Zooplankton occurrences and community structure in Lakes Victoria and Nabugabo

Study Extent

Sampling was conducted from 1992-98, 2000-06, 2008 and 2012 and was done majorly in northern Lake Victoria, including some parts of southern portion (Tanzania) and Lake Nabugabo.

Sampling

Zooplankton samples were collected with a conical plankton net (Nansen type; mesh size 60 µm; mouth diameter 0.25 m), towed vertically through the water column, as described by Mwebaza-Ndawula (1994). Each sample was washed with tap water in the laboratory over a 53 µm sieve to remove the preservative and then diluted to a suitable volume, depending on the concentration of organisms in each sample. Sub-samples of 2, 2, 5 and 10 mL were taken with a wide bore automatic pipette from a well agitated sample. The sub-sample series were performed to consider the more abundant organisms in 2, 2 mL series, and the rarer organisms in 2, 2, 5, 10 mL series. Each sub-sample was put into a counting chamber and examined under inverted microscope (Hund, Wetzlar, Germany) at X100 magnification for taxonomic determination, and X40 for counting and organism body measurements.

Quality Control

Some zooplankton were able to be identified to species level using published taxonomic keys (Sars 1895; Pennak 1953; Brooks 1957; Rutner-Kolisko 1974; Koste 1978; Boxshall & Braide 1991; Korinek 1999). Taxonomic names were cross-checked using the World Register of Marine Species (WoRMS). Volume densities of organisms were calculated from the counts data, with reference to the sample net mouth diameter and water column depth at each sampling site (Mwebaza-Ndawula, 1998).

Method steps

1. Collection of the zooplankton In the field, a conical plankton net (Nansen type; mesh size 60 µm; mouth diameter 0.25 m), towed vertically through the water column to have an integrated sample was used to collect the zooplankton. Three hauls were taken per site and were combined to make a composite sample.
2. Preserving the samples The composite sample was preserved with sugar-formalin mixture. The sugar was to stop the ballooning of cladocerans for easy identification.
3. Identification of zooplankton taxa In the laboratory, samples were washed using a sieve of 53 µm to remove the fixatives. Organisms were identified to the smallest taxonomic level possible using taxonomic keys (Sars, 1895, Pennak, 1953, Brooks, 1957, Rutner-Kolisko, 1974, Koste, 1978, Boxshall and Braide, 1991, Korinek, 1999). Density of organisms were calculated from the counts data, with reference to the sample net mouth diameter and water column depth at each sampling site (Mwebaza-Ndawula, 1998)

Freshwater zooplankton

1. Afrocyclops
   rank: genus
2. Alona
   rank: genus
3. Ascomorpha
   rank: genus
4. Asplanchna
   rank: genus
5. Beauchampiella eudactylota
   rank: species
6. Bosmina longirostris
   rank: species
7. Brachionus
   rank: genus
8. Brachionus angularis
   rank: species
9. Brachionus bidentatus
   rank: species
10. Brachionus budapestinensis
    rank: species
11. Brachionus calyciflorus
    rank: species
12. Brachionus caudatus
    rank: species
13. Brachionus dimidiatus
    rank: species
14. Brachionus falcatus
    rank: species
15. Brachionus forficula
    rank: species
16. Brachionus patulus
    rank: species
17. Brachionus plicatilis
    rank: species
18. Brachionus quadridentatus
    rank: species
19. Brachionus urceolaris
    rank: species
20. Brachionus variabilis
    rank: species
21. Calanoidae
    rank: family
22. Ceriodaphnia
    rank: genus
23. Ceriodaphnia cornuta
    rank: species
24. Ceriodaphnia dubia
    rank: species
25. Chydorus
    rank: genus
26. Cyclopoidae
    rank: family
27. Daphnia longispina
    rank: species
28. Daphnia lumholtzi
    rank: species
29. Diaphanosoma excisum
    rank: species
30. Euclanis
    rank: genus
31. Eucyclops
    rank: genus
32. Filinia longiseta
    rank: species
33. Filinia opoliensis
    rank: species
34. Harpacticoida
    rank: order
35. Hexanauplia
    rank: class
36. Hexathra
    rank: genus
37. Keratella cochlearis
    rank: species
38. Keratella tropica
    rank: species
39. Lecane
    rank: genus
40. Lecane bulla
    rank: species
41. Lecane luna
    rank: species
42. Macrochaetus sericus
    rank: species
43. Macrothrix
    rank: genus
44. Mesocyclops
    rank: genus
45. Moina micrura
    rank: species
46. Platyias
    rank: genus
47. Platyias quadricornis
    rank: species
48. Polyarthra
    rank: genus
49. Polyarthra vulgaris
    rank: species
50. Synchaeta
    rank: genus
51. Synchaeta pectinata
    rank: species
52. Testudinella patina
    rank: species
53. Thermocyclops
    rank: genus
54. Thermocyclops decipiens
    rank: species
55. Thermocyclops emini
    rank: species
56. Thermocyclops incisus
    rank: species
57. Thermocyclops neglectus
    rank: species
58. Thermocyclops oblongatus
    rank: species
59. Thermodiaptomus galeboides
    rank: species
60. Trichocerca
    rank: genus
61. Trichocerca cylindrica
    rank: species
62. Tropocyclops confinnis
    rank: species
63. Tropocyclops tenellus
    rank: species
64. Tropodiaptomus stuhlmanni
    rank: species

Lake Victoria and Lake Nabugabo