MEPS 327:247-255 (2006)  -  doi:10.3354/meps327247

ABSTRACT: Cannibalism has been assumed to strongly affect population dynamics of the calanoid copepod Calanus spp. during the pre-bloom phase. We hypothesised that Calanus finmarchicus females cannibalise on nauplii until there is enough phytoplankton available to fulfil their energy demands. We tested this experimentally by exposing females to different concentrations of algae Thalassiosira weissflogii (0.08 to 22.58 µg chlorophyll a l^–1) and nauplii (stages NI and NII, 0 to 20 nauplii l^–1). Clearance rates on algae and on nauplii were high (221 and 689 ml ind.^–1 d^–1, respectively), but were independent of algal concentration. Females ingested naupliar carbon at a higher proportion than was available, even when naupliar carbon accounted for <5% of the totally available carbon. Predation rates on nauplii increased linearly and significantly (p < 0.001) with increasing nauplii abundance. Compared with literature values, predation rates were considerably higher (up to 10 nauplii ind.^–1 d^–1) than predation rates of the sibling species C. helgolandicus and C. pacificus on their nauplii, and also higher than predation rates of the omnivorous copepod Metridia lucens on Calanus sp. nauplii. Based on our data, we estimated that as much as 20% d^–1 of the nauplii population may be preyed on by adult females. Thus, during the pre-bloom period when abundance of nauplii is small and that of females is large, cannibalism may prevent recruitment to the G1 population.

KEY WORDS: Calanus · Switching · Feeding · Food · Prey · Preference