Fig. 2

Effect of temperature, salinity, and pressure on density of seawater and lipids and on buoyancy of the coelacanth. a Density of Comoran seawater as a function of temperature with and without salinity (s) and pressure (p) adjustments (adj.). b Density of swim bladder lipid of Hoplostethus atlanticus (left vertical axis) as a function of temperature with and without pressure adjustment compared to density of Comoran seawater (right vertical axis). Notice that the density of the swim bladder lipid is more sensitive to pressure than seawater. Both vertical axes span 0.03 kg/l. c Density of oleyl oleate, the most prevalent wax ester in coelacanth (left vertical axis) as a function of temperature with and without pressure adjustment compared to density of Comoran seawater (right vertical axis). Notice that the density of oleyl oleate is more sensitive to pressure and temperature than seawater. Both vertical axes span 0.03 kg/l. d Absolute (left vertical axis) and relative (right vertical axis) buoyancy of the coelacanth at varying depths in Comoran waters. Prevalence (% of time) of coelacanths at different depths previously determined by ultrasonic telemetry [4] is presented in shades of red in the background of the graph. In its natural habitat at 190–400 m of depth, the coelacanth is close to neutrally buoyant. Venturing deeper, the coelacanth will become negatively buoyant. If brought rapidly to the surface (e.g., line fishing), the relatively cold coelacanth will initially be negatively buoyant but gradually become positively buoyant as it heats up to surface water temperature (exemplified from 190, 400, and 1000 m of depth to surface with increasingly dark blue circles and dashed lines)