Scientists at the University of Exeter have discovered that crabs of the same species do not always use the same camouflage techniques. The study revealed that the color patterns used by common shore crabs living in rock pools are distinctively different from patterns used by those living on mudflats.
Shore crabs are the most abundant crabs along the coast of Britain. The study was focused on crabs from six different sites in Cornwall.
The researchers found that the common shore crab, Carcinus maenas, closely resembled the natural surroundings when it lived on mud. The rockpool shore crab, however, was found to rely on a type of camouflage known as disruptive coloration, which uses high-contrast patterns to break up the appearance of an animal’s silhouette.
“The crabs are highly variable in color and pattern, and are often extremely difficult to see,” explained study co-author Professor Martin Stevens. “We used image analysis simulating predator (bird and fish) vision to test how shore crabs camouflage themselves.”
“As we predicted, rock pool individuals had significantly higher levels of disruption, and this seems an effective way to disguise the body’s outline in the complex rock pool backgrounds where matching the color of the environment is often not possible.”
“In contrast, mudflat crabs closely matched the mud in terms of color, brightness, and pattern but lacked high-contrast disruptive markings that might give them away in the uniform mudflat environment.”
Most of the research that has examined the use of background matching or disruptive coloration has been conducted in artificial systems. The current study, however, has investigated these strategies in natural settings.
“Shore crabs are often assumed to be dull and green, but in fact they can be extremely colorful and every individual can look completely different. Our study goes part of the way to explaining why shore crabs are so diverse,” said Professor Stevens.
The study is published in the journal Scientific Reports.
Image Credit: Martin Stevens