Invasive Anemone Continues Its Rapid Advance in Patagonia
Costa Humboldt warns about the expansion of Metridium senile in the channels and fjords of northern Patagonia.
This anemone, originally from the Northern Hemisphere, represents a growing threat to the benthic ecosystems of Chilean Patagonia and to commercially important species such as the sea urchin and the barnacle (picoroco).
During the scientific expedition conducted in April 2025, the Costa Humboldt team recorded high densities of the anemone Metridium senile in the Reñihué Fjord, reaching up to 1,236 individuals per square meter, with a general average of 248 individuals/m² across different sectors of this fjord. These data were obtained through benthic sampling using the standardized “photo-quadrat” method via autonomous diving, at depths up to 30 meters.
In contrast to the Reñihué Fjord, the presence of Metridium senile was not detected in the Palvitad Fjord, Desertores Islands, or on the continental coast up to Corcovado Bay, which opens a window of opportunity to prevent its expansion.
Based on these findings, it is relevant to establish a monitoring program that includes both the Palvitad Fjord and the Reñihué Fjord, in order to observe the potential advance of Metridium senile and develop management strategies to prevent its expansion into areas not yet colonized. Likewise, it is important to confirm the absence of this anemone in the Palvitad Fjord, as there are no previous studies specifically mentioning it, despite literature reporting its presence both north and south of the fjord. This is especially relevant considering that the literature describes this species as already present in the interior sea of Chiloé.
“These results reinforce the urgency of establishing permanent monitoring programs that allow us to anticipate the advance of this invasive species and design containment strategies before it reaches new areas. It is fundamental to develop prevention and adaptation actions, based on scientific evidence and collaborative work with local communities and authorities,” states Luciano Hiriart-Bertrand, Founder of Costa Humboldt.
Víctor Fuentes, leader of the Yene Purrun We environmental corporation of the Chaitén commune—an organization that requested the research from Costa Humboldt to identify and quantify the different taxonomic groups that make up the biodiversity of the continental coastal edge of the Chaitén commune—mentions: “The findings of this expedition mark a before and after: we now know which species need to be protected and the importance of establishing control and mitigation strategies. It is essential to continue the analyses to evaluate possible impacts of the invasive anemone on commercially valuable marine resources and on other species, such as cold-water corals. Collaborative work with local authorities, fishermen, indigenous communities, and organizations like Costa Humboldt are key to protecting these unique ecosystems, which are also a habitat for whales that visit the area every year.”
The plumose anemone, as it is commonly known, reproduces both sexually and asexually, which favors its rapid spread. Its high tolerance to a wide range of salinity, temperature, and substrates—from rocks to mollusk shells—makes it an especially resistant and difficult-to-eradicate species.
This invasive species alters trophic chains by modifying the feeding behavior of key species. It has been observed, for example, that in the presence of Metridium senile, the sea urchin (Loxechinus albus) significantly reduces its consumption of Macrocystis pyrifera (more commonly known as giant kelp or sargassum), which could generate cascading effects with serious ecological consequences, affecting native or even endemic species.
It is presumed that the Metridium senile anemone was introduced to Chile via ballast water from vessels originating in the Northern Hemisphere, a practice recognized as a source of marine biological invasions. This occurs when ships or vessels need to be balanced after being partially or unevenly loaded, for which the weight of water is used as compensation. Thus, vessels that left the Northern Hemisphere with water from places where Metridium senile inhabits transported it to Chilean Patagonia.
Despite the existence of The International Convention for the Control and Management of Ships’ Ballast Water and Sediments (2004), which requires safeguards in water transport, the risk persists. The absence of effective enforcement or complementary measures, as well as the lack of restrictions on the transport of benthic invertebrates from invaded areas to zones still free of this species, contribute to this anemone continuing to move towards other ecosystems where it is invasive.
Although the first report of Metridium senile in Chile was in 1904, its presence in central Patagonia was only confirmed in 2005. Since then, this invasive anemone has expanded its distribution southwards in Chile and Argentina.
“The proliferation of the invasive anemone Metridium senile on mussel beds can have a direct and negative effect on their feeding and growth, because by massively attaching to their shells, it obstructs the siphons and reduces the capacity to capture phytoplankton particles, potentially even generating low oxygen and low pH beneath their attachment discs. Furthermore, by covering the surface of the mussels or the rock, the slow movements of the anemone over the substrate have been shown to affect the recruitment of other species in the long term, compromising the regeneration of the bed and its long-term productivity. If this expansion continues, we could observe a progressive collapse of mussel populations in Patagonia, with serious economic consequences for local artisanal fishing and the loss of ecosystem services. Therefore, science must advance in monitoring using eDNA (environmental DNA), studies of benthic community dynamics, and the development of selective removal techniques to mitigate its impact,” mentions Javier Naretto, Co-founder of Costa Humboldt.
In addition to identifying the presence of M. senile, the Costa Humboldt expedition characterized part of the coastal biodiversity of the Chaitén commune, including continental zones, the Desertores Islands group, and the Reñihué and Palvitad fjords. For this, various sampling and recording methodologies were applied—including scientific diving, remote observation, visual identification, and sample collection—which allowed for an integral and comparative approach to the ecological complexity of these ecosystems. This characterization seeks to provide a baseline of knowledge for future conservation actions, environmental monitoring, and territorial management in these high-ecological-value sectors.
The results of the sampling and subsequent analysis of the data obtained in the expedition will be published shortly and disseminated by Costa Humboldt in various academic spaces and with local communities, so that different sectors become involved in addressing this problem that is already being experienced in various sectors of Patagonia with the presence of Metridium senile.
