Large oyster reefs could be found in the narrow Belfast Lough channel until the early 1900s, but overfishing, illness, and pollution eventually wiped off the colony, according to Ulster Wildlife.

Under the shadow of a busy downtown roadway and tall commercial buildings, the group's marine conservation manager, David Smyth, told AFP that “we're bringing back a lost habitat.”

Since prehistoric times, people have been gathering oysters from the vast natural beds that formerly covered the waters of Europe.

However, the organisation calculates that during the 19th century, oyster populations have dropped by 95%, making native oyster reefs one of Europe's most endangered ecosystems.

Approximately 700 molluscs were transported from Scotland by vehicle to Belfast Lough last month, where they were placed in more than a dozen cages with shelves after being measured and disease screened.

According to Mr Smyth, it should eventually produce a local “equivalent of a coral reef.” A team of experts is monitoring the oysters' development as part of a health check.

The group carefully lifted each oyster out of the water and set it on the pier for weighing and measurement after lifting the metal oyster houses out of the water.

According to Mr. Smyth, who was holding two oysters aloft, pairs of conjoined oysters are the first signs of constructing a reef.

“Imagine 100,000 of these all stuck together, this is what we are after, from them millions of larvae will settle around the shore and on the seabed,” he stated.

Ulster Wildlife listed improved water quality and increased marine biodiversity as two of the ecological advantages of a restored environment.

“Just as with a coral reef, once these animals start forming their beds then small fish and crustaceans like mussels, barnacles, worms, snails, and algae will come to live and feed there,” added Smyth.

He also mentioned oysters as “supreme water filters,” noting that a single oyster can filter more than 200 litres of saltwater per day.

Pollutants in the river make habitat regeneration difficult because passenger ferries and commercial ships use the nearby ports.

For a significant portion of the 19th and 20th centuries, Belfast's main industry was shipbuilding; the city's skyline is still dominated by the yellow gantry cranes of the shipyard where the Titanic was built, next to a brand-new museum honouring the tragic liner.

Long decades of environmental damage were also caused by tannin industries and a coal yard.

“It's very difficult for oysters' larvae to settle and become adults if they are exposed to the sort of pollutants present in an industrial shipping lane,” said Smyth.

Although many more oysters are scheduled to be planted in the upcoming years, he noted that the hardy nursery animals have “performed impressively” thus far with only two mortalities out of the 700 oysters installed.

Though there have been recent initiatives of this kind around Europe, the Belfast Nursery seeks to emulate an effective initiative in New York that was started ten years ago with the intention of reestablishing circumstances for millions of oysters to be as they were in the 1800s.

“New York's the shining example of how well these animals can do in an industrial area,” said Smyth.

He chuckled and then let a cage descend into the sea. “There were dolphins swimming around the Statue of Liberty for the first time in years recently. We don't know if we will ever have dolphins swimming in Belfast, but you never know,” he said.