Mongabay Series: Oceans
Mongabay interviewed Rohan Arthur, a scientist who heads the reef program at Nature Conservation Foundation, a conservation organization based in Mysore, India. Arthur’s team has been surveying coral reefs in the Lakshadweep Archipelago and documenting the corals’ bleaching and recovery.
Last month, scientists reported that Australia’s Great Barrier Reef corals were experiencing “the worst mass bleaching event in its history”. Of the 500 coral reefs they observed while flying over 4,000 kilometers (~2,485 miles) of the Great Barrier Reef, only four reefs did not show any sign of bleaching. Terry Hughes, convenor of Australia’s National Coral Bleaching Taskforce, called it the “saddest research trip” of his life.
Other scientists have called the underwater sight of widespread bleaching “catastrophic”.
In other parts of the world too, similar “catastrophic” scenes are playing out. Off the south-western coast of India, the lesser-known coral reefs of the Lakshadweep Archipelago in northern Indian Ocean are struggling to survive.
The record-breaking surface temperatures turn shallow reefs ghostly pale as they bleach. Photo courtesy of NCF.
A small team of six field biologists from the Nature Conservation Foundation in India, have observed soaring sea surface temperatures and widespread coral bleaching this year. In every reef that the team has surveyed in 2016 so far, corals are turning white or pale. Moreover, the heat stress has already killed many corals in the region, the team said in a statement.
Lakshadweep’s corals are not new to bleaching. In 1998 and 2010, similar El Niño events have had calamitous impacts on the reefs. While the Lakshadweep reefs recovered from the 1998 event, recovery following the 2010 event has been slower. And with the ongoing El Niño event, scientists are seriously concerned.
“We are currently halfway through a mixed recovery from the 2010 El Niño event, and we were only now beginning to see the first signs of regrowth in some areas,” Rohan Arthur, who heads NCF’s reef program, told Mongabay. “This makes the present El Niño even more heart wrenching since it has hit the Lakshadweep before these reefs have had the ability to recover completely from the last catastrophic disturbance.”
But Arthur is also hopeful. He said that Lakshadweep’s reefs have recovered in the past (following the 1998 El Niño event), and the reefs could show resilience once again.
Mongabay spoke with Arthur about the state of coral reefs in the Lakshadweep Archipelago and their ability to bounce back.
INTERVIEW WITH ROHAN ARTHUR
Mongabay: When did you first observe bleaching in Lakshadweep’s coral reefs this year?
Rohan Arthur. Photo by Vishnu Som.
Rohan Arthur: Well, we have been expecting unusual sea surface temperatures in the Indian Ocean since 2015 and have been on bleaching watch ever since last winter. Anticipating that this was going to be a cruel summer, we scrambled together a team of researchers in December to travel the archipelago and assess its reefs before our waters started heating up. Already back then we began noticing corals showing clear signs of heat stress: they were turning strange colors and feeding unusually during the day (most healthy coral feed actively only at night). By April, these stressed corals were everywhere. In our most recent surveys in early May, we have not found a single reef that has been spared the effects of the bleaching. Even at deeper, supposedly cooler, and therefore more protected reefs, corals are quickly giving up the ghost.
Mongabay: What environmental conditions result in coral reef bleaching in the Lakshadweep?
Rohan Arthur: Corals share a tight symbiotic relationship with photosynthetic algae that produce most of the nutrition that the corals require to survive. These algae live in the soft tissue of the coral polyp, giving corals their radiant colors. This relationship gets easily strained though, and when corals are stressed they respond by expelling their algal partners. This results in corals changing colors, becoming increasingly pale before bleaching completely white as this stress increases.
The mass bleaching of coral currently underway in the Lakshadweep is being caused by unusually high sea surface temperatures as the Indian Ocean swelters under particularly unforgiving El Niño conditions. The El Niño is a warm ocean current that spreads across Pacific and into the Indian Ocean when trade winds fail. The increasing intensity and frequency of these unusual events bears the clear fingerprint of human-caused climate change and this year’s El Niño is leaving behind a wave of untold devastation on the reefs of the world.
Seasonal variation in sea surface temperatures (SST) in Lakshadweep waters. The grey line shows the normal seasonal variation in water temperatures based on temperature records over the last 15 years – from 2000 to 2015. The light orange line shows how temperatures varied during the last El Niño year: 2010 – which resulted in major bleaching across the Lakshadweep. The dark orange lines shows current sea surface temperatures for the first few months of 2016 – already considerably worse than the last bleaching event. The bleaching threshold is around 30°C, representing the tolerance limit for most coral, beyond which they are most likely to start bleaching and dying. Graph courtesy of NCF.
