The seahorse relies heavily on its tail for survival in the ocean.
Have you ever seen a monkey hold onto a tree branch with its tail? The seahorse uses its tail in a very similar way. Seahorses are not very strong swimmers because of their stiff, bony armor, which means they cannot undulate, or wiggle, the way most fishes can to generate motion. Also seahorses lack a caudal (tail) fin, which is another main power source for locomotion in most fishes.
So the seahorse has a unique muscular tail that is prehensile, meaning it can grip objects the way your hand does. Seahorses often wrap their tails around sea grass stems, coral heads, sponges, mangroves, or any other suitable objects when they need to anchor themselves.
The seahorse starts using its tail immediately after birth. When seahorse babies are first born, some of them sink to the bottom and they use their tails to quickly grab the nearest steady object. Other babies sometimes curl their tails around each other and drift about in the water looking for food together. Adult male and female seahorses use their tails to grasp each other in mating and greeting rituals.
Seahorses love to eat tiny shrimp. Shrimp are often found in areas that have strong currents. Having a muscular tail helps seahorses hold onto any object making it easier to eat their food without being pushed around by the current.
Seahorses also use their tails as protection from predators. When threatened, a seahorse’s defense reaction is to tuck its head close to its body and tighten its tail-hold around an available anchor.
--Debbie Melechinsky, marine biologist at Birch Aquarium at Scripps Institution of Oceanography, UC San Diego