The Distribution and Abundance of Copepoda and Cladocera in Lake Victoria, Kenya

The distribution and abundance of Copepoda and Cladocera in Lake Victoria, Kenya.

Item Type Report Section

Authors Omondi, R.

Publisher Lake Victoria Fisheries Research Project

Download date 28/09/2021 15:38:37

Link to Item http://hdl.handle.net/1834/6940 The distribution and abundance of Copepoda and Cladocera in Lake Victoria, Kenya

R. OMONDI, KMFRL P.o. Box 1881, Kisumu, Kenya

Abstract: Zooplankton samples were collected in the Kenyan waters of Lake Victoria using a Nansen type plankton net. Twenty crustacean species were recorded, 12 copepods and eight cladocerans. Copepoda dominated both in the Nyanza Gulf and in the open lake. Thermocyclops decipiens (Kiefer) was the most common copepod while cladocerans were dominated by Diaphanosoma excisum Sars, Daphnia lumholtzi Sars and Moina micrura Kurz. There were higher densities of Copepoda and Cladocera in the gulf than in the open lake, suggesting a relationship between nutrient availability and crustacean abundance.

Introduction

Zooplankton is a major component of freshwater ecosystems (Gannon & Steimberger 1978; Sladecek 1983; Huys & Boxshall 1991), influencing water quality by grazing on phytoplankton. Zooplankton also forms a significant component of the diet of carnivorous invertebrates and fishes.

Lake Victoria is undergoing major ecological changes associated with the introduction of alien species in the 1950s. The commercial fishery of the lake is now based on three species, Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin). The latter is an obligate zooplanktivore while L. niloticus and 0. niloticus juveniles include zooplankton in their diet. There is a need to understand the role ofzooplankton in the energy transfer pathway.

Previous quantitative studies in Lake Victoria include Worthington (1931) on vertical distribution and Rzoska (1956) on species composition and distribution. Recently, Mavuti & Litterick (1991) and Mwebaza-Ndawula (1994) worked on composition, distribution and abundance. The preliminary results of research to assess the present status of zooplankton in Lake Victoria are discussed here.

Materials and methods

Fourteen stations (Table 1) were sampled in the Kenyan waters of Lake Victoria (Fig. 1). Seven stations were in the Nyanza Gulf while the rest were in the open waters of the lake.

Zooplankton samples were taken monthly using a 1.5 m long Nansen type plankton net of 243 !lm mesh size and 50 cm mouth opening diameter. The net was lowered close to the bottom without disturbing the bottom sediment, and hauled vertically to the surface. Samples were preserved in 5% formalin and transported back to the laboratory, where they were made up to 250 ml and thoroughly shaken for uniform distribution. Two to four sub-samples of 1 ml or 2 ml were taken and placed in a counting chamber using a pipette.

38 The organisms were sorted and counted under a dissection microscope. Representative specimens were dissected and identified to species level under a compound microscope. The following keys were used for identification: Lindberg (1955), Van de Velde (1984), Smirnov (1996) and Korovchinsky (1992).

Results

Composition and distribution

Twenty crustacean species were recorded, 12 copepods and eight cladocerans. In the former, there were ten species of Cyclopoida and two Calanoida while Cladocera was represented by one order, Ctenopoda. This was dominated by Daphnidae with five species with the other three families; Sididae, Moinidae and Bosminidae, contributing one species each. Table 2 lists the organisms recorded and mean densities at the sampling stations.

Copepoda were more abundant than Cladocera both in the gulf and open lake (Fig. 2). There was, however, no clear pattern in the composition of Calanoida and Cyclopoida between the gulf and open water stations (Fig. 3). Thermocyclops decipiens (Kiefer) was the most common copepod, occurring at all stations, while T neglectus (Sars)was only recorded at one station, Asembo Bay. Within calanoids, Thermodiaptomus galeboides Sars had a wider distribution than Tropodiaptomus stuhlmanni Mrazek. Diaphanosoma excisum Sars, Daphnia lumholtzi Sars and Moina micrura Kurz were the most abundant Cladocera. Daphnia laevis Birge was only found in two deep water stations, Rusinga Channel and Bridge Island, while D. longispina Muller was only recorded at Gingra Rock. Stations within the gulf had more species than those in the open lake (Fig. 4)

