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Heterogeneity of distribution and communitycomposition of zooplankton in upper layers of LakeSventeAija Brakovska a , Renāte Škute a & Artūrs Škute a

a Institute of Ecology, Daugavpils University , 13 Vienibas St, Daugavpils , LV-5401 , LatviaPublished online: 23 Oct 2012.

To cite this article: Aija Brakovska , Renāte Škute & Artūrs Škute (2012) Heterogeneity of distribution andcommunity composition of zooplankton in upper layers of Lake Svente, Zoology and Ecology, 22:3-4, 172-180, DOI:10.1080/21658005.2012.733553

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Heterogeneity of distribution and community composition of zooplankton in upper layers ofLake Svente

Aija Brakovska*, Renāte Škute and Artūrs Škute

Institute of Ecology, Daugavpils University, 13 Vienibas St, Daugavpils, LV-5401, Latvia

(Received 17 July 2012; final version received 20 September 2012)

The aim of the study was to determine whether groups of zooplankton exhibit ecological heterogeneity. Investigationwas done in Lake Svente, situated on the monticule of Ilukste, 137m above the sea level, in the Svente parish inDaugavpils district (Latvia). For this study, zooplankton samples were taken on 12 July, 3 and 30 August and 21September in 2007. The sampling was carried out in six localities of the lake with different depth. During the analysis,three zooplankton groups, i.e. Rotatoria, Cladocera and Copepoda, and 35 zooplankton species were identified. Rotatoriawas the most dominant group consisting of 18 species, followed by Cladocera with 16 species and Copepoda with onespecies and one genus. In all sampling localities, Polyarthra vulgaris, Asplanchna priodonta, Keratella cochlearis,Conochilus hippocrepis, Kellicottia longispina and Gastropus stylifer were dominant species in the Rotatoria group.Daphnia cucullata, Bosmina crassicornis, Ceriodaphnia affinis and Diaphanosoma brachyurum were dominant speciesin the Cladocera group, and Cyclops sp. and Eudiaptomus graciloides in the Copepoda group.

Tyrimo tikslas – nustatyti, ar zooplanktono grupėms Šventės ežere (Latvijoje, Daugpilio rajone, Alūkstos kalvose, 137mvirš jūros lygio) būdingas ekologinis heterogeniškumas. Zooplanktono mėginiai buvo paimti šešiose skirtingo gylio ežerovietose 2007m. liepos 12 d., rugpjūčio 3 ir 30 d. bei rugsėjo 21 d. Tyrimo metu identifikuotos 35 zooplanktono rūšys,priklausančios Rotatoria, Cladocera ir Copepoda grupėms. Dominavo Rotatoria grupės zooplanktonas (18 rūšių). 16 rūšiųpriklausė Cladocera grupei, 1 rūšis ir 1 gentis – Copepoda grupei. Visose mėginių ėmimo vietose dominavo šios rūšys:Polyarthra vulgaris, Asplanchna priodonta, Keratella cochlearis, Conochilus hippocrepis, Kellicottia longispina irGastropus stylifer (Rotatoria), Daphnia cucullata, Bosmina crassicornis, Ceriodaphnia affinis ir Diaphanosomabrachyurum (Cladocera), taip pat Cyclops sp. ir Eudiaptomus graciloides (Copepoda).

Keywords: Lake Svente; zooplankton; Rotatoria; Cladocera; Copepoda; Renkonen index; Shannon–Wiener index

Introduction

The formation of fauna in each body of water is deter-mined by the location as well as typological peculiarities,such as morphometry, stage of development, hydrologicaland hydrochemical regime characteristics (Pidgaiko 1984;Pinel-Alloul 1995; Fernandez-Rosado and Lucena 2001;Seda and Devetter 2000; Wetzel 2001). As a result, if theclimate forms all the fauna in the region, environmentalconditions in the lake determine the formation of a partic-ular plankton cenosis. It is known that abiotic environ-mental factors in the lake determine the presence or theabsence of the species, whereas biotic factors mainlydetermine the population or even the whole numericalvalue of the zooplankton cenosis (Pinel-Alloul 1995; Wet-zel 2001). Zooplankton plays an important role in thetransformation of material and energy in water bodies.Using phytoplankton and bacterioplankton, it participatesin water purification processes. Zooplankton is an impor-tant feeding base for juvenile fish and for planktonpha-gous fish as well as serves as a bioindicator of ecological

monitoring of water bodies and determines the trophicstate of the lake (Cimdinsh 2001; Pinel-Alloul 1995).

