rethink sustainability

Shellfish: the kidneys of the sea

For anyone holidaying in the US coastal town of Cape Cod, the plates of seafood in many of the restaurants hold a particular allure. But it is not just in feeding the locals and visitors that businesses have been relying on shellfish - they are using them to help clean the water.

Oysters effectively act as sieves in water where there is too much nitrogen, as in Cape Cod, where such excess levels might otherwise lead to rampant algae growth. Oyster shells incorporate the nitrogen as they grow, taking it into their shells and out of the water and preventing harmful algea blooms.

It is one example of the remarkable phenomenon of shellfish being a natural filter - and one that never switches off. Oysters can filter over 200 litres of water a day. The humble mussel acts as a vacuum cleaner for the sea, taking in microplastics, pesticides and other pollutants. Where man has created problems through pollution, the natural world has fought back.

 

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But shellfish around the world are under threat as reefs are destroyed as a result of rising temperatures and overfishing. Now it is time for us to fully realise the value of these silent workers in our seas and ensure that they will be able to continue to do what they are best at in the future.


A natural phenomenon

That the natural world can come up with so many solutions for our problems is a continuing marvel. And nestled on the rocks around water, the ability of shellfish to act as a natural cleanser is one of those phenomena. 

In the case of oysters, the creatures filter water through their gills1, in the process removing pollutants as they work to absorb nutrients and grow their shell. Excess carbon dioxide, the nitrogen from fertilisers and phosphorus are all absorbed. As a result, the water is left cleaner for other marine life. To see the before and after effect of an oyster in polluted water is remarkable - time lapse footage has been used to demonstrate how they defog the water around them and bring clarity. 

Excess carbon dioxide, the nitrogen from fertilisers and phosphorus are all absorbed. As a result, the water is left cleaner for other marine life

Clams, meanwhile, can filter 20 litres of water a day, allowing more sunlight to get through and foster the growth of seagrasses and increase oxygen levels. The mussel has been called the ‘hoover’ of the sea2 and takes in phytoplankton for nourishment as well as pollutants - filtering up to 25 litres in one day. They are often compared to canaries in a coal mine, with their health being an indicator of the greater condition of the water in which they are in.

Researchers from Stanford University illustrated the strength of the cleaning properties by putting California floater mussels and Asian clams into a tank with wastewater3. Three days later, some 80% of the contaminants from the water had been removed.

How they help

The effect of shellfish on local environments has been seen for some years. In Cape Cod, they have been used as one part of a scheme to reduce nitrogen in the waterways. 

In Poland, a system to test the quality of the water has been constructed whereby eight clams have triggers attached to their shells4. When the water gets too toxic, they close up, prompting alarms after which the water system can be shut down.

And in the Salmon Bay region of the Puget Sound on the northwestern coast of the US, scientists installed cages of mussels in the water to filter contaminants as the health of the local ecosystem is monitored.

Researchers have experimented with mussels in New York City’s Bronx river to see if they are robust enough to roll out to other polluted waters - such is the effect of their cleansing. 

 

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But problems persist

The world’s waters are in trouble and shellfish are also under threat. The number of oyster reefs have plummeted and they have been ranked amongst the world’s most endangered marine habitats. 

One of the major problems is the fact that there is now more carbon dioxide in the atmosphere as a result of increased carbon emissions. This, in turn, dissolves into the oceans, making the water more acidic, resulting in it being more difficult to produce shellfish. Researchers trying to find the reason behind a drop in the number of scallops, clams and oysters on the east coast came to the conclusion that it was a warming environment that was its cause, and not overfishing5. The result of such shortages means that the price of shellfish increase as they have to be sourced from elsewhere, usually from overseas.

 

Our next move

Without most of us knowing, we are being helped immeasurably by the static shelled creatures attached to rocks by our oceans. Oysters, clams and mussels are providing us with food and cleaning the water around them at the same time. They are the kidneys of the seas, filtering out impurities from the water around them. In a world where we’re striving for net zero, they contribute an active part, removing toxins from the sea whilst at the same time being attacked by rising carbon dioxide levels.

Shellfish are a quiet and unimposing presence on our oceans, yet one which give us immeasurable advantages. They are part of the Natural Capital which allows the oceans to thrive

All is not lost - there are initiatives such as the plan to return millions of oysters to the Solent area between England and the Isle of Wight6. An oyster restoration project was also initiated at Chesapeake Bay between Maryland and Virginia.

Shellfish are a quiet and unimposing presence on our oceans, yet one which give us immeasurable advantages. They are part of the Natural Capital which allows the oceans to thrive. And it is now up to us to ensure that this beating organ can continue to thrive for generations to come.

1 https://medium.com/proofofimpact/how-oysters-help-to-keep-oceans-clean-54356e0bbf02
https://phys.org/news/2019-08-mussels-super-filters-pollution.html
https://www.natureworldnews.com/articles/8682/20140822/clams-mussels-clean-up-ocean-pollutants.htm
https://www.economist.com/europe/2021/01/21/how-clams-help-keep-polish-water-clean

https://www.nbcnews.com/news/us-news/climate-change-not-overfishing-devastating-shellfish-environments-n934976
https://www.businessinsider.com/oysters-clean-oceans-solent-2018-12?r=US&IR=T

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