The effect of starvation on the size of mussels selected by the Green Shore Crab, Carcinus maenas

Abstract

The foraging behaviour of the green shore crabs, Carcinus maenas, of 24-26mm carapace width was observed over a 6 day starvation period. Edible mussels, Mytilus edulis, for each millimetre interval from 5-25mm were used to determine how prey size selection was effected by starvation. The most profitable mussel size for the studied crab size is approximately 9mm. At low starvation levels mussel size selection was relatively specific with the majority of selected mussels ranging in size from 7-12mm. Increased starvation caused greater variation in size selection with the majority of selected mussels ranging from 7-16mm, with a higher proportion of larger mussels being selected. After 4 days starvation random foraging behaviour and subsequent size selection was exhibited as mean mussel size values were close to the predicted random selection value of 12.5mm. Mussels were selected after progressively fewer encounters as starvation increased and consequently the maximum size of a mussel deemed profitable increased with elevated starvation. The findings are in accordance with the optimal foraging theory, since increased starvation is associated with decreasing encounter rates and low encounter rates cause broadening of a forager’s diet due to the selection of successively less optimal prey.