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1.
Francisco Rivera Vasconcelos Sebastian Diehl Patricia Rodríguez Per Hedstrm Jan Karlsson Pr Bystrm 《Global Change Biology》2019,25(2):504-521
Productivity and trophic structure of aquatic ecosystems result from a complex interplay of bottom‐up and top‐down forces that operate across benthic and pelagic food web compartments. Projected global changes urge the question how this interplay will be affected by browning (increasing input of terrestrial dissolved organic matter), nutrient enrichment and warming. We explored this with a process‐based model of a shallow lake food web consisting of benthic and pelagic components (abiotic resources, primary producers, grazers, carnivores), and compared model expectations with the results of a browning and warming experiment in nutrient‐poor ponds harboring a boreal lake community. Under low nutrient conditions, the model makes three major predictions. (a) Browning reduces light and increases nutrient supply; this decreases benthic and increases pelagic production, gradually shifting productivity from the benthic to the pelagic habitat. (b) Because of active habitat choice, fish exert top‐down control on grazers and benefit primary producers primarily in the more productive of the two habitats. (c) Warming relaxes top‐down control of grazers by fish and decreases primary producer biomass, but effects of warming are generally small compared to effects of browning and nutrient supply. Experimental results were consistent with most model predictions for browning: light penetration, benthic algal production, and zoobenthos biomass decreased, and pelagic nutrients and pelagic algal production increased with browning. Also consistent with expectations, warming had negative effects on benthic and pelagic algal biomass and weak effects on algal production and zoobenthos and zooplankton biomass. Inconsistent with expectations, browning had no effect on zooplankton and warming effects on fish depended on browning. The model is applicable also to nutrient‐rich systems, and we propose that it is a useful tool for the exploration of the consequences of different climate change scenarios for productivity and food web dynamics in shallow lakes, the worldwide most common lake type. 相似文献
2.
Spatial and seasonal changes of net plankton and zoobenthos in Lake Tonle Sap, Cambodia 总被引:1,自引:0,他引:1
Akifumi Ohtaka Ryusei Watanabe Sokrithy Im Rachna Chhay Shinji Tsukawaki 《Limnology》2010,11(1):85-94
To clarify spatial and seasonal differences in net plankton and zoobenthos in Lake Tonle Sap, Cambodia, quantitative surveys
were carried out at 14 stations in the north and south basins in high- and low-water seasons during 2003–2005. In the phytoplankton
communities, a diatom Aulacoseira granulata dominated throughout the lake in the high-water seasons, while blue-green algae, mostly composed of Microcystis, surpassed other algae in the low-water season when the lake water was very turbid and the Secchi disk readings were only
a few centimeters. In the low-water seasons, a bloom of floating blue-green algae occurred everywhere, especially prominent
in the coastal areas. Protozoans and rotifers dominated the zooplankton communities. In the open-water stations, diversity
was higher in high-water seasons in phytoplankton, while it was not significantly different between seasons in zooplankton.
Composition of plankton communities in Lake Tonle Sap appears to have changed little since the 1950s, at least in phytoplankton,
while the phytoplankton density appears to be higher in the present study. Among the macrozoobenthos, mollusks, oligochaetes
and chironomids dominated in density, and mollusks exceeded others in biomass in both basins and seasons. The total densities
of macrozobenthos were not high, being fewer than 1,300 m−2 throughout the stations and seasons. Possible reasons for the low zoobenthos abundance in the lake may include high predation
pressures by benthivorous fish or unfavorable unstable and flocculant substrates. 相似文献
3.
