title of learn-about section on goose barnacles of A SNAIL'S ODYSSEY
  Feeding & growth
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Research study 1

Goose barnacles are thought to feed mostly on particulate organics including algae and detritus, but laboratory observations at the Hopkins Marine Station, Pacific Grove, California show that both Pollicipes polymerus and Lepas anatifera also eat brine shrimps (5-11mm in length) and copepods Tigriopus californicus (1mm).  The barnacles capture the live prey by lassooing and caging them in their 6 pairs of cirri.  The basal regions of photograph of cirri of a goose barnacle Pollicipes polymerusthe anterior smaller cirri then push the prey items to the mouth region where they are compacted and swallowed.  Gut analyses of field-collected Pollicipes disclose a wide variety of food matter, including algae, organic particulates, copepods, cirripede moults, amphipods, nauplii and cypris larvae, small clams and polychaetes, and hydroids.  Guts of the oceanic Lepas contain similar food items, goose barnacles Lepas anatifera on a piece of woodbut with a greater variety of amphipods and caridean shrimps.  The presence also of snails, clams, pycnogonids, and algae suggest that the barnacles continue to feed while the floating object bearing them is being washed about in the intertidal zone.  The largest crustaceans eaten are almost half the length of the Lepas’ gut.  Howard & Scott 1959 Science 129: 717

Cirral filtering basket of a
goose barnacle Pollicipes polymerus 2X




Still-living goose barnacles Lepas anatifera being
washed about in the surf zone on a beach on the west
coast of Vancouver Island, British Columbia 0.5X

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Research study 2

There are 6 pairs of cirri in a goose barnacle Pollicipes polymerus. Cirri IV-VI are large, of similar size, and form the feeding basket or net.  Each cirrus is biramous so the entire basket is made up of 24 units or rami.  Cirri I-III are smaller and located anterior to their larger counterparts. The setae of adjacent segments overlap and those of one ramus meet and overlap those of adjacent rami. The drawing in the middle/top below shows the arrangement of cirri on a single ramus. Towards the base of each cirrus the setae become more brush-like.  Particles, both edible and inedible, that impinge on the large cirri are moved to the basal parts or pedicels and scraped free by Cirri I-III. The scrapings are moved to the mouth by a reciprocating action of the pedicels of Cirri I-III (see drawing below on Right). When live prey items are caught, the cirri curl in basket-like to prevent their escape. 

The mouth is situated at the anterior end of the body and is surrounded by several pairs of appendages (see green parts in the drawings). These include outer maxillae, maxillae, mandibles, and palps. A single segment, the labrum, forms an anterior part.  Particles moved into the mouth region by Cirri I are pushed towards the mouth by the maxillae and mandibles, while the palps push from the other side. The pushing motion of the outer maxillae is more along the midline, while that of the maxillae and mandibles is more of an inward sweeping motion. The combined action of the appendages gathers and moves food into the mouth. There appears to be little actual mastication, but the mouth appendages are well muscled and possess heavy jaws, and these features may aid in particles being ground up as they are moved along. The authors suggest that chemoreceptor cells around the mouth and on the appendages, especially the more bristly outer maxillae, probably are involved in rejection of inedible particles. Barnes & Reese 1959 Proc Zool Soc Lond 132: 569.

drawing showing ventral view into mantle cavity of a goose barnacle Pollicipes polymerus
The 6 cirri on each side have been cut at their bases. Each cirrus is comprised of 2 branches or rami, and each ramus bears setae
photograph of ventral side of goose barnacle Pollicipes polymerus
In this photo the 2 rami of each cirrus are lying close together and appear as one. When spread out for feeding the setae of adjacent rami overlap
drawings of segments of a cirrus of a goose barnacle Pollicipes to show the filtering setae
3 segments of a ramus to show setal arrangement. When the rami are extended the setae overlap
drawing of cirri of a goose barnacle Pollicipes polymerus in relation to oral cone area
Food captured by Cirri IV-VI is moved to the basal or pedicel regions of the cirri, scraped free by Cirri I-III, then pushed to the mouth by the pedicels. The mouth is surrounded by 4pr of appendages and an anterior labrum
drawing of mouth-part region of a goose barnacle Pollicipes polymerus to show appendages
The mouth is surrounded by 4pr offeeding appendages
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Research study 3

photograph of goose barnacles Pollicipes polymerus feeding at high tide in the wave swashUnlike acorn barnacles that actively sweep the water for particulate organic food, goose barnacles Pollicipes polymerus passively hold their cirri into the water flowing past, generally into the down-flow of water from waves striking the shore above them.  The cirral basket is moved around in the flow in response to local changes in current direction and velocity.  If currents are too fast, the cirri may be withdrawn.  In any case, the large feeding cirri are pulled into the shells periodically to allow the smaller cirri to scrape off edible particles, which are then passed to the mouth for consumption.  Estimates of growth of Pollicipes in southern California indicate that a large individual may be 20yr of age.  Barnes & Reese 1960 J Anim Ecol 29: 169.



