2000, Annual Reports of the Zoological Institute RAS.


Structure and function of pelagic zooplankton in lakes of different productivity (with reference to small lakes of north-western Russia)

Marina B. Ivanova

Zoological Institute, Russian Academy of Sciences, Universitetskaya nab., 1, St. Petersburg, 199034, Russia
 

Assessing the response of ecosystems to eutrophication, and the impact of antropogenic factors, is one of the major problems in current ecology. Analysis of the evidence obtained for a series of lakes situated in the same climatic zone that are similar in morphology, but different in production characteristics allows us to answer the question of relation-ship of zooplankton community characteristics and trophic status of the lake.

The study was performed on closed transparent lakes that are numerous in the north-western region of Russia: Akkakharyu Lakes (Goluboye 1 and Goluboye 2, Shkolnoye), in southern Karelia, Gladyshevskiye Lakes (Pridorozhnoye and Pionerskoye) in the centre of the Karelian Isthmus, and Syaberskiye Lakes (Bolshoi Okunenok and Malyi Okunenok) in Luga District of Leningradskaya Oblast. The major characteristics of the lakes are given in Table 1.

 Table 1. Basic characteristics of the studied lakes.

Characteristics

Lakes

Goluboye 2

Goluboye 1

Shkolnoye

Pridorozhnoye

Pionerskoye

Bolshoi Okunenok

Malyi Okunenok

Area, ha

2.9

10.9

3.4

3.7

5

5.8

2.7

Maximal depth, m

8.2

13

11

13

17

3

2.1

Mean depth, m

3.7

5.3

3.5

7.2

5.1

2

1.5

Total mineralisation, mg/l

24

24

16

46

30

19-44

39-25

Transparency, m

8

8

5.1

5.6

1.7

0.4-0.8

0.4-1.1

Color of water, grades

5

5

7

17

400

 

 

Ph

5.3

5.4

5.7

6

6.5

6-9.4

6-9.4

Total phosphorus, mg/l

8

 

10

22.3

238

 

 

BOD5, mgC/l

0.13

0.32

0.33

0.36

3.2

2.3

1.7

Chlorophyll "a", mg/l

0.49

0.99

1.33

3

9.5

53

65

 

Based on total phosphorus concentration, chlorophyll content and BOD5 value Akkakharyu Lakes and Lake Pridorozhnoye may be regarded as oligotrophic lakes, Pionerskoye as mesotrophic, Bolshoi Okunenok and Malyi Okunenok as eutrophic lakes. The latter two lakes in their hydrobiological characteristics were analogous to Akkakharyu Lakes until the early 1960s. The change in their trophic status is related to measures aimed at an increase of production and further use for fish culture. Gladyshevskiye Lakes are used for recreation, Pionerskoye Lake being exposed to a particularly strong impact. The notable similarity of morphology and salt content of Gladyshevskiye Lakes and Akkakharyu Lakes suggests that the initial state of the former was analogous to that of the latter. Therefore, a working hypothesis has been assumed that all the studied lakes previously belonged to the same type of acidic transparent lakes and that the difference in their present status is related to anthropogenic eutrophication.

 Table 2. Number of species in pelagial of the studied lakes 

 

Lakes

Goluboye 2

Goluboye 1

Shkolnoye

Pridorozhnoye

Pionerskoye

Bolshoi Okunenok

Malyi Okunenok

Rotatoria

2

2

2

7

18

29

25

Cladocera

4

4

5

5

7

10

4

Cyclopoidae

1

1

1

2

2

3

3

Diaptomidae

1

1

2

2

2

1

1

Chaoborus juv.

 

 

 

 

1

 

1

Sum

8

8

10

16

30

 43

34 

 

Zooplankton were collected in the central part of the lake from May through October using standard methods on Syaberskiye Lakes in 1986-1988, on Akkakharyu Lakes in 1992-1993, on Gladyshevskiye Lakes in 1997-1998. Species composition, abundance, and biomass of zooplankton were assessed. The functional characteristics of zooplankton were calculated according to the standard technique (Edmondson & Winberg, 1971). The value of the specific rate of population production was taken from the literature (Galkovskaya, 1968; Kajak & Ranke-Rybicka, 1970; Ivanova, 1985). Data on the feeding type and the kind of food were taken from the literature (Gutelmakher et al., 1988; Krylov, 1989; Monakov, 1998). Connectance of zooplankton was calculated according to Briand method (Briand, 1983), length of food chains - by May's method (Begon et al., 1989).

