Trophic links between blue whiting (Micromesistius poutassou) larvae and the winter planktonic community in the NW Mediterranean Sea

Abstract

We assessed the trophic ecology of blue whiting larvae in the NW Mediterranean by means of stomach content analyses in relation to their planktonic trophic environment. The trophic position of blue whiting larvae and that of the main taxa of the planktonic community was estimated by means of stable isotope analyses. Larvae and zooplankton were sampled in 2 oceanographic cruises conducted in the winters of 2017 and 2018. Blue whiting larvae showed a marked diel feeding pattern and high feeding incidence (~90%). Throughout ontogeny, dietary changes were observed in the taxonomic composition, size and number of ingested prey. The smallest larvae fed on small prey, Tintinnina and nauplii, shifting to larger more energetic prey, Calanoida copepods, as development progressed. From the flexion stage onwards, larvae showed a positive selection for Calanoida, and no major switch in prey size or type was observed due to the scarcity of larger prey in the field. This limitation forced the larger larvae to increase the number of ingested prey (reaching >300 prey larva-1) to meet their energetic demands. In line with the observed shifts in diet, larvae showed an increase in δ13C and δ15N values throughout development. The trophic position estimates of the planktonic taxa shed light on the trophic structure of the planktonic community, identifying blue whiting larvae as a primary carnivore. Overall, the results suggest that blue whiting larvae feed efficiently in the Mediterranean trophic environment.