Planktonic needle-shaped Nitzschia species from Lake Victoria, Africa, revisited

Abstract

Thin needle-shaped species of Nitzschia Hassall were found to form a key component of the diatom plankton in the deep Kenyan waters of Lake Victoria. An attempt was made to classify the six most common Nitzschia species of this growth form type on the basis of morphology, although they exhibit only small differences. Nitzschia lacustris Hustedt, previously described from Lake Victoria, was confirmed and recorded as an essential element of the phytoplankton. Three species were close to N. bacata Hustedt, N. graciliformis Lange-Bertalot & Simonsen and N. nyassensis O. Müller, but could not be definitively identified due to specific morphological deviations from the original descriptions, such as the overall size range, striation density and valve outline. Nitzschia bacata and N. nyassensis have repeatedly been recorded from the East African Great Lakes. Two more taxa are proposed as new to science, N. kavirondoensis sp. nov. and N. rusingae sp. nov., since neither could be matched to descriptions of the existing nitzschielloid taxa around N. acicularis (Kützing) W. Smith. Their morphological features were documented by light and scanning electron microscopy and differentiated from similar taxa recorded from Africa and other parts of the world.

Keywords:

• Planktonic diatoms
• tropical lake
• morpho-taxonomy
• ultrastructure
• eutrophication
• Nitzschia kavirondoensis
• Nitzschia rusingae

Acknowledgements

The authors wish to thank Jared Babu, Ephraim Odada and the staff of Kenya Marine and Fisheries Research Institute for help in the field and laboratory analysis, Christine Cocquyt (Gent) for many useful hints concerning literature and the identification of African taxa, and Doris Gesierich (Innsbruck) for making helpful suggestions on the manuscript. Assistance in the graphics was provided by Philipp Tschaikner and Fabian Martin (Innsbruck). This study was funded by the Austrian Agency for International Cooperation in Education and Research (OeAD–GmbH) as part of the North–South Dialogue program with additional support from the University of Innsbruck, Kenya Marine and Fisheries Research Institute and private funds from the second author. We also acknowledge the useful support by several anonymous reviewers and editors given within the revisions of the manuscript.