Like many introduced species, lionfish in the Atlantic don’t face natural population control mechanisms such as predation, disease and parasitism that limit their numbers in the Indo-Pacific. A 2011 study found that lionfish on reefs in the Bahamas were larger and more abundant than their Pacific counterparts.

Lionfish thrive in many marine habitats, from mangroves and seagrass beds to deepwater reefs and shipwrecks. They are aggressive, persistent hunters that feed on smaller fish, including species that keep coral reefs clean and others that are food for important commercial species like snappers and groupers. In a 2008 study, when lionfish appeared on reefs in the Bahamas, populations of small juvenile reef fish declined by 80% within five weeks.

Brazil’s northeast coast, with its rich artisanal fishing activity, stands on the front line of this invasive threat. Lionfish are present in coastal mangrove forests and estuaries – brackish water bodies where rivers meet the sea. These areas serve as nurseries for important commercial fish species. Losing them would increase the risk of hunger in a region that is already grappling with substantial social inequality.

Fishers also face the threat of lionfish stings, which are not lethal to humans but can cause painful wounds that may require medical treatment.

Biological invasions are easiest to control in early stages, when the invader population is still growing slowly. However, Brazil has been slow to react to the lionfish incursion.

The equatorial southwestern Atlantic, where the invasion is taking place, has been less thoroughly surveyed than the Caribbean. There has been little high-resolution seabed mapping, which would help scientists identifying potential lionfish habitats and anticipate where lionfish might spread next or concentrate their populations. Understanding of the scale of the invasion is largely based on estimates, which likely underrepresent its true extent.

Moreover, turbid waters along much of Brazil’s coast make it hard for scientists to monitor and document the invasion. Despite their distinctive appearance, lionfish are difficult to spot and record in murky water, which makes it challenging for scientists, divers and fishers to keep an accurate record of their spread.

Still another factor is that from 2018 through 2022, under former President Jair Bolsonaro, Brazil’s government sharply cut the national science budget, reducing funding for field surveys. The COVID-19 pandemic further reduced field research because of lockdowns and social distancing measures.

Brazil has a history of inadequately monitoring for early detection of marine invasions. The lionfish is no exception. Actions thus far have been reactive and often initiated too late to be fully effective.

As one of many Brazilian scientists who warned repeatedly about a potential lionfish invasion over the past decade, I’m disheartened that my country missed the window to take early action. Now, however, marine researchers and local communities are stepping up.

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