiphenyl (IUPAC # 3),2,2,5,5-tetrachlorobiphenyl (IUPAC # 52), and2,2,4,4,5,5-hexachlorobiphenyl (IUPAC # 153). EachPCB was incubated in triplicate seawater samples at 20 idref;Cover one week. Daily, samples were separated into four fractions; <0.2µm (dissolved), 0.2-2 µm (bacteria), 2-10 µm(flagellate), and > 10 µm (microplankton; phytoplankton andprotozoa) by selective filtration. Of the PCB fraction that initiallyadsorbed to particles, 60–100% was associated to the bacterialfraction and 0–5% to the microplankton fraction. The totaluptake was highest in the nutrient enriched samples, but when normalized tothe carbon biomass the concentration was lower or equal to the control inall particle fractions. The recovery of the PCBs in the particulatefractions depended on the degree of chlorination, as the highest values wereobserved for the 2,2,4,4,5,5-hexachlorobiphenyl and thelowest for the 4-chlorobiphenyl. The concentrations in the bacterial andflagellate fractions decreased over the first 48–96 hours whilst theconcentration increased in the highest trophic level (>10 µmfraction). Approximately 75% of the increase in concentration of the2,2,4,4,5,5-hexachlorobiphenyl in the > 10 µmfraction was estimated to be the result of bacterivory. Our results indicatethe microbial food web can contribute to a rapid uptake of higherchlorinated PCBs, particularly in oligotrophic ecosystems where thebacterial biomass dominates. 相似文献
2.
The occurrence of reductive dechlorination processes towards pre-existing PCBs and five exogenous coplanar PCBs were investigated
in a contaminated sediment of Porto Marghera (Venice Lagoon, Italy) suspended, under strictly anaerobic conditions, in water
collected from the same site. PCB dechlorination started after five months of incubation, when sulfate initially occurring
in the microcosms was completely depleted and methanogenesis was in progress. It was ascribed to sulfate-reducing bacteria.
Several pre-existing hexa-, penta- and tetra-chlorinated biphenyls were slowly bioconverted into tri- and di-, ortho-substituted PCBs from the 5th to the 16th month of experiment. Spiked coplanar PCBs, i.e., 3,3′,4,4′-tetrachlorobiphenyl,
3,3′,4,4′,5- and 2,3′,4,4′,5-pentachlorobiphenyls, 3,3′,4,4′,5,5′- and 2,3,3′,4,4′,5-hexachlorobiphenyls, were extensively
transformed (by about 90%) into lower chlorinated congeners, such as 3,3′,5,5′-/2,3′,4,4′-tetrachlorobiphenyl, 3,3′,5-, 2,4,4′-,
2,3′,4- and 2,3′,5-trichlorobiphenyl, 3,4-/3,4′- and 3,3′-dichlorobiphenyl and 2-chlorobiphenyl. The reductive dechlorination
of spiked PCBs did not influence significantly the biotransformation rate and extent of pre-existing PCBs. 相似文献
3.
The seasonal changes in the size-fractionated chlorophyll a concentrations (<3 μm, 3 to 25 μm, and >25 μm) were investigated at a pelagic site of the north basin of Lake Biwa during
June to December 1985. Autofluorescing plankton cells in the <3-μm fractions were also examined using the fluorescein isothiocyanate
staining epifluorescence microscopic technique. The <3-μm phytoplankton (usually dominated by chroococcoid cyanobacteria except
for a few cases dominated by small eukaryotes) showed a clearly different pattern of seasonal change compared with the larger
fractions. That is, from August to early September, chlorophyll a of the larger fractions declined considerably, while the <3-μm chlorophyll a did not decrease significantly. Moreover, cyanobacterial cell density in the <3-μm fraction showed a maximum value (2–3.5×10 5 cells·ml −1) during this period. The relative contribution of the <3-μm chlorophyll a to the total chlorophyll a increased from <5% to 45% during the course of this change. No clear vertical trend in the distribution and composition of
the <3-μm phytoplankton was found, except that relatively large cyanobacteria (>4 μm 3) appeared at a depth of 15m but not at 0,5 and 10 m from late July to August. These large cells were also found in November
and December. The drastic seasonal change of phytoplankton size structure occurring in this basin was discussed in relation
to grazing, nutrient depletion and sinking.
