COLOMBO — The discovery of the black mussel (Mytella strigata) in coastal shrimp farms in Sri Lanka’s northwestern coastal belt has raised concerns among scientists, who warn against its potential to disrupt the country’s fragile aquatic ecosystems.

Clusters of these mussels were first discovered attached to hard surfaces and each other at the bottom of drained shrimp ponds at a site that was being inspected for the development of a mangrove restoration project. According to Malik Fernando of the Wildlife & Nature Protection Society (WNPS), these ponds had been free of mussels just three and a half months earlier. “The owners confirmed the ponds were clear before, which points to a rapid local establishment,” Fernando told Mongabay.

From the Americas to Asia

Native to the Pacific and Atlantic coasts of the Americas, from Mexico and El Salvador down to Argentina and Venezuela, including the Galapagos Islands, M. strigata has become a notorious invader in parts of the United States such as Florida and Georgia and parts of Southeast Asia such as the Philippines, Singapore and Thailand. In 2019, it was first recorded in India’s Kerala backwaters.

In Sri Lanka, the mussel was detected in September 2023 during baseline mollusk surveys for a planned mangrove restoration project near the Anawilundawa Sanctuary, an important Ramsar wetland. As part of the ecological assessment, researcher Thilina Kumarasiri first spotted empty shells along a supply canal.

When Fernando examined the shells, he first suspected the marine brown mussel (Perna perna) but noted significant differences. Further analysis confirmed the identification as M. strigata, also known as the invasive black mussel.

Prawn farmworkers near the restoration site informed the visiting researchers that when a pond was drained during harvest, its bottom was covered in tightly packed bivalves resembling the empty shells, Kumarasiri said. In January 2024, Fernando visited the farm and found dense clumps of mussels attached via byssus threads to hard objects and partially buried in sediment.

“The speed at which this species spread in the pond was alarming,” Fernando noted. “It suggests the mussel could establish itself quickly in similar habitats.”

A competitive invader

According to Sevvandi Jayakody, Wayamba University’s chair professor of the Department of Aquaculture and Fisheries, M. strigata’s success as an invader lies in its biology. “It matures early, reproduces over extended spawning seasons and tolerates a wide range of salinity and temperature,” she told Mongabay. Its smaller, elongated shell also helps it disperse more easily and compete with native mussels in crowded or resource-limited environments.

Given the Anawilundawa Sanctuary’s network of natural and human-made waterways, Jayakody warned the mussel could quickly spread to other sensitive wetland habitats in the absence of swift containment measures.

The mussel’s multiple impacts in invaded regions are significant. In Kerala’s estuaries, dense infestations foul aquaculture infrastructure, clog nets in cage farms and interfere with harvesting. A study carried out in India found a 38% drop in oyster spat settlement and more than 60% of larval settlement occurring on cultured oyster shells, both of which threaten shellfish production.

Globally, management efforts have focused on early detection, targeted removal, awareness among aquaculture operators and preventing spread via shipping.

How it might have arrived

Fernando suspects the Sri Lankan incursion may have come through contaminated live feeds for shrimp. Other likely pathways include ballast water and biofouling from ships.

Samantha Gunasekara, chairperson of the Marine Environment Protection Authority in Sri Lanka explained that ballast water — seawater taken on by ships for stability — is often loaded in one port and discharged in another, unintentionally transporting marine life across oceans.

Biofouling, the buildup of organisms such as barnacles, mussels and algae on submerged surfaces like hulls and propellers, is another vector. “Unlike ballast water, which can be treated, biofouling organisms can be physically stubborn and harder to remove,” Gunasekara noted.

International responses and Sri Lanka’s gaps

Sri Lanka is one of 12 countries in the International Maritime Organization (IMO)-led GloFouling Partnerships project, which promotes good biofouling management practices. “Even though the project ended in May 2025, we continue to support partner countries with pilot projects and sustainable technologies,” IMO technical analyst Will Griffiths said.

Many biofouling species can survive extended journeys, even across different water temperatures and salinities, so the project spurred the development of good practices and standards for improved biofouling management, Griffiths said.

The IMO’s Ballast Water Management Convention, which came into force in 2017, aims to prevent harmful aquatic organisms from spreading via ballast water. The organization has also issued biofouling guidelines. However, Sri Lanka is yet to ratify the convention.

The black mussel is only the latest invertebrate invader Sri Lanka has to deal with. The giant African land snail (Lissachatina fulica) and apple snails (Pomacea spp.) are already established, introduced decades ago through trade. While apple snails have not yet caused major agricultural damage locally, their impacts in other countries remain a concern.

Fernando has also documented the acute bladder snail (Physella acuta), native to the Americas, in the Bomburu Ella area in Sri Lanka’s central highlands — likely spread via the aquarium trade.

Challenging invertebrate invasions

Jayakody noted that invasive invertebrates are particularly challenging to manage because they often have hidden life stages, reproduce quickly and spread undetected through human activities like shipping and trade. “Sri Lanka needs a strong pre-exposure preparedness strategy to fight invasive species” she said. “Authorities at ports, customs and quarantine points should be regularly updated on emerging invasive species threats,” Jayakody told Mongabay.

If an invasive species is detected, she stressed, rapid eradication is essential. She also called for a dedicated invasive species prevention law to strengthen legal tools against such incursions.

Scientists, she added, have a responsibility to go beyond publishing research and actively raise public awareness through media engagement. “Without public understanding and cooperation, containment will be far more difficult to dela with,” she warned.

With M. strigata already established in at least one shrimp farm inside a protected wetland, Sri Lanka faces a narrow window to act before the mussel spreads further. The country’s experience with other invasive species, both terrestrial and aquatic, offers a cautionary lesson: Early detection and decisive responses are far cheaper and more effective than long-term control, Jayakody noted.

Citations:

Fabiosa, M., Abao, C. A., & Fabiosa, N. (2021). First record of the invasive mussel Mytella strigata (Mollusca: Bivalvia: Mytilidae) in Panguil Bay, southern Philippines. Journal of Environment and Aquatic Resources, 6. doi:10.48031/msunjear.2021.06.03

Lim, J. Y., Tay, T. S., Lim, C. S., Lee, S. S., Teo, S. L., & Tan, K. S. (2018). Mytella strigata(Bivalvia: Mytilidae): an alien mussel recently introduced to Singapore and spreading rapidly. Molluscan Research, 38(3), 170-186. doi:10.1080/13235818.2018.1423858

Sanpanich, K., & Wells, F. (2019). Mytella strigata (Hanley, 1843) emerging as an invasive marine threat in Southeast Asia. BioInvasions Records, 8(2), 343-356. doi:10.3391/bir.2019.8.2.16

Banner image: Black mussel shells on sand. Image courtesy of Thilina Kumarasiri.

Credits

Dilrukshi Handunnetti Editor

Topics

AsiaSouth AsiaSri Lanka

See Topics