Friday, June 19, 2009

An earth shaking event

post-tsunami impacts in the Andaman and Nicobar Islands
By Pankaj Sekhsaria

Sanctuary Asia, Vol XXIX, No. 3, June 2009
---
Endless expanses of coral reefs that were once submerged even at low tide now lay exposed and dead, thrust by the forces of nature above the high tide line. Huge coral boulders studded with now-empty clam shells stood almost a metre in the air, with sand accumulating around them. We anchored that evening off the coast of the Interview Island Wildlife Sanctuary located towards the north of the Andaman group of Islands. I was with Harry Andrews and his colleagues at the Andaman and Nicobar Environment Team (ANET) as they conducted a rapid assessment survey two months after the deadly December 26, 2004 earthquake and tsunami that had ravaged South and Southeast Asia. This was the sight we had seen as we sailed up along the west coast of the Middle and North Andaman Islands and it was an eerie experience to explore the almost lifeless, ‘moonscapish’reefs that now surrounded Interview.

Coral reef uplift on the west coast of the Interview Island Wildlife Sanctuary
(Pic: Pankaj Sekhsaria)

Located relatively close to Aceh in Sumatra, where it all began, the Andaman and Nicobar Islands were particularly hard hit. Almost 3,500 people died, largely in the Nicobars. Huge coastal areas were submerged, basic infrastructure, schools, roads, power houses and thousands of homes were washed away. Post the event I visited the islands in February 2005 and was astounded to witness the brute force of the catastrophe.

THE ECOLOGICAL CHANGES
Justifiably the loss of human life and the destruction to private and public property dominated everyone’s concerns, but we could see that significant ecological changes had also occurred. The coastal systems were most impacted, as were many species of rare flora and fauna. From what I could see and the many scientific and anecdotal accounts I read, it was the 9.1 magnitude earthquake (which triggered the tsunami) that actually caused the greater damage. With a pivot roughly located near Port Blair, the islands witnessed a huge swing, like that of a see-saw, on account of the tectonic activity. Scientific assessments indicate that the Andaman group of islands were thrust upwards by 1.2 to 1.8 m. while Car Nicobar went under by 1.2 m. At the southernmost tip – Indira Point on Great Nicobar Island – the submergence was almost 4.5 m.

THE NICOBAR ISLANDS
Researchers who traveled to the devastated landscape around Great Nicobar Island reported that the small Megapode Island (a wildlife sanctuary) located west of Great Nicobar had been completely submerged. Coral reefs, beaches and low lying coastal forests across this island group were badly hit. The Nicobar reefs suffered a combination of submergence, increased turbidity and physical damage from tons of debris thrown back and forth by the lashing waves. Dr. R. Jeybaskaran of the Zoological Survey of India reported large-scale sedimentation on coral reefs around Great Nicobar Island. His post-tsunami surveys further revealed a reduction in the number of associated coral reef fauna, including nudibranchs, flat worms, alpheid and mantis shrimps and hermit and brachyuran crabs.

Submerged mangroves, littoral forests and paddy fields, Great Nicobar Island
(Pic: Pankaj Sekhsaria)

The submerged settlement of Campbel Bay, HQ of Great Nicobar Island
(Pic: Pankaj Sekhsaria)

Interestingly, immediately following the tsunami, fishermen from Great Nicobar reported a sudden and massive increase in their milk fish Chanos chanos catch, which was relatively rare earlier. So much so that fishermen began to refer to milk fish as ‘tsunami macchi’. No one can explain the phenomenon precisely but speculation centres around the findings of post-tsunami ocean salinity and temperature studies carried out in the islands by scientists of the National Centre for Antarctic and Ocean Research. This study found considerable thermohaline variability in the upper 300m column of ocean water and concluded that such changes could have a significant impact on primary production and fisheries.

Chanos chanos, Milkfish that has now become tsunami macchi in Great Nicobar
(Pic: Pankaj Sekhsaria)

Early surveys conducted by ANET in the Nicobars also indicated huge losses of Pandanus Pandanus leram and the Nypa palm Nypa fructicans. The latter, in particular, was virtually wiped out from the estuarine regions of Little Nicobar and Great Nicobar Islands. Both plants are important for the Nicobari community as a source of food and materials such as thatching. An effort is now being made with the help of the local communities to replant the islands with these species.

Permanent submergence also saw most of the beaches vanish, including many vital nesting sites of the four marine turtle species found here – the giant leatherback, the green sea turtle, the olive ridley and the Hawksbill. But this change was short-lived, as new beaches had begun to form along the altered alignment within months. Sure enough, the nesting turtles too returned soon after.

The damage to low-lying coastal areas, coastal forests and mangroves was more permanent. Large tracts were completely destroyed. Every island in the Nicobars without exception was encircled by an endless brown wall of dying and decaying mangroves, pandanus and other littoral species. A remote sensing and GIS-based study of the Central Nicobar group of islands (Nancowry, Camorta, Trinket and Katchal) by the Institute for Ocean Management at Chennai’s Anna University assessed that the damage ranged from 51 to 100 per cent for mangrove ecosystems, 41 to 100 per cent for coral reef ecosystems and 6.5 to 27 per cent for forest ecosystems.

