DISSEMINATION OF AQUATIC INVERTEBRATES ON WINDBLOWN VEGETATION MATS IN LAKE CHILWA, MALAWI

SUMMARY

Exceptionally high water levels in Lake Chilwa, Malaŵi, resulted in large tracts of the swamp vegetation becoming detached from the periphery of the lake. The open water became littered with large rafts of the bulrush, Typha domingeneis together with other plants such as the water lettuce, Pistia etratiotes and Ceratophyllum demersum. Many invertebrates from several taxa were found clinging to drifting vegetation and in soma cases were more abundant there than in sheltered parts of the peripheral swamp. Each species of drifting plant supported a characteristic fauna. Predaceous Coleoptera predominated on Pistia, while an ephemeropteran, Cloeon sp. was most common on Ceratophyllum. Drifting Typha mats supported the lowest biomass of invertebrates and this was comparable with samples collected in the swamp vegetation. Drifting plants were therefore able to disseminate invertebrates from one part of the swamp to another and this has implications for the dispersal of the snail vectors of bilharzia which clung to Ceratophyllum.

KEY WORDS:

• Ceratophyllum demereum
• Piatia stratiotes
• Typha domingensie
• insect dispersion
• swamp vegetation