Crown-of-Thorns Seastar: threatens Japanese coral reefs

A follow up to my coral reef posting of last Monday, The Japan Times Online reported an increase at the coral reefs of Shirahama in the number of crown-of-thorns seastars, a species of seastar that feeds - and feeds ravenously - on coral.

Shirahama is located on the western Kii Peninsula just below the middle of Japan. Normally, the crown-of-thorns' range would be held in check by its preference for warmer tropical temperatures where, within a healthy reef ecosystem, it is held in balance as a predator by virtue of the dominance of coral. But the temperatures have been increasing and, along with human development (eutrophication) that has increased certain nutrient levels which weaken the coral, this has allowed the crown-of-thorns to expand its range and explode in numbers.

Unfortunately, the only immediate solution to the problem is a controlled eradication of the seastar. A small group of local divers have been enlisted in this effort which could carry on for several years. Care must be taken as the crown-of-thorns is covered on the outside with many spines (hence its name) that are actually sheaths for sharp poisonous needles.

"'If we keep removing (the starfish) in limited areas on a regular basis, there should be some effect,' said Katsuyuki Nakaya, 53, who runs a shop catering to divers and chairs an environmentalist group based in the city of Wakayama."

I have experienced the effect of the seastar's defensive weapons firsthand. When I was a novice diver, a came across my first crown-of-thorns in Hawaii. Fascinated with this ornate creature, I carefully turned it over to examine its underside and when I placed it back on the reef, I noticed a countless number of green threads streaming from the palm of my hand. Odd, I thought, until I realized the green color was blood having lost its red hue in the ocean depths. For the rest of the day my hand tingled as a subtle reminder: look but don't touch.

Read online article.