Hansville, WA – When walking the beaches of the intertidal zone, I often feel like I’m stepping on someone… or someones. The intertidal zone consists of worlds within worlds and if I avoid one, I invariably step on another. There are some creatures who make it especially difficult because they tend to grow in colonies. One such species is the Aggregating Anemone.

These fascinating colonial anemones cover the ocean floor with texture and color as they filter the water for tasty morsels with their waving tentacles. However, if the tide is out or there is imminent danger, anemones will fold in on themselves and in so doing, protect delicate internal tissues from predators as well as the potentially damaging exposure to sun, wind and beach walkers like me. Sand and other beach debris cling to their sticky exteriors, adding even more protection as well as camouflage.

Aggregating Anemone with elegant pink tipped tentacles.

One characteristic that makes the Aggregating Anemones’ close and cozy lifestyle so interesting is how they build and protect their colonies.  Each colony is comprised of many genetically identical clones originating from one individual.  As they grow, they actually divide in half and split off, becoming two from one. This “budding” transformation happens relatively quickly over the course of a day or two. During the summer breeding season, they also reproduce sexually by releasing eggs and sperm into the water. The resulting free-swimming larvae eventually attach themselves to the substrate, essentially giving up their ability to move around.

IMG_4098The colony expands and thrives until they encounter another colony which has simultaneously been growing ever closer. Aggregating anemones can sense genetic differences when they encounter members of neighboring colony and will respond by using the stinging cells (nematocysts) in their “fighting” tentacles to establish a territorial boundary, usually a one to two inch no man’s land between the densely packed groups.

Life is rough in the intertidal zone and some species stick it out together. When you track wonder, take time to watch your step as you survey worlds within worlds underfoot.

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Where and When – Aggregating Anemones often form colonies, but can also live as a solitary animal. They are very common on our beaches and can be found not only in the nooks and crannies of tide pools, but also on sand and carpeting the surface of rocks. It is fun to examine the closed anemones during low tide, but it is stunning to watch these amazing animals open up again as the salty fingers of the tide creep back in.

If you are able to see them underwater, look for their trademark pink tipped tentacles. (Moon Glow Anemones look very similar, but have white bands on their tentacles) It is safe to gently touch anemones on the tentacles and outer column, but avoid touching the center disc where vital structures can be easily damaged.IMG_3792

Study individuals to see if you can identify those in the active process of budding or cloning. The animal will look more oblong and stretched in the center.  If you are spending a lot of time at the beach, come back later to see the progression.

Wonder Triggers for Young Trackers

  • Can you find an closed anemone on the beach? What do they look like? Do they remind you of anything you have seen before or some kind of land plant or animal?
  • Rinse you hands in ocean water. Never use soap or hand sanitizer before touching sea creatures. Gently touch the outside edges and tentacles with one finger. What do they feel like?  Can you feel the tentacles sticking to your finger? That sticky feeling is actually the little harpoons shooting out from the animal to catch its food or protect itself.
  • Anemones are primarily carnivores.  Do you know what that means? What kinds of animals do you think the anemone can catch to eat? (small marine fish, crabs, snails, etc. and sometimes plankton and algae)
  • Do you think there are marine creatures who would eat anemones? (sea slugs such as nudibranchs, snails, crabs, sea stars, some fish)
  • Are all aggregating anemones the same color? What do you think gives them different coloring? (the green coloring is caused by algae actually living inside the anemone)
  • How many different surfaces can you find where aggregating anemones are growing?

References and Resources

B. Cardone. California Diving

Monterey Aquarium – Aggregating Anemone

Toronto Zoo

 Thoughtco.com – Cnidarians

Slater Museum of Natural History

iNaturalist – Aggregating Sea Anemone

Science Daily – Anemone Armies Battle to a Standoff

Images – SPegany ©2018

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