Coral Reef Polychaetes

Coral reef polychaetes (as are all polychates) part of a larger groups of invertebrate animals popularly known as "worms". This somewhat informal term actually includes a vast assortment of animals that belong to many distantly related animal groups (phyla).

The polychaetes themselves are but a single class (Class Polychaeta) of only one such group (Phylum Annelida) which includes the segmented worms.

Coral reef polychaetes are among the most ubiquitous of all coral reef invertebrate animals. They may be found on reefs, as well as in seagrass meadows, mangrove forests, coral rubble, and sand plains.

Ecological Roles of Coral Reef Polychaetes

Polychaetes play a variety of roles in coral reef ecosystems. Many provide a primary food source for other animals, particularly certain fishes. Others erode recently dead coral and recycle mucus.

They vary widely in terms of feeding strategies, with some being subsurface deposit-feeders, carnivores, filter-feeders, surface deposit-feeders, or omnivores.

As a group, the polychates can be divided into two main types based upon their respective lifestyles; those that permanently attach to a particular place and remain there (sedentary or sessile forms), and those that move about freely (mobile or motile forms.

Sedentary Reef Polychates

Christmas tree worm. © Fotolia.com

Sedentary reef dwelling polychaetes generally build tubes within the substrate, and enlarge these homes as they grow. Some of these burrow into living coral colonies to form their homes.

The most familiar such polychaetes are the brightly colored feather dusters and Christmas tree worms that extend ornate feeding tentacles from concealed tubes within living coral colonies (see photo, left).

The tentacles, used to capture plankton, are quickly withdrawn if a diver or fish approaches too closely.

Motile Reef Polychates

In contrast, many of the mobile free-living polychaetes are voracious predators feeding upon a variety of other small invertebrate animals, sometimes including corals.

Bristle worm. © Fotolia.com

The notorious fire worms and bristle worms are (at least to coral reef scuba divers) among the best known examples of this group of polychaetes because they are quite painful to the touch.

The vast majority of motile coral reef polychaetes spend most of their life cycle as bottom dwellers, with most living in dead coral rubble or sand. However, some types undergo a dramatic shift in behavior as well as profound changes in physical characteristics when in the reproductive phase.

At this time, normally subsurface dwellers may develop swimming appendages and greatly enlarged eyes. On some unknown cue, they ascend in countless numbers up into the water column on a few consecutive nights to reproduce, some even reaching the sea surface.

Other Coral Reef Worms

In some regions of coral reef development, representatives of a few of the other major groups (Phyla) of worms such as the flatworms (Phylum Platyhelminthes) and ribbon worms (Phylum Nemertea) may also be common and readily observed by divers and snorkelers.

For more information on these groups readers are referred to more comprehensive guides to coral reef invertebrate animals.