Ingestion rate estimated from food concentration and predatory role of copepod nauplii in the microbial food web of temperate embayment waters

To quantitatively evaluate the role of copepod nauplii as predators in the microbial food web, the ingestion rate (IR) of copepod nauplii and the food requirement (FR) of microzooplankton were estimated monthly for 3 consecutive years in temperate embayment waters. The IR of dominant copepod nauplii (Acartia spp. nauplii) was estimated from water temperature, individual carbon weight and food concentration and peaked (>0.50 μgC ind(−1) d(−1)) with relatively high food concentration (>57.5 μgC L(−1)). This result suggests that food concentration should be considered to estimate copepod naupliar IR in marine environments, especially where biological conditions fluctuate largely. The comparison of copepod naupliar and microprotozoan FR showed the dominance of naked ciliate FR (77.0–90.2%) during the study period except in spring when comparable values were observed between the FR of naked ciliates (41.6%) and copepod nauplii (33.6%). During spring, transfer efficiency (10.5%) from primary production (PP) to microzooplankton production was lower than in other seasons (16.2–17.1%). This study indicates that copepod nauplii are seasonally important micro-sized predators in the microbial food web of temperate embayment waters and that carbon flow through copepod nauplii is a pathway which inefficiently transfers PP to higher trophic levels.