Off the coast of Mozambique, landscapes submerged thousands of years ago now shelter an astonishing variety of marine life.
In the Bazaruto Archipelago, researchers have discovered reefs that resemble coral reefs but are not built by corals. Their foundation consists of a much older material: peat, formed by plants that once grew on land.
Photographs comparing peat reefs and coral reefs in the Bazaruto Archipelago. The submerged peat deposits support a diverse array of marine life.
Source: Scientific Reports (2026), figure 2, CC BY 4.0.
We need to go back several thousand years to understand their origin. At that time, part of the coastline was covered by forests and wetlands. In these wet areas, dead plants accumulated in the soil without fully decomposing. Over time, they formed carbon-rich layers of peat.
Then the sea advanced. Ancient soils were covered by water, before erosion and shifting sands exposed some of their deposits. The researchers dated peat samples: their ages range from approximately 300 to 5,000 years.
These remnants of terrestrial landscapes have become genuine underwater refuges. Hardened peat forms ridges, holes and cracks amid often sandy areas. Fish can hide there, while sponges, algae and other small animals find surfaces on which to settle.
Map and diagrams tracing the submergence of former areas of vegetation in the Bazaruto Archipelago.
Source: Scientific Reports (2026), figure 1, DOI 10.1038/s41598-026-65430-7.
The researchers compared these formations with nearby coral reefs. They discovered that they also hosted numerous species, but not exactly the same ones. Some juvenile fish found on these peat reefs belong to species also encountered near corals.
The difference lies in how the reef is built. Corals gradually construct limestone structures through their animal colonies. Here, reef-building corals are not needed: an ancient vegetated soil directly provides a solid surface for marine life. Scientists therefore refer to them as “peat reefs.”
This peat also contains a great deal of carbon, sometimes up to 40% of its dry mass in the samples analyzed. However, the researchers have not yet measured the total amount of carbon stored throughout these reefs. They therefore cannot say precisely what role these formations play in the oceans’ climate balance.
The discovery mainly shows that an ancient terrestrial environment can acquire a new function after being submerged. This is not a forest still standing underwater, but rather its deposits transformed into a marine habitat. The team is now trying to determine whether other coastlines also contain these reefs, which went unnoticed for so long.