These anemones have a greenish-white column with diameter that reaches up to 2.5 in. There are radiating lines on the oral disc. Their tentacles are greenish to pinkish in color with a tentacular crown up to 3.1 in across.
Habitat
Only on rocky substrates. Will form dense colonies in the mid-intertidal zone. Both in bays and on outer coasts.
Diet
Copepods, amphipods, and isopods. Also receives carbon from its photosynthetic symbionts.
Life History
Aggregating anemones are long-lived, surviving up to 80 years old. These anemones can reproduce by both sexual and asexual reproduction. Sexual reproduction occurs in the spring and summer and results in a genetically unique, planktonic larva. Once this individual settles to the seafloor, it can undergo asexual reproduction to create a colony of genetically identical anemones.
IUCN Status
Not Evaluated
Ecosystem & Cultural Importance
These anemones feed many other small creatures, including sea stars, gray sea slugs, and opalescent nudibranchs.
Zoochlorellae, a microalgae, and zooxanthellae, a dinoflagellate, live in the tissues of the aggregating anemone. These are photosynthetic organisms that provide the anemone with food in exchange for a home. The anemone will bend towards or away from the sunlight, depending on the needs of these symbionts.
When two different aggregating anemone colonies meet, they undergo a battle. Just below the tentacular collar of an aggregating anemone are non-feeding tentacles called acrorhagi that are packed with stinging cells. The anemones at the border of a colony are smaller, often unable to reproduce, but have larger acrorhagi because they are specialized for battling with rival aggregating anemones from non-clone colonies. The battle ends with a neutral zone between the 2 colonies. After a battle, injured tissues touched by acrorhagi die and eventually slough off.
Citations & Other Resources
Hiebert, T. C., B. A., Butler, A. L., Shanks. 2016.Oregon Estuarine Invertebrates: Rudys’ Illustrated Guide to Common Species, 3rd Edition. University of Oregon Libraries and Oregon Institute of Marine Biology.
Monterey Bay Aquarium website: https://www.montereybayaquarium.org/animals/animals-a-to-z/aggregating-anemone
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