- The Sonneratia apetala plant is native to India, Bangladesh, Sri Lanka and Myanmar, yet biologists have found hundreds of specimens permeating the mangroves in the south of Brazil.
- Researchers believe the seeds were transported on ships from China and released at the port just 2 kilometers (1.6 miles) from the mangroves, where they were carried in the currents and rapidly spread.
- Experts warn that S. apetala could have severe ecological impacts, including the loss of biodiversity as it outcompetes native plants; they also fear it might spread to other mangroves.
- Since May 2023, researchers have been advocating for the total eradication of S. apetala in Brazil. However, Brazilian authorities only announced last month that they would remove the species, and the details of how this will be done have not yet been specified.
During a field trip in May 2023 to the Cubatão mangroves in the Brazilian state of São Paulo, a cluster of white flowers puzzled biologists Geraldo Eysink and Edmar Hatamura. They bloomed from trees unlike any they had ever seen in the area in 30 years of research. They gathered samples, and with the expertise of oceanographer and mangrove specialist Yara Schaeffer-Novelli, identified the plant as Sonneratia apetala, a species native to South Asian mangroves. It was the first time this species had been recorded anywhere in the Americas.
The significance of the discovery quickly became clear. S. apetala was an invasive species with the potential to wreak havoc on this ecosystem. Over the following months, Eysink and Hatamura found 80 more of these trees. Now, that number has soared past 250, with new specimens emerging each time they explore the mangroves.
“Mangroves are nurseries for many species of fish, crabs, oysters and mussels. If Sonneratia apetala spreads, it could harm the reproduction of all this fauna and the lives of more than 400,000 fisher-people along the Brazilian coast,” Eysink told Mongabay.
Native to India, Bangladesh, Sri Lanka and Myanmar, S. apetala was introduced to China in 1985 for mangrove restoration. Researchers believe it reached Brazil through ballast water from ships traveling from China to Santos Port, just 2 kilometers (1.2 miles) from the mangroves. Ballast water, used by ships for stability, is emptied when they load cargo, releasing foreign organisms into the surrounding ecosystem. It’s thought that the released ballast water carried the buoyant S. apetala seeds to the mangroves via estuary currents.
The plant is a fast-growing, highly adaptable species. A single tree can bear more than 2,000 apple-like fruits, each containing about 60 seeds. In a preliminary germination test conducted in a greenhouse, the survival rate of these seeds was found to be 14.7%, Eysink said.
“This viability is very high. It’s frightening — this seed is a monster,” Schaffer-Novelli said.
In China, S. apetala is present in about 95% of restored mangrove areas — an effort started in the 1990s to counter the 70% decline in mangroves since the 1960s. However, a 2023 study found that the species displaces local mangroves and stifles native growth. In Hong Kong’s Inner Deep Bay, the Agriculture, Fisheries and Conservation Department regularly removes S. apetala to protect native mangroves and maintain mudflats for waterbirds.
In São Paulo‘s Cubatão mangroves, these trees are four times taller than native species, reaching heights of up to 12 meters (39 feet), and experts warn their presence will cause serious environmental damage, both locally and in other mangroves.
“Exotic species in mangroves can have profound ecological and economic impacts, disrupting the restoration of native ecosystems,” according to a 2023 study authored by Eysink, Hatamura and Schaffer-Novelli. “The invasion of S. apetala in the Cubatão region’s mangroves could significantly alter the biological structure of these ecosystems and serve as a dispersal point for other areas.”
A setback for mangroves
The Cubatão mangrove is part of a 12,000-hectare (29,650-acre) expanse of mangroves in São Paulo’s Baixada Santista region, an area long affected by uncontrolled urban sprawl. In the 1970s, Cubatão was notorious as one of the most polluted marshes in the world.
Since 1994, Eysink and a team of biologists from the state’s environmental agency, CETESB, alongside local fishers, have been working to rehabilitate Cubatão, successfully restoring 1,200 hectares (2,965 acres). However, the recent discovery of the invasive S. apetala threatens this progress, as the species could displace native plants, undermining biodiversity in the region.
The researchers warned environmental authorities, including Brazil’s environmental agency, IBAMA, and the Forestry Foundation, of the S. apetala discovery in 2023. They also spoke with experts in the U.S. and China, who recommended the “urgent eradication of this species,” Eysink said, in order to protect native mangroves. According to Eysink, Hong Kong has been trying to remove this species for the last eight years without success.
More than a year after the first official recognition of the species in Brazil, the state’s Forestry Foundation announced in a statement released in August that, having assessed the scale of the problem alongside IBAMA and local researchers, they had contracted a company to remove the trees between August and November. The methods that will be used to remove the trees were not specified.
Since the mangroves are protected, IBAMA must authorize the removal of any trees in the region. They did not respond to Mongabay’s request for clarification on the removal of this species or if the removal process had started.