The first few months of 2016 have seen the hottest monthly sea surface temperatures in the Lakshadweep waters since accurate records have been kept. Sea Surface Temperatures (SST) recorded by NOAA’s Virtual Station (based on satellite readings) show average temperatures of around 30 degrees Centigrade (~86 degrees Fahrenheit) for the period between February and May in 2016. This is close to one degree above the average over the last 15 years, which represents a radical increase in SSTs for this year. Individually, we have recorded temperatures as high as 34-35 degrees Centigrade (93-95 degree Fahrenheit) within the first few metres of water — and at these temperatures we have been recording mortalities not merely of coral but of coral reef fish as well.
The Lakshadweep is only one of many reef regions that will potentially succumb to this event. It will be several months before we can properly assess the full scale of the damage it has wreaked.
Mongabay: What happens during coral reef bleaching in the Lakshadweep. What do the reefs look like? And how do the coral reefs and the associated fish community change during a bleaching event?
Rohan Arthur: As ocean temperatures rise, corals get increasingly stressed and start rapidly losing their symbiotic algae. The first thing you notice when diving on a heat-stressed reef is that several of the coral start taking on strange, almost fluorescent hues of blue, green and red. Every coral species responds differently of course, so the reef starts resembling a badly color-corrected image, almost kitsch in its choices of colors. Visit the same reef a week later and those exuberant shades give way to a much more ominous white as large stretches of the reef bleach completely. Another few days, and some of this coral will have died, being rapidly overrun by opportunistic turf algae that will, as the reef continues to die, quickly take over the entire reef.
Dying fish observed in the Lakshadweep Reefs by Nature Conservation Foundation’s Oceans and Coasts team during their Expedition. Photo courtesy of NCF.
Coral forms the basic architecture of the reef and a host of species uses this complex structure both as refuge and as ambush. Several other species depend directly on coral to feed, and these are the first ones to be affected by the bleaching. Many butterflyfish — quintessential of tropical reefs — feed almost exclusively on coral, and their numbers rapidly decline in the wake of a coral mass mortality. For many other fish the effects are seen over a longer period, as the dead coral breaks and erodes and the reef loses its complex topography. Many large territorial species like groupers need the complexity of a healthy reef to be effective predators and their numbers decline dramatically in post-disturbed reefs. These are often long-lived, human-aged species, and their return to these reefs can take decades or longer.
Of course there will be a subset of species that may actually benefit from the death of the coral — including several herbivore species, such as striated surgeonfish (Ctenochaetus striatus) and powderblue surgeonfish (Acanthurus leucosternon) — whose numbers may increase considerably in the wake of these events. These herbivores actually play critical roles in helping reefs recover by ensuring that dead reef substrates are kept clean of macroalgae that would otherwise muscle out any new coral seeking to recolonize these areas. Without their constant grazing, reefs may never recover at all after these events.
Some species like the powderblue surgeonfish could benefit from coral death, Arthur said. Photo by H Zell, Wikimedia Commons, CC By-SA 3.0
Mongabay: As scientists, how do you determine the full extent of bleaching?
Rohan Arthur: The mass bleaching of 2016 has triggered a genuine call-to-arms from the scientific community and in many parts of the tropics reef scientists have come together in large numbers to assess the damage to the world’s reefs. In the Great Barrier Reef for instance, scientists have been using low-flying planes to assess the scale and extent of bleaching across the length and breadth of the barrier. Their initial results are depressing — 93% of the reefs they surveyed show some signs of serious bleaching.
In India, we are limited to rather more modest means to quantify the damage. Our team in the Lakshadweep is a small one. We are a group of 6 field biologists (including researchers and students), surveying 11 atolls across the entire Lakshadweep archipelago. And we have been travelling as best we can from one atoll to the next with minimum gear, attempting to cover as much ground as we can before the monsoons make sampling impossible.
We are also coordinating efforts with a team of dedicated staff from the local department of Science and Technology to ensure that we can survey as much of the archipelago before the rains. We are limited by time, people, and the amount of air in our cylinders. Our teams make very rapid surveys of several reefs on every atoll we visit. On each survey we measure how much of the reef is covered in live coral, and how much of this live coral is currently showing signs of bleaching stress. Together with details of temperature, depth, water flow and other parameters this will eventually give us a fairly detailed picture of how badly the reefs of the Lakshadweep have been affected by the bleaching, which genera of coral have been hit the worst, and if there are any areas that (for one reason or another) have escaped the bleaching.
