Recent marine surveys by scientists in the Great Barrier Reef have found that an explosion in the population of the crown-of-thorns starfish has decimated parts of the region’s reefs and are now threatening part of the so-called Coral Triangle – one of the world’s richest regions of coral reef biodiversity.
Located between Indonesia, Malaysia, the Philippines, Papua New Guinea, Palau and the Solomon Islands, the Coral Triangle is home to some of the most genetically unique marine species. Researchers found that the predatory starfish have almost destroyed some of the beautiful reefs found near Halmahera, Indonesia, with 20% of the reefs already reduced to only 5% coral cover.
The crown-of-thorns starfish is a type of echinoderm with protective spines all over its body, which eject a neurotoxin. It can grow up to 40 cm in diameter, and is equipped with anywhere from 12 to 19 arms. Found in tropical coral reefs from the Red Sea to the Indian and Pacific Oceans, they devour coral reefs by climbing and extruding their stomach over them in order to excrete a digestive enzyme which transforms the reef into consumable, liquefied tissue.
Three similar ‘outbreaks’ have been recorded since the 1960s. Though the reason behind this current starfish outbreak is not entirely clear, it is believed that it could be linked to agricultural runoff, which increases algal blooms that nourish the starfish larvae. The removal of the starfish’s natural predators, water salinity, temperature and human impact on aquatic ecosystems are also contributing factors.
However, the promising presence of species such as the bumphead parrotfish and Napoleon wrasse indicate a still relatively-intact ecosystem. The surveyors are now suggesting that the best way to slow the starfish down is to ensure that human activity in the area is reduced.
"Once you've got an outbreak, there's almost nothing you can do to stop it. The only way to ensure you've got some reef left at the end of it is to protect lots of other areas," says Dr Andrew Baird, an Australian member of the survey team.
"At this point it's just the corals, so if we can minimize the impact from the crown of thorns, there's still a lot of hope."
Image: Jon Hanson