The development of zooplankton is determined by itsrequirements to the surrounding environment, primarilyto feeding resources, as well by their dependence onvarious environmental factors. Many studies have shownthat there is a clear correlation between the speciescomposition of the zooplankton cenosis and environmen-tal conditions (Liepa, Maurinsh and Vimba 1991;Pejler 1965). Zooplankton distribution patterns relatewith temperature, dissolved oxygen, pH, transparency,wind, social aggregates, water turbulence, trophicgradient and phytoplankton (Bertilsson, Bērziņš andPejler 1995; Bērziņš and Pejler 1987, 1989a, 1989b;Dagg 1977; Dumont et al. 1973; Hanazato 1991, 1992;Horppila et al. 2000; Locke and Sprules 2000; Maloneand McQueen 1983; Tallberg et al. 1999).

The factors governing the population and the size ofthe zooplankton cenosis are different in the lakes ofdifferent trophic degree. Only one factor is a limiting

*Corresponding author. Email: aija.brakovska@inbox.lv

Zoology and EcologyVol. 22, Nos. 3–4, September–December 2012, 172–180

ISSN 2165-8005 print/ISSN 2165-8013 onlineCopyright � 2012 Nature Research Centrehttp://dx.doi.org/10.1080/21658005.2012.733553http://www.tandfonline.com

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factor for the size of the zooplankton cenosis in the lakeswith the same trophic degree, and most often the effect ofsuch one factor excludes others. For example, zooplanktonabundance is not simultaneously affected by planktoneating fish and zooplankton prey (Chang and Hanazato2004; Cimdinsh 2001; Malone and McQueen 1983;Pinel-Alloul 1995; Wetzel 2001).

As we know, zooplankton differs in its species com-position in different parts of one lake, e.g. a near-shorezone, open water areas or river inflow areas, becauseaccording to the morphometry of different parts ofsurface water they are different both in thermal andhydrochemical characteristics of water and otherenvironmental conditions (Bertilsson et al. 1995; Bērziņšand Pejler 1989a, 1989b; Malone and McQueen 1983;Pinel-Alloul 1995; Seda and Devetter 2000). Therefore,this research was conducted to determine whetherzooplankton groups exhibit ecological heterogeneity indifferent places of Lake Svente.

Material and methods

Location of research

According to Tidrikis (1998), Lake Svente is includedinto the list of protected landscapes of Augshzeme andtogether with the surroundings form a complex landscapereserve. Lake area is 7.35 km2, the islands cover 4 hect-ares, average depth is 7.8m, the greatest depth is 38m(in the north-eastern part of the lake) and catchment areais 18 km2 (at a great reservoir of Daugava). Lake Sventeis the 10th deepest lake in Latvia. With coves, it is a per-fectly landscaped lake. Its three islands (at the southernend) are in a botanical reserve. The shores are high. Thetributary stream Laucese-Pakrace flows out of the south-eastern corner of Lake Svente. Due to a small size of thereservoir, the mass of water in Lake Svente changes overthe period of 13 years. Still in the middle of the twenti-eth century Lake Svente was a mesotrophic lake, one ofthe purest lakes in Latvia (7m transparency in 1957 and5m in the 1970s according to the Secchi disc measure-ments). The purity of water decreased due to the sur-roundings used for farming and recreation. The lake ismesotrophic (Urtane 1998).

