DNA Test Suggests Mussel Pest on Cochin Coast Could Be Invasive Foreigner

Mussels are among the most prominent biofouling agents in the world.

Mysuru: Marine biologists at the Cochin University of Science and Technology have found that a heavily fouling mussel growing in the backwaters of Cochin harbour could be a foreign species.

They compared the mussel’s genome with an international genetic database as well as with the DNA of other species of mussels. They concluded that the mussel seen near the shores of Cochin harbour is more like Mytilopsis sallei, found commonly in the Lam Tsuen River in Hong Kong.

Biofouling is the excessive growth of marine animals on structures and ships, and is a great economic nuisance. Extensive biofouling can weaken a harbour’s foundations and damage the hulls of shops. Unabated fouling can also make ships heavier and difficult to manoeuvre. If it happens in the ship’s ballast when it is filled with water, it could damage pumps and other machinery as well.

Mussels, especially of the Mytilopsis species, are among the most prominent biofouling agents in the world. The others are marine algae, microorganisms and corals.

A massive population of Mytilopsis was first noticed on wooden materials partially submerged in water in the Ezhupunna region of Vembanad Lake, according to the researchers. The lake is several kilometres inland. The population density was as high as 780 individuals growing per squared meter. Their bulk weight and ability to grow together in large numbers means, together, they could weigh down even the heaviest of ships.

Mytilopsis sallei, also known as black-striped mussel, is a well-known invasive mussel and has been known to populate strange seas across the world since the 16th century. It travels the world thus by hitching a ride on unsuspecting ships.

Dr. P.R. Jayachandran, M. Jima, Philomina Joseph, V.F. Sanu, and Dr. S. Bijoy Nandan (L to R)

“In India, Mytilopsis species were recorded from Visakhapatnam harbour during the 1960s for the first time and then from Mumbai harbour in 1975,” said Dr. Jayachandran, a member of the research team. “Our study records their presence [along] the southwest coast of India for the first time.”

In order to confirm if the species was indeed Mytilopsis or not, the team took samples of DNA from five specimens and compared them with unique DNA portions, or sequences, of Mytilopsis sallei from the Lam Tsuen River and with an Asian mussel (Congeria kusceri). It is difficult to distinguish between the two merely from their looks.

“The sequences of M. sallei exhibited 0% intraspecific divergence, which confirms that the sequence from Cochin mussels clearly matched with those from Lam Tsuen River,” the study notes.

This confirmed that a Mytilopsis mussel had mounted a bioinvasion of the Cochin backwaters.

“The results confirm that it is one of the several Mytilopsis species, if not Mytilopsis sallei. We can’t surely say that our specimen is Mytilopsis sallei because many researchers believe that the Indian and other Asian populations, including the Lam Tsuen River species, are indeed Mytilopsis adamsi, and are wrongly labelled Mytilopsis sallei,” Jayachandran clarified. A definitive conclusion would require matching the sequences with the mussels that are native to Guatemala. That data is not available now.

In any case, the mussels growing offshore, in the backwaters of Cochin, are surely not local. “This species is highly tolerant to salinity and temperature variations. Eradicating marine invasion is an extremely difficult [task]. A similar invasion in the harbour of Darwin Islands required 2.2 million Australian dollars to chemically clean the water,” the study said.

India does not have adequate control measures to avoid marine pest or fouler intrusion except using antifouling paints on ships. And these antifouling paints are marine pollutants.

The study was published in the journal Current Science.

Kollegala Sharma writes for India Science Wire and tweets at @kollegala.

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