The stealthy and increasingly persistent presence of an exotic species — the giant river prawn— in Brazil’s coastal ecosystems has been raising numerous alarms among scientists, fishers and environmental managers.
Introduced in the country in the late 20th century to supply the growing aquaculture industry, the prawn (Macrobrachium rosenbergii) is no longer limited to captive breeding. The species has established itself in extremely sensitive natural environments, including protected areas.
A study conducted by researchers from Brazil and Uruguay was published in February, revealing the extent of the problem and detailing the ecological and environmental risks associated with the giant prawn “invasion” — negative aspects that, according to experts, may intensify in the coming years.
Led by oceanographer Edison Barbieri, director of the São Paulo Fisheries Institute’s Southern Coast Regional Research Center, the work was driven by the scientific community’s growing concern regarding biological invasions in estuarine ecosystems. These systems, which also include mangroves, are located in areas of transition between rivers and the ocean and are widely recognized for their biodiversity.
Estuarine zones serve as nurseries for numerous aquatic species, including fish and crustaceans of ecological importance and economic potential. At the same time, these delicate transitional environments are susceptible to the introduction of exotic species, which then compete with native fauna for different vital resources.
According to Barbieri, the study — conducted between 2015 and 2025 — started from an observation: While the intrusive prawn had been seen in different regions of Brazil, there was no systematic monitoring in conservation areas. “Accidental or intentional introduction of species through aquaculture had already been observed, but we didn’t know how much it affected coastal conservation units,” he told Mongabay.
The work brought together a multidisciplinary team and combined different methodologies to map the occurrence of the species, assess its distribution and, above all, identify its potential impact on native fauna. “To do this, we employed four main approaches: Field sampling, participatory monitoring with small-scale fishers, consultation of databases, and scientific literature review,” Barbieri said.
Efforts focused on the Cananéia-Iguape-Comprida Island Estuarine-Lagoon Complex, in the far south of the state of São Paulo. That coastal area is listed by UNESCO as part of the Atlantic Forest Biosphere Reserve and as a Natural World Heritage Site, encompassing important points such as the Comprida Island EPA (Environmental Protection Area), which shelters restinga shrub, dunes, beaches and mangroves.
The relevance of that environmental complex was also recognized by the Ramsar Convention adopted in Iran in 1971. According to the Brazilian government, this intergovernmental treaty “establishes frameworks for national actions and cooperation between countries aimed at promoting the conservation and rational use of wetlands in the world.”
Barbieri said the presence of this exotic species in São Paulo’s biodiverse coast is significant and has resulted in substantial data. “From 2015 to 2025, in active collaboration with local fishers, we monitored the presence of the invasive prawn in the area. We recorded 68 unique occurrences of M. rosenbergii in 10 protected areas along the Brazilian coast.”
Most of these records (44) occurred in EPAs, where sustainable use of natural resources is permitted. However, some parts of these areas require full environmental protection, which increases the risks associated with the presence of the slim outlander prawn. “In the Cananéia estuary, for example, 90 individuals were captured over a decade of monitoring,” Barbieri said.
The easy reproduction of the giant river prawn in natural environments is, in itself, more worrying than its presence on the Brazilian coast. The study supported this by identifying ovigerous females — which carry fertilized eggs — and proving the occurrence of its reproductive cycle in the ecosystem. According to Barbieri, “this indicates that the species is not only surviving, but it’s also effectively established.”
Also important is the seasonal pattern observed in catches. The highest incidence of the invasive prawn occurs during warmer months, especially between spring and summer in Brazil, suggesting a direct connection between the occurrence of the crustaceans and water temperature. In a context of climate change, which makes ocean warming a global reality, the new ocean conditions may favor proliferation of the invasive species.
Study co-author Ernesto Brugnoli Olivera, professor of Oceanography and Marine Ecology at Uruguay’s Republica University, identified other characteristics that facilitate the prawn’s “successful” invasive journey: Its wide thermal tolerance and its ecological plasticity. “It’s a highly adaptable species that is able to survive in different salinity and temperature conditions, which facilitates its dispersal in estuarine and freshwater environments,” he said.
The origin of the invasion is directly linked to aquaculture activity.
Introduced in Brazil in the 1970s for commercial farming, the Malaysian prawn, as it is also known, started escaping from ponds and colonizing natural environments. Today, its distribution knows no borders: It has been recorded in both the North and South of the country.
The impacts are varied. Experts underscore the competition for food, shelter and space between the intruder and native species such as the Amazonian prawn (Macrobrachium amazonicum). According to conservationists, their battle may lead to smaller local populations and structural change in aquatic communities.
In addition, the outsider prawn is considered a vector for pathogens such as the white spot syndrome, caused by a dangerous virus that, in several parts of the world, has done significant damage to shrimp farming.
If these animals proliferate in natural environments, diseases that are difficult to manage may cause chain reactions in crustacean fauna.
The ecological effects also extend to the food chain: As an opportunistic predator, M. rosenbergii can alter trophic relations in estuarine ecosystems, affecting not only other crustaceans but also fish and smaller organisms. In the future, this could result in a potentially irreversible ecosystem imbalance, experts say.
