MEPS 572:57-76 (2017)  -  DOI: https://doi.org/10.3354/meps12139

ABSTRACT: The ingestion rates of Parvocalanus crassirostris and Bestiolina similis mid-stage (N3 and N4) nauplii feeding on a natural prey assemblage from a subtropical embayment were measured to evaluate differences in prey preferences and estimate the trophic impact of grazing by each species. During the 2 wk period of our experiments, the in situ 2–35 µm cell biomass increased over time and ranged from 45 to 187 µg C l^–1. The 2 studied copepod species overlapped in the range of prey removed; however P. crassirostris nauplii grazed less selectively than nauplii of B. similis, which selected against the 2–5 µm prey size group and increased selection over time for 20–35 µm prey. Total ingestion rates were comparable between the 2 species, and the majority of the grazing impact was due to P. crassirostris, which had a 2- to 11-fold higher in situ naupliar abundance. Grazing impacts by the 2 species combined ranged from 1.0 to 8.7% of the total 2–35 µm prey biomass. Prey removal on individual prey size groups by P. crassirostris ranged from 0.9 to 23.7%, with maximum impacts on prey >10 µm. Daily chlorophyll a removal was up to 12.9% by P. crassirostris, and 5.7% by B. similis. Our results suggest that naupliar ingestion rates and prey selectivity can vary on timescales of 2 to 3 d and differ between 2 closely related species, and also that nauplii can have a significant grazing impact on prey populations, particularly through positive selection for prey size classes that are less abundant.

KEY WORDS: Naupliar grazing · Copepod nauplii · Subtropical plankton · Parvocalanus crassirostris · Bestiolina similis