Analysis of zooplankton samples

For the study of taxonomic classification of zooplanktonin Lake Svente, zooplankton samples were taken on 12July, 3 and 30 August, and 21 September in 2007. Thesampling was carried out in six localities of the lake withdifferent depth (Figure 1).

Since the depth in the sampling sites was from 6 to36m, the optimum depth for collecting zooplankton sam-ples was considered to be 0.5–1m. Zooplankton sampleswere collected with an Apstein plankton net (65 μmmesh). Then water was poured with a water bucket intothe Apstein plankton net and 100 L of water were fil-tered. Zooplankton samples were usually stored in 0.33 L

bottles. The collected samples were fixed with a 37–40%formaldehyde solution. One part of formaldehyde solu-tions was added to nine parts of a sample. As a resultone sample was preserved with 4% formalin.

In the localities No 1 and No 2, we also determinedphysical and chemical parameters of water.

During the sampling, each zooplankton sample wasthoroughly mixed, then 2ml of zooplankton sampleswere taken with a Hensen-Stempel pipette into a GriddedSedgewick Rafter counting chamber and analysed undera light microscope Ampival (Carl Zeiss Jena) with amagnification of 16� 10 (160). Each sample wasanalysed three times (Brakovska and Škute 2009).Having studied the samples under a light microscope thezooplankton organisms were counted and identified asspecimens or families. We used the following zooplanktonkey books (Dussart and Defaye 2001; Krauter andStreble 1988; Kutikova 1970; Manuilova 1964;Pontin 1978; Scourfield and Harding 1994; Sloka 1981).

Hydrophysical measurements

The sonde HYDROLAB ‘Minisonde 4 Multiprobe’ wasused to measure water temperature (°C) and dissolvedoxygen (mg/l) per one imagined line. During the studythe Minisonde was lowered to the bottom of the waterbody. When the physical and chemical parameters stabi-lized on the Minisonde display, they were saved to theHYDROLAB memory. Then the Minisonde was movedone metre up. The procedure was repeated until theMinisonde reached the water surface. The final measure-ments were taken at the depths of one metre and half ametre. GIS software (Arc View 9.1) was used to form alocality map and analyse information on the geospatiallocalisation of Lake Svente.

Quantitative analysis of individuals and the number oforganisms in a sample

The collection of zooplankton samples and their quanti-tative and qualitative analysis was performed using theAmerican Public Health Association (APHA) standardmethod procedures for the water and wastewater analysis(APHA 2005; Wetzel and Linkens 2000). An analysis ofzooplankton abundance changes (median, quartiles andrange) along the sampling localities in Lake Svente wasperformed by the SPSS 11.5 for Windows software pack-age (Archipova and Balina 2003).

The following formula was used to calculate thenumber of organisms in a sample:

N ¼ ða� b� 1000Þ=ðc� dÞ=1000

where a is the calculated number of organisms (average),b is the volume of the concentrated sample, c is samplevolume, d is the volume of filtered water and N is thenumber of organisms per 1 l (litre). The zooplankton bio-mass in a sample was calculated as follows:

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N ¼ ða� b = 100Þ

where N is the biomass of organisms per 1 l (L), a isthe number of organisms per 1 l (L) and b is the numberof organisms (mg) in a wet weight sample.

Statistical analysis of zooplankton samples

The similarity of zooplankton quantitative compositionwas verified using the percentage similarity Renkonenindex (Renkonen 1938):

P ¼X

minimum ðp1i; p2iÞ

where P is percentage similarity between samples 1and 2,p1i is percentage of species in community sample 1 andp2i is percentage of species in community sample 2.

The Shannon–Wiener function (H′) was used to cal-culate as (Margalef 1958):

H 0 ¼ �XS

i¼1

ðpiÞ ðln piÞ

H′ is the index of species diversity,S is the number of species andpi is a proportion of the total sample belonging to i

th species.Since the resulting equation is a measure of bits, we

used the following equation to move from the bits unitto the species unit (Krebs 1999; MacArthur 1965):

N1 ¼ eH0

where e is equal to 2.71828 (base of natural logs),H′ is Shannon–Wiener function (calculated with base

e logs) andN1 is the number of equally common species that

would produce the same diversity as H′.

