A hatchery in the Channel port city of Portsmouth in the UK is helping to revive the native species of oyster after decades of over-fishing and pollution made them near-extinct.

Across Europe, the population of the European flat oyster species, Ostrea edulis, has fallen by 90 percent since the end of the 19th century, according to the University of Portsmouth, and is almost extinct in some regions.

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In the Solent, a strait between the Isle of Wight and Great Britain, these native oysters have almost disappeared where they were once thriving.

"If you take it back to the 1970s, there were about 15 million oysters taken out from the fishery each year," Luke Helmer, a restoration science officer at the Blue Marine Foundation based in the UK, told AFP.

"That has now declined to almost nothing," he added.

Human intervention for a human-made problem

According to researchers, this diminishing number of oysters is caused mostly by human-related factors.

Monica Fabra, a PhD student in marine biology at the University of Portsmouth, said the reasons are "mainly overfishing and harvesting," while there were other factors at play, including pollution and the introduction of non-native species which compete for space and food, such as the Pacific oyster.

Scientists and researchers at the university's Institute of Marine Sciences say human intervention and active management are now needed to help undo the damage caused to the species. 

They've set up a hatchery – the first in Britain to focus solely on saving oysters, without any commercial motivation – aiming to reintroduce millions of the European flat oysters to the region. 

The research center is stacked full of salt water tanks housing adult oysters that are fed and placed in the right conditions by the team of scientists. 

"In the wild environment, the oysters will be reproducing roughly May through to September, and we're hoping that that will be mimicked here in the hatchery," said Helmer.

The team will soon start slowly raising the water temperature to match that of nearby seawater, triggering the oysters to release their larvae.

The larvae will live in incubators in the hatchery before being released in June into the Solent.

"They cannot really survive in the water if the water is polluted, and many other factors," Fabra explained. "So actually, making them reproduce in the hatchery is a safer environment that we can control and we can ensure that they survive until the very end of the production," she added.

Important to the ecosystem

Even though it will take a while to reverse the drop in the oyster population, Helmer hopes to reintroduce "somewhere between half a million and a million larvae" into the Solent in the next year or so. 

If successful, this won't just be positive for the species itself, but also for the entire ecosystem in which it is introduced. 

That's because these oysters play a considerable role in improving water quality in the area due to their constant filtering.

Each oyster can filter up to 200 liters of water a day "which is a phenomenal amount," said Helmer. "Oysters are known as an ecosystem engineer, so they enhance the environment that they're restored to or that they weren't present in," he added. 

In addition, the oysters will also improve the biodiversity of the reef where they settle, as their shells can shelter many other species, explained Fabra.

During a preliminary trial, researchers put oyster cages down into the sea and were astounded when they pulled them up and discovered 97 species.

This result is particularly spectacular for European oysters since it has evolved to live alongside local species, they said. 

The hatchery's findings could be rapidly duplicated around Europe as the researchers are collaborating with similar projects in Germany and the Netherlands.

Video editing: Nuri Moseinco