The Elements of Evolution (49-10-5) Shore Crabs

 Shore Crabs

Common British shore crabs in the same species (Carcinus maenas) carefully camouflage themselves using distinct stratagems. Whereas crabs in mudflats look like mud, those in rock pools rely on disruptive coloration: high-contrast patterns which break up body outline appearance.

The crabs are highly variable in colour and pattern, and are often extremely difficult to see. Rock pool individuals have high levels of disruption. This is an effective way to disguise the body’s outline in the complex rock pool backgrounds where matching the colour of the environment is often not possible. In contrast, mudflat crabs closely match the mud in terms of colour, brightness, and pattern but lack high-contrast disruptive markings that might give them away in the uniform mudflat environment. ~  Martin Stevens

Such specific camouflage is exemplary of adaptation as a teleological exercise, conducted by localized coherence.