Abundance

There were higher densities of Copepoda and Cladocera in the gulf than in the open water stations. The highest densities in the gulf were at the mouth of Sondu Miriu River with densities of 99 and 123 organisms L- 1 for copepods and cladocerans respectively. The other stations with substantial numbers of organisms were Kisumu Bay and Homa Bay. Asembo Bay had the lowest densities of copepods and cladocerans in the gulf, 9 and 2 organisms L- 1 respectively. In the open waters, the highest density of Copepoda was recorded at the mouth of Kuja River (9), 33 1 organisms L- • The mouth of Sio River had the highest number of Cladocera, 6 1 organisms L- • An unusually dense population of Daphnia barbata in January 1999, 1 194 organisms L- , was recorded at the mouth of the Sondu Miriu River.

Discussion

The low number of crustacean zooplankton species recorded can be attributed to the limited ecological habitats sampled. Mavuti and Litterick (1991) found 19 copepods and 12 cladocerans in 28 stations while recent studies of Mwebaza-Ndawula (1994) in the northern part of Lake Victoria in the Uganda waters yielded nine species of Copepoda and five species of Cladocera in four stations.

39 The dominance of Cyclopoida in the open waters corroborates the findings of Rzoska (1956) and Mwebaza-Ndawula (1994) in the Ugandan waters of Lake Victoria. In the present study, Thermocyclops decipiens was the main copepod followed by T. incisus Kiefer and Tropocyclops conjinis (Kiefer). Mavuti and Litterick (1991), however, found T. neglectus and T. emini Mrazek to be the most dominant copepods. Daphnia lumholtzi, one ofthe dominant cladocerans in this study, did not feature in Mavuti and Litterick's list of most dominant species. These changes show the dynamic nature of zooplankton in the lake and could be attributed to changes in water quality and predation. There is a need for a full description of the lake's fauna, especially copepods, as the use of identification keys from other regions may lead to erroneous identification.

The higher crustacean population in the gulf than in open water is possibly a result of influx of nutrients from rivers. Increase in nutrient input results in increase in phytoplankton production hence more food for zooplankton. Siltation and macrophyte establishment in the gulf also contribute to increase in ecological habitats. Relatively high densities of organisms at river mouths is further evidence that more nutrients result in high abundance of organisms. Similar results have been observed by Masundire (1994) and Magadza et al. (1989) in Lake Kariba. The large differences in cladoceran populations, especially at river mouth stations, arise from the effect of water current on distribution. Such effects were noted by Masundire and Magadza (1990) in Lake Kariba. The unusual dominance of Cladocera over Copepoda at the mouth of Sondu Miriu River was the result of a high population of Daphnia barbata in January 1999.

Acknowledgements

The study was funded by the European Union Lake Victoria Fisheries Research Project (Ref: ACP-RPR 227). I would like to thank J. Muli, R. Oketch and R. Mechoke for their assistance in this study.

References

Gannon E. J. & Sternberger S. (1978) Zooplankton as indicators of water quality. Trans. Amer. Micros. 97, 16-25. Huys R. & Boxshall G.A. (1991) Copepoda Evolution. Unwin Brothers Ltd. 486 pp. Korovchinsky N. (1992) Sididae and Holopediidae (Crustacea: Daphniifonnes). Guides to the identification of the micro-invertebrates of the continental waters ofthe world. The Netherlands, SPB Academic Publishing bv, 82 pp. Lindberg K. (1955) Cylopoids (Crustaces; Copepodes). Recoltes au par Le De Hemad De Macedo. Anuaro dela Estacion Altoandina de Biologia Hacindinda Chacayani Azimgaro Puno-peru. 1, 18 pp. Magadza C.H.D. (1990) The distribution of zooplankton in Sanyati Bay, Lake Kariba; a multivariate analysis. Hydrobiologia 70,57-67. Magadza C.H.D., Heineman A & Dhlamo E.J. (1989) Some preliminary results on the limnochemistry of Kariba, with special references to nitrogen and phosphorus. In: C.H.D. Magadza (ed), Ecology of Lake Kariba. ULHRS Bulletin. 1190,6 20.

