Diver and artisanal fisherman Daniel Caniullán recalls with frustration the day he went to collect shellfish from a natural bank in northern Chile, only to find hundreds of the plumose anemones covering the seabed. “I found an anemone plague where there used to be locos [edible sea snails]. It is upsetting, because these are places we protect, where we feel safe,” says the Indigenous leader from the Guaitecas archipelago in northern Chilean Patagonia.

This invasive anemone species (Metridium senile), also known as the frilled anemone, is native to the Atlantic and North Pacific oceans. In 2005, a group of researchers, including marine biologist Vreni Häussermann, recordedM. senile for the first time in central Patagonia. In 2011 and 2015, its presence was confirmed in northern and southern Patagonia, respectively.

These anemones occupy large areas of the seabed, displacing species such as sponges, bivalves and barnacles. Experts are therefore concerned about the “devastating” impact this species could have on Chile’s marine ecosystems. In addition, there are warnings about the loss of commercially significant resources, such as the locos (Concholepas concholepas), red sea urchin (Loxechinus albus) and the giant barnacle (Austromegabalanus psittacus), on which artisanal fishing communities depend.

Häussermann, a principal investigator at San Sebastian University, explains that the anemone could have arrived in Chile in ballast water, used to stabilize ships when they are partially loaded or under different loading conditions. Upon arrival, the water is discharged into the ocean. In other words, ships that left the northern hemisphere with water from places where M. senile live transported this species to Chilean Patagonia.

“It is a fairly common dynamic that has caused many invasions around the world,” says the expert. In the 1970s, the scientific community began to examine the problem in detail, and it was not until 2004 that the International Convention for the Control and Management of Ships’ Ballast Water and Sediments was adopted. The agreement requires the 90 signatory countries, including Chile, to install filters or treatment systems for this water.

Although this measure seeks to prevent the introduction of more exotic species, the damage is already done in some regions. Häussermann estimates that M. senile larvae arrived in Chile in ballast water at the end of the 20th century. The species has also invaded the seas of Argentina and South Africa.

An ‘indestructible’ species

Häussermann explains that, in 2017, she saw a plumose anemone for the first time in the Comau Fjord in the Los Lagos region. Three years later, hundreds of thousands of individuals covered large areas of the seabed.

Like many species of anemones, the plumose anemone has characteristics that make it attractive to look at. It can grow up to 30 centimeters (almost 12 inches) tall, its base is wider than its column, its color ranges from creamy white to orange, and its numerous tentacles form a kind of feather on top of the column when it expands.

“It shows a wide range of thermal and saline tolerance, ideal for its individuals to thrive in areas such as Patagonia,” says Alejandro Pérez Matus, marine biologist and an academic at the Catholic University of Chile. M. senile can live in temperatures between 0 and 20 degrees Celsius (32 and 68 degrees Fahrenheit). In addition, it tolerates a wide range of salinities, ranging between 14.8 and 37.5 parts per thousand. In other words, it can live in brackish water, such as that found in areas where freshwater and saltwater mix, and also in water that is slightly more saline than the average ocean water. They are also “very resistant to disturbances.”

Its most amazing feature is that it has three forms of propagation, according to an article by Häussermann and colleagues from 2022. The first occurs in the adult stage. The species has been observed to spread when carried by detached algae or marine debris, or when disturbances remove it from the seabed.

The second way it propagates is via sexual reproduction, which occurs between summer and fall in the northern hemisphere, and has not yet been confirmed in Chile. In this process, planktonic larvae are produced, which live suspended in the water and form part of the plankton. Currents can carry them over long distances.

The third way is asexual reproduction. This occurs through movement during the adult phase and when the pedal disc or base of the anemone is lacerated, leaving behind small fragments that then grow and become identical specimens. “It is indestructible,” says Häussermann. “If you try to remove it manually, the pieces that remain can generate new anemones.”

It spreads quickly

Luis Henríquez-Antipa, senior researcher in the restocking and cultivation department at the Fisheries Development Institute (IFOP in Spanish) in Puerto Montt, points out that this species is an encrusting organism that sticks to practically any floating surface. In his opinion, buoys, abandoned boats, aquaculture infrastructure and mussel cultivation lines or mollusk cultivation ropes facilitate its spread.

For Häussermann, mussel farming lines are the most problematic structures. She explains that mussel (Mytilus chilensis) producers, to cite one example of the species produced using this mechanism, unintentionally purchase ropes with larvae and then transfer them to sea farms where they are installed for the mollusks to grow. “They are not only transporting mussels, but other species as well. That is how I think it got to Comau,” says the scientist, who has studied this fjord for more than 20 years.

Today, it is found throughout Chilean Patagonia, from the shores of Puerto Montt to the Beagle Channel at the southern tip of the country.

In 2024, Pérez Matus was part of an expedition to the Melimoyu Reserve in northern Patagonia, where he says he observed that, in some places, the plumose anemone covered 100% of the rocky substrate. Three years earlier, the species had not yet been recorded. In Caleta Manzano, also in the north of the region, Henríquez-Antipa says he observed that hundreds of specimens of M. senile were suffocating a bed of cholga mussels (Aulacomya atra) on which they were spreading. “It sticks very strongly, like a rubber covering the entire seabed and the species beneath it,” explains the IFOP expert.

