Marine epilithic diatom abundance and species richness are highly variable along the South African coastline. To determine the variability in spatial diversity and benthic–pelagic​ exchanges, we conducted a baseline study of the Bird Island ecosystem in Algoa Bay. Diatom samples were collected from the rocky substrate and the adjacent water column in conjunction with physico-chemical variables at five localities around the island. Species belonging to Achnanthes, Cocconeis, Licmophora and Navicula genera were found to be widely distributed around the island. Diatom species abundance and diversity varied around the island and a dominance of typically benthic species in the surf zone, coupled with a low abundance of truly planktonic species, was evident. The low number of planktonic diatoms in the water column and their absence in benthic samples in this study suggests an intertidal system driven largely by benthic diatoms. Elevated dissolved inorganic nitrogen (DIN), indicative of the guano influence from resident seabirds, along with temperature and turbidity, influenced the observed diatom composition and distribution. This study reveals an interplay between benthic and planktonic diatoms in the nearshore environment providing some insight into their contribution to the intertidal and subtidal food web. It further provides important information for future comparisons of benthic diatoms on Bird Island in light of their ecological indicator properties under global environmental change scenarios for this region.

沿南非海岸线，海洋表层硅藻的丰度和物种丰富度变化很大。为了确定空间多样性和底栖-上层交换的可变性，我们对Algoa湾的Bird Island生态系统进行了基线研究。从岩石基底和邻近的水柱中收集了硅藻样品，并结合了该岛周围五个地点的理化变量。属于Achnanthes，Cocconeis，Licmophora和Navicula的物种发现属在岛上广泛分布。硅藻物种的丰富度和多样性在岛上各不相同，并且在冲浪区中典型的底栖生物占优势，加上真正的浮游生物的丰富度很低。在这项研究中，水柱中的浮游硅藻数量很少，而在底栖样品中却没有这种现象，这表明潮汐系统主要由底栖硅藻驱动。升高的溶解性无机氮（DIN）表示常驻海鸟对鸟粪的影响，以及温度和浊度影响了观察到的硅藻的组成和分布。这项研究揭示了底栖硅藻和浮游硅藻在近岸环境中的相互作用，从而为它们对潮间带和潮间带食物网的贡献提供了一些见识。