The song of the sea

“As silent as a fish”
– A saying from ancient Greece

In 1953, Jacques Cousteau co-authored a book titled The Silent World: A Story of Undersea Discovery and Adventure. It was long assumed that the ocean was a quiet world, empty of sound.  But we have since discovered that this is far from the truth.  The seas that surround us are filled with a vast array of sounds.

“The underwater soundscape can be as noisy as any rainforest”
Kate Stafford

Underwater sound is generated by a variety of natural sources, such as breaking waves, rain, the sound of bubbles popping and of volcanoes erupting at the bottom of the ocean.  There is the creaking and cracking of ice, screeching and popping and groaning.  The noise from ships at the surface and the sound of the earth quaking.  And of course, the sounds of marine life.

Because sound travels five times faster through water than through air it is a useful tool for aquatic animals.  Especially given that sight and smell are less effective underwater.  All it takes is a bit of murky water and your vision is severely restricted but sound can travel for thousands of miles in the ocean.

Animals use sound to study habitat (echolocation) and to detect predators and prey.  Sound is used for communicating about reproduction and territory and some animals even use sound to stun their prey, such as the pistol shrimps.

Whales and dophins

Probably the most well known sound from the sea is probably that of the whale song.  The haunting, eerie moans gave the whale a voice and in doing so, probably aided conservation efforts.  Whale song is now part of human culture and helps us feel connected to these mysterious creatures.

The humpback whale has the loudest voice in the animal kingdom, carrying for miles.  And it is thought that they may have one of the most complex songs in the animal kingdom.  Their songs are sung by the males and the songs are always changing although whales from one area sing the same song, whales from different areas sing different songs.  Almost like they have accents.

In contrast to the melancholic songs of the whale, we find the excited pips of dolphins who use high pitched beeps to paint a picture of the world around them.  Their language of squeaks and chirps lets them communicate with each other and whistles are used in a similar way to names, they are unique to each dolphin and seem to be a sort of greeting, an announcement that you’re there.

Apparently, dolphins are also able to mimic sounds and one scientific paper suggest they may even sleep talk in whale song.

We have long been fascinated by dolphins, ancient Greek mariners listened to them through the hulls of their ships and according to Aristotle in about 344 BC, they even heard dolphins snoring!  NB, there doesn’t seem to be any evidence that they do actually snore…

Crustaceans

The term crustaceans covers a vast array of marine species including crabs, lobsters, shrimp and barnacles.  They are united by their exoskeleton and some use this to produce sound.

For example, the snapping shrimp are rather noisy creatures, especially given their size.  They produce a crackling, sizzling sound by clicking their claws.  They do this to stun prey,deter predators, and to communicate with others.

Hermit crabs make a noise by rubbing its body parts together or rubbing against the inside of their shell and do so as a sign of aggression.  Male fiddler and ghost crabs use acoustical signals to call to females during breeding season and are apparently unique amongst crustaceans in doing so.  Other species use sound once they’ve found a potential mate but not to call out.

Spiny lobsters make a rasping sound by rubbing a piece of soft tissue, called a plectrum, against a smooth, stuff file near their eye.  Essentially they move the plectrum over the file in the way that a bow is moved over the strings of a violin.

Fish

We tend to think of fish as silent, except for the occasional little noise of their mouths opening and closing but this isn’t the case.  They produce sound using their swim bladders and their teeth that include grunts, croaks, clicks and snaps.

When it comes to mating, it is usually the male that makes the sound.  Some fish come together in large groups to ‘sing’ and may continue for hours, dominating the local soundscape.  Fish, such as the oyster toadfish, that live in murky water, need to make use of sound to find a mate as vision is limited.

The other key reason that fish make noise is when they are threatened, want to show aggression or need to defend their territory.

For some fish, instead of producing sound, it is listening that is crucial.  Many coral reef fish have a stage in their life where they go away from the reef, returning at a later time to mature.  These fish, such as the clownfish, need to know how to return and it’s thought the song of the reef provides a road map.

The song of the reef

A healthy coral reef is not a quiet place.  When they are teeming with life, they are one of the noisiest places in the ocean, making a sound like crackling popcorn thanks to the snapping shrimp.

