Cabayugan River

• Category: Inland Aquatic Biomes.
• Geographic Location: Asia.
• Summary: The Cabayugan River in the Philippines is part of a critical mountain-to-sea ecosystem and threatened by soil erosion, illegal logging, and a decline in water quality, which the government has promised to mitigate.

The Cabayugan River flows down the slopes of Mount Bloomfield, on the island of Palawan in the Philippines, before disappearing beneath Mount Saint Paul to become an underground river for its last 5 miles (8 kilometers) before emptying into the Philippine Sea. The river has become popular with tourists because of its ease of navigability and its promotion in 2011 by the Swiss-based New7Wonders Foundation. As a tourist destination, it is often called the Underground River; the Saint Paul Underground River; or the Puerto Princesa River. In the case of the latter, it was so named because of its association with Puerto Princesa Subterranean River National Park, located in the Saint Paul Mountain range 30 miles (48 kilometers) north of Puerto Princesa.

Until 2007, the Cabayugan was the longest known underground river in the world. The caves through which it flows include major stalactite and stalagmite formations and several large chambers; the lower portion of the river is tidal. The ecosystem here was named a World Heritage Site by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) in 1999, and the river contains important habitats for biodiversity conservation.

Vegetation and Wildlife

The lowland forest of the Cabayugan River includes large trees such as the dao (Dracontomelon dao), dita (Alstonia scholaris), and apitong (Dipterocarpus gracilis). Terrestrial plants include the almaciga (Agathis philippinensis) and rattan (Calamus); shoreline species here include Indian beech (Pongamia pinnata) and bitaog (Calophyllum inophyllum).

Numerous animals live in the vicinity of the river, among them at least 165 species of birds—including all 15 of the island's endemic (found only here) bird species—such as the blue-naped parrot (Tanygnathus lucionensis) and Palawan hornbill (Anthracoceros marchei). The nearby forest canopy is home to the island's only primate, the long-tailed macaque (Macaca fascicularis), as well as the bearded pig (Sus barbatus) and the Palawan stink badger (Mydaus marchei).

Reptiles include eight endemic species and eleven others, including the monitor lizard (Varanus salvator), green-crested lizard (Bronchocoela cristatella), and reticulated python (Phython reticulatus). The river itself is occasionally home to the Philippine woodland frog (Rana acanthi), the island's most common amphibian, and the endemic Philippine flat-headed frog (Barbourula busuangensis). In some of the tributaries and the aboveground stretch, the Philippine crocodile (Crocodylus mindorensis) may be found. This crocodile is one of the smallest crocodile species, with males growing less than 10 feet (3 meters) long. It feeds principally on aquatic invertebrates and builds nests where the smaller female guards seven to twenty incubating eggs.

The underground cave through which the river passes is home to nine species of bat, two species of swiftlet, and the whip spider (Stygophyranus). The dominant species of freshwater crab in the river is a Parathelphusa, not described until 2004 but composing as much as 90 percent of the crab population. The remaining 10 percent are members of more than thirty species endemic to the Philippines. Two Parathelphusa species are endemic to the river: P. cabayugan and P. manguao. The former, which constitutes most of the river's crab population, has a flat carapace dorsal surface with deep cervical grooves, whereas P. manguao has a convex carapace dorsal surface with shallow cervical grooves. Unlike the more typical P. palawenensis, both species have a subdistal spine. These endemic crabs are found in headwaters of moderate to low turbidity, farther from areas of anthropogenic activity.

It is common in the Philippines for fish inhabiting the freshwater regions to return to the sea to spawn, and those of the Cabayugan River are no exception. More than two hundred species of freshwater fish use the river on their way to the sea. Some of the country's endemic fish species, however, including Puntius lindug, P. baoulan, and P. tumba, have been pushed toward extinction by the introduction of carp (Cyprinus carpio) and goby (Glossogobius giuris). Both were introduced as food species for recreational and commercial fishing, and they have competed with the native endemics to the detriment of the latter.

Ecosystem Threats

The Cabayugan River, in recent years, has shown signs of murkiness and reduced water quality, partly as a result of erosion, which was principally caused by forest clearings. In many cases, the clearings were done illegally. Although the Philippines government has criminalized swidden agriculture, also known as slash-and-burn agriculture—in which agricultural fields are created by burning woodlands—the practice continues in the country, especially among the native Palawan people.

The loss of the forest root systems destabilizes the soil and destroys ecosystems. It has a destabilizing effect that ripples through the entire community. Destabilized soil near the riverbank—at the point where the Cabayugan goes underground—contributes to the buildup of silt in the river system that, in turn, reduces the amount of dissolved oxygen. This causes muddy waters and destroys some of the river vegetation and spawning grounds. It also changes the salinity, acidity, and chemical balance of the river by introducing new solids that leach out of the eroding soil. The government, motivated by the river's importance to the tourism industry, has promised to work to repair erosion damage and prevent the illegal logging that has contributed to it.

Mining and agriculture contribute some level of threat to the river as well. Although erosion has received more attention because of the visible change to the quality of drinking water in the area, the contaminants introduced by even small-scale commercial agriculture are much more serious. Fertilizers, pesticides, livestock feces, and soaps enter the river waters via runoff carrying the potential to affect the whole food web of the ecosystem.

In the twenty-first century, threats from climate change and severe weather have increasingly impacted the Cabayugan River. In 2021, typhoon Odette hit the region, damaging the river and the facilities vital to the tourism industry built around the river. The surrounding forest suffered significant damage, with forest management estimating that over 80 percent of the canopy around the Central Park station had been destroyed. As global temperatures rise, scientists predict that the world could see more extreme weather, including increased frequency and intensity of typhoons and other storms.

Bibliography

Formoso, Celeste Anna. "Odette Damages Puerto Princesa Underground River Forest and Tourism Facilities." Palawan News, 26 Dec. 2021, palawan-news.com/odette-damages-puerto-princesa-underground-river-forest-and-tourism-facilities/. Accessed 29 Oct. 2024.

Freitag, Hendrik. "Composition and Longitudinal Patterns of Aquatic Insect Emergence in Small Rivers of Palawan Island, the Philippines." International Review of Hydrobiology, vol. 89, no. 4, 2004, pp. 375-91.

Freitag, Hendrik, and Darren C. J. Yeo. "Two New Species of Parathelphusa H. Milne Edwards, 1853, From the Philippines." Raffles Bulletin of Zoology, vol. 52, no. 1, 2004, pp. 219-31.

Goldoftas, Barbara. The Green Tiger: The Cost of Ecological Decline in the Philippines. Oxford University Press, 2006.

Laririt, Patricia. "Residents of Cabayugan Urged to Protect and Care for PPSRNP." Palawan News, 22 Feb. 2022, palawan-news.com/residents-of-cabayugan-urged-to-protect-and-care-for-ppsrnp/. Accessed 29 Oct. 2024.