ATTACK BEHAVIOR AND PREDATORY SUCCESS OF ASTERIAS-RUBENS L RELATED TODIFFERENCES IN SIZE AND MORPHOLOGY OF THE PREY MUSSEL MYTILUS-EDULIS-L

The temporal variation in force application of uni sized Asterias rube ns on mussels of three different sizes was monitored by equipping muss el shells with electronic indicator devices and connecting them to a d ynamometer. Three types of behaviour were observed. On small mussels a short pulse of approximate to 150 s was applied whereas on medium siz ed mussels the pulse exceeded 500 s. On large mussels a short pulse of approximate to 150 s was followed by a change in position to the dors al side of the mussel. Sometimes a pulse was applied from this positio n. The maximum force during a pulse was between 7.6 and 70 N and not c orrelated to size of either mussel or starfish. Asterias seems to be a ble to respond to mussel size and morphology by changing its attack st rategy. If the starfish is not able to open the mussel by a short forc e pulse or by exhaustion, it seems to use a siege strategy and wait ou t its prey. A high variability in mussel morphology was found between and within three different habitats in the North Sea. 70% of Mytilus e dulis of North Sea origin were able to resist the force applied by Ast erias rubens whereas all mussels of Baltic Sea origin were opened with in one hour. Differences in mussel height, muscle size and muscle atta chment were found between surviving and non-surviving mussels. These d ifferences can also be noted between habitats with high versus low pre dation pressure.