Q Why don't marine animals that live deep down in the ocean get crushed by the sheer weight of the water's volume above them?

A Hi Graeme,


Unlike mammals like us that have lungs with large air spaces in them, most marine animals such as fish and invertebrates have little or no air spaces in their bodies. As it is only gases that can be compressed, increased depth has little effect on the watery bodies of most marine animals.

For diving mammals such as whales, they have a variety of strategies such as thick rib cages and collapsible lungs that allow them to cope with the pressure changes.

One part of some fish that is filled with gases are their swim bladders, used to maintain bouyancy. When these fish from depths are brought quickly to the surface the decrease in pressure causes therir swim bladders to expand rapidly and the fish become bloated or can even explode!

If you are teaching this concept if you put some air into a strong large plastic syringe you can press down on the plunger and it will compress the air into a smaller space. Fill the syringe with water and repeat to show that liquids (and solids) are not easily compressed.


I hope that helps.

Cheers, Mark

A Hi Graeme,


Unlike mammals like us that have lungs with large air spaces in them, most marine animals such as fish and invertebrates have little or no air spaces in their bodies. As it is only gases that can be compressed, increased depth has little effect on the watery bodies of most marine animals.

For diving mammals such as whales, they have a variety of strategies such as thick rib cages and collapsible lungs that allow them to cope with the pressure changes.

One part of some fish that is filled with gases are their swim bladders, used to maintain bouyancy. When these fish from depths are brought quickly to the surface the decrease in pressure causes therir swim bladders to expand rapidly and the fish become bloated or can even explode!

If you are teaching this concept if you put some air into a strong large plastic syringe you can press down on the plunger and it will compress the air into a smaller space. Fill the syringe with water and repeat to show that liquids (and solids) are not easily compressed.


I hope that helps.

Cheers, Mark