40 Masundire H.M. (1994) Seasonal trends in zooplankton densities in Sanyati basin, Lake Kariba multivariate analyses. Hyrobiologia 272, 211-230. Mavuti K.M. & Litterick M.R. (1991) Composition, distribution and ecological role of zooplankton community in Lake Victoria, Kenya. Verein. Int. Limnol. 24, 1117-1122. Mwebaza-Ndawula, L. (1994) Changes in relative abundance of zooplankton in northern Lake Victoria, East Africa Hydrobiologia 272,254-264. Rzoska J. (1956) Notes on the crustacean plankton of Lake Victoria. Proc. Linm. Soc. Lond. 168, 116-125. Sladececk V. (1983) Rotifers as indications of water quality. Hydrobiologia, 100, 169-201. Smirnov N.N. (1996) Cladocera: the Chydorinae and Sayciinae (Chydoridae) of the world. Guides to the identification ofthe microinvertebrates ofthe continental waters ofthe world. The Netherlands, SPB Academic Publishers bv, 197 pp. Vande Velde 1. (1984) Revision of the African species Mesocyclops Sars, 1914 (Copepoda: Cyc1opidae). Hydrobiologia 109, 3-66. Worthington V. (1983) Vertical movement of freshwater macroplankton. Int. Rev. ges. Hydrobiol25, 394-436.

Table 1. Sampling stations for zooplankton in the Kenyan waters of Lake Victoria.

Station Station name Station co-ordinates Depth(m) No. 1 KisumuBay 00006'07"S; 34°44'34"E 3 2 Maboko 00°10'51 "S; 34°36'38"E 5 3 Sondu-Miriu mouth Oool7'OO"S; 34°45'20"E 4 4 Ndere 00°13 '56"S; 34°34'20"E 5 5 HomaBay 00028'33"S; 34°27'22"E 5 6 Gingra 00020'36"S; 34°26'03"E 11 7 Asembo Bay 00°11 '04"S; 34°24'03"E 4 8 Rusinga Channel 00°21 '04"S; 34°13'56"E 51 9 Kujamouth 00055'00"S; 34°08'01"E 3 10 Matara Bay 00044'53"S; 34°03'42"E 20 11 Bridge Island 00°20'31"S; 34°06'54"E 40 12 Yalamouth 00003'37"S; 34°02'13"E 3 13 Nzoiamouth 00003'32"N; 33°56'48"E 3 14 Sio mouth Ooo13'26''N; 34°00'21"E 3

41 Table 2. Mean densities (ind. Lot)ofvarious groups ofzooplankton in different stations in the months ofNovember and December 1998 and January 1999 (T indicates trace).

