Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Posts from the ‘Crabs’ category

Decorator Crabs! The best-dressed in the NE Pacific Ocean.

Are you ready? I’ve been collecting these photos for a long time. Now, finally, I think I have enough to deliver this marine fashion show to you – the best dressed of the NE Pacific Ocean!

Decorator crabs are camo-crabs. They pluck bits of life from their surroundings and attach it to themselves. AND, if their surroundings change, they change their outfit.

Graceful Decorator Crab covered with hydroids including the “Raspberry Hydroid” which was only recognized as a new species in 2013 and is only known to live near Telegraph Cove (Weynton Pass) and Quadra Island (Discovery Passage). ©Jackie Hildering.

This is highly functional fashion. Not only does this covering of life allow the crabs to hide from potential predators, it also apparently changes the way the crabs feel and taste in a way that deters their predators. Sponges taste bad or are even toxic to many predators and animals like hydroids and other “cnidarians” have stinging cells. Thereby, if you cover yourself with sponges or cnidarians, predators be gone!

Graceful Decorator Crab adorned with “Strawberry Anemones” (not actually an anemone species but a “corallimorph”. ©2017 Jackie Hildering.

Indeed, even though decorator crab species look like walking gardens, often what they attach are not algae but other animals – hydroids, sponges and bryozoans.

Additional bonuses of carrying other organisms on your back may be:

  • You have potential snacks within a pincher’s reach.
  • Your camouflage allows you to get closer to your prey.
  • You are carrying weapons!

From A Snail’s Odyssey: “Apart from passive camouflage from potential predators, other functions of the behaviour may include disguise for closer approach to prey, and provision of tools for active defense, such as a branches of hydroids containing functional stinging cells or pieces of sponges or tunicates containing toxic chemicals.”

Graceful Decorator Crab with snippets of sponge attached to his/her carapace (Hooded Nudibranchs in the background). This individual realized it had been seen and switched to the defence strategy of looking big since “so many fish predators are limited by the size of their mouths” (Source: Crabs and Shrimps of the Pacific Coast); ©Jackie Hildering.

Note too that not all growth on the back of crabs is the result of decorating and remember that crabs moult, crawling out the back of their shells in order to grow. Also from A Snail’s Odyssey:  “In some cases these camouflagings result from settlement of spores and larvae . . . . Passive buildup of growths is greater with increasing age as moulting frequency decreases.  Also, in many species there is a final or terminal moult which, if the species’ exoskeleton is receptive to settlement of larvae and spores, leads to an even greater build-up of cover.”

Graceful Decorator Crab adorned with (and atop of) Glove Sponge. ©Jackie Hildering.

“Spider crab” (superfamily Majoidea) species are the ones that most often adorn themselves. From Greg Jensen‘s Crabs and Shrimps of the Pacific Coast: “Many spider crabs . . . mask themselves with algae or encrusting organisms so that they can hide in plain sight. The decorator crabs are equipped with curved setae much like the hook part of Velcro fasteners: after shredding material a bit with their mandibles, they press it into place. The largest species tend to stop actively decorating once they outgrow most of their predators.”

Crab predators include the Giant Pacific Octopus and fish species like Cabezon, some rockfish, Surfperch, Wolf Eel and the Staghorn Sculpin. Of course, at low tide, birds and mammals are also predators.

Hoping this adds to the wonder, connection and respect for our marine neighbours. Enjoy the rest of the show!

[For research on decorator crabs with great diagrams explaining how how attachment occurs see this link.]

Well that’s unique! Decorated with Sea Vases (species of tunicate). ©2017 Jackie Hildering.

Try not to smile!

Another Graceful Kelp Crab adorned with Raspberry Hydroids.

Here you can even see where the Graceful Decorator Crab has clipped off bits of sponge. AND s/he’s in the act of attaching clippings. ©Jackie Hildering.

Longhorn Decorator Crab. ©Jackie Hildering.

Heart Crab (I THINK) – not likely to have decorated itself but rather this is the result of the settlement and accumulation of organisms = a walking ecosystem. ©Jackie Hildering.

Graceful Kelp Crab with adornment of Sea Lettuce. ©Jackie Hildering

Graceful Decorator Crab in front of a Painted Sea Star. S/he had just moved from being camouflaged among kelp to moving in front of the sea star. ©Jackie Hildering.

This Graceful Decorator Crab has adorned him/herself with bits of Barnacle Nudibranch egg masses for camouflage. You can see the egg masses behind the crab.

Decorator crab species in the NE Pacific include:

  • Graceful Decorator Crab – Oregonia gracilis
  • Graceful Kelp Crab – Pugettia gracilis 
  • Longhorn Decorator Crab – Chorilia longipes
  • Other species too will sometimes put a bit of camouflage on their rostrum e.g. Northern Kelp Crab – Pugettia producta

Challenge – Find the Crab!

 

 

Typical shape of members of the kelp crab family. Species in this family are usually from 5 to 9 cm across the carapace.

This week I bring you the “Where’s Waldo?” of the marine invertebrates. There is a decorator crab in each of the images at the link below. But first, here are some clues for you.

Most of the species of crabs that decorate themselves to be masters of camouflage are in the spider crab family (Majidae family – also known as “kelp crabs”).  The image to the right shows you an undecorated kelp crab with the typical long legs and distinctly shaped shell (“carapace”) of this family.

Some crabs only partially camouflage themselves, especially when they are juveniles. Others “plant” so many marine neighbours onto themselves that you can’t tell them apart from their environment until they move.

Although they look like walking gardens, the organisms they attach to the stiff, curved hairs on their legs and backs are algae and animals, not plants. The animals can be soft corals, sponges or unique creatures like “bryozoans” and “hydroids”.

Not only does this covering of life allow the crabs to hide from predators, it also changes the way the crabs feel and taste. For example, sponges taste bad or are even toxic to many predators so, if you cover yourself with sponges, predators be gone! The bonus of carrying other organisms on your back is that you also have a food supply within a pincher’s reach.

It is truly astounding how well the decorator crabs match their immediate surroundings which added another mystery to my list: Is the range of decorator crabs really small so that they always match their background OR do they know to “adjust” their camouflage when they move to an area where they no longer blend in?

I have learned that the latter appears to be the case. Experiments with captive decorator crabs have shown that, if moved to a background that no longer offers camouflage, the crabs will “adjust” their decorations!

Click here to find the decorator crabs in my images or view gallery below.