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Free keywords:
δ¹³C; δ¹⁵N; trophic position; competition; plankton
Abstract:
Feeding studies have suggested interspecific differences in the food sources and trophic position of cyclopoid copepod species. We measured δ¹³C and δ¹⁵N of five sympatric cyclopoid copepod species and of bulk POM from a eutrophic lake over a one-year period, to determine if stable isotope derived-data from the field supported the hypotheses from feeding studies. Cyclops abyssorum and C. vicinus differed significantly in δ¹⁵N but not in δ¹³C, inferring assimilation from similar carbon sources but differentiation in their trophic position. Cyclops abyssorum δ¹⁵N typically was 1-2% higher than C. vicinus, suggesting a more predatory feeding mode compared to its congener. The summer species Mesocyclops leuckarti, Thermocyclops oithonoides and Diacyclops bicuspidatus exhibited considerable differences in δ¹³C. The lower δ¹³C of the hypolimnetic D. bicuspidatus compared to the two epilimnetic species indicates a food niche differentiation by vertical separation. All copepod δ¹³C and δ¹⁵N signatures showed seasonal fluctuations, with low values in winter and high values in summer. The δ¹³C of seston was generally higher than copepod δ¹³C. We regard selective feeding from the bulk POM, spatial separation of feeding and assimilation of ¹³C depleted food sources responsible for this phenomenon.
