Underwater meadows of grass
Along parts of the shoreline, gently rippling underwater, they look like seaweeds, but in fact, are not. These are seagrasses: flowering, seed-bearing, rooted in the mud, growing completely underwater, found exclusively in marine coastal waters and in some coastal wetlands.
Like grasses in terrestrial habitats, they form meadows on the beds of shallow coastal seas, estuaries and lagoons. They depend on light for photosynthesis and therefore, they generally grow only in clear, shallow waters. They are sometimes exposed during low tides but cannot survive out of water for extended periods. It may seem like a stretch of imagination but these seemingly innocuous habitats are extremely important both ecologically and economically. Many edible fish are found living in seagrass meadows, which provide feeding, breeding and nursery grounds for many commercially important fish, shellfish and marine invertebrates. These meadows also provide protection. Because of this, seagrasses are critical in sustaining coastal fisheries.
Threatened by human actions: An underwater meadow of seagrass. Pix by Terney Pradeep Kumara
Although there are relatively few species of seagrasses, they can house hundreds of other species — microorganisms, algae, invertebrates and vertebrates. Because of their three-dimensional structure in the water, seagrass meadows provide protection for juvenile fish, many marine organisms, their eggs and larvae. It is estimated that a single acre of seagrass may support as many as 40,000 fish, and 50 million small invertebrates! In the tropics, threatened species such as seahorses, marine turtles and Dugongs are also found in these ecosystems. A single acre of sea-grass is estimated to produce over nine tonnes of leaves per year, providing a vast amount of food for many animals hiding among their leaves.
Seagrasses take up nutrients from the soil, and cycle them back into coastal waters. Seagrasses absorb carbon dioxide from the water when they photosynthesize. Like forests on land, they function, therefore, as carbon sinks. Per square metre per year, seagrasses absorb 33 grams of carbon dioxide, which is similar to absorbing the carbon dioxide emissions of a car that has travelled 2,500 kilometres.
Seagrasses have been called ‘biological sentinels’ or ‘coastal canaries’. Like canaries that were taken into coal mines to test the quality of the air, seagrasses respond to changes in the quality of water, indicating deterioration of the environment by degrading and declining before dying. These changes are visible very quickly so that it is possible to take management action.
Fifteen species of seagrasses have been recorded in Sri Lanka. There may be more species, but there is a lack of information about the distribution and species composition of seagrass meadows in Sri Lanka. Partly because of the security situation that prevailed in the northwest during the last three decades — where seagrasses are abundant — and partly because of the need for specialised swimming, diving and snorkelling skills for studying seagrasses, there has not been sufficient research carried out in the area.
Studies on the diversity and distribution of seagrasses in Sri Lanka, are, therefore, important.
Dr. Terney Pradeep Kumara, Head of the Department of Oceanography and Marine Geology, University of Ruhuna, and his team, with funding from the Small Grant Facility (SGF) of Mangroves for the Future (MFF) set out to study the species diversity, relative abundance and distribution of seagrasses in the Puttalam Lagoon.
During a period of one year, he and his team selected 14 different sites, representing almost all the areas in the Puttalam Lagoon. Following standard scientific methods, these areas were assessed.
Eight different seagrass species were observed in the Puttalam Lagoon during their study, the most common of which are Enhalus acoroides, Halophila uninervis, Halodule pinifolia, Cymodacea rotundata, C. serrulata and Syringodium isoetifolium.
When the team mapped the seagrass habitat, they found that seagrass meadows were found along almost all the edges of the Lagoon.
But what Dr Pradeep Kumara and his team found were that these valuable ecosystems, like most others, were battered by a range of human actions that threatened their survival and the survival of species living within them.
Prime among these threats was pollution. Around the Lagoon are shrimp farms — which started in the 1980s and increased during the 1990s. Shrimp farms release untreated effluents — containing chlorine, pesticides and antibiotics —into the Lagoon, and these include sediments. There is also cultivation. Agriculture is the second most important livelihood in the district, with 29.3% of the population involved. One of the major and common threats to seagrass meadows is the deterioration of water clarity when sediments increase. When there is excessive sedimentation and the water becomes muddy, then seagrass meadows are affected, because they cannot photosynthesize. When there is too much sediment, seagrasses also become smothered.
