The rain in Spain is hard to ascertain, according to a scientific investigation into a recent unusual weather phenomenon in the northwest of the Iberian peninsula. Residents of the province of Zamora were somewhat perturbed when, for parts of last fall and winter, a blood-red rain fell from the sky, and while geologists have now identified the microorganism responsible for the unusual coloration, they are at a loss to explain how it got there.
In a recent paper published in the Spanish Royal Society of Natural History Journal (in Spanish), researchers explained that the red tint was caused by a freshwater microalgae called Haematococcus pluvialis. Though normally green in color, it synthesizes a red pigment called astaxanthin when under stress. According to the study, the organism is “especially sensitive to variations in the intensity, quantity and quality of light, which can affect the distribution, size and morphology of its cells.”
Samples were collected from the village of Ayoó de Vidriales and examined at the University of Salamanca. Though researchers were quickly able to identify the microalgae, they could offer little explanation as to how it ended up in the region. Previously, H. pluvialis had been observed in bodies of water in North America and some parts of Europe, though its sudden unexpected arrival in Spain is somewhat baffling.
Unable to solve the riddle, the study closes by stating that the organism’s origin can only be ascertained by first identifying its possible arrival sources, such as water or wind. Regardless of where the algae came from, local residents needn’t worry too much, as not only is it not considered dangerous, but H. pluvialis extracts have even been found to improve cognitive function.
Though rare, the phenomenon of “blood rain” is far from unheard of, and can be caused by a range of factors. For instance, in 2010, parts of the U.K. experienced crimson downpours after storms caused red sand and dust to blow over from the Sahara Desert.