Hedgehog Seahorse

The Hedgehog Seahorse (Hippocampus spinosissimus) is a spine-covered species in the family Syngnathidae, found across the Indo-West Pacific from the Persian Gulf to Australia and Japan. It is among the spiniest of all seahorses, with numerous sharp bony projections covering the head, trunk, and tail, a feature that gives the species its common name and likely helps deter predators. It shares the family's characteristic upright swimming posture and male-brooded reproduction. The Hedgehog Seahorse is currently assessed as Vulnerable by the IUCN, primarily due to bycatch in trawl fisheries and degradation of coastal reef and seagrass habitat across much of its wide range.

The Hedgehog Seahorse is identified primarily by the density and sharpness of its body spines.

• Spines: numerous, long, and sharp, covering the head, back ridge, and tail more heavily than in most other seahorse species
• Coronet: prominent, spiny crown structure atop the head
• Color: typically pale tan, grey, or brown, sometimes with faint mottling
• Body: slender, elongated trunk with a moderately long snout
• Size: adults reach roughly 10-17 cm Its heavier spine coverage compared to smoother-bodied species like Barbour's or the Zebra Seahorse is the most reliable way to separate it from similar-sized relatives.

The Hedgehog Seahorse ranges widely across the Indo-West Pacific, from the Persian Gulf and East Africa through Southeast Asia to northern Australia and southern Japan. It inhabits shallow coastal waters, typically from the intertidal zone down to about 60 meters, favoring sandy or rubble bottoms, seagrass beds, and the base of coral or rocky reefs where it can anchor its tail. The species tolerates a range of turbidity and is often found in areas with mixed soft coral, sponges, and algae. It prefers warm tropical waters and calm, current-sheltered microhabitats, similar to many other reef-associated seahorse species.

Hedgehog Seahorses are slow, sedentary fish that anchor themselves with a prehensile tail to seagrass, sponges, or rubble and remain largely stationary for long periods, relying on camouflage and spines for defense. They feed by ambush, drawing in small crustaceans such as copepods and mysids through rapid suction generated by their tubular snout. Reproduction follows the typical seahorse pattern: during courtship the female deposits eggs into the male's brood pouch, where he fertilizes and carries them through gestation before releasing independent young. Individuals often show some site fidelity and may form temporary pair bonds during the breeding season. Their heavy spination likely discourages predation by fish that would otherwise swallow them whole.