Bleached soft coral in the Lakshadweep Reefs. Photo courtesy of NCF.
The monsoons will mask the full extent of the damage from us. We will have to wait until the monsoons retreat before we can dive the reefs again. Only then will we know how much of this bleached coral managed to survive the bleaching. Once we have that information, we should be able to make tentative projections of the potential of different reefs to recover. That is a more distant horizon. Right now, we are still trying to get a sense of the immediate impact. And that, given our resources and the race we are running against the rains, is a mammoth task in itself.
Mongabay: Lakshadweep’s reefs have been previously hit by El Niño events in 1998 and 2010. How long did it take for the reefs to recover from both these events?
Rohan Arthur: The El Niño of 2016 is certainly not the first large temperature anomaly to hit the Lakshadweep and we have learnt a lot from these earlier events. The 1998 mass bleaching left behind a catastrophe from which I was hard pressed to determine how the reefs would ever recover. And yet, the reefs recovered in ways that I would hardly have dared to imagine. Within a few years many reefs received large numbers of new coral recruits and these grew at astounding rates. While this was certainly not a universal picture, within less than a decade, many of these reefs were looking very healthy once again.
Then 2010 brought another large El Niño and with it another decline in coral. We are currently halfway through a mixed recovery from that event, and we were only now beginning to see the first signs of regrowth in some areas. This makes the present El Niño even more heart wrenching since it has hit the Lakshadweep before these reefs have had the ability to recover completely from the last catastrophic disturbance.
Mongabay: How has reef fishing impacted the rate of recovery of the reefs?
Rohan Arthur: Our work in the Lakshadweep over the last two decades has shown that a large part of the reason why these reefs recovered so robustly after the 1998 El Niño was that reef fish populations were remarkably healthy in these reefs. Most tropical reefs in the developing world are heavily overfished, and the critical roles that many of these fish normally play in grazing down algae or keeping sea urchins or coral-eating starfish in check are lost. In these heavily fished reefs, recovery can be very protracted, if it happens at all. The Lakshadweep was a heartening example of how lightly fished reefs could weather even major coral losses.
Freshly caught reef fish, for sale in Lakshadweep. Photo courtesy of NCF.
Although fishing was a mainstay of the economy, fishers here focused on deep-sea tuna to earn a living, thus conferring the reefs with a remarkable resilience. This happy situation is on the cusp of a change as fishers are now being drawn to fishing the reefs as well as a source of income. The fear is that these reefs — already disturbed and struggling to cope — may not be able to sustain the inevitable loss of function that will result from unchecked fishing. The ability of these reefs to recover is clearly linked to how heavily fishers use the reef in the months and years to come. Their actions can take the reef down very different trajectories: towards a rapid recovery or towards irreversible decline.
Mongabay: Why are the Lakshadweep’s coral reefs important? And what would happen if these reefs failed to recover?
Rohan Arthur: The Lakshadweep is a string of coral atolls, and the tiny islands that make up this archipelago are almost completely dependent on healthy growing coral reefs for their existence. The coral creates a constantly self-repairing wall around the lagoon that protects the island and its people from the worst storms and waves that would otherwise cause huge coastal erosion and inundation. Perhaps more critically, as this wall erodes in a declining reef, sea water increasingly infiltrates the precious fresh water resources of the island rendering it unfit for consumption. The availability of fresh water makes these islands habitable and without it the Lakshadweep islanders would be left with very few workable options. While this is true for reefs everywhere, for low-lying atolls like the Lakshadweep it is particularly true that the health of the reefs is linked completely with the habitability of the land. The failure of these reefs to recover from these repeated disturbances would be as much a human catastrophe for the people of the Lakshadweep as it would be an ecological disaster.
The reefs of the Lakshadweep have surprised me in the past and I am sure (with more hope that conviction) that they will surprise me with their resilience once again. In that uncertain resilience lies more that just the health of an incredibly beautiful ecosystem — it is the key to the future of the archipelago itself.
Lakshadweep’s tiny islands are almost completely dependent on healthy growing coral reefs for their existence, Arthur said. Photo by Lenish Namath, Wikimedia Commons, CC By-SA 3.0.
Article published by Shreya Dasgupta on 2016-05-11.
original story HERE.
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