Cerianthid Tube Anemones - Flowers of the Deep

by B. N. Sullivan

When most people think of scuba diving in tropical waters, they think of coral reefs. Granted, coral reefs are lush, often colorful habitats. They're a feast for the eyes, and home to a huge diversity of creatures. We love our coral reef dives, but we like to point out to people that coral reefs are not the whole show.

Awhile back I wrote a few posts about muck diving, i.e., the practice of rummaging around in the sand and rubble in places that may look less than pretty to the casual observer, but which turn out to be home to an incredible assortment of tiny creatures that can't be found elsewhere. Most avid macro photographers engage in muck diving regularly.

Most muck diving is done in locations where the water is relatively shallow, but we also do a deep water variant of muck diving. The ideal locations, we have found, are sandy areas or mud flats located near the base of reefs at depths between 100 and 150 feet (30 to 45 meters). Whole communities of creatures live in these areas -- creatures never seen around the reefs themselves.

One creature we look for when muck diving in deep water is the Cerianthid tube anemone. These creatures are related to corals and 'regular' anemones, but they usually are much smaller -- only a few inches in diameter at most. They look like beautiful flowers, and their delicate beauty is all the more striking because they are found in environments that are rather stark.

Cerianthid tube anemones differ from 'regular' anemones in a number of ways. For one thing, they live inside tubes (hence the name 'tube anemone'). Cerianthids build the rubbery tubes they live in with their own mucus secretions. Most of the tube is buried, and most of the animal stays inside that tube all the time.

A crown of tentacles protrudes from the tube to feed. The tentacles, which are armed with stinging nematocysts, are arranged in two sets. The outer set of tentacles are longer. The inner set of tentacles are much shorter, and often are a different color or shade. I think it's this arrangement that makes the Cerianthids look like flowers. The outer tentacles are like flower petals, while the short inner tentacles resemble the center of a flower.

The outer tentacles are the food grabbers. Tidbits of food -- plankton, for example -- are snagged by the longer, outer tentacles, and then transferred to the shorter, inner tentacles, which then move the food along to the mouth in the center of the array. One thing we find fascinating about Cerianthids is that they can (and do) move each long tentacle independently and purposefully. We have watched them snag a tidbit on one outer tentacle, then bend that tentacle in toward the center and deposit the catch onto the shorter tentacles. We've never seen a regular reef anemone that is able to do this.

Cerianthids come in assorted, mostly pale, colors, but one variety that we have here in Hawaii is a dark maroon color. In fact, because it lives in deep water where most of the color spectrum of natural light is filtered out, when we first came upon this variety, it looked black. You can't tell what its true color is until you illuminate it with artificial light from a flashlight or camera strobe.

Cerianthids can be difficult to photograph for several reasons. First of all, since they live in deeper water, well offshore, it's almost impossible to get to the area where they live, find them (they're small!), set up the shot and photograph them adequately within the time limits for a 'no decompression' dive. Thus, in order to have enough time to do all that needs to be done to photograph Cerianthids, a planned decompression dive usually is necessary, with all of the advance preparations that requires.

Another reason Cerianthids are difficult to photograph is that the creatures are, well, touchy! They do not like to be disturbed. If you happen to touch their tentacles -- zip! -- they retract into their tubes. In fact you don't even have to actually touch them to elicit that response. A bit of turbulence in their immediate area will do the trick, so you have to be sneaky in your approach. Many Cerianthids react to light, as well -- especially the big blast of light emitted by a camera strobe. So, often you get only one or two shots of a Cerianthid before it retracts, pulling its pretty flower-like crown inside the tube. Once that happens, you might as well leave. It won't re-emerge very quickly.

Of course, you can always take a photo of the tube!