Fiddler Crabs and the Tropical Malaise

Been awhile but finally an adventure worth writing about! We are up in the far north of Aus at the moment helping out with a study on the sexual behaviour of a small species of crabs with one giant yellow claw…

After a serious case of the back in town blues after getting back from the islands and foolishly taking up a 9-5 job for awhile, I have found my feet again and am back on the good foot, with life heading down a good path with enough uncertainty to make it exciting again!

So right now we are up in Darwin, the most northerly and smallest state capital city in Australia. Well, for all you non-Aussies its actually the capital of the Northern Territory, which is not technically a state. Bit different in the way the laws are made and who’s the boss and all that, but lets face it that shits pretty boring.

Interesting how the far north became settled actually. The colonial Brits tried to set up an outpost up here in the 1830s, for a number of reasons, including stopping the French from colonising the North! Unfortunately the soldiers kept dying of various tropical fevers, and it sounds like it was a hellish place. Imagine wearing those old British army uniforms in this heat….

Port Essington in 1845 – from Leichhardt’s “Journal of an Overland Expedition in Australia”

Well, people have got a bit smarter, and now dresses shorts and singlets rule the town. It’s really tropical here, lush vegetation everywhere. We are being put up at the ANU Northern Australian Research Unit, pretty sweet little research facility I must say. This is our place:

Erin and Soph outside 'Malkany' cabin

So anyway, my friends Tim and Soph have been coming here for the last 3 years, studying these little crabs on the mudflats. Now its pretty damn interesting, they are basically looking at the sexual behaviour of the crabs, and whilst the actual deed gets done deep in their underground burrows, there is plenty of showing off, claw-muscle-flexing, flirting, and crab-teasing going on on the surface.

The males have one ridiculously oversized claw, which they wave to attract the females who are less loud looking. Kinda like peacocks 🙂 The little fella below is a good example. When they wave the claws, they are strangely graceful, and look a bit like a violinist which I guess gives them their name. While very few of these claws are longer than 2cm, I have been told they can still give you a mighty nip on the finger! Havent got me yet though…

A Male Fiddler Crab - Uca mjoebergi species

 Each of the fiddlers has a burrow in the mud, which goes down quite deep, up to 20cm below ground. They have to go deep enough to hit the water table under the mud, where the crab sucks up a reserve of water before it ventures outside: they need this water to breathe actually, because they have gills not lungs. As Erin pointed out its kind of like Reverse Crab Scuba.

On the pic above you can see this fellas burrow, his legs are in it on the left. Putting their legs in the lip of the burrow actually reminds the crab where its burrow is: as they scuttle away from it its position is locked in a kind of muscle memory, so that they can reverse their movements and scuttle back VERY quickly when scared. Crabs try occasionally to flip each other off their legs to steal burrows, and if that happens, the flipped crab can’t remember which burrow is his and another one can just take it!

The team here is running a bunch of experiments during the mating seasons. These are aligned with the tides, so that the crabs will mate in time to go underground an incubate their eggs long enough to release them all simultaneously on the next high tide, where they will float out to sea and float around for 2 weeks eating plankton, then float back in to land as tiny Fiddler crabs! They then have special senses that allow them to find a group of adult Fiddlers, and take their place in the cycle of life.

The experiments are basically to do with how and why the crabs select mates to breed with.

The males will go pretty much anything, so as we are probably all familiar with the females do the choosing, and it seems that these choices are mostly based on the waving of the big claws.  The males will all stand up on the surface and wave their claws at passing females. If their claw and wave are right, he will get lucky.

Sophie has had a series of robot crabs made up, that uncannily simulate the wave pattern of the claws. These were actually hand made by a really clever man who made automated christmas decorations, like ho-ho-ing Santas swinging sacks of presents etc. They look a bit rudimentary, but it is amazing to think that all the little parts have been made by hand! The wave rates and patterns are actually controlled by the audio output of an ipod, this plays a track of noises that controls the robo-crab. Inspired thinking if you ask me!

Field Assistant Boss Tim with ROBOCRAB

A row of these suckers will be buried in the sand, each with a different claw size and wave rate. Then we see which one attracts the most ladies! Tim is hoping to translate the results into a testable hypothesis for Friday and Saturday nights…

It is amazing how much life there is around here. All kinds of animals all over the place, birds everywhere, cicada choirs so with so many thousands of members that they hurt your ears! And even these frilled neck lizards. Oh, and for those of you who dont know, there are massive crocodiles in the sea and rivers here this time of year. One was spotted a kilometer from the mudflat where we are working, yesterday…

Frilled Neck Lizard going jogging

Suprise, when I bent to pick up a cool shell it walked...

One of the many lizards, this one about 25cm long

Its a pretty great place to be, but man, do you move slowly here! The temperatures have been around 37 degrees, with humidity up around 70%. Sweat pours off you constantly, and my usual stride has been modified into a persistent shuffle. But the good side effect of this is that everyone is really relaxed and laid back. Not a bad way to be I reckon…

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A bit of the old Tropical Malaise 🙂


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