Invasive algae species found in Tamil Nadu

Dr. Felix Bast holds up the invasive seaweed Sargassum zhangii.

Researchers at the Central University of Punjab have identified a seaweed Sargassum zhangii, growing along the rocky shores from Vedaranyam to Pattukottai and Thondi to Pamban in Tamil Nadu. This is the first reported case of the seaweed outside China. The team led by Dr. Felix Bast from the Centre for Biosciences, Central University of Punjab, found luxuriant growth of the seaweed all around the rocky shore. The results were published recently in the Journal of Plant Taxonomy and Geography.

This is the first time that the seaweed has been reported outside China. Its presence in Indian shores far away from China highlights its invasive potential and the need to take immediate action to prevent its spread to other regions.

“In addition to studying the morphological features, we also carried out DNA barcoding using two loci — a mitochondrial gene (COX1) and a spacer sequence (ITS) — to identify the algae. We found the algae from the Tamil Nadu shores matched with

S. zhangii of China,” says Dr. Bast, senior author of the paper.

“We have no clue how it spread to India. It could be through spores transported in ballast water or through natural dispersion. It is endemic in China but now found in India. It is possible that with time it may spread to other areas,” he says.

The team was able to make an inference of the evolutionary relatedness of the algae collected from Indian shores and those in China by measuring the pair-wise genetic distance between the two isolates of the algal species. “The genetic distance is very low and so the algae is closely related to the one found in China. Also, the introduction into Indian shores has been recent as the genetic distance between the two isolates is low,” says Dr. Bast.

The researchers did not rely entirely on the morphological features of the algae for identification as morphological features can change in response to biotic and abiotic factors. So they relied on DNA barcoding as well. According to Dr. Bast, many algal species in GenBank have been wrongly identified by relying on DNA barcoding. “BLAST identity alone will be error-prone due to cross-amplification of DNA of epiphytic algae growing on host seaweed,” he says. So the researchers combined DNA barcoding with phylogenetic-based approach to identify the species.

“This is the first time DNA barcoding has been used in India for characterising invasive species,” Dr. Bast says. By using two loci instead of one for DNA barcoding the researchers increased the reliability 10 times. Since the two loci are from two different genome compartments (one is from the nucleus and the other is from the mitochondria) it increases the reliability of the inference.