Acanthaster Planci or, the “Crown of Thorns” starfish has received both fame and notoriety in recent years for its mysterious invasion and decimation of sclaractinean corals on Australia’s Great Barrier Reef. Although there are other contributing factors for the decline of corals along the Great Barrier Reef, significant credit for the destruction is due to this predator’s invasion and subsequent decimation of entire colonies of corals along the Barrier Reef.
The starfish digests stony coral polyps by regurgitating its stomach onto the polyps and allowing digestive enzymes dissolve the polyps, and then digested by the starfish. The extreme flexibility of the animal enables it to twist into limitlessly convoluted shapes in order to reach an infinite number of configurations to accomplish its objective.
The exact reasons for the massive populations of starfish decimating coral reefs remains unknown however hypothesis put forward for the recent population explosions include an increase in the concentration of nutrients for the phytoplankton food for the crown of thorns starfish larvae and removal of key predators such as the triton (a mollusk) and red emperor (Lutjanus sabae) increases survivorship.
Recent evidence supports the first hypothesis even though effects from reducing predation through fishing pressure cannot be ruled out. Exacerbating the problem is pressures on existing coral populations such as coral bleaching believed to be the result of rising sea surface temperatures.
Once reaching adulthood, the crown of thorns starfish is a formidable opponent with thorns reaching over the entire surface of its upper body. Thorns that produce a neurotoxin to animals that attempt to attack the animal. These thorns are strong enough to pierce wetsuits and create significant wounds affecting divers as well as other animals encountering the creature.
Recent studies have shown the possibility of using a chemical produced by sea urchins to lure starfish away from the corals to prevent decimation of reef colonies. Although only small quantities of starfish were lured away from the reef in the study, the important “proof of principle” was established.
It is estimated that 27 percent of all coral reefs have been destroyed with up to 40 percent being destroyed by the year 2010. The crown of thorns starfish is expected to play a significant role in this destruction. Most attempts to control starfish populations have been unsuccessful. Poisoning those harms other creatures, cutting them up just creates more starfish due to their ability to regenerate complete bodies from the cut parts.
On the Great Barrier Reef, fishing bans seem to have a positive impact on the survival of coral reefs. Although the specific reason why this is remains unknown, outbreaks of large predatory crown of thorns starfish occur lees often in protected zones. When outbreaks occur, thousands of starfish dot the reefs amongst the white skeletons of dead corals.
It is believed that eventually the starfish die out due to starvation and disease; however, their larvae are carried downstream to other reefs to infest and decimate further regions. Trough extensive monitoring, results have shown that areas that are protected from fishing exhibit significantly decreased invasions from the deadly starfish infestations.
Surveys have found that outbreaks were 3.75 times higher in regions where fishing was allowed verses the no-take reefs in the mid-shelf regions where most outbreaks occur. This has caused The Great Barrier Reef Marine Park to increase the no-take zones from 4.5 percent to 33 percent of the area of the park.
Whatever the reasons for the outbreaks, increasing protections for fish in the area seems to be a significant breakthrough in preserving the reefs from destruction from the deadly crown of thorns starfish invasions.