Number of exotic mollusk species in Brazil increases 215% in 15 years

The number of exotic (non-native) mollusc species found in Brazil has increased from 26 to 82 over the past 15 years, according to the first national-scale inventory ever produced on these organisms in the country.

Of these, 20 are considered invasive — that is, capable of causing ecological, socioeconomic, or health damage — including the golden mussel and the African giant snail. The complete list includes terrestrial, aquatic (freshwater), and marine (saltwater) organisms.

"We observed an accelerated rate of introduction of non-native molluscs in Brazil and persistent gaps in taxonomic and ecological knowledge of these species," says Marcel Sabino Miranda, who participated in the study during a postdoctoral fellowship at the Oceanographic Institute of USP (University of São Paulo), funded by Fapesp.

The study, published in April in the journal Biological Invasions, was led by Fabrizio Marcondes Machado, from the Institute of Biology at Unicamp (State University of Campinas), in collaboration with scientists from various institutions and Brazilian states.

The authors highlight the urgent need to strengthen biosecurity measures and early detection efforts, as well as to establish long-term monitoring programs across all environments. They also argue that, where impacts exist, their nature and magnitude should be properly defined.

"Some species are quite problematic, such as the golden mussel and the African giant snail, but for most of them we don't know whether they are causing any harm or may do so in the future," says Miranda, who is currently completing a postdoctoral fellowship at the University of Alabama in the United States.

The golden mussel (Limnoperna fortunei) likely arrived in Brazil in the early 1990s, following a long trail of invasions from China. Widespread across South America, it causes blockages and efficiency losses at hydroelectric plants, among other problems. Despite being the target of a control plan, the mollusc continues to thrive. It is estimated that around US$ 10 million (approximately R$ 51 million) has already been spent to combat it in Brazil.

The African giant snail (Lissachatina fulica), in turn, was introduced into the country as an alternative to escargot, but its cultivation was abandoned and today it is spread throughout the territory. It can be an agricultural pest, as well as an intermediate host for a parasite that causes meningitis — the nematode Angiostrongylus cantonensis.

According to the researchers, there is little information about invasive molluscs in Brazil, despite biological invasions being identified as one of the main threats to biodiversity protection worldwide. In Brazil, the predominant focus has been on fish, arthropods (insects), and mammals.

Sea, rivers, and land

The survey also lists 13 species whose origin could not be determined, known as cryptogenic species. The caution in classification arises from the fact that many species descriptions are old and lack biogeographic or molecular studies to reliably determine their origin — that is, whether they are native to Brazil or not. The terminology avoids confusion such as that which arose regarding the mussel species Perna perna, for example.

Present along the entire Brazilian coastline and farmed for human consumption, Perna perna has previously been identified as having been introduced into the country by human activity, since it also occurs in Africa, the species' region of origin. According to this version of events, the species would have arrived in Brazil in the 16th century during the Age of Sail.

Subsequently, however, archaeological and molecular studies indicated that a population of the species, separated 2,000 years ago from the African lineage, had already been present in Brazil even before the arrival of the Portuguese in 1500. The species, therefore, is native to South America and was not introduced by human action, as had previously been thought.

Non-native species are distributed across three types of environments. There are 32 marine and estuarine species, along with four cryptogenic ones. In freshwater environments, which include rivers, lakes, and ponds, there are 17 non-native species and no cryptogenic ones. Among terrestrial species, 33 non-native and nine cryptogenic species have been documented.

They were also classified according to guidelines from the Ministry of Environment and Climate Change and the Environmental Impact Classification for Alien Taxa of the International Union for Conservation of Nature, known by the acronym IUCN.

"Contained non-native" species, for example, are those with restricted propagation (such as in captivity) or under control within a given geographic area.

In the "detected" category are those present in the environment but with isolated occurrences and no evidence of population growth that has resulted in establishment or spread.

"Established" species are those that complete their life cycle in the natural environment and show signs of population growth, but with no apparent negative impacts.

"Invasive" species are non-native species already established in national territory that cause some ecological, socioeconomic, or health-related impact.

Finally, the "data deficient" category includes those with evidence of a native population but without sufficient information to determine their identity or level of impact.

"Most of them we have only detected — we don't have much information. Ideally, major studies and policies should be carried out to assess the possible impacts and develop plans to contain or eradicate the species that cause harm. A study like this, however, is an important first step in that direction," says Miranda.