Copepods take to the air to avoid predators

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The notion that zooplankton just sit around waiting to be eaten has been dismissed as a recent study has found that some zooplankton leap out of the water to escape predators – and there's a video to prove it!

In a paper to be published in a forthcoming issue of the Proceedings of the Royal Society B, Brad Gemmell and co-authors found that some copepods in the family Pontellidae achieve flight distances of many times their body lengths as they jump out of the water to avoid predators.

Although many copepods are known to avoid fish predators by powerful escape jumps, it has long been thought that they limit their escape response within the liquid medium and never break the water surface to do so.

By using video recordings in the field and high-speed video in the laboratory, the authors demonstrate that aerial jumps provide an effective escape mechanism in response to visual fish predators for two species of copepods (Anomalocera ornata and Labidocera aestiva).

By analysing the videos, the authors found that the copepods lost anywhere from 58-88% of the energy from their escape reflex to overcome surface tension of the water as they break its surface (flying fish by contrast lose only 0.07% of this energy doing so).

However, once in the air, the copepods fly much further than larger organisms relative to its body length (up to 60 times), because of the much lower air resistance they encounter.

Because the copepods travel so far, they recoup more energy flying through the air than they lose leaving it.

The escape response is very effective, too. In the 89 instances the authors observed, only one fish managed to target the same copepod when it landed back in the water.

For more information, see the paper: Gemmell, BJ, H-S Jiang, JR Strickler and EJ Buskey (2012) Plankton reach new heights in effort to avoid predators. Proceedings of the Royal Society B: Biological Sciences, doi:10.1098/rspb.2012.0163.

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