Austral winter marine epilithic diatoms: Community composition and distribution on intertidal rocky substrate around the coast of South Africa

The knowledge on the composition and spatial distribution of marine benthic diatoms around the coast of South Africa remains limited. Epilithic diatom assemblages from natural intertidal rocky substrate and physicochemical variables were investigated during July-August in 2016 and 2017 along the South African coastline. A total of 85 diatom taxa from 31 genera were observed at 15 sites along the coast. Taxa with the highest contribution included Nitzschia (9 species), Cocconeis (7 species) and Achnanthes (6 species) and the observed Shannon-Wiener diversity (H') during the study varied from 0.44 (Kraalbaai) to 2.09 (Bird Island). Non-metric multidimensional scaling ordination (nMDS) separated the diatom assemblages into three groups with 20% similarity among sites (grouped according to coastal sections) and PERMANOVA analysis revealed a significant difference between the coastal sections. The observed diatom composition was shown to be influenced by both nutrient concentrations along the west coast and temperature along the east coast. This study provides insights on the abundance and distribution patterns of marine littoral diatoms along the coastline and the potential environmental drivers. The observed variations in diatom composition and distribution warrant further investigations if they are to be considered as potential indicator species of change.