In order to meet the demands for salmon, many salmon farms have developed along the coasts of Scandinavia and Scotland. These operations are governed by strict environmental regulations. Farms are required to determine how their fish production is affecting the marine benthic ecosystem. Therefore, they analyse the presence of so-called bioindicator organisms such as crustaceans and worms on the sea floor. This process is time-consuming and expensive.
Researchers at the University of Kaiserslautern together with colleagues from the University of Geneva are developing faster and more efficient methods. They utilize the DNA from microorganisms to characterise changes more precisely that was previously possible. Their studies have been published in the renowned journals Ecological Indicators and Marine Pollution Bulletin.
At more than 1.2 million tonnes annually, Norway is one of the largest salmon producers in the world. These fish are cultivated in large cages off the coast for approximately two years. The feed residues and fish excretions from these operations sink down to the sea floor and may affect the benthic ecosystem: bacteria break down these organic substances in a process that consumes oxygen. As a result, oxygen levels can drop low enough that most larger benthic organisms such as many worms, crustaceans or sea urchins are not able to survive these low-oxygen conditions.
For this reason, environmental authorities have imposed strict regulations for salmon farms. “Water exchange from ocean currents must be sufficient to supply the fish with oxygen and carry away as much as possible of the organic waste,” notes Professor Dr. Thorsten Stoeck, an ecologist at the University of Kaiserslautern. “Moreover, environmental regulations allow only significant environmental impacts immediately beneath the fish cages. Within very short distance from the farm the environment needs to recover.”