Diatom biodiversity and endemism in tropical Africa.

Ancient lakes are well known to possess a large number of endemic taxa. For Lake Baikal for instance 55 % of the 672 reported specific and infraspecific taxa are considered to be restricted to the lake. This high percentage is mainly due to the taxonomic research conducted the last decades. For Lake Tanganyika, 10 % of the about 500 reported taxa are endemic to the lake. Recent taxonomic revision of a couple of genera, e.g., Iconella, Surirella and Amphora, together with the actual species concept showed an increase in the number of the endemic taxa in the lake from 30 to 50. Beside the African Great Lakes, diatoms in tropical Africa have less attired the attention during the 20th century. Except at the beginning of the 1900 when material collected during the German “Nyassa-See und Kinga-Gebirgs-Expedition” was studied by Otto Müller from which he described more than 100 new diatom taxa. This material is the subject of re-investigation. The genera Cymatopleura, Iconella and Surirella, and Epithemia subgenus Rhopalodiella (formerly Rhopalodia “sippe” Eurhopalodiae) are accomplished; the study of Epithemia subgenus Rhopalodia, Placoneis and Nitzschia has been initiated. Afrocymbella, Actinellopsis (recently described from Zambia) and Epithemia subgenus Rhopalodiella have a distribution restricted to tropical Africa or to the African continent. In the frame of ecological and paleoecological projects, some taxonomic diatom investigations were undertaken in tropical East Africa and the Democratic Republic of the Congo. These studies have led among others to the description of three new diatom species (Afrocymbella barkeri, Nitzschia fabiennejansseniana and N. pseudoaequalis) from a small crater lake near Mount Kilimanjaro, and up to now only known from that lake. Since 2010 a diatom monitoring started in streams and rivers in central part the Democratic Republic of the Congo. First results showed that cosmopolitan species were found only in very polluted (eutrophicated) waters with Nitzschia palea as dominant species in the river Makiso, running through Kisangani, the third largest city of this country. On the other hand, less human impacted sites such as small rivers and streams in the Biosphere Reserve of Yangambi, 100 km north of Kisangani, showed many diatom unknown to science, or resembling species described from the Amazon basin (e.g., Encyonopsis frequentis, Eunotia enigmatica). However, in-depth study of each taxon is needed to know if a species is new to science, if it distribution is restricted to tropical African or if it has indeed a pantropical distribution. This led already to the description of eight diatom species, up to now only known from the Congo Basin. Because the small rivers and streams are acid in the Congo region, these taxa have not been found up to now in tropical East Africa where the waters are typical alkaline. However, we must remark that the description of the species is done on morphologic characteristics. It is the aim that genetic analyses should start soon, but the Nagoya protocol can slow down the progression. Cocquyt C. & Ryken E. 2016: Afrocymbella barkeri sp. nov. (Bacillariophut), a common phytoplankton component of Lake Challa, a deep crater lake in East Africa. – Eur. J. Phycol. 51: 217-225.Cocquyt C. & Ryken E. 2017. Two needle-shaped Nitzschia taxa from a deep Eats African crater lake. – Diatom Res. 32: 465-475. Cocquyt C., Kusber W.-H. & Jahn R. 2018. Epithemia hirudiniformis and related taxa within the subgenus Rhopalodiella subg. nov. in comparison to Epithemia subg. Rhopalodia stat. nov. (Bacillariophyceae) from East Africa. – Cryptog. Algol. 39: 35-62.Jahn R., Kusber W.-H. & Cocquyt C. 2017. Differentiating Iconella from Surirella (Bacillariophyceae): typifying four Ehrenberg names and a preliminary checklist of African taxa. – Phytokeys 82: 73-112.Taylor J.C., Karthick B., Kociolek J. P., Wetzel, C.E. & Cocquyt C. 2014. Actinellopsis murphyi gen. et spec. nov.: A new small celled freshwater diatom (Bacillariophyta, Eunotiales) from Zambia. – Phytotaxa 178: 128-137.

ISBN:978-3-946292-27-2

Publication year:2018