Hard of her­ring? Not us crabs

The Star Malaysia - Star2 - - SCIENCE -

CRABS have a sort of in­ner ear that helps them to hear nearby preda­tors, US sci­en­tists have found. An or­gan called the sta­to­cyst, pre­vi­ously shown to play a role in crus­tacean bal­ance, is also used for the crab equiv­a­lent of hear­ing, they re­ported last week in the Bri­tish jour­nal Pro­ceed­ings Of The Royal So­ci­ety B.

Bi­ol­o­gists at North­east­ern Univer­sity in Mas­sachusetts con­ducted lab ex­per­i­ments on mud crabs – small crus­taceans found in reefs in the Gulf of Mex­ico – to see how they re­sponded to un­der­wa­ter sounds.

The team placed a thin sen­sor un­der the crab’s shell to mea­sure elec­tri­cal ac­tiv­ity in the sta­to­cyst.

They then placed the crabs in a tank and played record­ings of for­ag­ing sounds made by three preda­tor fish species – the hard­head cat­fish, black drum and oys­ter toad­fish.

They found that the crabs abruptly stopped hunt­ing for clams, a be­hav­iour that is a pre­lude to scur­ry­ing for shel­ter, when­ever they heard the sounds from the cat­fish and toad­fish. They were far less both­ered by the acous­tics of the black drum, a fish whose loud for­ag­ing noise can be heard from afar and thus may not present an im­me­di­ate threat.

The team ruled out vi­bra­tions or pres­sure dif­fer­ences as the stim­uli to which the crabs re­acted. The an­i­mals “can de­tect sound across a range of fre­quen­cies,” they con­cluded. — AFP

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