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Summer Science Exhibition 2008

How do sharks and crabs sense depth? Crabs in space and out of their depth









The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG


Green crab showing moveable eyestalks housing the compound eye (credit Brian Stewart).

University of Aberdeen

Crabs and sharks are providing useful models for human systems of balance and orientation. Now it is also known they can sense water depth.

‘For many years it was a mystery how crabs and sharks knew their depth in the sea, as they had no gas volume which would change with increased pressure,’ says Peter Fraser, University of Aberdeen. ‘Then I accidentally discovered that crabs used a mechanoreceptor - a receptor that responds to movement rather than chemicals - for sensing the small volume changes caused by a change in water pressure.’ The pressure receptors were also found in the balance systems of sharks.

What is most surprising is the level of sensitivity of these systems with the mechanoreceptors responding to nanometre scale movements. ‘How we make sense of and recognise such tiny nanometre changes at these receptors in a world where movement is constant and on a far grander scale is puzzling,’ says Peter.

One application of the research is in space travel where astronauts exist in a world without gravity. ‘Adverse effects of zero gravity on balance such as misjudgements of distance could be countered by introducing a varying pressure system to the space craft to compensate for reduced stimulation,’ suggests Peter.

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How do sharks and crabs sense depth? Crabs in space and out of their depth The Royal Society, London 6-9 Carlton House Terrace London SW1Y 5AG UK