Would you believe that this small, unusual, innocent-looking fish is a master of camouflage, a predator, and a vital part of coastal ecosystems? The lined seahorse belongs to the family Syngnathidae, which includes other species, such as sea dragons or pipefish. Its scientific name is Hippocampus erectus, and its other common names are northern seahorse and spotted seahorse.

Featured image credit: Brian Gratwicke (CC BY 2.0)


Appearance

Just like other seahorse specimens, the lined seahorse has a horselike head and a prehensile tail that allows it to grip and hold onto objects. Two small pectoral fins on either side of the head are used for steering and stability, while the dorsal fin allows for swimming. These upright-swimming fish do not have scales to protect their bodies. Instead, they are covered with a thin skin layer stretching over rectangular bony plates. On the top of their head is a bony structure that resembles a crown – a coronet. Research suggests that each individual has a uniquely shaped coronet which could be used for identification, similarly to how we use human fingerprints.

Hippocampus erectus
Hippocampus erectus

Credit: MattSullivan (CC BY 2.0)

The most distinguishing characteristic of the Hippocampus erectus is its unique color pattern of fine lines. Since lined seahorses change color to better match their environment, their base color can vary from pale yellow, orange, red, brown, and grey to black. They can also have white lines along the contour of the neck and white dots on the tail.

The lined seahorse belongs to the larger species of seahorses. The maximum size it is recorded to grow to is 19 cm (7.5 in). Males also have a brood pouch and tend to be bigger than females.

Diet

The lined seahorse, just like other seahorse species, is a carnivore. It feeds on live prey, such as fish larvae, small crustaceans like little shrimp, and worms like nematodes and polychaetes.

Seahorses have a voracious appetite due to their lack of stomach, so they need to feed almost constantly.

Although lined seahorses are not fast enough swimmers to chase after their prey, they are very efficient ambush predators. They rely on their camouflage skills and elongated toothless snouts that allow them to wait hidden and stretch the snouts to suck up any passing prey.

A lined seahorse holding onto vegetation

Credit: Marco Almbauer (CC0)


Habitat

Lined seahorses live in the coastal waters of the western Atlantic ocean. They can be found from Mar del Plata in Argentina, up the coast of South America, the shores of the Gulf of Mexico, and the Caribean to Cape Cod in the US, with a few sightings as far north as Nova Scotia, Canada (iNaturalist).

map of the range of the lined seahorse
This map shows the range of the lined seahorse

They typically inhabit calmer coastal waters in order to anchor themselves to seagrass beds, corals, mangroves, sponges, seaweed, or even man-made structures.
Hippocampus erectus is known to live at depths up to 73 meters (240 ft). While they don’t migrate long distances, they tend to stick to shallow water during summer and move into deeper waters during winter months.

Reproduction

Lined seahorses reproduce sexually; however, it is the male who carries and gives birth to the young ones. Male seahorses have an enclosable brood pouch. During a mating dance female lined seahorse transfers around 250-650 eggs into the male’s pouch. The male then fertilizes the eggs and, after approximately 21-day pregnancy, goes into labor. (animaldiversity.org). During labor, the male holds onto some type of marine vegetation and propels the young from the pouch.

pregnant seahorse
Pregnant seahorse

Credit: Owen Evans (CC BY-SA 2.0)

The newborns are completely independent and able to swim immediately after birth. Once the male is ready to mate again, it will inflate its pouch to signal the female. Many seahorses are monogamous. If a pair forms a long-term bond, they will greet each other in the morning with a dance and then go about their day separately.

Threats

Lined seahorses are listed as vulnerable species on The IUCN Red List of Threatened Species, which means their population is continuously decreasing and might become endangered. The most severe threat to lined seahorses is commercial fishing, both targeted and non-selective fishing. In fact, Project Seahorse – a marine conservation team – estimated that 70 million seahorses (of various species) are caught annually.

Lined seahorses are targeted primarily to be dried and used for traditional Chinese medicine or as tourist curios, and sometimes to be sold for aquarium display. However, the bigger part of the problem is non-selective fishing. Many seahorses are caught as bycatch by bottom trawls and other non-selective fishing gear such as entangling nets, seine nets, or traps. Moreover, bottom trawling and the destruction and pollution of coastal areas can lead to seahorse habitat degradation.

Dried seahorses
Dried seahorses for sale on a seafood market

Credit: Fovea Centralis (CC BY-ND 2.0)

When it comes to their natural enemies, seahorses are not believed to be particularly vulnerable to any predators. Though, since they are not very efficient swimmers, lined seahorses (especially the young) can fall prey to skates, crabs, rays, or larger fishes. These weak swimmers are also vulnerable to strong storms and currents, just like their close relative – the leafy sea dragon.

Facts about the Lined Seahorse

  1. It can move its eyes independently of one another, like a chameleon.
  2. Lined seahorses have male pregnancies.
  3. Their offspring are independent right after birth but are very vulnerable to predators and strong currents.
  4. Their coronets are believed to be similar to human fingerprints.
  5. Aside from mating, lined seahorses are solitary creatures.
  6. Due to its lack of stomach, lined seahorse typically feeds at least 30 times a day.
  7. They prefer to live in shallower waters, where they can use their tails to anchor themselves to marine vegetation because they are not the strongest or fastest swimmers.
  8. Their ability to remain still and blend with their environment makes them efficient ambush predators.
  9. The lined seahorse has a long snout it uses to suck in live food.


FAQs

How long do lined seahorses live?

Lined seahorses are believed to live between 3 to 5 years.

Can lined seahorses be kept as pets?

Technically yes, lined seahorses can be kept in an aquarium. However, if you really want to buy one, you should make sure that the seahorse is captive-bred and not wild-caught.

Where do lined seahorses live?

Lined seahorses live in the coastal waters of the western Atlantic. This includes the east coast of Argentina, Uruguay, Brazil, Suriname, Guyana, French Guiana, the shores of the Gulf of Mexico, Central America, the Caribbean, Bermuda, the Caribbean sea coastline of Venezuela and Columbia, the east coast of the United States, and also the shores of Nova Scotia, Canada.

What is the biggest threat to the lined seahorse?

Lined seahorses are endangered primarily due to overfishing and the destruction and pollution of their habitats caused by human activities.

What does a lined seahorse eat?

The lined seahorse eats small crustaceans such as amphipods and little shrimps, but also fish larvae and worms like nematodes and polychaetes.

Does a lined seahorse lay eggs?

The female uses an ovipositor to deposit her eggs into the male’s brood pouch. The male then fertilizes them, carries them, and gives birth to them.