By Sophia Read
For The Bali Times
SEMINYAK ~ Last month the front page of this publication carried a disturbing report from the ARC Centre of Excellence for Coral Reef Studies, and its partner the Wildlife Society. The notorious crown of thorns starfish is threatening the heart of Indonesiaâ€™s reef system. The importance of Indonesiaâ€™s reefs to the global marine ecology simply cannot be overestimated â€“ they are widely viewed as the nursery and the origin of corals around the globe, most notably those of the Australian Great Barrier Reef.
The crown of thorns eats coral, arriving on healthy, flourishing reefs and leaving them white and dead. Ten years ago in Bali, a combination of this voracious predator and an El Nino event decimated the pristine reefs of Menjangan, leaving them destroyed and lifeless for many years, before their eventual regeneration to more varied and fascinating than before.
The starfish takes its name from its covering of toxic spines. These spines are impregnated with a neurotoxin that causes the affected area to turn blue and swell up for days or weeks, along with associated pain, and sickness. They can grow to immense size, though they normally end up about the size of a dinner plate.
The starfish eats coral by settling on a coral polyp, extruding its stomach (complete with acid) over it, and then absorbing the resulting liquefied goop. A single starfish can eat up to 13 square meters of living reef a year. In small concentrations this poses no problem to the reef, and is even beneficial, as they ensure diversity, and encourage new coral growth. Also, and luckily, they appear to have a preference for the faster-growing forms of coral â€“ the acorapora, which is quickly replaced or replenished. The problem arises when large groups of starfish (many thousands) all congregate on one particular reef â€“ armies of thorny coral devourers. This is what scientists term an outbreak.
Like many marine creatures, the lifecycle of the crown of thorns starfish is not yet well understood. In fact, the creature itself is fairly new to science, having been first noticed and studied as recently as the 1960s. The length of an outbreak varies wildly â€“ some may last only a couple of years, and others half a decade before the marauders vanish. Unsurprisingly, it is hypothesized that the main limiting factor of the length of the outbreak is the size of the affected reef â€“ the starfish will eat all the available coral, so less coral means less time.
It is estimated that, on average, it takes more than 12 years for a reef to recover from an outbreak, and if ideal conditions are not met, the reef may never recover to pre-outbreak levels of coral cover. In Bali, we have been extremely fortunate. The Menjangan reef system has regenerated within a 10-year period, and may even be more attractive to humans now than before the starfish â€“ the coral cover is more varied, and is mostly the faster-growing forms of coral, which are more visually spectacular.
There are many mysterious and little-understood things about these outbreaks. Most amazingly, we still have no clear proof of where all the starfish come from, or, in fact, where they go. Hundreds of thousands of prickly dinner plates cannot just vanish, but they do. Various suggestions have been made about this phenomenon, including some form of submarine alien invasion.
Some scientists have argued that when one food source is exhausted, they simply link arms and march away across the ocean floor to the next one. This is difficult to believe, as, although many individuals have been sighted crossing the sandy ocean floor in groups, they simply cannot move very fast, or very far, without some form of food. The most obvious explanation would be that, deprived of food, they either starve to death or succumb to a deadly disease, but this does not appear to be the case. Reefs at the end of an outbreak are frequently under close scrutiny, and there has never been a report of massive die-off among starfish. Even if they all died together, instantaneously, in some Jim Jones-style suicide plot, they are so hardy that it takes almost a week for their corpses to decompose (very few fish will eat them), so one would have thought that some evidence would be found.
Intervention in a natural habitat is always a difficult call to make. We understand so very little about the complex interactions of the ecosystem, and so often our attempts to help nature have wildly backfired (cane toads, anyone?). We do not know whether these sporadic outbreaks serve a greater purpose. To the human eye, the devastation is terrible, and seems to call out for action, for intervention.
There are various difficulties here, the main one being that these outbreaks are almost impossible to contain, or to control â€“ and we have tried. Scientists on the Great Barrier Reef – which has suffered badly at the hands, or rather the stomachs, of these voracious beasties – have tried various methods, from the gruesome to the macabre, with limited success.
First, they tried cutting them into pieces. But this has various drawbacks. The pieces into which the starfish were cut remained alive for more than two weeks, and while it is unlikely that they would have done so, some starfish can regenerate a whole body from a single leg. More importantly, to cut them up, they need to be removed from the reef, and the removal process not only damages the reef, but is extremely likely to damage the diver (swelling, pain, nausea = lack of volunteers).
Fencing has been tried, and may prove to be a valuable method in the future, but it cannot stop the migration of starfish larvae and is difficult to build and expensive to maintain. Also, as the most likely reason for wishing to eliminate an outbreak is that it is on an area of reef used as a tourist attraction, ugly steel fences would not heighten a visitorâ€™s underwater experience.
Which brings us to the last and most effective method â€“ poison. After various chemicals have been tried with varying degrees of success, scientists opted for an ecologically sound (introduces no artificial chemicals into the environment) control method. Divers inject the leg of the starfish with either its own stomach acid or a solution of sodium bisulphate. Divers can inject over 100 starfish an hour after training, but the process is extremely labor intensive â€“ hundreds of divers are needed, and the program must occur under proper supervision, and control.
To give an idea of the figures involved, one control program in Australia cost AUS$54,000 (US$47,637). It took place in half a square kilometer, and succeeded in killing 3,100 starfish. Here in Indonesia, we face considerably more problems – of training, adequate supervision, planning, logistical support and execution of any such control program. However, if tourist income is threatened, such a program may be the only answer to this thorny problem.
The writer is sales manager of AquaMarine Diving â€“ Bali.Filed under: The Island