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Jan '06

Tsunami Less Destructive than Overfishing to Sumatran Reefs

The December 26, 2004 earthquake and tsunami precipitated one of the greatest humanitarian crises in history with an estimated 232,000 lives lost and 1.2 million people displaced.  It was also feared that the earthquake and ensuing giant tsunami waves, reaching as high as 20 meters in some areas, had severely damaged coral reefs. These fears were confirmed by a rapid Reef Check, Quiksilver and Surf Aid expedition in February 2005 that documented large areas of reef raised out of the water at Simeulue Island , resulting in widespread coral mortality.

In April 2005, a review of post-tsunami assessments of damage to coral reefs revealed that with the exception of Western Sumatra, Indonesia, many of the areas hit by the tsunami, (e.g. Thailand , Maldives , Sri Lanka , and India ) had already been well-surveyed. Recognizing the importance of closing the remaining knowledge gap, Reef Check asked the Khaled bin Sultan Living Oceans Foundation and the World Conservation Union (IUCN) to partner in a survey of Aceh’s coral reefs to determine the extent of tsunami damage in close proximity to the earthquake and tsunami epicenter.

A multinational team of seven scientists and three support crew carried out the Aceh expedition from 17 to 30 October aboard the vessel, Mermaid of the Equator.  Starting from Sibolga, the expedition covered the area affected by the earthquakes and tsunami — over 660 kilometers to Pulau Rondo, the northern-western tip of the Indonesian archipelago. Unfortunately, high turbidity due to heavy rainfall limited the ability of the team to effectively survey many of the reefs adjacent to the mainland coast. Surveys were carried out using manta tows and the globally-standard Reef Check protocol.  The surveys recorded food fish sizes and abundance, as well as mobile and attached invertebrates including corals. A special survey was carried out to detect newly settled corals as a measure of recovery.

The results of the underwater surveys indicated that relatively minor physical damage to coral reefs was caused by the tsunami as compared with the well-documented devastation experienced on land. Tsunami damage recorded included overturned corals and swathes of broken corals where large tree branches and tree trunks had been washed across the reef as the waves receded.

No tsunami damage was observed at more than half of the reefs surveyed. Even in areas where severe tsunami damage was recorded, there were still large areas of intact, living coral reef present nearby. These areas may act as an important source of larvae for recolonization of the damaged reefs. However, of the 5,280 quadrats surveyed for recruits, only 18 recruits were recorded, and 15 of these were in the Banyak Island group. This low density of coral recruits indicate that recovery is proceeding very slowly.

The earthquake damage to coral reefs was more severe than that caused by 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 2 m 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 the ecological zonation.

On land, the earthquakes and tsunami caused slope failures and removed vegetation facilitating increased erosion, sediment transport, and discharge during rainy periods. A longer-term and more insidious type of reef damage could occur if the observed turbidity and sedimentation continue. In addition to inhibiting coral settlement, sedimentation can directly injure and kill adult corals.

A low abundance and small mean size of the ten primary food fish families in Aceh was recorded suggesting that stocks of these fish are overfished. Evidence of destructive fishing practices was common. Overfishing can lead to an imbalanced ecosystem in which the lack of herbivorous fish allows fleshy algae to overgrow corals and dominate the coral reef.

The findings from this study suggest that sedimentation (exacerbated 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.

The earthquakes and tsunami have left the Acehenese more dependent than ever on their marine resources for survival. 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.

Table of contents 2
Executive Summary 3
Introduction 5
Methods 6
Manta Tow  6
ReefCheck Plus Survey  6
Results  10
Patterns of Earthquake and Tsunami damage  10
Substrate Composition  13
Reef Fish  16
Coral Recruitment  18
Turbidity and Sedimentation 18
Discussion  20
Earthquake Damage  21
Tsunami Damage 21
Human Impacts  23
Prospects for Recovery of Aceh Coral Reefs 24
Conclusions  26
Literature Cited  27
Appendix I. Substrate Cover  29
Appendix II. Fish Data  30

The report, ” Tsunami and Earthquake Damage to Coral Reefs of Aceh, Indonesia ,” is online at: [2MB]
Check the entire report here (PDF format)

Source : Robert Foster, Annelise Hagan, Nishan Perera, Cipto Aji Gunawan, Ivan Silaban, Yunaldi Yaha, Yan Manuputty, Ibnu Hazam, and Gregor Hodgson. 2006. Tsunami and Earthquake Damage to Coral Reefs of Aceh, Indonesia. Reef Check Foundation, Pacific Palisades, California, USA. 33 pp.

Sumber : (al)  SOCP

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