Buoyancy of Calanoides acutus changes when wax esters change from saturated (single bond, top) to unsaturated (double bond, below) Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.
"Levels of wax ester in the copepods were correlated with depth, with deeper animals containing higher amounts...The level of unsaturation can affect the physical conditions at which lipids make a transition between the liquid and solid phase. This in turn alters the specific volume of the lipid store, so altering buoyancy." (Pond and Tarling 2011:1311)
"[I]t was found that levels of unsaturation of the wax esters in the lipid pool differed significantly with depth, with animals deeper than 400 m consistently containing high levels of unsaturation (~50%)...wax ester samples with higher levels of unsaturation underwent a phase transition from liquid to solid state at typical deep-water pressures and temperatures." (Pond and Tarling 2011:1313)
"A transition from the liquid to the solid phase reduces the specific volume and hence the buoyancy of the large lipid pool, so assisting lipid-rich diapausing copepods in overcoming their positive buoyancy." (Pond and Tarling 2011:1314)
"A comparable mechanism of buoyancy regulation is utilized by sperm whales...sperm whales contain their lipid in a large spermaceti organ within the head space. To descend, the lipid is cooled to the point at which it solidifies, and the increase in density makes the whale able to sink without large amounts of downward swimming." (Pond and Tarling 2011:1316)