Is mass coral bleach­ing reach­ing a tip­ping point?

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THEGOOD news is that the cur­rent El Niño, a warm ocean cur­rent that drove tem­per­a­tures up world­wide, is fi­nally on its way out. But the bad news is that the un­prece­dented coral bleach­ing that El Niño trig­gered in 2014 shows lit­tle signs of slow­ing down. Ac­cord­ing to the Oc­to­ber 3, 2016, up­date by the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion ( noaa), El Niño is cur­rently in a neu­tral phase and is likely to re­main so dur­ing the win­ters. noaa’s four-month coral bleach­ing out­look, how­ever, says reefs in the east­ern side of the In­dian Ocean, the west­ern side of the Pa­cific and the Caribbean are likely to sus­tain bleach­ing un­til Jan­uary 2017.

The cur­rent global coral bleach­ing event, which is the long­est and most wide­spread event on record, be­gan in mid-2014 from Hawaii and has so far left coral reefs in at least 38 coun­tries and is­land groups ghost white (see ‘Coral grave­yard’). From Aus­tralia’s Great Bar­rier Reef—the largest in the world—to the Lak­shad­weep is­lands in In­dia, the cur­rent bleach­ing event has spared none. Sci­en­tists fear the world stands to per­ma­nently lose over 15,000 sq km or 10 per cent of coral reefs be­cause of the cur­rent bleach­ing event. Aerial sur­veys in April this year re­veal that about 93 per cent of the Great Bar­rier Reef had suf­fered bleach­ing to some ex­tent. Of the 911 sur­veyed reefs, around a third are severely bleached. With as much as 50 per cent of the reef cover al­ready es­ti­mated to have been lost, fears are that 50 per cent of what is left might be lost dur­ing the cur­rent event. The north­ern section of the 2,300-km Great Bar­rier Reef has been the worst hit in the cur­rent bleach­ing event, with 81 per cent of the 522 reefs sur­veyed in­di­cat­ing se­vere bleach­ing. “Though it has been pre­dicted for many months, it’s not quite the same as see­ing the dev­as­ta­tion,” says Sa­man­tha Craven of UK-based Reef World Or­gan­i­sa­tion.

De­spite cov­er­ing just 0.2-0.25 per cent of the earth’s ocean area, coral reefs sup­port up to 2 mil­lion species or a quar­ter of all marine life. For sev­eral is­land na­tions and trop­i­cal coun­tries with long coast­lines, corals pro­vide pro­tec­tive ser­vices from se­vere trop­i­cal weather. Corals, such as man­groves, cush­ion the im­pact of trop­i­cal storms that would oth­er­wise dam­age in­fra­struc­ture close to the coast. It is es­ti­mated that for the Cen­tral Amer­i­can na­tion of Belize, the eco­nomic value of the in­fra­struc­ture pro­tected by coral reefs is equal to 10-15 per cent of the na­tion’s Gross Do­mes­tic

Prod­uct ( gdp). Reef struc­tures also act as in­dis­pens­able ge­netic li­braries and are often de­scribed as rain­forests of the sea for their rich­ness.

De­cay over time

Ex­perts have, for quite a while now, be­lieved that corals are among the most sus­cep­ti­ble or­gan­isms to cli­mate change. All three of the mass bleach­ing events ever wit­nessed have hap­pened in the past 20 years—the first in 1997-98, the sec­ond in 2010 and the third is on­go­ing. In fact, the large-scale dev­as­ta­tion caused by the cur­rent event, par­tic­u­larly in the United King­dom and the re­mote pa­cific atolls that had been rel­a­tively bleach­ing-free thus far, has trig­gered spec­u­la­tion of how far the world is from com­pletely los­ing its coral cover. “In the first global bleach­ing in 1998, it was re­ported that the world lost 16 per cent of its corals. The cur­rent bleach­ing event ap­pears to be the most se­vere and there­fore has the po­ten­tial to cause greater coral mor­tal­ity than that seen in 1998,” says Ty­rone Ridge­way, pro­fes­sor at the Univer­sity of Queens­land.

