From a radiation protection perspective, 14C is an important radionuclide as it is one of the major contributors to effective dose commitments to man. One of the anthropogenic sources of 14C originates from nuclear power plants. Therefore it may be found enriched, via photosynthesis, in living species in the surroundings of a nuclear power plant. In an environmental surveillance program it is thus of interest to determine the 14C concentrations in terrestrial and marine biota to monitor plausible enrichment of anthropogenic 14C originating from release from nuclear power plants. In order to set up a cost-efficient method for the determination of 14C activity concentration in marine biota in the surroundings of a nuclear power plant, a method has been implemented and validated for the determination of 14C in bladder wrack, blue mussels and fish using liquid scintillation counting (LSC) as measurement technique. A pilot study of the determination of 14C in seawater has also been performed. For the determination of 14C in biota, a dried, homogenised sample was combusted at temperatures up to 900°C during five hours, and the carbon dioxide produced during the process was collected and later measured with respect to 14C using LSC. The presented method gave a chemical yield of 81.5(1.2) % for samples containing up to 0.5 g carbon. Samples containing 14C in the range of 18-10 000 Bq per kg dry sample weight can be determined, and an expanded uncertainty of 10 % (k=2) at activity concentrations at about 230 Bq/kg C can be achieved. It was found that most likely any organic matrix could be analysed with this method as long as the total carbon content would be kept to a maximum of 0.5 g per sample. In this work 14C activity concentrations in bladder wrack, blue mussel and fish samples collected during an annual cycle are presented. The pilot study for the determination of 14C in seawater led to the design of a plausible method that can be tested and validated in the future.