Why slow-and-steady jellyfish beat fish in oceanic contest

By Martin Leggett - 15 Sep 2011 18:0:1 GMT
Why slow-and-steady jellyfish beat fish in oceanic contest

Jellyfish vs fish? In a competition hunting for plankton prey, it seems like a no-brainer. The visually clued- up and faster-moving fish should be an easy winner over the ponderous and blind jellyfish. But new research shows that jellyfish may, in fact, have got things just as well-sussed as their vertebrate competitors. And in oceans where fish numbers are being pushed down worryingly fast, thanks to numerous man-made challenges, that could have big implications. We might be about to welcome in the dawn of the jellyfish era.

The research on the comparative hunting strategies of jellyfish and fish comes from three ecological researchers - two from Spain and one from the UK. It looks at mathematical models of the behavior of over 600 fish and jellyfish species, in order to answer the 'jellyfish vs fish' face-off conundrum. And it seems that the size, swimming speed and energy efficiency of jellyfish have a big part play in answering why jellyfish are winning out, against hard-pressed fish. The work is published tomorrow in the journal Science.

Jellyfish boom: nuclear attack

The increasing dominance of jellyfish, particularly in those parts of the seas where fish numbers have been seriously depleted, has been noted for some time. These are not only causing problems for beach-goers, and nuclear power stations - they are likely to change the whole nature of the ocean's ecosystem, according to some recent research.

But many scientists have wondered why jellyfish have been so successful. If you compare the rates at which prey can be captured, for equal-sized fish and jellyfish, agile. fast fish win hands down. They can hoover up their plankton prey much more quickly than the jellyfish, which rely on a primitive billowing of their bodies to draw plankton onto their tentacles. However, the researchers - led by Jose Acuna of the Universidad de Ovied - realized that this size-based comparison was something of a false one.

Playing field surprisingly level

That's because jellyfish and plankton-eating fish are very different animals. Jellyfish bodies are largely made of water and gelatinous material; their slow wafting swimming style is also very efficient, from a point of view of energy expended; and because they're not reliant on light, jellyfish don't stop feeding all day. When the team rephrased the models to compare prey clearance rates for these factors, the playing field was quickly leveled.

It seems the jellyfish strategy was just as able to deliver success - and growing numbers - as that employed by hyperactive fish. The team was also able to show that the slow cruising speed of most species of jellyfish was exquisitely finely tuned. Going too fast burned up more energy than could be gained through gathering their prey. So jellyfish have slowed things down to the sweet-point that nets the most food, for least effort.

Slow-and-steady might be just what is needed to help jellyfish win the race for dominance, in the world's fast-changing oceans.

Top Image Credit: © LeonardoRC