Con­sid­er­ing that the world has al­ready lost 3040 per cent of its to­tal doc­u­mented coral cover, the cur­rent bleach­ing event is ex­pected to have con­sid­er­able ram­i­fi­ca­tions.

The World Wide Fund for Na­ture ( wwf) cal­cu­lates the to­tal global as­set of reefs at US$800 bil­lion, with around 850 mil­lion peo­ple de­pen­dent on reef­based ecosys­tems for food se­cu­rity and liveli­hood. Close to 100 coun­tries ben­e­fit from coast­line pro­tec­tion, tourism and fish­eries, sup­ported by the bio­di­ver­sity hosted by coral reefs. And a quar­ter of the 100 coun­tries ben­e­fit­ting from coral reefs de­pend on tourism for more than 15 per cent of their gdp. Ac­cord­ing to a 2003 re­port made by wwf, the global an­nual ben­e­fit from coral reefs is close to $30 bil­lion. It adds that fish­eries and tourism sec­tors lose close to $5.7 bil­lion and $9.6 bil­lion a year re­spec­tively due to coral bleach­ing and death.

The great­est eco­nomic threat from global coral degra­da­tion is likely to be felt in South­east Asia, Aus­tralia and the is­lands of Ocea­nia. Reefs in the trop­i­cal Indo-Pa­cific stretch are es­ti­mated to ac­count for more than 60 per cent of the $30 bil­lion con­trib­uted an­nu­ally to the global econ­omy by coral reefs.

Im­pact on In­dia

While it ini­tially looked that coral reefs in In­dia would es­cape the bleach­ing event, the story changed by April this year. Ex­pe­di­tions by the Nat­u­ral Con­ser­va­tion Fund ( ncf) in Lak­shad­weep in April and May re­vealed a stag­ger­ing scale of bleach­ing (see ‘Lak­shad­weep peo­ple may soon be the first cli­mate change refugees in In­dia’, p32). Shreya Ya­dav of ncf, a re­search or­gan­i­sa­tion pro­mot­ing the use of sci­ence for wildlife con­ser­va­tion in In­dia, says, “Around 80 per cent of the reefs in the seven is­lands vis­ited by us have ex­pe­ri­enced bleach­ing. Water tem­per­a­tures re­mained very high, be­tween 32 and 34 de­gree Cel­cius, which for me was un­heard of in this re­gion. It was quite dev­as­tat­ing to see the ex­tent of bleach­ing, but we don’t have the num­bers yet since the re­ports are be­ing an­a­lysed now.” The Gulf of Man­nar too has ex­hib­ited 40-50 per cent bleach­ing, says P Kr­ish­nan, a re­searcher at the Union en­vi­ron­ment min­istry’s Na­tional Cen­tre for Sus­tain­able Coastal Man­age­ment. Ac­cord­ing to J K Pat­ter­son Ed­ward, direc­tor of Tamil Nadu-based Su­gan­thi De­vada­son Marine Re­search In­sti­tute, the per­cent­age of reefs that ex­pe­ri­enced bleach­ing in the gulf is close to 60 per cent. “We have again had in­tense heat­ing with sus­tained tem­per­a­tures up to 33.6 oc so we ex­pect 10-12 per cent of coral cover will be lost again this year. The cy­clonic ac­tiv­ity in May in south In­dia brought respite but heat­ing started early this year,” says Ed­ward. So far, there has been good news from An­daman and Ni­co­bar as the ma­jor­ity of the reefs sur­veyed have been spared large-scale dev­as­ta­tion.

