When it comes to the sounds of the ocean many people begin
to think of the splashing of waves, the rising of bubbles, or even the flopping
of a fish. What is not thought about is
how much sound these creatures make by just doing every day activities; these
sounds can be feeding or even a form of communication.
This communication is mostly a territorial response or an attempt
to mate. Besides simple communication
they are also able to use their sounds to protect themselves, locate food,
navigate underwater, and to understand their environment.
If you were to dive in an area with plenty of fish, then it
is possible to hear all of there actions and this is mainly due to some of the
properties of water. Its main advantage
over air is that the molecules of water are fair close together compared to air,
so the sound can travel farther and clearer.
The two main things that determine how far an animal is able
to make a sound are pressure and temperature.
This is because the sound will begin to travel down due to the decreasing
temperature until it hits a thermocline and then it will bounce back up due to
the increasing pressure. It is then
possible that it can continue to do this for thousands of miles in an area call
the “sound channel”, all depending on how loud the initial sound was.
Besides marine mammals, which are the animals that most
people think of when it comes to communication in the water, many invertebrate
and fish can use sounds as well. They tend
to use grunts, croaks, clicks, and snaps in varying combinations.
Once a whole ecosystem is going, it is then possible to even
hear it out at sea. This is the case
with coral reefs, in which juvenile fish hear the sounds and make their way to
it. It has been tested at different coastal
environments create different sounds, so it is possible that this is how most juvenile
fish make their way back to their specific environment.
One very cool use of sound is seen by the cleaner
shrimp. It will clap its hands, making a
small snapping sound, that allow reef fish to know that it is there and
available to clean a fish from parasites or if its lucky, left over scraps.
https://oceanservice.noaa.gov/facts/sound.html
I would assume that fish can hear underwater a lot better than humans - they have their otoliths (earbones), lateral lines (which detect vibrations), and swim bladders (which act like an echo chamber). Plus, since sound travels further underwater than in air, they can probably hear things from far away. In short, the world must be a very noisy place for fish since they can probably perceive a lot of sounds that we can't. A coral reef probably sounds like the equivalent of a city to them. I also think it's interesting how many different signalling mechanisms there are for animals underwater; there's sound, bioluminescence for sight, and pheromones for scent. If coral reefs are that noisy for fish, it must be really smelly for them too. How unfortunate.
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