Feeding behaviour

The topic of feeding behaviour is considered here, while that of FOODS EATEN is found in its own section

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Research study 1

On first glance, sea anemones seem to be fixed in place without an ability to move.  Indeed, early observers (mid-1800s) thought that individuals were permanently fixed to the substratum by a kind of proteinaceous glue. However good this glue is, it is readily breakable, because most or all species can move about.  In laboratory aquariums, anemones will crawl about quite actively, perhaps in search of areas with good current flow and available food.  Like all cnidarians, sea anemones have decentralised nervous systems in net-like form with no photograph of sea anemone Urticina piscivora in a water currentaggregations of nerves into control centres, such as ganglia or a brain.  The final “decision” as to where to reside may relate as much to the absence of irritating stimuli (such as wave swash or excessive light) as to the presence of positive stimuli (such as availability of prey). Batham & Pantin 1950 J Exp Biol 27: 377.


Fish-eating anemone Urticina piscivora in a stiff current.
Note the tight fit of the pedal disc to the rock 0.5X



schematic showing locomotory mechanism in a plumose anemone MetridiumNOTE an early account of locomotion in plumose anemones Metridium describes how contractile waves pass along the pedal-disc surface to produce single-“step” displacements (see schematic on Right). Waves may occur singly or in pairs. Wave frequency will depend on factors such as age, size, temperature, and so on, but in a large specimen (15-20cm basal diameter) a single wave may take 3min or so to pass across the pedal disc, moving the individual about 5-10mm. As a wave moves along, adhesion to the substratum is momentarily lost, then re-established after the wave passes. Adhesion is effected through mucus stickiness. Although one might assume that the pedal-disc contractile tissuess are ectodermal in origin, the author notes that they are actually endodermal. The contractile tissues are comprised of bands of intertwining radial, circular, and longitudinal fibres oriented at right angles to one another. The system functions hydrostatically, with contractions being opposed by fluid-filled spaces within the pedal disc. When an advancing wave reaches the column, the epidermis visibly bulges out from the pressure, then re-attaches to complete the “step”. If at this time the bulge is pricked with a pin, fluid is forcibly released and the bulge momentarily collapses. Movement appears to take place in any direction. An individual whose oral disc is experimentally removed from the column will continue to creep along, indicating that the neuromuscular mechanism necessary for the behaviour is still functional. Parker 1917 J Exp Zool 22 (1): 111.

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Research study 2

photograph of several plumose anemones Metridium seniledrawing showing several post-ingestive behaviours of a plumose anemone Metridium senileNot only do anemones crawl around their habitats, but they exhibit defined feeding and other behaviours.  This is seen in a laboratory study of Metridium senile collected in Devonshire, England.  For example, food ingestion involves expansion of the pharynx through contraction of radial contractile tissues in the complete mesenteries (note the expanded diameter of the individual featured in the drawings below Right). 30min after ingestion the anemone resumes its feeding posture, often with the column base partially constricted (see drawing). 6h after exposure to a food-extract stimulus, an anemone may sway around seemingly in search for the food.  An upwards peristaltic contraction of the column leads to egestion of food residues. Shrivelled, or fully contracted, individuals are often seen, although the stimulus that causes this is not well known (the authors note that exposure to sunlight sometimes causes this in M. senile). 

In the laboratory, contraction can happen in just a few moments.  Fully contracted individuals are commonly seen in the field and, to the eye, seem frozen in this state – perhaps for days, weeks, or even longer.  However, laboratory animals can re-inflate in about 2h, and sometimes this leads to an apparent over-expansion of the body. Batham & Pantin 1950 J Exp Biol 27: 377.

