title for learn-about section of A SNAIL'S ODYSSEY
  Life in the intertidal zone
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  Gas exchange
 

Topics dealing with life in the intertidal zone include gas exchange considered here, and TEMPERATURE EFFECTS, HEAT-SHOCK PROTEINS, WAVE EFFECTS, SALINITY EFFECTS, TRANSLOCATION STUDIES, and WATER-CHEMISTRY EFFECTS, considered in other sections.

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Research study 1
 

graphs showing effects of air exposure, then re-immersion, on oxygen content of mantle water and heart rate in sea mussels Mytilus californianus

 

Studies at Friday Harbor Marine Laboratories, Washington on sea mussels Mytilus californianus indicate that several things happen with respect to gas exchange when a mussel is emersed by the falling tide and remains tightly closed.  First, oxygen concentration in the trapped mantle-cavity water drops to about one-third of its normal level within 1hr. At the same time, heart rate decreases from about 20 beats . min-1 to about 8 beats . min-1 (at 13oC).   On re-immersion after 6hr in the air, both return within about 10min to normal levels (see graphs on Left).

 

graph showing effect of air exposure and re-immersion on oxygen uptake in mussels Mytilus californianus

Gaping, thought to be a possible strategy for evaporative cooling, may alternatively be a way of enabling at least some aerobic respiration during air exposure. Within 5hr after air exposure, oxygen consumption in air is 2.5 times the previous rate in water.   On re-immersion, oxygen consumption returns to normal levels within 2h (see graph on Left). 

graph showing effect of air-exposure on ammonia levels in the mantle water of mussels Mytilus californianus

 

 

As a consequence of a mussel being closed when emersed, excretory products in the form of ammonia have no way of escaping, so concentrations rise. On re-immersion after 6hr, the ammonia is quickly flushed out and levels quickly return to normal.  Bayne et al. 1976 Oecologia 22: 229.

NOTE  part of this increase may owe to air temperature being 19oC as compared with water temperature of 13oC

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