Oyster nursery extension benefits Craignish

A plan to grow 300,000 native oysters annually in Loch Craignish to help repopulate Scottish waters has been approved by Argyll and Bute Council.

 

The protected species was once abundant in most Scottish sea lochs, so much so they were used as currency to pay taxes at Ardtornish Estate in Morvern, but predation, disease, trawling and centuries of guzzling have destroyed most populations.

 

Seawilding, 'a community-led and non-commercial marine habitat restoration project' with its headquarters in Ardfern, aims to grow one million flat, round European native oysters (Ostrea edulis) over five years before releasing them to the seabed.

 

Its chief executive officer Danny Renton already runs a floating oyster nursery, but this newly-granted extension of 192 floating baskets will increase its capacity in the intertidal waters off Eilean Buidhe to 300,000 (10 gram) oysters annually.

 

'The conservation project currently employs one full-time employee and five part-time employees,' a planning report said. 'The additional nursery capacity would create one additional full-time job.'

 

Oysters may be only small - five to 11cms - but they can make a big change in the marine environment. Each oyster can filtrate and clean up to 200 litres of water a day. Beneath the waters of the Dornoch Firth, thousands of reintroduced filter-feeders are transforming whisky waste from Glenmorangie Distillery into clean water in the Dornoch Environmental Enhancement Project.

 

Oysters also remove excess nutrients from water, such as nitrogen, which in high levels can promote harmful algal blooms, oxygen depletion and fish mortality.

 

Native oysters begin life as male then – upon reaching sexual maturity at two to three years of age – they spawn, after which they switch to females, capable of producing eggs. This trait, of switching sex many times, defines them as ‘protandrous alternating hermaphrodites’.

 

A female oyster around 8cms in size can produce one million larvae. Oysters are highly gregarious, meaning the larvae prefer to settle with others.

 

If left to multiply, oysters cement together into reefs, reducing coastal erosion and creating habitats for other marine life, such as fish spawning grounds. Oysters are therefore called ‘ecosystems engineers’.

 

Scientists are developing this super-strong 'oyster glue' into surgical adhesives, bone and dental cement and even anti-fouling paint for ships. Currently copper-based paints are used, but they can be toxic to marine organisms.

 

Oyster shells are made of calcium carbonate and, as the reefs grow, they capture carbon, mitigating climate change. Researchers are investigating if this is offset by the oysters' respiration. Like all animals, they create carbon dioxide as they breathe.

 

Shells from oysters, mussels, scallops, whelks, crabs and lobsters are all composed of calcium carbonate, the same as limestone, and there is a long history of burning shells to produce construction materials such as lime mortars and plasters. It is different to cements in that it cures and hardens by absorbing carbon dioxide from the air, re-crystallising back to its original limestone chemistry.

 

Lime mortar containing crushed shell is commonly found in old buildings in Scotland's Western and Northern Isles, such as in Argyll's Castle Sween and Lochaber's Inverlochy Castle, in the limpet-lime of St Ronan's chapel on North Rona, the cockle-lime in the medieval buildings of Harris, the Uists and Barra, the coral (maerl) lime of Cubbie Roo’s Norse chapel and castle on Orkney and the oyster-lime of Lismore Cathedral.

 

When a van crashed into a stone archway at Scone Palace, the ancient crowning place of Scottish kings, in 2010, experts began piecing the rubble together like the 'world's largest jigsaw' - and found builders 1,000 years ago had shored up the historic monument with their lunch packaging, oyster shells.

 

Recently workmen renovating Gladstone’s Land, a 17th century tenement in Edinburgh's Royal Mile, uncovered an entire wall of oyster shells. They almost certainly came from the basement, one of the city's famed oyster cellars.

 

The Firth of Forth was once home to enormous oyster beds, or scalps. In the 17th century, it is estimated up to 100,000 oysters were eaten a day in Edinburgh, as bar snacks like munching a bag of crisps or peanuts today. Over-harvesting led to their downfall.

 

In 1882, only 55,000 oysters were landed from the Forth, with the number falling to 6,000 the following season. A decade later and the catch was down to 1,200, with the population declared extinct in 1957.

 

In UK waters, native oyster populations have declined by 95 per cent since the mid-19th century, but more restoration projects are popping up to repopulate the seabeds.

 

Last year, the Kilchoan Native Oyster Restoration Project introduced 12,000 hatchery-raised native oysters to suspended cages in Loch Melfort, while the Community Association of Lochs and Sounds is also expanding its native oyster nursery in Lochaline.