Where does sand come from?

A lot of us dream about tropical holidays, listening to waves breaking on a deserted beach, palm  trees swaying in the breeze and the perfect golden sands to stretch ourselves out on with a good book and a cold drink.  Maybe we love beaches because it reminds us of holidays and more relaxing times.  Maybe the sound of the waves is calming and brings us peace of mind.  Beaches are also fun places where we can take part in activities like surfing, flying kites and we also see a lot of sand under the water when diving too! 

But where does sand come from? How does it form?   

Sand comes from many sources but is formed from decomposed and broken down rocks that are weathered and eroded over thousands, even millions of years.  Sometimes starting a long way from the ocean, rocks travel down streams and rivers headed to the ocean where they get further broken up by the constant movement of the waves and tides.  Different coloured sands originate from different types of rock, such as the black sand beaches that are found in Hawaii and the Canary Islands that are formed from volcanic materials such as basalt and lava.  

A more unusual source of sand is through Parrotfish, specifically their poop, especially in the formation of the soft white sand beaches of tropical waters where corals are found.    

Corals have a limestone skeleton that is covered with a very thin layer of living tissue.  Parrotfish are so named for their large front teeth which resemble a parrots beak and are some of the strongest teeth in the world.  Whilst feeding on the living coral, the parrotfish inevitably bite off quite a bit of the limestone too.  This is then passed through the digestive system of the fish and comes out the other end as finely ground sand particles!  

You may have seen this whilst diving, all of a sudden there is a small line of falling sediment in front of you and you wonder where it has come from if the fish moved off too fast for you to see it.  Yes, parrotfish poop out sand!  

Some scientists estimate that up to 85% of sand on a tropical beach can be made from parrotfish poop!  It is thought that a large parrotfish can produce 1000lbs/450kgs of sand per year. 

By feeding on corals the parrotfish, like constant gardeners, are also eating the algae that cover reefs and hinder the growth of corals.    In places where parrotfish have been overfished, algae takes over and leads to a much less productive and less diverse ecosystem.  Some areas in the caribbean have brought in conservation measures to try to prevent the parrotfish from being fished and so maintain a healthy reef.  

So next time you see a parrotfish underwater you can wave and thank them for your afternoons spent lounging on a tropical beach and for keeping our reefs healthy.

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