Crimson anemones.

Mouth of a crimson anemone.

By Doug Pemberton

Over 1000 species of anemones are distributed throughout the world's oceans and all the habitats encompassed within them. They have adapted to the severe conditions of the intertidal area, the abyssal depths and everywhere in between. And divers in Canada are fortunate to have more species of anemones along our three coasts than anywhere else in the world.

Anemones belong to the Anthozoans, a distinguished group of animals that includes the anemone's most famous cousin, the coral polyp, which is responsible for some of the greatest architectural feats in nature. Anemones range in size from a few millimeters to well over a meter and few colours are missing from the anemone's pallette. Some advertise their presence with long flowing tentacles and bright colours while other species shy away from the spotlight and live buried in the sand, making rare and only necessary appearances.

Anemones all have a central stalk crowned by an array of tentacles that can number in the dozens or hundreds. The tentacles can be short and stubby or trail over a foot in length. The stalk can be as skinny as a pencil, or several feet across as in the case of the tropical carpet anemone. Most anemones attach themselves to something solid so as not to get carried off by currents or wave action. The tough but pliable basal disc at the bottom of the stalk conforms to irregular surfaces such as rocks, pilings and anchor lines, and acts like a muscular suction cup. A few anemones though, such as the tube-dwelling anemone, prefer to live in soft, muddy or sandy bottoms where suction would be of little use. Instead of a basal disc these anemones are anchored by a muscular, water-filled bulb that may be buried up to two feet below the substrate. Pumping water into the bulb and thereby increasing its size, makes it difficult to be pulled from the bottom.

The anemones' beauty contrasts their formidable defensive and food gathering abilities. Their stalk and tentacles are bristling with an arsenal of stinging cells, or nematocysts. The double walled microscopic stinging cells contain a hollow thread with a minute, harpoon-like barb at the end. When the cell is stimulated either physically or chemically, it explodes and fires the barb and attached thread with incredible force into the potential predator or prey and simultaneously injects a potent poison. An individual cell's effect would not be cause for worry but usually hundreds or thousands are activated at once, which can paralyze prey or deter most predators. Anyone who has touched the tentacles of an anemone with bare or gloved hands might say that it feels 'sticky'. That stickiness is caused by a few thousand stinging cells being fired into your skin. Due to the toughness of the skin on our hands, the effect is minimal but if we were to expose more sensitive areas of our bodies such as the inside of the wrist or tongue (Don't try this at home!), the effect might be far more bothersome.

After being immobilized, the prey which may include shrimp, crabs, jellyfish or small fish is manoeuvred by tentacles toward the mouth where it is consumed whole. Any indigestible material or waste will be excreted through the mouth as well.

Even with its formidable arsenal of nematocysts, anemones are a favoured prey for other animals. Many nudibranchs feed on anemones and are not only immune to the anemone's defenses, but have the ability to absorb undetonated packets of stinging cells which are then used for the nudibranch's own defense. Sea stars and some fish are also regular predators.

Most species of anemones are capable of small and slow movements by creeping along on their basal discs but there is at least one exception. When the swimming anemone, Stomphia coccinea, is put in contact with one of its predators such as the leather star, it will quickly detach itself and swim through the water with an undulating motion or somersault across the bottom to get out of harm's way.

But one of the most interesting forms of reproduction borders on parental responsibility and belongs to the little, brooding anemone, Epiactis prolifera. The brooding anemone is a colonial hermaphrodite that fertilizes and incubates its eggs internally. The embryos develop into planula larva and make their way out of the adults' mouth and then embed themselves in grooves along the adult's stalk. Here they stay and grow until they are big enough to crawl away and fend for themselves.

Anemones are a common sight on any dive anywhere, but their presence, like that of any other marine animal, is also a rare treat, an opportunity for a glimpse into the fascinating world of the life around us.