When it comes to marine biology, vibrant images of sea-animals, corals, sponges and reefs come to our minds. Little is known about the seagrasses – the gentle yet very important residents of the shallow seas. Seagrasses are the lesser-known aquatic treasures of the ocean that are rated as the third most valuable ecosystem – globally.
SeaGrasses are marine flowering plants that live underwater, forming an important link in the eco-system. Seagrasses alter the flow of water, recycle the nutrients, impact the food chain of marine life systems and provide nurseries, shelter and food for a variety of underwater plants and animals. Their contribution to the maintenance and sustenance of aquatic life is immeasurable, as these delicate green structures support hundreds of other plants and animal, underwater.
Seagrasses are the ancient species that have adapted themselves to exist fully submerged in seawater. It is believed that 100 million years ago, seagrasses originated on land and later went on to adapt to underwater life. Seagrasses are the only flowering plants that have colonized the ocean floor since the time of the dinosaurs.
Their global composition ranges from 0.1 to 0.2% of the aquatic flora as it is restricted by its necessity to thrive on the shallow sea areas. Seagrasses are found in most parts of the world spanning about 60 species that live underwater and flourish in submerged conditions.
Seagrasses are closely related to the gingers and lilies rather than the grasses. They are active photosynthetic plants that require abundant sunlight and other nutrients for survival. The seagrass grows well in sunlit sea beds, where there is shelter from strong wind and water currents. The depth range of the meadow is determined by the availability of sunlight on the sea floor. They are particularly found in areas where there is not intense wave action or dry outs due to low tide. Seagrasses can grow at more than 32 meters depth. In clear water condition, they even grow at the depth of 65 meters.
The sea grass beds are one of the most beautiful sights in the world. Like the grass expanses on land, seagrasses grow in vast meadows under water. The long slender green leaves that reach up to the light above are a sight to behold. It is sheer beauty and to see such a marvel of nature submerged is indeed a soul warming experience. It is hard to believe that these grasses, slender and delicate, form a very important link in the eco-system.
Seagrass Sustains the Marine Ecosystem
Seagrasses, living along the coastal water of land, are essential to the underwater eco-system. From plants to animals, seagrasses are an answer to their existence. The leaves are a source of anchorage for other plants and share a symbiotic relationship. Some animals such as the sea-dog (Dugong), Sea Urchins, Turtles and some fish feed directly on the grass blades. Without the seagrasses, these animals cannot survive. Seagrasses are a safe haven for smaller species such as prawns and fish. They not only provide natural habitat to smaller marine species but also help keep that water clear by absorbing the coastal runoff.
Seagrasses have very dense root system comprising of rhizomes that not only help in effective nitrogen fixing but also helps bind the sea sediment and prevents sediment erosion. The seagrass are very efficient in carbon absorption and binding. It is estimated that seagrasses per square meter are capable of binding about 1000grams of carbon, every year. This amazing ability makes them 3-5 times more effective than near shore phytoplankton.
Seagrasses in India
It is estimated that seagrasses were abundant in the Asia-pacific region 45 million years ago. Today, India is home to more than fifteen species of seagrasses found in different coastal areas of Eastern, Southern and Western parts of India. Most of the species are found in healthy numbers along the Southeast coast (which is the Gulf of Mannar and the Palk Bay), coast of Tamil Nadu, and the sporadic islands of Lakshadweep and Andaman & Nicobar. The most important location for seagrasses in India is the Gulf of Mannar Biosphere Reserve, which is estimated to have more than 13 of its species.
The most common species of seagrasses found in India are:
- Cymodocea rotundata
- Cymodocea serrulata
- Thalassia hemprichii
- Halodule uninervis
- Halodule pinifolia
- Halophila beccarii
- Halophila ovata
- Halophila ovalis
Seagrasses are known to flourish in coastal areas that have good salinity levels, clear waters, adequate sunlight, and minimal strong water currents. The coastal belt of India is favorable for the seagrasses as it provides the optimal conditions for the growth and survival of seagrasses.
Threat to Seagrasses in India
When it comes to global ecological crisis, little is known about one delicate link called seagrass that is silently marching towards extinction. Any damage to the region’s seagrass beds is a strong indicator of deteriorating ecological conditions in that area. The change in seagrass habitat signals an immediate deviation in the marine plant and animal life of that region.
Seagrasses survive in clear shallow seas and grow up to a certain level in the sunlit seabeds. With rising sea levels, the sea grasses face the threat of being relegated to deeper depths of the ocean that makes it impossible for these species to thrive. With ice caps melting, fresh water is being added to the seas, everyday, giving rise to the mean sea levels, which in turn is dissolving the salinity levels. These factors have an adverse impact on the seagrasses for which the sea levels and salinity levels are very important to survive and flourish. These delicate plants have been bearing the brunt of environmental damage since a long time.
Most marine biologists contend that there has been considerable amount of damage done to seagrasses in the last four decades. Some animal species face grave threat of extinction. With human pressure growing along the coasts of South-East Asia and the Caribbean, there is likely to be huge losses to the seagrass beds. This accelerated damage to seagrass groups is mostly due to climatic changes, global warming which in turn refers to changes in oceans salinity levels, shift in water quality, increase in sea surface temperatures, frequency of natural disasters, and more.
