Why do shore crabs not prefer the most profitable mussels?

Area of Science:

• Marine Biology
• Animal Behavior
• Ecology

Background:

• Shore crabs (Carcinus maenas L.) exhibit complex prey selection behaviors.
• Understanding the factors influencing prey size selection is crucial for marine predator-prey dynamics.

Purpose of the Study:

• To investigate the relationship between handling time, feeding techniques, prey profitability, and bivalve prey size selection in shore crabs.
• To determine the constraints influencing prey selection in Carcinus maenas L.

Main Methods:

• Prey size was quantified as the ratio between mussel width and major chela length (MW:MCL).
• Prey profitability was standardized to the ratio between prey mass eaten per unit breaking time and predator mass (1/h Tb).
• Crabs were observed using either a crushing or a cutter feeding technique, with technique switching analyzed against prey size and profitability.

Main Results:

• Shore crabs employed a cutter technique for larger mussels (MW:MCL ratio > 0.24), coinciding with maximal prey profitability.
• When offered a range of prey sizes, crabs selected a smaller MW:MCL ratio (0.14-0.16) than the predicted optimal ratio (0.16-0.22).
• Crabs preferred smaller, crushable mussels (MW:MCL ratio 0.16) over larger, more profitable ones (0.24) in dichotomous choices.

Conclusions:

• Shore crabs prioritize minimizing claw wear and tear by selecting smaller, crushable mussels over larger, more profitable ones.
• The risk of claw damage significantly influences prey selection, potentially overriding energy maximization strategies.
• Claw integrity is critical for mating success and individual fitness in shore crabs, shaping foraging decisions.