Aggregating Anemone
Anthopleura elegantissima

Physical Description

A tube-shaped body crowned with tentacles, attached permanently to a hard surface.
Have a green body with white tentacles that are pink-tipped.
Tube about 2.5 inches in diameter, tentacles about 3.5 inches in diameter.
When exposed to air, the anemone will close up completely and cover itself with broken shells and sand, which provides camouflage and prevents it from drying out.

Range

Habitat

Reproduction

They can reproduce by broadcast spawning eggs and sperm into the water.
They can also reproduce by binary fission, where they create whole colonies of genetically identical anemones all of the same sex.
Binary fission often occurs in the fall and winter.
Spawning often occurs in the spring and summer.
Binary fission rapidly spreads colonies across rocks; sexual reproduction adds genetic diversity and allows larvae to colonize new areas.

Diet

They eat plankton like copepods, isopods, amphipods.
They eat falling mussels, acorn barnacles, small crabs, chitons, and small fishes.

Predators

Nudibranchs (that disable the stinging nematocyst cells of the anemone tentacles).
Leather stars, wentletrap snails, sea stars, and fishes.

Interesting Facts

A microalgae (zoochlorellae) and a dinoflagellate (zooxanthellae) live inside the anemone’s tissues and photosynthesize, or use the energy of the sun, to provide food and energy for the anemone. In turn, the anemone gives them shelter. The anemone also bends towards the sun to give them optimal sunlight.
Their tentacles have stinging cells called nematocysts that paralyze their prey and defend them from predators.
When one group of genetically identical clones encounters another, they will battle for territory by stinging each other. In the end, they often leave a large neutral zone between colonies.

Sources: Monterey Bay Aquarium; University of Puget Sound; California Diving News; Walla Walla University; Californiatidepools.com

Photo: Mark Royer