• Exploring one of quietest, yet most vital ecosystems

Sri Lanka’s waters hide a complex ecosystem that is easy to overlook but essential to the health of the ocean: seagrass meadows. Often mistaken for seaweed, seagrasses are flowering plants that have adapted to live in shallow, sunlit marine environments. Rooted in the seabed, they form dense underwater meadows that provide food, shelter and nursery grounds for a remarkable variety of marine life. They also help stabilise sediments, improve water clarity, recycle nutrients and store large amounts of carbon. In Sri Lanka, around 15 seagrass species have been documented across lagoons, estuaries and coastal waters, including Palk Bay, the Gulf of Mannar, the Jaffna Peninsula and Puttalam Lagoon. These habitats support fishers and coastal communities while providing refuge for species such as sea turtles, sea cucumbers and the endangered dugong. 

Yet seagrass meadows remain largely out of sight and, as a result, out of mind. Pollution, coastal development, destructive fishing and physical disturbance are steadily damaging them. 

In order to sustain awareness on the nature of seagrass, Marine Conservationist Susantha Udagedara, conducted a lecture at the University of Colombo, Faculty of Science. 

More than underwater grass

Seagrasses are flowering plants, not algae. Their roots anchor them to the seabed, while their leaves grow through shallow coastal waters where sunlight can reach them.

Sri Lanka is home to species including Enhalus acoroides, Halophila ovalis, Halodule pinifolia and Thalassia hemprichii. Together, they create complex habitats that support fish, shrimp and other marine organisms.

Seagrass meadows are also important  blue carbon ecosystems. 

“They absorb and store carbon, helping to reduce the amount of carbon dioxide in the atmosphere,” Udagedara said. “Their roots and surrounding sediments can hold carbon for long periods, making healthy seagrass beds valuable allies in responding to climate change.”

Nurseries for marine life and people

For many marine species, seagrass meadows are nurseries. Young fish and other animals find food and shelter among the leaves, increasing their chances of survival.

The benefits extend to coastal communities. Healthy seagrass habitats support fisheries and contribute to the productivity of lagoons and shallow coastal waters. They also help protect shorelines by stabilising sediments.

In Northern Sri Lanka, these ecosystems are particularly important because they provide habitat for dugongs, one of the country’s most vulnerable marine mammals. 

“Protecting seagrass therefore means protecting not only plants but an entire network of marine life,” he said. 

A habitat under pressure

Despite their importance, seagrass meadows face growing threats. Poor water quality, urban runoff and sedimentation can reduce the amount of sunlight reaching the seabed. 

“Without sufficient light, seagrasses struggle to photosynthesise, grow and survive,” Udagedara said. 

In the Negombo Estuary, seagrass beds have declined significantly as water quality has deteriorated. In Chilaw Lagoon, activities such as trampling, anchoring and shellfish collection have damaged seagrass habitats.

Coastal development, aquaculture, untreated wastewater, sand mining and poorly managed tourism add further pressure. Because seagrasses generally grow in shallow coastal areas, they are particularly exposed to human activity.

The damage caused by bottom trawling

One of the most serious threats in Northern Sri Lanka is bottom trawling. Heavy nets are dragged across the seabed to catch fish, shrimp and other species. In the process, they can uproot seagrasses, damage their underground rhizomes and disturb the sediments in which they grow.

The damage is not limited to the plants themselves. 

“When a seagrass meadow is destroyed, the fish and other marine organisms that depend on it also lose their habitat,” Udagedara said. 

In areas such as the Gulf of Mannar, where destructive fishing practices remain a concern, the loss of seagrass can have consequences for both biodiversity and the fishing communities that depend on healthy marine ecosystems.

Protection 

Science alone will not be enough. Seagrass conservation must involve the people who live and work along the coast.

Fishers can play an important role in monitoring and protecting seagrass habitats, particularly when conservation measures are designed with local communities rather than imposed on them. 

“Education can also help change perceptions of seagrass from an overlooked plant to an essential part of the marine ecosystem,” Udagedara said.

Stronger enforcement of existing fisheries, coastal and biodiversity laws is equally important. Sensitive seagrass areas should be incorporated into marine protected areas, while destructive activities such as bottom trawling should be prevented in vulnerable habitats.

Giving seagrass a future

Sri Lanka’s seagrass meadows may not have the visibility of coral reefs or mangrove forests, but their importance is no less profound. They support biodiversity, sustain fisheries, store carbon and help protect coastal environments.

Their future will depend on better research, stronger protection and meaningful community participation. Regional cooperation will also be important, particularly in the Gulf of Mannar, where marine ecosystems cross national boundaries.

Seagrass meadows are quiet ecosystems, but their message is clear. If Sri Lanka wants resilient oceans and resilient coastal communities, it must protect the habitats that make both possible. The meadows beneath the sea deserve to be seen, valued and protected before more of them disappear.