Don’t let their delicate, graceful appearance fool you: seahorses are efficient and effective killing machines. They are among the most successful hunters in the sea, often reaching a 90 percent success rate (two to three times that of many other predatory fish). But unlike many marine predators, they don’t have lightning-fast speed, strong suction, or creepy catapulting jaws on their side. Instead, seahorses have another evolutionary trick up their sleeve.
Seahorses creep up slowly on their unassuming prey, then snap their head around and slurp the snack into their mouth—experts call this strategy “pivot feeding.” But it’s no easy feat, especially in the calm seagrass beds where seahorses spend most of their time. Here, prey tends to rely on hydrodynamic clues to sense predators. Even a slight disturbance in these calm waters can signal to prey that there’s danger approaching.
Until recently, it’s been unclear how hunting seahorses can escape detection so effectively. But now, new research in Nature Communications demonstrates that the seahorse’s oddly shaped head plays a major role in its sneaky behavior and hunting success.
The researchers studied the dynamics between dwarf seahorses and one of their preferred prey items, a type of tiny crustacean called a copepod. Copepods are some of the most sensitive creatures in the sea, detecting and reacting to even tiny fluid deformations in the water around them. To catch a copepod, seahorses must be nearly invisible, at least hydrodynamically.
And it turns out that they are. Using high-speed recordings, the researchers found that the seahorses’ elongated snouts actually create a “quiet zone” that minimizes the fluid disturbance of the surrounding water, allowing them to approach undetected. Within this zone—which extends directly out from a seahorse’s mouth and right toward its intended prey—the fluid velocity of the water averages less than 0.8 mm/s. Outside this zone, the surrounding water moves more than five times faster.
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