Global warming threatens Lakshadweep’s coral reefs
An 18-year-long study has found that the island’s corals are in dramatic decline.Updated: Oct 20, 2018 07:25 IST
For most of us, thinking about Lakshadweep islands conjures images of pristine beaches, clear blue seas and fascinating coral reefs that are home to a diversity of plant and animal life.
This might not be far from reality but recent research questions how long will these serene islands remain the same.
A nearly two-decade-long study by the Oceans and Coasts Program of the Nature Conservation Foundation’s (NCF) has found that the absolute coral cover in these islands has reduced from 51.6% in 1998 to 11% in 2017, a staggering 40% decline.
They have found that the alarming rate of coral mortality and their shifting species compositions, combined with their slow rate of recovery, could severely limit their ability to resist future disturbances due to climate change.
“The enormous drop in coral cover is a result of repeated and increasingly severe climate change-related disturbance,” says Shreya Yadav, who along with Teresa Alcoverro and Rohan Arthur published their findings in the journal Coral Reefs earlier this month.
“By monitoring the same reefs since 1998 through a series of El Niño disturbance events, we found that the way a single reef responds to and recovers from a stressor can change drastically through time,” Yadav says.
“Reefs are infamously complex and dynamic systems, but our study shows that in the Lakshadweep, a changing community of corals in a warming environment has led to a four-fold drop in recovery rates since 1998,” she adds.
Death by El Niño
Over their research period, the team monitored six reefs across three islands to find out answers for two questions. How resistant the reefs were to climatic anomalies? And, how well did they recover from them?
The Lakshadweep islands are an archipelago of 36 atolls - ring-shaped reef, island, or a chain of islands formed of coral - in the eastern Indian Ocean, off the south-west coast of India.
They found that El Niño events, sudden increases in ocean temperatures that kill large tracts of coral, are occurring more regularly than ever before. Three mass bleachings of corals have been witnessed in the islands in the last 20 years, in 1998, 2010 and 2016 respectively.
“Each of this was linked to an El Niño current, and each was of a higher intensity than the previous one,” says Arthur, the senior author of the paper.
“The good news is that with every subsequent El Niño event, less coral is dying—the reefs are becoming more resistant. The bad news is that their ability to recover from each event has declined dramatically. The even worse news is that the frequency of these disturbance events is increasing all the time—killing the reef before it is able to limp back to health again,” he adds.
As they state in their paper, “The structural and functional consequences of these losses can have far-reaching effects. In addition to an absolute loss in coral cover, shifts to stress-tolerant, structurally simpler species could result in smaller colonies and flatter reefs, resulting in a loss of critical habitat for fish and invertebrates that depend on the structure.”
This is also having adverse consequences on the 70,000 people who live on the island, most of whose livelihood is fishing.
“As complex and life-giving as they are, corals are also extremely sensitive to changes in temperature. Raise the temperature just a little over what is normal for the time of year, and they expel the algae they depend on—turning a deathly white as they lose their colour—and their main source of food. Without the algae, bleached coral are way more vulnerable to disease and death,” Arthur says.
What has alarmed the researchers most is the speed at which coral life is being destroyed.
“Increases in sea surface temperature were once a decadal event. When they happened, the ecosystem had enough time to heal from it. In the last 20 years, something seems to be broken in the circulatory system of the ocean,” says Yadav.
A sliver of hope
While the overall findings indicate that the Lakshadweep islands are facing full frontal assault due to climate change, there are small slivers of hope to hang onto.
“We also found that the amount of coral death following each disturbance event has been declining since 1998. This is because a more resistant community of corals now dominates these reefs,” Yadav says.
“But while these species are more adapted to warm waters, this comes at a cost - they do not grow very fast, and the shapes and forms they grow in do not always provide the kind of habitat required for many coral-dependent fish,” she adds.
The need of the hour to tackle this decline before it has even more disastrous consequences for India seems to be more research and collaboration.
“Corals are the harbingers of climate change and this study gives us profound insights into how the coral reef ecosystems of Lakshadweep are responding to climate change impacts,” Naveen Namboothri, a marine biologist at the Dakshin Foundation who has worked on coral reef ecology in the Andamans, says.
“I think institutions and researchers need to come together to address these issues collectively. No agency in isolation can bring about a sea change.”