Aquaculture and the environment
To meet the demand for salmon, there are many salmon farms on the coasts of Scandinavia and Scotland, among other places. Strict environmental regulations apply to them. The farmers have to check how fish farming affects the ecosystem. To do this, they analyze which animals, such as crabs and worms, are found on the seabed. But this is time-consuming and expensive. Researchers at the Technical University of Kaiserslautern (TUK) are working on a faster and more efficient method. They are using the DNA of microorganisms. This allows changes to be characterized more precisely than was previously the case. The study was published in the renowned scientific journal "Ecological Indicators".
Every German eats around 14 kilograms of fish on average per year - with salmon being particularly common. With more than 1.2 million tons annually, Norway is one of the largest salmon producers in the world. The fish are reared in large cages off the coast for around two years. Feed residues and excrement from the fish affect the ecosystem in the water and on the seabed: Bacteria break down these substances and consume oxygen in the process. As a result, the oxygen content can drop to such an extent that many animals such as worms, crabs and sea urchins die.
This is why the environmental authorities have imposed strict conditions on salmon farms. "The water exchange through ocean currents must be large enough to supply the fish with oxygen and remove as much waste material as possible," says Professor Dr. Thorsten Stoeck, who researches ecology at TUK. "There should also only be massive changes to the ecosystem directly below the farms."
To check how the flora and fauna on the seabed are changing, the farmers have to take samples from the seabed. "Based on the creatures present, you can see how healthy the seabed is, for example. The animals serve as indicators," continues the professor. However, this process is expensive and very time-consuming; it often takes up to six months before results are available. Too long to take action if the ecosystem is under too much pressure.
Stoeck and his team are currently developing a simple, faster and more cost-effective method in their laboratory on the Kaiserslautern campus. The researchers obtain samples from the farms and isolate microorganisms, for example ciliates. The scientists use their DNA for their method. "Their genetic material is like a fingerprint that can only be assigned to one person," says the ecologist. "Results are available after around a week." With the help of the little animals, it is also possible to make a more precise statement about the degree of pollution than is the case with the conventional method. "Many crustaceans and worms die when the oxygen concentration in the water drops," says Stoeck. "Microbes are much more resistant here. They cope better with pollution and contaminants and adapt more quickly to changing conditions."
The aim of the project is to create a database in which DNA fingerprints of the various microorganisms are stored. "We will use this to create so-called DNA barcodes, similar to the barcodes for food in the supermarket," continues Stoeck, who will take sediment samples from various fish farms around the world with his team. "These will allow the farmers to quickly identify the health of the ecosystem."
In the long term, farmers could, for example, use a DNA chip to analyze the sediment samples directly on site. The displayed barcode would then provide them with timely information about the condition of the sea. This would also enable the farmers to react more quickly to problems. At present, they only examine the prevailing environmental conditions before the fish are placed in the cages and after they have been "harvested".
The project is funded by the German Research Foundation. The Kaiserslautern researchers are working closely with colleagues from the University of Geneva as well as Norwegian and Scottish salmon farms. The results of their work have now been published in the study "Metabarcording of benthic ciliate communities shows high potential for environmental monitoring in salmon aquaculture" in the renowned journal "Ecological Indicators".