O Christmas tree worm, we can see you underwater in the Keys

It is almost Christmas. Time to get a Christmas tree.

We all know the song, which originally referred to the fir tree’s evergreen quality — a symbol of constancy and faithfulness.

“O Christmas Tree! O Christmas Tree! Thy leaves are so unchanging;

Not only green when summer's here, But also when 'tis cold and drear.

O Christmas Tree! O Christmas Tree! Much pleasure thou can'st give me.” (From “O Tannenbaum,” lyrics written in 1824 by the German organist, teacher and composer Ernst Gebhard Salomon Anschütz.)

Even though we live in the sub-tropics, many folks in the Florida Keys like to adorn their houses with a decorated Christmas tree. But, they don’t have the possibility of hopping in the family wagon with mom, dad, the kids and Fido (like in some nostalgic Christmas movie) and going out into the snow filled woods to chop down the “perfect tree”

We settle for imported trees for sale at supermarkets, churches and other organizations. Or, we end up buying artificial trees that can be decorated year after years without worrying if the base has been kept full of water.

But, not to be outdone by our northern friends, we do have our own special Christmas trees that live underwater in the colorful offshore reefs.

They are not fir trees; They are marine worms called Christmas tree worms (Spirobranchus giganteus), which can be easily spotted because of their distinctive shapes, beauty, and colors. The Latin term Spirobranchus translates to "spiral gills," referring to the worm's unique crown.

OK, because Christmas tree worms live underwater, unless they are in an aquarium, you have to get wet to see one.

Now comes the scuba part.

Many student divers are nervous, which makes perfect sense.

They have completed bookwork and practiced diving skills in a pool, but this is different. They may live far inland. This may be their first time in the ocean, let alone stepping off the back-end of a boat to get there.

One of my sneaky instructor tricks to calm new divers is to get them to focus on the amazing little things to see on the reef.

When finning along about 25 feet below the surface with a new diver, I like to slowly approach a large brain coral.

Next, I take hold of the new diver’s hand and bring it close to the colorful looking organism that resembles a tiny Christmas tree. When the diver’s hand gets a few inches away the tiny Christmas tree quickly withdraws into its hiding place in the coral.

At this point the startled diver snaps back his or her hand and I hear a happy laugh from the diver’s regulator.

Now we are in business and the new diver calmly enjoys the remainder of the dive.

As we depart, the worm very slowly re-emerges about a minute later, testing the water to make sure those strange bubble blowing monsters have left before fully extending its plumes

Christmas tree worms come in a variety of red, orange, blue, green, white and other bright colors. They are some of the most widely recognized polycheates, or marine burrowing and segmented worms.

The worms are about 5 inches long, with the Christmas tree part about 1.5 inches in length.

Each worm has two brightly colored crowns, specialized mouth appendages, which protrude from its tube-like body. The crowns are composed of hair-like appendages radiating from the worm’s central spine.

The rest of its body stays safely inside a calcium carbonate tube anchored in burrows bored into living coral. When sensing movement it retracts its crowns and tightly shuts off the tube.

The worms have a complete digestive system, and well-developed circulatory and nervous systems. Because they do not move outside their tube, the worms do not have any specialized appendages for movement or swimming.

The crowns are used for respiration and to catch food, which typically consists of microscopic plants, or phytoplankton, floating in the water. Christmas tree worms eat using a technique called filter feeding. They use their brightly colored crowns to filter microorganisms from the water.

Food is passed down from the crown by small hair-like projections and is deposited into a digestive tract. Large particles are discarded, and smaller grains of sand are stored for tube building.

Christmas tree worms live in corals that are between 10-100 feet deep. They range from South Florida, the Bahamas, the West Indies and the Caribbean.

They reproduce through open water spawning, when the males and females release sperm or eggs into the water. After being fertilized the eggs develop into larvae that settle on and then burrow into coral to create a tube that becomes the worm’s home.

It is estimated that Christmas tree worms live for up to 40 years.

Predators of Christmas tree worms include sea urchins, parrot fish, lobsters and stingrays.

Most new divers visiting the Keys hope to see large marine life like nurse sharks, rays, moray eels and grouper. These sighting make great stories when back home.

Many underwater photographers, however, eventually become interested in small subjects, like Christmas tree worms, that often are missed by new divers.

Even if you aren’t an underwater photographer that takes macro-photography, close-up photography of very small subjects, try swimming slower and looking for the interesting tiny creatures that inhabit the waters near the Florida Keys. You will be surprised by all you have been missing.

Many serious aquarists purposely include Christmas tree worms in their aquarium.

Back on the dive boat our new, very relaxed diver asks” what was that pretty thing you put my hand near?” I say it was a Christmas tree worm. “Cool, I hope we see more stuff like that on the next dive.”

So, if you live in the Keys you may not have the opportunity to go out and chop down the family’s Christmas tree. But, if you dive you can see colorful tiny Christmas trees on many of the coral reef. And, the good part is that they are available all year – not just November and December at your favorite Christmas tree store.

For more on Christmas tree worms see: http://www.thenakedscientists.com/HTML/content/interviews/interview/1503/

Don Rhodes, in addition to a career in government affairs, has taught scuba for 30 years. He and his wife retired to Tavernier five years ago, where he works as an instructor for Conch Republic Divers. He can be reached at donrrhodes@gmail.com.

This story was originally published December 16, 2016 at 11:59 AM with the headline "O Christmas tree worm, we can see you underwater in the Keys."