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THE EFFECT OF EARTHQUAKE/TSUNAMI IN THE MARINE INTERTIDAL ORGANISM.

Impact of Tsunami on Marine Ecosystem

General impacts by tsunami:

There is likely damage to the structure and function of the coastal ecosystems(coral reefs, mangroves, sea grasses, estuarine mudflats):

The Physical structure has been damaged by the force of the wave itself, physical removal of flora and fauna and increased sediment load which would have killed sediment sensitive corals and sea grasses by smothering. The extent of this damage is being assessed and would vary considerably depending on the local topography and hydrology.

Chemical changes have included saltwater intrusion, eutrophication (enrichment) of the water resulting from increased runoff, raw sewage and decomposition of flora and fauna including unrecovered bodies. There will be the slower decomposition of timber from mangroves, fishing boats and buildings.

Non biodegradable waste such as plastics has contributed to a build up in marine debris.

Exotic (introduced) species used for aquaculture have escaped.

Finally, the biological stricture of the ecosystem could be disrupted as various species at different trophic levels were differently removed. With the structure altered, ecosystem functions could be altered.

Tropical Ecosystems

Coral reefs have been thought of as “nature defense” and there is an early suggestion that the ecosystems in such areas were largely intact. For e.g., the Surin Island, chain off Thailand’s west coast, may have survived better than areas where the coast has been modified by urban development, aquaculture and tourism. Keeping the reefs intact around the Maldives is credited with reducing the loss of life.

Mangroves are an important natural barrier as well as a profitable timber resource. Areas in Pichavaram and Muthupet, in the state of Tamil Nadu, India with dense mangroves suffered fewer human casualties and less damage to property compared to areas without mangroves. On Penang Island, the worst affected area in Malaysia, representatives of the Penang Inshore Fishermen Welfare Association observed that in areas where the mangrove forests were intact, there was reduced property damage and less impact on the cost.

Sandy beaches have been seriously damaged by the tsunami in some areas and sea turtle nesting sites have been destroyed. Coconuts are an integral part of the economy for many coastal communities and feature prominently in tsunami survival stories: people surviving by eating coconuts, people who survived by clinging on to coconut trees so as not to be washed away, and the Acehenese man who clung to a coconut palm and survived at sea for 9 days. Replanting coconuts to restore the sandy beach ecosystem will be an important part of the recovery process.

Direct Impacts

The direct impact of severe wave energy on shallow near shore habitats (include coral reef ecosystems, sea grasses 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 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 sea grass habitats – many of which could have been completely torn free of their roots-would aloes 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 in to 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 near shore 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 near shore 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.

Thus biotic communities, physical habitats and their heterogeneity, nutrient distribution and exploitable resources of these zones could be disturbed significantly. Future studies should focus on tsunami-disturbed changes in:

· Distribution, habitat and yield of exploitable resources like fishes, crustaceans and mollusks.

· Species richness and rates and sequences of recovery, in cases of species loss; primary productivity by phytoplankton.

· Species composition, distribution and abundance of the principle tax a of primary producers (dinoflagellates in BB).

· Tropic status of the regions in the ocean around AN.

· Species richness, community structure and standing crop of macro and micro fauna.

· Zooplankton biomass as estimate of secondary production in BB.

· Impact of sedimentation and mud shield on coral reef communities.

· Changes in nutrients of BB due to massive influx of organic and inorganic matter from coastal mainland.

· Deviations, if any, in unique hydrographic and oceanographic features of the disturbed zones.

· Species loss, changes in habitat heterogeneity and biotic interactions at inter-tidal zones of BB and AN and species recovery rates and sequence.

http://www.ias.ac.in/currsci/mar252006/772.pdf
http://dgukenvis.nic.in/Art8.htm
http://geology.com/records/biggest-tsunami.shtml
http://www.dakshin.org/DOWNLOADS/ECOLOGY%20REPORT.pdf
http://www.bbc.co.uk/news/world-asia-pacific-12903072