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.
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.