• Seagrass is among the most productive marine ecosystems and is ecologically and economically vital
• Seagrass meadows support global food security as a nursery habitat for large fisheries;
• It also stores and sequesters organic carbon; protects shorelines and provides coastal resilience

Beneath Sri Lanka's coastal waters lies an unsung climate hero, often overlooked, rarely discussed, yet keeping the ocean alive: seagrass.

Regardless of their being fishing nurseries, contributing to coastal protection and nutrient recycling, disease reduction and, most importantly, being biodiversity supporters, the attention given towards their conservation is very low, which is gradually causing the decrease of them. So, where will that lead us?

In an interview with The Daily Morning, the Director of the Seagrass and Climate Change Programme at the Blue Resources Trust, Susantha Udagedara explains why protecting these "blue carbon" ecosystems is urgent, and what is at stake if we do not.

Following are the excerpts of the interview:

What is the scientific definition of seagrass? What are the various types of seagrass found in Sri Lankan waters?

Seagrass are a unique group of submerged flowering plants (angiosperms) that live in shallow oceanic and estuarine waters. They evolved from a single lineage of monocotyledonous flowering plants between 70–100 million years ago, and possess leaves, stems, rhizomes (horizontal underground runners), and roots. Unlike seaweeds (which are algae), seagrass are true vascular plants with a complete root-stem-leaf structure. They have developed unique ecological, physiological, and morphological adaptations to a completely submerged existence, including internal gas transport, epidermal chloroplasts, submarine pollination, and marine dispersal. Globally, seagrass are divided into six families - Zosteraceae, Hydrocharitaceae, Posidoniaceae, Cymodoceaceae, Ruppiaceae, and Zannichelliaceae - comprising 72 species across 12 genera.

What is its importance? 

Seagrass is ecologically and economically vital, providing a wide range of ecosystem services valued at approximately US $ 34,000 per hectare (ha) per year. It supplies food for a vast diversity of organisms including shrimps, sea urchins, clams, various fish species, and endangered species such as sea turtles and dugongs. Seagrass meadows provide a nursery habitat to over one-fifth of the world's 25 largest fisheries, supporting global food security. They also store an estimated 19.9 petagrams of organic carbon and sequester carbon up to 35 times faster than tropical rainforests per unit area, making them critical in combating climate change. Their root and rhizome systems stabilise sediments, reduce wave energy by up to 80–90 per cent, and protect shorelines from erosion and storm surges. They play an important role in nutrient cycling and maintain the water quality.

Seagrass have been shown to reduce potentially disease-causing bacterial pathogens on coral reefs by up to 50 per cent. They are considered among the most productive marine ecosystems, alongside mangroves and coral reefs.

What is the species seen in Sri Lankan waters?

Sri Lanka belongs to the Indo-Pacific seagrass bioregion. Fifteen true seagrass species belonging to seven genera have been recorded, with an estimated extent of 37,137 ha.

The species are: Family – Hydrocharitaceae (Enhalus acoroides; Halophila beccarii — rare/endangered species found in patchily distributed localities; Halophila decipiens; Halophila ovalis; Halophila major — first recorded in Sri Lanka via genetic identification; Halophila minor; Halophila ovata — Recorded from limited localities, with the identification needing verification; Halophila stipulacea — Newly reported, and considered a global invasive species; and Thalassia hemprichii); Family – Cymodoceaceae (Cymodocea rotundata; Cymodocea serrulata; Halodule uninervis; Halodule pinifolia; and Syringodium isoetifolium); and Family – Ruppiaceae (Ruppia maritima — Typically found in estuarine and lagoon habitats).

There are no endemic seagrass species in Sri Lanka, possibly because propagules are distributed widely by ocean currents throughout the Indo-Pacific region.

Where is seagrass mainly found in Sri Lankan waters?

Seagrass in Sri Lanka are found in calm, shallow marine and estuarine waters on sandy, salty, or clayey seabeds. The main locations include the Gulf of Mannar which supports extensive seagrass meadows, including large-scale beds affected by commercial trawling. In the Jaffna Peninsula lagoons and surrounding waters, the largest extent, with approximately 21,225 ha has been recorded. The Puttalam Lagoon is one of the historically well-studied seagrass sites in Sri Lanka. Other than that, in the Palk Bay, Kalpitiya (the Dutch Bay), Mannar, Mullaitivu, Kilinochchi, the Negombo Estuary, the Western coast, the Chilaw Lagoon, the Batticaloa Lagoon, the Valaichchenai Lagoon, the Eastern coast, the Trincomalee Bay, the North-Eastern coast, the Weligama Bay, the Mawella Lagoon, the Koggala Lagoon, Rekawa, and the Southern coast are also places where you can find seagrass.

