Excerpts from Jim Conrad's
Naturalist Newsletter

DUNALIELLA SALINA making water pink at the salt ponds at Las Coloradas, Yucatan, Mexico

from the March 15, 2015 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
DUNALIELLA SALINA & THE PINK SALT PONDS AT LAS COLORADAS

Often during flamingo viewing trips when we're in the vicinity of Las Coloradas, the boatman veers from the estuary's center channel and heads for the northern shore. The boat noses onto a narrow bank just below what seems to be a long chest-high ridge, but which in fact is a levee that's part of an extensive system of artificial embankments that surround and contain numerous large evaporation ponds of the saltworks at Las Coloradas. Here tourists can climb atop the levee and enjoy the view shown above.

In that picture Paco, a member of Diego Nuñez's guiding crew, stands with two ladies from San Francisco who are astonished by the water's pinkness. You can see an aerial view of part of the sprawling salt-pond system on the Spanish-language page of the Mexican company operating the Las Coloradas saltworks at http://www.isysa.com.mx/plantas.htm.

In that page's aerial view, all the ponds are pink, though some are pinker than others. Often only one or a few ponds are vividly pink, and the pinkest ponds are those clustering around the instillation where the salt is mechanically gathered from the ponds' floors.

This can be explained by the fact that the water's pinkness results from the presence of algae containing unusually high levels of pigments called carotenoids, especially beta-carotene, or ß-carotene, which is a strongly colored red-orange pigment found in certain plants and fruits. Beta-carotene gives tomatoes, carrots, pumpkins and sweet potatoes their color. Carotenoids also give flamingos and Rosette Spoonbills their pink color. When the birds eat carotenoid-rich algae, as well as tiny crustaceans who also feed on the algae and therefore contain large concentrations of carotenoids, enzymes in the birds' livers break down the carotenoids into pink and orange pigment molecules. These pigment molecules then migrate through the birds' bodies to their feathers, bill, and legs, making them pink.

In the salt ponds of Las Coloradas, the main alga species contributing to the salt-ponds' pinkness is DUNALIELLA SALINA, belonging to the Green Algae Phylum, not the Red. Few organisms can survive such highly saline conditions as Dunaliella salina, which doesn't have a good English name.

In normal ocean water Dunaliella salina doesn't impart pinkness to the water, but in the salt ponds as evaporation causes the remaining water's salt content to increase, the alga prospers and causes a pink algal "bloom." One reason Dunaliella salina thrives in very salty water is that other alga species can't survive in it, allowing Dunaliella salina to take over. Since in very salty water about 14% of the dry weight of Dunaliella salina can consist of red-orange ß-carotene, the waters turn red. At Las Coloradas the ponds nearest the salt refining plant are pinkest because the network of evaporation ponds are configured so that regular seawater enters the farthest ponds, then as evaporation concentrates the water's salt, the saltier water is pumped into ponds closer to the factory, and as the water gets saltier, Dunaliella salina creates an ever-more-spectacular algal bloom, and the water becomes pinker and pinker.

Dunaliella salina isn't the only alga species in the saltponds' water, or even the only species of the genus Dunaliella, but it's the one overwhelmingly causing the water to be pink. A 2006 paper in English by Francisca García et all, entitled "Physiological characterization of Dunaliella sp. (Chlorophyta, Volvocales) from Yucatan, Mexico," technically describes the biological details of Dunaliella algae found in the salt-ponds of Las Coloradas and nearby San Crisanto. It can be freely downloaded in PDF format here.

Dunaliella salina is famous for much more than causing the waters of Las Coloradas's salt-ponds to turn pink: The alga is grown commercially as a source of beta-carotene. Different technologies are used, from low-tech, extensive cultivation in lagoons to intensive cultivation at high cell densities under carefully controlled conditions. Beta-carotene is valued as a natural food coloring, plus in the body it's changed into vitamin A, needed for good vision, a strong immune system, and for healthy skin and mucous membranes, so it's an important presence in the health-food industry. Also, beta-carotene is an antioxidant, and you've heard of the therapeutic value of antioxidants.


from the January 21, 2018 Newsletter issued from Rancho Regensis north of Valladolid, Yucatán, MÉXICO
UPDATE ON THE PINK PONDS OF LAS COLORADAS

This week I accompanied a family on a flamingo-viewing tour to Río Lagartos on the Yucatan's northern coast, getting to see old friends from my year of being there. The tourism scene at Río Lagartos has changed dramatically during the last two or three years. Now many more packaged tours find their way there in big tourist buses from Cancún and other eastern-coast, Caribbean destinations. Also, in Río Lagartos new hotels have sprung up, and sightseeing boats on the estuary seem to have doubled or maybe tripled.

My guide friends tell me that nowadays many visitors express less interest in watching flamingos than in seeing firsthand the pink waters of the big salt ponds a few kilometers east of Río Lagartos, at Las Coloradas. They think that the interest in seeing the pink ponds is fueled by social media -- people want to take selfies with pink water behind them, for Facebook.

Also among the guides you hear that at least in one pond -- the last pond in the chain of evaporation ponds and also the pinkest -- is made pink by the addition of chemicals used to encourage salt to crystallize quicker. Of course, when you hear that, you worry.

One of my friends learned that the chemical being used is potassium permanganate, KMn04. A quick check on Wikipedia's potassium permanganate page gave the reassuring information that this compound is so nontoxic that it's used medicinally for cleaning wounds and dermatitis. It's so important medicinally that it's on the World Health Organization's "Model List of Essential Medicines," a list of the most important medications needed in a basic health system. It's even used by municipalities in water treatment, mainly to remove iron and the rotten-egg smell of hydrogen sulfide from well water. Historically it was employed to disinfect drinking water.

The reason that potassium permanganate is used at Las Coloradas is that it causes salt to form more quickly in the evaporation pond or ponds. And, when it dissolves in water, it does indeed produce an intensely pink or purple solution. As far as I can tell, it's just coincidental that the pinkness of the untreated ponds with their carotenoid-producing Dunaliella salina alga and potassium permanganate's pinkness are so similar.

Potassium permanganate seems safe for humans. In water, potassium permanganate quickly transforms into non-toxic manganese dioxide, which precipitates out -- turns to gunk that settles to the bottom. It does have some effect on the environment, though. It kills phytoplankton, such as our carotenoid-producing Dunaliella salina, which similarly clots together and settles to the bottom. Also, it's slightly to moderately toxic to marine fish. This environmental-impact information is in a 2009 article called "Environmental aspects of drug and chemical use in aquaculture: An overview" by Hervé Le Bris and others, freely downloadable in PDF format.

The chemical reason potassium permanganate is of such versatile use is that it's a strong oxidizing agent, with an oxidation state of +7. That means that during the oxidation process seven electrons are lost. It's such an aggressive oxidizer that it was used in the flash powder of early photographers.