A quantitative diving survey of benthic vegetation and fauna in Lake Kariba, a tropical man‐made lake

SUMMARY. 1. The biomass distribution of submerged vascular vegetation and benthic fauna were investigated by diving in Lake Kariba. The vegetation was well correlated with transparency of the water. Maximum biomass (1400 g dryweight m −2 ) and a depth penetration of 6 m were found in areas little influenced by river inflow, while these were only 110 g m −2 and 2 m, respectively, in the basin receiving water from the Zambezi river. 2. The lake is mesotrophic‐oligotrophic. The total biomass for the lake was 101,000 tons dryweight of rooted vegetation composed of Lagarosiphon ilicifolius Oberm. (52%), Najas pectinata (Parl) Magnus (33%), Vatlisneria aethiopica Frenzl (11%), Ceratophyllum demersum L. (3%) and Potamogeton octandrus L. (0.5%). Average plant biomass for the potentially colonizable depth zone of 0‐12 m and for the total lake amounted to 79.9 g m −2 and 18.8 g m −2 , respectively. 3. The distribution of the benthic fauna generally followed that of the vegetation. The total animal biomass of 118,840 tons dryweight. including shells, consisted of mussels (95.8%), snails (4.1%) and insect larvae (0.1%). Four species of mussels were found: Caelatura mossambicensis (von Martens) (81% of mussel biomass), Corbicula africana (Krauss) (9%). Mutela dubia (Gmelin) (5%) and Aspatharia wahlbergii (Krauss) (5%). Among the snails Melnoides tuberculuta (Müller), Cleopatra spp. and Bellamya capillata (Frauenfeld) dominated. 4. The average animal biomass was high compared to most other lakes perhaps due to lack of predators. For the colonizable 0‐12 m depth interval and the total lake it was 96.2 g m −2 including shells (15.0 g m −2 shell‐free dryweight) and 22.6 g m −2 including shells (3.4 g m −2 shell‐free dryweight). respectively. Biomass of plants and animals was even higher prior to the recent lowering of the water level by 7 m, which was estimated to have stranded 84,000 tons of mussels on the shore.