Sagitta setosa predation on Calanus helgolandicus in the English Channel

Abstract

We used a long-term monitoring data set at station L4 (1988-2004), Western English Channel, to assess the predation pressure by the chaetognath Sagitta setosa on the copepod Calanus helgolandicus. Maximum abundances of Calanus helgolandicus are correlated with years when Sagitta setosa and the Siphonophore, Muggiae atlantica, abundances are low, between February and June. As a significant correlation does not necessarily imply a prey-predator interaction, we analysed the gut content of S. setosa to investigate the presence or absence of Calanus helgolandicus in the chaetognath diet. Molecular analysis of the gut content of three Sagitta each month during a year shows that C. helgolandicus is present in the diet of S. setosa throughout the year. Estimates of S. setosa minimal predation pressure suggest that up to 19 of the C. helgolandicus population can be removed. Peaks of S. setosa follow peaks of Calanus helgolandicus total egg production. We suggest that S. setosa is an important predator of C. helgolandicus at station L4 and might be an important influence on its population dynamics. © The Author 2010. Published by Oxford University Press. All rights reserved.