Nordland in sub-arctic Norway is home to the world's largest cold-water coral reef, yet most of the people that live there have never seen it. Researchers are now investigating how these corals are affected by chemicals used in salmon aquaculture.

Did you know that Nordland has the world's largest reef of cold-water corals? The Røst Reef in Lofoten consists mainly of the stony cold-water coral species Desmophyllum pertusum and stretches approximately 35 kilometers in length.

Desmophyllum pertusum is a widespread species in the North-east Atlantic ocean, able to build reefs along the Norwegian coast and lives commonly on rocks between 200 and 1,000 meters below the sea surface. Perhaps this is one reason why this species is relatively unknown.

Desmophyllum pertusum is a sessile cold-water coral species that grows slowly, typically only a few millimeters per year. Coral colonies can therefore become several hundred years old, while entire reef structures can be several thousand years old.

Desmophyllum pertusum corals are important for the biodiversity in the ocean

These corals are among the most important habitat forming species in Norwegian marine areas. They function as shelter, nursery grounds, and feeding grounds for cod, saithe, redfish, and a wide range of other fish and small invertebrates.

In this underwater world, life has proceeded quietly for thousands of years, but not unaffected by human activities. Researchers at Nord University are investigating how D. pertusum respond when exposed to chemicals used in today’s salmon aquaculture industry.

The research is part of the project “VDWS Transitioning – from a precautionary to a science-based approach for managing fish farms close to vulnerable deepwater species,” which is led by the Institute of Marine Research in Norway.

– An estimated twenty-five percent of this coral species is found in Norway, which gives us a special responsibility to protect it, says Professor and supervisor Henning Reiss.

From the deep sea to the laboratory

To understand more about the physiology and behavior of D. pertusum and how they respond to chemicals used in salmon aquaculture, the researchers collected alive Desmophyllum pertusum corals from approximately 300 meters depth in Steigen, Nordland county in Norway. In the laboratory at Nord University, the corals are exposed to two toxic chemicals used in salmon aquaculture.

– In my PhD project, I investigate how vulnerable, long lived species, such as corals, are affected by emissions from aquaculture, says Birte Katarina Schuppe, PhD candidate.

Desmophyllum pertusum corals are suspension-feeding animals that can potentially take up everything that drifts past them in the water masses.

– Corals eat both phytoplankton and zooplankton, but they can potentially also take up dissolved chemicals if these are present in the water, says Schuppe..

Two common chemicals from the aquaculture industry are investigated

In the experiment, the corals are exposed to two chemicals used in aquaculture:

• Azamethiphos, an anti sea lice bath treatment
• Tralopyril, a newer antifouling substance in the PFAS group, used to prevent biofouling on aquaculture net pens.

– Tralopyril is a fairly new substance, and there is still limited knowledge about how it affects the environment. We do know that it is a PFAS compound, explains Schuppe.

Three ways to read the corals’ response

In the project, Birte Schuppe, together with assistant bachelor’s and master’s students, uses three methods to understand how the corals are affected:

1. Chemical analyses
Small fragments of the corals are taken out, frozen, and then sent to the Institute of Marine Research for analysis of potential uptake of these chemicals into the corals.

– We do not know whether the corals actually take up these chemicals. Therefore, it is important to measure tissue concentration of these substances directly, says Schuppe.

2. Behavioral studies with cameras
GoPro cameras take images of the corals every two minutes, day and night, to record changes in behavior:

– Corals can show stress through reduced tentacle activity or increased mucus release, she explains.

3. Measurement of metabolism
The corals are placed in incubation chambers where oxygen consumption and excretion of ammonium are measured.

– Oxygen consumption and ammonium excretion tell us about the corals’ energy use and metabolism, says Schuppe.

Coral reefs in northern Norway – an important habitat type

– We still know little about where these coral reefs are located in our fjords, but when we survey the seafloor, we often find them. This must be considered as human activity in the fjords increases, for example within aquaculture.

– In addition, we lack knowledge about how corals are affected by both natural conditions and human activities. Therefore, the basic research we are doing here together with the Institute of Marine Research is very important to better understand these key habitats and how they are affected, says Professor Henning Reiss.

These coral reefs along the coast host a diversity of species and are considered near threatened. The slow growth and ecological importance of the corals aslo make them important indicators of environmental changes.

Professor Henning Reiss emphasizes how important the knowledge from the research is:
– Coral reefs are key habitats. If we are to manage the coast in a sustainable way, we must understand how different types of human activity affect them.
This research contributes to a more detailed picture of how Desmophyllum pertusum corals respond to toxic chemicals exposed in the water column. This knowledge can be useful in future management of both natural environments and aquacultural activity along the coast.