Masson Stephane; Pinel-Alloul Bernadette; Dutilleul Pierre 《Journal of plankton research》2004,26(12):1441-1458
Environmental control of zooplankton biomass size structure(53100, 100202, 202500 and >500 µm)was investigated in the three limnetic strata of 25 southernQuébec Shield lakes, Canada. Among-lake differences werethe greatest source of variation of zooplankton biomass, whereasthe strong lakebystratum interaction observedindicated that the vertical variations of zooplankton biomassand its size fractions were not constant from lake to lake.The analysis of spatial and local factors based on thermal stratais consistent with conceptual models of predation and nutrientcontrol on the biomass and size structure of the zooplankton.Productivity of the aquatic systems, which was driven by lakedepth, flushing rate and total phosphorus concentration, wasthe primary factor influencing total zooplankton biomass andsize structure at among-lake scale in epilimnetic waters. Theeffects of the planktivorous fish on the large zooplankton biomass(>500 µm) was more clearly perceived when the effectof lake depth was removed by partial redundancy analysis. Thisstudy showed that although bottom-up and top-down forces arecomplementary in structuring of zooplankton communities, theycan also act differently on the community attributes (e.g. biomassand size structure). Among-lake zooplankton biomass is predictablefrom lake trophy, but the size structure and vertical distributionof zooplankton communities appear to be controlled by lake stratificationand by inference to interactions with size selective predationby fish. In metalimnetic waters, the 53100 and 100202µm zooplankton biomass fractions were primarily dependenton abiotic factors, while the 202500 and >500 µmfractions were related to planktivory and picophytoplanktonconcentrations. The well-oxygenated and cold hypolimnetic watersof some lakes offered a refuge from surface turbulence and planktivoryto large zooplankton size fractions (202500 and >500µm). 相似文献
4.
This work presents new empirical and dynamical models for benthic algae in lakes. The models were developed within the framework of a more comprehensive lake ecosystem model, LakeWeb, which also accounts for phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), macrophytes, prey fish and predatory fish. The new dynamic model provides seasonal variations (the calculation time is 1 week). It is meant to account for all factors regulating the production and biomass of benthic algae for lakes in general. This work also presents and uses a new data-base established by us from published sources. Many of the lakes included in this study are situated in the former Soviet Union. They were investigated during the Soviet period and the data and results have up until now been largely unknown in the West. We present empirical models for benthic algae, and show that the biomass of benthic algae in whole lakes can be estimated from the ratio between the lake area above the Secchi depth to the total lake area and the primary production of phytoplankton. We also present several critical tests of the dynamical model. The dynamical and empirical models give corresponding results over a wide limnological domain. We provide algorithms for (1) the production rate of benthic algae (2) the elimination rate (related to the turnover time of benthic algae), (3) the rate of benthic algae consumption by zoobenthos, and (4) the rate of physical erosion of benthic algae. Our results indicate that the production of benthic algae is highly dependent on lake morphometry and sediment character, as well as water clarity, and less dependent on nutrient (phosphorus) concentrations in water and sediments. This work provides new quantitative support to such conclusions and also a useful model for predictions of production and biomass of benthic algae. 相似文献
5.
Grazing experiments were carried out in a limed lake (Lago d'Orta) during the periods, 23–24 March and 28–29 June 1990. A
simple in situ technique based on cell counts before and after incubation was used in order to evaluate the impact of the natural zooplankton
community on the lake phytoplankton. An estimation of the daily consumption by the natural zooplankton community showed that
about 4.6% and 1.04% of the standing algal biomass was removed during March and June respectively. The differences in grazing
activities were likely due to the difference in zooplankton community structure and to the surrounding environmental conditions,
mainly influenced by the liming intervention, started in the lake water since 1989. 相似文献
6.
Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine
whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined
whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range
in size from 125 to 1730 km2 and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one
species of calanoid copepod—Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8–12) was consistent with Dodson’s predictions based on lake area. The
average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson’s
results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios
of zooplankton to phytoplankton biomass (0.01–0.1) are among the lowest reported in the literature, and the zooplankton displayed
short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to
occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high
summer water temperature. 相似文献
7.
Satu Estlander Leena Nurminen Mikko Olin Mika Vinni Jukka Horppila 《Hydrobiologia》2009,620(1):109-120
The dynamics of crustacean zooplankton in the littoral and pelagic zones of four forest lakes having variable water qualities
(colour range 130–340 mg Pt l−1, Secchi depth 70–160 cm) were studied. The biomass of zooplankton was higher in the littoral zone than in the pelagic zone
only in the lake having the highest transparency. In the three other lakes, biomass was significantly higher in the pelagic
zone than in the littoral zone. In the two lakes with highest transparency, the littoral biomass of cladocerans significantly
followed the development of macrophyte vegetation, and cladoceran biomass reached the maximum value at the time of highest
macrophyte coverage. In lakes with lowest transparency, littoral zooplankton biomass developed independently of macrophyte
density and decreased when macrophyte beds were densest. The seasonal development of the littoral copepod biomass did not
follow the development of macrophytes in any of the lakes. The mean size of cladocerans in the pelagic zone decreased with
increasing Secchi depth of the lake, whereas in the littoral zone no such phenomenon was detected. Seasonally, when water
transparency increased temporarily in two of the lakes, the mean size of cladocerans in the pelagic zone decreased steeply.