Data on the number of species found in lakes are given in Table 2. Comparison of species composition of zooplankton in the studied lakes has shown that the number of species in lakes of similar area, but different in the trophic status depends on the food resources and can be approximated by the equation:
 

Y=(8.01 3.85)+(0.290.07)*X1 + (6.751.52)* X2,   r2 = 0.95                        (1),
 

where Y is the number of species of zooplankton, X1 is mean seasonal chlorophyll "a" concentration in water, mg*l-1, X2 - BOD5, mgC*l-1.

 

Table 3. Total biomass of zooplankton and the percentage of individual zoo-plankters

 

Lake, Year

1

2

3

4

5

6

Goluboye 2, 1992
                  1993
Goluboye 1, 1992
                  1993
Shkolnoye,  1993

0.5
0.6
0.5
0.6
0.8

0
0
0
0
0

97.5
98.3
81.4
88.6
92.5

2.0
1.1
18.1
12.8
6.7

0
0
0
0
0

2.46
0.84
0.82
0.93
1.83

Pridorozhnoye, 1997
                      1998

1.3
3.3

0
0

57.0
22.7

41.7
74.0

0
0

1.02
0.69

Pionerskoye,
1997, epilimnion,
hypolimnion
from surface to bottom
1998, epilimnion,
hypolimnion
from surface to bottom


30.8
77.6
60.2
12.1
0.40
0.70


31.7
7.9
14.4
1.1
0.01
0.05


19.6
1.2
9.1
35.8
0.05
1.2


16.0
2.1
8.9
50.8
0.14
1.75


2.1
11.0
7.3
0.2
99.4
96.3


2.8
0.43
0.62
1.04
3.13
2.93

B.Okunenok, 1986
                   1987
                   1988

65.7
76.8
66.5

9.8
7.6
6.7

6.4
4.1
5.9

17.8
11.5
18.6

0.3
0
2.6

2.74
4.17
1.80

M.Okunenok, 1986
                    1987
                    1988

37.9
44.21
49.0

0
0
0

44.2
41.2
36.2

0
0
0

17.9
14.6
14.8

4.22
4.41
4.99

 

* Numeration: 1 - Rotatoria (without Asplanchna priodonta), 2 - Asplanchna priodonta, 3 - Cladocera, 4 -Copepoda, 5 - Chaoborus juv., 6 - mean seasonal total biomass (kcal*m-3).

 

Seven major trophic groups in the lakes can be defined by their feeding characteristics (Fig. 1). The trophic structure of a zooplankton community is also related to trophic status of a lake. The most complicated structure has been noted in mesotrophic Lake Pionerskoye. Only obligatory predatory Crustacea (group 6) were not noted in zooplankton of this lake during the years of study. In Akkakharyu Lakes characterized by low production, Crustacea filtrators (groups 2 and 3) and facultative predators Cyclopida (group 3) were only present in zooplankton. As trophy of the lake increases, the role of planktonic rotifers in the total zooplankton biomass and in the energy flow distribution grows. Rotifers attain maximal values under the conditions of a eutrophic body of water. The total biomass of zooplankton and the portion of Rotatoria, Cladocera and Copepoda are given in Table 3.

 

Table 4. Mean seasonal values of numbers of connectance (Cs), maximal values of index of species diversity (ISD, bit* kcal), production of zooplankton (Pz, kcal*m-2 per season), and respiration of zooplankton (Rz, kcal*m-2 per season)

 

Lake, Year

Cs

ISD

Pz

Rz

Pz/Bz

Pz/Rz

Goluboye 2,   1993
Goluboye 1,   1993
Shkolnoye,    1993

0.24

1.72-1.85

34.9
24.7
47.5

87.7
70.6
133

10.4
6.6
6.5

0.40
0.35
0.36

Pridorozhnoye, 1997

0.22

2.82

76.1

205.3

10.4

0.15

Pionerskoye, 1997

0.21

2.63

114.2

428

14

0.26

B.Okunenok,  1986
                    1987
                    1988

0.20

2.38

180
226
102

1157
522
281

32.8
27.1
28.3

0.16
0.43
0.36

M.Okunenok,  1986
                     1987
                     1988

0.15

2.24

170
185
200

288
306
412

27
28
26.7

0.59
0.60
0.68

 

The total biomass of zooplankton is also related to the food supply, and this relationship can be expressed by the equation

logY = (-0.0540.224)+(0.2420.094) * logX1+(0.1700.179) * logX2,     r2 = 0.87               (2),

where Y is the mean seasonal biomass of zooplankton, kcal*m-3, X1 and X2 are as in equation (1).