Extensive seagrass meadows have been recorded particularly on the North-Western side, extending from the Dutch Bay in Kalpitiya to the western end of the Jaffna Peninsula and across the Palk Bay. Note that reliable distribution data for the North, North-West, and North-East coasts were historically limited due to the three-decade civil conflict in the region. The total estimated extent of seagrass in Sri Lanka is approximately 37,137 ha.

Are there any threats to seagrass in Sri Lankan waters?

Seagrass in Sri Lanka face numerous and serious threats, both direct and indirect.

Destructive fishing practices including the use of drag nets, push nets, and trawling directly damage seagrass beds, and also, large-scale commercial trawling heavily impacts seagrass in the Gulf of Mannar and the Palk Bay. Digging for polychaete worms (used as brood stock feed for shrimp hatcheries) causes severe physical damage, especially in the Chilaw Lagoon and the Negombo Estuary. Push nets used to catch ornamental fish also cause significant harm. Agricultural runoff and nutrient loading cause micro-algal proliferation (eutrophication) that smothers seagrass beds. In the Negombo Estuary, about 20 per cent of the total seagrass cover was lost due to micro-algal growth from nutrient loading. Solid waste and chemical contaminants from river discharge affect the water quality. Oil contamination in shallow coastal waters, unplanned port, harbour, and anchorage development increases water turbidity through sediment disturbance. Boat anchoring and propeller damage physically destroy seagrass beds. Land-use changes lead to high river turbidity, with sediment eventually depositing in coastal habitats.

In the Negombo Estuary, the seagrass cover declined by approximately 96 per cent between 1997 and 2004 - a dramatic loss in just seven years. Globally, seagrass loss has accelerated from less than 1 per cent per year before 1940 to 7 per cent per year since 1990. An estimated 29 per cent of global seagrass cover has been lost since the beginning of the 20th Century.

There are research and awareness gaps as most seagrass research in Sri Lanka is short-term and limited to a few locations.

What are the conservation methods for seagrass in Sri Lanka?

Sri Lanka has implemented several conservation methods to protect its seagrass ecosystems. The country's policy framework includes the Coastal Zone and Coastal Resource Management Plan (SLCZCRMP, 2018), which acknowledges the seagrass extent and distribution, while the Sixth National Report to the Convention on Biological Diversity (2019) includes seagrass biodiversity profiles. In a landmark global conservation commitment, Sri Lanka led the successful United Nations (UN) Resolution to declare 1 March as the World Seagrass Day (Resolution A/76/L.56, 2022), which was co-sponsored by 24 countries.

In terms of protected areas and projects, Sri Lanka has been actively working through the Dugong and Seagrass Conservation Project to identify additional areas for declaration as Marine Protected Areas (MPAs) to protect dugongs and their seagrass feeding habitats in the Gulf of Mannar and the Palk Bay. This is particularly significant given that only 26 per cent of recorded seagrass meadows globally fall within MPAs, and Sri Lanka is working to increase this coverage.

Research and monitoring efforts are ongoing, with institutions such as the Blue Resources Trust and the Open University conducting species checklist and distribution research. There have been calls for establishing a national seagrass monitoring network with a centralised temporal database for scientists to share data, and seagrass mapping using advanced technologies is being employed to inform management decisions. Additionally, genetic and molecular studies have been recommended to clarify species identification, especially for the Halophila and Halodule genera.

Community engagement and awareness programs target coastal communities to raise awareness of seagrass value and the dependence of livelihoods on healthy meadows, while also promoting ecotourism, nature-based education, and science-based sustainable use. Long-term monitoring through non-governmental organisations and local communities empowers people and reconnects them with natural resources.

Recommended conservation actions include the systematic documentation of the distribution, ecology, and anthropogenic impacts, the development of a national seagrass conservation action plan aligned with global frameworks such as the Sustainable Development Goals, Nationally Determined Contributions (NDCs), and the Paris Agreement, island-wide comprehensive research and genetic studies to fill data gaps, the establishment of seagrass nursery techniques and restoration programs (not yet implemented in Sri Lanka, though practiced elsewhere), and multiple overlapping strategies including sustainable coastal management, pollution control, and community engagement.

What are the impacts of climate change on seagrass?

Climate change poses one of the most significant long-term threats to seagrass ecosystems in Sri Lanka and globally, with several key impacts. Rising sea temperatures are a major concern, as global sea surface temperatures increased by 0.6 plus/minus 0.2 degrees Celsius during the 20th Century, already causing significant ecological changes across seagrass ecosystems. Elevated water temperatures stress seagrass plants, reducing their growth, productivity, and resilience, and thermal stress can cause bleaching or the die-off of seagrass meadows in shallow coastal waters.

