Sunday, 3 March 2013

Camouflage crabs I have met ~

Camouflage crabs are charming little creatures, so carefully decked out in just the style and colour of their surroundings as to make their emergence from shelter a complete surprise.  They decorate themselves by gathering up weed and suchlike from their surroundings and attach these to their shells, and having done so blend into their settings to the point of invisibility. 

I've only come across them twice so far, the first time when Rewi brought home a bag of mussels and the second time when I was walking on the beach.  The great value of having made the acquaintance of various life forms is that one then knows them to notice them.  If I hadn't had that first meeting I might not have noticed them on second occasion...

On that day I had been feeling really miserable.  It was late in the afternoon and I decided that a long lonely walk on the deserted beach could be helpful, so off I set, carrying my camera, because you never know what you will come across, and glad to be out of doors by myself.

The tide was going out so there was plenty of hard damp sand to walk on.  It was a bit chilly but very restful:

I didn't feel much like paying attention to anything, but inevitably found my interest caught by a range of shells and other flotsam that the sea had brought in, and gradually I became calmer.  I loved this tangle of seaweed tightly anchored to the mussel which must have been torn loose from its rocky home.  An oyster shell adorns its side.  The oyster shell was empty but the mussel shell was shut tight, so it was still alive.  I tossed it back out into the water where the tide might carry it out to sea again, and continued my walk. 

I walked a long way before it felt like time to turn back.  I admired the green hills that are characteristic of this part of the coast:

 There were quite a few empty crab shells of the common variety:

...but it was not until I examined this small object lying on the wide expanse of wet sand that I found something really interesting.  Since I had come across one of these before I realised right away that it was a camouflage crab...

Isn't it beautiful!  It's handsomely decked-out claws are shielding its face.  I wondered how long it had been since the tide had brought it in, turned it over and left it helpless:

It lay motionless so I assumed it was dead, but gently turned it over none the less:

Hmm, slightly less beautiful, but certainly miraculously clad - all in mussels beard!  And no sooner was it the right way up than it began cautiously to move.  How wonderful - it was alive after all!

A scattering of seagulls were patrolling the beach and would very likely make a meal of this one if they recognised it as food, so I coaxed it into the shelter of an empty but heavily bearded mussel shell that lay nearby - and found that there were two more sheltering underneath it.  They may have been long term tenants of this shell's covering if their camouflage garments were anything to go by.  Something had wrenched the mussel shell from its former home, possibly a fishing boat dredging for other sorts of crabs.  You can see two of the crabs here.  The more exposed one is the one I had just turned the right way up:

Feeling that I had done my share of looking after their welfare I left them under their little wigwam:

I felt much happier from this little encounter and went home with lighter steps.  When I got back and sat at dinner telling Rewi the story I looked out along the beach and suddenly wondered if the tide was still out.  I checked the chart and found that it was within half an hour of turning.  With sudden animation I plucked up my beach shoes, reached for an ice cream container and caught up my car keys - these little creatures have their lodgings in rocky places and on the wide open beach there was no place for them to latch onto or creep underneath; I was going back to the beach to fetch them, then take them to the rocky area further around which I know so well.

I also took gardening gloves so I could handle them easily, and set off at speed.  I didn't have much time.  Would they still be where I had left them or had they already been washed away?  Yes, when I came puffing up, they were still there.  I popped them into the tub and set off once more.  

Around the rocks the tide comes in fast and the rocks there are steep and potentially dangerous.  I didn't have much time and it took me a while to decide which pool would be best, but we made it.  Here are the crabs ready to go.  Aren't they odd looking!  I was delighted with them! 

The first two disappeared into watery crevices with quick, gliding movements just as soon as they got into the water, leaving me no time at all to draw my camera.  The last one was slower, possibly it was the one which I had found on its back and needed recovery time.  Here it is pausing to have its picture taken:

Very gently, I lifted it into the pool.  There it is, slightly up and to the left of centre:

I stood up awkwardly and looked out towards the incoming tide.  Within the hour the waves would be beating in strongly, but for the meantime all was calm - and there was plenty of growth and lots of interesting crevices for the crabs to withdraw into and explore.  It is a lovely spot:

My spirits lifted and I returned home with a happy heart.  These connections with the natural world can be magical - tiny glimpses into and connections with worlds completely different from our own.  I treasure them.  When I think about the crabs now I wonder what they are doing... or what has become of them.

The first time I came across one of these camouflage crabs was when I was empting out the sack in which Rewi had brought home his mussels: right in the bottom of the sack a little knob of seaweed was moving about apparently of its own volition.  Realising it must be a little sea creature I carefully scooped it up and put in a make-shift aquarium: a bowl filled with sea water.  Here it is next to one of the mussels - you can see how tiny it is and how wonderfully disguised.  Note also the presence of the 'Noble' chiton on the side of the mussel!  The crab is quite a lot smaller than the three I have already described.

The crab did a rapid reconnoitre of the bowl and its contents and then hastily took cover underneath the mussel shell.

Here is the same little crab seen from underneath.  To photograph it I placed it on the glass of an old picture frame inside a pen made from the sides of a small cardboard box: 

When it came time to take it back to the beach I looked for a spot around the rocks which was similar in general appearance.  Here it is waiting in its small jar:

I took the photo below immediately after I released it but cannot now see where it is, so the camouflage worked perfectly!

Further information can be found on the website of Otago University's Aquarium Guide:
These are also called Masking or Decorator crabs.  Their scientific name is Leptomithrax longipes and their Maori name is Papaka Huna.

There seem to be plenty of them as the site mentions that...
Pots set in the Otago Harbour have been known to collect more than 100 camouflage crabs in a single catch.  There are several species of crab which camouflage themselves.
In going back to this site I looked for the source of the further quote below.  I was unable to do so, so hope it is allowable to publish it here without acknowledging whatever source it has come from.  If anyone knows it please let me know.  The information about the decoration and moulting process is very interesting:
These crabs plant their camouflage deliberately, cutting branches of algae and sessile animals such as sponge with their claws.  They then rub these pieces on their shell where tiny hook-like bristles dig in and hold them in place.  Once attached sponge and seaweed will grow!  Some bits need to be replaced from time to time.  The entire covering needs to be replaced of course after moulting making them even more susceptible to being eaten at this vulnerable time.  Research has shown that if the crab is placed in an environment containing man-made cover such as fabrics, the crab will use the synthetic materials.  These crabs are scavengers.
As mentioned above, once one knows what one is looking at all kinds of things become noticeable: I had already taken photos of these shells without realising quite what sort of creature they would have come from.  Yes, now it's obvious: they are from camouflage crabs, due either to moulting or death:

And here is its under-side.  How delicate it is and how perfectly suited to its purpose!

Other articles about my explorations of the beach and rocky shore can be found via the link below:

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