Un­favourable cli­mate

The most cited rea­son for the stress on corals has been global warm­ing and as­so­ci­ated cli­mate change. The world has al­ready wit­nessed a 0.8 oc rise in av­er­age global tem­per­a­ture since the prein­dus­trial era and all fore­casts pre­dict fur­ther in­crease at the same or higher rate in the fore­see­able fu­ture. More than 90 per cent of the ac­cu­mu­lated an­thro­pogenic heat ends up in the oceans. To give an idea of how much en­ergy this is, the heat stored by the oceans in the past 30 years is roughly equiv­a­lent to the en­ergy re­leased by one nu­clear bomb dropped into the ocean ev­ery sec­ond of the 30 years. This up­take of en­ergy has been in­creas­ing in the past 40 years and ac­cord­ing to most re­li­able cli­mate mod­els yet, the up­ward in­cline is set to con­tinue for a few more decades at least. Ac­cord­ing to noaa, sea sur­face tem­per­a­tures ( ssts) have been higher in the past 30 years than at any other time since records were es­tab­lished in 1880 and around 70 per cent of the trop­i­cal and sub-trop­i­cal oceans, where most of

Fish­eries and tourism sec­tors stand to lose over $15 bil­lion a year due to coral bleach­ing and death

the reefs are lo­cated, con­tinue to show a strong decadal heat­ing trend.

Coral sys­tems gen­er­ally live in a sym­bi­otic re­la­tion­ship with di­noflag­el­late al­gae called zoox­an­thel­lae. The coral skele­ton pro­vides the al­gae with a home and some nutri­tion while the pho­to­syn­thetic al­gae, in ex­change, pro­vides the host with nutri­tion that en­ables reef-build­ing and other crit­i­cal ac­tiv­i­ties. About 90 per cent of the coral’s en­ergy re­quire­ment comes through this ar­range­ment. Al­gae, liv­ing in the nooks and cran­nies of coral skele­ton, are what give reefs the mag­nif­i­cent vi­brant ap­pear­ance (see ‘Red hot prob­lem’) .

Corals are stressed eas­ily by dis­tur­bances in tem­per­a­ture, light, ra­di­a­tion and water com­po­si­tion. Un­der ther­mal stress, even with an in­crease of just 1-2 oc, the sym­bi­otic re­la­tion­ship, vi­tal to the health of both the coral and the al­gae, breaks down and the al­gae are sys­tem­at­i­cally ex­pelled. The ex­pul­sion causes the coral reefs to lose their colours and at­tain a pale and deathly look.

Bleach­ing, by it­self, does not im­ply mor­tal­ity. Small scale, short du­ra­tion bleach­ing events have been re­ported from sev­eral lo­ca­tions over the past cen­tury and often these events are fol­lowed by a pe­riod of re­cov­ery when tem­per­a­tures re­cede to nor­mal lev­els. “If con­di­tions re­turn to nor­mal quickly af­ter the stress, the corals have the abil­ity to re­cover. In do­ing so, the al­gae re­main­ing in the coral tis­sue asex­u­ally re­pro­duce and re­pop­u­late the coral tis­sue,” says Ridgewell.

Of late though, bleach­ing events have in­creas­ingly be­come a global af­fair with ther­mal stress con­di­tions per­sist for sev­eral months and this is dan­ger­ous. noaa im­agery of the ssts re­veals a nearly uni­form band along the equa­tor that has ex­pe­ri­enced above nor­mal tem­per­a­tures in April and May this year. Bleach­ing leaves corals weak and with­out en­ergy to con­tinue with vi­tal pro­cesses es­sen­tial to their sur­vival. So sus­tained bleach­ing dras­ti­cally re­duces the chances of re­cov­ery.

Another prob­lem is that dead reefs are often taken over by non-sym­bi­otic al­gae, which are detri­men­tal to the marine-life sup­ported by the reefs. Reef Check Foun­da­tion, an in­ter­na­tional non­profit ded­i­cated to con­ser­va­tion of two trop­i­cal coral reefs and Cal­i­for­nia rocky reefs, has re­ported that dead coral reefs off Hong Kong are cur­rently un­der a cover of red al­gae.

