For the seahorse, a stealthy approach and lightning strike speed, help it catch its prey: the copepod. A recent study shows that the shape of a seahorses head helps give it the edge in its hunt.
Although copepods have no eyesight, they rely on a remarkable sensitivity to fluid disturbances to sense predators approaching. Copepods on are nearly everyone's menu in the ocean and have evolved some impressive ways to avoid being eaten including sensitivity and speed.
Seahorses are slow swimmers yet capture copepods using a technique known as the pivot feeding. Pivot feeding involves rapid movement to overcome prey escape capabilities. However, this feeding mode functions only at short range and requires approaching its prey within close proximity without being detected.
The study shows shape of the seahorses head helps it stealthily move into position to catch its prey without disturbing the water flowing around it. Its likely seahorses head shape is the result of natural selection favoring a shape that produces lower water disturbance than other fish.
The seahorse snout is narrow, elongated, and rounded on top, and since it's quite small, it creates less disturbance in the water, allowing it to get within one millimeter of a copepod. It then sucks in prey with its mouth, which isn't much bigger than the prey itself. It can also extend its mouth away from the thicker part of its head and swing it forward and upward and cover the distance to the prey in about one millisecond.
So even the zippy copepod's getaway speed of two or three milliseconds is no match for the one millisecond strike of the seahorse. Check out this video below showing a cool closeup of a seahorse striking a copepod:
<iframe src="http://player.theplatform.com/p/ngs/ngm-embed/embed/select/ucJzOboNtUVe?form=html" height="375" width="609" seamless="seamless" allowfullscreen="" frameborder="0"></iframe>
The researchers used high-speed digital techniques to capture the movements of the live dwarf seahorse, Hippocampus zosterae, and fluid disturbance in 3-D imagery at the strike zone. They also used preserved seahorse specimens and positioned them in flume studies, a method that allows researchers to control the flow of the water so that any disturbance would be clearly generated by the head of the animal (not a motion created by the live seahorse).
Seahorses are less successful in more turbulent environments where other fish have an easier time capturing copepods. The seahorses advantage works in the calmer environments of deep water and coral reefs.