From pre-history to deaths by drowning, diatoms tell it all

PUNE: In the 1950s, renowned algae expert H P Gandhi had collected samples from a lake in Kolhapur and reported 11 species of a group of algae called diatoms from it, two of them endemic to the Western Ghats.

A re-evaluation of the samples collected by him using state-of-the-art technology now available, a group of scientists were able to identify eight species, but six which are endemic to the region.

“The time has come to relook at our biodiversity in the Western Ghats when it comes to microscopic organisms like diatoms,” said Karthick Balasubramanian, scientist at the Biodiversity and Paleobiology group of Agharkar Research Institute (ARI) in Pune. He has discovered 25 new species of diatoms in just over four years since 2011.

Diatoms are a group of algae that have a unique feature; they are enclosed in a cell wall made of silica (the most abundant material in the earth’s crust). The incorporation of this silica in their cell walls known as frustules renders them nearly-indestructible and imparts the ability to survive in diverse environments.

“While the bulk of diatoms are found in the oceans, you can find them in lakes, streams, on rocks, on the bark of trees, near waterfalls, in the soil, etc. Even in the most polluted environment, you will find that some species of diatoms have managed to survive,” said Aditi Kale, another researcher working on diatoms at ARI.

This ability of diatoms makes them an ideal candidate as bio-indicators to assess the quality of a water body. “Diatoms are very sensitive to factors such as temperature, levels of nutrients and chemicals and salinity of water. The species of diatoms that grow in pristine waters will be very different from those found in polluted sources. Moreover, statistical models can be created where the presence of diatoms can be quantified,” Balasubramanian said.

Pollution monitoring tests are usually done periodically and chemical tests would notice an anomaly only if there is a variation from the normal at the time the test is done. If there is a release of contaminant in between that comes back to normal over a period of time, it would go undetected. However, if there is a sudden change in water quality then living things like diatoms would be adversely affected.

“If on conducting a test you suddenly find a change in diatom community in the water you would know something went wrong in between,” he added. But he rued the paucity of information about the species diversity of diatoms in India.

“As per present records, there are about 25,000 known species of diatoms in the world. Of these, about 8,000 species are recorded in the Indian sub-continent, 80% of which are also found in Europe and America. The current list of known species needs to be revised,” he said.

Most of the studies on diatoms conducted in the past were done using European literature for reference. As a result it is possible that a number of species were “misidentified” as was illustrated when the reevaluation of the samples collected from Kolhapur was done, he added.

For comparison, he pointed out that about 78% of amphibians, 76% of the molluscs and 53% of fishes found in the Western Ghats are endemic to the region. “How can the level of endemism for diatoms be so low,” he asked.

Research on diatoms has several applications. The near indestructible nature of the diatom cell wall means that frustules of diatoms from prehistoric times are available in the sediments of natural lakes. Careful analysis of these frustules can go a long way in understanding the environmental history of the region, he said.

Perhaps even more fascinating is the use of diatoms in forensic science. The presence of diatoms in the lung tissue of a body found inside a lake can tell a forensic expert whether the person died of drowning or if they were killed elsewhere and the body dumped there afterwards.

Diatoms have evolved skills that allow them to survive in a variety of habitats inluding the crevices of rocks, the top layer of soil, near waterfalls, in lakes, rock-pools, etc.


View original article at: From pre-history to deaths by drowning, diatoms tell it all



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