Natural disasters and ocean ecosystems

How did the Japanese earthquake and resulting tsunami affect the oceans?

Really, we don't know, but it's nearly certain that ocean effects are less dramatic than effects on people.

Here's an excerpt from an interesting article on the 2004 tsunami in Southeast Asia:

"...man was not alone in feeling the impact. Ecosystems and other species were also hit.

To be sure, photographic and video images relayed by the media have shown trees swept away by waves and water-drenched lands. Other reports have mentioned wildlife that escaped the destruction, as some sort of instinct seemed to tell them to seek higher ground prior to the arrival of the tsunami waves. And yet the full scope of the tsunamis’ environmental impact remains under-reported, despite its obvious importance for the recovery of the affected areas and the well being of the survivors.

Experience from previous tsunamis and other major floods suggests that the environmental damage they inflict is linked to saltwater intrusion in ground water and to the disappearance or relocation of beaches. Tsunamis may make small, low islands uninhabitable. Vegetation in large stretches of lowland can be hurt substantially as saltwater-tolerant mangroves and grasses take over from other species. For rare animals with specific reproduction sites, like marine turtles, the tsunami’s effects could spell extinction.

But whereas the damage to the environment on land can be seen, the ravages imposed on the marine environment are hidden. Obviously, when extremely strong waves hit coral reefs, some coral breaks off. But this is a comparatively small problem. The surface of coral is highly sensitive, and will now be exposed to major damage from all sorts of silt and debris carried back by water receding from flooded land.

At the same time, the material brought back from land to sea include nutrients and trace elements that cause a boom among plankton, which in turn feed other marine biota. Locally, but sometimes still at a grand scale, the shock waves cause major sediment slides on steep underwater slopes such as those of the continental shelves.

Closer to the shore, many natural ecosystems, most notably coral reefs and mangroves, act as natural shock absorbers and wave breakers. During the past several decades, these ecosystems have been damaged and reduced in most countries along the Indian Ocean. Indeed, the damage from the tsunami waves was far more devastating than it would have been had they still been intact.

Wildlife may fare better than the physical environment. This is particularly true of fish stocks, owing to large-scale destruction to fisheries. More than 13,000 fishermen were killed and another 5,000 evacuated in Sri Lanka alone, with 80% of the fishing fleet lost or severely damaged. On the Thai coast, according to the UN Food and Agriculture Organization, 4,500 fishing vessels were smashed, jeopardizing the livelihoods of 120,000 people in fishing villages there.

The situation on Sumatra is similarly grim, and it is perhaps even worse in the Maldives, Laccadives, Andamans, and Nikobar islands, where not only fishermen and boats were lost, but harbours were ruined. Along the coast of the Indian states of Andhra Pradesh and Tamil Nadu, some 30% of the fishery capacity was lost. Mozambique, Somalia, and Tanzania on the African side of the Indian Ocean have also reported severe damage to their fishing.

Such major losses in fishing capacity, with their far-reaching negative socio-economic consequences on the human populations affected, are bound to have major, mostly favourable, effects on the fish stocks. The reason is simple: with most fish populations nowadays hit hard by over-fishing, fewer fishermen will mean more fish. Another factor that will help fish stocks is a religiously motivated hesitation by the public in some areas to eat marine fish, as they are perceived to have fed on human corpses washed to sea."

And here's an index of tsunami information from National Geographic.

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