Figure 1. Sites of zooplankton sampling in Lake Svente.

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The sampling distributions for the Shannon–Wienerindex (H′) have been determined by Good (1953) andBasharin (1959). The Shannon–Wiener index (H′) is usedfor the quality control of the environment in accordancewith bioindication by principle (Krebs 1999; Lebedeva,Drozdov, and Krivolutskij 2004; Margalef 1958;Tereshenko, Tereshenko, and Smetanin 1994).

Results and discussion

During the research, three groups of zooplankton, i.e.Rotatoria, Cladocera and Copepoda, were identified inall six sampling sites in Lake Svente. On the basis ofliterature analysis (Cimdinsh 2001), the zooplanktonqualitative composition in Lake Svente was similar tozooplankton composition in other eutrophic lakes inLatvia. Cimdinsh (2001) emphasises that one of thetrophic levels of the food chain is filter-feeders, such asRotatoria, Cladocera and Copepoda (Cimdinsh 2001).Within this taxon many species are predators, omnivorous,etc. (Kutikova 1970; Liepa, Maurinsh, and Vimba 1991;Manuilova 1964). In comparison with the data receivedwith the Apstein plankton net it can be concluded that inall six sampling sites (Figure 1) the Rotatoria group wasthe most dominant, followed by Copepoda andCladocera groups (Figures 2–5).

In the samples collected on 12 July (Figure 2), thebiggest number of Rotatoria was in sampling site No 1(140 ind./L) and in locality No 3 (106 ind./L). But the big-gest number of Cladocera was in sampling sites No 2(5 ind./L) and No 1 (7 ind./L). The similar situation wasalso observed in the Copepoda group. A significantdifference was in the sampling site No 4, where theCladocera group was not present. It is difficult to explainthe reasons of this difference, because physical and chem-ical characteristics of water were not analysed in thesampling site No 4. In the samples collected on 3 August(Figure 3), the biggest number of Rotatoria was in thesampling sites No 4 (64 ind./L) and No 2 (56 ind./L).

The biggest number of the Copepoda group wasobserved in the sampling site No 1 (39 ind./L) and in thesampling site No 4 (33 ind./L). The Cladocera group wasrepresented similarly in all sampling sites. But in thesamples collected on 30 August (Figure 4), the biggest

number of Rotatoria was in the site No 3 (329 ind./L)and in the site No 4 (111 ind./L).

The biggest number of Copepoda was also in thesampling site No 3 (124 ind./L) and in the sites No 2 andNo 5 (93 ind./L). The biggest number of Cladocera wasin the site No 5 (33 ind./L) and in the sampling sitesNo 2 and No 3 (13 ind./L). In the samples collected on21 September (Figure 5), the biggest number of Rotatoriawas in the sampling sites No 4 (79 ind./L) and No 2(75 ind./L). The biggest number of Cladocera group wasin the sampling site No 1, but in other places Cladocerawas represented similarly. The biggest number of Copep-oda was in the sampling site No 1 (60 ind./L) and in thesampling site No 2 (57 ind./L). The fluctuations in thenumber and species composition of zooplankton could beexplained by the seasonality of each species, variation ofphysicochemical parameters and species interactions

020406080

100120140160

1 2 3 4 5 6

Sampling site

indi

v./l

Rotatoria Cladocera Copepoda

Figure 2. The abundance of the organisms of Rotatoria,Cladocera and Copepoda groups on 12 July (sampling sites No1–6).

0

20

40

60

80

100

1 2 3 4 5 6

Sampling site

indi

v./l

Rotatoria Cladocera Copepoda

Figure 3. The abundance of the organisms of Rotatoria,Cladocera and Copepoda groups on 3 August (sampling sitesNo 1–6).