Contribution from Otsu Hydrobiological Station, Kyoto Univeristy (No. 308, foreign language series). 相似文献
4.
In a mesocosm nutrient enrichment experiment the species (orcategories) and abundances of diatoms, dinoflagellates, flagellates,monads and ciliates were identified and counted over a 16-monthperiod. Diatoms and ciliates increased with increasing nutrienttreatment while monads and flagellates, <10 µm in size,did not. By contrast, in the field diatoms sometimes appearedto decrease while small phytoplankton µ10 µm appearedto increase under eutrophic conditions. In the experiment, insome instances, grazing controlled abundances to low levelsin nutrient-enriched treatments. Self-shading by phytoplanktonlimited upper levels of abundance when nutrients were excessive.While nuisance species were occasionally present in variousnutrient treatments, the intensity and frequency of their presencedid not tend to increase with nutrient treatment. Generallyspecies (or categories) did not appear to change with nutrienttreatment. 相似文献
5.
Effects of fish predation propagate through aquatic food webs, where the classical grazing food chain and microbial loop are
interwoven by trophic interactions. The overall impact on aquatic food webs is further complicated because fish may also exert
bottom-up controls through nutrient regeneration. Yet, we still have limited information about cascading effects among fish,
zooplankton, phytoplankton, and microbes. In this study, we performed a mesocosm experiment to evaluate effects of fish introduction
on plankton communities. Six plots were set in factorial combination with fish introduction and rice straw plowing in a paddy
field, and the experiment was continued for 4 weeks. Introduction of fish significantly increased chlorophyll a concentrations in smaller size fractions (<15 μm) and abundances of filamentous bacteria (>5 μm in length) and heterotrophic
nanoflagellates in 3–15 μm fraction. Microbes in 0.8–3 μm fraction showed increasing but not significant trends in response
to fish introduction. These results indicate cascading effects of fish predation operating via two pathways, one through grazing
food chain and the other through microbial food web. Phytoplankton community compositions shifted in similar fashion in all
plots until 1 week after fish introduction, and then diverged between plots with and without fish thereafter. Bottom-up effects
of fish introduction were suggested by increases of total chlorophyll a and inedible phytoplankton species in response to fish introduction. This study provides an example of how fish predation
regulates biomass and structure of phytoplankton and microbial communities. 相似文献
6.
Mature male Sprague-Dawley rats received a single IP injection of either 2,2',4,4',5,5'-hexachlorobiphenyl (HCB), 3,3',4,4'-tetrachlorobiphenyl (TCB) (300 microm/kg) in corn oil (10 ml/kg) or the corn oil vehicle alone, and were killed four days later after having been fasted overnight. The vehicle control group consisted of rats which were allowed free access to feed as well as pair-fed animals. Lipid analyses were conducted on liver, hepatic microsomes and serum. TCB- (but no HCB-) treatment resulted in a statistically significant increase in total liver lipids and triglycerides. Liver phospholipids remained unchanged. Both PCBs increased the cholesterol and phospholipids content of the liver microsomal fraction. Serum lipids measured were not statistically different from control values. While HCB had little effect on the fatty acid composition of liver lipids, TCB caused an increase in C 18:1 (n-9) and a decrease in C 20:4 (n-6). Both PCBs increased C 18:0 in the hepatic microsomal fraction, but TCB also decreased C 16:0. Neither PCB altered the fatty acid composition of serum total lipids. These data are consistent with the concept that specific alterations in lipid metabolism are dependent on the structure of the PCB. 相似文献
7.
