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.
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.
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.
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.
- Ashley, Kevin. Anthopleura xanthogrammica – Animal Diversity Web
- Encyclopedia of Life. 2010. “Anthopleura xanthogrammica” – EOL.org.
- Giant Green Anemone Factsheet – Monterey Bay Aquarium
- Habecker, Bullis, et al. “GIANT GREEN ANEMONES CONSUME SEABIRD NESTLINGS ON THE OREGON COAST.” Marine Ornithology 42 (2014): 1-2. (PDF available here)
- Ricketts, E., J. Calvin, J. Hedgpeth, D. Phillips. 1992. Between Pacific Tides: Fifth Edition.
- White, B. 2004. Anthopleura xanthogrammica – Walla Walla University