Stations 1 2 3 4 5 6 7 8 9 10 11 12 13 14

COPEPODA 32.4 13.9 99.0 18.4 21.7 16.5 9.0 31.1 32.6 11.5 7.0 7.4 5.8 9.3 Cyclopoida . 17.9 3.3 25.6 9.7 8.1 7.3 2.7 15.4 20.8 4.1 3.9 4.8 2.3 6.0 Thermocyclops decipiens (Kiefer, 1929) 15.0 1.7 18.6 7.2 7.5 4.7 1.4 7.2 20.0 3.2 2.4 1.2 1.3 3.5 T. incisus Kiefer, 1932 0.6 0.3 0 0 0 1.7 0 7.0 0 0.8 0.3 1.4 0.2 0 T. neglectus (Sars, 1909) 0 0 0 0 0 0 1.1 0 0 0 0 0 0 0 Mesocyclops ogunnus Onabamiro, 1957 0 0 0 0 0 T 0 0 0 0 0 0 0 0 Mesocyclops equatorialis equatorialis (Kiefer, 1929) 1.9 0 1.9 0 0 0.5 0.2 0.2 0 T 0 0 0 T Mesocyclops aspericomis (Daday, 1906) 0 0 0.2 1.9 0 0 0 0 0 0.1 0 0 0 0 Mesocyclops major (Sars, 1927) 0.1 0 2.6 0.4 0.2 0.3 0 0 0.1 0 0 0.6 0 0 Mesocyclops kieferi (Vande Velde, 1984) 0 1.3 0 0 0.4 0 0 0.9 0 0 0 0 0 0 Microcyclops varicans (Sars, 1927) 0 0 1.4 0 0 0.1 0 0 0 0 0 0 0 0 Eucyc10pinae Tropocyclops conjmis(Kiefer, 1927) 0.3 0 0 0.1 0 0 0 0.1 0.5 0 0 0.5 0 0 Calanoida 14.5 10.6 73.4 8.7 13.6 9.2 6.3 15.7 11.8 7.4 3.1 2.6 3.5 3.3 CLADOCERA 13.0 6.2 122.8 7.0 4.2 11.4 2.2 2.7 2.7 0.9 0.2 0.3 0.3 0.3 Daphnidae Daphnia lumholtzi Sars, 1885 0.4 0.1 15.8 0.7 1.4 0.1 0.1 0.1 0.1 0.2 0 0.2 0 0 Daphnia laevis Birge, 1878 0 0 0 0 0 0 0 0.2 0 0 T 0 0 0 Daphnia barbata WeHner, 1895 0.1 0 75.9 0.5 0 T 0 0 0 0 0 0 0 0 Daphnia longispina Muller, 1785 0 0 0 0 0 T 0 0 T T T 0 0 0 Ceriodaphnia comuta Sars, 1885 0 0.4 3.0 0.2 T T 0.1 T 0 T 0 0 0 0 Sididae Diaphanosoma excisum Sars, 1885 2.5 2.1 5.3 1.6 0.6 4.1 0.7 2.0 2.2 0.6 0.2 0 0 0 Bosminidae Bosmina longirostris Muller, 1885 0.4 0.1 0.5 0.5 0.1 0.5 T 0.2 T T 0 0 0 0 Moinidae Moina micrura Kun, 1874 9.6 0.8 17.5 3.6 1.9 6.5 1.3 0.2 0.3 0.1 T 0.1 0.3 0.1 Total Crustacea 45.4 20.1 221.9 25.4 25.9 27.9 11.2 33.8 35.8 12.4 7.2 7.7 6.1 9.6

42 1 Appendix I. Densities (ind. L- ) of various groups of zooplankton in different stations in November 1998 (T indicates trace).

Stations 1 2 3 4 5 6 7 8 9 10 11 12 13 14 COPEPODA 23.3 23.3 39.3 23.8 37.4 5.1 9.8 14.7 8.6 26.0 8.6 5.7 9.3 11.9 Cyclopoida 7.2 4.9 17.3 11.6 17.2 0.8 2.2 7.3 6.9 9.2 3.9 2.7 3.0 6.9 Thermocyclops decipiens (Kiefer, 1929) 5.8 0 9.6 5.8 16.7 0 2.2 7.1 5.6 9.0 3.3 2.3 2.6 7.0 T. incisus Kiefer, 1932 0.7 1.0 0 0 0 0.5 0 0 0 0 0.6 0.4 0.3 0 Mesocyc/ops ogunnus Onabamiro, 1957 0 0 0 0 0 0.1 0 0 0 0 0 0 0 0 Mesocyc/ops equatorialis equatoria/is (Kiefer, 1929) 0 0 0 0 0 0 0 0 0 0.1 0 0 0 0 Mesocyc/ops aspericornis (Daday, 1906) 0 0 0.6 5.8 0 0 0 0 0 0.2 0 0 0 0 Mesocyc/ops major (Sacs, 1927) 0 0 0 0 0.5 0 0 0 0 0 0 0 0 0 Mesocyc/ops kieferi (Van de Velde, 1984) 0 3.8 0 0 0 0 0 0.2 0 0 0 0 0 0 Microcyclops varicans (Sacs, 1927) 0 0 4.2 0 0 0.2 0 0 0 0 0 0 0 0 Eucyclopinae Tropocyc/ops conjinis(Kiefer, 1927) 0.7 0 0 0 0 0 0 0 1.3 0 0 0 0 0 Calanoida 16.1 18.4 22.0 12.2 20.2 4.2 7.6 7.3 1.7 16.8 4.7 3.0 6.4 5.0 CLADOCERA 9.6 6.3 85.2 6.5 6.9 3.5 4.4 1.9 0.4 0.3 0.2 0 0.4 0.4 Daphnidae Daphnia lumholtzi Sars, 1885 0 0.2 2.1 1.0 3.3 0.2 0 T 0.2 0 0 0 0 0 Daphnia longispina Muller, 1785 0 0 0 0 0 0 0 0 0.1 T T 0 0 0 Ceriodaphnia cornuta Sars, 1885 0 1.3 0 0.2 0 0 0.1 0 0 0.1 0 0 0 0 Sididae Diaphanosoma excisum Sars, 1885 1.3 4.0 2.6 2.1 0.6 1.2 1.8 1.7 0 0.1 0.2 0 0 0.4 Bosminidae Bosmina longirostris Muller, 1885 0 0.2 0.8 0.8 0.1 0.1 0.1 T 0 0 0 0 0 0 Moinidae Moina micrura Kurz, 1874 8.3 0.5 29.8 2.5 2.8 1.9 2.4 0.1 0.2 0 0 0 0.4 0 Total Crustacea 32.9 29.6 74.5 30.3 44.3 8.6 14.2 16.6 9.0 26.3 8.8 5.7 9.7 12.3