The influence of the size distribution of phytoplankton on changes in the planktonic food web structures with eutrophication
was examined using natural planktonic communities in two world-famous lakes: Lake Baikal and Lake Biwa. The size distribution
of phytoplankton and the ratio of heterotrophic to autotrophic biomass (H/A ratio), indicating the balance between primary
production and its consumption, were investigated in the lakes of different trophic status. The results revealed that microphytoplankton
(>20μm) in mesotrophic Lake Biwa, and picophytoplankton (<2μm) or nanophytoplankton (2–20μm) in oligotrophic Lake Baikal,
comprised the highest proportion of the total phytoplankton biomass. The H/A ratio was lower in Lake Biwa (<1) than in Lake
Baikal (>1). The low H/A ratio in Lake Biwa appeared to be the consequence of the lack of consumption of the more abundant
microphytoplankton, which were inferior competitors in nutrient uptake under oligotrophic conditions but less vulnerable to
grazing. As a result, unconsumed microphytoplankton accumulated in the water column, decreasing the H/A ratio in Lake Biwa.
Our results showed that food web structure and energy flow in planktonic communities were greatly influenced by the size distribution
of phytoplankton, in conjunction with bottom-up (nutrient uptake) and top-down (grazing) effects at the trophic level of primary
producers. 相似文献
8.
1. Enrichment factors have been calculated for several persistent PCB congeners in the adipose tissue for five species of fish-eating sea birds (female razorbills, puffins, guillemots, shags and cormorants) obtained from the same sites during 1978–1984 (see preceding papers).2. The enrichment factor of an individual PCB is expressed as its concentration in the tissue compared with its abundance in commerical mixtures of PCBs or compared with the concentration in the tissue of the abundant congener 2,2',4,4',5,5'-hexachlorobiphenyl (congener 153, IUPAC system of numbering).3. There were no significant differences between the five species in the enrichment factor of individual persistent PCBs compared with congener 153, indicating similar levels of diminished metabolism of this group of congeners.4. Of the 47 individual PCBs identified, ten congeners had enrichment factors of > 1 in all of the species and these accounted for up to 70% of the concentration of total PCBs present. Some of these persistent congeners had approximately coplanar configurations (i.e. non- ortho -substituted congeners). Five congeners, which accounted for about 35% of the total concentration of PCBs in the tissues, shared the molecular feature of chlorine substituents at adjacent meta-para carbon atoms.5. A number of congeners were identified with enrichment factors of <1 compared with their abundance in Aroclor 1260, and very striking differences were observed between the five species in the ratio of non-persistent congeners to the persistent congener 153. These non-persistent congeners share the molecular feature of at least one pair of adjacent unsubstituted meta-para carbon atoms in the rings. This agrees with our molecular “rule” (see preceding papers) that congeners with this structural feature are subjected to metabolism by the cytochrome P-450 component of hepatic microsomal monooxygenases.6. Evidence is presented that this molecular rule applies to the persistence or non-persistence of classes of PCBs in other biological systems and that the complete absence of H atoms at adjacent carbon atoms is an essential structural requirement for the accumulation of PCBs in tissues.7. The persistence or non-persistence of individual PCBs is compared with their ability to induce specific isoforms of the cytochrome P-450 components of hepatic microsomal monooxygenases, and the toxic effects of individual PCBs that accumulate is discussed in terms of the potential environmental hazard that they represent. 相似文献
9.
