When life gives you crabs…

…you put them in a centrifuge!

This past week, we were given free reign during our lab time to conduct our own experiments, and some of the resulting projects were… interesting – to say the least. But more on that later. First, a little about our subjects!

The star of the show.

The star of the show.

On September 17th, we made our way to Tower Beach near UBC and collected several buckets worth of specimens – mostly the green shore crab (Hemigrapsus oregonensis) and the purple shore crab (Hemigrapsus nudus). These little guys are super common underneath rocks and inside all sorts of nooks and crannies in the intertidal zone – which is exactly where we found them. Fast forward two months or so, and you find our class splitting off into pairs to subject these crabs to all sorts of unusual testing.

My group was one of the more tame ones – we decided to test if the crabs would prefer an environment that was more similar in colour to their own colouration, in order to be better camouflaged. To test this, we placed coloured felt (red, green, white, and black) underneath a clear-floored aquarium (in quadrants, with each colour taking up about 25% of the aquarium floor). We then put the crabs in the centre and waited to see where they eventually ended up after allowing them to wander for one minute.

Our set-up.

Our set-up.

We tested in various conditions over successive trials: both wet and dry, crabs placed facing both towards and away from us, etc. – but none of theses factors made much difference. In all conditions, the crabs surprisingly seemed to avoid the coloured area where they would be best camouflaged, but instead tended to go for the white felt. Perhaps the white colour most closely resembled natural sand colour? In any case, it was an interesting result.

This guy digs the green though

This guy digs the green though

But as I said, our experiment was one of more tame ones. Some of the other groups performed tests that were a bit… stranger. For example, one group did a sweet vs salty environment preference (which involved dumping snack foods into the quickly-clouding water), the effects of calm music and loud/annoying/scary/MORDOR music on crabs (spoiler alert: crabs don’t seem to care all that much about what they listen to), and the effects of dizziness on crab behaviour (which involved spinning the little dudes in a ‘centrifuge’ of a plastic test tube suspended in a cup of water for one minute, and then placing them inside of a circle and recording their reactions). Interestingly in the centrifuge experiment, there was a pronounced gender difference – females were more likely to bolt after a good spinning, but tended to stay put when un-spinned. Males had the exact opposite result.

Dizzy-fying crabs.

Dizzy-fying crabs.

All in all it was a very unusual, yet informative lab!


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