The interactions between bed structure of Mytilus edulis L. and the predator Asterias rubens L

The feeding behaviour of asteroids is usually analyzed with optimal foraging models, which assume that asteroids maximize the ratio of energy uptake relative to energy used in the feeding process. The behaviour of Asterias rubens feeding at subtidal beds of Mytilus edulis was studied in order to evaluate effects of mussel bed structure on predation rate and size selection of prey. Field observations showed that Asterias feeds on mussels whose size were the same or larger than the mean size for the population. The solid structure of interconnected mussels forming the bed restricts Asterias predation to only those mussels situated at the bed surface. A field experiment demonstrated that Asterias consumption rate of mussels was higher at beds with an intact structure of mussels compared to beds where the bands interconnecting the mussels were broken and mussel orientations changed. A laboratory experiment revealed that attachment of mussels did not affect starfish predation rates and indicated that change in orientation of mussels may reduce predation rates. In field and laboratory experiments, increased attachment of mussels was observed when exposed to Asterias. The study demonstrated that the feeding behaviour of Asterias is restricted by the complex structure of interconnected mussels in beds, which has to be integrated in optimal foraging models. (C) 1998 Elsevier Science B.V. All rights reserved.