We compared the metabolism of eight di- and trichlorobiphenyls by eight bacterial strains chosen to represent a broad range
of degradative activity against polychlorinated biphenyls (PCBs). The PCB congeners used were 2,3-, 2,3′-, 2,4′-, 3,3′-, 2,3,3′-,
2,4,4′-, 2,5,3′-, and 3,4,2′-chlorobiphenyl. The bacterial strains used were Corynebacterium sp. MB1, Alcaligenes strains A. eutrophus H850 and A. faecalis Pi434, and Pseudomonas strains LB400 and H1130, P. testosteroni H430 and H336, and P. cepacia H201. The results indicated that both the relative rates of primary degradation of PCBs and the choice of the ring attacked
were dependent on the bacterial strain used. The bacterial strains exhibited considerable differences in their relative reactivity
preferences for attack on mono- and dichlorophenyl groups and in the degree to which the attack was affected by the chlorine
substitution pattern on the nonreacting ring. For MB1 the reactivity pattern was 3-≥4-≫2-chlorophenyl with no attack on 2,4-
or 2,5-chlorophenyl groups. This strain was relatively insensitive to the chlorine substitution pattern on the nonreacting
ring. Strains H1130, H430, H201, and Pi434 exhibited the same reactivity preferences as MB1, but for these strains (and for
all others tested) the chlorination pattern on the nonreacting ring had a strong effect. For strain H336 the reactivity preference
was 4-≥2->2,4-≥3-chlorophenyl, with no evidence of attack on 2,5-chlorophenyl rings. For strains H850 and LB400 the relative
reactivity was 2->2,5->3-≫2,4->4-chlorophenyl. On this basis we propose that the eight bacterial strains represent four distinct
classes of biphenyl/PCB-dioxygenase activity.
The types of products formed were largely strain-independent and were determined primarily by the chlorine substitution pattern
on the reacting ring. When the reacting ring was an unsubstituted phenyl or a 2-chlorophenyl group, the products were chlorobenzoic
acids in high yields; for a 3-chlorophenyl ring, both chlorobenzoic acids and chloroacetophenones in moderate yields; and
for a 4- or 2,4-chlorophenyl group, chlorobenzoic acids in low yields with an apparent accumulation of meta ring-fission product. Strains H850 and LB400 were able to degrade the 3-chlorobenzoic acid that they produced from the degradation
of 2,3′-chlorobiphenyl. We conclude that despite differences among strains in the specificity of the initial dioxygenase,
the specificities of the enzymes responsible for the subsequent degradation to chlorobenzoic acid and/or chloroacetophenone
are quite similar for all strains. 相似文献
10.
Toxic coplanar polychlorinated biphenyls (Co-PCBs) were used as substrates for a degradation experiment with white-rot fungus, Phlebia brevispora TMIC33929, which is capable of degrading polychlorinated dibenzo- p-dioxins. Eleven PCB congener mixtures (7 mono- ortho- and 4 non- ortho-PCBs) were added to the cultures of P. brevispora and monitored by high resolution gas chromatography and mass spectrometry (HRGC/HRMS). Five PCB congeners, 3,3′,4,4′-tetrachlorobiphenyl, 2,3,3′,4,4′-pentachlorobiphenyl, 2,3′,4,4′,5-pentachlorobiphenyl, 3,3′,4,4′,5-pentachlorobiphenyl, and 2,3′,4,4′,5,5′-hexachlorobiphenyl were degraded by P. brevispora. To investigate the fungal metabolism of PCB, each Co-PCB was treated separately by P. brevispora and the metabolites were analyzed by gas chromatography and mass spectrometry (GC/MS) and identified on the basis of the GC/MS comparison with the authentic compound. Meta-methoxylated metabolite was detected from the culture containing each compound. Additionally, para-dechlorinated and -methoxylated metabolite was also detected from the culture with 2,3,3′,4,4′-pentachlorobiphenyl, 2,3′,4,4′,5-pentachlorobiphenyl, and 2,3′,4,4′,5,5′-hexachlorobiphenyl, which are mono- ortho-PCBs. In this paper, we identified the congener specific degradation of coplanar PCBs by P. brevispora, and clearly proved for the first time by identifying the metabolites that the white-rot fungus, P. brevispora, transformed recalcitrant coplanar PCBs. 相似文献
11.
