Diversity, distribution and abundance of macro-invertebrates in areas with different pollution levels in Lake Victoria

Study Extent

Sampling of the sites was conducted in 2011, 2012 and 2013.

Sampling

At each sampling station, a ponar grab of 238 cm2 open jaw area was used to pick 3 hauls of sediment. Triplicate samples from each station were either individually concentrated or concentrated as a composite sample using a filtering bag of 400 µm mesh of nitex webbing. The concentrated samples were placed in sample containers, preserved in 5% formalin solution, labeled and taken to the laboratory for analysis. In the laboratory, the samples from each container were individually rinsed in water to wash away formalin and placed on a white flat-bottomed tray. Some water was added to spread the sample and all the benthic macro-invertebrates were sorted out using a pair of forceps. The organisms were classified and identified under a dissecting microscope (at 25X eye piece and 4X or 16X objectives) where detailed structures were required. Taxonomic identification keys: Merritt and Cummins (1997), Pennak (1978), and Mandahl-Barth (1954) were used in identification of the invertebrates. Individual members of each taxon were enumerated.

Quality Control

The samples were immediately processed in the field and treated with formalin to keep the organisms of interest intact and prevent them from rotting. To avoid loss of organisms during sample processing, appropriate mesh sizes during sieving. Appropriate taxonomic keys were used.

Method steps

1. Collection of the macroinvertebrates In the field, sediment samples were collected using a Ponar grab with an open jaw surface area of 238 cm2. At each site, three sediment samples were obtained. The three samples were mixed and concentrated to form one composite sample for each site.
2. Preserving the samples The composite sample for each site was separately preserved in 5% formalin to maintain the organisms in good condition prior to analysis in the laboratory.
3. Identification of macroinvertebrates In the laboratory, formalin was rinsed off from each sample and placed in white flat-bottomed trays. Using pairs of forceps, all benthic macro invertebrates were sorted from the sediment and the individual taxa identified to the lowest possible taxonomic level using appropriate identification keys and a dissecting binocular microscope at 4x 25 magnification.

Freshwater macroinvertebrates

1. Ablabesmyia
   rank: genus
2. Baetidae
   rank: family
3. Bellamya unicolor
   rank: species
4. Biomphalaria
   rank: genus
5. Bulinus
   rank: genus
6. Byssanodonta parasitica
   rank: species
7. Caelatura
   rank: genus
8. Caelatura hauttecoeuri
   rank: species
9. Caelatura monceti
   rank: species
10. Caenis
    rank: genus
11. Caridina nilotica
    rank: species
12. Ceratopogonidea
    rank: family
13. Chaoborus
    rank: genus
14. Chironomidae
    rank: family
15. Chironomus
    rank: genus
16. Clinotanypus
    rank: genus
17. Cloeon
    rank: genus
18. Conchostraca
    rank: genus
19. Corbicula africana
    rank: species
20. Corixidae
    rank: family
21. Cryptochironomus
    rank: genus
22. Economus
    rank: genus
23. Ephemeridae
    rank: family
24. Gabbia humerosa
    rank: species
25. Gomphidae
    rank: family
26. Hirudinea
    rank: class
27. Lentorbis junodi
    rank: species
28. Leptoceridae
    rank: family
29. Leptophlebidae
    rank: family
30. Libellulidae
    rank: family
31. Melanoides tuberculata
    rank: species
32. Mutera bourguignat
    rank: species
33. Oligochaeta
    rank: class
34. Ostracoda
    rank: class
35. Pisidium victoriae
    rank: species
36. Povilla adusta
    rank: species
37. Procladius
    rank: genus
38. Segmentorbis
    rank: genus
39. Sphaerium
    rank: genus
40. Tanypus
    rank: genus
41. Tanytarsus
    rank: genus

Lake Victoria, Uganda