All seahorses have the same basic body shape, that is, a horse-like head held at right angles to an erect body.
The tail is highly flexible although it cannot bend directly backwards very far (N. Garrick-Maidment, pers. comm.).
Seahorse population density tends to be low (Vincent, 1996). However there are no published data about population trends or total numbers of mature animals for this species.
Hippocampus hippocampus has the potential (like all seahorses) to grow appendages on its body for camouflage and protection. However, none have ever been identified (Garrick-Maidment, 1998).
Hippocampus hippocampus is better suited to manoeuvrability than speed (Blake, 1976). Only the dorsal fin on their back provides propulsion, while the 'ear-like' pectoral fins below the gill openings are used for stability and steering. Hippocampus hippocampus is able to use its prehensile tail as an anchor, wrapping it around the stems of seagrass, coral heads or any suitable object. It uses its tail to hold on in strong currents (N. Garrick-Maidment, pers. comm.) and the tail is used by both sexes to grasp a partner in mating and greeting rituals. The tail is also used a great deal for climbing and is used as a hand when grasping for climbing (N. Garrick-Maidment, pers. comm.).
Growth rates have not been investigated in any detail but young fry are known to exhibit growth inflection points as they switch between prey types (Boisseau, 1967; cited in Vincent, 1996). Adults are known to grow more slowly as they grow larger (Vincent & Sadler unpublished; cited in Vincent, 1996).
On average, an adult seahorse will eat between 30-50 mysid shrimp a day (Garrick-Maidment, 1997). Hippocampus hippocampus is an ambush predator that feeds on live, moving food. Hippocampus hippocampus will remain motionless until a small animal such as a mysid shrimp passes within reach. Within a second, the seahorse will flick its head and suck its prey out of the water column through its long tubular snout. Hippocampus hippocampus has no teeth or stomach, therefore prey that are caught are swallowed whole and pass rapidly through the digestive system.
Few predators appear to target adult seahorses. Lourie et al. (1999) suggested that this could be due to camouflage and immobility that makes the seahorse difficult to detect. They are, however, taken by crabs, and large pelagic fish (Lourie et al., 1999). There are also records of sea gulls and penguins eating seahorses of which the former appear to eat them commonly (N. Garrick-Maidment, pers. comm.).