Sound and Pressure

     Sound travels nearly 5 times faster underwater than through air.  In water, sound is transmitted by water molecules; since water molecules are densely packed (more so than molecules in air), they transmit sound more quickly.  Because sound waves travel more efficiently underwater than light waves, marine organisms frequently rely on sound (hearing), much more so than light (vision).  Blues Whales produce deep rumbling sounds; deep, low-pitched sounds that are the loudest noise produced by any animal.  You will feel a Blue Whale vocalization before you ever hear it!  Whale vocalizations can travel over entire ocean basins!

(Taken by professor McNamara)

     Another factor that changes dramatically with depth is pressure Pressure = Force/Area (P=F/A).  Organisms on land are exposed to 1 atmosphere of pressure at sea level.  Marine organisms, on the other hand, are under the weight of the water above them and as well as the atmosphere.  Pressure increases dramatically with depth; for every 10 meters of increased depth, another atmosphere is added.  As pressure increases, gases are compressed.  Gas-filled structures inside organisms which provide more buoyancy than the storage of body lipids, such as AIR BLADDERS and lungs shrink or collapse under the pressure.  This limits the depth range of many organisms.  Others have evolved physiological adaptations to survive in the depths (we'll come back to this).          

Every 10 meters = +1 atmosphere of pressure