Why the seahorse wins by a head

Close examination of the seahorse has shown that the cute little fish is a master of stealth, using streamlined features in its head to sneak up on its prey, scientists reported on Tuesday.

At first glance, the seahorse is an unlikely candidate for hunter of the year.

Swimming vertically, its tail curled, it progresses through coral reefs and shallow beds of seagrass thanks to a little dorsal fin that flutters three dozen times per second.

Its top speed is no more than 150 cms (five feet) an hour, a pace politely described as dignified.

By this yardstick, the species should not give planktonic copepods any sleepless nights. These are tiny crustaceans that are super-attuned to any water movement caused by an advancing predator.

The critters can move at super-speed, reacting to a peril within as little as two thousandths of a second.

They can propel themselves away at the speed of than 500 body lengths per second -- the rough equivalent of a human clearing 10 football fields in a single leap.

Given these challenges, how is the ponderous seahorse able to eat?

The answer, according to a study published in the journal Nature Communications, lies in the extraordinarily hydrodynamic -- the watery equivalent of aerodynamic -- shape of its head.

With a long snout and sleek cheekbones, the organ offers minimal resistance to water, which enables the seahorse to ever-so-slowly sidle up on a copepod without being detected.

Once it gets within about 1mm (0.04 of an inch) of its target, the seahorse strikes, using a system of elastic-like tendons in its neck to drive its head forward, covering the distance in less than one thousandth of a second.

Laboratory tests using 3D holographic video found that dwarf seahorses (Hippocampus zosterae) were 84 per cent successful at getting within range of a copepod without triggering an escape response.

Once they were in the 1mm strike zone, they were 94 per cent successful in grabbing their prey.

The study, led by Brad Gemmell at the University of Texas at Austin, suggests that these insights could have applications in industry, when manufacturing processes need hydrodynamic microstructures that can be immersed into a fluid yet not disturb it.


 

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