8,893 photographs. Six districts. Two marine parks. Combining our northern Dar es Salaam and southern coast benthic surveys under the USAID Heshimu Bahari programme produced the most detailed picture of Tanzania's underwater world ever created. Here is what the data showed and why it matters.
Most people who think about Tanzania's southern coast picture the beaches of Kilwa or the fishing boats of Mtwara. Very few have ever thought about what lies beneath — the seabed stretching down through the water column, hosting habitats that support the entire coastal food chain.
Between 2022 and 2024, under the USAID-funded Heshimu Bahari programme, we set out to document exactly that. Our task was to conduct a systematic benthic survey — a scientific mapping of the ocean floor — across four districts: Kibiti, Kilwa, Mafia, and Lindi. The survey covered both the Mafia Island Marine Park and the Mnazi Bay-Ruvuma Estuary Marine Park, as well as areas outside protected area boundaries.
The methodology was straightforward but demanding. We worked on a one-kilometre grid system, capturing high-resolution photographs of the seabed below 50 metres depth at each grid point. Every photograph was documented, uploaded to the Coral-Net platform, and annotated to identify what habitats were present — whether coral, seagrass, sand, rubble, or algae — and how healthy they were.
By the time the survey was complete, we had captured 6,737 seabed grids. That is the largest systematic benthic survey ever conducted in southern Tanzania.
What did we find? The data revealed a coastline of remarkable diversity — areas of healthy coral alongside zones showing clear signs of degradation, seagrass meadows of varying density, and habitats that had never been formally documented before. The data also showed clear patterns in where healthy habitats were concentrated and where threats were most severe.
This information is now in the hands of marine managers, government planners, and conservation partners. It is being used to improve how marine protected areas are managed, to identify where restoration efforts should be focused, and to build the scientific case for investment in the southern coast's blue economy.
Before this survey, decisions about southern Tanzania's marine resources were being made with very limited information. That has changed.
“Before this survey, decisions about southern Tanzania's marine resources were being made with very limited information. That has changed.”
Published by BlueGreen Tanzania
Field notes from our work across the Tanzanian coast.