Feeding and production of the carnivorous copepod Pareuchaeta norvegica in the Skagerrak

The vertical and horizontal distribution of the carnivorous copepod Pareuchaeta norvegica Boeck and its potential prey were analysed in the Skagerrak during spring 1999 and autumn 2000. Feeding by P. norvegica was assessed by measuring egestion of faecal pellets. Pellet production at night was significantly higher than during the day. Feeding rates for females ranged from 1.4 to 5.2 prey d(-1) in the spring and from 6.2 to 8.6 prey d(-1) in the autumn. Feeding rates for juveniles were higher in both seasons. Peak spermatophore attachment and fertilisation occurred during spring when the proportion of males was also highest. The weight-specific egg production rate was estimated by the egg ratio method and ranged from 0.31 to 0.73% d(-1) in the spring and from 0.42 and 0.66% d(-1) in the autumn; no significant difference between seasons was found. The number and the total volume of the eggs were positively correlated to prosome length of the females. The population of F norvegica ingested 2.0 to 4.6% of the spring copepod population daily and 2.4 to 6.5% of the autumn population. The predation impact of F norvegica was equivalent to 6 to 14 and 9 to 16% of the copepod population production in spring and autumn, respectively, illustrating the importance of this species in the Skagerrak pelagic ecosystem. Compared with the other important invertebrate predators, the chaetognaths, the impact of R norvegica was 10 to 100 times higher in both seasons.