Salt flats where Dunaliella algae turn evaporation ponds blood red, producing beta-carotene 100 times more concentrated than carrots. Flamingos feeding here accumulate so much pigment their feathers turn pink. Birds raised elsewhere stay white. The algae are now farmed for supplements.
Didier Baertschiger, CC BY-SA 2.0
The extremophile that colors the area
The pink and red colors of the Aigues-Mortes salt marshes are not caused by minerals or pollutants, but by a microscopic, single-celled organism. This is Dunaliella salina, a type of green microalgae that thrives in hypersaline environments. These salt pans, where water from the Mediterranean is left to evaporate, create conditions too extreme for most life. As the salinity increases, often reaching levels ten times that of seawater, the algae must adapt to survive the intense osmotic pressure and high levels of solar radiation.
To protect itself, Dunaliella salina undergoes a biological change. Under stress, it shifts its energy from growth to producing massive quantities of beta-carotene, a red-orange pigment. This carotenoid acts as a protective shield for the alga's photosynthetic machinery against intense sunlight. The alga also produces high concentrations of glycerol within its cell to counteract the external saltiness and prevent water from being drawn out, which would otherwise cause it to dehydrate and perish. This adaptation is so effective that the algae turn the water a pinkish-red color visible from space.
A diet-driven coloration. The bright pink plumage of the Greater Flamingos (Phoenicopterus roseus) that congregate here is caused by the microscopic life in the water. Flamingos are not born pink; their feathers are initially grey or white.%%CITE_5%% Their famous color is acquired entirely through their diet.%%CITE_8%% The food chain begins with Dunaliella salina. Tiny brine shrimp, Artemia salina, graze on the beta-carotene-rich algae.%%CITE_4%%%%CITE_9%% The flamingos then consume vast quantities of these brine shrimp and the algae itself.%%CITE_5%%
Inside the flamingo's digestive system, enzymes break down the beta-carotene. These pigment molecules are then absorbed by fats in the liver, transported through the bloodstream, and deposited in the growing feathers, skin, and even the beak and legs. The intensity of a flamingo's color indicates health and diet; a brighter pink suggests a well-fed bird that has consumed a high quantity of carotenoids. This dietary dependency means that flamingos in captivity must be given food supplemented with carotenoids to maintain their pink hue. The same biological process is responsible for the pink flesh of salmon. The salt works, managed by the Compagnie des Salins du Midi since 1856, thus create and maintain an ecosystem that directly supports one of Europe's largest flamingo populations.
💡Fun Facts
Salt has been harvested in Aigues-Mortes since at least the 4th century BC, with a Roman engineer named Peccius first organizing production.
The salt marshes cover an area of approximately 8,000 hectares, an area roughly equivalent to the city of Paris.
*Dunaliella salina* lacks a rigid cell wall, which allows it to rapidly swell or shrink in response to drastic changes in salt concentration.
The beta-carotene produced by the algae is a potent antioxidant, leading to its commercial cultivation for use in cosmetics and dietary supplements.
