Mangroves and their importance to food security

Dick M. Melana, Ph.D.

angroves are one of the coastal resource ecosystems (e.g. seagrass and coral reefs) found at the crossroads between the land and the sea. The tidal flat constitutes its theoretical boundary, which sometimes extends to the shallow waters in the coastal areas.

The mangrove ecosystem in the Philippines generally includes the following components:

1. Trees and other plant species constituting about 47 true mangroves and associate species. There are 26 common species dominated by the bakauan (Rhizoporaceae) family.
2. Terrestrial animals such as shorebirds, which include more than 600 species of migratory ones, snakes and other reptiles, monkeys and other mammals, polychetes and other soil-dwelling fauna
3. Aquatic fauna dominated by fishes, crustaceans (shrimp and crabs) and mollusks.
4. The coastal community, which greatly influences the other components (mangroves, sea grass and coral reef ecosystems) and may be the primary factor that determines their existence in the area

FUNCTIONS OF MANGROVES

1. Ecological
   

• Environmental protection
  
  • Mangroves protect coastlines and coastal communities from waves, tidal currents and typhoons
    
    • Crown and stems collectively serve as wind breaks
      
    • Specialized roots trap and hold sediments and siltation from the uplands, thus promoting water quality and growth of corals andseagrasses
      
• Nursery of the sea
  
  • Mangroves provide nourishment, habitat and refuge to the larvae and fry stages of varied species of fishes, crustaceans andmollusks whose grown ups replenish the coastal waters and the deep marine ecosystem.
    
  • For every hectare of mangroves cleared, fish catch is reduced by an estimated 1.08 tons per hectare per year
    
• Organic matter and carbon production
  
  • Mangroves contribute about 3.65 tons of litter per hectare per year; this enters the food chain of the coastal cosystem
    
  • Mangroves fix 1,800 - 4,200 grams of carbon per square meter per year (approximating that of the tropical rain forest and 10times higher than the primary production in the open ocean)
    
• Aesthetic
  
  • Mangroves refresh the air through the production of oxygen and assimilation of carbon dioxide
    
  • Mangroves provide wholesome shoreline landscape
    
• Shelter for wildlife
  
  • Mangroves serve as roosting and foraging grounds for local and migratory wildlife species, especially birds
    
• Pollution sink
  
  • Mangroves absorb air and water pollution, especially organic waste (no indication of absorption of toxic wastes has been noted,however)
    
• Land builder
  
  • Mangroves build land at the rate of about 7cm per year as observed in the 15-year-old bakauan bangkau or bakauan bato(Rhizophora stylosa) plantations (with trees planted at 0.5m x .05m spacing) on Banacon Island
    
• Economic as source of:
  
  • Wood and timber
    
  • Firewood and charcoal
    
  • Nipa shingles and alcohol
    
  • Tan bark
    
  • Poles and piles
    
  • Propagules/seeds
    
  • Crustaceans, mollusks and fishes

IMPORTANCE TO FOOD SECURITY

About 75% of Filipino diet is derived from the sea. In this regard, the role of mangroves in promoting food security in the Philippines may be viewed in two ways:

1. Direct. The direct role of mangroves is expressed in terms of providing habitat and food for edible and commercial species of fish, mollusks and crustaceans. Productivity data on mangroves available locally and abroad are shown below:

G.T. Silvester and D. Pauly (1989), estimating yield and economic rent from Philippine demersal stocks (1946-1984) using vessel horsepower as an index of fishing effort (White, A.T. and A. Trinidad, "The Values of Philippine Coastal Resources: Why Protection and Management are Critical," 1998), showed the following net annual economic value (in USD/ha) of Philippine mangrove areas for different levels of management:

Note: Wood harvest value based on average price of about USD 12/Cu. m. of wood; fish products based on average annual weight of fish and shrimp/ha associated with mangrove areas and an average price of USD 0.80/kg; values based on Philippine pesos. USD 1 = 25 pesos in 1991.

2. Indirect. The indirect role of mangroves in addressing food security can be related to the impacts of the ecological functions of mangroves as previously stipulated, such as for environmental protection, nurseries of the sea, and others.

MANAGEMENT INITIATIVES

Management initiatives designed to enhance the ecological and economic potentials of mangroves are relegated to the overall coastal resources management (CRM) efforts (community organizing, IEC, ICM planning, enterprise development, etc) as well as the Community-Based Forest Management Program (CBFM) of the DENR. The CBFM program is designed to insure the sustainable development of the country's forestland resources. This program encourages the participation of coastal communities in the protection, rehabilitation and maintenance of mangroves and other coastal resources through the issuance of a tenurial instrument called Community-based Forest Management Agreement (CBFMA).

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