THE UNSUNG AND ELUSIVE PROTECTORS OF THE COAST: SEAGRASS

WHAT ARE SEAGRASSES?

Seagrass is a marine flowering plant found in meadows in the shallow intertidal and deeper subtidal sloping coastlines in the world. There are approximately 72-75 species of seagrass that belong to different families.

ARE SEAGRASSES ANOTHER NAME FOR ‘SEAWEED’ OR ARE THEY COMPLETELY DIFFERENT?

They are often confused with seaweeds due to their ‘similar’ appearance. In contrast to seaweed, they can photosynthesize using their long blade like leaves, transport nutrients and water in stems all the while using little air pockets to keep themselves afloat. They have rhizomes and root nodules which help them to stabilise and anchor in the sediment. Seagrasses also have flowering periods especially during the summer (Early December to February in the southern hemisphere and July to September in the northern hemisphere).

On the other hand, seaweed mostly consist of macro algae bodies with no leaves, stems and roots save for a hold-fast that anchors seaweed to hard surfaces and transport nutrients via diffusion.

WHAT SERVICES DO SEAGRASSES PROVIDE TO THE ENVIRONMENT AND TO THE SOCIETY?

a) Seagrasses stabilise sediment in the coastline and prevent erosion in the coast like mangroves.

b) They act as habitats and places of refuge for crabs, lobsters, starfish, mollusks, fish, clams, and various species of shellfish. As they are closer to the coastline, existence of seagrass supports local fishing communities.

c) They have a higher carbon sequestration ability than that of landbased plants as they can deposit large amounts of atmospheric carbon to the seabed allowing them to reduce the effects of man-made climate change.

d) They are reported to influence filtering heavy metals and pollutants like petroleum which essentially make seagrass an improver of water quality.

e) Large grazing animals like dugongs, manatees and turtles consume seagrass and their faeces act as fertiliser for growth of new seagrass meadows. This suggests certain large marine animals support seagrass habitats and vice versa.

f) In early history, some cultures in Asia and Europe have used seagrass as a raw material to build houses and baskets.

WHERE CAN YOU FIND THEM IN SRI LANKA?

In Sri Lanka, they can be found in lagoons and coastal embayments like the Negombo Lagoon, Batticaloa, Puttalam, Jaffna, Palk Bay and Mannar. Seagrasses are often found in meadows but can also occur in patches.

IN WHAT KIND OF AREAS DO YOU FIND SEAGRASS?

Seagrasses preferably grow in areas with high amounts of sunlight to help them release oxygen into the water column, increasing erosion and construction in the coastline creates disturbance in the environment resulting in sedimentation, seagrasses respond quickly to its environmental changes and often release its seeds or adjust its plant morphology to adapt to its new environment.

ARE SEAGRASSES UNDER THREAT OR ARE THEY UNDER THE RISK OF BEING ENDANGERED?

Like most organisms around the world, seagrasses are under threat due to increasing coastal development projects that disregard the importance of seagrasses for fisheries communities and to the environment. Not to mention, harmful fishing practices that utilise explosives, trawling and dredging damage the seabed thereby increasing sediment suspension that eventually smother and destroy seagrass meadows in the process. Other destructive development projects are seen with the construction of shrimp farms in mangrove forests and in lush seagrass meadows especially in Puttalam Kalpitiya area.

Seagrasses are typically resistant to damages occasionally caused by heavy storms like cyclones which are prevalent in the tropical climate. Yet they are powerless to the effects of climate change that are now exacerbated by increasing ecologically insensitive coastal development projects.

ARE THERE WAYS TO SAVE SEAGRASSES?

In most countries around the world, seagrass is being restored in areas where seagrass meadows are severely degraded since the past century and are also used as an alternative to existing and unsustainable coastal protection devices like sea walls and breakwater lines. In most countries, seagrasses are extracted from ‘donor’ meadows and their shoots are transplanted in a degraded meadow where their growth is actively monitored until they are fully established. In Sri Lanka, seagrasses exist in areas where large dugongs roam around, there have been dugong conservation programmes implemented in the past which looks at ways to protect dugong populations and to help conserve seagrass meadows. However, there are no direct seagrass conservation seeking to restore degraded seagrass meadows in large coastal development coastlines in Sri Lanka. There is also a need to further the knowledge of local seagrass species in this country as Sri Lanka possesses aunique biodiversity that is not limited to terrestrial mammals alone.