The root growth, changes in Superoxide dismutase (SOD, EC 1.15.1.1) activity, malonyldialdehyde (MDA) and total soluble protein level of broadbean (Vicia faba) seedlings were researched at different soil concentrations of chlorobenzene (CB), 1,2,4-trichlorobenzene (TCB) and hexachlorobenzene (HCB). The results showed that root growth of seedlings was interrupted after 5d of 50–200 μg · g−1 TCB treatment. During a 3 d of recovery period, root growth was, however, restored to some extent although there was a delay in returning to the control level. The total soluble protein content in seedlings increased with TCB concentration and duration of exposure. Effect of TCB stress on SOD activity in seedlings displayed a significant dose-effect relationship for 1–5 d of 50–200 μg · g−1 treatment. When broadbean seedlings were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water for 3 d, SOD activity at 50 μg · g−1 TCB recovered towards control level (P> 0.05) while a significant increase in SOD activity was observed at 100 and 200 μg · g−1 TCB compared to control (P< 0.05). The experiments also revealed that a significant increase of MDA level in seedlings occurred after 3 and 5 d of 100 and 200 μg · g−1 TCB treatment (P< 0.05 andP< 0.01), and there was a positive correlation between TCB concentration and MDA level. All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil. Compared to TCB, the toxicity of 50−1000 μg · g−1 CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure. 相似文献
12.
The root growth, changes in Superoxide dismutase (SOD, EC 1.15.1.1) activity, malonyldialdehyde (MDA) and total soluble protein level of broadbean ( Vicia faba) seedlings were researched at different soil concentrations of chlorobenzene (CB), 1,2,4-trichlorobenzene (TCB) and hexachlorobenzene (HCB). The results showed that root growth of seedlings was interrupted after 5d of 50–200 μg · g ?1 TCB treatment. During a 3 d of recovery period, root growth was, however, restored to some extent although there was a delay in returning to the control level. The total soluble protein content in seedlings increased with TCB concentration and duration of exposure. Effect of TCB stress on SOD activity in seedlings displayed a significant dose-effect relationship for 1–5 d of 50–200 μg · g ?1 treatment. When broadbean seedlings were placed in clean tap water for 3 d following exposure to 5 d of TCB stress to clear tap water for 3 d, SOD activity at 50 μg · g ?1 TCB recovered towards control level ( P> 0.05) while a significant increase in SOD activity was observed at 100 and 200 μg · g ?1 TCB compared to control ( P< 0.05). The experiments also revealed that a significant increase of MDA level in seedlings occurred after 3 and 5 d of 100 and 200 μg · g ?1 TCB treatment ( P< 0.05 and P< 0.01), and there was a positive correlation between TCB concentration and MDA level. All the above results showed that SOD activity and MDA level of broadbean seedlings might be proposed as the biomarkers for short-term TCB contamination in soil. Compared to TCB, the toxicity of 50?1000 μg · g ?1 CB or HCB in soil to broadbean seedlings was not observed after a 3 d exposure. 相似文献
13.
Although both nutrient inputs and zooplankton grazing are importantto phytoplankton and bacteria in lakes, controversy surroundsthe relative importance of grazing pressure for these two groupsof organisms. For phytoplankton, the controversy revolves aroundwhether zooplankton grazers, especially large cladocerans like Daphnia, can effectively reduce phytoplankton populations regardlessof nutrient conditions. For bacteria, little is known aboutthe balance between possible direct and indirect effects ofboth nutrients and zooplankton grazing. However, there is evidencethat bacteria may affect phytoplankton responses to nutrientsor zooplankton grazing through direct or apparent competition.We performed a mesocosm experiment to evaluate the relativeimportance of the effects of nutrients and zooplankton grazingfor phytoplankton and bacteria, and to determine whether bacteriamediate phytoplankton responses to these factors. The factorialdesign crossed two zooplankton treatments (unsieved and sieved)with four nutrient treatments (0, 0.5, 1.0 and 2.0 µgphosphorus (P) l 1 day 1 together with nitrogen(N) at a N:P ratio of 20:1 by weight). Weekly sieving with 300µm mesh reduced the average size of crustacean zooplanktonin the mesocosms, decreased the numbers and biomass of Daphnia,and increased the biomass of adult copepods. Nutrient enrichmentcaused significant increases in phytoplankton chlorophyll a(45x), bacterial abundance and production (1.3x and 1.6x,respectively), Daphnia (3x) and total zooplankton biomass (2x).Although both total phytoplankton chlorophyll a and chlorophyll a in the <35 µm size fraction were significantly lowerin unsieved mesocosms than in sieved mesocosms, sieving hadno significant effect on bacterial abundance or production.There was no statistical interaction between nutrient and zooplanktontreatments for total phytoplankton biomass or bacterial abundance,although there were marginally significant interactions forphytoplankton biomass <35 µm and bacterial production.Our results do not support the hypothesis that large cladoceransbecome less effective grazers with enrichment; rather, the differencebetween phytoplankton biomass in sieved versus unsieved zooplanktontreatments increased across the gradient of nutrient additions.Furthermore, there was no evidence that bacteria buffered phytoplanktonresponses to enrichment by either sequestering P or affectingthe growth of zooplankton. 相似文献
14.