Goose barnacles Pollicipes polymerus feeding
at high tide in the wave swash. Note the
extended cirri of all individuals. The image of
barnacles and algae is being reflected
off the water's undersurface 0.25X

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photograph of goose barnacles Pollicipes polymerus feeding taken from a video

CLICK HERE to see a video of goose barnacles Pollicipes polymerus feeding. Note the cirral baskets being extended into the water current and the 2 occasions when a barnacle retracts its cirri, possibly to scrape them clean of food particles.

NOTE  the video replays automatically

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Research study 3.1
  graph showing growth and survival of goose barnacles Pollicipes polymerus over 6-yr periodSettlement of goose barnacles Pollicipes polymerus on a bare patch of intertidal rock at Mukkaw Bay, Washington provides opportunity for a University of Washington scientist to follow growth and survival over a 6yr period. Initial recruitment numbers are 180 in June 1964, diminishing to zero in August 1970 (see graph). Growth, as measured by increase in rostral-carinal distance, is continuous through the period, reaching about 40mm. The presence of even larger specimens in nearby clumps suggests that death owes not to some natural limit but, rather, to other influence. The author opinines that competitive exclusion (crushing) from a steady inpushing of adult mussels Mytilus californianus from beds surrounding the original open patch may have caused Pollicipes’ demise. Paine 1974 Oecologia 15: 93.
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Research study 4

graph showing effective separation distance in goose barnacles Pollicipes polymerus leading to sterilityA 26-mo study on growth and reproduction of goose barnacles Pollicipes polymerus at 2 sites in San Juan Island, Washington shows that growth is fast during the first year, to a rostrum-carina length of 17mm, but subsequently slows to 2mm . yr-1.  Breeding in this area occurs in late April to early October.  The accompanying graph suggests that reproductive sterility is realised at an inter-individual separation distance greater than 11cm. This distance must represent the maximum extensibility of the penis. Comparison of populations at wave-exposed and wave-sheltered sites discloses differences in the proportion breeding (57 vs. 50%, respectively) and number of broods per year (4.2 vs. 2.4, respectively).  Lewis & Chia 1981 Can J Zool 59: 893.

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Research study 5

graph showing cirral beat rate in goose barnacles Pollicipes polymerus of different sizes (ages)photograph showing rostral-carinal length measurement on a goose barnacle Pollicipes polymerusJuvenile goose barnacles Pollicipes polymerus use a different mode of feeding from adults.  Instead of holding their cirri out into the water flow the way the adults do, the juveniles slowly beat their cirri in the manner of acorn barnacles.  Beat frequency is about 1-2 . min-1 in the absence of food and about double that in the presence of food.  While an acorn barnacle Balanus spends about 60% of its beat time extending its cirri and 40% on the beat itself, a juvenile goose barnacle Pollicipes spends 80% of its beat time on extension and 20% on the actual beat.  Beating is done by the juveniles only in slow currents or in still water.  In fast currents the juveniles extend their cirri like adults.  Beat frequency is inversely correlated with body size in individuals of 7mm rostral-carinal length and less (see accompanying graph). Only intermitent beating is observed in individuals of 10-12mm size, and no beating occurs in animals of 15mm size or greater.  Gut analyses of Pollicipes at Friday Harbor Laboratories, Washington indicate that the food of juveniles is small particulate matter made up mainly of detritus and diatoms, while the food of adults additionally includes eggs, barnacle exuviae, and small copepods, polychaetes, and molluscs.  As to the significance of cirral beating, the author thinks that it may provide a food-getting benefit to the juveniles, living as they do on the upper parts of the adult stalks just below the adult cirral nets, where competition for particulate food may be intense. Lewis 1981 Crustaceana 41: 14.

NOTE  average for larger-sized juveniles at 11oC

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Research study 6

histrograms comparing sizes of goose barnacles Pollicipes polymerus at 2 sites in California: on an oil platform and on the shoreA comparison of 2 populations of Pollicipes polymerus in Santa Barbara, California reveals that growth of individuals on an offshore oil platform HOLLY (3km from shore) is 3.5 times faster than growth of comparable-sized individuals living on the shore at GOLETA POINT.  The difference likely relates to both quantity and quality of food available at the 2 locations.  The oil-platform population is also distinctly larger and has a bimodal size-structure as compared with the shore population (see histograms). The author speculates that part of the reason for the size differences may owe to reduced long-term survival of the shore population because of erosion of the soft shale-rock substratum that they inhabit.  The author’s data indicate that a goose barnacle of 34mm capitulum height is probably 5yr of age.  Page 1986 Mar Ecol Progr Ser 29: 157.

