The other direct effect of pressure is on the tissues themselves.
The first effect of pressure is exhibited by the nervous
system, and shows up in humans as tremors at 150 m,
and convulsions at 500 m. This is referred to as high pressure
nervous syndrome or HPNS. The great majority of
marine mammals and seabirds do not dive deep enough to
experience HPNS. However, deep-diving elephant seals,
sperm whales and beaked whales that routinely dive to
depths between 500 and 1000m should be susceptible
to HPNS. While it is hard to imagine a seal or a whale
routinely diving to these depths and experiencing HPNS,
there are no data on whether these animals do encounter
HPNS, and if so how they tolerate it or avoid it.