Amazing Sea Anemones
Sea Anemones are beautiful creatures, whose delicate tentacles in shades of green, pink, red, orange or white resemble strange underwater flowers. Though they appear innocently flower-like, these beauties are predatory and carnivorous, and consume small fishes, crustaceans, and other prey. Touch the tentacles of the sea anemone, and you will feel the sticky grip that grabs and paralyzes unwary prey. Fortunately, humans aren’t usually affected by the toxic sting of the tentacles, so tentacle touching is a fairly safe game.
Sea Anemones are classified as Cnidaria, a group that also includes, corals, sea pens, hydroids, jellyfish and others. Anemones, and other cnidarians, have an oral disc ringed with tentacles. At the center of the disc is an opening, which is the anemone’s mouth. Material that can’t be digested is discarded through this same opening. The anemone has only one opening to its digestive tract, which functions both as mouth and anus.
The tentacles are covered with millions of cells called cnidocytes, each of which has a miniature harpoon-like structure. When the tentacles come into contact with prey, the cnidocytes go into action, firing the mini harpoons, often toxic, that disable the prey so that the anemone can sweep it into its mouth, where it is consumed whole.
A column-like body supports the tentacle-ringed oral disc. At the base of this columnar body is a foot, which is attached firmly to a rock or other surface. Anemones can move slowly, inching the foot forward, and move only if there is more prey available elsewhere.
Anemones are easy to find on the beach, though some of the exotically beautiful species are more often encountered subtidally (time to take up diving!). One of the most common anemones is the aggregate, or pink-tipped anemone (Anthopleura elegantissima). Like most anemones, when exposed to air the aggregate anemone withdraws its pretty pink/purple tentacles, and becomes a blob of green with a depression in the center, like a little donut. Shards of shell, and bits of gravel adhere its surface, which camouflage these little anemones very well. Scientists believe that this camouflage helps the anemone reflect sunlight and retain moisture when exposed at low tides.
Aggregate anemones crowd together in colonies that may cover large expanses of rock and beach. Interestingly, these colonies are made up of clones, and are the result of one anemone that has divided repeatedly.
On the west coast of Vancouver Island, the giant surf anemone (Anthopleura xanthogrammica) is most impressive. A large anemone that can measure 25-30 cm wide, the green surf anemone lives along surf swept surge channels, and rocky tide pools near the open coast. The colour of this anemone, described by Eugene Kozloff as “a beautiful, muted emerald green” is the result of microscopic green algae that have taken up residence in the translucent flesh of the anemone. This provides the algae a safe place to reside, and the algae is thought to be of some nutritional value to the anemone. This relationship is of mutual benefit.
By peering down the pilings of a wharf, one may spot the beautiful plumose anemone (Metridium senile). The column of this anemone is very long, and it is crowned with feathery tentacles that may be pure white or orange. It feeds on small organisms rather than larger prey. Plumose anemones can “clone” by splitting vertically in two. Like many anemones, they also reproduce sexually. Egg and sperm are released directly into the sea from the anemone’s mouth. The fertilized eggs develop into free-swimming larvae, which eventually settle and metamorphose into small anemones.
The brooding anemone (Epiactis prolifera) has a more unusual reproductive strategy. Fertilization happens within the body of the anemone, after which the larvae become mobile and escape through the mouth. They then slide down the column of the parent and attach to its base. When they reach a certain size, these young anemones leave the parent. The brooding anemone, a small anemone, may be green, red or brown and has a striped oral disc and column. It favours quiet bays, and may be found attached to blades of eelgrass.
Sea anemones thrive along the Pacific Northwest, and are found in many different marine habitats. They vary greatly in size and colour, and have several means of reproduction, depending on the species. Despite their carnivorous nature, anemones dazzle us with their beauty. They are the ocean’s flowers.
Leave a Reply