On the shores and within the Laguna de los Cisnes (Swan Lagoon), located near the city of Porvenir in Chile, we find formations that at first glance appear to be rocks with elliptical or elongated dome shapes. These towers can reach a height of up to 80 cm, a width of 100 cm, and a length of over 500 cm. However, what appears to be rock at first glance, when examined with a magnifying glass, reveals filaments of green algae composed of chains of filamentous cyanobacteria. These are organo-sedimentary deposits called stromatolites, which exist in only a few seas and saline lakes worldwide. They are the product of the first living organism on Earth, dating back 3.4 billion years (though those in this lagoon could belong to the Holocene, between 10,000 and 12,000 years ago). Only 14 places in the world are known to contain still active stromatolites, which makes the Lagoon of the Swans an environment with high conservation value.
The objective is to understand what the key role of these organisms was in the evolution of life on the planet and what role they play today in the lake environment of Laguna de los Cisnes.
Stromatolites and Their Key Role on Earth
Earth formed approximately 4.5 billion years ago. The earliest key evidence of life consists of stromatolite fossils, which have been dated to approximately 3.4 billion years ago. During the Archean eon (2.5 to 3.7 billion years ago), Earth's environment was extreme: the atmosphere was hot and dusty, and like the seas, rich in toxic volcanic gases and lacking in oxygen. Stromatolites, formed by cyanobacteria (photosynthetic bacteria), adapted to live on the margins of the oceans. These photosynthetic bacteria captured some of the carbon dioxide (CO2) from the early atmosphere and were primarily responsible for increasing oxygen levels, thus changing the composition of the atmosphere and oceans over geological time.
With the increase in oxygen, the evolution of the diverse life forms we know today became possible. Thanks to the new opportunity offered by technological advances in space exploration, we can search for evidence of life in the solar system and perhaps also beyond it, on extrasolar planets. Research reveals that on Mars and Jupiter's moon Europa, fluids and gases are present under extreme physicochemical conditions. These findings suggest the possibility of extraterrestrial life, for which the best candidates would be extremophile bacteria similar to those found on Earth.
Their current role in Swan Lagoon, Chile
These stromatolite colonies form a unique ecosystem for other organisms present in Swan Lagoon. For example, brine shrimp, a brachiopod crustacean that has barely evolved its morphology since the Triassic period (250 million years ago), live and feed within them. At the same time, the brine shrimp are consumed by other birds, such as the Chilean flamingo, a migratory resident that visits the lagoon at least twice a year. A large number of shorebirds are also found there, such as the cormorant, and especially the Magellanic plover, a bird exclusive to the lagoon and highly sought after by birdwatchers. In addition, various migratory birds of prey, such as the peregrine falcon and the falcon, can be seen. The two swan species, the black-necked swan and the coscoroba swan, frequent the lagoon in large flocks, mostly in its center, where they feed on phytoplankton and some invertebrates. All of this, together with the Fuegian landscape, the steppe, the wind, and the silence, creates a special and unique experience for those who have the opportunity to visit this place.
In addition to its biological importance, Swan Lagoon is a site of archaeological value. Recently, the drop in water level has revealed archaeological sites indicating that in the past, this was a suitable location for the indigenous people of Tierra del Fuego (Selk'nam), who may have hunted swans or collected their eggs and feathers, as well as held ancestral ceremonies there. The value of this ecosystem is evident, both in its relevance to science and biotechnology and in its potential for sustainable tourism. In 1982, the Stromatolite Park was declared a Natural Monument, which protects it from activities that could harm its ecosystem. However, it is important to continue research and the development of its biological, historical, and cultural resources.