Hedgehog seahorse  (Hippocampus spinosissimus)

The hedgehog seahorse is classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Aptly named for its spiny appearance, the hedgehog seahorse (Hippocampus spinosissimus) is, like all seahorses, an unusual and intriguing-looking fish, with an upright posture, curved trunk and a grasping, prehensile tail. The head, which is positioned at right angles to the body, bears a long, tubular snout, and the eyes are able to swivel independently of each other. Unlike most fish, the body lacks scales, and the skin is stretched over a series of bony plates, which appear as rings around the trunk and tail. The dorsal fin is used for propulsion, and the two small, ear-like pectoral fins for steering (2) (4) (5) (6). Unusually for a seahorse, very young hedgehog seahorses possess a reduced caudal fin, but this is lost in adults (6).

The hedgehog seahorse is quite variable in colouration (2) (7), often plain or pale with darker markings across the back and dark cross-bands on the tail (2). There are four or five sharp spines on the top of the head, and well-developed spines on the body and tail, while the male has strongly developed, blunt-tipped spines around the brood pouch (2). Seahorses are able to change colour or possibly even grow skin filaments over time to better blend in with the surroundings, and rapid, short-term colour changes can also occur during social interactions or courtship (2) (4) (6).

The hedgehog seahorse occurs in the Indian Ocean and western Pacific Ocean, and has been recorded around Australia, China, India, Sri Lanka, and South East Asia (1) (2) (7).

Typically found on coral reefs or on muddy or sandy bottoms near reefs, the hedgehog seahorse has been recorded at depths of up to 70 metres, although depths of up to 8 metres are more usual (1) (2) (7).

Seahorses have an intriguing method of reproduction, in which the male rather than the female becomes ‘pregnant’. The female seahorse deposits the eggs into a specialised brood pouch at the base of the male’s tail, where they are fertilised and then protected and nourished for several weeks, before the male actively expels the fully-formed young from the pouch (2) (4) (5) (6).  The newborn seahorses are independent at birth, and enter the water column as plankton, receiving no further parental care (2) (4) (6).

The hedgehog seahorse is believed to breed year-round, with peaks between May and October, and may undergo repeated ‘pregnancies’ throughout the year. A maximum of 683 young have been recorded from a single brood (2) (6) (7). This species is believed to start breeding from around six months to a year old (6), and, like other seahorses, is likely to form monogamous breeding pairs, with the pair bond reinforced with daily greetings and ‘promenading’ courtship displays (2) (4). Seahorses are opportunistic predators, ambushing passing prey and sucking it into the long snout, which lacks teeth. Any prey that can fit into the snout is taken, including small crustaceans, invertebrates and fish fry (4) (6).

Like many seahorses, the hedgehog seahorse is under threat from both targeted and incidental catch, as well as from habitat degradation (1) (7). Although reported to be less desirable for traditional Chinese medicine than some other species (1), its use may be increasing with a rise in the use of Chinese herbal patent medicines, and the species is also caught for the curio and live aquarium trades (1) (2) (7). The shallow, inshore habitats typically used by seahorses are often highly affected by human activities, with seahorses being negatively affected by pollution, siltation, and damaging fishing techniques. The unique life history and behaviour of seahorses also makes them particularly vulnerable to population declines. For example, removal of one partner may stop the other reproducing, and adults may not disperse far to re-colonise depleted areas (1) (2) (4) (6). Seahorse declines have been reported in the Philippines and Indonesia, although the exact rate of decline for the hedgehog seahorse is currently unknown (1).

All seahorses were added to the Convention on International Trade in Endangered Species (CITES) in 2004, which should go some way towards controlling international trade in these species (3). In Australia, permits are required for the export of hedgehog seahorses, and are only granted for approved management plans or captive bred animals (1) (2). Many Australian states also have their own controls on capture and trade in seahorses (1), and various conservation actions for these fish are underway in Australian waters (8). In India, the species was placed under Schedule I of the Wildlife Protection Act (1972) in 2001 (2), and efforts to develop sustainable seahorse farming are underway in some countries (5), although such initiatives may bring their own problems, such as the discharge of potentially contaminated waste water (8).

Further conservation measures recommended for the hedgehog seahorse include recognising the impacts of trawling, enforcing existing legislation against illegal fishing, and considering the species as a ‘flagship’ species for its habitat (7). Habitat protection and restoration are also likely to be needed. In addition, further research into the ecology and life history of this and other seahorses will be vital in developing appropriate conservation and management strategies for these fascinating fish (2) (6) (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about the conservation of this and other seahorses see:

• Project Seahorse:
  http://seahorse.fisheries.ubc.ca/
• The Seahorse Trust:
  http://theseahorsetrust.co.uk/