For copepods, no relationship between water transparency and body size was observed. The results suggested that in humic lakes
the importance of the littoral zone as a refuge decreases with decreasing transparency of the water and that low water transparency
protects cladocerans from fish predation. All the observed between-lake differences could not be explained by fish predation,
but were probably attributed to the presence of chaoborid larvae with variable densities. Feeding efficiency of chaoborids
is not affected by visibility and thus they can obscure the relationship between water quality, fish density, and the structure
of crustacean zooplankton assemblages.
Handling editor: S. I. Dodson 相似文献
8.
Modelling production and biomasses of zoobenthos in lakes 总被引:5,自引:0,他引:5
This work presents a dynamic model to predict zoobenthos in lakes. The model has been developed within the framework of a more comprehensive lake ecosystem model, LakeWeb, which also accounts for the following functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), macrophytes, prey fish and predatory fish. This work also presents a new data-base for zoobenthos in lakes. Many of the lakes included in this study are situated in the former Soviet Union. They were investigated during the Soviet period and those results have been largely unknown in the West. Using this data-base, this work also presents new empirical models for zoobenthos. The new dynamic model gives seasonal variations (the calculation time, dt, is 1 week using Euler's method and enough iterations to get stable solutions). The basic aim of the dynamic model is that it should capture general functional and structural patterns in lakes. We have demonstrated by several model tests along limnological gradients (total phosphorus concentrations, pH, lake colour, latitude and lake size) that the dynamic model gives predictions that agree well with the values given by the empirical regressions, and also expected and requested divergences from these regressions when they do not provide sufficient resolution. It would have been very difficult indeed to carry out such tests regarding ecosystem responses using traditional methods with extensive field studies in a few lakes. We have given algorithms for (1) production of zoobenthos from eating macrophytes, benthic algae and sediments, (2) elimination (related to the turnover time of zooplankton), and (3) zoobenthos consumption by prey fish, and the factors influencing these processes/rates. The model is driven by data easily accessed from standard monitoring programs or maps a prerequisite for practical utility in contexts of lake management. 相似文献
9.
DIEDERIK VAN DER MOLEN & PAUL BOERS 《The Plant journal : for cell and molecular biology》2003,35(1):189-202
1. The flow of phosphorus and nitrogen through the food web of the shallow, eutrophic lake Wolderwijd was analysed for 2 different years before and for 1 year after food web manipulation.
2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.
3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.
4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column. 相似文献
2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.
3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.
4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column. 相似文献
10.
1. The flow of phosphorus and nitrogen through the food web of the shallow, eutrophic lake Wolderwijd was analysed for 2 different years before and for 1 year after food web manipulation.
2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.
3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.
4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column. 相似文献
2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.
3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.
4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column. 相似文献
11.
Biomanipulation development in Norway 总被引:2,自引:2,他引:0
Since 1974 several studies have been carried out in Norway to investigate the interactions between planktivorous fish, zooplankton,
phytoplankton and water chemistry. Since 1978 a long-term national research program has been conducted by the Norwegian Council
for Scientific and Industrial Research (NTNF). In this program several whole lake manipulations of the fish stocks have been
performed to test hypotheses about trophic interactions. It was predicted that manipulations of planktivorous fish populations,
might also improve water quality in lakes undergoing eutrophication.
Two examples are given to illustrate the achieved results.
I: Whole lake fertilization experiment (1974–1978) carried out by Langeland and Reinertsen. The results revealed the importance
of top-down effects in the lake ecosystem. When cladocerans dominated, the zooplankton community was able to maintain a more
or less constant phytoplankton biomass and a rather low phytoplankton production even when nutrient levels were increased.
