Christmas tree worms – colorful treasures underwater
Christmas tree worms are colorful marine worms that can be found all over the world in tropical waters. These little creatures are popping out from their tube decorating coral reefs like ornaments a Christmas tree. They are favorites of underwater macro photographers because of their vibrant colors and detailed structure. From this little marine biology summary, you will know what these interesting creatures are and how they live.
10 facts about Christmas tree worms
We love learning about sea creatures we use to spot while snorkeling and hope you share our passion. We have already talked about why lionfish is a dangerous fish and how sea stars move, and today we will teach you a bit about the beautiful Spirobranchus by sharing 10 facts about Christmas Tree Worms.
Tip: To become a responsible snorkeler, learn more about coral and reef species and read some marine life books!
Christmas tree worms live on shallow tropical coral reefs
Spirobranchus can be found on coral reefs waters over the world from the Caribbean to the Indo-Pacific, usually between 10 and 100 ft (3-30 m). Thanks to its shallow water presence, you can see them while snorkeling as well. It seems, there are regions they prefer over others and at some places you can find incredibly big populations. For example, we were impressed by the amount of Christmas tree worms in Thailand while snorkeling in Koh Tao where you can find thousands of them on shallow water reefs!
They really look like tiny colorful trees
These tiny (1-2 inches -4-5 cm- long) worms have a central tube and two spiraling structures that give them a tree-looking shape. You only can see the feathery part of them that can pink, red, yellow blue, as well as white and brown. The rest of their body, the legs, and the bristles are always in the tube and are about twice as large as the visible feathery part.
They spend their whole life on the same coral
These worms build a calcium carbonate tube in the coral as their home. This tube system is so complex and looks like tree-roots. Depending on the water and reef conditions, they can live up to 40 years. Their normal lifespan is between 10-20 years.
Christmas Tree worms can disappear in milliseconds
They sense movement in the water and can retract when feeling threatened. Moreover, they can seal themselves using an operculum, a specialized body structure that opens and closes like a door and equipped with spines to keep predators away. The worm slowly re-emerges when the surrounding is clear than fully extends.
Spirobranchus feed by using their feathers to catch planktons
The hair like cilia that covers their spiraling structure helps them to trap food and pass it to the mouth. Christmas tree worms are filter feeders. Their menu consists of planktons, ciliates, and organic detritus. They filter the small microorganisms from the water by trapping on their plumes and deposit straight into the digestive tract.
Reproduction happens with the help of currents
If it is time to reproduction, the male releasing sperm while the female eggs into the water and fertilization happen. The developed larvae drift with the currents until settle on a coral by constructing the tube where they will live the rest of their life.
They have two sections in their life
Christmas tree worms start their life with a short larval phase. It only lasts for a few hours but maximum several weeks. The larva worms live in open water and feed only on plankton. After settling down on a coral, the adult phase starts by building their home tube.
What are their predators?
These tiny tube worms are protecting themselves simply by hiding in their tube but of course, there are some predators in the ocean they feed on them. Usually, sea urchins, crabs and shrimps eat Christmas tree worms as well as some larger reef fish. Although if the predator did not manage to eat the whole worm and caused damage only on the tentacles, the worm is able to regrow in a short time.
Christmas tree worms can save coral reefs
In spite of their small size, the presence of Christmas tree worms is crucial on coral reefs. Like the rainbow parrotfish, they have an important role in keeping marine ecosystems healthy. They can protect the corals from invasive sea stars like the crown of thorns sea star and also preventing the overgrowth of algae. Moreover, it was confirmed that Spirobranchus help coral reefs to recover after coral bleaching events.
Threats to Christmas tree worms
Good news is that these colorful creatures are under no threat of extinction, however, they are also in danger. The coral bleaching, ocean acidification, and rising sea temperatures affect them directly. Unfortunately, they are collected for the aquarium industry as well, but in artificial environment, they live not so long.
How does the “Christmas tree” retraction process work. Is the tree just a fixed part of the worm that shows when the worm edges out of the coral, or does the worm stay put and somehow the “Tree” telescopes in and out? Nothing I have read explains this. Several articles say the trees help with eating and breathing, while only one said the trees had the animal’s eyes on it. What is correct here?
The “trees” of the Christmas tree worm, or radioles, are not fixed; they telescope in and out while the worm remains in its coral burrow. These appendages can swiftly retract into the worm’s burrow in response to danger, thanks to muscle contractions, without the worm itself moving in and out.
The radioles play roles in feeding and breathing. They have hair cilia that capture organisms, from the water for food and help, with oxygen absorption. While the worm does have eyespots to detect changes these are located on its body near the head not on its radioles. These eyespots help the worm sense dangers and react by retracting its radioles for protection.
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