Trophic position of Calanus finmarchicus (Copepoda, Calanoida) in the Trondheim Fjord

The trophic position of Calanus finmarchicus in the Trondheim Fjord in 2004 was determined through stable isotope analyses. Wild specimens were sampled monthly in the fjord and δ13C and δ15N signatures of the developmental stages from CIII to adults were measured. There were statistically significant differences in the δ13C and δ15N signatures of three identified groups: overwintered parental generation, developing new generation and new generation preparing for overwintering. C. finmarchicus individuals raised in a laboratory on a pure algal diet (Dunaliella tertiolecta and Isochrysis galbana) provided stable isotope signatures for purely herbivorous copepods. With these signatures as comparison, the trophic position of C. finmarchicus in the Trondheim Fjord in 2004 was determined as trophic level 2.4, thus indicating omnivory under natural conditions. Additionally, our data suggest that seasonal differences in the δ13C signatures of C. finmarchicus are due to the varying lipid content of the different developmental stages.