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Concrete reefs for corals finally in place in the Koster Sea

All 160 artificial reefs that will save Sweden’s coral reefs are finally in place in the Koster Sea. Launching them has taken longer than expected, since the project was affected by the windy summer weather. Now there will be a few years of anxious waiting before they know whether the experiment has succeeded or not. But until then, the reefs will be a hotel for other marine animals, such as fish, squat lobsters, and sea anemones.

2024-10-31

*Early one morning in October, the last artificial reefs were finally launched into place. The picture shows the type of artificial reefs that are 3D printed in concrete. Photo: Susanna Strömberg*

Are you glad that all artificial reefs are now in place?

“Yes, we are very happy that all 160 artificial reefs are in place! There are 132 ‘Star’ type artificial reefs and 28 artificial reefs that are 3D printed in concrete. We had hoped to have them all in place before the summer, but unfortunately this type of job is very weather-sensitive,” says Susanna Strömberg, research engineer at the Department of Marine Sciences and the Life Lophelia project.

Why has it taken until now?

“If the wind or wave height is too high, it’s not possible to launch giant chunks weighing 600 kilos with the small vessels we have. We had quite a windy early summer this year and August was also windy. So many days of planned launches have simply ‘blown away’ for us. But in September we got a whole week of calm weather and the final ones we managed to get down this week in October. So now all the reefs are finally in place,” says Susanna Strömberg.

What are you hoping for now?

“Firstly, we hope that some larger marine animals will find our artificial reefs and start to move in, such as fish, squat lobsters, and crabs. Fish like to hide in cavities to get protection from bigger fish or dogfish hunting in the area. Squat lobsters like to stick their bottoms into a burrow for protection, where they sit with their large claws ready to capture food or defend themselves. When burrows are scarce, there can be fights over the few that are available. Now they have a few more holes to sit in, like a hotel!” says Susanna Strömberg.

Concrete reefs with small cavities and other structures on their surface to help coral larvae attach. With their hard structures and crevices, they are also a haven for squat lobsters, fish, — The concrete reefs have small cavities and other structures on their surface to help coral larvae attach. With their hard structures and crevices, they are also a haven for squat lobsters, fish, and sea anemones.
Photo: Susanne Liljenström

How long do we have to wait until we get a result?

“We’re obviously very curious to see how this goes, so we’ll take every opportunity to go out and have a sneak peek at what’s happening and how our reefs will be received by the animals in these areas. But in a year’s time we should be able to see other reef-associated marine animals that have started to grow on our reefs. Sea urchins and sea anemones are often seen utilising artificial structures. If coral larvae settle, it will probably take 1-2 years before they are visible. We don’t yet know whether there are coral larvae in circulation every year, or whether they are sporadic events,” says Susanna Strömberg.

“We have tried to give the coral larvae the best possible conditions. My hope is that we will see living corals on the reefs within five years,” says Anita Tullrot, project manager for LIFE Lophelia and marine manager at the County Administrative Board of Västra Götaland.

Writer: Annika Wall