NOTE  these mesenteries extend from the outer body wall to the pharynx and have both longitudinal and radial contractile tissues

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Research study 2.1

Tentacles of the burrowing anemone Pachycerianthus fimbriatus are arrayed in 2 sets of concentric circles, one around the mouth (labial tentacles) and one around the disc periphery (marginal tentacles; see photograph). Observations at the University of Calgary and Biological Station, Nanaimo show that food particles (mostly small crustaceans) are caught by the marginal tentacles and transferred directly to the mouth without involvement of the labial tentacles. Inanimate particles, such as a piece of plain filter paper, are moved up the marginal tentacles and photograph of burrowing anemone Pachyceriathus fimbriatusdiscarded. Undigested remains are later egested, possibly via a so-called “anal” pore located on one side of the mouth, although this is not specifically observed by the author. The pore has a sphincter consisting of contractile radial tissues and, if it does function to eliminate digestive wastes, could act to separate incoming food streams from the outgoing egesta stream. Tests with various chemical substances suggest that the tentacular-transfer response is initiated by a water-soluble protein, polypeptide, or amino acid. Arai 1971 J Fish Res Bd Can 28: 1677; Arai 1972 Can J Zool 50: 311; Arai & Walder 1973 Comp Biochem Physiol 44A: 1085.

NOTE sea anemones lack a complete digestive tract so, if this pore works for digestive-waste removal, it is acting as a functional anus, but is not a morphologicial one


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Research study 3

Metridium senile is a passive filter-feeder, straining the water of small planktonic crustaceans and other photograph of sea anemones Metridium farcimenparticulate organic matter.  Field studies in Maine on feeding behaviour of M. senile show that more individuals are expanded when the tide is running than when it is slack. Laboratory tests show that while current and food combine to produce tentacle expansion and column elongation, food alone has little effect.  Other experiments in the laboratory show that M. senile has the ability to take up radiolabelled glycine directly from solution, suggesting an ability to utilise DOM (Dissolved Organic Matter). Robbins & Shick 1980 p.101, In Nutrition in the lower metazoa (Smith & Tiffon, eds.) Pergamon Press, Oxford.

NOTE  apparently, good food for laboratory Metridium are nauplii of brine-shrimps Artemia salina

Shown here, several large anemones
Metridium farcimen 0.05X

photograph of several sea anemones Metridium senile in various states of expansion and contraction

drawing of plumose anemones Metridium senile in current and slack water conditions
Feeding postures of M. senile in current (Left) and slack water (Right)

Three plumose sea anemones Metridium senile showing
3 different states of expansion and contraction 0.5X


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Research study 4

  schematic/graph showing how plumose anemones Metridium senile attached to mussels move upwards from areas of low current velocity to areas of high velocitiesStudies in Sweden show that plumose anemones Metridium senile living on mussels quickly move from locations of low current velocity to ones of high current velocity.  Note in the depiction below that currents increase markedly with height above the bottom of the flume tank in which the experiments are conducted.  Within 48h of being in the flume tank the anemones have moved from conditions of low-flow to conditions of high-flow rate. Anthony & Svane 1995 MEPS 124: 171; drawing adapted from original by Beth Beyerholm.
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What benefit does Metridium get by living in areas of high currents?  Think about the validity of the answers provided, then CLICK HERE to see explanations. Ideas from Robbins & Shick 1980 p.101, In, Nutrition in the lower metazoa (Smith & Tiffon, eds.) Pergamon Press, Oxford.

It is energetically advantageous in feeding. 

It aids in locomotion.

It increases the efficiency of reproduction.

It aids in elimination of wastes.

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Research study 5
  Although sea anemones risk being damaged or dislodged by drag forces, they depend upon the seawater moving over them to bring food, flush away waste products, and disperse gametes.  Giant plumose anemones Metridium farcimen are flexible and, like the proverbial willow, bend readily in currents and thus reduce drag forces that may tend to rip them from attachment to the substratum. 

photograph of a giant anemone Metridium farcimen being bowed over in the current
A specimen of M. farcimen being bent over by the current 0.1X

photograph of a great green anemone Anthopleura xanthogrammicaIn comparison, great green anemones Anthopleura xanthogrammica, especially ones living in surge channels, employ a different strategy to reduce drag forces.  They are much less flexible than plumose anemones, but are built much lower to the substratum and are effectively hidden from mainstream current velocities. Koehl 1977 J Exp Biol 69: 87.





