The diatom types of M. Giffen from Kidd’s Beach, Eastern Cape, South Africa

Abstract

Marine littoral diatoms are rarely studied and are important in the littoral zone ecosystem. Diatoms contribute to numerous aquatic ecosystem functions including: primary productivity, sediment binding, and stability. There is relatively little taxonomic work related to marine littoral diatoms, especially in South Africa (SA). Malcolm Giffen was one of the pioneers in this field of study and described many marine littoral diatoms taxa in South Africa. Giffen collected 10 marine littoral diatom samples from the Kidd's Beach area between 1946 and 1963. These were documented with line diagrams which could be potentially misinterpreted. Recently several of Giffen's taxa have been reexamined; however, this research is restricted mostly to the West Coast of South Africa. For this reason, this present project focus on taxa that he described from Kidd's Beach in the Eastern Cape. Of the 10 marine littoral diatom samples Giffen had collected from Kidd's Beach area, 8 were used to describe 27 new diatom species. Twenty-six of these taxa were documented with light microscopy and 23 with electron microscopy. Taxa were evaluated, descriptions emended and some were re-described or transferred to more appropriate genera, based on morphological characteristics observed with LM and SEM. After examinations of the SEM micrographs, 8 of the 27 species were transferred to more appropriate genera (Niztschia erosa to Entomoneis erosa; Amphiprora galerita to Entomoneis galerita; Navicula pragmatica to Fallacia pragmatica; Stauroneis exilissima to Olifantiella exilissima; Navicula pseudogamma to Moreneis pseudogamma; Amphora tenellula to Seminavis tenellula; Opephora perlonga to Tabularia perlonga and Opephora perlonga var. clavata to Tabularia perlonga var. clavata). One status change Petroneis capensis (synonym: Navicula humerosa f. capensis) was also made after the examination of the cell morphology under SEM. Additionally, the 8 sites as described by Giffen were re-sampled in October of 2018 and October 2019, to determine if any temporal changes occurred during the past circa 57 years. DCA bi-plots were used to illustrate the temporal changes of the two re-sampled years also comparing these samples with those collected by Giffen. Physico-chemical data were also measured in 2019 to determine if there was any external driving factor influencing the diatom community at Kidd's Beach. A CCA bi-plot was used to present the influence of the physicochemical variables on the diatom community. From the DCA bi-plots, it was apparent that the diatom community structure in 2018 was remarkably different from the diatom community structure sampled by Giffen. However, the diatom community structure in 2019 was in some respects more similar to the diatom community structure sampled by Giffen. It was found that there was no direct external factor influencing the diatom community and that the main internal driving factor determining community structure is salinity. The resampling of the 8 sites in question only yielded 6 of the 27 taxa described as new by Giffen. From these results, it was clear that the diatom community at Kidd's Beach is constantly in flux and that the resampling at original sites where type material was collected is not guaranteed to contain the species in question, therefore, the preservation, maintenance and documentation of extant types is of the utmost importance.