The sound landscape changes throughout the day, with a rhythm like birds on land.  Fish have dawn and dusk songs and different creatures call at night than during the day.

Sea urchins are one of the contributors to the evening chorus.  Kina sea urchins dominate New Zealand waters with the sound of their eating.  And that specific local flavour to the music of the ocean is important for our little critters which are searching for home, or for a healthy reef to start new life on.

Listen

The song of the ocean is not a static one, it is not a consistent one.  It changes as the day passes, it changes by season and by locality and it changes based on the health of the sea.

There are many recordings of ocean music and of particular species but these are two I found helpful:

Plant, animal or other? Coral

Most of us know coral when we see it and I think everyone has probably seen a picture of a coral reef at some point but what exactly is it?

An individual coral is a polyp, a very small, simple creature which has been described as essentially just being a stomach and a mouth surrounded by tentacles.  Living inside the polyps are algae which provide the coral with food and gives it colour. Thousands of identical polyps live together in a colony and this forms the reefs we are familiar with.  Different coral grow at different rates but to form a reef takes a very long time, with estimates for todays reefs being started 5-10,000 years ago.  That being said, not all coral are reef builders.

An alternative take on the creation of reefs comes from Greek mythology.  It was said that they were created from the blood that was shed when medusa was decapitated.  This blood mixed with the seaweed to create the stone reefs.

“With no Pharaoh to lead them, this army of tentacled midgets has built the greatest of the ocean’s wonders, working together for millions of years on their mighty projects.”
– Jeffrey Levinton

Cooperation is a theme amongst the creatures of the reef.  A symbiotic relationship between coral and algae allows the reef to grow and provides the coral with their colours. Coral reefs are home to lots of organisms and provides cracks and crevices for fish and crabs to live in.  So when a starfish comes along and attacks the coral, the fish and crabs step in and defend it.  This allows the coral to keep growing and creating more cracks and crevices for future fish and crabs.  There are also fish which ‘farm’ on the coral, growing algae and in doing so, they are creating ideal conditions for more coral to grow.  And then there are the cleaner wrasse; fish which clean other fish, a service which improves the health of the sea life around the reef.

“No other marine habitat shows so well the intricacies of biological interdependency”.
– Jeffrey Levinton

But despite this incredible interdependency, the reef is a dangerous, cut throat world.  Coral use barbed, venomous tentacles to catch zooplankton and tiny fish and they can also extrude their stomach and digest neighbouring coral…

The competitive nature of the habitat means some coral dwellers have developed nasty chemical defences.  For example, the sea squirt makes sulphuric acid to burn predators and also a poisonous metal that could kill a horse.  The sea whip produces higher amounts of prostaglandin than other creatures making them taste terrible to most predators (although a type of snail and worm can eat them).  Poisonous fish live among the coral and sharks patrol the edges.  This beautiful underwater garden can be a deadly place.

But those deadly poisons and chemicals may actually be of use to us.  We may be able to use some of them to develop cancer cures, to help neurological diseases, to treat infections and to fight drug resistant bugs.  Corals themselves can be used in bone graft surgery as well.

As well as medical value, coral reefs provide coastal defences, tourism, food (an estimated 0.5 billion people rely on coral reef fisheries worldwide for 95 percent of their protein) and jobs.  The Great Barrier Reef has been valued at at AUD $56 billion, contributing 64,000 jobs and $6.4 billion a year to the Australian economy.

But despite their importance, we are not treating them kindly.  Coral reefs are threatened by overfishing, pollution, invasive species and ocean warming and acidification caused by rising carbon dioxide levels.  In the last 30 years, we have lost 50% of the coral and scientists predict that we will lose 90 percent of coral reefs globally by the year 2050.

This would be catastrophic.  Life on the reef is a diverse one, paralleling that of the rainforests.  Apparently, despite reefs covering less than 1% of the earths surface, a quarter of ocean biodiversity depends on reefs for food and shelter.  Without the reefs, the health of the ocean will suffer and without a healthy ocean, we cannot have a healthy planet.

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