A microbial cocktail
Lake Hillier is a salt lake on the edge of Middle Island, the largest of the islands in the Recherche Archipelago off the south coast of Western Australia. It measures about 600 meters (2,000 feet) long by 250 meters (820 feet) wide. The lake is a hypersaline environment, with a salt concentration around 28%, which is comparable to the Dead Sea and about eight times saltier than the ocean. This extreme salinity creates conditions where few organisms can survive.
For many years, the cause of its pink color was a scientific puzzle. It is now understood that a community of microorganisms is responsible. Metagenomic analysis has identified a diverse mix of archaea, bacteria, algae, and viruses. The main contributors to the color are the microalga Dunaliella salina and the bacterium Salinibacter ruber.
Dunaliella salina is a type of unicellular green algae known for its ability to thrive in high-salt environments. To protect itself from intense sunlight, the alga produces large amounts of beta-carotene, a red-orange pigment. This is the same pigment that gives carrots their color. Salinibacter ruber, a red-pigmented halophilic (salt-loving) bacterium, also contributes to the lake's coloration. The lake's permanent pink hue is a result of the pigments produced by this cocktail of microorganisms.
History and exploration
The first documented sighting of Lake Hillier by Europeans was on January 15, 1802, by the Matthew Flinders expedition. Flinders, a navigator and cartographer, observed the "rose colour" lake after climbing the island's highest peak. He noted that the water was so saturated with salt that crystals formed near the shores. The lake was named after William Hillier, a crew member of HMS Investigator who died of dysentery while the expedition was at Middle Island in May 1803.
In the late 19th and early 20th centuries, there were brief attempts at commercial salt mining. Edward Andrews investigated the possibility in 1889, but the enterprise was short-lived. Another attempt at salt extraction occurred for about six years in the early 20th century. These ventures Failed, reportedly due to the "toxicity of the salt collected for consumption".
More recently, scientific interest in the lake has grown. In 2015, the Extreme Microbiome Project collected water and sediment samples to analyze the lake's microbial DNA. This research led to the identification of the specific organisms responsible for the color, including Dunaliella salina, Salinibacter ruber, and several species of archaea. The study also revealed the presence of Dechloromonas aromatica, a bacterium capable of breaking down chemical solvents, which may be linked to past tanning activities on the island in the early 1900s.