It is a known fact that there has been steady decline in the Sea-grass population around the world. It is estimated that around 30000 kilometers of sea grass has been lost in last ten years. The accelerated damage is due to man – mechanical destruction of the habitat and over-fishing.
The bigger threat to seagrass is not from the environment but from the humans. Mans need and greed is one of the biggest threat to these delicate sustainers of the marine ecosystem and the other eco systems surrounding it. Man has been generous in contributing to the endangerment of seagrasses by causing disturbance in the shallow seas. Coastal activities such as ports, harbours, construction, garbage dumps, urban pollution, industrial dumps, terrestrial erosion, coastal development, breakwaters, fish farming, aquaculture, eutrophication, siltation, dredging, anchoring, are taking heavy toll on the fragile plants. While they have taken centuries to adapt to the changes in their environment, it is yet to be soon how these grasses will adapt to the rapid and artificial changes in the seascape. Or rather will they survive this?
There any many associations that focuses on monitoring the seagrass levels and the rate of changes in their habitat. There is a significant amount of effort undertaken by global researchers to study and prevent the destruction of seagrasses. India still has a long was to go to employ such practices but is keenly following the environmentalists for saving the seagrass. A case in point is the recent Sethusamudram project.
SethuSamudram Project, India – Potential Damage to the Seagrass Beds
No other project in the world is so steeped in political, economical, ecological, and mythological significance, that extinction of seagrasses is of no consequence to any of the parties involved.
The SethuSamudram Ship Canal Project is an active proposal to construct a canal between India and Sri Lanka, to facilitate passage of sea-vessels. The Adams Bridge region is a rich biodiversity site, which lies in the path of the proposed canal. The proposed project threatens to destroy the fragile ecosystem – the flora and fauna of Gulf of Mannar Marine Biosphere. Not only seagrasses, but also fragile marine life such as coral reefs, fishes, and all types of flora and fauna of that region are facing a grave danger of extinction.
As part of the Sethusamudram project to make the Palk waters navigable, considerable amount of mechanical activity such as dredging is proposed. Dredging is an excavation activity that involves digging, collecting and clearing the waterways, mostly to keep it navigable. Usually carried on coastal areas, this activity adversely impacts the aquatic ecosystem. Dredging not only causes disturbance in the seabed, uprooting the fragile flora and fauna, but also causes turbidity in water and unnatural sedimentation at the bottom. The seagrasses, being default residents of the dredging site, end up facing harsh environmental conditions ranging from change in water depths, turbulence, sea bed composition, chemical imbalance, toxicants, and much more.
Associated with dredging is the added risk of siltation in which fine grain like particles settle on the sea-bed. Optimal amount of silt helps the seabeds but excessive deposition or accumulation of silt threatens the anchorage of seagrasses and other plants. Also, too much sediment on the seagrass root system can lead to root rot due to clogging.
Continuous development along the coastal areas by way of port and harbours development is resulting is accelerated and sustained damage to marine ecology along the coastal areas, including the seagrasses. While the effects of damage are not being felt instantly, there have been slow and continuous changes to the life form along the coastal areas, which in turn is affecting the life in the ocean. There is indeed no end to man’s quest for developing the land for economic and social reasons, very little thought is being paid to damage to crucial links of life’s sustenance. We are indeed taking great pride in tilting nature’s delicate balance.
Added to the climatic and mechanical onslaughts on seagrasses is cultivation of marine species. Fish Farming, Aquaculture and Mariculture are different types of cultivation of water organisms and animals under controlled conditions, and in this case, the marine environments. This leads to creation of unnatural sea system in the coastal areas, where sea grasses are found. Abnormal levels of fish waster, nutrients supply, mechanical operations, garbage, disrupt the balance environment wherein the seagrasses thrive.
When seawaters receive too many nutrients, it leads to growth of undesired vegetation that harms the natural ecosystem. This is called Eutrophication. Seagrasses are delicate sea plants that need the vital balance of salinity, nutrients, sunlight and oxygen. Eutrophication is a process by which too many nutrients are supplied to a particular aquatic region. This sudden increase in nutrients causes new types of vegetation such as phytoplankton, algae, seaweeds, etc., to grow. With this accelerated growth in vegetation, the amount of dissolved oxygen available to seagrasses reduces. This unnatural disruption in the eco-system causes reduction in oxygen that is required by the dependent animals. Due to increase in vegetation and in its decomposition, the water becomes unclear and unsuitable for seagrasses.
While studies on seagrasses are gaining ground in most parts of the world, the future is still bleak to these residents of Indian waters. Neither fully on land nor completely underwater, their twilight-like existence has left them vulnerable and threatened by many possibilities of extinction. Though ecologically classified as sensitive, seagrasses remain forgotten in the grand scheme of things. Seagrasses are almost on the threshold of extinction, given mans greed beyond need.
While we ruminate, argue, and write, these gentle seagrasses continue to sway in their battle of survival, midst the water tides. They seem to be praying for a better death.
(Image Credits: Green Seagrasses Illustration by Ishrath Humairah)