The role of nutrient availability in the decay of Typha latifolia and Cladium jamaicense litter and associated microbial responses were studied under controlled experimental conditions. The experimental setup consisted of three 14 m 2 mesocosms: (i) an experimentally enriched (N&P) mesocosm containing organic soil, (ii) a mesocosm with organic soil but no external enrichment, and (iii) a mesocosm with no external nutrient inputs and a mineral soil, each equally divided into two areas predominated by T. latifolia and C. jamaicense. Air dried senesced material of each plant species from the three units were placed in litterbags and were introduced back into their respective communities on the soil and water interface. Litter from T. latifolia degraded significantly faster than that of C. jamaicense. The half life of T. latifolia litter averaged approximately 274 days, C. jamaicense litter half life was extrapolated to approximately 377 days. Nutrient enrichment significantly increased the decay rates of T. latifolia, the nutrient effect on C. jamaicense decomposition was less apparent. The microbial biomass carbon in T. latifolia and C. jamaicense litter increased significantly as the litter decomposed. No significant differences between the litter types or amongst mesocosms were found. The relative activities of the extracellular enzymes acid phosphatase and β-glucosidase were significantly ( P < 0.001 and P = 0.0284, respectively) affected by litter type and mesocosm over time. Litter associated alkaline phosphatase activity was largest in the mineral mesocosm, followed by the organic control and then organic enriched irrespective of litter type, β-glucosidase activity showed an inverse effect, enriched organic > organic control > mineral. The litter CO 2 and CH 4 microbial production rates showed a significant litter type and mesocosm effect ( P = 0.0003 and 0.001, respectively). T. latifolia litter had larger associated methanogenic and microbial respiration rates than C. jamaicense litter. Nutrient enrichment enhanced both forms of microbial metabolic activities (CO 2 and CH 4 production). The effect of nutrient enrichment was primarily evident in the initial (3–6 months) period of decay, extracellular enzyme activities and the litter associated microbial metabolic activities showed most response during this decay stage. 相似文献
16.
The goal of this study was to address the top-down and bottom-up controls on different microbial web components (bacterioplankton,
picophytoplankton, and >3 μm phytoplankton) in an Antarctic lake. Two experiments using a size fractionation approach and
nutrient addition were conducted at microcosm scale (2.5 l). The variation in net growth rates ( k′) of bacterioplankton and phytoplankton size fractions was analyzed after 5 days. The results determined significant differences;
whereas bacterioplankton and large phytoplankton showed an increase in their k′ when their predators were removed, the picophytoplankton showed a decrease. All the studied plankton components presented
the highest k′ when nutrients were added. It is suggested that, in this lake, both the top-down and bottom-up regulations account for the
regulation of bacterioplankton and large phytoplankton. As for picophytoplankton, the bottom-up control was evident and grazing
did not pose a negative impact and rather, had a positive effect probably due to liberation of nutrients. 相似文献
17.
