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CRITTER: Meet kio the Christmastree worm

Can a worm help save a coral reef? Yes and that is exactly what kio the Christmastree worm does. Kio is only three inches long and it makes a ridged calcium carbonate tube right into a live coral. When the worm has its spiral fans out of its tube it looks like two Christmas trees side by side. The circular fan-like structures filter zooplankton from the sea water and these fans come in many colors from blue, yellow, red to white. At any given time the fans can retract back into the tube that buried deep into the live coral. Kio even has a trap door with spikes on top to protect the worm in its tube.

Live healthy coral polyps can clean the outside of their calcium carbonate home and that is why not much can live on a live coral. When a baby Christmas tree worm lands on the live coral it does not get removed and is allowed to burrow right into the coral and make its long rock hard tube.

Why would the coral allow this intruder to invade its home? I have seen some live corals that have over 20 Christmas tree worms growing along its surface and the different colors of the worms exposed fans make the corals look quite beautiful.

A live coral reef can be killed quite quickly by the crown of thorns starfish. These poisonous foot wide stars eat live coral polyps and when the crown of thorns get too widespread they can eat up an entire coral reef. The corals that house kio on their surface are avoided by the starfish so they won’t get eaten. How the coral adopts their little body guards is quite a mystery and why do the crown of thorns leave the corals with kio alone?

Out in the ocean there are all kinds of amazing relationships being made by animals that do not have eyes but they have learned how to work together to protect each other from potential predators. Every square foot of live coral reef has dozens of connections with other species in order to survive and we still know very little about kio the Christmas tree worm and its working relationship with live coral.

You can see kio in action in my free documentary movie about marine life at Sharks Cove O‘ahu on my underwater educational YouTube channel at Underwater2web.


Terry Lilley is a marine biologist living in Hanalei and co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawai‘i go to
Source: The Garden Island

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