Coral colonies, once dead, can still re­cover but take a longer time—rang­ing from a few years to decades. This de­pends on the lo­cal en­vi­ron­men­tal fac­tors as well as the type of corals. Car­rie Man­frino, pres­i­dent of the Cen­tral Caribbean Marine In­sti­tute, cites coral re­cov­ery at Cay­man Is­lands as an ex­am­ple. “(Af­ter the 1998 bleach­ing,) We con­ducted an­nual sur­veys and dis­cov­ered that though the corals did not die im­me­di­ately due to the ther­mal stress, a white plague dis­ease set in and over a pe­riod of four years, we lost 40 per cent of the coral com­mu­nity. It was not un­til 2009, when all of the sud­den, we be­gan see­ing a rapid re­growth across the en­tire reef sys­tem and among all of the

long-term sur­vival is not guar­an­teed. The stress of bleach­ing leaves corals in a com­pro­mised po­si­tion. Apart from in­creased sus­cep­ti­bil­ity to any im­pend­ing bleach­ing event, re­cov­er­ing corals suf­fer a re­duced re­pro­duc­tive po­ten­tial which ad­versely af­fects reef-build­ing abil­ity. More­over, bleached corals are also more vul­ner­a­ble to dis­eases and coral-eat­ing or­gan­isms. In fact, af­ter the mass bleach­ing episode in the Caribbean in 2005, much of the death as­so­ci­ated with the event was not a direct con­se­quence of bleach­ing, but due to dis­eases. “Once the corals re­gain their colour and full com­ple­ment of al­gae, it does not nec­es­sar­ily mean that they are fully healthy straight away,” says Ridgewell.

Ocean acid­i­fi­ca­tion

To say that warm­ing alone is re­spon­si­ble for the mas­sive coral cover losses in re­cent decades would be an over­sim­pli­fi­ca­tion. Ocean acid­i­fi­ca­tion, another by-prod­uct of global warm­ing, is equally re­spon­si­ble for the de­cay of coral reefs world over. Since the be­gin­ning of the in­dus­trial era, the con­cen­tra­tion of an­thro­pogenic green­house gases (ghg) in the at­mos­phere has sky­rock­eted. The ocean, be­ing a mas­sive car­bon sink, has se­questered much of these emis­sions. While this has con­trib­uted in mit­i­gat­ing rising tem­per­a­tures on the land, the im­pact on un­der­wa­ter has been less sober­ing. Car­bon diox­ide (CO2) re­acts with water to form car­bonic acid. Over time, the car­bonic acid dis­so­ci­ates to form a bi­car­bon­ate ion and a pro­ton, ef­fec­tively re­duc­ing the car­bon­ate con­cen­tra­tion in the water.

This re­ac­tion has turned the oceans more acidic, or less al­ka­line to be more pre­cise. It is widely ac­cepted now that an­thro­pogenic ghg emis­sions have caused ocean pH to drop from nat­u­ral lev­els of 8.2 to 8.1. While this change might seem minis­cule, it rep­re­sents a 30 per cent in­crease in acid­ity in the world’s oceans since the pH val­ues are cal­cu­lated on a log­a­rith­mic scale. The change in ocean acid­ity does not have any prece­dence for hundreds of thou­sands years and the im­pact on reef-based ecosys­tems are likely to be tremen­dous.

