The Work of Countering Hydrostatic Pressure 



Given realistic figures for siphonophore float volumes 

 and colony weights, and measured values for oxygen con- 

 sumption, it is now possible to arrive at an estimate of the 

 physical work required to prevent collapse of the pneumato- 

 phore, or conversely, the work required to compress the 

 necessary volume of gas to the volume of the float at depth. 



Kanwisher and Ebeling have utilized an equation 

 which is said to give the work necessary for a vertically 

 migrating fish to maintain its swim bladder at a constant 

 volume and therefore keep the fish at neutral buoyancy: 



Pa 

 W = 2.3 v p^ log — 

 2 P, 



where v is the volume of the swim bladder of a fish migrat- 

 ing downward from pressure p to p . W is in ergs when v 

 is in cc and p in dynes /cm . 



If the assumption of neutral buoyancy maintained by 

 continuous gas secretion is taken for a downward migrating 

 siphonophore possessing a pneumatophore volume of 1 mm , 

 and the total distance traversed is from 100 to 400 meters, 

 ^equals approximately 0.001 gm-cal. It is readily apparent 

 from figure 9 that the total work of countering the hydro- 

 static pressure increases with increasing depth for each 

 unit increment in gas content of the pneumatophore. 



If the siphonophore, on the other hand, performs 

 the vertical descent without maintaining buoyancy, at its 

 daytime depth it must secrete up to a maximum of 30 mm 3 

 of gas under the above conditions. Production of this quant- 

 ity of gas against the high pressure will cost more energy 

 than would continuously maintained neutral buoyancy during 

 descent; however, the energy cost of swimming downward 

 can be expected to be greater in the latter case. 



The work required to compress a given amount of 

 carbon monoxide across a known pressure range, and at a 

 stated temperature, is given by 



P 1 

 W = 1.99 nT 2.3 log — 



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