An overview of current knowledge on microalgae and macrophytes in South African estuaries, highlighting progress made and future research directions

Abstract

South Africa’s 3000 km coastline, 290 estuaries and high levels of biodiversity provide an outdoor laboratory for studies on microalgae and macrophytes. The history of botanical research on estuaries is presented, focusing on studies of primary producers, highlighting progress made since 2016. Published articles were organised in seven categories representing the dominant primary producers in estuaries. Research priorities were identified for each category based on the systematic review of literature from 2017 to January 2025, complemented by expert input on emerging trends and knowledge gaps. Invasive alien aquatic plants and forested wetlands (swamp forest) are emerging research themes. Early studies focussed on autecology and ecophysiology. More recently, research has addressed ecological status, drivers of biodiversity, provision of ecosystem services, responses to climate change and the restoration and management of Blue Carbon Ecosystems. Since 2016, 212 articles have been published on these emerging themes. In South Africa, we have a good understanding of primary producers as indicators of water quality changes in estuaries. Research has informed the implementation of Estuary Management Plans and the National Water Act, which guides estuary environmental flow requirements. Taxonomic studies on salt marsh plants to inform the National Biodiversity Assessment and using artificial intelligence and automation to provide real time monitoring of priority systems were identified as knowledge gaps. We have long term monitoring sites to measure responses to sea level rise, and to measure the growth and survival of mangroves across biogeographic zones. However, a growing concern is personal safety and security that impacts field work, constraining ecological research and the maintenance of long-term datasets that are needed to track future responses to global pressures. We are well positioned to inform global research and policy agendas such as the Kunming-Montreal Global Biodiversity Framework that aims to expand protection and restoration of coastal ecosystems to 30 % by 2030.