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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (International Institute for Rural Reconstruction (IIRR))
close this folderFreshwater and marine ecosystems
View the documentFreshwater ecosystems
View the documentEstuarine-mudflat ecosystems
View the documentSeagrass ecosystems
View the documentMangrove ecosystems
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View the documentHuman intrusions into the water cycle
View the documentDiversity of coastal and marine resources
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View the documentMarine turtles
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View the documentThe menace of algal bloom
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Seagrass ecosystems


Seagrass ecosystems

SEAGRASS ECOSYSTEMS

Seagrasses have distinct physical features and the presence of roots and a vascular system and the ability to flower distinguish seagrasses from other marine plants like the seaweeds.

Found along the coast, supporting the mangroves in the tropics and the marshes in the temperate regions, seagrasses (commonly called isay or lusay) comprise one of the most conspicuous ecosystems of the shore. Thus, they have often been attributed a fundamental ecological importance as well as economic significance. Seagrass ecosystems have several features as shown in the preceding illustration.

From the viewpoint of coastal productivity and protection, the presence of extensive seagrass meadows is favorable. Also, the interaction of some, if not all, of the above factors is responsible for the seagrass bed's function as a spawning, nursery or feeding ground of fishes, shrimps and other animals. However, as human population increases, so does the multiplicity of demands on the marine environment. Since seagrass beds occupy the shallow waters along coastal fringes, they are vulnerable to man's activities (e.g., dredging operations). And once the seagrass cover is lost, it is often difficult to restore.

Sadly, despite this fact, the economic implications of such dependence has not been well documented. Here in the Philippines alone, most studies have been on taxonomy. Perhaps, with the exception of about two or three studies, no other work on Philippine seagrass fisheries has been carried out. One of these was a survey conducted by Estacion and Alcala in 1986. According to that survey, edible mollusks harvested by fishermen in two primarily seagrass beds in Bais Bay, Negros Oriental, included 27 species of bivalves and gastropods.

Other invertebrates collected were holothurians (e.g. trepang) and sea urchins. Both are gathered for food although the first serves as a substantial source of income as well. In fact, this industry has been in existence in the Philippines for years. Then, too, certain medicinal properties are attributed to some species controlling hemorrhage and fungal action and possibly with some tumor-inhibitive potency.

Five species of sea urchins were found common in seagrass beds in the Central Visayas. The most favored for local consumption is Tripneustes gratilla. Its gonads and other soft tissues are usually eaten raw. Sea urchin caviar can be found in local markets. Approximately 1.3 tonnes are harvested per year.

Egg masses of the sea hare, Dolabella curicularia, are also a popular food fare in the region. Anti-cancer agents have been isolated from this organism. Annual harvests are estimated at 1,000-2,000 kg.

Around eight species of juvenile (e.g. Penaeus monodon or sugpo, P. indicus) and three species of adult crustaceans (e.g. Matuta sp., Portunus sp., Thalamita sp.) have been observed.

In additions adults of approximately 50 fish species in 31 families have been been found. Popular food fishes are the carangids, clupeids, lutjanids and scarids. Another survey revealed 64 species of juvenile fishes in 40 families, 33 of which are considered economically important.

Other fauna found in seagrass beds are sea snakes (e.g., Acrochordius granulatus), small fishes like eels, the Green Sea turtle (Chelonia mydas) and the dugong (Dugong dugon) which is considered as an endangered species throughout its range.

To date, there still exists many gaps in our knowledge of seagrass ecosystems. 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?