Car­bon­ates are vi­tal for shell build­ing or­gan­isms liv­ing un­der water, in­clud­ing corals. A drop in the con­cen­tra­tion of car­bon­ates in the water re­duces or­gan­isms’ abil­ity to pro­duce cal­cium car­bon­ate. Reef-based ecosys­tems sur­vive due to a del­i­cate bal­ance be­tween cal­ci­fy­ing rates of corals and bi­o­log­i­cal ero­sion aris­ing from pre­da­tion and nat­u­ral dis­tur­bances. As much as 90 per cent of the cal­cium car­bon­ate de­posited by corals and other cal­ci­fiers are lost due to ero­sion. In such a sce­nario, a de­clin­ing rate of cal­ci­fi­ca­tion due to acid­i­fi­ca­tion threat­ens to dis­rupt the ex­ist­ing bal­ance that is crit­i­cal to main­tain­ing reef-based ecosys­tems. A

2016 study by the Univer­sity of West­ern Aus­tralia shows ex­ten­sive skele­tal de­for­ma­tion among ju­ve­nile corals in acid­i­fied wa­ters, which re­duces their abil­ity to pro­tect against preda­tors.

In late Septem­ber, the con­cen­tra­tion of CO2 in the at­mos­phere broke a cli­mate bar­rier by reg­is­ter­ing sta­ble lev­els above 400 parts per mil­lion (ppm), an in­crease of about 35 per cent com­pared to prein­dus­trial lev­els. The tip­ping point for corals is said to be when CO2 lev­els reach about 450 ppm. At this point car­bon­ate con­cen­tra­tion in water will no longer sup­port coral growth. A 2008 pa­per pub­lished in the jour­nal Geo­phys­i­cal Re­search Letters has shown that corals will ac­tu­ally start dis­solv­ing as CO2 lev­els reach dou­ble of what they are to­day.

Grim fu­ture

In an ever-warm­ing world, most cli­mate change stud­ies pre­dict mas­sive coral losses. The World Re­source In­sti­tute es­ti­mates that about 90 per cent of the coral species in the world will be in dan­ger of bleach­ing and death by 2030. A study pub­lished in the An­nual Re­views in July 2016 has claimed that warm­ing and acid­i­fi­ca­tion to­gether will make coral bleach­ing an an­nual event be­tween 2030 and 2060.

A 2015 study pub­lished in the jour­nal Global Change Bi­ol­ogy used his­tor­i­cal data de­rived from the fos­sils of the Eocene era (pe­riod be­tween 56 mil­lion years ago and 33.9 mil­lion years ago) when cli­matic con­di­tions were com­pa­ra­ble to cur­rent times and mapped the suit­abil­ity for corals in the

world’s oceans un­der cli­mate sim­u­la­tion sce­nar­ios for the com­ing hun­dred years. The re­searchers found that over­all suit­abil­ity of the oceans to har­bour corals would re­duce con­sid­er­ably in the fu­ture, with the trop­ics, which house the max­i­mum coral hotspots, af­fected the most. Sci­en­tists in Aus­tralia ran a sim­i­lar sim­u­la­tion and found that corals would, on an av­er­age, grow 7 per cent faster un­der pre-in­dus­trial con­di­tions.

Nat­u­rally re­silient

With cli­mate mod­els pre­dict­ing global tem­per­a­ture rise of up to 4 oc by the end of the cen­tury, corals are an ob­vi­ous can­di­date for ex­tinc­tion in the near fu­ture. But corals en­joy the ad­van­tage of di­ver­sity. In their hundreds of mil­lions of years of ex­is­tence, corals have sur­vived five pe­ri­ods of mass ex­tinc­tion be­cause of their di­ver­sity. The world is cur­rently be­lieved to have en­tered the sixth mass ex­tinc­tion and if corals stand any chance of sur­viv­ing, it will be be­cause of the vari­a­tion in coral re­sponses.

Re­searchers have iden­ti­fied traits that might aid corals to adapt to higher tem­per­a­tures. Corals that store high quan­ti­ties of fat within their struc­ture and those with good growth rates have high chances of sur­vival un­der ther­mal stress. Cer­tain species in the Caribbean and the In­dian Ocean have been found to swap al­gal part­ners with coral va­ri­eties that have higher ther­mal tol­er­ance to cope with tem­per­a­ture in­creases.

