The sea-star,Asterias rubensL., as predator on the ascidian,Ciona intestinalis(L.), in Borgenfjorden, North-Tröndelag, Norway

Abstract

Ascidians, especially Ciona intestinalis, serve as food for the fishes, Limanda limanda, Pleuronectes platessa, and Gadus morhua in Borgenfjorden. Biomass investigations have provided evidence that large reductions in the biomass of C. intestinalis also resulted from invasions of Asterias rubens. This suggests that this sea-star uses the ascidians as food and thus competes with the fishes for this type of food. Feeding experiments, where C. intestinalis were fed to A. rubens, gave a daily rate of feeding of 22.7% (15.6–29.3%) and an efficiency of conversion of 4.3 (3.5–5.2).