By Anoop Raj Singh and Nehru Prabakaran
The Andaman Islands, home to diverse communities and rich mangrove forests, tell a compelling tale of coastal damage, resilience, and adaptation following the catastrophic 2004 tsunami. Let's delve into the complex relationship between the islanders and the mangroves, and explore the aftermath of the seismic event.
The people of the Andaman Islands, including Indigenous tribes such as the Great Andamanese and the Jarawa, along with settlers from mainland India (Tamil Nadu, Andhra Pradesh, West Bengal, and Jharkhand), share a close association with the mangroves. Picture this: along the banks of mangrove creeks stand India's tallest mangrove trees, some reaching a whopping 30 m. in height. These intertidal ecosystems serve as vital resources for fishing and gathering marine delicacies, and even their twisted roots aren't just for show; they provide shelter for fishermen battling fierce winds and waves.
A Ranchi settler, equipped and ready for routine fishing in the newly-uplifted mangrove site of the Mayabunder region. Photo: Anoop Raj Singh
A Bengali settler hunting for a mud crab Scylla serratta, considered delicious and expensive, during low tide in the remnant old-growth mangrove forest of the Mayabunder region. Photo: Anoop Raj Singh
Mangrove forests – where land meets sea – aren't just plants; they are entire ecosystems, teeming with life. They harbour a diverse array of taxonomically distinct plant species uniquely adapted to intertidal environments. The name ‘mangrove’ itself is a blend of Portuguese, Spanish, and English words – ‘mangue' and 'mangle' mean trees that are found in muddy shores, while 'grove' hints at a group of trees. Covering approximately 13 per cent of India's mangrove cover, the Andaman and Nicobar Islands boast an astonishing diversity of mangrove species (39 species), comprising 86 per cent of India's true mangrove species (44 species), and over half of the globally recognised species (70 species).
Mangrove forests require just the right amount of water and salt to thrive. Their growth depends on how often and how long they get soaked by the tides, along with other environmental factors. Different species have their own favourite spots along the coast, from landward to seaward. Some, such as Rhizophora apiculata and Avicennia marina, love hanging out in the water most of the time, so mostly colonise the area in the seaward zone where the tides never leave them dry. Others, such as Bruguiera gymnorhiza and Ceriops tagal, prefer to be in the water only part of the time, so they set themseves up in the mid-zone often where the tides come and go. Then there are the beach bum mangroves such as Excoecaria agallocha and Heritiera littoralis – they're cool with just a splash of water now and then, so they hold back on the landward side. But here's the thing: if the tides change or the sea level alters, it can throw off the whole mangrove ecosystem.
A pristine Rhizophora apiculata mangrove forest at Yerrata, Middle Andaman. Photo: Anoop Raj Singh
On the morning of December 26, 2004, the world witnessed the colossal impact of a tsunami triggered by the third-largest earthquake in recorded history. Originating near northern Sumatra, the tsunami's towering waves threatened the lives of coastal communities of several South and Southeast Asian countries, including the Andaman and Nicobar Islands in India. It was a terrifying ordeal, but the mangroves acted as nature's shield, softening the force of the waves and safeguarding many lives. Despite this, the tsunami claimed countless lives, especially among those who were fishing in shallow coastal areas.
The destructive tsunami waves originated from a interaction between two tectonic plates – the Indian plate duking it out with the Burmese plate. This clash forced the Indian plate to slide beneath the Burmese one, setting off a seismic seesaw on the Andaman Islands. Imagine one end of the island going up, and the other end going down, like a giant teeter-totter. Up went the North Andaman and Mayabunder region (by 1.35 m.), while down sank the South Andaman (by ~1 m.). The coastal subsidence in South Andaman led to the permanent inundation of mangrove forests, terrestrial forests and agricultural lands. Conversely, the coastal uplift in North Andaman altered tidal water dynamics, resulting in permanent receding of tidal water from mangrove forests. Both profoundly affected the coastal ecosystems in this continuum. People living on the west coast of North Andaman suddenly had to walk over a kilometre just to reach fishing spots which were a few yards away just the day before – before the tsunami. Meanwhile, people in South Andaman watched helplessly as their farmland disappeared under the rising sea. It was a tough time for everyone, each grappling with the island's dramatic makeover in their own way.
A dead patch of Bruguiera gymnorhiza and Ceriops tagal caused by frequent inundation of tidal water on account of tectonic subsidence in Red Skin Island of South Andaman. Photo: Anoop Raj Singh
The uplifted dead coral reefs are acting as a new intertidal area, where mangrove have started colonising across the North Andaman Island, showcasing the seaward shifting of mangrove forests. Photo: Anoop Raj Singh
A study by Shivshankar and his team estimated that about 1,150 ha. of mangrove forest were wrecked by permanent flooding caused by the tsunami. However, five to six years later, something unexpected happened: the subsidence has created new wetlands, where mangroves started moving in. These wetlands, covering about 1,070 ha., are now being watched closely to see how and which mangroves settle in. The first ones to move into the wetlands are pioneers such as Rhizophora apiculata and Avicennia marina, ready to make a new home. But here's the twist: as the land sinks, the mangroves creep towards the land, away from the sea. While at the same time, the increasing South Andaman population – on account of a boom in the tourism industry – pushes the mangroves back towards the water. Hence, the coastal marginal families living near the mangroves are feeling the squeeze too. Some have lost their fields completely, while others can't grow crops because of the salty soil. And for fishermen, life's gotten tougher. Some fish they once caught in large quantities – such as red snappers and moray eels – are scarce now. It's a wild ride for the people of South Andaman Islands.
