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An unprecedented discovery made in Acre during the extreme drought of 2024 surprised scientists and raised an alert about the impacts of climate change in the Amazon. For the first time, researchers have identified reef-like formations, previously typical of the marine environment, in an Amazon river.
The structures were found in the Muru River and described in a study published in the scientific journal Amazon Actbased on research conducted by National Amazon Research Institute (Inpa). The original report is from the website
The so-called “reefs” are formed by dense aggregations of freshwater oysters Bartlettia stefanensisattached to natural limestone platforms known as calcrete, which were exposed with the drastic drop in the river level.
Unexpected discovery amid drought
The find occurred in August 2024, at the height of the drought, when river levels were exceptionally low. It was in this scenario that the researchers noticed something unusual: extensive areas covered in shells, forming continuous structures similar to marine oyster beds.
According to the biologist Fábio Olmoslead author of the study, the discovery was completely unexpected.
“When I saw that, I thought: what is this doing here?” reported the researcher, who has experience with coastal ecosystems.
Until then, this species was known to live hidden in submerged cavities or on the banks of rivers, which made observation difficult. The formation of reef structures in freshwater has never been documented in the Amazon.
During the expedition, researchers found areas more than 20 meters long covered in shells, in addition to the presence of other species of molluscs.
The formations also attracted birds such as the great cowbird and jacana, which fed there — indicating that these “reefs” function as important microhabitats for fauna.
Furthermore, oysters play a relevant ecological role: they depend on fish to complete their life cycle and, at the same time, help create environments that shelter other aquatic organisms.
The discovery is directly linked to the severe drought that hit Acre in 2024. Data from National Water Agency (ANA) indicate that the state faced a period of “exceptional drought” between August and October of that year.
Oysters were also found/Photo: Reproduction
This extreme scenario not only revealed the phenomenon, but also exposed a problem: many of the oysters found were dead or in the process of dying, possibly due to adverse environmental conditions.
Experts warn that the intensification of extreme weather events — worsened by deforestation — could compromise the survival of the species.
According to the environmental engineer Gabriel Caramthe discovery is as relevant as it is worrying.
“Environments that were previously inaccessible are more exposed, increasing the risk of loss of species even before they are fully known by science,” he highlighted.
Although the discovery expands the known area of occurrence of the species, this does not mean greater security. THE Bartlettia stefanensis It has already been classified as vulnerable in Brazil and today appears as “insufficient data” in national assessments, as well as “almost threatened” in international lists.
The researchers warn that the repetition of severe droughts could make it difficult for these populations to recover and even lead to the definitive loss of habitats.
The revelation of the Amazon “reefs”, therefore, goes beyond scientific curiosity: it exposes an ecosystem that is still little known — and increasingly threatened before it is even fully understood.