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photograph of wave coming up a surge channel taken from a video

CLICK HERE to see a video showing what life is like for an anemone living in a surge channel.

NOTE the video replays automatically

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Research study 6

It is usually thought that both chemical and physical stimuli are required to initiate natural feeding responses in sea anemones.   However, experiments at Friday Harbor Laboratories, Washington show that the response can be induced mechanically in Epiactis prolifera by touching the tentacles with a piece of clean filter paper.  The tentacles begin to curl inwards and, about 30-60sec after the first touch, the mouth begins to open.  If the anemone is then fed a clam the response to later mechanical stimulation is lost, even though the anemone may still respond to a bit of fish.  Within a few days the anemone will again respond to an inert object.  Lenhoff 1965 Nature 207: 1003.

NOTE  depending on species, experimental exposure to certain chemicals, such as reduced glutathione (a feeding stimulant in other animals), will also initiate the response


Rows of capture tentacles on the brooding anemone Epiactis
. Note that the mouth is open, perhaps releasing the
small chunk of matter visible in the centre of the photo 2X


photograph of capture tentacles on a brooding anemone Epiactis prolifera
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Research study 7

Field observations on 40 adult sea anemones Epiactis prolifera in Bodega Bay, California disclose an average daily movement over a 77d study period of less than 1mm.  Movements appear to be non-directional.  Although individuals that are brooding juveniles move more than ones not brooding, the author notes that the brooding individuals are generally larger; hence, relative rates of movement turn out to be about the same for the 2 groups.  Selection of good feeding location may be involved. Dunn 1977 Mar Biol 39: 67.


Juvenile Epiactis lisbethae festooned in the branches
of a coralline alga, possibly Calliarthron sp. While
adults move hardly at all, the juveniles are more
lively, especially soon after leaving the parent 3X

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Research study 8

drawing of laboratory flume apparatus used in feeding study of corallimmorpharians Corynacts californicaResearchers at California State University Northridge note that densities of corallimorpharians Corynactis californica living under kelp canopies Eisenia arborea in Catalina Island, California are significantly greater than outside the canopies (1200 vs. 300 polyps . m-2, respectively). One obvious difference in the 2 habitats is the presence in the under-canopy area of the branching red alga Gelidium robustum, and in the outside-canopy area the foliose brown alga Dictyopteris undulata. The authors hypothesise that the outside-canopy foliose species could be interfering more with food capture by the polyps than the under-canopy branching species. Indeed, results of laboratory experiments using a unidirectional flume apparatus (see diagram) support the theory, with the foliose D. undulata inhibiting food-particle capture by Corynactis by 40% and the branching G. robustum having only non-significant effects on food capture. The food particles used in the experiment are hydrated cysts of brine shrimps Artemia sp. that are neutrally buoyant and known to be readily eaten by Corynactis. Close observation of the flow pattern in the flume shows that proximity of upstream foliose algae tends to redirect particles around the polyps and causes their feeding tentacles to photograph of corallimorpharians Corynactis californica with unidentified membranous red algacontract. In contrast, the blades of the branching red alga G. robustum remain more erect even at higer current velocity and interfere less. The data provide at least one explanation for superiority of under-kelp habitat for Corynactis. Morrow & Carpenter 2008 Mar Biol 155: 273.

NOTE population densities of up to 2400 polyps . m-2 are not uncommon in the Catalina Island area

NOTE there are likely to be other factors at play. In this regard, it is unfortunate that the authors do not investigate flow rates, understory algal densities, and possibly even in situ feeding rates, in the field

Colony of Corynactis californica
intermixed with blades of an unidentified
membranous red-algal species 0.25X
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