Foods eaten
  The following accounts are arranged by genera.
 

Sea anemones are mostly carnivorous, and their feeding methods and digestive abilities are adapted for intake and processing of live prey. Food is captured in 3 different ways: 1) filter feeding, where small organic particles, both live and dead, are removed from the seawater passing over the outspread tentacles, 2) raptorial capture, where zooplankters and motile benthic prey are caught by the tentacles, and 3) passive capture, where sessile prey are dislodged by foraging predators or wave action and carried onto the tentacles.  Any plant matter ingested occurs by this means. 

Examples of each type of capture mode are given below for various genera.

Vegans?  Although it is not unusual to see seaweeds being
“eaten” by sea anemones, it is unlikely that the plants are
actually being digested. It may be, however, that the
anemones are removing epizoitic growths before discarding
the plant bits. Urticina crassicornis with Laminaria or
Pterygophora
( Left) and Egregia ( Right) bits 0.5X

photograh of a sea anemone Urticina crassicornis eating a piece of kelp photograh of a sea anemone Urticina crassicornis eating a piece of kelp
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Metridium spp.

 

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Research study 1

 
Plumose anemones Metridium senile feed on small organic particles (including small zooplankters) that they strain from the water on their finely structured tentacles.  The upper part of the body column of Metridium is quite flexible, allowing the anemone to bend in strong currents, with the tentacles splayed-out like an inside-out umbrella.  This reduces drag forces, yet still allows the anemone to feed.  Koehl 1977 J Exp Biol 69: 87. photograph of a large aggregation of sea anemones Metridium senile
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Research study 2
 

A comparison of feeding energetics in 3 anemone species Metridium farcimen, Anthopleura elegantissima, and A. xanthogrammica collected from various locations in Washington state shows that number of prey captured is closely related to the total surface area represented by the oral disc and tentacles.  Since a large M. farcimen can have over 10,000 tentacles versus 100-200 for a large-sized A. elegantissima or A. xanthogrammica, then the potential exists for capture of many more food items by Metridium.  In areas where they are sympatric, the 3 species inhabit different levels on the shore, thus minimising the potential for food competition. In general, prey items for the 3 species differ in type and by 1-2 orders of magnitude in size, thus further reducing the potential for food competition between them. Note from the graph that the food particles eaten by Metridium are much smaller in size than in the other 2 species, probably owing to the comparatively small size of the tentacles. drawing showing shore zonation of 3 species of west-coast sea anemonesSebens 1981 Biol Bull 161: 152.

NOTE the author cites the species name as senile, but its large size and subtidal position suggests that it is likely farcimen

graph showing sizes of prey eaten by 3 species of west-coast sea anemones

A. elegantissima lives highest on the shore, A. xanthogrammica inhabits tidepools and surge channels and generally lives somewhat lower on the shore, and M. farcimen is subtidal. The author provides this drawing to show relative size differences in the 3 species
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Research study 3
 

Tabulation of prey items consumed by Metridium farcimen in Harper, Washington shows that over 80% are invertebrate larvae, mostly barnacle cyprids. Data from Sebens 1981 Biol Bull 161: 152.

NOTE  a total of 538 prey items in the guts of 107 individual anemones

table of prey items consumed by the sea anemone Metridium farcimen
  Anthopleura spp.
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Research study 1
 

Aggregating anemones Anthopleura elegantissima feed by capturing planktonic prey from the water column and by having benthic prey blunder into their tentacles. At least 30 species of small planktonic and benthic invertebrates are eaten. Most abundant of these are small mussels, acorn barnacles, small motile crustaceans (crabs, isopods, and copepods), littorine snails, and chitons, and these make up about 60% of the diet. Some plant material is also ingested, but is likely not be digested.  Sebens 1981 Biol Bull 161: 152.

NOTE  the data represent 113 prey items in the guts of 112 anemones in Tatoosh Island, Washington

photograph of a tight cluster of aggregating sea anemones Anthopleura elegantissima

 

 

 

The close-packed nature of clonal Anthopleura elegantissima
leads to more effective prey capture, including (possibly) a
mussel Mytilus sp. being eaten by the individual at upper Left

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Research study 2
 

photograph of 2 sea anemones Anthopleura xanthogrammica eating mussels and a piece of seaweed, respectivelyGreat green sea anemones Anthopleura xanthogrammica live in tidepools and in surge channels below mussel beds where they feed on mussels dislodged by waves and by depredations of sea stars.  In the Tatoosh Island area of Washington most dislodged prey are sea mussels Mytilus californianus and these, along with acorn barnacles and their moults, comprise over 90% of the food items eaten.  Sebens 1981 Biol Bull 161: 15.

NOTE  the data represent 177 prey items in the guts of 481 anemones in Tatoosh Island, Washington



Anthopleura xanthogrammica eating small sea mussels Mytilus sp. (Left)
and a piece of brown seaweed Colpomenia sp. (Right)

  Other examples of unusual and/or adventitious feeding by sea anemones Anthopleura spp.:
 
photograph of a sea anemone Anthopleura xanthogrammica eating a piece of dead octopus
Anthopleura xanthogrammica eating a piece of dead octopus Enteroctopus dofleini
photograph of sea anemone Anthopleura elegantissima eating a moult of shore crab Hemigrapsus nudus courtesy Rebecca Kordas, Biodiversity Research Centre, UBC
Anthopleura elegantissima "consuming" a shore crab Hemigrapus nudus. The prey is actually a cast-off moult, as shown by empty eyestalks and antennules
Photograph of anemone and crab courtesy Rebecca Kordas, Biodiversity Research Centre, UBC, Vancouver
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  Urticina & Cribrinopsis
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Research study 1
 

Analyses of gastrovascular cavity contents of Urticina piscivora in San Juan Islands and Tatoosh Island, Washington indicate evidence of fishes, crustaceans (decapods, amphipods, cumaceans, and barnacles), molluscs (snails), sponges, hydroids, and insects (10 individual anemones examined).  Urticina lofotensis from the same areas show evidence of crustaceans, asteroids, and fish eggs in their diet.  Tests in Friday Harbor Laboratories of the ability of several species of sea anemones (U. piscivora, U. lofotensis, U. coriacea, and U. crassicornis) to catch and eat different species of fishes (up to 15cm in length), show that only U. piscivora is capable of doing this.  Sebens & Laakso 1977 The Wasmann J Biol 35: 152.

 

Upper photo: Cribrinopsis fernaldi egesting the
remains of what appears to be a worm

Lower photos:
Urticina coriacea (Left),
and Urticina piscivora (Right)


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Research study 2
  photograph of sea anemone eating a fish courtesy Roland Anderson, Leo J. Shaw, and Seattle AquariumThe fish-eating Urticina piscivora may possess extra-potent nematocysts that enables its unique feeding habit. Photograph courtesy Roland Anderson, Leo J. Shaw, and the Seattle Aquarium.
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