Tack­ling the prickly prob­lem of the crown of thorns starfish.

On top of bleach­ing caused by warm­ing oceans, acid­i­fi­ca­tion and pol­lu­tion, corals may be eaten to ex­tinc­tion by the crown of thorns starfish.

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CORALS HAVE A LOT ON THEIR PLATE, some­times l it­era l ly. Warm­ing ocea ns a re pro­duc­ing wider out­breaks of bleach­ing and fur­ther dam­age is be­ing done to reef struc­tures by acid­i­fi­ca­tion, pro­jected to get much worse over the com­ing decades. On top of all this, there’s a nat­u­rally oc­cur­ring scourge, the crown of thorns starfish or COTS for short, which seems to be en­joy­ing coral’s mis­for­tune. Any­where in the world that’s home to coral reefs, you’re likely to find COTS. A pur­plish blue, red­dish grey or green in colour, they are cov­ered in long poi­sonous spines. Un­like the typ­i­cal five-tipped starfish, the COTS grows many limbs and sur­vives by crunch­ing on coral. They have been known to wipe out six to 10sqm of reef in a year and dur­ing out­breaks, de­fined as when 30 or more re­side in a hectare, th­ese deadly preda­tors can strip a reef al­most com­pletely of living tis­sue. A 1970s out­break on the north­ern Great Bar­rier Reef, saw a peak of 1,000 starfish per hectare, wip­ing out 150 en­tire out­crops of coral and leav­ing 500 more dam­aged. Or­gan­isms that de­pend on th­ese habi­tats were af­fected too: two species of coral-eat­ing but­ter­fly fish and two species of plank­ton-feed­ing fish also saw dra­matic de­clines. Though the de­fin­i­tive cause be­hind out­breaks is still to be fully un­der­stood, COTS has been in­creas­ingly ev­i­dent over the past decades. That has re­sulted in an in­creas­ing num­ber of pop­u­la­tion con­trol pro­grammes ini­ti­ated by lo­cal groups and many are look­ing for vol­un­teers. Carp e Di em Mal­dives, a wa­ter sports op­er­a­tor with a fleet of three live a boards, is one pri­vate com­pany that has part­nered with a con­cern group, in this case, Coral Reef CPR Con­ser­va­tion Char­ity and Con­sul­tancy. Fol­low­ing their first ex­pe­di­tion two years ago, when a total of 900 COTS were col­lected from 15 reefs in North and South Male Atolls, they are now look­ing for 20 Padi-qual­i­fied divers to help in the re­moval of the coral-munch­ing cul­prits, as well as to con­duct quan­ti­ta­tive reef sur­veys and data anal­y­sis un­der the su­per­vi­sion of Chief Sci­en­tist, Dr An­drew Bruck­ner. Th­ese up­com­ing week-long ex­cur­sions will take place from Septem­ber 10-17 and Oc­to­ber 22-29. “The ma­rine bi­ol­o­gists were con­duct­ing COTS clean-ups and sur­veys in July 2015 when there were wide­spread re­ports of an out­break. They were work­ing with sev­eral re­sorts in the Mal­dives to ac­cess house reefs and nearby dive sites,” said Carpe Diem Mal­dives head of brand­ing Liz Smailes, who adds that her cruises have since been trans­port­ing the con­ser­va­tion teams to more re­mote ar­eas. “Our guest divers on those trips were al­ways in­ter­ested to hear more a nd wanted to get i nvolved, so our

