Gabriel Akoko Juma
From rivers to oceans:
How climate change is reshaping southern Africa’s coastal food webs
Rivers do not end where they meet the sea. They carry water, sediment and nutrients far beyond their banks, shaping estuaries, coastal waters and the ocean systems that depend on them.
At the foundation of these systems are plankton, microscopic organisms that form the base of the marine food web and play a key role in regulating how carbon moves between land and sea.
Gabriel Akoko Juma, a finalist for the 2026 Jennifer Ward Oppenheimer Research Grant, is studying how climate change is altering this river–ocean connection across southern Africa.
His research focuses on four major river systems: the Zambezi, Limpopo, Tugela and Orange, which span a range of climatic zones from tropical catchments in the north to more temperate systems in the south.
Crucially, these rivers empty into two contrasting ocean systems: the warm Agulhas Current in the Indian Ocean and the cold Benguela Current in the Atlantic. Together, they offer a natural laboratory for understanding how climate-driven changes in rainfall and river flow propagate from land to sea.
As rainfall patterns shift and droughts and floods become more extreme, the flow of freshwater, sediment and nutrients to the coast is also changing. Juma is examining how this affects water quality, nutrient availability, plankton communities and carbon cycling in aquatic systems.
To track these changes over time, he is combining field sampling from river mouths and estuaries with 10 to 20 years of satellite observations, alongside computer modelling. This allows him to follow shifts from upper catchments all the way to coastal waters and to identify which parts of the river–ocean system is most sensitive to disruption.
These changes matter because shifts in plankton communities can ripple through entire food webs, affecting fish populations, coastal fisheries and the livelihoods that depend on them. To translate this science into practice, the research is intended to inform coastal and estuarine management approaches within regional frameworks such as the Southern African Development Community (SADC) and guidance from the Intergovernmental Oceanographic Commission.
The project also includes a strong capacity-building component. Working across South Africa, Mozambique and Namibia, it will support and train three master’s students in marine science and conservation.
Ultimately, the research aims to clarify how climate change is reshaping the biological foundations of southern Africa’s rivers and oceans—and what that means for ecosystems and the people who rely on them.
About the researcher
Dr. Gabriel Akoko Juma is a 33-year-old ecologist and researcher at the University of KwaZulu-Natal. His fascination with aquatic ecosystems began in his childhood, growing up near the River Nyando in Kenya. He would often watch the water flow and wonder where it eventually ended up, a simple curiosity that ultimately inspired his career to explore the connections between rivers, estuaries and the ocean.
His scientific approach was deeply shaped during his undergraduate studies at Chuka University. While assisting his mentor, Professor Adiel Magana, with field sampling in the River Tana, Juma asked if the river water was safe to drink. Instead of answering directly, his professor pointed to the aquatic insects they were collecting, explaining that the presence of mayflies indicated the water was likely less polluted. That moment was a revelation for Juma. He realised that living organisms could tell a more revealing story about the health of an ecosystem than a single chemical water sample.
Professor Magana went on to become his master’s supervisor, helping Juma secure a research project at the Kenya Marine and Fisheries Research Institute, which opened the door to the field of marine and coastal science, and encouraging him to always consider the broader ecological and societal context of his work.
Today, Juma is driven by the urgent need to address habitat degradation and the unsustainable use of Africa’s freshwater resources. He finds great hope in the rapid advancement of Earth observation technologies, satellite remote sensing and AI-assisted tools.
For Africa, where long-term observational infrastructure like research vessels is often limited, these technologies allow scientists to monitor ecosystems in near real-time, shifting conservation from a reactive approach to a proactive one. Through his research on plankton, the critical but poorly studied foundation of aquatic food webs, Juma aims to contribute a vital African perspective to a global scientific challenge and guide the sustainable management of the continent’s interconnected waters.
2026 Jennifer Ward Oppenheimer Research Grant finalist Gabriel Akoko Juma is studying how climate change impacts the vital plankton communities that connect southern Africa’s rivers to its oceans.