Mangrove forests and its functions

• What are mangrove forests?

MANGROVES are highly productive forests growing along tropical tidal mudflats and along shallow water coastal areas extending inland along rivers, streams and their tributaries where the water is generally brackish.

Mangrove forests are interconnected with other ecosystems such as the seagrassess, coral reef, and marine ecosystem. (with illustration) It is a home and feeding and spawning ground for so many animals such as mollusks, crabs, bivalves, insects, fish, worms, and birds, amphibians, reptiles. There are 13.8 to 15.2 M ha of mangroves in 123 countries in the world.

Brief discussion on coping mechanisms: Mangroves has salt glands for high salinity of saltwater; It has specialized roots and breathing structures; seeds are viviparous; it has thick, waxy and succulent leaves to conserve water. There are 70-74 species of mangroves in the world. In the Philippines, we have 37 species.

As an ecosystem, mangroves form a unique association of plants dominated by the mangrove forest as the primary producers interacting with associated fauna and the physical environment.
Mangrove ecosystems have extremely high natural productivity in terms of plant growth and all the associated organisms. Much of this productivity translates into useful products for people in the form of wood, fish and crustaceans and various other ecological and economic benefits.

• Ecological services

Mangroves provide benefits which have not yet been measured in monetary terms within the Philippine context. These include disturbance regulation including natural processes such as stabilizing land from erosion, preventing floods and absorbing organic wastes.

In addition, mangroves provide habitats for animals (estuarine fish and terrestrial mammals) which may be valuable to people and biodiversity in general.

Many Uses of Mangrove Products and their Values

1. Provision of nursery grounds for fish, prawns and crabs and support of fisheries productions in coastal waters;
2. Protection of shore of the lagoons and the estuaries from storm waves and erosion.
3. Reproduction of some organic pollution in near shore waters by trapping or absorption.
4. Recreational grounds for bird watching and observation of other wildlife
5. Access to a high diversity of mangrove plants and animals, and their adaptations, making them ideal field laboratories for biology and ecology students and researchers.

Benefits of Mangroves to Humans:

1. Clean Water
2. Fish, shellfish, mollusks, etc.
3. Medicines
4. Tannins
5. Wood (Fuel and Construction)
6. Honey
7. Alcohol
8. Shore Protection
9. Recreation and Biodiversity

Role of mangrove forest on fishery production

Healthy mangrove ecosystems continue to supply fish products, wood and other useful products to people regardless of other factors as long as basic environmental parameters are honored.

In contrast, intensive aquaculture is plagued with disease, acid soil, market fluctuations and water quality problems, all of which undermine economic viability.

This is why many shrimp farms have closed in the Philippines and elsewhere in Southeast Asia, leaving many abandoned and degraded mangrove habitat areas.

Mangroves Improve Our Environment

As Anchor:
Extensive lateral roots of some mangroves which provide effective anchorage. They also help to bind and stabilize the soils along the coast.

As Buffer:
Collectively standing together, these mangrove trees provide a wall against strong winds and waves. Their leaves, branches and trunks break the force of storm winds and typhoons. They help protect coastal habitats from storm damage. They serve as buffer zones.

As Filter or Strainer
They also stop sediments that are washed by rivers to the coast, thereby protecting reefs and sea grasses. These sediments include large amounts of harmful substances such as excess nutrients from fertilizers, pesticides from agricultural lands in the upper watersheds or heavy metals from mining.

As Sponge:
Mangroves catch storm waters, soaking them up like sponges, and releasing them slowly after the storm has passed. They help to prevent flash floods. At the same time, mangroves serve to protect coral reefs and sea grass beds from sediments and sudden flooding of fresh water.

As Food Basket:
Mangrove ecosystems are among the most productive in the world. They trap large amounts of carbon, turning it into food for other plants and animals, such as fish and mollusks.

As nursery and shelter
Mangroves are good nurturing places for small animals. The tangled roots offer protection for young fish and small animals against predators. The mangrove branches provide resting places for birds.

As air cleaner
The green canopy of leaves and branches produces oxygen through photosynthesis. This promotes clean air. Mangroves have the ability to act as sinks (natural catch basins) for carbon and sulfur, which cause air pollution from the burning of fossils and peat.

For fresh/salt water balance
Some mangroves in the coastal wetlands catch fresh water. They help maintain the balance between sea water and fresh ground water.

Economic value
Fisheries: P45,000-P620,000 / hectares/year
Wood products: P460,000 / hectares/year
Erosion control: P3000/household/year
Waste disposal: P264,000 / hectares/year or P59,500 / hectares/year
Coastal protection and waste disposal: P420,750 / hectares/year

Total economic value (conservative estimate): P987,000/hectares/year or nearly 1M/hectares/year

Fisheries: P45,000
Wood products: P460,000
Erosion control: P3000
Waste disposal: P59,500
Coastal protection and waste disposal: P420,750

US$ 1.6B in 1997 – total estimate value of mangroves (2010)
US$ 1000 to US$35,000 / hectares/year (1997 & 2001)
US$200,000 to 900,000 / hectares/year (2006)

Status of Philippine Mangrove Forests

The Philippines is an archipelago of around 7,100 islands bordered by 6,300 km of coastline along mangrove forests, seagrass beds and coral reefs. These marine habitats are important in providing food and other goods and services to more than half of the country’s 1,500 towns and 42,000 villages.

Mangroves in particular contribute a wide array of fishery (seaweeds, fish, crabs, prawns, mollusks and other invertebrates) and forestry (timber, firewood, tanbark for dyes, fibers and ropes, corks, etc.) products. Mangrove amenities include coastal protection from typhoons and storm surges, erosion control, flood regulation, sediment trapping, nutrient recycling, wildlife habitat, and nurseries.

Major and minor Mangroves in the Philippines total some 30–40 species belonging to 15 families. At the turn of the century, mangroves covering around 450,000 hectares were so widespread that many coastal areas including the country’s premier city of Manila were named after mangroves. Mangrove forest decline to only 120,000 hectares in 1994–1995 may be traced to overexploitation and conversion to agriculture, salt ponds, industry and settlements. Namria (2003) data is 247,362 hectares.

However, aquaculture remains the major cause—around half of the 279,000 hectares of mangroves lost from 1951 to 1988 were developed into culture ponds. Ninety-five percent of Philippine brackishwater ponds in 1952–1987 were derived from mangroves.

To minimize the impacts of pond construction on mangrove ecosystems and their associated fisheries, the amount of mangrove forest converted into fishponds should not exceed 1 hectare of ponds for 4 hectares of natural mangrove kept untouched.’’ The increase of fish/shrimp culture ponds to 232,000 hectares in 1994 gives a ratio of only onehalf hectare of remaining mangroves to 1 hectare of pond.

To mitigate or reverse this extremely vulnerable condition, there is urgent need for immediate and massive mangrove replanting.