The ‘decorator’ crab – eccentric fashionistas

‘Decorator’ crabs are members of the spider crab family (superfamily Majoidea) and come in all shapes and sizes, each with their own unique sense of style. The majority of ‘decorator’ crabs are recent graduates, clinging on to the dream of when it was acceptable to walk about in a hilarious onesie plastered in rave paint. Just messing, crabs don’t go to university. They are known as ‘decorator’ or ‘masking’ crabs due to their penchant for picking up and adorning themselves in materials from their surrounding environment. By creating a mask of marine growth the crabs conceal themselves from any potential predators. So, essentially, these crabs uproot sessile invertebrates such as coral polyps, sponges and sea anemones without even buying them breakfast first. However, these organisms seem pretty mellow about the whole exploitation thing and carry on growing like normal on the crab’s body or ‘carapace’. Some ‘decorator’ species even go all art attack on the situation, secreting a PVH-like gluey substance on their backs. They then grab poisonous seaweed and slap it on, turning their shell into a slightly sadistic scrapbook. However, this method of camouflage can have its drawbacks; especially when your items of choice actually weld themselves onto you, and you end up looking like this mug with a sponge for a lid.

decorator crab drawing

‘Decorator’ species have hooked setae (posh word for a bristly hair) on their carapace and legs that act as velcro, enabling items to be affixed to them. In some cases the crabs have adapted legs that allow items such as large sponges to be held in place. This avoids any toupees inadvertently sliding off. Like most aspiring fashionistas, a keen eye for detail is crucial for success. A pair of scissors is never far away, and the crabs use these and their mouth to fray material for added flair if necessary. Their real runway potential shows when optional extras are added to the situation (obviously by humans, because who doesn’t want to see a crab suit up). Have a look at this in-no-way-set-up video of ‘decorator’ crabs making themselves look pretty;

They also seem to go through quite a thought process in selecting their materials, picking up and dropping several items before selecting the perfect accessory. The large front claws known as ‘chelae’ are used to snip materials to quite a precise size, suggesting the crabs know what materials are already attached, and where. Some species of ‘decorator’ crabs such as Notomithrax ursus will affix algae on their back for dual use as camouflage and a food source when other resources are low. Imagine if you had infinite snacks growing on your back; not so silly now, are they. Remarkably these crabs won’t shell out (apologies) for a new outfit when they shed their exoskeletons. Instead they pick off their cherished accessories and kit out their new skin. Their process of shedding is actually quite a fascinating process; once they shed, their soft exoskeleton underneath absorbs water and expands, which is how they grow. This then hardens (a bit like how we regrow a nail) and becomes the new shell. Neat. So whilst a decorator crab’s neighbourhood might be likened to the edgy end of the red light district, remember that they have a few tricks up their tailored sleeves.

References

Cruz-Rivera, E. (2001). Generality and specificity in the feeding and decoration preferences of three Mediterranean crabs. Journal of Experimental Marine Biology and Ecology266(1), 17-31.

Kilar, J. A., & Lou, R. M. (1984). Ecological and behavioral studies of the decorator crab,< i> Microphrys bicornutus</i> Latreille (Decapoda: Brachyura): A test of optimum foraging theory. Journal of experimental marine biology and ecology74(2), 157-167.

Kilar, J. A., & Lou, R. M. (1986). The subtleties of camouflage and dietary preference of the decorator crab,< i> Microphrys bicornutus</i> Latreille (Decapoda: Brachyura). Journal of experimental marine biology and ecology,101(1), 143-160.

Stachowicz, J. J., & Hay, M. E. (2000). Geographic variation in camouflage specialization by a decorator crab. The American Naturalist156(1), 59-71.

Wicksten, M. K. (1980). Decorator crabs. Scientific American242, 146-154.

Wicksten, M. K. (1993). A review and a model of decorating behavior in spider crabs (Decapoda, Brachyura, Majidae). Crustaceana, 314-325.

Woods, C. M., & McLay, C. L. (1994). Use of camouflage materials as a food store by the spider crab Notomithrax ursus (Brachyura: Majidae). New Zealand journal of marine and freshwater research28(1), 97-104.

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