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Crown-of-Thorns Threatens Hawaiian Reefs

    By Marc Peraino. March 2, 2016 - 3:13 pm

COTS_and_coral_scars_-_excellentThere’s a predator in Hawaii’s waters and it poses a serious threat. No, it’s not sharks; it’s a starfish, and a very thorny one at that.

The crown-of-thorns starfish is a predatory species of starfish that feeds on coral polyps found in coral reefs, like the ones in Hawaii. With a disc-shaped body, up to 21 arms, prehensility (an ability to grasp), and numerous sharp spines covering its body, the crown-of-thorns is a special starfish wreaking havoc on reefs around the world.

The crown-of-thorns feeds on coral by climbing onto a coral colony, using its arms and flexible body to shape itself closely to the coral surface. The starfish then extrudes its large stomach through its mouth and secretes digestive enzymes that liquefy the coral polyps. The nutrients are then absorbed through the stomach, leaving behind a white coral skeleton.

One crown-of-thorns starfish can consume 65 square feet of coral per year. They prefer to eat branching corals and table-like corals, staying away from corals with a more rounded shape.

The habitat of the crown-of-thorns spans a wide range across the Indo-Pacific. The species is most commonly found in Australia, but it ranges from the Red Sea and the coast of East Africa all the way across the Indian and Pacific Oceans to the west coast of Central America.

The crown-of-thorns starfish can arrive at a reef in waves of outbreaks as starfish larvae are carried by ocean currents. The larvae feed on phytoplankton, which is normally low in numbers in tropical reef waters. Phytoplankton can increase though with run-off of fertilizers and pollution caused by seasonal storms, leading to an outbreak of the crown-of-thorns.

Efforts to control the crown-of-thorns involve divers seeking out and killing the starfish using injectable toxins or physically removing the starfish from the water. A healthy reef can recover from an attack, but recovery can take between 10 and 20 years. The Great Barrier Reef in Australia and reefs in Indonesia, among other places, have experienced significant damage from crown-of-thorns outbreaks.

According to a report from The Guardian, researchers at James Cook University have recently discovered that the use of simple household vinegar can be used to kill the starfish by injection.


Triton’s trumpet

The crown-of-thorns has only a few natural predators. The Triton’s trumpet, a large mollusk found in the Indo-Pacific region, has been known to prey on the crown-of-thorns using its long sharp radula (tongue). Another predator is a type of polyp belonging to the genus Pseudocorynactis, similar to a sea anemone, that has been seen attacking and ingesting a crown-of-thorns whole.

The problem of the crown-of-thorns starfish highlights the vulnerability of reef ecosystems to human pollution and the delicate and intricate balance that reefs require to thrive. Divers in Hawaii are employing the same methods as those in Australia to eradicate crown-of-thorns outbreaks and protect our precious reefs.

Photos courtesy of www.wikipedia .org.

One Response to Crown-of-Thorns Threatens Hawaiian Reefs

  1. Carlos

    March 28, 2016 at 1:02 pm

    The information in the article is correct. But, without quotes from interviews and only one report mentioned, I wonder if this is journalism or just a rewording of internet sources. You could have interviewed HPU professors and provided some unique information that is not easily accessible through a Google search.