43 1 Appendix II. Densities (ind. L- ) of various groups of zooplankton in different stations in December 1998 (T indicates trace).

Station 1 2 3 4 5 6 7 8 9 10 11 12 13 14 COPEPODA 11.7 14.4 88.1 6.1 11.8 28.2 5.5 42.8 1.5 3.3 5.4 9.1 2.2 6.7 Cyclopoida 2.6 3.3 20.6 2.1 0.2 17.0 3.3 23.5 0.5 0.5 3.9 6.9 1.6 5.1 Thermocyc/ops decipiens (Kiefer, 1929) 0.8 3.3 15.0 2.1 0 10.8 0 0 0 0.5 3.9 0 0 0 T. incisus Kiefer, 1932 1.2 0 0 0 0 4.7 0 20.9 0 0 0 3.9 0 0 T. neg/ectus (Sars, 1909) 0 0 0 0 0 0 3.3 0 0 0 0 0 0 0 Mesocyc/ops equatoria/is equatoria/is (Kiefer, 1929) 0 0 5.6 0 0 1.6 0 0 0 0 0 0 0 0 Mesocyc/ops major (Sars, 1927) 0.4 0 0 0 0 0 0 0 0 0 0 1.2 0 0 Mesocyc/ops kieferi (Van de Velde, 1984) 0 0 0 0 0 0 0 2.4 0 0 0 0 0 0 Microcyc/ops varicans (Sars, 1927) Calanoida 9.1 11.1 67.5 4.0 11.6 11.2 2.2 19.3 1.0 2.8 1.5 2.2 0.6 1.6 CLAD0 CERA 3.0 3.3 62.6 1.9 1.4 18.6 1.4 1.4 0.2 0.3 0.2 0.5 0.1 0.1 Daphnidae Daphnia /umholtzi Sars, 1885 0.2 0.2 9.6 0.1 0.8 0.1 0.1 0.1 0.1 0 0 0.4 0 0 Daphnia /aevis Birge, 1878 0 0 0 0 0 0 0 0.3 0 0 0.1 0 0 0 Daphnia barbata Weltner, 1895 0 0 33.7 0 0 0 0 0 0 0 0 0 0 0 Daphnia /ongispina Muller, 1785 0 0 0 0 0 0.1 0 0 0 0 0 0 0 0 Ceriodaphnia cornuta Sars, 1885 0 0 0 0 0 0 0.1 0.1 0 0 0 0 0 0 Sididae Diaphanosoma excisum Sars,1885 1.1 1.4 2.6 0.6 0.4 7.4 0.3 0.7 0.1 0.3 0.1 0 0 0 Bosminidae Bosmina /ongirostris Muller, 1885 0 0.1 0.7 0.1 0 0.8 0 T 0 T 0 0 0 0 Moinidae Moina micrura KUIZ, 1874 1.7 1.6 16.0 1.1 0.2 10.2 0.9 0.2 0 0 T 0.1 0.1 0.1 Total Crustacea 14.7 17.7 150.7 8.0 13.2 46.8 6.9 44.2 1.7 3.6 5.6 9.6 2.3 6.8

44 I Appendix III. Densities (ind. L- ) ofvarious groups ofzooplankton in different stations in January 1999 (T indicates trace).