During years with rotifer dominance, algal biomass and productivity increased, despite the low amounts of added nutrients.
II: Experiment performed by Reinertsen, Jensen, Koksvik, Langeland and Olsen in the eutrophic Lake Haugatjern, total elimination
of the fish populations by rotenone in late 1980, resulted in a 4-fold decrease in the algal biomass. The species composition
changed from the dominance of large-sizedAnabaena flos-aquae andStaurastrum luetkemuelleri to smaller, fastgrowing species and gelatinous green algae.
The results are discussed in relation to management of inland waters by combined techniques of biomanipulation and reduced
external nutrient supply which increase food-chain efficiency. 相似文献
12.
A. V. Krylov 《Inland Water Biology》2020,13(1):41-50
The article describes quantitative and structural characteristics of zooplankton of polytypic sites of a water system including a lake, canal, and a water reservoir. It is shown that in the littoral zone of lakes and water reservoirs, the number of species and communities is higher, and biomass, lower. However, in the littoral zone of shallow lake zooplankton in number, took priority due to Rotifera, in the deep part of the water body – Rotifera and Cladocera; in the center of the lake zooplankton dominated by biomass due to Cladocera and Copepoda, in the water reservoir—due to the Copepoda. The dam area of the water reservoir had the highest species richness of zooplankton among all studied sites. The greatest number and biomass of zooplankton within a waterbody are noted in upper part, where a sedimentation zone had formed, and as a whole for the system of the investigated waterbodies, the maximum quantity indices are typical of lake communities. It is revealed that the starkest interannual changes in zooplankton were observed in the shallow lake: the number of species decreased—in the littoral zone at the expense of Rotifera, and in the center, the biomass increased at the expense of Cladocera; in deep-water area of the dam area of the reservoir, conversely, the number of species, as well as the number and biomass of the community, increased due to Copepoda. 相似文献
13.
During a North Sea survey in late spring 1986, zooplankton biomass (g dry weight/m2) as well as pollutant concentrations in zooplankton (ng/g dry weight) were determined at 127 stations. On the basis of these
data, the load of several cyclic organochlorines in zooplankton (ng/m2) was estimated. It appeared that the highest loads of these pollutants were incorporated in the large zooplankton stocks
of the northern and central North Sea, north of 56°N, whereas the highest concentrations were found in zooplankton of the
southern North Sea. An explanation for the accumulation of pollutants in sediments as well as in benthos organisms of the
central and northern North Sea as found by several authors is discussed in connection with the assumption of a considerably
high vertical flux of organic material in these areas. The calculation of total zooplankton content in the North Sea during
the late spring survey amounted to about 5 million tons dry weight. This biomass was estimated to contain about 2.6 t PCBs,
19.3 kg p,p′-DDE, 12 kg τ-HCH, 6.4 kg HCB und 5.6 kg α-HCH. These results agree with those on other compartments of the North
Sea ecosystem (benthos, fish) found in recent literature. The estimated annual turnover of PCBs in zooplankton (15.2 t) is
of the same order of magnitude as the estimated amount transported yearly into the North Sea by rivers and the atmosphere
(6–13 t). 相似文献
14.
Jonathan Carlo Briones Cheng-Han Tsai Takefumi Nakazawa Yoichiro Sakai Rey Donne S. Papa Chih-hao Hsieh Noboru Okuda 《PloS one》2012,7(12)
Body size and environmental prey availability are both key factors determining feeding habits of gape-limited fish predators. However, our understanding of their interactive or relative effects is still limited. In this study, we performed quantitative dietary analysis of different body sizes of goby (Gymnogobius isaza) specimens collected from Lake Biwa between 1962 and 2004. First, we report that the diet was composed mainly of zooplankton (cladocerans and copepods) before the 1980s, and thereafter, shifted to zoobenthos (gammarids). This foraging shift coincided with, and thus can be linked to, known historical events in the lake at that time: decrease in zooplankton abundance with the alleviation of eutrophication, increase in fish body size resulting from fish population collapse, and increase in gammarid abundance due to reduced fish predation pressure. Supporting this view, our data analyses revealed how the long-term changes in the diet composition would be co-mediated by changes in fish body size and environmental prey availability. Specifically, while zoobenthos abundance strongly affected the fish diet composition, larger (smaller) fish preferred zoobenthos (zooplankton). Furthermore, the body size effects were stronger than those of prey availability. These results provide the best long-term evidence that fish feeding habits vary over decades with its body size and prey community due to anthropogenic disturbances. 相似文献
15.
