| Summary: | International audience Thiamine (vitamin B1) is vital for life-sustaining enzymes in cells. Previous studies have reportedepisodes of thiamine deficiency in marine ecosystems, and suggested that this have contributedto population declines of seabirds breeding in the Baltic Sea and elsewhere. Many Norwegianseabird populations have shown a strong decline in population size, but thiamine status hasnever been assessed. The objective of this pilot study was, thus, to document thiamin levels inselected species and their associated food webs, and explore methodological issues relevantfor future studies or monitoring.The methodological tests showed that storage freezing temperature did not affect thiamine levelsin egg yolk samples, and that thiamine levels in eggs could not be corrected for incubation time.Furthermore, the quantified thiamine levels differed between two laboratories, and we developeda predictive equation to convert thiamine levels in egg yolk samples between the laboratories.This pilot study has, for the first time, investigated thiamine levels in seabird eggs from selectedspecies and populations in Norway mainland and Svalbard, and in their food webs. We revealedvariation among species, populations and prey types. The lowest levels were found in eggs fromcommon eiders and in blue mussel which is their prey. Eggs from herring gulls had also relativelylow levels. The levels for common eiders and herring gulls were higher than previously reportedfrom the Baltic Sea. Nevertheless, the levels from common eiders, herring gulls and blue musselsshould be classified as thiamine deficient according to effect-ranges reported in these previousstudies. The highest levels were found in eggs from kittiwakes and Atlantic puffins. The dietsamples from kittiwakes and Atlantic puffins had higher thiamine levels compared to bluemussels. This is the first time thiamine levels are reported for kittiwakes and Atlantic puffins.This pilot-study cannot answer whether Norwegian seabird population sizes are affected bythiamine ...
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