Nitzschia fenestralis: A new diatom species abundant in the Holocene sediments of an eastern African crater lake

David Grady,David G Mann,Rosa Trobajo

doi:10.5507/fot.2019.011

Abstract

Nitzschia is common in the phytoplankton of several East African lakes. A new species, Nitzschia fenestralis, sp. nov. D. Grady, D.G. Mann et Trobajo was encountered at numerous depths in a 16 m sediment core from Lake Babogaya, Ethiopia and is described using light and scanning electron microscopy. It is compared with several other morphologically similar taxa described from East and Central Africa (especially N. aequalis, N. mediocris, N. obsoleta and N. fabiennejansseniana), and from Europe (N. fruticosa). An unusual feature of some of these species (N. fenestralis, N. obsoleta and N. fabiennejansseniana) is that in the raphe canal each stria is represented by two narrower areolae (alternatively interpreted as a single subdivided areola). It is this feature that suggested the name of the new species (through the resemblance to a series of sash windows). Another characteristic of N. fenestralis and N. obsoleta, apparently never reported previously in any diatom, is that the more advalvar bands end approximately halfway along the frustules, rather than at the poles. In most respects (shape and size, stria and fibula densities, valve and girdle structure), N. fenestralis and N. obsoleta are very similar, but confusion is unlikely because they differ in whether central raphe endings are present (N. fenestralis) or absent (N. obsoleta). In Nitzschia fenestralis, and perhaps to a lesser extent in N. obsoleta, the striae usually become strongly radiate towards the poles. A preliminary assessment, based on the literature, suggests that N. fabiennejansseniana may be synonymous with N. obsoleta, which was described earlier.

Highlights

Lake sedimentary archives have long been recognized, and regularly used, as the principal source of information in reconstructing the past climate and environments of tropical Africa (Verschuren 2003)
The abundance of Nitzschia in modern eastern African assemblages is well documented from surveys in lakes Kivu (Sarmento et al 2006), Victoria (Kling et al 2001; Stager et al 2009) and Tanganyika (Cocquyt & Vyverman 2005), and more generally across the continent (Gasse 1986; Mills & Ryves 2012)
Recent palaeolimnological analyses conducted at an eastern African crater lake, Lake Babogaya (Grady et al in prep.), have revealed another example of Nitzschia dominance (100% of total diatom abundance in some samples) in assemblages through the last 5,000 years of the Holocene

Summary

Introduction

Lake sedimentary archives have long been recognized, and regularly used, as the principal source of information in reconstructing the past climate and environments of tropical Africa (Verschuren 2003). The abundance of Nitzschia in modern eastern African assemblages is well documented from surveys in lakes Kivu (Sarmento et al 2006), Victoria (Kling et al 2001; Stager et al 2009) and Tanganyika (Cocquyt & Vyverman 2005), and more generally across the continent (Gasse 1986; Mills & Ryves 2012). Their importance has been documented in fossil assemblages. High abundances of Nitzschia spp. have been a feature in the flora of Lake Victoria for 10,000–11,400 years (Stager et al 1997; 2003) and for the past 25,000 years in Lake Challa (Milne 2007; Wolff et al 2014)

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