Winter fish kills can be intense under ice in shallow lakes, and have cascading effects on the food web and ultimately on
lake water clarity. In maritime Western Europe, winters are usually mild, but occasional colder periods may also have strong
effects on lake fish communities. Global warming may have disproportionate effects by delaying freezing and shortening the
period of ice coverage. We studied differences in zooplankton (cladocerans, copepods, and rotifers): phytoplankton biomass,
zooplankton community structure, and individual body size among 37 Danish lakes of various depths, chemical characteristics,
and trophy, by comparing four winters of different severity (mean winter temperatures ranging from −1.19°C in 1996 to +2.9°C
in 1995). We found that crustacean mean body sizes were significantly larger in the summer following a severely cold winter.
The zooplankton communities in the summer after a cold winter had a significantly larger proportion of larger-bodied species
and taxa. Phytoplankton biomass, expressed as chlorophyll-a (chl-a), was lower and zooplankton herbivory (chl-a:TP index), higher, in the summer after the severely cold winter of 1995/1996. All these effects were stronger in shallow
lakes than in deep lakes. Changes in zooplankton during summer 1996, compared with other years, were likely caused by fish
kills under ice during the preceding severe winter of 1995–1996. Fish kills due to under ice oxygen depletion would be expected
to occur earlier and be more complete in the shorter water columns of shallow lakes. With climate change, severe winters are
predicted to become less frequent and the winters to be milder and shorter. In general, this is likely to lead to higher winter
survival of fish, lower zooplankton grazing of phytoplankton the following summer and more turbid waters, particularly in
shallow eutrophic lakes. 相似文献
16.
Samuel Teissier Anatoly Peretyatko Sylvia De Backer Ludwig Triest 《Hydrobiologia》2012,689(1):147-159
Phytoplankton biomass–nutrient relationship is widely used by lake managers to assess the eutrophication impact and to set
the nutrient targets. Submerged vegetation and large zooplankton grazing have long been identified as factors weakening the
relationship by decoupling phytoplankton from nutrients. Proving this decoupling unambiguously is difficult because, in natural
systems, many factors act together, blurring each other’s effect. In this article, we present the results of continuous monitoring
of 13 ponds where the effects of submerged vegetation and zooplankton grazing were enhanced by biomanipulation (fish removal).
The monitoring allowed these effects to be assessed and compared with the pre-biomanipulation situations when phytoplankton
biomass was mainly nutrient driven. The comparison showed a strong weakening effect of submerged vegetation and large zooplankton
grazing on the chlorophyll a–total phosphorus relationship suggesting that a considerable degree of ecological quality of ponds affected by eutrophication
can be restored even when nutrient-loading reduction is not feasible. 相似文献
17.
Dynamics of a Boreal Lake Ecosystem during a Long-Term Manipulation of Top Predators 总被引:1,自引:0,他引:1
David L. Findlay Michael J. Vanni Michael Paterson Kenneth H. Mills Susan E.M. Kasian Willie J. Findlay Alex G. Salki 《Ecosystems》2005,8(6):603-618
We assessed the long-term (16 years) effects of introducing piscivores (northern pike) into a small, boreal lake (Lake 221,
Experimental Lakes Area) containing abundant populations of two planktivorous fish species. After the introduction, pearl
dace were extirpated and yellow perch abundance was greatly reduced. Daphnia species shifted from D. galeata mendota to larger bodied Daphnia catawba, but the total zooplankton biomass did not increase, nor did the biomass of large grazers such as Daphnia. Phytoplankton biomass decreased after the northern pike introduction, but increased when northern pike were partially removed
from the lake. Phosphorus (P) excretion by fish was ∼0.18 mg P m−2 d−1 before pike addition, declined rapidly to approximately 0.03–0.10 as planktivorous perch and dace populations were reduced
by pike, and increased back to premanipulation levels after the pike were partially removed and the perch population recovered.
