Ever Wish You Could Dissapear Into Your Surroundings? Fiddler Crabs Do!

You’re fifteen minutes late to a 35 person class. Right about now you’re probably wishing there was some way to sneak in undetected. Unfortunately for you, no matter how hard you try, you’re going to be conspicuous. Fast forward to the beach. Lucky you, you’re a Fiddler crab. While basking in the sand you can avoid being someone’s lunch. How, you ask? It’s all about camouflage.
As I’m sure you know, there are several benefits to being able to roam a habitat undetected. For the Uca vomeris crab, this carries extra weight. Living on an open mud flat, this species of Fiddler crab is especially vulnerable to attack from birds. Fortunately for them, they have developed chameleon like shells. It has been noted in the past that ordinarily, these shells remain various depths of blue. When the crab feels that it is in danger, its shell morphs into a muted brown.
Jochen Zeil, a researcher at the Australian National University studied the cause of this interesting behavior. Taking two crabs, both of notable bright blue color, he separated them with a screen. The variable subject was bombarded with a foam ball attached to fishing line. This was enough stimuli to make the crab feel threatened and catapult it into survival mode. Soon enough, the crab’s shell had lost its blue brilliance, and turned brown. Upon repeating the trial, the results were duplicated.
This led Zeil to further investigate full colonies of this species of crab. He and his collogues found that entire groups of these crabs were less blue than their geographical neighbors. This led researchers to believe that this coloration is dependant on the ratio of predators in the area. Sure enough, areas that had more birds feeding on the crabs contained the individuals with the least blue coloration.
I think this study was interesting but still leaves many questions unanswered. Is the blue coloration a sign of fitness? Or only a weakness to the owner? How does this behavior compare to other techniques employed by the species to avoid predators? In the future, Zeil plans to study the effect of color in the relation between colonies of Uca vomeris.

Posted by JLB (10)