Häussermann says she believes that ecosystems weakened by pollution from salmon farms and other threats are more vulnerable to colonization by this anemone. “A balanced ecosystem is more resistant to invaders than an altered ecosystem,” she says.

Impacts on biodiversity and artisanal fisheries

Once established, it forms dense, carpet-like colonies that suffocate the seabed, displacing other species in the area. A study led by scientist Carlos Molinet of Austral University of Chile analyzed changes in ecosystems and biodiversity in the presence of M. senile in the Chacao Channel, north of Chiloé Island.

The research found that the invasive anemone increased its coverage by 39% between 2016, when it was first recorded, and 2021, the date of the study. The team of scientists also found that species diversity on the seabed declined dramatically. The Shannon diversity index, which measures the number of species and evenness of their distribution in a habitat, fell from 1.43, or moderate diversity, to 0.016, which points towards no diversity and only one dominant species.

Häussermann points out that everything that lives on the benthos or at the bottom of aquatic ecosystems can be affected. The plumose anemone not only occupies space and displaces multiple species, but also feeds on a variety of elements, including algae and planktonic larvae, preventing the reproduction of crustaceans, mollusks and even cold-water corals.

When diving in the affected areas, the landscapes look different. The diversity of shapes and colors characteristic of Chilean Patagonia is being replaced by the monotony of plumose anemone carpets, says diver and fisher Caniullán.

Research led by Molinet confirmed that the density and size of red sea urchin (Loxechinus albus) patches decreased significantly between 2019 and 2021.

Caniullán says that artisanal shellfish fishers are concerned, as sea urchins are the marine species of the greatest commercial interest in the region. “In the last two years, we have not been able to meet our quotas for the season,” he says, referring to the decline in both quantity and quality of the product.

Other commercially important species are also being displaced, including piures (Pyura chilensis), several species of oysters, mussels and cholga mussels. Henríquez-Antipa points out that this translates into trophic disruption at several levels, which can trigger a major imbalance in marine ecosystems.

This situation hits those from the local communities who have no other job opportunities. “Not everyone can work in salmon farms or public offices. Many see that it is no longer profitable to continue with artisanal fishing,” says Caniullán, who is also a recognized Indigenous leader. In some localities, fishers are reportedly selling their boats.

An uncontrolled threat

Chile’s Undersecretary of Fisheries (Subpesca) is responsible for formally declaring M. senile a pest, but has not yet done so, according to information from the communications department of the National Fisheries Service (Sernapesca). Therefore, Chile does not have an official strategy to contain or eradicate the invasion. IFOP is currently gathering information so that Subpesca can take action.

Caniullán says that Subpesca set up benthic committees in different regions with the aim of involving fishers, divers and shellfish gatherers in the design of management plans for fisheries. However, after the first period, between 2020 and 2025, the institution has not called for new members. For the Indigenous leader, this abandoned strategy, if reactivated, could support the surveillance, monitoring and control of the exotic species. Mongabay Latam asked Subpesca why it had not reactivated the committees, but did not receive a response before the publication of this article in Spanish in May.

Scientists have conducted experimental trials with nudibranchs — mollusks that feed on anemones — but they are not viable. “Tons of nudibranchs would have to be released, and that would be another invasion,” Häussermann says.

Henríquez-Antipa says that Molinet is leading research that suggests that cholga mussel reefs could play a role in structuring the ecosystem, limiting the spread of plumose anemones.

Pérez Matus and Häussermann agree that monitoring programs should be established. The marine biologist from the Catholic University of Chile emphasizes that protecting Patagonia’s marine ecosystems is key, as they are reservoirs of biodiversity and carbon sinks. He also says he believes that restrictions should be imposed on the transport of benthic invertebrates and, above all, that mollusk farming should be avoided in protected areas.

Despite the severity of the situation, there is some hope. “The encouraging part is that we have local capacity to research and understand the impact on the area,” Henríquez-Antipa says.

Banner image: An anemone of the species M. senile grows amidst a bed of mollusks. Image courtesy of Luis Henríquez-Antipa / IFOP.

This article was first published in Spanish on May 15, 2025.

Citations:

Häussermann, V., Molinet, C., Gómez, M.D., Försterra, G., Henríquez, J., … Mena, D.S. (2022). Recent massive invasions of the circumboreal sea anemone Metridium senile in North and South Patagonia. Biological Invasions, 24, 3665-74. doi:10.1007/s10530-022-02878-4

Molinet, C., Häussermann, V., Astorga, M., Barahona, N., Espinoza, K., … Soto, D. (2022). Population expansion of the invasive sea anemone Metridium senile in the spatial mesoscale of a sea urchin bed in north-western Patagonia. Springer Nature, 25, 1101-18. doi:10.1007/s10530-022-02965-6