Researchers from Conicet and the Universidad Nacional del Comahue confirmed the presence of the freshwater jellyfish Craspedacusta sowerbii in the Escondido and El Trébol lakes, near San Carlos de Bariloche.
Originally from the Yangtze River in China, this species, typically found in warm waters, has managed to adapt to temperate-cold Andean-Patagonian environments, a phenomenon never before documented in the region.
The discovery, published in the journal Desde la Patagonia in 2025, marks a scientific milestone and adds a new challenge for the conservation of local biodiversity.
The global expansion of Craspedacusta sowerbii
The jellyfish began its expansion in the 19th century, first in Europe and then in America, favored by the trade of aquatic plants and animals and passive transport through birds and fish. Today it is considered a cosmopolitan species, present on all continents except Antarctica.
Its success depends on its ability to survive the “journey,” adapt to new conditions, and reproduce. In Patagonia, the species has shown a surprising ability to overcome geographical and climatic barriers.
Pioneering study in Bariloche
The research team —Sharon Allen Dohle, Mariana Reissig, Patricia García, and María del Carmen Diéguez— analyzed the presence, abundance, size, distribution, and diet of the medusa phase in Escondido Lake.
- 33 sampling points were surveyed with plankton nets.
- Jellyfish were captured ranging from 4 to 67 specimens per cubic meter, with an average of 24.
- The average size was 7.1 mm, with specimens up to 12 mm.
- The diet consists of 96.6% Bosmina crustaceans, as well as copepods, rotifers, and insect larvae.
The jellyfish prefer illuminated areas near the surface, especially on sunny days.
Environmental differences and life cycle
Escondido Lake, more transparent and amber-colored, contrasts with El Trébol Lake, richer in nutrients and with less light penetration. In both environments, the jellyfish coexist with native fish and the introduced rainbow trout.
The life cycle alternates between a polyp phase —fixed and almost invisible— and a medusa phase, free and observable in summer. The presence of jellyfish ensures the existence of polyps, meaning the species can be in the lake even if not seen for much of the year.
Citizen science and conservation
The researchers recommend constant monitoring and community participation through platforms like iNaturalist or the Instagram account @fotolabgesap. Citizen records allow for the detection of new appearance spots and a better understanding of the species’ actual distribution.
This contribution is crucial because the medusa phase is brief and seasonal and can go unnoticed. The more data collected, the greater the ability to anticipate ecological impacts and make decisions about the conservation and management of Patagonian aquatic ecosystems.
The arrival of the freshwater jellyfish Craspedacusta sowerbii in northern Patagonia adds a new challenge for regional biodiversity. Its ability to adapt and disperse forces a rethink of monitoring and conservation strategies, where collaboration between scientists and citizens will be essential to face the challenge of invasive species.
