Ögonkorallen släpper ägg och spermier i vattnet
The Lophelia coral is releasing lots of eggs and sperm in the aquariums at Tjärnö marine laboratory.
Photo: Susanna Strömberg

Renewed hope for Swedish coral reefs: Full seed ahead in the Coral Factory


In a cool, damp, temperature-controlled room at the Tjärnö Marine Laboratory, Susanna Strömberg is surrounded by rippling aquariums. She is culturing baby coral that will help researchers save Sweden’s unique coral reefs.

The “coral factory” consists of large aquariums in which the coral Lophelia pertusa release eggs and sperm that become larvae. The parents were collected in November from a large reef in the Norwegian Hvaler area, north of Koster islands. They were full of eggs and sperm at the time, and now in February, the spawning season is in full swing.

A Lophelia coral colony
The little bush is a coral colony. A colony begins with a single, tiny larva, which attaches to a suitable surface and develops into what is called a polyp. New polyps bud from that polyp, leading to the formation of an entire coral reef over time.
Photo: Susanna Strömberg

“Once we see that the corals have released eggs and sperm in the water, we transfer them from the aquariums to big, 2–3 litre glass bowls, where fertilization takes place. We give them a stir now and then to improve the chances of the eggs and sperm bumping into one another,” explains Susanna Strömberg, research engineer at the Department of Marine Sciences.

Reefs can regrow

The larvae will be used as “test pilots” to see what surfaces they prefer. They like to squeeze into small spaces that are only a bit wider than they are themselves. Here, they are protected from predators until they have completed the transformation into polyps and developed the hard, calcium-based exoskeleton into which they can retreat.

Susanna Strömberg peers into the glass jar that is filled with fertilized coral eggs.
Susanna Strömberg peers into the glass jar that is filled with fertilized coral eggs. The larvae that develop will be used to test suitable materials to put out on the ocean floor for new coral reefs to form.
Photo: Nina Luckas

The only known presence of this coral in Sweden is in the Koster-Väderö Fjord, a Natura 2000 site in northern Bohuslän. But of six original reefs, only two currently have living corals. Susanna Strömberg and her colleague Ann Larsson hope that new coral reefs will form by deploying artificial reef structures with appealing surfaces to which the coral larvae can attach.

“It was discovered a few years ago that corals had started growing on the remains of old reefs out by the islands Väderöarna. Dense carpets of fairly evenly sized corals had attached to dead clumps of coral skeletons. So, it’s clear that coral can regrow if there is a suitable three-dimensional structure.”

Looking for the right surface

The researchers are using a 3D printer to make different kinds of surfaces, with pits and grooves of various sizes, in two different materials. One is made of corn starch and potato starch, and the other of finely ground lime.

“We’re also testing metallurgical slag – a calcium-rich waste product from metal manufacturing that resembles volcanic rock. The small pieces of slag have complex surfaces, with holes of various sizes. We’re going to try to make surfaces that the larvae attach to permanently, says Susanna Strömberg.

Nina Luckas loads coral larvae settlement panels on research vessel "Nereus".
Project assistant Nina Luckas loads up star-shaped concrete panels to which the Lophelia coral larvae can attach. The panels will be placed on six known reefs in the Koster-Väderö Fjord to study the incidence of larvae in the water.
Photo: Ann Larsson

Corals want the water to be  turbulent and do not like it when the water contain a lot of sediments, which forces them to spend significant energy keeping their polyps clean. This is why all of the water is filtered. The corals are fed three times weekly, twice with small copepods and once with special feed from an aquarium store.

“It takes about three weeks for the larva to develop a mouth. That is when it’s time to start feeding them. They also like copepods, but we usually blend them into a smooth soup.”

Small parasites are a challenge

It takes a lot of work to keep the coral factory up and running. But the researchers seem to be succeeding, since the corals appears to thrive in the aquariums on Tjärnö. Even the corals that have lived in the lab since last year are now spawning.

One challenge they are facing at the moment is that some type of single-celled parasite has gotten into the water and is attacking the larvae. So, the researchers are testing different methods of filtering and treating the water and have also mixed their own seawater with sea salt and purified tap water.

The work environment is another challenge. Many hours are spent in the damp and cold, so dressing accordingly is key, says Susanna Strömberg.

“We’ve set the air and water temperature to about 7–8 degrees Celsius. That’s the temperature at a depth of about 100 metres, where the coral reefs are located. But what wouldn’t we do for science; we want the corals to thrive so that we can learn more about them!”

Text: Susanne Liljenström

Sweden´s only coral reefs

The coral Lophelia pertusa forms coral reefs in deep and cold seas. The three-dimensional environment is inviting for fish and many other animals. More than 1,300 species have been observed on Lophelia reefs, a species richness fully comparable to that in tropical coral reefs.

The LIFE Lophelia project will recreate coral reefs in the Natura 2000 area of Kosterfjorden-Väderöfjorden. It is the only known locality in Sweden with Lophelia coral. The project is a collaboration between the University of Gothenburg and the County Administrative Board of Västra Götaland, and is funded by the European Union's LIFE program and by the Swedish Agency for Marine and Water Management.