Seagrasses in deep trouble

Posted: 1 March 2005

Author: Henrylito D. Tacio

Seagrasses are the least studied and least protected among the marine habitats. These underwater plants, which provide an array of environmental services from filtering sewage and trapping sediments to providing refuge to marine species, are threatened with extinction in many parts of the world. Henrylito Tacio reports.

Seagrasses. Photo: Dr Miguel Fortes
Seagrasses. Photo: Dr Miguel Fortes
Seagrasses help mitigate against pollution and provide sanctuary to a host of marine species© Dr Miguel Fortes
"A vital marine ecosystem whose importance has largely been overlooked until now." That is how Dr. Klaus Toepfer, the executive director of the United Nations Environment Programme (UNEP), describes seagrasses.

Found along the coast, supporting the mangroves, seagrasses comprise one of the most conspicuous ecosystems of the shore. They are not true grasses neither alga nor seaweeds. They are the only group of underwater living plants in the marine environment that flower.

Unknowingly, seagrasses in some parts of the world are on the verge of rapid disappearance, according to "The World Atlas of Seagrasses," the work of UNEP's World Conservation Monitoring Centre (WCMC), based in Cambridge, UK.

The Atlas estimates the area of seagrasses in the world at 177,000 square kilometres, an area about two-thirds the size of the UK. But this is likely to be an underestimate, because there have been no surveys of seagrasses off the western coasts of Africa and Latin America.

The 60 or so species of seagrass, which grow in large meadows in both tropical and temperate seas, are extremely varied. They range in length from the 2-3-centimetre leaves of sea vines in deep water off Brazil to the strands of eelgrass that grow to more than four metres in the Sea of Japan.

According the World Conservation Monitoring Centre (WCMC), fifteen percent of the world's seagrasses have been lost in the last 10 years. "The scientists have presented us with a worrying story. In many cases, these vitally important undersea meadows are being needlessly destroyed for short-term gain without a true understanding of their significance," says Dr. Toepfer of the atlas.

This is particularly true in the Philippines, which has 18 species of seagrasses along its coasts, ranking it second only to Western Australia. "We have already lost from 30 to 50 percent of our seagrass habitats in the last 50 years," says Dr Miguel D. Fortes, a marine scientist and the country's leading expert on seagrasses.

As in other parts of the world, little is known about the way and the time seagrasses reproduce in the country. "Seagrasses are the least studied among the habitats in our coastal zones," says Dr Fortes, the only Filipino to receive the prestigious International Biwako Prize for Ecology for his work on seagrasses. "Despite their high biodiversity and abundance, seagrass habitats are still poorly understood in this country."

In the Philippines, major distributions of seagrass beds occur in Bolinao Bay in Luzon, Palawan, Cuyo Islands, the Cebu-Bohol-Siquijor area, Zamboanga, and Davao. Other beds are scattered throughout the coastal expanse of the other islands.

Most coral reefs in Southeast Asia are associated with seagrasses. "These two ecosystems could potentially supply more than one-fifth of the fish catch in the region," says Dr. Fortes, who now heads the UNESCO Intergovernmental Oceanographic Commission Regional Secretariat for the Western Pacific in Bangkok, Thailand.

A total of 1,384 individuals and 55 species from 25 fish families have been identified from five seagrass sites in the Philippines alone. "All have economic value mostly as food and aquarium specimens," Dr. Fortes reports. "Five times as many fish live in seagrass beds as above sea floors of mud, shells, and sand."

Environmental service

According to the Filipino marine scientist, seagrasses are among the most productive of coastal ecosystems, rivaling coral reefs and mangroves in environmental and economic importance. "Seagrass beds filter sewage, reducing the pollution that could harm the coral reefs and mangroves," he explains. "They are also biotic heavy-metal reservoirs or sinks and help to stabilize the coast by trapping sediments."

More importantly, the seagrass system provides primary refuge for economically and ecologically important species. Among those found in the seagrass beds are sea cucumbers, sea urchins, crabs, scallops, mussels and snails. Shrimps spend the early stages of their lives in seagrass areas. The sea cow ("dugong"), an endangered sea mammal, is almost completely seagrass-dependent.

