Efforts underway to save Sweden's last coral reef

06 March, 2023

In the laboratory’s aquariums, lush corals glow ghostly white in the dark. But out in the sea, below the surface, there is almost only gravel and dead skeletons left. Here are the scientists who will save Sweden’s last coral reef.

Anna Larsson, Iga-Maria Nestorowicz, Anita Tullrot and Susanna Strömberg are researching the coral Lophelia at the Tjärnölaboratoriet outside Strömstad.
Photo: Adam Ihse/TT

A brilliant spring sun glistens in the waters of Kosterhavet and casts sun cats against piers and boathouses. But inside the lab at Tjärnö marine laboratory outside Strömstad, it is dark.

In large aquariums, eye corals glow white in the dark. What looks like thin, light dust grains slowly swirl around in the water. It’s eggs. “We are doing a test here to see if they develop even better in motion,” says Susanna Strömberg and shows another aquarium where a kind of paddle is whisking around the coral embryos.

The corals in the lab are taken from the Norwegian Tisler reef. There are almost none left in Swedish waters.

“It has been in a total of six locations that we know of. On most of them, there is only coral gravel left,” says Ann Larsson, research leader for the Life Lophelia project.

Today, there are only living coral reefs left in two locations in Swedish waters: Väderöarna and Säcken. Graphics: Anna-Lena Lindqvist/TT

For just over three years, she and her colleagues have been working on raising eye coral larvae to study the conditions under which they thrive. The goal is to re-establish them in Swedish waters – and to save the coral reefs in the Koster Sea.

Over a thousand species

Among the aquarium’s white underwater forests are squishy barnacles, swaying sea brush worms, and pale pink spiny lobsters as big as fingernails. In the sea outside, at a depth of just over 80 meters, there are even more spectacular ecosystems adjacent to the reefs.

“There are species of all kinds. Animals of various sizes live there and find food and shelter, and they attract several species of fish that find their food there. That is why in the past fishing has been done close to the reefs,” says Anita Tullrot, project manager at the county administrative board.

More than 1,300 species have been observed on eye coral reefs, a species richness fully comparable to that of tropical coral reefs. “It is quite common that people do not know that we have Swedish coral reefs. Spreading the knowledge is part of the project. If people know they exist, you might want to preserve them,” says Ann Larsson.

The eye coral grows deeply and slowly, about 25 millimeters a year under good conditions. Photo: Adam Ihse /TT

Two living reefs

Exactly when they disappeared is unknown. There are many theories as to why. Trawling for shrimp is likely to have broken up the sensitive reefs, while eutrophication and sedimentation may have affected the environment in the area.

Still, hope lives on. After trawling and anchoring bans were introduced, the corals have recovered naturally in one of the locations: at the Väderöarna, which are off Fjällbacka. It is currently around 300 square meters in size.

“The corals grow about 25 millimeters per year, and about ten years ago, there was nothing there. So there must have been many larvae that settled, otherwise the reef would not have been able to grow so quickly,” says Anita Tullrot. Even at Säcken, north of Strömstad, there are today a few living coral colonies.

It is known that the larvae, only 0.2 millimeters in size, are found in Swedish waters. They drift with the currents from the Tisler Reef or even as far as foundations to oil platforms in the North Sea. The problem is that they don’t stay.

At the two living coral reefs, there are old, dead coral skeletons left for the larvae to attach to. At the four other sites, everything is gone.

“If there is no three-dimensional skeleton left for the larvae to attach to, the reef cannot recover,” says Susanna Strömberg, a researcher at the University of Gothenburg. While coral gravel can be found on the seabed in some areas, it does not provide a suitable attachment surface for the coral larvae.

3D printers

To solve this problem, the researchers are using 3D printers to create artificial reefs that mimic the natural structure of the coral. In the lab at Tjärnö marine laboratory, plastic prototypes with various cavities and structures are being tested to determine the best materials and conditions for attachment. “We look at what materials they like, surface structures, and under what conditions they can get stuck,” explains Ann Larsson, another researcher involved in the project.

This is a model of a structure designed to provide an optimal environment for the growth and thriving of Lophelia coral. Photo: Adam Ihse /TT

In April, the final construction will be completed, and this fall the artificial reefs will be placed in the sea, with the hope that they will become home to new larvae and reefs.

According to the researchers, this project is the only one of its kind. While attempts have been made to transplant eye corals on a small scale in some places, setting out reef structures adapted to the larvae is unique, says Ann Larsson. She adds, “As far as I know, it hasn’t been done anywhere before.”

The Life Lophelia project is a collaboration between the County Administrative Board in Västra Götaland and the University of Gothenburg. The project is co-financed by the EU Commission and the Norwegian Sea and Water Authority. It began in September 2019 and is set to continue until 2025.

The project aims to restore the eye coral reefs at six locations in Kosterfjorden and Väderöfjorden, which are protected as a Natura 2000 area, Kosterhavet national park, and Väderöarna nature reserve.


Source: Life Lophelia, University of Gothenburg

The eye coral, Lophelia pertusa, is a cold-water coral that builds reefs. Over 1,300 species have been observed on eye coral reefs, which is comparable to the species richness of tropical coral reefs.

Eye corals can grow about 25 millimeters per year in good conditions and reproduce sexually by releasing eggs and sperm into the water, forming small embryos when they meet.

The occurrence of eye coral has rapidly declined in Sweden, the North East Atlantic, and throughout Europe. Today, live eye coral can only be found in two locations in Sweden: at Säcken, north of Strömstad near the Norwegian border, and east of the Väder Islands, at a depth of just over 80 meters. In the past, it has existed in at least four other locations.

Source: Life Lophelia, University of Gothenburg.

Graphics: Anna-Lena Lindqvist/TT

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