These bivalve molluscs were hard at work around the British coastline for thousands of years, in such large numbers that many estuaries we now think of as being murky were once quite clear, thanks to each oyster\u2019s ability to filter at least 200 litres of water a day. <\/span><\/p>\n In Victorian times, there was an oyster reef in the Firth of Forth 20 miles long by six miles wide, with 30 million oysters clinging to it. And the North Sea had one the size of Wales. So prolific were oysters that almost everyone could afford them. But due to huge demand, stocks withered and vanished across the world. <\/span><\/p>\n \u201cIt\u2019s a tragic fact that has been overlooked for 100 years or so,\u201d says marine ecologist Dr Bill Sanderson of Edinburgh\u2019s Heriot-Watt University. <\/span><\/p>\n \u201cMuch of it happened before records were kept. They were one of the first fish stocks to be over-fished and only now are we realising the ecological impact.\u201d<\/span><\/p>\n More related content:<\/p>\n Lower Fishguard\/Credit: Simon Whaley<\/em><\/p>\n <\/p><\/div> Their rarity today makes them something of a luxury food \u2013 and the quality of the waters they once inhabited suffers from their absence, because oysters function like the sea\u2019s kidneys. They suck in nitrogen, carbon dioxide, phosphate and even microplastics through their gills, absorb nutrients to grow their shells, and deposit what is left as harmless \u2018oyster poo\u2019. During this filtering process, they clean and clarify the water around them and boost the level of carbon sealed-up in the seas.<\/span><\/p>\n With ever-growing concerns about marine pollution, there are calls to bring back these underwater vacuum cleaners. One of the most ambitious projects is in the USA, with plans to install one billion oysters in the grimy waters of New York Harbour. More modestly, in the UK, a hatchery that will produce one million native oysters every year has just opened in Hampshire<\/a>, in a bid to improve water quality in the Solent and help restore its oyster-fishing industry \u2013 once the largest in Europe \u2013 which collapsed 30 years ago. Already, cages full of spawning oysters have been dangled from pontoons in marinas. Recently, when I was filming for Countryfile<\/i><\/a> on a Hampshire beach, a marine biologist was thrilled to discover a native oyster washed up on the sands. The scheme is working.<\/span><\/p>\n![\""Fishing\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/22\/2021\/06\/Lower-FIshgaurd--e162d9d.png?quality=45&resize=556,556"\" "\\"\"Lower\\"")
<\/div><\/div> <\/div> <\/section>Building an oyster army<\/span><\/h3>\n