A study by Ramakrishnan and his team estimated 6,600 ha. of mangrove forest was wrecked on account of the tidal flooding. The impact wasn't the same everywhere – on the east coast, the land only rose a little (up to 50 cm.), while on the west coast, it shot up higher (up to 135 cm.). The steep land rise on the west coast led to losing more than 90 per cent of mangroves, while the gentler land uplift on the east coast meant a 40-70 per cent mangrove loss. The mangroves on the west coast died off a while ago, but on the east coast, they're still fading away. This mangrove loss has hit the people in North Andaman hard. Folks who depended on the mangroves for their livelihood – for fishing, crabbing, oyster hunting – felt the crunch. Fishermen had to double their effort to catch the same amount of crab they used to before the tsunami. For some families, crabs became a luxury they couldn't afford anymore. But amidst the devastation, there's a glimmer of hope: some mangrove species, such as Rhizophora apiculata and Avicennia marina, have started to colonise the dead coral reefs, bringing life back to this graveyard, which was once a vibrant area. And, in areas where mangroves were lost, terrestrial plants are now stepping in to take their place, showing that life finds a way, even in the toughest conditions.
A dead Ceriops tagal patch on account of permanent receding of tidal water caused by tectonic upliftment on the west coast of North Andaman Island. Photo: Anoop Raj Singh
The aftermath of the tsunami reshaped the Andaman's mangrove ecosystem and jeopardised the livelihoods of local marginal families. A quick recovery of mangrove ecosystem, would also speed up the recovery of ecosystem services for the families dependent on them. But mangrove recovery is facing a bunch of human-made problems. The wetlands that were formed post-tsunami in South Andaman are mostly on private land, and folks are filling them in, trying to claim the space for themselves. Cattle from nearby settlements are munching away at the newly-recruited mangrove seedlings, slowing down mangrove recovery even further. Even the isolated areas, where no humans live, are not safe – invasive spotted deer, introduced from the mainland, are chomping down on them. It is very difficult for mangroves to colonise on the new intertidal habitat of North Andaman on account of strong tides, unsuitable soil, hard calcareous surface for root penetration, and limited seed stock. Even when the seedlings manage to sprout, they're at risk of getting grazed by invasive spotted deer and domestic cattle. The herbivores are keeping the mangroves at bay, making it harder for them to spread and grow.
Letting nature take its course might seems like a good idea, but it could take forever for things to return to normal – and in the meantime, we could lose precious endemic plants and animals. Andaman needs urgent of conservation efforts. That's why we need a mix of a holistic approach combining natural regeneration and human-assisted planting, guided by scientific insights, which offers hope for the speedy restoration of mangroves in the island. Community engagement is paramount through spreading awareness about why mangroves matter and how they help us all. By ingraining sustainable practices of resource use in the local people through collective action, we can ensure the preservation of these invaluable mangrove habitats for generations to come.
A Forest Department planted mangrove propagule struggles to survive because of herbivory by spotted deer at Kishorinagar, North Andaman. Mangrove regeneration at disturbed sites is under immense pressure on account of herbivory by invasive chital (spotted deer) and domesticated cattle across Andaman Island. Photo: Anoop Raj Singh
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Anoop Raj Singh is a Rufford Grant recipient, and Ph.D scholar at Gurukul Kangri (deemed to be) University, Haridwar, in collaboration with the Wildlife Institute of India, Dehradun. His research quest is to understand the response of the mangrove ecosystem in the aftermath of natural and anthropogenic disturbances. Currently, he studies the natural colonisation and recovery patterns of mangroves at tsunami-impacted sites of Andaman and Nicobar Islands. You can find him on Instagram and X.
Nehru Prabakaran is Scientist-D at the Wildlife Institute of India. He was a recipient of the Leibniz-DAAD Post-Doctoral Fellowship 2014, Germany, and the DST-INSPIRE Faculty Award, India 2018. He has vast research experience working in the coastal ecosystem of Andaman and Nicobar Islands. His research mostly focuses on the response of coastal and marine ecosystems to various disturbance factors. You can find him on X at nehrutp, and Facebook.
Ackowledgements
The authors are thankful to the Rufford Foundation [1st Rufford Small Grant-32387-1] for the grant, and DST-Inspire Programme [DST/INSPIRE/04/2018/001071]. We are grateful to the Department of Forest and Environment, Andaman and Nicobar Island for providing field permissions and facilitations. We would also like to thank the Dean, Director, faculty, and researchers of the Wildlife Institute of India for their motivation.