Over 1,500 species of fishes, invertebrates, and algae that call the nearshore waters of Hawai’i home
My wife and I were on the most amazing snorkel trip of my life on the day that I took this photo. We had been in the water for about two hours, and we were heading back to the boat for the day when I saw this Long-spined Crown-of-Thorns off in the distance. It was a bit deeper than the other creatures that I had been photographing throughout the day, but I decided to freedive down to take this picture.
This day of snorkeling was arguably the best day of snorkeling that I’ve ever had. It was also in the same location as my first snorkel back in 1999 when I went out with the same company with my grandparents. This time I was with my wife for her birthday. The location of the dive is called Kealakekua Bay. Within the bay there is a marine protected area called Kealakekua Bay Marine Life Conservation District. This area is managed and protected by the State of Hawai’i Division of Aquatic Resources. This and other conservation districts around the islands are meant to protect the over 1,500 species of fishes, invertebrates, and algae that call the nearshore waters of Hawai’i home.
So, what is this blob of thorns that looks like a bullseye pillow with pins sticking out of it?! This is a long-spined crown-of-thorns. It is a type of large starfish that preys upon the coral. They will eat the polyps of stony coral. Its name is derived from the venomous thorn-like spines that protrude from its upper surface which resemble the biblical crown of thorns. What you’re looking at is one of the largest starfish in the world!
Like most starfish, the long-spined crown-of-thorns is made up of a body with radiating arms. This species of starfish is special in its disc shape and its large ratio of stomach surface to body mass (said more plainly, its arms are small for the size of its body). The adult long-spined crown-of-thorns starfish have up to 21 arms and grow to about 14 inches in diameter including the arms. Their spines are about 2 inches long, are stiff, can puncture soft surfaces, and contain venom.
The biology for how these starfish eats is both incredible and damaging. They will climb on top of the hard coral and extrude its stomach out through its mouth. The long-spined crown-of-thorns will then release digestive enzymes that it uses to digest the coral tissue. This leaves a white scar on the coral skeleton. A single starfish can consume 65 square feet of living coral in a year. This is understandably highly damaging to a reef. When there are outbreaks of these starfish on a reef, coral cover can go into decline. This can cause loss of biodiversity because they focus their consumption on specific types of coral.
The adult long-spined crown-of-thorns starfish have up to 21 arms
Did you know?
- An invasion of long-spined crown-of-thorns is commonly known as a plague.
- Their populations can grow when tritons are over-collected. That’s because tritons are one of their natural predators. Tritons are a type of sea snail.
- Individuals can be purple, purple-blue, reddish grey or brown with red spine tips, or green with yellow spine tips.
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