SERIES: Invertebrate of the Week

Invertebrate of the Week #6 – Giant Green Sea Anemone (Anthopleura xanthogrammica)

If you’re a young seabird, this week’s invertebrate is an absolute nightmare.

A recent article in Marine Ornithology demonstrated that these flashy tide-pool denizens are capable of consuming young avian prey that happens to get too close. On at least two occasions, researchers discovered the bodies of seabird chicks in the grip of these large anemones.

In one instance, a very young cormorant chick fell from its nest and became trapped head-first in the clutches of an Anthopleura xanthogrammica in a tide pool below. A similar observation was made several years earlier in which a nestling gull hybrid was completely engulfed by a giant anemone, leaving only the bird’s feet exposed.

Dorsal (A) and ventral (B) views of a Giant Green Anemone consuming a cormorant chick in a tide pool in Cannon Beach, Oregon, on 24 July 2013. Underwater photographs by Lisa Bullis Habecker. Source: Marine Ornithology 42: 1–2 (2014)
Dorsal (A) and ventral (B) views of a Giant Green Anemone consuming a cormorant chick in a tide pool in Cannon Beach, Oregon, on 24 July 2013. Underwater photographs by Lisa Bullis Habecker. Source: Marine Ornithology 42: 1–2 (2014)
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Giant green anems at Hazard Reef.jpg
Anemones at Hazard Reef by Peter D. Tillman CC BY 3.0, Link

A Large and Conspicuous Anemone

At a maximum column size of 30 cm high x 17 cm wide with a crown reaching a diameter between 25cm and 30 cm,  A. xanthogrammic is a mammoth when compared to most other temperate anemones.

They are typically found in small groups in the intertidal and subtidal zones and are able to survive at depths as great a 15m as long as they remain within their estimated optimum temperature range of 15-22.2° C.

Anthopleura xanthogrammica. Source: http://goo.gl/U8mdXR
Anthopleura xanthogrammica. Source: http://goo.gl/U8mdXR

While young seabirds are obviously on the menu, these anemones seem to subsist mainly on a diet of mussels, crabs, sea urchins, and small fish which they capture with the help of their cnidocytes (stinging cells which are present in all Cnidarians) arranged along each tentacle.

When exposed to adequate levels of sunlight, A. xanthogrammic will also get some of its nutritional intake from the activity of endosymbiotic zoochorellae (green algae) or zooxanthellae which live within the tissues around the gut. While these endosymbionts may partly contribute to A. xanthogrammic’s characteristic green ensemble, much of the color comes from its own pigments.

Giant green anemone (Anthopleura xanthogrammica), Fitzgerald Marine Reserve, San Mateo County, CA. Source: http://goo.gl/8OLTA6
Giant green anemone (Anthopleura xanthogrammica), Fitzgerald Marine Reserve, San Mateo County, CA. Source: http://goo.gl/8OLTA6
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A. xanthogrammic is a long-lived anemone with at least one recorded instance of a captive specimen surviving for 80 years! Of course, life can still be cut short. A. xanthogrammic still has its predators to worry about and its greatest threats include the seastar Dermasterias imbricata (Leather Star) and the snail Opalia borealis (Boreal Wentletrap), among others.

Further Reading

2 comments

  1. That’s amazing! Have you come across any information on how this anemone catches e.g. mussels, and how it deals with their hard shells?

    1. Hi! It’s my understanding that the anemone feeds on mussels that have detached from the mussel bed and fallen within reach. As far as how it deals with the shell, I don’t know for sure but it is likely that the detached mussels are weakened, dead, or otherwise damaged at the time they are captured. This would allow the anemone some means of opening or penetrating the shell and accessing the mussels interior. If the mussel is alive and intact, it would be very difficult for the anemone to make much progress and it might just give up. For instance, a study on anemone diet published in the Marine Ecology Progress Series, demonstrated that the anemone Actinia equina would often ingest intact live mussels only to egest (i.e. vomit) the mussel unharmed after a period of about 1-2 hours if it couldn’t get into the shell.

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