0

60

120

180

240

300

360

indi

v./l

Sampling site1 2 3 4 5 6

Rotatoria Cladocera Copepoda

Figure 4. The abundance of the organisms of Rotatoria,Cladocera and Copepoda groups on 30 August (sampling sitesNo 1–6).

0

20

40

60

80

indi

v./l

Sampling site1 2 3 4 5 6

Rotatoria Cladocera Copepoda

Figure 5. The abundance of the organisms of Rotatoria,Cladocera and Copepoda groups on 21 September (samplingsites No 1–6).

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(Kutikova 1970; Liepa, Maurinsh and Vimba 1991;Manuilova 1964; Pidgaiko 1984; Pinel-Alloul 1995;Fernandez-Rosado and Lucena 2001; Seda and Devetter2000; Wetzel 2001).

Thirty-five zooplankton species were identified inLake Svente (Table 1). The biggest number of specieswas of the Rotatoria group (18 species), followed by 16species of the Cladocera group and 1 species and 1 genusof the Copepoda group. In all sampling localitiesPolyarthra vulgaris, Asplanchna priodonta, Keratellacochlearis, Conochilus hippocrepis, Kellicottia longispinaand Gastropus stylifer were dominant species in theRotatoria group. Daphnia cucullata, Bosmina crassicornis,Ceriodaphnia affinis and Diaphanosoma brachyurumwere dominant species in the Cladocera group, andgenus Cyclops sp. and Eudiaptomus graciloides in theCopepoda group. An extensive analysis of the samplescollected in July revealed that Polyarthra vulgaris and

Keratella cochlearis were the most numerous species inthe Rotatoria group in all sampling localities, withTrichocerca similis and Kellicottia longispina also com-monly occurring and taking the second and the thirdplace. Among Cladocera, Diaphanosoma brachyurum,Daphnia cucullata and Bosmina crassicornis werecommon. An analysis of the samples collected from thesampling site No 4 showed that there were no Cladoceraspecies there in July. However, in the samples whichwere collected in August and September there was a sig-nificant number of Diaphanosoma brachyurum andDaphnia cucullata species in sampling site No 4. In allsampling sites young cyclops Copepodite and Naupliiwere abundant, then Eudiaptomus graciloides followed.In the samples taken in August, the species mentionedbefore continued to dominate in the Rotatoria group aswell as Polyarthra major and Ascomorpha ecaudis,which had not occurred before. Ceriodaphnia affinis of

Table 1. Zooplankton species composition in Lake Svente in 2007.

Species (taxon)

Sampling sites

No 1 No 2 No 3 No 4 No 5 No 6 Common species

RotatoriaAscomorpha ecaudis Perty, 1850 + + + + + + +Ascomorpha saltans Bartsch, 1870 +Asplanchna priodonta Gosse, 1850 + + + + + + +Brachionus angularis Gosse, 1851 + +Conochilus hippocrepis (Schrank, 1803) + + + + + + +Euchlanis dilatata (Ehrenberg, 1832) + + + + +Filinia longiseta (Ehrenberg, 1834) + +Kellicottia longispina (Kellicott, 1879) + + + + + + +Keratella cochlearis (Gosse, 1851) + + + + + + +Keratella quadrata (Müller, 1786) + + + +Lecane luna (Müller, 1776) + + +Polyarthra major Burckhardt, 1900 + + + + + + +Polyarthra vulgaris Carlin, 1943 + + + + + + +Pompholux sulcata Hudson, 1885 + + + + +Synchaeta tremula (Müller, 1786) + +Gastropus stylifer (Imhof, 1891) + + + + + + +Trichocerca capucina (Wierzejski & Zacharias, 1893) + + + + + + +Trichocerca similis (Wierzejski, 1893) + +CladoceraAlona affinis (Leydig, 1860) +Bosmina coregoni Baird, 1857 +Bosmina crassicornis (P. E. Müller, 1867) + + + + + + +Bosmina longirostris (O. F. Müller, 1785) + + + + +Bosmina longispina (Leydig, 1860) + + + + +Bythoterphes longimanus (Leydig, 1860) +Ceriodaphnia affinis (Lilljeborg, 1900) + + + + + + +Ceriodaphnia reticulata (Jurine, 1820) + +Chydorus sphaericus (O. F. Müller, 1776) + + + + +Daphnia cristata Sars, 1862 + + + +Daphnia cucullata Sars, 1862 + + + + + + +Daphnia longispina O. F. Müller, 1776 + +Diaphanosoma brachyurum Liévin, 1848 + + + + + + +Leptodora kindtii Focke, 1844 +Polyphemus pediculus (Linnaeus, 1758) +CopepodaCopepodite + + + + + + +Cyclops sp. + + + + + + +Eudiaptomus graciloides (G.O. Sars, 1863) + + + + + + +Nauplii + + + + + + +Total: 29 26 22 24 20 23 15

