The red rain that occurred in parts of Kerala and Sri Lanka in 2011 was caused by the aerial dispersal of algal spores from Europe to the Indian subcontinent, scientists have reported.
A team of scientists from the Central University of Punjab; SB College, Changanassery; SN College, Kollam; and University of Salzburg, Austria, have established that the alga, Trentepohlia annulata , never before reported from India, was responsible for the blood rain.
The team used DNA fingerprinting techniques to trace the origin of the species to Europe. The findings, published in a recent issue of the Phylogenetics and Evolutionary Biology , an open access journal, postulate that the spores were transported to India through transcontinental atmospheric circulation patterns and climatic systems.
It is also the first time that aerial dispersal of algal spores on continental and global scale has been reported, though the phenomenon has been documented for bacteria and fungi.
Global attention
The red rain phenomenon in Kerala attracted global attention in July 2001 when it occurred in parts of Kottayam, Pathanamthitta, Ernakulam, Alappuzha, and Idukki districts. Following widespread concern, the government appointed a committee of experts from the Centre for Earth Science Studies and Tropical Botanic Garden and Research Institute to analyse the causes.
The panel reported that the red rain was due to algal spores of local origin. The scientists, however, could not isolate the species though they had identified the genus as Trentepohlia.
Terrestrial origin
“The identification of the species conclusively establishes the terrestrial origin of the red rain phenomenon”, says C.N. Mohanan, former scientist at CESS, who was a member of the government-appointed committee. He, however, feels that the species could have reached India through legal or illegal plant trade rather than aerial transportation.
“The algal spores released from trees could have been washed down by the rains. Only a detailed microclimatic study will confirm this hypothesis”, he says.