When there is runoff from inland waters (for example from shrimp farms and cultivation) — carrying with it nitrogen and phosphorus from fertilisers, animal and domestic waste, there is an extreme burst of growth of algae. The water then turns cloudy and green, further blocking light penetration. The balance in the ecosystem is destroyed by this process — which is called eutrophication. Seagrass meadows are extremely susceptible to eutrophication.
In addition, fishermen use damaging fishing methods, such as push and pull nets — which are placed on the bottom of the shallow Lagoon — and pushed or pulled as the names imply. These nets damage seagrass meadows. There is also dynamite fishing which decimates ecosystems.
Another emerging threat is from recreational activities that are rapidly increasing in the Puttalam lagoon. Mooring, propellers, kite-surfing and jet skis are emerging as major threats to seagrass meadows. When boats — either for fishing or recreation — enter into areas where there are seagrass meadows, their propellers can slash leaves, as well as underground stems of seagrass, leading to fragmentation of the habitat, which, in turn, leads to erosion. Irresponsible mooring and recreation can endanger these habitats.
Dr Pradeep Kumara says that the biggest issue is that there is so little knowledge about seagrasses: there is a paucity of scientific knowledge; the general public knows little about their ecological importance and the fishermen are no better. Even though fishermen know that shrimp larvae and young fish take refuge among the leafy ‘canopy’ of seagrasses, they do not realise the connection when asked “What will happen if seagrass meadows disappear?”
According to Dr Pradeep Kumara, the simple answer is that if seagrass meadows around Puttalam Lagoon disappear, fisheries in the Lagoon will be severely affected. Currently, there are about 6,000 fishermen fishing directly in the Lagoon. Their livelihoods will be ruined.
Creating public awareness about seagrass meadows and their importance for humans has now become a priority. Under this MFF project, a brochure is being prepared for distribution among coastal communities. The scientific data obtained during the study will feed into the next cycle of the Ministry of Environment and Renewable Energy’s Red Listing process (assessing the threat status of animals and plants of Sri Lanka) and has already been shared among the scientific community.
With the support from MFF for a second grant, Dr Pradeep Kumara and his team have now expanded their reach to assess the diversity of and threats to seagrass meadows from Kalpitiya beyond Puttalam lagoon to Thalaimannar.
As scientific studies proceed, the creation of awareness among the general public remains a priority. The first step towards conservation is appreciating the beauty of natural habitats. Each time we go to the beach, a lagoon or a national park, we are doing just that. But the next, crucial step in conservation is understanding the vital link between the well-being of ecosystems and our own well-being. We need healthy ecosystems for food and firewood; for the air that we breathe; to protect our watersheds; to prevent floods and erosion; to clean our waters; to soak up the carbon that we spit out into the atmosphere.
We need to understand clearly that ‘without the land, the rivers, the oceans, the forests, the sunshine, the minerals and thousands of natural resources, we would have no economy whatsoever’ (Satish Kumar, 2008)
| Mangroves for the Future
Mangroves for the Future (MFF) is an regional initiative comprising a consortium of international intergovernmental organisations such as IUCN, International Union for Conservation of Nature, the United Nations Development Programme (UNDP), the United Nations Food and Agriculture Organization (FAO) and the United Nations Environment Programme (UNEP), as well as CARE International and Wetlands International (WI).MFF seeks to achieve demonstrable changes and results across four key areas of influence: regional cooperation, national programme support, private sector engagement, and community action. The MFF Small Grants Facility (SGF) is a window for financing sustainable, local level initiatives in coastal areas, through small grants. The main objectives of the SGF are to finance small projects to support local community action for the restoration and management of coastal ecosystems and their use on a sustainable basis. |
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