Aggregating anemone

Natural history

The anemone is a voracious feeder that eats almost anything that passes by, such as falling mussels, barnacle molts and small fishes. Stinging cells (nematocysts) on its tentacles paralyze prey. The aggregating anemone can even ingest small crabs and spew out the shells.

Aggregating anemones can reproduce by spawning or asexual division (also known as binary fission). Asexual division often occurs in the fall and winter seasons, followed by spawning in the spring and summer seasons. Asexual division creates colonies of genetically identical anemones.

Conservation

Because the aggregating anemone can rapidly clone itself, it’s abundant on rocky shores. Oil spills or oil that washes to the ocean from storm drains, however, can destroy anemone habitats—and it can take two years or more for habitats to recover from such catastrophes.

If you go tidepooling, be careful not to walk on or disturb anemones and other tidepool creatures.

Cool facts

• Aggregating anemones have knob-like swellings, called acrorhagi, just underneath their tentacular collar. The acrorhagi are packed with large stinging cells called nematocysts. If under duress, the nematocysts can be activated.
• When one genetically identical colony encounters another, they can battle over territory. The anemones that border a colony are expected to protect the colony. These anemones are typically smaller, often unable to reproduce and have larger acrorhagi. During a battle they can make contact and sting one another; their injured tissues will eventually die and slough off. In the end, the colonies will draw away from each other, leaving a neutral zone between them.
• An anemone exposed to air retracts its tentacles and shrinks in size. Sticky bumps on its body collect sand and bits of shells, which provides camouflage and prevent the anemone from drying out. Remember to watch your step when tidepooling—more than one tired tidepooler has sat down on a rock for a short rest, only to discover she's sitting on a wet and squishy anemone!
• An aggregating anemone lives on rocks in tide pools and crevices, either alone or in dense masses. Each mass is a group of clones that are genetically identical and of the same sex. To clone itself, an anemone splits in half—literally tearing itself apart (asexual reproduction). Asexual reproduction spreads new animals rapidly over rocks. An aggregating anemone also reproduces sexually by broadcasting eggs and sperm. Sexual reproduction results in new combinations of genes, and larvae that establish new colonies in other locations.