Olango Island Group coral reef

• Category: Marine and Oceanic Biomes.
• Geographic Location: Asia.
• Summary: These coral reefs are highly diverse but threatened by overexploitation—although government programs and education have slowly helped increase the fish population.

The Olango Island Group is a cluster of seven islands in the central Visayas region of the Philippines, just off the coast of Cebu. This seven-island group has a total land cover of 3.9 square miles (10.3 square kilometers). The islands are raised coral reefs; in the center of the group is a tidal flat that supports a 3.5-square-mile (9.2-square-kilometer) area of the Olango Island Wildlife Sanctuary.

The Olango Island Group has a tropical climate, with temperatures ranging from 73° to 86° F (23° to 30° C) and average rainfall of 57 to 62 inches (144 to 160 centimeters). Approximately 20,000 people lived in this island group in the late 1990s, but by the mid-2020s, the population had doubled to an estimated 40,000. Around 75 percent of the population engages in fishing or related activities for subsistence.

More than half of Olango is composed of diverse coastal and marine habitats. This island series, which is no more than 33 feet (10 meters) above sea level, is especially known for its low-lying, limestone intertidal mudflats, mangroves, wide fringing coral reefs, seagrass beds, and hard reef-building coral. This cluster of islands is accompanied by six satellite islets that are bounded by a steep coral reef wall to the west and a sloping reef to the east of Olango.

The Philippines has a coral cover of approximately 10,425 square miles (27,000 square kilometers), of which only 5 percent is in excellent condition. Of this area, Olango Island Group’s coastal habitat, including seagrasses and coral reefs, occupies only 15 square miles (40 square kilometers). Seagrass represents an average of 44 percent of live cover, while coral represents only 22 percent.

Super Typhoon Odette, which struck in December 2021, severely affected the reef of Olango. Much of the coral was damaged, and areas of the reef were flattened. Coral recruitment is the process by which coral becomes reestablished after a natural disaster or another event destroys the organisms. In the 2020s, recruitment of the Olango Reef was slow. Furthermore, soft corals and bamboo coral were taking over the reefs. These organisms prevent coral larvae from attaching and thus growing.

Biodiversity

At the southern end of the islands is the large intertidal bay that is now the Olango Island Wildlife Sanctuary, which was declared a Wetland of International Importance under the Ramsar Convention in 1994. The complex structure of coral reefs offers shelter to diverse fauna, many of which are food for the Olango Island Wildlife Sanctuary birds. Around one hundred bird species have been identified in the Olango Island Group, of which, around half are migratory. Among the migratory species are the Chinese egret, Asiatic dowitcher, tern, eastern curlew, plover, sandpiper, black-tailed godwit, and red knot.

There are over 2,300 coral-reef-associated fish species in the Philippines, including those of the Olango Island series. Species richness and diversity in fish have been shown to correlate with certain characteristics of coral diversity, such as architectural complexity, biological diversity, species richness, abundance, colony size, coverage of living coral, and coverage of massive and encrusting coral. Overall, the Olango Island reefs have an annual fish yield of 5.5 tons (5 metric tons) per 0.4 square mile (1 square kilometer), which is quite low compared with the 17 to 22 tons (15 to 20 metric tons) per 0.4 square mile (1 square kilometer) estimated for other Philippines reefs. Experts attribute this low annual fish yield to overfishing, destructive fishing methods, and few protected areas.

Human Impact

Although illegal fishing has decreased considerably in the region due to government intervention, fish yields remain below their true potential, due to years of damaging harvesting methods. The Olango coral reefs, although diverse in nature, are generally in poor condition. Coral reefs in the area have been impacted by what is known as the “tragedy of the commons.” As oceans and coral reefs are considered a shared pool of resources, they are frequently exploited.

Over 75 percent of households on the island cluster are engaged in fishing or related livelihoods. The Olango coral reefs are greatly depleted by local fishers, due to incorrect fishing methods and siltation from island logging activities. As coral cover decreases, the diversity and abundance of reef fish also decrease. Studies have shown a 2.4 percent decrease in reef fish biomass for every 1 percent annual decrease in coral cover.

Government programs protecting natural fish habitats, including mangroves, seagrasses, and mudflats, as well as education for local fishers about the consequences of incorrect fishing methods, have resulted in slow increases in fish yields. The government of the Philippines began using a conservation program called Community-Based Coastal Resource Management in the early 2000s, in which the daily users of a resource set the rules and regulations that govern the resource. It also implemented a conservation method called co-management, a system in which responsibility is distributed equally between the government and resource users.

As a result of these conservation efforts, marine sanctuaries have been built to protect and nurture the region’s coral reefs. Gilutongan Island Marine Sanctuary, a section of the Olango coral reef complex, protects the designated marine habitat from fishers and other threats. The sanctuary has an average coral cover of 40 percent. Although coral recovery from damaging methods may be slow, it is essential that the government of the Philippines continue to protect this important biodiversity hot spot. In the meantime, research continues to investigate the effects of climate change trends on the islands and surrounding reefs. With sea levels rising and the frequency and strength of storm surges increasing, damage to these reefs and their hosted marine species will continue.

Tourism is also a significant threat to the Olango coral reef. While essential for the islands’ economy, excessive, unregulated, and rising tourist activities from 2013 to 2022 contributed to significant water pollution. Plastic pollution and waste management caused considerable strain on the islands’ infrastructure, with much of the excess waste and litter accumulating in the ocean and beaches. This pollution threatens the biodiversity of the reef, which is an essential resource for the islands’ inhabitants.

Bibliography

Fabro, Keith A. S. "Polluted Paradise: How Plastic Trash and Wastewater Imperils Lives and Biodiversity in the Philippines’ Top Tourism Draw." Earth Journalism Network, 12 June 2024, earthjournalism.net/stories/polluted-paradise-how-plastic-trash-and-wastewater-imperils-lives-and-biodiversity. Accessed 15 Dec. 2024.

Finlayson, C. M., and Rick Van Dam, et al. Vulnerability Assessment of Major Wetlands in the Asia-Pacific Region—Summary Report on the Project Workshops for Olango Island and Yellow River Delta. Environmental Research Institute of the Supervising Scientist (ERISS), 1998.

Sotto, Filipina B., et al. Coastal Environmental Profile of Olango Island, Cebu, Philippines. Coastal Resource Management Project, 2001.

"What Is the Impact of a Well-Designed MPA during Strong Storm Surges? The Story of Sumilon Island and San Vicente, Cebu after the Typhoon." Coastal Conservation and Education Foundation, 31 Mar. 2022, www.coast.ph/ccef-news/03/what-is-the-impact-of-a-well-designed-mpa-during-strong-storm-surges. Accessed 15 Dec. 2024.