Young damsels can smell danger!

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Larval damselfishes settling on reefs can smell danger and avoid predators using their noses, according to a paper to be published in a forthcoming issue of the journal Biology Letters.

Nearly all reef fishes hatch out as pelagic larvae that drift in the open seas, arriving at the reef for the first time around the same time that they metamorphose into juveniles.  

During this settlement, the very young fish are very vulnerable to predation, and it makes sense for them to settle in predator-free environments.  

As the most likely mode of detecting predators is through olfaction (smell), Alexander Vail and Mark McCormick conducted a field experiment to determine whether damselfish (Pomacentridae) use their noses to sniff out trouble and avoid reef patches manipulated to emit predator odour.

The authors constructed 30 patch reefs and treated groups of five patch reefs with one of five possible treatments:

  • bare controls, in which the reefs were untouched;
  • empty stimulus emission devices (SEDs), which were white cylindrical plastic containers with opaque mesh ends that did not allow its inhabitant to be seen, but which allowed its scent to be dispersed;
  • a single large herbivorous fish in the SED (the Brown surgeonfish Acanthurus nigrofuscus);
  • a single predator in the SED (the Freckled hind Cephalopholis microprion) fed squid and
  • a single predator in the SED (the Freckled hind Cephalopholis microprion) fed young damselfish. The authors used two predator diet treatments because previous studies have shown that chemical alarm cues from conspecifics in a predator’s faeces can elicit a heightened reaction to the predator’s odour.

The results of the experiment showed that the reef patches subjected to the two predator treatments attracted significantly fewer young damselfish (the authors scored for the presence of the Blue-scribbled damselfish, Pomacentrus nagasakiensis, the Ambon damselfish, Pomacentrus amboinensis, and all other species).  

This provides strong evidence that settling damselfish use smell to recognise and avoid predators in the wild.  

This ability to discriminate predators from smell is believed to be innate, according to the authors.

For more information, see the paper: Vail, AL and ML McCormick (2011) Metamorphosing reef fishes avoid predator scent when choosing a home. Biology Letters doi:10.1098/rsbl.2011.0380

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