Stockholm, Oct 23 (IANS): Sweden's only remaining cold-water coral reef, the Sacken reef in the Koster Fjord, may become extinct, warn scientists.

Alarmed by the possibility, University of Gothenburg researchers have started a restoration project where healthy corals from nearby reefs in Norway are being removed and placed on the Sacken reef.

Coral reefs are known for their rich biological diversity.

In Sweden, only one reef-building coral species exists, a cold-water coral called Lophelia pertusa, according to a Gothenburg statement.

"We've known since the mid-1920s that cold-water coral reefs exists here in Sweden," said marine biologist and researcher Mikael Dahl from Gothenburg.

"At that time, corals could be found in three locations in the Koster Fjord. Today, only the Sacken reef remains, and it's in poor condition."

Some of the causes to this are the impact of trawling and increased sedimentation. Continuous observations with remotely operated vehicles (ROVs) shows that the health of the reef slowly continues to decline.

"The red list assessment is currently in the 'under immediate threat' category. The Sacken reef has been protected against trawling for more than a decade, but trawling damage have been observed on the reef several times after the legislation was set in place," said Dahl, who led the study.

Three years ago, the protection of the reef was further strengthened when Sweden's first national marine park, the Kosterhavet National Park, was created.

However, the Sacken reef remains in poor condition.

The genetic diversity on the Sacken reef is also much lower than observed in any other reef of this type.

"This means that it is highly unlikely that the Sacken reef will recover naturally. Instead, interventions are needed in order to ensure the survival of the reef," he added.