The shape of the seahorse head has evolved to allow the animals to closely approach their prey while remaining undetected, reports research published in Nature Communications this week. The work suggests that this unique head shape allows for movement with minimal disturbance to the water immediately surrounding it.
Seahorses are very slow swimmers, yet they feed mainly by hunting evasive prey that is able to detect even a slight deformation in the surrounding water. Seahorses’ feeding mechanism relies on their arched necks acting as a spring and allowing the attack to relatively distant prey. This mechanism, and the distance they can capture the prey, is however limited to the actual length of the neck. Thus far it remained unknown as to how the slow swimming seahorses managed to get close enough to their prey while remaining undetected.
Brad Gemmell and colleagues used digital in-line holography to investigate the function of the head morphology of seahorses. This technique allowed for the capture of 3D images and the subsequent tracking of water movement around the seahorses. The authors find that the water around the seahorse snout hardly moves while it approaches prey, helping the seahorse to close in undetected. Comparisons with the water disturbances created by pipefish, close relatives to seahorses but with a different head shape, provided further evidence that it is the head shape itself that produces this hydrodinamically silent region in front of the seahorse.