Aggregating Anemone (Anthopleura elegantissima)

Description: The aggregating anemone is a common smaller species of anemone found in tide pools (up to 9 cm across). They typically live in huge colonies with other aggregating anemone. This kind of anemone is recognizable by its pale green or olive color with pink tips on the tentacles surrounding its mouth.

Habitat: These creatures are found living on the rocks in tide pools and sometimes they are found partially covered by sand or other kinds of sediment. They range from Alaska to Baja California, Mexico.

Diet: They’ll eat almost anything that passes by, including mollusks (like mussels that fall on them), barnacle molts, and small fishes. To catch prey, they use the stinging cells in their tentacles to paralyze their target and then pull the food into their mouth. 

Reproduction: There are two options for reproduction in aggregating anemones, sexual or asexual. Sexual reproduction is via broadcast spawning - releasing gametes into the water for external fertilization. Asexual reproduction is via asexual division (a.k.a. binary fission) - stretching their body out and splitting themselves in half, creating genetically identical clones.

Tide Pool Tidbits:

• Aggregating anemones reproduce by cloning themselves: individual anemones will split in half to create a new clone. This is how aggregating anemones got their name, since their huge colonies are formed from this process of splitting and cloning. Sometimes you can see an anemone in the middle of splitting itself; an anemone mid-split simply looks like one that’s gotten very stretched out in one direction!

• Since space is such a valuable resource for these cloning creatures, aggregating anemones are incredibly territorial. They have a ring of white knob-shaped specialized tentacles around their base called acrorhagi that are used specifically for stinging aggregating anemone from other colonies that come too close. If you’re at the tide pools, look for these real-life clone wars on the rocks! You’ll see colonies with a distinct line of empty space dividing them, because any anemone that crosses that line will be stung. 

• The green coloring of these anemone comes from symbiotic zooxanthellae (dinoflagellates) and zoochlorellae (algae) that live in the tissues of the anemone. Sometimes there will be aggregating anemones at tide pools that are a more white color with pink tips rather than green with pink tips; this is because those anemones live in low-light conditions and have lost their symbiotic algae.

Reference: Monterey Bay Aquarium