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the Cladocera group was also recorded. There were nosignificant changes in the species composition in anysampling site in September. The number of species in

the samples varied according to the sampling site andthe bulk of filtered water.

Having summarised the physical and the chemicaldata, it can be concluded that the lake was slightly pol-luted, because the content of dissolved oxygen duringthe research period ranged from 7.5 to 9mg/L in theupper layers of the lake from 0.5 to 3.5mg/L in thedeepest layers of the lake (Figure 7). Moreover, therewas no drastic change in the water temperature through-out the season. In the upper layers of water temperatureranged from 14.5 to 19.5 °C, and deeper it was 9 °C(Figure 6). This suggests a favourable environment forthe development of zooplankton in the lake.

Having analysed the quantity of zooplankton species(Renkonen similarity index) according to the samplingsites and dates, it is clearly seen that on 12 July this sim-ilarity was in the range of 30 – 89% (Table 2). As shownin the table, the smallest similarity was between the sam-pling sites No 1 and No 6, i.e. 29.5%, and the biggestbetween the sites No 3 and No 4, i.e. 88.7%. On 3August, the numerical similarity between organisms wasin the range of 65 – 86% (Table 3). When looking at thepercentage differences between the sampling sites, theyare very small as can be seen very well in Figure 3. On30 August, the numerical similarity was in the rangefrom 38 to 86% (Table 4) and it was similar to the datareceived on 12 July (Tables 2 and 4). The data receivedon 21 September showed (Table 5) that the numericalsimilarity of Renkonen index was very high, from 81 to88%, respectively.

The analysis of similarities of sampling sites showedthat according to changes in the number of specimens thebiggest difference was observed in the sampling site No5 (Figure 9). By contrast, in terms of the number of taxa,a greater difference was observed in the sampling sites

Table 3. Similarity of zooplankton quantitative composition (Renkonen index, the average of samples on 3 August).

Sampling site No 1 No 2 No 3 No 4 No 5 No 6

No 1

No 2 74.3

No 3 77.6 69

No 4 66.3 66.2 85.9

No 5 64.7 73.3 72 72.6

No 6 70.1 65.6 74.2 74.4 68.5

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8

Dissolved oxygen, mg/l

Dep

th, m

12 Jul 2007 3 Aug 2007 30 Aug 2007 21 Sep 2007

9 10

Figure 7. Comparison of dissolved oxygen parameters ofwater in Lake Svente in 2007.

0

5

10

15

20

25

30

35

7 9 11 13 15 17 19 21

Temperature,C °

Dep

th, m

12 Jul 2007 3 Aug 2007 30 Aug 2007 21 Sep 2007

Figure 6. Comparison of temperature parameters of water inLake Svente in 2007.

Table 2. Similarity of zooplankton quantitative composition (Renkonen index, the average of samples on 12 July).

