Christmas tree worms (Spirobranchus sp.) are aptly named for the whorled structures they extend into the water for feeding and respiration. These worms are members of the family Serpulidae, and are characterized as being tube-building worms with a trap door that can close-off the tube when they withdraw inside. They secrete tubes made of calcium carbonate, or limestone. Marine organisms that build shells and tubes out of calcium carbonate will likely be severely impacted by the acidification of ocean water that is occurring as a result of increasing carbon dioxide in the atmosphere being absorbed by the ocean.
These beautiful worms are found in tropical waters throughout the world and are even found in some temperate waters, like those off the coast of southern California. The animal pictured here was seen on a dive on Rainbow Reef off the coast of Vanua Levu in the Republic of Fiji. The bright blue whorls are used for both feeding and respiration. These specialized mouth appendages are composed of feathery tentacles covered by hair-like cilia that sweep prey down the spiral and to the mouth. They feed by filtering plankton out of the passing water. Also used for respiration, the whorls are also often referred to as gills.
Commonly seen by divers, these worms are nonetheless a highlight of any dive. Their bright colors often stand in clear contrast with their surroundings, which are usually corals. The worms often bore holes into an existing coral head before secreting their tube. Encased in a limestone tube, and buried within a thick wall of coral provides an almost impenetrable defense.
I made today’s photo using my Canon EF100mm f/2.8 macro lens on my Canon 5D Mk. III camera in an Ikelite underwater housing. I illuminated the scene with two Ikelite DS-161 strobes in eTTL mode. The exposure was set to 1/60 sec. at f/11 and ISO 200.