Corals, be­ing sim­ple crea­tures, also en­joy high rates of evo­lu­tion. It has been ob­served that some species have the abil­ity to ac­cli­ma­tise to warm­ing con­di­tions and then pass on the re­quired re­sponses to the next gen­er­a­tion in a process called trans­gen­er­a­tional ac­cli­ma­tion. This gen­er­a­tional learn­ing in­creases the ther­mal stress thresh­old in the spe­cific species. In the warm wa­ters of the Mid­dle East, where bleach­ing has al­most be­come an an­nual af­fair, cer­tain species of corals are able to sur­vive and re­cover in wa­ters at tem­per­a­tures up to 4 oc above nor­mal.

A re­cent re­port by the United Na­tions En­vi­ron­ment Pro­gramme has high­lighted the role of deep water reefs (about which rel­a­tively much less is known) as po­ten­tial refu­gia for coral and fish pop­u­la­tion. As tem­per­a­tures climb, some species of shal­low water coral might have to adapt by re­lo­cat­ing to deeper colder wa­ters. For ex­am­ple, coral species Mille­pora In­tri­cata, found in the Gulf of Chiriqui in Panama, can live both in shal­low and deep wa­ters. Fol­low­ing the bleach­ing event of 1998 it was ob­served that while the shal­low water M in­tri­cata had been wiped out, small colonies sur­vived in deeper wa­ters. Within four years af­ter the bleach­ing event, colonies started reap­pear­ing in shal­low wa­ters.

The suc­cess sto­ries as­so­ci­ated with some species in deal­ing with warm­ing con­di­tions have trig­gered sug­ges­tions that nat­u­ral adap­ta­tion of corals may of­fer a way out of the cur­rent mess. “Macro cli­matic pro­cesses are very dif­fi­cult to mit­i­gate but na­ture has its own cop­ing and im­mune mech­a­nism, de­vel­op­ment of re­silient species is go­ing on,” Kr­ish­nan says.

Sev­eral lead­ing ex­perts in the field, how­ever, doubt the nat­u­ral adap­ta­tion strat­egy. As cli­mate change in­creases, global tem­per­a­tures will get closer to coral thresh­olds, giv­ing the corals less lee­way be­fore bleach­ing. For ex­am­ple, species of fast-grow­ing corals that suf­fered se­vere bleach­ing in south­east Asia dur­ing 2004 re­cov­ered only to face another spell of mass bleach­ing in 2010. Sci­en­tists say the cur­rent bleach­ing event will leave the species un­der tremen­dous stress. So putting all eggs in the adap­ta­tion bas­ket will prob­a­bly lead to stag­ger­ing losses in marine bio­di­ver­sity, just as what likely hap­pened un­der pre­vi­ous pe­ri­ods of mass ex­tinc­tion.

As tip­ping points get closer, calls for hu­man in­ter­ven­tion to con­serve corals have grown in vol­ume. Translo­ca­tion of re­sis­tant corals is one of the most com­mon sug­ges­tions. But swap­ping of one coral species with another in­volves risks of dis­turb­ing nat­u­ral bal­ances and in­tro­duc­ing pathogens novel to the re­gion. “While re­lo­ca­tion of re­silient corals may work in the short term, they are some­what of a band-aid so­lu­tion. It also re­duces the ge­netic di­ver­sity of the reef,” says Ridgewell.

Another sug­ges­tion has been the use of ge­netic ma­nip­u­la­tion to in­crease ther­mal thresh­olds of corals. How­ever ex­perts say that in­tro­duc­ing ge­netic changes in corals is ex­tremely ex­pen­sive and time con­sum­ing. Gre­gor Hodg­son of the Reef Check Foun­da­tion says tar­get­ing the al­gae that in­habit corals in­stead will be a lot cheaper. “Zoox­an­thel­lae re­pro­duce quickly many times per day. So the key is to make zoox­an­thel­lae more re­silient through nat­u­ral and as­sisted evo­lu­tion such as ge­netic en­gi­neer­ing and then seed them on reefs,” he says.

