Range: Indo-Pacific and Australian waters Habitat: Coral reefs and deep marine waters Size: Up to1.3 feet (40cm) in diameter Diet: Algae as larvae; Coral and scallops as adults Threats: Giant triton snails, humphead wrasse, pufferfish, triggerfish, and humans Life span: Five years or older

Transcript:

Today on Animal Fact Files we’re discussing crown-of-thorns sea stars. There are technically two known species of crown-of-thorns sea stars and only one is really held responsible for reef habitat destruction, but we’ll come back to that in just a bit. The less well known species is typically found in deeper waters and tends to stick to soft bottom areas. The more well known species is usually found in more shallow waters and lives in coral reef habitats.

It should be relatively obvious where these animals get their name as they’re both covered in spines - though the spines of the more well known species can get longer than the others and reach up to 2 inches (5cm) in length! These spines aren’t just for show, either! They help protect against predators and can even inject venom. While a spiny sea creature might not seem like a tasty treat, crown-of-thorns starfish are eaten by giant triton snails, humphead wrasse, pufferfish, and triggerfish - some of which are commonly fished by people. Keep this in mind as we continue.

The venom in a crown-of-thorns sea star can even affect humans. If stung, a person may experience pain, nausea, and vomiting, so it’s generally advised not to handle these animals - their spines are strong enough to pierce through wetsuits! Generally speaking, however, people are stung by these animals when they’re accidently stepped on. Ouch! Crown-of-thorns sea stars can grow up to 1.3 feet (40cm) in diameter and are considered some of the largest sea stars in the world.

While the more well known species is specifically well known for its coral eating behavior, it’s actually only the adults that consume coral. Crown-of-thorns sea star larvae actually eat algae! And the less well known species doesn’t even eat coral, or at least there isn’t any documentation of this. They instead eat scallops. The sea star will sneak up behind a scallop and then startle the mollusc. The mollusc will swim backwards, right underneath the waiting starfish. Once caught, the crown-of-thorns sea star will begin eating and these animals do this by releasing their stomach out through their mouth on the underside of their body and then digest the food until it is liquified enough to be pulled back in. Crown-of-thorns sea stars reproduce via broadcast spawning which means the males and females release their gametes, or sperm and eggs, into the water column at the same time and the eggs become fertilized externally. It only takes about a day for the eggs to hatch, two to four weeks before they settle to the ocean floor, and then about six months before they begin eating coral, though this can take longer depending on environmental conditions with one study finding they can survive on this algae diet for more than six years! A crown-of-thorns sea star may live to be five years old or older and the two species are able to reproduce with one another!

All right, so of course the elephant in the room is that these animals are sort of despised, especially in areas where they have shown up and hurt reef systems. Crown-of-thorns starfish live throughout the Indo-Pacific region and in some places, such as the Great Barrier Reef in Australia, these animals have severely damaged coral reefs due to their over abundance and thus intense eating behavior. But let’s consider some points that have been noted in crown-of-thorns sea star research.

It’s not unusual for these animals to go through cycles where they are more and less abundant; and, in fact, they’re known to help diversity in a reef system. Because crown-of-thorns sea stars specifically eat fast growing, hard corals, when they show up in droves, they actually reduce the amount of hard coral to the point that other slower growing corals are able to gain some space. There is also suggestion that in places with little human disturbance, such as areas protected from commercial fishing and where agricultural runoff isn’t as high, these animals don’t cause complete reef death - even when they show up in their large, cyclical outbreaks.

So, our question is this, are these sea stars really as bad as humans have painted them to be, or are we simply pointing fingers and putting bandaids on bullet wounds. People purposely kill these animals by injecting them with poison, throwing them on beaches, and even building robots to search them out, but is that the best solution or is there another layer to all of this?

For more facts on crown-of-thorns sea stars, check out the link in the description. Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files!