This specie of seagrass, Enhalus acoroides, is an important source of food. Photo: Dr Miguel Fortes
This specie of seagrass, Enhalus acoroides, is an important source of food. Photo: Dr Miguel Fortes
This specie of seagrass, Enhalus acoroides, is an important source of food.© Dr Miguel Fortes
Seagrasses, like seaweeds, can also be eaten. The seeds of Enhalus acoroides, for instance, are eaten raw. The young leaves of the other species are eaten as salad when mixed with tomato and other vegetables. Dr Fortes reports that a former colleague at the Marine Science Institute of the University of the Philippines, Dr Marco Nemesio Montano, has discovered that the seeds of Enhalus acoroides could be made into flour, a viable substitute for the ordinary flour use in baking. "In addition, he has added pickled Syringodium leaves to our salad menu. And it tastes good," he says.

The marine scientist warns, however, that while a great potential for the use of seagrasses exists, "we should be careful in promoting it without first knowing their vulnerability in the face of environmental change and extremely high food and income demands."

Rapid disappearance

Despite their importance, seagrasses are fast disappearing from Philippine waters. "My present estimate of seagrass areas in the Philippine is roughly 978 square kilometres; but this is only from 48 sites in the country, comprising only about 13 percent of the entire length of its coastline. So you can imagine its huge extent if the entire coastline of the country is surveyed," says Dr Fortes.

Marine experts traced these to various destructive disturbances caused by both natural and man-induced influences. Among the natural threats are cyclones, typhoons, tidal waves, and volcanic activity. Man-made causes include agricultural cultivation and mining, which led to heavy siltation in estuarine areas which, in turn, resulted in lower productivity and even burial of seagrasses, says the recent environmental quality report from the Department of Environment and Natural Resources (DENR), a government agency.

"Seagrass beds are under pressure due to the basic need of human beings for food production, transportation, waste disposal, living space and recreation," commented Ingrid Gevers, a marine biologist who once worked with the European project in Western Samar.

Human activities such as industrialization, development of recreational areas along the coast, dredge and fill operations have also led to the decline of seagrass beds.

Pollution has also taken its toll. Sewage and domestic wastes from municipalities are carried by rivers and flushed into the coastal areas. Simultaneously, wastes from coastal communities are directly dumped into the sea.

Like most plants, seagrasses need sunshine to grow. Dirty or muddy water shades the seagrasses, thus limiting their growth. "Dirty or muddy water results primarily from upland runoff, boat traffic, wind mixing and gleaning (panudsod)," explained Gevers. "Sediments, caused by deforestation in upland and watershed areas, are washed into streams and into coastal areas," she added.

Eutrophication or nutrient loading intensifies the problem. "In seagrass beds, the heavy nutrient load promotes the growth of algae which become so huge that they cover the seagrass beds and prevent the sunlight from reaching the seagrasses," deplored Gevers.

Saving seagrasses

To save seagrasses disappearing from Philippine waters, Dr Fortes recommends three environmental measures for better management of the resources: preservation, conservation and production intensification.

Preservation or non-use of selected areas will guarantee the continued survival of seagrass beds or meadows, which may be available for scientific and educational purposes only.

Conservation or wise-use means maximum yield in minimum time. "In time, the seagrass becomes a renewable resource," explained Dr Fortes.

Production intensification encourages "activities which have shown remarkable potentials and benefits for sustainable user application."

On what the Philippine government can do, the marine scientist who now heads the UNESCO Intergovernmental Oceanographic Commission Regional Secretariat for the Western Pacific in Bangkok, Thailand, suggests: "By all means mention, explicitly, the word 'seagrass' in all its coastal environmental laws and regulations. Most of these laws merely say 'coral reefs,' 'mangroves,' 'coastal habitats,' 'fisheries'."

Dr Fortes continues: "But to the uninitiated who implement these laws, and who know nothing about seagrasses, they will focus effort and resources on the usual corals, mangroves, fisheries. This is where I admire Indonesia and Thailand, which now do have laws mentioning seagrasses. But nowhere in the world can you find a regulation solely for the protection and management of seagrasses, except in Puerto Galera, Oriental Mindoro, where the mayor made it the subject of his first Executive Order in 2002."

However, despite recent developments, "there still exist many gaps in our knowledge of seagrass ecosystems," says Dr Fortes. "Yet, action must be taken if man hopes to gain the most from this resource. Simply by taking an interest now, aren't you glad that you have taken the first step?"

Henrylito Tacio is People & the Planet's Contributing Editor in Southeast Asia.