Sampling site No 1 No 2 No 3 No 4 No 5 No 6

No 1

No 2 38.7

No 3 45.7 83.7

No 4 36 88.7 87.3

No 5 30.5 73.8 68.7 69.8

No 6 29.5 69.8 71.6 70.6 66.3

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No 2, No 4 and No 5 (Figure 10). According to the bio-mass average, the most distinctive was the sampling siteNo 4 (Figures 2–4, 10 and 11). This is because therewere fewer specimens of Cladocera and Copepoda, andCladocera taxa did not occur at all in July.

As can be concluded from the analysis of biodiver-sity of zooplankton samples (Shannon–Wiener index),the biggest biodiversity of zooplankton samples amongall six sampling sites in Lake Svente was on 30 Augustand 21 September (Table 6 and Figure 8) Figure 11.

The analysis of the average index of species diversity(Shannon–Wiener index) in all six sampling sites showedthat the biggest diversity was in the sites No 1 (7.65)and No 2 (6.8), i.e. in the localities with the biggestdepth, but the index of biodiversity was low in the sam-pling site No 5 (5.6) (Table 6). These figures correspondto the data received during the analysis of species quanti-tative structure. Summarising the data of the research,we can state that zooplankton species diversity did notdiffer in the quality index in all six sampling sites, inparticular in Rotatoria and Cladocera groups. The differ-ence in the quality index was recorded only in theCladocera group. The biggest diversity in all groups wasobserved only in the quantity index.

Table 4. Similarity of zooplankton quantitative composition (Renkonen index, the average of samples on 30 August).

Sampling site No 1 No 2 No 3 No 4 No 5 No 6

No 1

No 2 40.7

No 3 72.8 74.6

No 4 66.9 86.1 78.4

No 5 51.2 58.8 42.6 55.3

No 6 38.1 44.8 58.5 73.8 78.7

0

2

4

6

8

10

12

1 Jul 2007 1 Aug 2007 1 Sep 2007 1 Oct 2007

Month, 2007

N1

No 1No 2No 3No 4No 5No 6

Figure 8. Taxonomic classification of the zooplankton groupsin Lake Svente (Shannon–Wiener index).

indi

v./l

4000

3000

2000

1000

0

Sampling site1 2 3 4 5 6

Figure 9. Zooplankton taxa abundance changes (median,quartiles and range) along the sampling sites in Lake Svente in2007.

Num

ber

of ta

xa

20

18

16

14

12

10

8

6

4

Sampling site1 2 3 4 5 6

Figure 10. Number of zooplankton taxa abundance changes(median, quartiles and range) along the sampling sites in LakeSvente in 2007.

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Acknowledgements

The authors would like to thank Jana Paidere, MSc in biol., forher help in identifying plankton and for comments on themanuscript. The research was supported by the EuropeanSocial Fund Project Formation of Interdisciplinary ResearchGroup for Securing the Sustainability of Salmonid Lakes inLatvia No 2009/0214/1DP/1.1.1.2.0/09/APIA/VIAA/089.

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Table 5. Similarity of zooplankton quantitative composition (Renkonen index, the average of samples on 21 September).

Sampling site No 1 No 2 No 3 No 4 No 5 No 6

No 1

No 2 82.8

No 3 88.3 83.7

No 4 83 88 82.9

No 5 81.8 85.2 81.4 85

No 6 85.6 80.8 81.5 82.1 85.1

5 6

Sampling site

1 2 3 4

Bio

mas

s

0.4

0.3

0.2

0.1

0

-0.1

Figure 11. Biomass of zooplankton taxa abundance changes(median, quartiles and range) along the sampling sites in LakeSvente in 2007.

Table 6. Zooplankton diversity in the sampling sites in Lake Svente in 2007 (Shannon–Wiener index, N1).

Sampling date

Sampling site

No 1 No 2 No 3 No 4 No 5 No 6

12 July 6.98 4.57 5.43 4.29 3.60 5.003 Aug 7.17 4.12 6.31 4.98 3.55 6.1830 Aug 8.05 9.22 5.62 5.31 7.44 5.9221 Sep 8.42 9.26 9.00 8.70 7.69 8.79Average: 7.6 6.8 6.6 5.8 5.6 6.5

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