Decorator Crabs

Hello and welcome to the first article on my blog! It’s exciting to finally have it up and running, to kick things of I would like to tell you a little bit about Decorator crabs.

 

Decorator crabs are Decapods belonging to the superfamily Majoidea, not all of whom are decorators, which also include spider crabs like the Japanese spider, the largest living species of crab. I prefer to talk about decorators as the behaviour which lends them their name is quite fascinating.

 

Decorator_crab_(Oregonia_gracilis)_covered_with_baby_sea_stars
By Minette Layne from Seattle, Washington (Upon thars) [CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

 

Decorator crabs are known through their use of plants and animals as camouflage, they will attach various organisms such as seaweed, sponges, anemones, and have even been seen to use pieces of discarded human clothing! So why would they do this? There are multiple reasons to explain this behaviour. First of all in coral reefs, crabs with sponges or corals attached to them can become almost invisible, providing safety from predators who hunt visually and allowing easier hunting of prey. Another form of protection from predators is provided by the attached organism masking the chemical signature of the crab or, in the case of those which wear sea anemones, protection by the anemones stinging tentacles.

There is also research suggesting that decoration can be useful for slowing their decent when a crab jumps of a ledge escaping from a predator, slowing itself down so it can be pulled away by the ocean current. It may also provide a benefit when dealing with other crabs of the same species. By increasing their apparent size with decorations, it could increase their chances in successfully driving off a competing male for a mate or for a food source.

 

Graceful_Decorator_Crab_(Oregonia_gracilis)
By Ed Bierman from CA, usa (Decorator Crab) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

 

The behaviour of ‘dressing’ in crabs can be quite varied and so can the mechanisms used to attach the organism to the shell. Research on the dressing behaviour of Hyastenus elatus revealed that when some specimens which were camouflaged with small pieces of local seaweed were transferred into a different environment they shed all their original decorations and redressed themselves with local materials in just one night. In some species, a certain thriftiness is displayed. Once they have gone through the process of moulting, when the new shell hardens they will remove the old decoration and apply it to their new shell.

 

By Andrepiazza (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
By Andrepiazza (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

These crabs have a few ways in which they attach such materials to themselves. Stenorhynchus and Inachus will tear off pieces of plant material, likely seaweed, chew it and then rub it on their shells where they posses setae, curved hairs which act like Velcro and keep the camouflage in place. Some crabs can use a glue like secretion to hold their decoration in place, whilst another mechanism used by sponge crabs is to utilise specially adapted legs to hold the sponges in place. These crabs have also been observed to trim down sponges to make a perfect match for their shell.

Decorator crabs can be found in every ocean, from the intertidal up to 2000m deep and perhaps even further beyond, so these fascinating creatures are not just restricted to tropical areas however exotic their behaviour may seem. Here are some videos of these wonderful creatures in their habitat.

2 thoughts on “Decorator Crabs

  1. Hi Jay, thanks for commenting! They really are, the complex behaviour of dressing is really interesting and can be great fun to watch.

Tell me what you think!