col­lab­o­ra­tion evolved nat­u­rally from there… It’s also a re­ward­ing ad­di­tion for our Mal­di­vian di­ve­mas­ters to get in­volved in sci­en­tific ma­rine con­ser­va­tion.” Phys­i­cal re­moval is one way to get rid of COTS, with them put care­fully into mesh bags. Full loads are sent to the sur­face with a sur­face marker buoy for col­lec­tion and anal­y­sis. Once dried out, t hey’re buried underground on beaches or burned. Al­ter­na­tively, they can be in­jected with a mix­ture in­clud­ing bile salts or sim­ply with vine­gar. This is much less labour­in­ten­sive but the starfish have been known to shed the in­jected limb and re­grow it rapidly. If re­gen­er­at­ing poi­sonous starfish sound like some­thing out of a Hol­ly­wood first-con­tact movie, it’s im­por­tant to re­alise that they are part of the nat­u­ral order: just an ex­tremely re­silient, fe­cund part wit h few preda­tors. In t y pica l cir­cum­stances, they oc­cur in low num­bers on reefs and play their role in main­tain­ing di­ver­sity in the ecosys­tem by con­sum­ing faster-grow­ing corals, which they pre­fer, to make space for slower-grow­ing ones. It’s not un­til over­popu- la­tion brings a scarcity of their pre­ferred coral species that they are forced to adopt an in­dis­crim­i­nate diet which so de­pletes reefs. To date, sci­en­tists can only spec­u­late as to why out­breaks oc­cur but pos­si­ble cul­prits in­clude over­fish­ing of the starfish’ preda­tors such a s Napoleon wrasse, puf fer f i sh a nd trig­ger­fish; ex­ces­sive plank­ton blooms fu­elled by agri­cul­tural run-off that pro­motes the growth of COTS lar­vae; and in­creas­ing sea tem­per­a­tures. What is known is that th­ese out­breaks of COTS are cycli­cal, oc­cur­ring ap­prox­i­mately ev­ery 17 years. Lack­ing any per­ma­nent con­trol mea­sures though, re­moval and on-site con­trol re­main the most wide­spread ap­proaches. Al­to­gether, divers have re­moved more than 17 mil­lion starfish from Indo-pa­cific coral reefs alone since the 1960s, but the high cost of this labour-in­ten­sive work re­stricts pro­grammes to small reefs with so­cioe­co­nomic or bi­o­log­i­cal sig­nif­i­cance, such as spawn­ing sites, tourist at­trac­tions or ar­eas with high bio­di­ver­sity. And col­lec­tion is not easy: ma­rine bi­ol­o­gist Bruck­ner cited a num­ber of in­juries in­curred on an ex­pe­di­tion on Ai­tu­taki in his 2015 blog on the Khaled bin Sul­tan Living Oceans Foun­da­tion, comparing the process to: “a wrestling match that may in­volve many sec­onds hold­ing your breath and splash­ing about up­side down”. “A spine to the leg/knee/hand does not feel good, and tends to bleed pro­fusely… even af­ter re­peated cuts, col­lect­ing th­ese deadly coral preda­tors doesn’t get any eas­ier,” he con­tin­ued. On top of the dan­gers in­her­ent in han­dling a toxic crea­ture, he says its dis­posal is a lso prob­lem­atic as the starfish is highly aque­ous, mak­ing i nci nerat ion a di f f icult feat while dis­pos­ing of them in a land­fill brings the stink of rot­ting fish. Still, un­til bet­ter meth­ods are found – even a Cots-killing ro­bot is be­ing tri­alled – the fight must con­tinue. “All th­ese chal­lenges can­not stand in the way of our de­ter­mi­na­tion to in­ter­cept the re­peated dev­as­ta­tion of coral reefs here on Ai­tu­taki, and de­spite the chilly hours spent in wa­ter, and the grazes, bruises, cuts and punc­tures, it had been a re­ward­ing ex­pe­ri­ence,” he wrote. Such is the prob­lem that or­gan­i­sa­tions of all kinds are pitch­ing in, from the Great Bar­rier Reef Ma­rine Park Au­thor­ity in Aus­tralia to high-end re­sorts such as Anan­tara’s Dhigu and Veli in the Mal­dives; and from global non-prof­its like Reef Re­silience, NOAA and The Nature Con­ser­vancy to grass­roots com­mu­ni­ties like Sikat in the Philippines, who gath­ered lead­ers from vil­lages for a COTS re­moval pro­gramme on Romblon Is­land in 2005. Nat­u­rally most of th­ese pro­grammes re­quire a level of div­ing pro­fi­ciency, but even non-divers can some­times get in­volved in mon­i­tor­ing and as­sess­ment. In the case of the Great Bar­rier Reef, for in­stance, you can down­load the Eye on the Reef app at www.gbrmpa.gov.au to re­port sight­ings or of­fer in­for­ma­tion on any as­pect of reef health. – By Joyce Yip

THE POSTCARD SHOT How reefs should look, with­out the men­ace of the crown of thorns starfish, shown top left and right.

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