Environmental physiology
  Not much research has been done on whole-animal physiology of west-coast holothuroids. Presented here are accounts of light effects on zonation, salinity effects on body-fluid concentration, and a short account of gas exchange via the respiratory trees.
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Light effects on zonation

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Research study 1
 

Sea cucumbers Pseudocnus lubricus in the San Juan Islands, Washington are distributed subtidally from about 7-17m depth, with a preference for vertical rock walls, and with a maximum zone of abundance in some areas at 12m depth reaching 4000 individuals . m-2. Over photograph of sea cucumbers Pseudocnus lubricus10mo of investigation of possible influencing environmental factors such as temperature, salinity, turbidity, food, and light, researchers from the Shannon Point Marine Center identify light as the only factor varying significantly with depth. Indeed, in laboratory experiments using light boxes at 4 natural intensities (equivalent to 9, 16, 20, and 26m depth) the scientists observe that locomotory activity over a 3h period is greater in individuals at high and low light levels than at intermediate ones. A photokinesis of this kind would tend to lead to clustering at intermediate depths, a behaviour that may be advantageous for fertilisation of eggs at breeding times. Rodgers & Bingham 1996 J Exp Mar Biol Ecol 204: 113. Photograph courtesy Phil Lambert, Royal British Columbia Museum, Victoria.

NOTE since publication the name of the species has been changed from its original Cucumaria lubrica

NOTE movement in response to light stimulus. Another, possibly better, design for the experiment might have been to measure locomotory response in a vertical light gradient, which would have simulated more closely the natural situation

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Salinity effects

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Research study 1
 

Salinity fluctuations may have significant effects on internal osmotic concentrations in interidal invertebrates, especially in estuarine areas where strong seasonal haloclines occur.  This is true in southeastern Alaska where glacier meltwaters create a layering of freshwater over saltwater during summer.  While these layers wash over the invertebrates there can be sudden and sometimes severe effects on osmotic concentration of internal body fluids, exacerbated in soft-bodied invertebrates such as sea cucumbers.  As an example, when subjected to seawater of 12‰ during normal tidal fluctuations the osmotic concentrations of body fluids of Cucumaria vegea (+0.6m level on the shore) and Eupentacta quinquesemita (-0.9m) drop by photograph of sea cucumbers Eupentacta quinquesemita30 and 20%, respectively.  The difference likely relates to the relative times of exposure to the freshwater lens, but the authors note that the deeper-living species is able to regulate ion levels to some extent.  Air exposure appears to have no effect on osmotic concentration in Cucumaria, or on other intertidal species included in the study. Stickle & Denoux 1976 Mar Biol 37: 125.

NOTE  lit. “salt bend/slope” G., referring to abrupt change in salinity

NOTE  the authors also present data on a few chitons, sea urchins, and sea stars.  The effects are similar for all species, and only the effects on sea cucumbers are considered in the ODYSSEY





Two Eupentacta quinquesemita in a shallow subtidal
area in Barkley Sound, British Columbia 0.8X

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Gas exchange

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  drawing of sea cucumber to show location of respiratory trees
Gas exchange is accomplished by diffusion from seawater contained in the paired respiratory trees to the coelomic fluid. The trees are ventilated by muscular contractions of the cloaca. Usually several inhalations precede a single exhalation. Each inhalation involves opening the anus, expanding the cloaca, closing the anus, then contracting the cloaca. The water is forced into the respiratory trees. On exhalation, the body musculature contracts, and the resulting pressure forces water from the trees and out the anus.
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CLICK HERE to see a video of Parastichopus californicus ventilating its respiratory trees.

NOTE  the video replays automatically

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