Lined Seahorse

The lined seahorse is a small fish of the western Atlantic, ranging from south of Nova Scotia to Venezuela. It swims upright, steering with its dorsal and pectoral fins, and grips seaweed and coral with its prehensile tail. A weak swimmer, it ambushes tiny crustaceans by blending into its surroundings and sucking them in through its snout, while its eyes move independently to scan around. Colours range from grey and black to red, green and orange, and shift with mood, diet and surroundings. As in other seahorses, the male carries the young: the female sprays her eggs into his brood pouch, where they incubate for 20 to 21 days.

About the lined seahorse

The lined seahorse is a small Atlantic seahorse that lives in seagrass beds, floating seaweed and mangroves from Nova Scotia's southern waters to Venezuela, including the U.S. East Coast and Gulf of Mexico. It belongs to the family Syngnathidae, with pipefishes and other seahorses, and is named for the white lines that often outline its neck.

Its scientific name is Hippocampus erectus, given by George Perry in 1810. "Hippocampus" comes from ancient Greek words for a horse or sea monster. The lined seahorse is also called the northern seahorse or spotted seahorse, and it is the only seahorse native to the Chesapeake Bay.

Adults usually measure 12 to 17 cm (4.7–6.7 in), with a maximum reported length of 19 cm (7.5 in). The body is sturdy and upright, encased in an armor of about 50 bony plates that together form an outer skeleton. Colors range widely: black, grey, brown and green through orange, red and yellow, usually paler on the front. A lined seahorse can change color in response to its surroundings, diet, stress level and mood. Besides the neck lines, many have tiny white dots on the tail.

The prehensile tail is made of many rings, between 34 and 39 of them, and the seahorse uses it to grip seaweed and coral. The snout is about half the length of the head. A crown-like bony crest called a coronet sits on the back of the head, and each one is unique to the individual, like a fingerprint. The eyes can work together or move independently, letting the seahorse scan its surroundings.

The sexes are easy to tell apart. Males have a brood pouch on the abdomen, are slightly larger, and have longer tails. Females have slightly larger dorsal fins set lower on the back.

Behavior and diet

The lined seahorse is a diurnal fish and a weak swimmer. It swims upright, pushed along by its dorsal and pectoral fins, which beat 20 to 30 times a second, fast enough to be nearly invisible. Its body is large compared with its fins, so it rarely swims for long or travels far except when migrating.

Because it cannot chase prey, the lined seahorse ambushes it. It changes color to blend in, locates a target, then jerks its head upward and sucks the prey in through its tubular snout. It is very accurate, especially when prey is within about 2.5 cm (1 in) of the snout. The diet is mostly tiny crustaceans, mollusks and zooplankton. A growing seahorse may feed for up to ten hours a day and swallow about 3,600 baby brine shrimp.

Lined seahorses are monogamous. Pairs perform ritual dances every morning to renew their bond. During courtship they also make clicking sounds: as the seahorse lifts and lowers its head, the edge of the skull slides under the coronet and clicks. Mates swim slowly together trading clicks until they embrace, when their sounds merge into one louder, continuous sound. If a partner dies, the survivor does not quickly replace it and often never finds a new mate in its short life.

The male is the pregnant parent. During mating the female sprays her eggs into his brood pouch, where they are fertilized and sealed. A male's brood can range from 97 to 1,552 eggs. Inside the pouch, a network of capillaries supplies the embryos with oxygen and adjusts the pouch chemistry until, near birth, it closely matches seawater. After 20 to 21 days the male anchors his tail and arches back and forth until all the young are expelled. Newborns are about 11 mm (0.4 in) long. Courtship starts again right after birth.

Very few young survive. Scientists estimate that only about two of the hundreds born grow into adults. Predators include crabs, rays, skates, seabirds, sharks, tuna and dolphinfish. Seahorses can be sexually mature as early as four months, though eight months is more typical.

Range and habitat

The lined seahorse lives in the western Atlantic Ocean, from the waters south of Nova Scotia to Venezuela. Along the U.S. East and Gulf coasts it has been recorded from New York and New Jersey through the Carolinas, Georgia and Florida to Louisiana. It also lives around Bermuda, Cuba, Mexico, Central America and the Caribbean. It has been recorded from the Azores, but it is not clear that a population exists there.

Its habitat includes floating Sargassum seaweed, seagrass, sponges and mangroves, along beaches, oyster beds, vegetated banks, bays and salt marshes. It is found at depths of up to 73 m (240 ft). Lined seahorses often wrap their tails around crab pots. In winter they move into deeper water, and in warmer months they return to the shallows. Juveniles usually swim near the surface.

Conservation status

The lined seahorse is listed as Vulnerable on the IUCN Red List (2017). It has been listed as Vulnerable since 1996, and its population has fallen by at least 30 percent, probably since that year.

Threats include habitat loss and damage from coastal development and pollution, accidental capture, and deliberate collection. The species is widely used in Chinese medicine and for ornamental decoration, and it is very common in the aquarium trade, although the large majority of lined seahorses sold to aquarists are captive-reared. Commercial aquaculture could ease pressure on wild populations if it proves practical.