El Niño and climate variability bring anomalously warm sea surface temperatures to the Indian Ocean region, which can trigger mass seagrass die-offs in affected shallow coastal areas. Increased water temperatures during El Niño events can lead to hypoxic (low-oxygen) conditions in seagrass beds, while changes in rainfall patterns associated with El Niño/La Niña cycles affect freshwater input into lagoons, altering salinity levels that seagrass are sensitive to. Additionally, increased storm intensity and frequency during climate events can cause physical damage to seagrass meadows through uprooting and sediment disturbance.

Ocean acidification, driven by rising carbon dioxide levels, increases ocean acidity, which can affect the physiology of seagrass and the organisms that depend on them, including calcifying organisms in seagrass beds. The sea-level rise can cause increased water depth, reducing the light available to seagrass for photosynthesis, and also increases the risk of coastal flooding and changes to coastal sediment dynamics, affecting seagrass habitat suitability. An estimated 20–90 per cent of current coastal wetlands are at risk of being lost by 2100. Furthermore, more frequent and intense cyclones and storm surges (partly linked to climate change) physically damage seagrass beds and increase turbidity, limiting light availability.

Despite being threatened by climate change, seagrass also help mitigate it through Blue Carbon sequestration, and including seagrass conservation in NDCs under the Paris Agreement can help Sri Lanka meet its climate commitments. Healthy seagrass meadows provide coastal resilience by reducing wave energy and protecting shorelines against the increased storm surges driven by climate change. In Sri Lanka, climate change-associated studies on seagrass are identified as a research priority, and extensive studies on ecology, mapping, restoration techniques, and climate change impacts are considered essential for the conservation and sustainable management of the country's seagrass ecosystems.

Any other special details about seagrass that you would like to share?

Sri Lanka has demonstrated remarkable global leadership in seagrass conservation by playing a pivotal role in securing global recognition for these ecosystems. The Government led the successful adoption of the UN General Assembly Resolution A/76/L.56 on 23 May 2022, officially declaring 1 March as the World Seagrass Day, a Resolution co-sponsored by 24 countries that represents a landmark global commitment to raising awareness and protecting seagrass ecosystems. This positions Sri Lanka as a genuine champion of marine conservation on the world stage.

Also, there is a common misconception that seagrass and seaweeds are the same, they are fundamentally different. Seagrass are true flowering plants (angiosperms) with roots, stems, rhizomes, and leaves that anchor into the seafloor sediment, whereas seaweeds are marine algae lacking true roots and stems, attaching to surfaces via rhizoids or floating freely. This distinction is ecologically crucial because seagrass stabilise sediments and form structured meadows, while seaweeds do not.

Seagrass evolved 70–100 million years ago, making them among the oldest flowering plant lineages on earth. The scientific investigation of seagrass in Sri Lanka dates back to the 18th Century, with a herbarium sheet of Thalassia hemprichii from the Puttalam Lagoon deposited in the National Herbarium on 23 March 1826 — nearly 200 years ago.

The dugong-seagrass connection is particularly significant, as dugongs (sea cows) are entirely dependent on seagrass as their primary food source and are found in Sri Lankan waters, particularly in the Gulf of Mannar and the Palk Bay. The Dugong and Seagrass Conservation Project has been active in mapping seagrass beds and identifying new species, including reporting Halophila stipulacea for the first time in Sri Lanka, and also identified potential new MPAs. The relationship between dugongs and seagrass is bidirectional: dugongs help maintain seagrass health by preventing the overgrowth of certain species, while the seagrass provides the nutrition essential for dugong survival.

Seagrass have been called the 'ugly duckling' of the conservation world, and despite being as ecologically important as mangroves and coral reefs, they receive far less attention, funding, and protection. Only 26 per cent of seagrass meadows globally fall within MPAs, compared to 40 per cent of coral reefs and 43 per cent of mangroves, representing a critical conservation challenge. Scientists and policymakers are increasingly calling for seagrass to be incorporated into biodiversity frameworks, climate action plans, and sustainable finance mechanisms at both national and international levels.

Regarding the restoration potential, while Sri Lanka has not yet initiated formal seagrass restoration programs, advanced seagrass nursery techniques and restoration methods have been successfully implemented in other countries such as the Virginia Coast in the United States and the Moreton Bay in Australia, and these could be adapted for Sri Lanka once the underlying causes of seagrass decline are addressed. Restoration holds significant promise as a tool to recover lost meadows and rebuild coastal resilience.

The views and opinions expressed in this column are those of the interviewee, and do not necessarily reflect those of this publication