Impact of Tsunamis on Coral Reefs

Indian Ocean Tsunami and Coral Reefs

On 26 December 2004, a major earthquake off Sumatra and a series of secondary earthquakes throughout the Andaman and Nicobar Islands caused many simultaneous tsunamis that radiated around the Indian Ocean. The tsunamis arrived as huge surges of water that powered over the coral reefs to smash on the land, resulting in enormous loss of life and destruction of property. Immediately following the tsunami, many in the local community and volunteers organised beach and reef clean up activities to minimise damage to the coral reefs from debris (sediment and rubble).

The new report Status of Coral Reefs in Tsunami Affected Countries: 2005 concludes that the major threats to the coral reefs of the Indian Ocean continue to be from human activities, such as over-fishing, deforestation and climate change. These are far more damaging to coral reefs than the tsunami. The report calls for:
  • the establishment of a tsunami early warning system;
  • capacity building in integrated coastal management;
  • improved fisheries management and coral reef monitoring;
  • the establishment of more marine protected areas;
  • careful reparation and rehabilitation of tsunami damage; and
  • development of stronger national oceans policies.

Impact of the tsunami on coral reefs

Damage to the coral reefs in the Indian Ocean was patchy, site dependent and heavily influenced by local environmental conditions such as coastal bathymetry and damage on land. Most of the damage to coral reefs resulted from sediment and coral rubble thrown about by the waves, and smothering by debris washed off the land. Coral reef damage was greatest in Indonesia, Thailand, the Andaman and Nicobar Islands, and Sri Lanka. Within the affected areas, there was 30% damage in Indonesia and 13% severe damage in Thailand. There was little damage to coral reefs in countries further away from the source of the tsunamis because much of wave energy had dissipated. Fortunately, most of the coral reefs of the region escaped serious damage and will naturally recover within 5 to 10 years providing that effective management is implemented to reduce damage from human activities. A small number of coral reefs were significantly damaged and may take 20 or more years to recover; and they may not return to their previous structure.

Impact of the tsunami on mangroves, seagrasses and beaches

Mangroves and coastal forests afforded the most protection to infrastructure on the land and probably reduced the loss of life in these areas. The coral reefs absorbed some of the tsunami energy, thereby possibly providing some protection to the adjacent land. Damage to mangroves was highly variable, ranging from little damage in many areas, such as Thailand, to the destruction of entire forests in some areas, such as Aceh province, Indonesia. Replanting of mangrove forests will be important to assist recovery. Seagrass beds were largely unaffected in the region as a whole, although some areas were either eroded or smothered by sediments. For example, in the Pulo Aceh islands, seagrass beds were seriously damaged which may affect the dugongs in the future. Again, in the Aceh region, coconut trees were uprooted and turtle nesting beaches completely destroyed; in India, many such beaches were seriously eroded.

Based on the report Status of Coral Reefs in Tsunami Affected Countries: 2005. The partners in the International Coral Reef Initiative requested that the Global Coral Reef Monitoring Network in partnership with Reef Check, ReefBase and the CORDIO (Coral Reef Degradation in the Indian Ocean) program update their report on the Status of Coral Reefs of the World: 2004 with a focus on the affected countries and assemble recommendations on how to mitigate similar disasters in the future.