NOTE  the author also observes that the guts of shore animals typically contain sand stirred up by waves, while those of the oil-platform animals contain only food matter

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Research study 7

drawing of a goose barnacle Pollicipes polymerus showing external featuresGrowth of goose barnacles Pollicipes polymerus occurs both in the stalk or peduncle and in the shell plates. The peduncle exterior is comprised of a tough but flexible epidermis containing embedded calcareous spicules, presumably for extra protection, covered by an outer cuticle.  Lengthening of the stalk occurs mainly at the capitulum-peduncle junction (see drawing on Left). Growth of shell plates occurs on the inner sides and edges through secretion of calcium carbonate from underlying tissues. Unlike the cuticle covering the body parts within the mantle cavity and the mantle-cavity lining itself, the peduncular cuticle is not shed.  Rather, it lengthens at the capitulo-peduncular junction and, at the same time, exhibits a banding pattern in the freshly deposited material.

Studies at San Diego, California show that the width and colour of the bands provide a record of conditions present during growth. Thus, if P. polymerus is fed on differently coloured foods it will produce new coloured bands in the cuticle of the growth zone within a week or so.  These easily identifiable bands of new cuticle, measuring 1-3mm in width, are associated with high densities of white spicules embedded in regular patterns in the cuticle. The spicules change in size and shape in a repeating pattern from band to band.  The authors speculate that these bands of new cuticle explain the preferential settlement of cyprids onto the upper regions of peduncles of adults.  Such areas are unfouled and presumably exude fresh chemical signals to the larvae.  Moreover, the authors suggest that the tiered arrangement of adults in colonies lead to exposure of relatively large areas of desirable settlement zones to the cyprids being carried along in the current.  Chaffee & Lewis 1988 J Exp Mar Biol Ecol 124: 145.

photograph of cave-dwelling goose barnacles Pollicipes polymerusNOTE  the authors inject radio-labelled thymidine to identify regions of the peduncle showing greatest mitotic activity; hence, greatest growth.  Injections of 35SO4 and 45Ca provide information, respectively, on deposition of organic matrix and calcium in the shell plates and peduncular spicules

NOTE  goose barnacles readily eat juvenile brine shrimps Artemia.  If hatchling brine shrimps are fed on each of green flagellates Tetraselmis suecica, golden flagellates Isochrysis galbana, and colorless yeast, 3 differently pigmented foods can be created for test groups of Pollicipes, and these pigments come to be deposited in the freshly produced cuticle

Colours of goose barnacles Pollicipes polymerus are also
responsive to habitat. These individuals live in a cave
with markedly reduced light. In addition to the
lighter-coloured peduncles, the cirri of
these individuals are quite red 0.6X.

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Research study 8

graph showing relationship between live mass and length in a goose barnacle Pollicipes polymerusA 7yr stock-assessment study around Amphitrite Point in Barkley Sound, British Columbia by a researcher from the Pacific Biological Station, Nanaimo, British Columbia indicates that sexual maturity is attained by Pollicipes polymerus in 1yr and harvestable size in 5yr (see graph). The main breeding season is March-July and an individual may produce 2-5 broods per year.  The author discusses aspects of harvesting, including storage and shipping, and generally concludes that a modest fishery is sustainable.  At the same time the author owns to the fact that no recolonisation of previously cleared sites has occurred during the 7-yr period of the study.  This may not be the best recommendation for maintenance of such a fisheries, at least not without further study.  Bernard 1988 Fisheries Res 6: 287.

NOTE it is not clear whether these data are from animals attached to the rock substratum, or whether they also include juveniles attached to adults.  The author does not address the issue of loss of attached juveniles during harvest procedures  

NOTE  other studies on P. polymerus (see Research Studies above) indicate that the cypris larvae settle preferentially on the peduncles of adults, perhaps in part explaining the lack of recolonisation on cleared rock surfaces seen in the present study


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Research study 9

graph showing growth of goose barnacles Pollicipes polymerus in the La Jolla, California regionGrowth of Pollicipes polymerus on rock substratum around La Jolla, California is shown here.  The larvae settled about a week or so before the first measurement of size.  By 5mo they have a rostral-carinal length of almost 15mm.  The author notes that there is no method to determine age of a goose barnacle accurately, but estimates are that an individual of rostral-carinal length >30mm may be 20yr old.  Hoffman 1989 J Exp Mar Biol Ecol 125: 83.

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