3-D print­ing, too, of­fers new av­enues for con­ser­va­tion and re­build­ing although such pos­si­bil­i­ties are yet to be fully ex­plored. In fact, most

The world might lose 90 per cent of its coral pop­u­la­tion by 2030 be­cause of cli­mate change and ocean acid­i­fi­ca­tion

Over 40 per cent of to­tal reef dev­as­ta­tion has been di­rectly caused by lo­cal pol­lu­tion from ur­ban ar­eas, while 10 per cent loss is at­trib­uted to cli­mate change

sug­ges­tions for hu­man in­ter­ven­tion are yet to be fully stud­ied for prob­a­ble con­se­quences and suit­abil­ity. “The sci­en­tific com­mu­nity is try­ing to un­der­stand the mech­a­nisms within corals that lead to re­silience, but things are still ex­per­i­men­tal,” says Man­frino. The cost of such in­ter­ven­tions is another in­hibit­ing fac­tor. “These as­sis­tance schemes are ex­pen­sive and can usu­ally only be ap­plied on small scales. For ex­am­ple, the Great Bar­rier Reef is about the size of Italy, so any schemes to re­store it us­ing re­silient corals will largely be cost pro­hib­i­tive,” says Ridgewell.

In­ci­den­tally, while global warm­ing and acid­i­fi­ca­tion are cited as lead­ing threats to coral pop­u­la­tions, re­gional/lo­cal con­trib­u­tors are often un­der­es­ti­mated in their con­tri­bu­tion to coral reef dev­as­ta­tion. It is es­ti­mated that over 40 per cent of to­tal reef dev­as­ta­tion has been di­rectly caused by lo­cal pol­lu­tion from ur­ban ar­eas, while around 10 per cent loss is at­trib­uted to cli­mate change. Is­lands de­void of hu­man ac­tiv­ity still have al­most pris­tine corals de­spite global warm­ing and acid­i­fi­ca­tion. Dis­charge of sewage, in­dus­trial waste and fer­tilis­ers (which cause ni­tri­fi­ca­tion), over-fish­ing, dredg­ing and ir­re­spon­si­ble tourism have all been as­so­ci­ated with ad­verse im­pact on marine bio­di­ver­sity.

The most sen­si­ble way for­ward would ac­tu­ally be to reg­u­late dis­charges and eco­nomic ac­tiv­ity bet­ter. “With­out putting con­trols on hu­man im­pacts on corals on a lo­cal scale, none of this (in­ter­na­tional pacts for cli­mate change ac­tion) re­ally mat­ters. Hu­mans are the big­gest is­sue for corals. We mine them, blast them, step on them, dump sewage on them,” says Man­frino.

The in­ter­na­tional con­sen­sus to limit global warm­ing to un­der 2 oc of­fers a ray of hope for coral sur­vival. But un­less im­me­di­ate ac­tion is taken to reg­u­late lo­cal pol­lu­tion in coastal re­gions with coral pres­ence, am­bi­tious global agree­ments on cli­mate change will be im­ma­te­rial to the fate of coral reefs. „

Coral bleach­ing in the Mal­dives in May 2016 PHO­TO­GRAPHS: XL CATLIN SEAV­IEW SURVEY

De­cem­ber 2014 Fe­bru­ary 2015

How a healthy reef (left) in Amer­i­can Samoa bleached (cen­tre) and even­tu­ally died dur­ing the cur­rent bleach­ing event

Au­gust 2015

March 2016

The im­age on the left shows the bleach­ing of a coral reef at Lizard Is­land on the Great Bar­rier Reef. The im­age on the right, clicked two months later, shows the reef dead

Coral bleach­ing at Ja­pan's Ok­i­nawa is­land in Septem­ber 2016

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