title of learn-about section on goose barnacles of A SNAIL'S ODYSSEY
  Physiological ecology
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Research study 1

graph showing body temperature of goose barnacles Pollicipes polymerus on cloudy and sunny daysGoose barnacles Pollicipes polymerus occur on the Pacific coast of North America from Alaska to Baja California.  They live in the upper part of the intertidal zone and are exposed to extremes of seasonal temperatures.  Although the shell plates are white, the rest of the body is dark; hence, heat-absorbing.  Measurements in spring/summer in San Juan Island, Washington show that while body temperatures graph showing temperatures of peduncles and capitula of goose barnacles Pollicipes polymerus under conditions of different air temperaturesof Pollicipes are generally higher than air temperatures, they are less than temperatures at the rock surfaces (see graph upper Left). Differences are most apparent during sunny days; on cloudy days, body temperatures may actually be cooler than the air. If specimens are kept in experimental chambers at different temperatures, at 55% RH and a wind velocity of 1-2 m . sec-1, there graph showing relationship of hemolymph osmolality of goose barnacles Pollicipes polymerus in relation to the salinity of external seawateris evaporative cooling, and the peduncle stays at a somewhat lower temperature than the capitulum (see graph upper Right). The authors note that Pollicipes can tolerate 5-10h of air-exposure at 36oC.  

Over a range of experimental salinities from 300-900 milli-osmoles (≈33-100% normal seawater) Pollicipes' hemolymph is isosmotic with the external medium. Hemolymph osmolality in field animals increases by only about 10% after several hours in the sun, and decreases by only 5% after several hours being rained on. The amount of increase in the sun is equal to that calculated from the decrease in body water through evaporation. As expected, water loss from the capitulum is almost negligible in comparison with that from the peduncle.  On immersion by the incoming tide, desiccated individuals quickly rehydrate. The authors note a high internal hydrostatic pressure in Pollicipes.  Fyhn et al. 1972 J Exp Biol 57: 83.

NOTE  the authors note that animals easily recover from 40-50% water loss

NOTE the pressure in the peduncular sinus is sufficient to fill a syringe on its own (for a follow-up study on this see below)

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Research study 2

graph showing rates of oxygen consumption of goose barnacles Pollicipes polymerus when air-exposed and when submergedWhen covered by the tide goose barnacles Pollicipes polymerus are usually actively feeding.  When air-exposed by the tide, their shell plates often gape and their cirri protrude from the opening.  Studies at Friday Harbor Laboratories, Washington show that gas photograph of goose barnacles Pollicipes polymerus in the splash zone with cirri partially extendedexchange occurs in both air and water and, surprisingly, is more than 4-fold greater in air than in water at any given tempera-ture.  Gas exchange likely occurs across surfaces within the mantle cavity, the cirri, and the general body surface.  A considerable portion of this may be via the peduncle cuticle, which seems to be readily permeable to water and air.  Petersen et al. 1974 J Exp Biol 61: 309.

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Research study 3

Support of the stalk, or peduncle, of Pollicipes polymerus is mainly through hydrostatic pressure generated by high pressure in the circulatory system.  Studies at Friday Harbor Laboratories, Washington show that the internal pressure in Pollicipes reaches 33 kN . m-2, about 10 times higher than photograph of a large clump of goose barnacles Pollicipes polymerusrecorded in other crustaceans.  A system of protein fibers in the peduncle and the presence of chitin in the integument contribute to the ability of the peduncle to act as a pressurised vessel.  The fiber system doesn’t wrap around the pressure cylinder as in flatworms, anemones, squids, and other soft-bodied invertebrates but, rather, it extends through the lumen of the peduncle, around muscles, and through the ovary.  The author comments that although the structural arrangement of the peduncle is different from most other hydrostatically supported organisms, the functional role is similar.  Crenshaw 1979 Comp Biochem Physiol 62A: 423.

Large cluster of goose barnacles Pollicipes polymerus
comprised of at least 2 separate cohorts. With strong
shell plates and turgid peduncles, such clusters can
resist even the strongest storm waves. Note the uniform
orientation of individuals. This owes to the propensity
of goose barnacles to "face" their cirri into a current
or wave swash for more effective feeding. Do the larvae
"know" which way to face when they settle, or do they
adjust their orientation later in life?

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