Seasonal changes in growth and composition of the kelp Saccharina latissima cultivated in salmon-driven IMTA
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- Institutt for biologi 
The primary objective of this Master s thesis was to study the growth and biochemical composition of Saccharina latissima in salmon-driven IMTA. The differences in the seasonal changes in growth and composition between kelp cultivated in the immediate vicinity of a salmon farm and at stations along a transect away from the farm were therefore investigated from February to September 2013. This transect included one station in an empty fish cage close to the farm (100 meters away), one station 200 meters away from the farm, and two reference stations one kilometer away. Whether the dissolved inorganic nutrients released from the salmon farm could be efficiently accumulated into seaweed growth and biomass was investigated by analyzing the content and isotopic signatures of nitrogen and carbon. In addition to analysis of the assimilation and depth dependency of commercially interesting carbohydrates in the field study, an initial methodological study of the stability of carbohydrates was also conducted in order to evaluate the importance of storage temperature prior to analysis. The growth and biochemical composition of S. latissima varied considerably throughout the season, and showed large differences between the kelp cultivated closest to the salmon farm and the kelp cultivated at the reference stations. As a result of the increased concentration of dissolved inorganic nitrogen around the salmon farm, the kelp cultivated there had a significantly higher growth rate and length compared to the other stations, as well as an increased content of nitrogen and a lower content of carbon. In spring with low nitrogen availability, the isotopic values of nitrogen in the kelp grown at the farm and 200 meter station were similar to the signatures of the salmon faeces, while the values of the kelp at the reference stations were similar to that of the ambient seston in the seawater. This difference was not seen in late summer as other mechanisms regulate the nitrogen isotope values during periods of high nitrogen availability. There was an apparent gradation in the possibility of exploitation of salmon farm effluents with the station at the farm benefiting most from the increased availability of nutrients, followed by the station 200 meters away from the farm, while there was no influence on the reference stations one kilometre away.