DIATOM DIVERSITY IN HAUSBURG TARN, A GLACIAL LAKE ON MOUNT KENYA, EAST AFRICA

Abstract

The investigation of 30 fossil diatom samples found in a 500-year sediment record from Hausburg Tarn, a glacial lake located in the Alpine zone of Mount Kenya, revealed a diatom diversity of 57 specific and infraspecific taxa. Of the eight taxa (14% of total species diversity) with a distribution restricted to the African continent, two species (3.5%) are unique to Mount Kenya. These afro-alpine diatoms are: Pinnularia coei and Surirella coei. An earlier study on other alpine lakes of Mount Kenya, undertaken in the 1960's, reported two more endemic taxa, Navicula coei and N. kenyae, which were not observed in the Hausburg Tarn samples. A number of taxa could not be attributed to known diatom species and were referred to with the qualification cf, e.g. Navicula cf. brevissima, N. cf. pseudoventralis. Some of these are probably new to science, but a more thorough investigation will be needed to properly assess morphological variability within the species. The presence of four and possibly more endemic taxa on Mt. Kenya makes its diatom flora unique.

Although the most abundant taxa in Hausburg Tarn, Achnanthidium minutissimum and A. affine, and the major part of other recovered taxa have a cosmopolitan or palaeoarctic distribution, the recovered diatom flora has a distinct alpine and boreal character.

Besides a brief description, each taxon is depicted on a LM photograph. For a number of taxa SEM images are presented in addition. A description of the SEM features of the external and/or internal valve is also given for one of the endemic diatoms, Pinnularia coei, and for Achnanthidium kenyae, an Afroalpine taxon also reported from the Ruwenzori Mountains. Based on these observations a new combination was made for the latter: Achnanthidium kenyae (Cholnoky) Cocquyt comb nov.; basionym: Achnanthes kenyae Cholnoky.