To clarify the ecological significance of the association of sulfate-reducing bacteria (SRB) with sediment particle size,
SRB utilizing lactate ( l-SRB), propionate ( p-SRB) and acetate ( a-SRB) were examined with different sizes of sediment particles in a hypertrophic freshwater lake using the anaerobic plate
count method. The numbers of l-SRB and a-SRB were 10 4–10 5 colony forming units (CFU) per ml in the 0–3 cm layer and 10 2–10 3 CFU ml −1 in the 10–13 cm layer while the numbers of p-SRB were one or two orders lower than those of l-SRB and a-SRB. A sediment suspension was fractionated into four fractions (<1, 1–10, 10–94 and >94 μm). The highest proportions of l-SRB and a-SRB were found in the 10–94 μm fraction: 66–97% for l-SRB and 53–98% for a-SRB. The highest proportion of p-SRB was found in the >94 μm fraction (70–74%). These results indicate that most SRB were associated with sediment particles.
One isolate from an acetate-utilizing enrichment culture was similar to Desulfotomaculum acetoxidans, a spore-forming sulfate-reducing bacterium. When lactate and sulfate were added to sediment samples, l-SRB and a-SRB in the <10 μm-fraction grew more rapidly than those in whole sediment for the first 2 days. This result suggests that
nutrients uptake by free-living and small particle-associated (<10 μm) SRB is higher than that by SRB associated with larger
particles. 相似文献
18.
Size-fractionated chlorophyll-a concentrations of surface seawater were measured for pico-, nano-, and micro-size fractions
(<2 μm, 2–10 μm, and >10 μm respectively) during commercial krill fishery operations in the waters north of the South Shetland
Islands. The proportion of green krill (individuals discoloured due to active feeding on phytoplankton) had significant regressions
with chlorophyll-a concentrations in micro- and nano-size fractions. Between these two fractions, chlorophyll-a concentration
in the micro-size fraction showed the higher partial regression coefficient. This result shows the importance of phytoplankton
larger than nano-phytoplankton, especially micro-phytoplankton, in terms of a phytoplanktonic food source for Antarctic krill
in the natural environment.
Accepted: 6 February 1999 相似文献
19.
Size-fractionated chlorophyll a (Chl a)-specific productivity (μgC μgChl a
−1 h −1) was measured at 11 stations off the northern coast of the South Shetland Islands during summer. The Chl a-specific productivity of the 2- to 10 or 10- to 330-μm fraction was highest at 100% and 23% light depths. The Chl a-specific productivity of the 2- to 10-μm fraction was generally highest, and that of the <2 or 10- to 330-μm fraction was
sometimes highest at 12% and 1% light depths. Temperature was less than 3°C within the euphotic zone at all stations. The
hypothesis of Shiomoto et al., according to which Chl a-specific productivity of picophytoplankton (<2 μm) is not significantly higher than that of larger phytoplankton (>2 μm)
in water colder than 10°C, was supported on condition that light is not limited for larger phytoplankton.
Received: 16 September 1997 / Accepted: 8 December 1997 相似文献
20.
We investigated seasonal variation of grazing impact of the pigmented nanoflagellates (PNF) with different sizes upon Synechococcus in the subtropical western Pacific coastal waters using grazing experiments with fluorescently labeled Synechococcus (FLS). For total PNF, conspicuous seasonal variations of ingestion rates on Synechococcus were found, and a functional response was observed. To further investigate the impact of different size groups, we separated
the PNF into four categories (<3, 3–5, 5–10, and >10 μm). Our results indicated that the smallest PNF (<3 μm PNF) did not
ingest FLS and was considered autotrophic. PNF of 3–5 μm in size made up most of the PNF community; however, their ingestion
on Synechococcus was too low (0.1–1.9 Syn PNF −1 h −1) to support their growth, and they had to depend on other prey or photosynthesis to survive. The ingestion rate of the 3–5 μm
group exhibited no significant seasonal variation; by contrast, the ingestion rates of 5–10 and >10 μm PNFs showed significant
seasonal variation. During the warm season, 3–5 μm PNF were responsible for the grazing of 12% of Synechococcus production, 5–10 μm PNF for 48%, and >10 μm PNF for 2%. Taken together, our results demonstrate that the PNF of 3–10 μm consumed
most Synechococcus during the warm season and exhibited a significant functional response to the increase in prey concentration. 相似文献
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