Weekly Sea Discovery: Aggregate Green Anemone

These small greenish anemones with bright pink tips are an easy find in our local rocky intertidal, and can form large colonies. To survive in these turbid, shallow environments, aggregate green anemones stick to the substrate below them, enabling them to endure massive wave forces without being pulled away.

Being attached to the ground may not seem like the best adaptation for a marine creature, especially in the intertidal at low tide, when there is no water around them. Anemones have overcome the risk of drying out by retracting their tentacles (like the image below) as the tide recedes, storing water within them. Aggregate green anemones thrive in the intertidal and shallow subtidal because the constant movement of water brings their food to them.

Aggregate green anemone at low tide. Photo: Sharon Mollerus
How exactly do anemones eat?
An aggregate anemone in the shallows by St. John Point.

Anemones feed by using their tentacles to pull organisms like fish and crustaceans into their mouth.  They’re able to grab hold and paralyze prey that moves by using tiny harpoon-like stinging cells along their tentacles, called nematocysts. This phenomenon is what is happening when their tentacles stick to our fingers, but our skin is so thick, and the level of toxin so low, it doesn’t harm us. These anemones are picky eaters and can use their tentacles to taste their environment, they will activate their nematocysts when they sense prey, and hide if it is a predator. You may wonder what kind of creature would want to eat an anemone, risking a dangerous sting! Other intertidal organisms like sea stars, nudibranchs and crabs are their common predators.

Crowded aggregate green anemones. Photo: Eva Funderburgh

These sessile creatures may not look like much at a glance, but often these colonies can be in a battle with each other when competing for space. The aggregate sea anemone has specialized tentacles for these battles, that sting opposing anemones to ward off attack, or to conquer new territory. Check out this video to see an example of these anemones at war over space in a tidepool.


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