NICOBAR'S FAUNA
The late Dr. Ravi Sankaran of the S├ílim Ali Centre for Ornithology and Natural History (SACON) was the first to conduct a rapid impact assessment of the Nicobars after the disaster. His main interest was the Nicobari Megapode, a ground-nesting endemic bird that scrapes together a mound of earth as a nest in low-lying coastal forests. I had seen and photographed the megapode in 2002 near the turtle camp on South Bay at the mouth of the Galathea river and it was difficult to learn that nothing of that coastline remained. We feared the worst for the extremely vulnerable bird across its range in these islands. Sankaran’s report was therefore anxiously awaited and his findings turned out to be bitter-sweet. He reported that the permanent submergence had destroyed a huge part of the birds’ nesting habitat and that nearly 1,100 nesting mounds had been lost. He, however, reported sighting a few birds and also some active nesting mounds.

Subsequently, in early 2006, Dr. K. Sivakumar of the Wildlife Institute of India surveyed almost 110 km. of the coastline along 15 islands in the Nicobar group. He estimated that only about 500 active nesting mounds of the bird had survived and that the megapode population was down to under 30 per cent of the numbers estimated during surveys he had conducted around a decade ago. While the bird was badly hit, mercifully it was not wiped out. Little is known, however, of the other equally vulnerable, coastal forest-dwelling fauna, such as the giant robber crab, the reticulated python and the Malayan box turtle. There is almost no idea of how these have been impacted and there are indications that these may be worse off than the megapode.

Initially scientists worried that the giant robber crab had become locally extinct in the Nicobars as it inhabited one of the worst hit sections of the coast – a 100 m.-wide strip of forest adjacent to the sea. Reports that some were occasionally sighted were confirmed in late 2006 when Vardhan Patankar of Reefwatch sighted four individuals – two on Camorta Island and one each on Great Nicobar and Menchal.

THE ANDAMANS
Areas around Port Blair also experienced permanent submergence of about 0.6 to 0.9 m. It was a fate similar to the Nicobars and is best visible in the low-lying area of Sippighat just a few kilometres outside the capital town. Mangrove marshes that had been converted to paddy fields over the years were now permanently submerged. Comparative aerial images shot regularly from 2005 onwards, showed mangrove stands drying along the creeks at Sippighat. Today, the area is dominated by large expanses of water and one prominent waterbody. A study conducted by scientists from the Port Blair-based Central Agricultural Research Institute (CARI) found a similar impact on mangroves in the creeks of Shoal Bay, Chouldhari and the Mahatma Gandhi Marine National Park at Wandoor. This is probably on account of high salinity stress and permanent inundation. As in the case of the Great Nicobar, this also led to one dramatic, though short-lived change here. For the first few months immediately after the tsunami, the Sippighat Creek became a huge production ground for the best prawns that residents of Port Blair had ever eaten.

Ariel view of Sippighat, just outside Port Blair, that also experience subsidence and submergence like was seen in the Nicobar Islands (Pic: Pankaj Sekhsaria)

CARI studies revealed that mangroves stands at Deshbandhugram, Laxmipur, Milangram and Swarajgram in North Andaman remained exposed even during the high tides. Sea water did not reach the mangroves at all and within a few months of the event they had started to wilt.

As far as the coral reefs are concerned, it was initially estimated that an expanse of nearly 50 to 60 sq. km. had been exposed and killed – the largest area being nearly 25 sq. km. west and north of Interview Island, which we too had witnessed. Similar impacts were reported from parts of Indonesia. Interestingly a report by Living Oceans, Reef Check and IUCN suggests that the most dramatic damage to the Aceh reefs was also caused by the earthquakes: “Hectares of reef flat at Pulau Bangkaru Island and Simeulue were uplifted to a level above the high tide mark resulting in total mortality of previously healthy and intact reefs.”

The situation for sea turtle nesting beaches appears to have turned up a mixed bag in the islands. Flat Island, a small outcrop on the west coast of the main Andamans, was, for instance, an important sea turtle nesting site prior to the tsunami. The uplift caused by the earthquake exposed the reefs around the island creating a barrier for sea turtles. Some beaches such as the ones in Little Andaman Island have become wider and the gradients more gentle. The ANET team also reported extensive damage to sea grass beds. This will affect green sea turtles and many carcasses were observed in the course of the ANET surveys.

IN CONCLUSION
While there has been concern on the negative impact of all these dramatic changes, experts and those working on the ecology of the islands have suggested that the best intervention would be no intervention at all. The magnitude of the change is so huge that little can be done anyway. It has also been argued that if seen in the context of geologic time cataclysmic events such as the tsunami may even have been responsible for the creation of the archipelago in the first place. Such natural events have been occurring cyclically and species and habitats are bound to respond suitably in the course of time. The conversion of Sippighat into a big, open waterbody, the reformation of beaches where they had been destroyed, filling up of sand in uplifted coral reefs and movement of the line of mangroves are evidence of such changes.
Nevertheless, the entire coastline of the islands has been altered and there is an urgent need to re-calibrate our own developmental plans in response. The area must, for instance, be resurveyed from the point of view of the Coastal Regulation Zone Rules.

Such mega-geologic events provide us with unprecedented opportunities to observe and understand the long-term changes that have take place naturally down the ages. These are the very forces that have shaped the coral reefs, coastal forests, mangroves and coastlines we see before us today. The dramatic increases in catches of specific fish species and the re-formation of beaches are only two of the many phenomena we should carefully study. Some may take years, even decades to reveal themselves. Hopefully, scientists will find the support they need to document such changes.

No comments: