Seahorses use their arched necks as springs to pivot their heads forward and catch prey. This limits the distances at which they can seize victims to only the length of their necks, about 0.04 inches (1 millimeter). However, seahorses nevertheless could get close enough to copepods to capture them.
"We found they captured copepods more than 90 percent of the time, which is extremely effective for any sort of predator, much less with such elusive prey," Gemmell said.
To find out how these fish catch their victims, the researchers experimented with the dwarf seahorse Hippocampus zosterae, which is native to the Bahamas and the United States and is only about 1 inch (2.5 centimeters) long. They suspended these fish with copepods in water loaded with hollow glass beads about one-sixth the average diameter of a human hair. They shone lasers into this water that illuminated the beads.
By analyzing how the beads moved as seahorses preyed on copepods, the scientists could deduce how they made the water flow around them in three dimensions. They found that the water around the seahorse snout barely moves while the hunter approaches its victims, helping the seahorse to close in undetected.
The seahorse appears to achieve this stealth by virtue of how its mouth is located at the end of a long snout. "This gives its head a narrow shape," Gemmell said. "This is the same reason why ships and boats have triangular-shaped bows -- it makes it easier for them to move through fluid, results in less drag and disturbance."
Gemmell and his colleagues Jian Sheng and Edward Buskey detailed their findings online Nov. 26 in the journal Nature Communications.
This story originally appeared on LiveScience.com.
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