Zooplankton occurrences and abundance in the Lake Albert system, Uganda

Study Extent

The water bodies covered were sampled within 2002 to 2020. However, sampling was not consistent for the water bodies over that period. Data is available for specified water bodies for a periods; 2002, 2007, 2013-14, 2016 and 2020.

Sampling

Zooplankton samples were collected with a conical plankton net (Nansen type; mesh size 60 µm and mouth diameter of 0.25 m), towed vertically through the water column, as described by Fernando (2002) and Mwebaza-Ndawula (1994). Three hauls were taken and combined to make composite samples, preserved in 5% formalin and transferred to laboratory for taxonomic analysis and generation of abundance. In the laboratory, each sample was washed with tap water 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 A conical plankton net (Nansen type; mesh size 60 µm; mouth diameter 0.25 m) was used to collect the zooplankton. It was towed vertically through the water column to have an integrated sample. Three hauls were taken per site and were combined to make a composite sample. Preserving the samples Samples were preserved in a sugar-formalin mixture. The sugar was to stop the ballooning of cladocerans for easy identification. 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. Alona
   rank: genus
2. Ascomorpha
   rank: genus
3. Asplanchna
   rank: genus
4. Brachionus angularis
   rank: species
5. Brachionus bidentata
   rank: species
6. Brachionus budapestinensis
   rank: species
7. Brachionus calyciflorus
   rank: species
8. Brachionus falcatus
   rank: species
9. Brachionus patulus
   rank: species
10. Brachionus quadridentatus
    rank: species
11. Calanoidae
    rank: family
12. Ceriodaphnia cornuta
    rank: species
13. Ceriodaphnia dubia
    rank: species
14. Chydorus
    rank: genus
15. Cyclopoidae
    rank: family
16. Daphnia barbata
    rank: species
17. Daphnia longispina
    rank: species
18. Daphnia lumholtzi
    rank: species
19. Diaphanosoma excisum
    rank: species
20. Euclanis
    rank: genus
21. Eucyclops
    rank: genus
22. Filinia longiseta
    rank: species
23. Filinia opoliensis
    rank: species
24. Hexanauplia
    rank: class
25. Hexathra
    rank: genus
26. Keratella cochlearis
    rank: species
27. Keratella tropica
    rank: species
28. Lecane bulla
    rank: species
29. Lecane signifera
    rank: species
30. Macrothrix
    rank: genus
31. Mesocyclops
    rank: genus
32. Moina micrura
    rank: species
33. Platyias quadricornis
    rank: species
34. Polyarthra vulgaris
    rank: species
35. Simocephalus
    rank: genus
36. Synchaeta
    rank: genus
37. Synchaeta pectinata
    rank: species
38. Testudinella parva
    rank: species
39. Thermocyclops incisus
    rank: species
40. Thermocyclops neglectus
    rank: species
41. Thermodiaptomus galeboides
    rank: species
42. Trichocerca cylindrica
    rank: species
43. Tropocyclops confinnis
    rank: species
44. Tropocyclops tenellus
    rank: species

This work was part of research and monitoring studies done in predetermined localities of Lake Albert, Luzira lagoon, and river mouths of Rivers Nkusi, Waki, Muzizi, and Wambabya.