Some of Tanzania’s most important coral reef ecosystems are already suffering devastating impacts from climate change with severe consequences for nature, fish, tourism, and people’s livelihoods.

Global leaders, scientists, and environmentalists recently gathered in Mombasa for the global Our Ocean Conference, being held in Africa for the first time. On the agenda was the effect rising sea temperatures are having on vital underwater habitats.

Our partner Wild Impact, who attended the conference, run their Oceans Without Borders programme to protect and restore coral reefs in Tanzania. Recent monitoring around Mnemba Island in Zanzibar revealed the growing scale of climate-driven coral bleaching (the process that results in corals losing colour and becoming more vulnerable to disease) across the Western Indian Ocean. Sea temperatures around the island reached as high as 31°C at depths of 30 metres in early 2024, triggering one of the most severe coral bleaching events ever recorded.

Wild Impact have recorded coral mortality rates of between 60% and 70%, with some branching coral species suffering losses of up to 80%.

As reefs decline, fish populations fall, coastal protection weakens, and communities that depend on fishing and tourism face increasing economic hardship.

The consequences extend far beyond the reef itself however. As coral dies, fish that depend directly on live coral, particularly butterfly fish, are often the first to disappear. The loss of coral also removes vital shelter and nursery habitat for young reef fish such as damselfish, wrasses, and parrotfish, leading to an inevitable decline in their populations. As these smaller fish become less abundant, larger predators, including groupers, snappers, and trevallies, also decline, triggering a ripple effect throughout the marine food web.

“The reefs are telling us something important. We are seeing ecosystems under immense stress from temperatures that would have been considered extraordinary just a few years ago. Communities across East Africa are already feeling the impacts through declining fisheries and threats to tourism livelihoods. The decisions taken by governments, investors, and conservation leaders will help determine whether these ecosystems have a realistic chance of recovery.” – Dr Camilla Floros, Scientific and Programme Lead at Wild Impact