Appearance of new taxa: invertebrates, phytoplankton and bacteria in an alkaline, saline, meteorite crater lake, South Africa

Abstract

Data generated during 12 fitrips in 2006 were used to investigate possible changes in the biota com- munities of Lake Tswaing after a borehole was sunk in 1988/89 near the centre of the crater lake. The Tswaing meteorite crater lake is a small (0.07 km 2 ), shallow (maximum depth 2.1 m), alkaline (surface water pH varied from 9.6 to 10.3), meromictic lake with a Secchi disk transparency of between 6 and 12 cm. The lake had a distinct surface layer of cyanobacteria (Arthrospira fusiformis), located above a layer of purple sulphur bacteria, that was located, in turn, above a layer of green sulphur bacteria. This is the fi rst report on the presence of sulphur bacteria in the lake. The absence of submerged and emergent aquatic macrophytes in the lake limits habitat diversity for attached diatoms in the littoral regions. Both the numbers of families and the density of the benthic invertebrates were very low. The dominant invertebrate groups present were Nematodes, Muscidae and Hydrophilidae. Seven macroinvertebrate families were recorded, fi ve of which are new to Lake Tswaing. In addition, the periphytic ciliate Blepharisma sp. was also observed for the fi rst time within the land/water contact zone of Lake Tswaing. Benthic diatoms were scarce and the dominant species present was Gyrosigma rautenbachiae, while Nitzschia quadrangula was the dominant planktonic diatom, previously not recorded in the main basin of the lake. The diatom species Nitzschia communis, although in low numbers, was also not reported in previous studies of Lake Tswaing.