Meet the quirky underwater worm that looks like a Christmas decoration and can even see through its gills! "Christmas tree worm" is the common name for a marine worm that lives on tropical coral reefs around the world. These tiny creatures are decked out in bright reds, yellows, oranges, blues and whites.They all belong to the same species: Spirobranchus giganteus.
Scuba divers enjoy approaching coral boulders slowly, taking care to observe clusters of Christmas tree worms without startling them. When they get too close (without touching), the worms quickly retract into their tubes embedded in the coral and seal up with small lids called operculums. It can take a few seconds to over a minute before they feel safe enough to come back out.
- Christmas tree worms can grow up to around 3.5 cm in length, with most of their bodies hidden inside their tubes. What you see sticking out are their festive, feathery spiral-shaped tentacles called radioles. These radioles serve a dual purpose: they act as gills to absorb oxygen from the seawater and filter out food particles and plankton. The microscopic hairs on the radioles help move the captured food towards the worm’s mouth, functioning like a tiny conveyor belt.
- The Christmas tree worms' hypersensitivity comes from their unique feature: bright orange eye spots among their radioles. These eye spots allow them to "see" with their gills, detecting shadows of potential predators while their bodies are hidden in coral.
- Interestingly, worms in crowded areas are more skittish than those living alone or in small groups. The more worms there are on a coral, the longer they stay hidden. It seems that, for these worms, being in a crowd doesn’t offer more safety; instead, their bright colors make them stand out even more in busy colonies.
- Christmas tree worms have both males and females. These worms are quite fascinating in their reproductive approach. Both genders release their eggs and sperm directly into the water, where fertilization occurs. The eggs develop into larvae that drift in the ocean for about 9-12 days before settling on a suitable coral. The worms then build their tubes in the coral, which they will inhabit for their long lives. They’re pretty selective, often choosing specific coral species like brain corals, though the exact criteria for their choice remain a mystery.
Did you know?
- Each Christmas tree worm has two crowns, or "Christmas trees," which are always the same color. While the worms themselves come in a variety of vibrant colors, each worm’s twin crowns match perfectly.
- Christmas Tree worms can live up to around 30 years, although their lifespan can be affected by environmental factors like pollution and climate change.
- Christmas tree worms eat phytoplankton by catching it with their feathery radioles. They move the food to their mouth using tiny hair-like extensions and filter out anything too big. They also save grains of sand in special sacks to build their tubes.
- Christmas tree worms bolster coral reef health by defending corals from invasive sea stars and algae, enriching habitat structure, and improving water quality through filter feeding. Their presence helps maintain the overall balance and resilience of the reef ecosystem.
Where to Find Christmas tree worms on Koh Tao
When you find a “field” of Christmas tree worms while diving in Koh Tao, gently flick your fingers around them (but don’t touch). Watch how fast they retract into their tubes!
Tanote Bay
Hin Wong Bay,
White Rock,
Japanese Garden,
Mango Bay,
Twin Peaks
Shark island,
Aow Leuk
(etc)
