Zooplankton occurrences and abundance in the Lake Edward system, Uganda

Study Extent

The water bodies covered were sampled between 1998 and 2020. However, sampling was not consistent for the water bodies over the period. Data is available for specified waterbodies for 1998-99, 2011-14, 2016 and 2020.

Sampling

This work was part of research and monitoring studies conducted in predetermined sites and localities on water bodies within the Lake Edward system, including two nearby small lakes in the Lake Victoria basin. The lakes covered include Edward, George, Mutanda, Mulehe, Chahafi, Nakasanda, Bunyonyi and Kayumbu. The rivers covered are Rwimi and Lubilia. The wetlands covered are Kyase, Kiruruma and Ruhuma. The sites sampled represent different habitats based on the factors such as depth, distances from shoreline and water flow (lentic or lotic).
In lakes, zooplankton samples were collected with a conical plankton net (Nansen type; mesh size 60 µm or 100 µm; mouth diameter 0.25 m), towed vertically through the water column, as described by Fernando (2002) and Mwebaza-Ndawula (1994). In rivers and wetlands, sampling was done using Schindler trap with 5 litre capacity. 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 as per Fernando (2002).

Method steps

1. Collection of the zooplankton In lakes, a conical plankton net (Nansen type; mesh size 60 or 100 µm; mouth diameter 0.25 m), towed vertically through the water column to have an integrated sample was used to collect the zooplankton. Collection of samples in rivers and wetlands used a Schindler trap. Three hauls were taken per site and were combined to make a composite sample.
2. Preserving the samples Samples were preserved in a 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.

The taxa include three broad groups of zooplankton: Copepoda, Cladocera and Rotifera

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

Lake Edward system, including two nearby small lakes (Chahafi and Kayumbu) in the Lake Victoria Basin)