Some functional characteristics of zooplankton are given in Table 4. The ratio of production of the community per vegetation season (Pz) and energy expenditures for the same period can be regarded as the coefficient of efficiency of the community. Pz/Rz is closely connected with the structure of the community, which can be characterized by the Shannon index and connectance calculated by Briand method (Table 4). Relationship of these values can be approximated by the equation

Y=(2.2570.256)- (0.3680.033) * X1 -(5.1600.442) * X2,    r2= 0.99                                (3)

where Y is Pz/Rz, X1 is maximal value of the Shannon index bit/kcal, X2 - connectance according to Briand.

The relationship obtained allows us to conclude that the longer the food chains, and the higher the Shannon index, the lower the coefficient of efficiency of a community. According to May's hypothesis based upon the study of mathematical models of communities an increase in the number of species and an increase of connectance fosters growth of instability (Begon, et al., 1989). If we assume this point of view, oligotrophic weakly acidic Lake Pridorozhnoye should be regarded as the most resistant one to the external impact. Connectance in the community increases with a decline of pH; the number of species increases abruptly with an increase of pH and growth of trophy. Acidic lakes can be regarded as unstable ecosystems. Two or three years of intensive fertilization are sufficient for this body of water to change completely (Ivanova, 1993). On the other hand ecosystems of eutrophic lakes Bolshoi Okunenok and Malyi Okunenok are vulnerable to fish pressure.

 

 

Fig. 1. The food webs in zooplankton. 1 - microphages (Rotatoria without Asplanchna, Copepoda), 2 - filtrators (Daphnia sp., Ceriodaphnia sp., Bosmina longirostris, Chydorus sphaericus), 3 - filtrators (Diaphanosoma brachiurum, Holopedium gibberum, Eudiaptomus sp.,), 4 - facultative predators (Asplanchna priodonta), 5 - facultative predators (Cyclops scutifer, Thermocyclops oithonoides, Mesocyclops leuckarti), 6 - carnivorous Crustacea (Heterocope appendiculata), 7 - carnivorous Insecta (Chaoborus flavicans juv.)

 

The existence of the trophic structure of Malyi Okunenok (Table 4) is only possible in the absence of fishes. One year after introduction of fishes into Lake Malyi Okunenok zooplankton in that lake became analogous to zooplankton in Bolshoi Okunenok (Bioticheskiye vzaimootnosheniya ..., 1993). Apparently we can agree with the opinion of the authors cited above that there is no such general characteristic of a community as steadiness. This parameter depends on the studied component of an ecosystem and on the nature of the impact. Analysis of the response of a zooplankton community to external impact suggests that oligotrophic lakes are not resistant to an increase of nutrient flow and highly productive ones to the impact of fish pressure.

 

The studies were carried out with financial support of the Russian Foundation for Basic Research, (grants 99-04-49614 and 00-04-63100).

References

Begon, M., Harper, J.L. & C.R. Townsend. 1989. Ekologija [Ecology]. Moskva. (Russian translation).

Bioticheskie vsaimootnosheniya... 1993. Bioticheskie vzaimootnosheniya v ecosisteme ozerpitomnikov [Biotic relationships in ecosystem of nursery lakes]. St.Petersburg. 350 pp. (In Russian).

Galkovskaya, G.A. 1968. Production of planctonic Rotatoria. In: Metody opredeleniya produktsii vodnykh zhivotnykh [Methods for the assessment of production of water animals]. pp.135-141. Minsk.

Gutelmakher, B.L., Sadchikov, A.P. & T.G. Filippova. 1988. Pitanie zooplanktona [Feeding of zooplankton]. Moskva. 156 pp. (In Russian.)

Edmondson, W.T. & G.G.Winberg (Eds.). 1971. A manual on methods for the assessment of secondary productivity in fresh waters. London. 358 pp. (IBP Handbook 17).

Ivanova, M.B. 1985. Produktsiya planktonnykh rakoobraznykh v presnykh vodakh [Production of planktonic crustaceans in fresh water]. Leningrad, Nauka. 220 pp. (In Russian).

Ivanova, M.B. 1993. Essays about the history of Sjaberskiye Lakes. In: Bioticheskie vzaimootnosheniya v ecosisteme ozerpitomnikov [Biotic relationships in ecosystem of nursery lakes]. pp. 4-17. St.Petersburg. (In Russian).

Kajak, Z. & B. Ranke-Rybicka. 1970. Feeding and production efficiency of Chaoborus flavicans Meigen larvae in eutrophic and dystrophic lakes. Pol. Arch. Hydrobiol. 17: 73-90.

Krylov, P.I. 1989. Pitanie presnovodnogo khishchnogo zooplanktona [Feeding of freshwater carnivorous zooplankton]. Moskva. 146 pp. (In Russian).

Monakov, A.V. 1998. Pitanie presnovodnykh bespozvonochnykh [Feeding of freshwater invertebrates]. Moskva. 318 pp. (In Russian).