Feeding of the chaetognaths Sagitta elegans and Sagitta setosa at different seasons in Gullmarsfjorden, Sweden

Die1 feeding regimes of Sagitta elegans and S. setosa were investigated by gut content analyses on 24 301 Sagitta, taken in hourly plankton hauls during 24 h sampling programmes at different seasons. Feeding was most intensive at night in both species except for S. elegans in wnter . Diet differed considerably between the specles, S. elegans taking almost only copepods and S. setosa taking small copepods, nauplii, appendicularians and other S. setosa: the dfference is believed to reflect differences in size (the larger S. elegans talung larger prey) and vertical distribution (S. setosa talung smaller prey in the surface layer). The cannibalism of S. setosa, found during the breeding period in autumn, is believed to contribute to the sharp decrease in numbers of S. setosa at that time. Daily feeding rates (in numbers of different prey categones) of S. elegans were estimated by combining gut content analysis with digestion time data obtained in the laboratory at 6°C. Mean digestion time varied from 9.3 to 4.9 h depending on prey category. Total feeding rate varied from 1.0 to 0.2 prey items d-', being highest for the breeding generation in spnng and lowest for the immature generation in autumn and winter. Total feeding rate of S. setosa in autumn was est~mated to be roughly 2.3 items d-l.