Aggregating Anemones (Anthopleura elegantissima) are the most common and most abundant sea anemones on the southern Oregon coast. Though an Aggregating Anemone can be found alone, most often they will be in large colonies covering rocks in the high tide zone (first exposed when the tide recedes). They live on the protected sides of rocks, sheltered from the pounding surf.
At a low tide, when they are above the water line, Aggregating Anemones look like small gelatinous blobs and are often overlooked because they blend into their surroundings so well (see photo below). Sand, gravel and bits of shell adhere to the "sticky" cells on their columns, enhancing their camouflage as well as acting as a sunblock to keep them from dessicating (drying out).
If you unconsciously walk on a mass of aggregating anemones, water will squirt out, and some people mistake them for "sea squirts". The anemones retain water in their body cavities to keep from drying out during a low tide, and when you step on them and water is expelled from their bodies, you are threatening their very existence!
Though sea anemones look like the most sessile (stationery) of all animals, they are able to move about on their "pedal disks"- the foot or base of the anemone - to escape encroaching sand or predators or invaders.
- The photo below is a small group of Aggregating Anemones under water and open.
Aggregating Anemones can grow to 4" in diameter, live up to 50 years, and reproduce by dividing in half (cloning). Each colony is composed of identical cloned Aggreating Anemones. If a second colony of different cloned anemones encroaches across the one-inch "no-man's land" between the two colonies, "fighting" anemones located on the perimeter will aggressively sting the intruders with special stinging cells. Sometimes they actually kill another Aggregating Anemone, but more often than not, the loser will just roll away. There has been documented underwater footage taken of aggressive battles between two colonies of Aggregating Agemones during high tides (when the anemones are submerged).
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