Decline of fisheries production partly due to mangrove decimation

Mangroves are good for aquaculture. (Henrylito Tacio)

By Henrylito D. Tacio 

“Mangroves are like the kindergarten, seagrasses are the secondary schools, and coral reefs are the high schools and colleges for fishes! And, once (the fishes) graduate from university, they return to kindergarten to spawn.” – Khun Psit, cofounder of Thailand’s Yad Fon mangrove preservation project 

Most experts cite overfishing as the culprit of the dwindling fish supply in the country. But that’s part of the equation. Also to be blamed for the downtrend of fish production is the decimation of the country’s mangroves.

Mangroves are good for aquaculture. (Henrylito Tacio)

“Yes, the loss of our mangroves has contributed to the decline of our fisheries production,” admitted Dr. Rafael D. Guerrero III, former director of the Philippine Council for Marine and Aquatic Resources Research and Development.

Mangroves are considered “fish factories.” “They serve as nursery grounds for fishes by providing their fry with food such as zooplankton,” said Dr. Guerrero, an academician with the National Academy of Science and Technology. “They also serve as breeding or spawning grounds for fishes, shrimps and mollusks.”

Mangroves are essential to fish production. “Mangroves are critical spawning, nursery, feeding and transient shelter areas to hundreds of fish species, crustaceans and invertebrates and support an abundant and productive marine life,” explains the FISH (Fisheries Improved for Sustainable Harvest) Project, an initiative implemented by the Bureau of Fisheries and Aquatic Resources-Department of Agriculture (BFAR-DA).

Mangroves have specialized above ground roots called breathing roots or pneumatophores. (Henrylito Tacio)

The muddy waters around mangroves are rich in nutrients from decaying leaves and organic matter produced by the mangroves themselves and also from the sediment that is trapped around the roots.

“Many commercial marine species such as bangus (milkfish) and prawns spend their early life within the mangrove area where they find food and protection from predators,” FISH Project states. “Juveniles of some deep-sea fishes also spend some time in the mangroves before moving on to other ecosystems such as seagrasses or coral reefs. 

Dr. Miguel D. Fortes, a coastal ecosystem expert, says mangrove forests occupy “the area of the coastal zone between the mean sea level and extreme high water of spring tides.” They thrive in sheltered tidal flats, coves, bays, and river estuaries. Generally, mangroves are associated with thick stands of medium-sized and even-aged trees, nipa palms and other plants.

Around the world, there are 54 species of true mangroves (34 major and 20 minor) and 60 mangrove associates. True mangrove species are those that strictly grow in the mangrove environment while associated species may thrive on other habitat types such as beach forest and lowland areas.

This is a mangrove forest in Siargao. (Henrylito Tacio)

The Philippines has around 47 “true mangroves” and associated species belonging to 26 families. Most of the remaining mangroves can be found in Mindanao (29% of the total) and the remaining can be found in Luzon and Mindoro. Old-growth mangrove forests are mainly located in Mindanao and Palawan.

Mangroves offer a wide array of multifarious benefits.  For one, they are important sources of both major and minor forest products. The major forest products include timber, firewood, charcoal, and pulp and paper. The minor products derived are extractives (tannin and dyes), nipa sap and nipa shingles, oil, medicine, resin, tea, and livestock supplements.

Timber products from mangroves are poles, house post foundation, pilings, bridges, ship planking and mine timber props. Wood quality is excellent for making furniture and tool handles.

More than 3,000 fish species are found in mangrove ecosystems, according to Dr. Fortes.

Mangrove seeds are technically called “propagules” because unlike most other plants’ seeds, mangrove propagules germinate while still on the tree. (Henrylito Tacio)

“Mangrove leaves are a source of food for fish, shrimps and crabs and other marine animals,” says the FISH Project. “When a leaf falls, it breaks up and decomposes into smaller pieces, until they become too small to be seen with the naked eye.”

Detritus is what the decomposing plant matter is collectively called. “Detritus is covered with large amounts of small organisms which take up the nutrients in the leaves,” the FISH Project explains. “Individually, these organisms are too small to be of much value to any larger animal, but together they form a coating around leaf particles which many different animals use as food.”

Leaves eaten by animals – birds, monkeys, rats, reptiles and insects, all of which use mangroves as places to roost, breed or take shelter from strong winds or heat of the sun – are not totally digested. They are excreted almost intact, again coated with organisms, and then eaten by marine animals.

Mangroves have specialized above ground roots called breathing roots or pneumatophores. (Henrylito Tacio)

“This process is repeated several times, so that one leaf can literally nourish a juvenile fish for much of its life in the mangrove area,” the FISH Project says, adding that mangroves contribute about 3.65 tons of litter per hectare per year.

In its website, the American Museum of Natural History said that an estimated 75% of commercially caught fish spend some time in the mangroves or depend on food webs that can be traced back to these coastal forests.

Unfortunately, mangroves are disappearing at a rate of 1-2 percent per year, a pace that surpasses the destruction of adjacent ecosystems, coral reefs and tropical rainforests.

“The rate of disappearing mangroves in this century is up to 50% in countries such as India, the Philippines, and Vietnam,” said a report.

“The loss of mangroves will have devastating economic and environmental consequences,” said Greg Stone, senior vice president of the marine programs of Conservation International.

All over the country, mangroves are cut down for various reasons. “Mangrove forest cover in the Philippines has declined substantially during this century,” wrote Alan T. White and Roy Olsen D. de Leon, who once worked with the Coastal Resource Management Project and Silliman University Marine Laboratory, respectively.

The two authors said that only 150,000 hectares of mangroves remain of the 450,000 hectares reported in 1918, the most rapid decrease occurring during the 1960s and 1970s when government policies encouraged the expansion of aquaculture.

The conversion of mangrove areas to fishponds, the two authors claimed, is the final step in a process of destruction that started with over-harvesting of mangroves for fuelwood, frequently by persons other than those who ultimately built the fishponds.

“Cutting of mangroves for fuelwood, charcoal making and construction is probably the second most pervasive intrusion on the resource,” White and de Leon pointed out. Small bakeries, for instance, prefer mangrove wood. The demand for these products leads to illegal cutting, over harvesting, and subsequent degradation of the habitat and ecosystem. This, in turn, contributes to the decline of nearshore fisheries.

The economic boom has likewise contributed to the denudation of mangrove forests. “Mangrove areas are the site for reclamation for urbanization and human settlements, expansion of highways, ports, and factories and tourism and recreational facilities,”said Prof. Rodolfo B. Baldevarona, of the University of the Philippines-Visayas (UPV). “As [a] human settlement, mangrove is preferred because of its proximity to the sea and the fisheries along the shoreline.”

Pollution has also taken its toll. The mangrove areas have been used as disposal for solid and liquid domestic wastes, oil, garbage, and pesticides. “Mangrove forests [continue] to be abused, degraded and removed,” experts pointed out. “Impoverished coastal dwellers throughout the country understand that their existence is being threatened by these processes.”

Dr. Guerrero urged Filipinos to stop the wanton destruction of the country’s mangroves. “Because of the interconnectivity between mangroves, seagrass beds and coral reefs, the loss of one will cause the decline in productivity of the others,” he said. “Fisheries production in our coastal waters will consequently decline.” 

Photos by Henrylito D. Tacio

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