Tsunami Less Destructive than Overfishing to Sumatran Reefs

LOS ANGELES, California, January 13, 2006 (ENS) - Coral reefs fringing the coast of western Sumatra suffered minor physical damage from the December 2004 tsunami compared with the destruction on land, newly published research shows. Reef Check, the California organization that conducted the first global reef survey, sent a scientific team to the Indonesian island nearest to the epicenter of the quake and tsunami. They found overturned and broken corals in some areas, but no tsunami damage at more than half of the reefs surveyed.

But overfishing with destructive methods has damaged the reef ecosystems more than the earthquake and tsunami, the scientists found.

"On most reefs we surveyed, fish were few and far between, and most were less than 25 cm (10 inches) long," said Reef Check scientist Bob Foster. "The small size and low abundance of 10 primary food fish families indicate serious overfishing that can destabilize the ecosystem. Poison and blast fishing are common in the region."

Reef Check partnered with the Khaled bin Sultan Living Oceans Foundation and IUCN, the World Conservation Union, for an underwater survey of Aceh’s coral reefs to determine the extent of tsunami damage there.

“Very little was previously known about the health of the reefs in this area,” said Dr. Gregor Hodgson, Reef Check founder and executive director. “This expedition points to the need for better management of coral reefs in this mega-biodiversity region. The wonderful thing about reefs is how quickly they can recover if we take care of them.”

The multinational team of seven scientists and three support crew carried out the Reef Check expedition along the coast of the hard-hit Sumatran province of Aceh from October 17 to 30 aboard the vessel Mermaid of the Equator.

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Shattered blue coral on Pulau Weh October 28, 2005. The pattern of destruction suggests that an earthquake shattered a seven kilometer long series of patches of blue coral, Heliopora coerulea. Brown patches indicate living coral. (Photo by Annelise Hagan courtesy Reef Check)
Starting from Sibolga, the expedition surveyed more than 200 sites over 660 kilometers to Pulau Rondo, the northwestern tip of the Indonesian archipelago. The scientists saw overturned corals and swathes of broken corals where large tree branches and tree trunks were smashed across the reef by receding waves.

Surveys were carried out using manta tows and the globally-standard Reef Check protocol. But the scientists found that high turbidity due to heavy rainfall limited the ability of the team to survey many of the reefs adjacent to the mainland coast. The surveys recorded food fish sizes and abundance, as well as mobile and attached invertebrates including corals.

The team learned that the earthquake damaged these reefs more severely than the tsunami. Damage included uplifted reefs, shattered beds of coral, and overturned coral colonies.

Several islands such as Simeulue were tilted, with one end rising as much as two meters (6.5 feet) while the other end descended a similar amount. This caused tens of hectares of living coral reef to be raised above the high tide level and killed, while other reefs descended into deeper water, altering their ecological zone.

Corals killed by uplift of reefs are now above sea level and will not recover, the scientists said. Other types of damage will recover with time, including broken and overturned corals and patches of dead coral.

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Live overturned table coral at 10 meters water depth, Pulau Rondo, October 29, 2005. Some overturned corals on offshore islands were alive 10 months after the tsunami. (Photo by Annelise Hagan courtesy Reef Check)
Even in areas where severe tsunami damage was recorded, there were still large areas of intact, living coral reef present nearby, the team found. Reef Check says these areas may act as an important source of larvae for recolonization of the damaged reefs.

A special survey was carried out to detect newly settled corals as a measure of recovery, but the scientists found very few coral recruits, indicating that recovery is proceeding slowly.

On land, the earthquake and its aftershocks and the giant tsunami caused slope failures and removed vegetation facilitating increased erosion, sediment transport, and discharge during rainy periods.

Reef Check says a longer-term and more insidious type of reef damage could occur if the turbidity and sedimentation continue. In addition to inhibiting coral settlement, sedimentation can directly injure and kill adult corals.

More alarming to Reef Check than the extent earthquake and tsunami damage was the evidence of stress caused by human activities on Aceh’s coral reefs. "Overfishing and destructive fishing practices are destabilizing these reef ecosystems. When these stresses are combined with increased sedimentation, the reef systems are more susceptible to shifting to an algal dominated, low diversity system," the group warns.

The report concludes that a routine, long-term monitoring program to guide management decisions and to involve the local community in actively protecting their valuable reef resources is essential.

Millions of people depend on these reefs for their sustenance and the continued degradation of Aceh’s coral reef ecosystem will have a long term negative impact on human welfare and quality of life. Relatively modest funding and human resources are needed to implement resource monitoring and management that could reduce stress and reverse the degradation of Aceh’s coral reef ecosystem, Reef Check says.

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Heavy rainfall before the survey resulted in high turbidity and sedimentation along the Aceh coast. (Photo courtesy Reef Check)
The report warns that "the destruction of key infrastructure in the region has already stunted economic growth and may force more residents to rely on ocean resources for survival. The survey results indicate that the fish stocks in Aceh are far from robust."

Both the abundance and size of the 10 common families of food fish are very low. Only in Pulau Rondo were food fish greater than 50 centimeters (20 inches) in length commonly observed.

"Additional demands on the already overfished stocks could push local coral reef fish populations to the point of collapse," warns Reef Check.

The findings from this study suggest that sedimentation, worsened by the tsunami; overfishing; and the use of destructive fishing methods may represent a greater threat to Aceh’s reef ecosystems than the immediate impacts of the earthquakes and tsunami.

Reef Check says that because coral reefs can recover relatively quickly following a reduction in fishing pressure, there is now an opportunity to invest in a long-term strategy to rehabilitate the marine resources of Aceh through education, coastal management, regular monitoring and the establishment and maintenance of marine protected areas.

The results from Aceh are similar to those from other locations hit by the tsunami, the group says. Posttsunami reef studies in Thailand last year found that 66 percent of the 174 sites surveyed showed no or very little damage, with only 13 percent showing severe damage with more than 50 percent of colonies affected. A recovery time of three to five years is expected. The reefs of Sumatra appear to have suffered similar levels of damage.

The Aceh Expedition was a joint project of the Reef Check Foundation, Khaled bin Sultan Living Oceans Foundation and the IUCN. Primary funding was provided by a grant from the Khaled bin Sultan Living Oceans Foundation to Reef Check. Additional funding was provided by Reef Check, IUCN/CORDIO and Dow Chemical Foundation.

The report, "Tsunami and Earthquake Damage to Coral Reefs of Aceh, Indonesia," is online at: http://www.reefcheck.org