When perch were abundant, P excretion by fish supported about 30% of the P demand by primary producers, decreasing to 6–14%
when pike were abundant. Changes in phytoplankton abundance in Lake 221 appear to be driven by changes in P cycling by yellow
perch, whose abundance was controlled by the addition and removal of pike. These results confirm the role of nutrient cycling
in mediating trophic cascades and are consistent with previous enclosure experiments conducted in the same lake. 相似文献
18.
Book reviews 总被引:5,自引:5,他引:0
Michael A. Gates 《Hydrobiologia》1984,108(3):233-238
No previous study of plankton in lakes has estimated the relative contribution of ciliated protozoa to the biomass of the
total plankton community, including phytoplankton. In a series of south-central Ontario lakes, ciliates comprise on the order
of 5 to 10% of the total planktonic biomass of these relatively oligotrophic lakes and exist there in densities of 20–40 ml−1. Therefore, ciliates constitute an important component of lake ecosystems that should not be ignored in limnological studies
of zooplankton abundance and distribution. 相似文献
19.
Eshete Dejen Jacobus Vijverberg Leopold A. J. Nagelkerke Ferdinand A. Sibbing 《Hydrobiologia》2009,636(1):89-100
Growth, biomass and production of two small barbs (Barbus humilis and Barbus tanapelagius) and their role in the food web of Lake Tana were investigated. From length–frequency distribution of trawl monitoring surveys
growth coefficient, Φ′ values were estimated at 3.71–4.17 for B. humilis and 3.70–4.14 for B. tanapelagius, respectively. Values for B. humilis were confirmed in pond experiments. Mean biomass of the small barbs was 13.3 kg fresh wt ha−1, with B. humilis being most abundant in the littoral and sub-littoral zones, whereas B. tanapelagius was most abundant in the sub-littoral and pelagic zones. The two small barbs had a production of 53 kg fresh wt ha−1 year−1. Although their P/B ratios of about 4.0 were relatively high for small cyprinids, both their biomass and production were low in comparison with
other small fish taxa in other tropical lakes. Of the zooplankton production only about 29% was consumed by the small barbs.
However, they did not utilize calanoid copepods, which were responsible for approximately 57% of the zooplankton production
and it is likely that small barb production was food limited during certain periods of the year. Piscivorous labeobarbs consumed
about 56% of the small barbs production annually, but additionally, Clarias gariepinus, and many bird species were also preying on them. Therefore, limitation of Barbus production by predation during certain periods in the year cannot be excluded. 相似文献
20.
Bizina EV 《Zhurnal obshche? biologii》2000,61(6):601-615
The relative strength of "top-down" versus "bottom-up" control of plankton community structure and biomass in two small oligotrophic lakes (with and without fish), located near the Polar circle (Russia), has been investigated for two years, 1996 and 1997. The comparative analyses of zooplankton biomass and species abundance showed strong negative effect of fish, stickeback (Pungitius pungitius L.), on the zooplankton community species, size structure and biomass of particular prey species but no effect on the biomass of the whole trophic level. An intensive predation in Verkhneye lake has lead to: 1) sixfold decline in biomass of large cladoceran Holopedium gibberum comparing to the lake lacking predator, 2) shift in the size mode in zooplankton community and the replacement of the typical large grazers by small species--Bosmina longirostris and rotifers. Their abundance and biomass even increased, demonstrating the stimulating effect of fish on the "inefficient" and unprofitable prey organisms. The analysis of contributions of different factors into the cladoceran's birth rate changes was applied to demonstrate the relative impact of predators and resources on zooplankton abundance. An occasional introduction of the stickleback to Vodoprovodnoye lake (the reference lake in 1996) in summer 1997 lead to drastic canges in this ecosystem: devastating decrease of zooplankton biomass and complete elimination of five previously dominant grazer species. The abundance of edible phytoplankton was slightly higher in the lake with fish in 1996 and considerably higher in the lake where fish has appeared in 1997 showing the prevailing "top-down" control of phytoplankton in oligotrophic ecosystem. The reasons of trophic cascade appearance in oligotrophic lakes are also discussed. 相似文献