Evidence for resource partitioning by ontogeny and species in calanoid copepods

Abstract

In marine ecosystems, copepods provide an important link between primary producers and secondary consumers. However, resource partitioning in copepods within the water column remains unknown. We investigated inter- and intraspecific differences in resource utilization and feeding migration ranges among five species of filter-feeding copepods: Calanus sinicus, Mesocalanus tenuicornis, Metridia pacifica, Neocalanus cristatus, and N. plumchrus, within the epipelagic zone (0–200 m depth) in the East Sea (Japan Sea) during autumn using stable isotope analysis. In the study region, the numerical abundances of these copepods accounted for over 87% of the total number of copepods. Trophic relationships between these copepods and the vertical profiles of three types of cell-size-fractionated organic matter (POM) including pico- (<2 μm), nano- (2–20 μm), and micro-POM (20–200 μm) indicated inter- and intraspecific differences in prey-size preference and feeding migration range. The prey-size preferences of copepods appeared to be closely related to their body size. Moreover, the feeding migration ranges of C. sinicus, M. tenuicornis, and N. cristatus were confined to the surface layer during the developmental progression of copepodid stages, whereas those of M. pacifica and N. plumchrus extended from the surface to deeper layers. Therefore, we suggest that coexistence of these copepods is determined primarily by size-dependent prey-size preference, and inter- and intraspecific differences in the patterns of feeding migration.