1 2 3 4 S 6 7 8 9' 10 COPEPODA 62.1 4.0 170.0 2S.0 16.1 16.4 11.7 3S.7 87.6 S.2 Cydopoida 43.9 1.8 39.0 IS.3 7.0 4.1 25 IS.3 S4.9 2.6 Thermocyclops decipiens (Kiefer, 1929) 38.3 1.8 31.1 13.6 S.8 3.3 2.0 14.4 S4.4 0 T. incisus Kiefer, 1932 0.0 0.0 0.0 0.0 0.0 0.0 0 .0 0 2.S Mesocyclops equatoria/is equatorialis (Kiefer, 1929) S.6 0.0 0.0 0.0 0.0 0.0 O.S 0.7 0 0.1 Mesocyclops major (San, 1927) 0.0 0.0 7.9 1.3 0.0 0.8 0 0 0.4 0 Mesocyclops kieferi (Van de Velde, 1984) 0.0 0.0 0.0 0.0 1.3 0.0 0 0 0 0 Eucyclopinae Tropocyclops conjinis(Kiefer, 1927) 0 0 0 0.4 0 0 0 0.1 02 0 Calanoida 18.2 2.2 130.7 9.8 9.1 12.3 9.2 20.S 32.7 32.6 CLADOCERA 26.4 1.2 270.S 12.6 4.2 12.0 0.7 4.6 7.S 2.2 Daphnidae Daphnia lumholtzi Sars, 188S 1.0 0 35.6 0.9 0.1 0.1 0.2 0.1 0 0.6 Daphnia laevis Birge, 1878 0 0 0 0 0 0.0 0 0.2 0 0 Daphnia barbata Weltner, 189S 0.4 0 194.1 I.S 0 T 0 0 0 0 Ceriot!aphnia comuta Sars, 188S 0 0 8.9 O.S 0.1 0.1 0 0 0 T Sididae Diaphanosoma excisum Sars, 188S 5.2 0.9 10.8 2.0 0.9 3.7 0.1 3.6 6.5 1.3 Bosminidae Bosmina longirostris Muller, 1885 1.1 0 0 0.5 0.3 0.7 0 0.4 0.1 T Moinidae Moina micrura Kmz, 1874 18.7 0.3 21.0 7.2 2.8 7.3 0.5 0.4 0.8 0.2 Total CrustaQca 88.S 5.2 44O.S 37.6 20.3 28.4 12.4 40.3 95.1 7.1

4S L. Tur1

o·

L. Victoria

L, Tanganyika \ Q ' D \12 , !0e", 0 I I I .i0~ 0030'S I t 1 I 1 I I KENYA kilometres 1000'S o 10 20 30 40 50 I I I I , I

'34°00'E 3S000'E

Figure 1. Map of Kenyan waters of Lake Victoria, showing the 14 sampling sites described in Table 1.

...... 140 .....:.....

U) 120 (ij ::l 100 "'C l!J Copepoda :~ 80 "'C C .Cladocera ::::: 60 U) Q) :e 40 U) c Q) 20 0 ~-"""---.LI 0 -,--"'__,.....-.__....,._-,--"'_..... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Stations

1 F-igure 2. Mean densities (ind.L- ) of Copepoda and Cladocera for the months of November and December 1998 and January 1999.

46 80 -7' 70 ...J ~ 60 <11 ..c 50 III Cyclopoida E E 40 IIIICalanoida -en CD 30 :.0::; 20 'wc: ~ 10 o 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Stations

1 Figure 3. Mean densities (ind. L- ) of Cyclopoida and Calanoida for the months of November and December 1998 and January 1999.

10 9 en Q) 8 'u Q) 7 0en 0 6 -~ Q) ..c 5 E ::J 4 C c co 3 Q) ::E 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Stations

Figure 4. Mean number ± SD of zooplankton species recorded at the sampling stations, numbered as in Table 1.