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POTENTIAL ECOLOGICAL IMPACTS OF INDIAN OCEAN TSUNAMI ON NEARSHORE MARINE ECOSYSTEMS

The effects of the tsunami at Leworahang, Indonesia. The measured runup height at this location is 36 feet. The unofficial height was 46 feet. A paved road comes to an abrupt halt at the edge of the vertical cliff.Jan. 6, 2005 — In addition to causing tremendous loss to human life and property, the tsunami that devastated coastal communities along the Indian Ocean on Dec. 26, 2004, may have also caused extensive environmental damage throughout the nearshore marine ecosystems in this region. At this time, it is difficult to know just how far offshore the damage extends and little research has focused on this topic. (Click NOAA image for a larger view of the effects of the September 1, 1992, tsunami on the near coastal shore of Leworahang, Indonesia. The measured runup height at this location was 36 feet. The unofficial height was 46 feet. A paved road comes to an abrupt halt at the edge of the vertical cliff. Click here for high resolution version, which is a large file. Please credit "NOAA.")

NOAA researchers have found that tsunamis usually have little, if any, effect on deep open ocean waters, however, they rapidly intensify and become highly destructive once they enter shallower coastal waters—exactly where this area’s valuable coral reefs are known to thrive. Nearshore mangroves and sea turtle nesting areas are also likely to have been inundated by the powerful tsunami waves. Unfortunately, many of these habitats have already been dramatically affected by tourism, overfishing and pollution, so a natural disaster of this magnitude would only add to an already threatened nearshore marine environment.

“The nearshore marine ecosystems affected by the recent Indian Ocean tsunami are likely to have experienced direct damage from severe wave action and indirect damage from sedimentation and excessive amounts of debris,” said Rusty Brainard, chief of the coral reef ecosystem division within the NOAA Pacific Islands Fisheries Science Center.

It is likely that coastal beaches and nearshore land areas devastated by this tsunami could be restored within a few years, but the most severely impacted nearshore marine ecosystems could take centuries to fully recuperate. The future of marine resources in the region could also be dramatically affected, especially the coastal fishing and tourism industries.

Direct Impacts
The direct impact of severe wave energy on shallow nearshore habitats (including coral reef ecosystems, seagrasses and mangroves) could be extensive but also depends on the amount of wave energy these ecosystems are normally exposed to. Areas normally exposed to significant wave energy from large swells or tropical storms are less likely to be severely impacted. On the other hand, shallow bays typically protected from high wave action could have suffered more extensive damage.

Damage by wave energy is also species specific. Some species of coral, algae and other marine invertebrates are extremely delicate and cannot withstand turbulent high energy environments. As a result, these species would be particularly susceptible to the damaging wave energy generated by this tsunami.

Extensive damage to nearshore estuaries, mangrove and seagrass habitats — many of which could have been completely torn free of their roots — would also be expected. However, these habitats would be expected to recover over several months or years.

This powerful tsunami could have substantially altered some shallow water benthic habitats, reducing their effectiveness as nurseries and shelters for fish and benthic organisms — organisms living on, attached to, or burrowing in the sediment of the ocean floor. As a result, some nearshore fisheries could be impacted by very low recruitment success over the next few years. Unfortunately, such impacts could ripple through the entire food chain for decades, however, they will not likely cause lasting impacts.

Indirect Impacts
A major indirect impact of the tsunami on nearshore marine ecosystems includes sedimentation from extreme runoff and the churning up of coastal silt, sand and organic matter. Some ecosystems could have been buried by sediments flushed into shallow nearshore environments. For areas normally exposed to high wave energy or strong currents, this sedimentation will probably be washed away over several weeks or months, depending on degree of sedimentation. In more protected areas (not typically exposed to significant wave energy or currents), it could take years or decades for the ecosystem to recover.

Other major indirect damage could have been caused by excessive amounts of debris, including buildings, vehicles (cars and buses), boats, refrigerators and/or any large, non-buoyant object that ended up in the shallow marine environment. When debris of this type is caught up in strong nearshore waves and current, it can easily 'bulldoze' corals and other benthic substrates (i.e., ocean bottom).

Many of these items and other debris flushed out to sea could have contained hazardous chemicals, oils, paints, freons, cleansers, etc., which could be deposited in and cause stress to nearshore marine ecosystems. These stressors could cause disease in corals, algae, fish and other invertebrates. Because most benthic organisms are filter feeders, this group of organisms is likely to be most severely affected. Unfortunately, these impacts could be long-lived and not become apparent to researchers for months or even years.

Debris, such as lost fishing gear (e.g., lines, nets, traps, etc.) from sunken and damaged boats could entangle and/or drown protected species (marine mammals, turtles, etc.). Because fishing gear is often composed of plastic and/or other non-biodegradable materials, it can last in the marine environment for years or even decades. Metal objects deposited into the nearshore marine environment can also trigger blooms that often outcompete corals for benthic substrate.

NOAA Fisheries is dedicated to protecting and preserving the nation's living marine resources and their habitat through scientific research, management and enforcement. NOAA Fisheries provides effective stewardship of these resources for the benefit of the nation, supporting coastal communities that depend upon them, and helping to provide safe and healthy seafood to consumers and recreational opportunities for the American public.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources. NOAA is part of the U.S. Department of Commerce.

Relevant Web Sites
NOAA Pacific Tsunami Warning Center Bulletins and Map

NOAA Tsunami Page

Deep-ocean Assessment and Reporting of Tsunamis (DART)

NOAA Water Level Observation Network

NOAA and Tsunamis

NOAA Tsunami Research Program

NOAA TsunamiReady Communities are Prepared

NOAA Tsunami Warning System Receives High Marks

NOAA Leading the Way in Tsunami Research and Education

NOAA Reacts Quickly to Indonesian Tsunami

NOAA and the Indian Ocean Tsunami

NOAA Pacific Islands Fisheries Science Center

NOAA Coral Reef Conservation Program

Media Contact:
Jana Goldman, NOAA Research, (301) 713-2483 x 181; Delores Clark, NOAA Weather Service, (301) 713-0622 or Connie Barclay, NOAA Fisheries, (202) 441-2398