Eysink and Novelli have criticized the delay in authoritative actions to remove S. apetala, which they told Mongabay was likely down to not knowing how to deal with exotic species as well as a failure to internalize the problem that invasive species present. The Forestry Foundation claimed in a statement that the trees were first identified in February this year, failing to acknowledge the evidence of their discovery in May last year.
Scientists are concerned that if S. apetala is not removed quickly and completely, it could spread up the São Paulo coast and possibly beyond.
“[The seeds] keep spreading,” Schaffer-Novelli said. “The worst-case scenario is they go to Cananéia, a nearby mangrove and an estuary [in the state of São Paulo] recognized by UNESCO,” adding that the researchers are in contact with other scientists in the region, warning them to keep an eye out for unusual trees with white flowers.
Best removal methods
While experts stress that eradicating the species is the best bet for protecting the Cubatão mangroves against major losses in biodiversity, finding the most effective removal method is a challenge. Researchers in Brazil have carried out several tests on possible methodologies, which were discussed with experts in China.
They found that simply cutting down the trees was ineffective, as they quickly regrew. Girdling, which involves stripping the bark to stop nutrient flow, will eventually kill S. apetala, although this takes a few months. Another method is covering the cut stump with mud to prevent shoots from growing. Although effective, this approach is labor-intensive, as the tide often washes away the mud, requiring frequent reapplication.
According to the experts, the most effective method has been with chemicals.
“Of course, the use of chemicals is always questionable, especially if these products reach the water,” Eysink said. “[But] the results and efficiency of this method are greater than the impact of any drops of this product on the environment; a paradigm that needs to be accepted by environmental agencies.”
To minimize the risk of contamination, the researchers drilled the trunk of the species, injected it with the chemical and then sealed the holes. “Not a drop reached the water, even at high tide, because the holes were made above the high tide line. The results were fantastic,” Eysink said.
Researchers in Hong Kong have found similar results. According to a 2009 study, the most effective method involved cutting and covering stumps with mud to prevent regrowth, and although they found the herbicide glyphosate also to be effective, they cautioned against its use. “The application of herbicide should be avoided due to its uncertain impact to the native flora and fauna.”
Despite the researchers’ recommendations for using chemicals, the environmental agencies did not approve them. Eysink said that he and other researchers are exploring alternatives with IBAMA, including the use of specific herbicides as long as they don’t harm other species. But experts lament the delay and call for prompt action, emphasizing the need for immediate monitoring of mangroves and the swift eradication of invasive species as soon as they are identified.
“It would be a shame and a disgrace if we did not carry out this total eradication in Cubatão, because, in this way, [it] would become the supplier of new seeds, putting mangroves throughout Brazil at risk,” Eysink said.
The researchers also advocate for improved ways of emptying ballast water, as it can carry other harmful species such as mollusks and fish that may threaten Brazilian mangroves. They recommend an urgent inspection of other ports in Brazil to determine if similar issues are occurring.
According to Eysink, the presence of invasive species poses an immediate danger to Brazil’s vulnerable mangroves. “If this issue is not combated, the change and impoverishment of our biodiversity will be fatal.”
Citations:
Teng, Z., & Lin, X. (2024). Sediment nitrates reduction processes affected by non-native Sonneratia apetala plantation in South China. Science of The Total Environment, 906, 167523. doi:10.1016/j.scitotenv.2023.167523
Hu, Z., Wu, J., Wang, J., Zhang, Y., Zhou, H., Gao, C., … Wu, G. (2023). How exotic Sonneratia species affect the spatiotemporal dynamics of mangroves in Shenzhen Bay, China: A remote sensing perspective. Ecological Indicators, 153, 110479. doi:10.1016/j.ecolind.2023.110479
Eysink, G. G., Hatamura, E., & Schaffer-Novelli, Y. (2023). First occurrence in mangroves of South America of the exotic species Sonneratia apetala Buch.-Ham. from the Indo-Malayan region. Biota Neotropica, 23(4). doi:10.1590/1676-0611-bn-2023-1575
Schmiegelow, J. M., & Gianesella, S. M. (2014). Absence of zonation in a mangrove forest in southeastern Brazil. Brazilian Journal of Oceanography, 62(2), 117-131. doi:10.1590/s1679-87592014058806202
Tang, W. S. (2009). The distribution, ecology, potential impacts and management of exotic plants, Sonneratia apetala and S. caseolaris, in Hong Kong mangroves (Unpublished master’s thesis). City University of Hong Kong. https://scholars.cityu.edu.hk/en/theses/the-distribution-ecology-potential-impacts-and-management-of-exotic-plants-sonneratia-apetala-and-s-caseolaris-in-hong-kong-mangroves(84d89fcf-3be9-4000-8ebe-f3732c4051a0).html
Banner image: The Cubatão mangrove is part of a 12,000-hectare (29,653-acre) expanse of mangroves in São Paulo’s Baixada Santista region, an area that has been severely impacted by urban expansion and pollution for decades. Image courtesy of Edmar Hatamura.
FEEDBACK: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.