Ever thought of a seahorse as a ferocious predator? Probably not, but recent research shows that their skills at catching prey are pretty amazing - and it's all in the head!
"A seahorse is one the slowest swimming fish that we know of, but it’s able to capture prey that swim at incredible speeds for their size," said Brad Gemmell, research associate at the University of Texas Marine Science Institute.
Seahorses and other syngnathids such as pipefish, are extremely fond of copepods. These tiny crustaceans escape predators when they detect waves produced in advance of an attack, and they can jolt away at speeds of more than 500 body lengths per second. That equates to a 6'/1.8m person swimming under water at 2,000 mph.
Under calm conditions it was found that seahorses caught their intended prey 90% of the time — better than any of the fish tested.
Using high-speed digital 3-D holography techniques, researchers then studied the Dwarf seahorse (Hippocampus zosterae) and some copepods in action (scroll down for video).
What they found was that the seahorse’s head is shaped to minimise the disturbance of water in front of its mouth before it strikes. Just above and in front of the seahorse’s nostrils is a kind of "no wake zone", and the seahorse angles its head precisely in relation to its prey so that no fluid disturbance reaches it.
"It’s like an arms race between predator and prey, and the seahorse has developed a good method for getting close enough so that their striking distance is very short," Gemmell said.
Seahorses feed by a method known as pivot feeding. They rapidly rotate their heads upward and draw the prey in with suction. The suction only works at short distances; the effective strike range for seahorses is about 1mm. And a strike happens in less than one millisecond. Copepods can respond to predator movements in 2-3 milliseconds — faster than almost anything known, but not fast enough to escape the strike of the seahorse.
In the video below, you can watch a seahorse sneak up on a copepod and use its "pivot feeding" technique to suck the copepod into its mouth.
"People don't often think of seahorses as amazing predators, but they really are," Gemmell added.
The study is published in Nature Communications.
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