BIOTIC

BIOTIC Species Information for Hippocampus hippocampus

Researched by

Marisa Sabatini & Susie Ballerstedt

Data supplied by

MarLIN

Refereed by

Neil Garrick-Maidment

Reproduction/Life History

Reproductive type

Gonochoristic

Developmental mechanism

Viviparous (Parental Care)

Reproductive Season

April to November

Reproductive Location

Brood chamber / Pouch

Reproductive frequency

Annual episodic

Regeneration potential

Life span

3-5 years

Age at reproductive maturity

<1 year

Generation time

Insufficient information

Fecundity

Up to 250 young

Egg/propagule size

Not relevant

Fertilization type

Internal

Larvae/Juveniles
Larval/Juvenile dispersal potential	100-1000m	Larval settlement period	Not relevant
Duration of larval stage	Not relevant

Reproduction Preferences Additional Information

Sexual maturity
Hippocampus hippocampus becomes sexually mature during the first reproductive season after birth i.e. at age six to twelve months (Lourie et al., 1999). Sexual maturity in males can be recognized by the presence of a brood pouch, although the size of the pouch will vary with its reproductive state. Any physical manifestation of sexual maturity is less obvious in females (Vincent, 1996).

The length and timing of the reproductive season varies with location, and will be influenced by light, temperature and water turbulence. It was originally thought that Hippocampus hippocampus and Hippocampus guttulatus only bred from Spring (April) to the Autumn (October) (Lourie et al., 1999) but recent work (Garrick-Maidment, British Seahorse Survey 2004) has found juveniles in February that would have been born in November (N. Garrick-Maidment, pers. comm.).

Pair bonding
Hippocampus hippocampus like all seahorses are monogamous and form faithful pair bonds. The male seahorses are the predominant competitors for access to mates as they compete more to get pregnant than females do to give their eggs away (Vincent, 1994a). In courtship, males exhibit higher levels of aggressive competitive behaviour patterns (wrestling and snapping) than females. Competitive wrestling and snapping are described below.

Snapping occurs when a male aims his snout at his competitors opercular flap before flicking his snout hard in order to propel the rival male away. A well aimed powerful snap could propel a seahorse as much as 10 cm and lead to the recipient darkening and flattening in a submissive posture (Vincent et al., 1994a).
When two seahorses are wrestling, one male will refuse to release his competitor from its grasp. Both males may then tumble with locked tails. Eventually, the submissive male will darken and flatten in a submissive posture until it is released by the dominant male (Vincent et al., 1994a).

Tail wrestling and snapping with the snout is confined to males (Vincent et al., 1992). Although females do compete for access to males (in the sense that they exhibit higher levels of courtship when in the presence of another member of the same sex than when courting alone) but to a far lesser extent than males (Vincent, 1994a). Courtship included the following behaviour.

Both seahorses may grasp a common holdfast with their tails and rotate around it.

Male and female may promenade together often holding tails.

Head tilting and quivering (Vincent, 1994a).

Hippocampus hippocampus forms sexually faithful pairs that endure through multiple mating and breeding seasons. Pair bonding is more on a seasonal basis in temperate species and there is no evidence from the wild to prove that they pair for life (N. Garrick-Maidment, pers. comm.). The male and female reproductive state changes are always synchronized within a pair and only within a pair, confirming that they are faithful to each other (Vincent, 1996). Pair bonding is reinforced by daily greetings performed only with an individuals partner. These greetings commonly last six to eight minutes (Vincent et al., 1992).

Reproduction
The seahorse has a unique method of reproduction in which the male plays the dominant role. It is the male rather than the female that becomes pregnant (Vincent, 1994a). At the beginning of the mating season the males prepare their brood pouches. Females eggs ripen in an assembly line ovary, throughout the reproductive season. In order to mate males must eliminate the previous brood from the pouch and females must hydrate their eggs. Each sex provides a signal of readiness to mate, males pump water in and out of their pouch and females point their head towards the water surface (Fiedler, 1954; cited in Vincent, 1994b). Females also have a trunk which is visibly distended with hydrated eggs, which becomes concave after the egg transfer (Vincent, 1994b). The female aligns the base of her trunk with the males pouch opening and inserts her ovipositor into the pouch. The female then deposits her eggs into the brood pouch where they are fertilized (Dipper, 2001). Egg transfer takes about 6-10 seconds (Vincent, 1994a).

Once the eggs are fertilized the brood pouch then seals up. The pear shaped eggs become embedded into the pouch wall and enveloped by tissues. Oxygen is provided via capillaries in the pouch wall (Carcupino et al., 2002; Dipper, 2001). The pouch acts like the womb of a female mammal, complete with a placental fluid that bathes the eggs and provides nutrients and oxygen to the developing embryos while removing waste products. Nevertheless most of the nutrition comes from the mother. The egg yolk provides nutrients, while the male secretes a hormone called prolactin (Boisseau, 1967b; cited in Lourie et al., 1999; Dipper, 2001). Prolactin induces enzymatic breakdown of the outer part of the egg (chorion) to produce a placental fluid (Boisseau, 1967b; cited in Lourie et al., 1999). The pouch fluid is altered during pregnancy from being similar to body fluids to being more like the surrounding seawater. This helps reduce the stress on the offspring at birth (Dipper, 2001).
Pregnancy in male Hippocampus hippocampus can last for about 20-21 days (Garrick-Maidment, 1998). At the end of this period the male goes into labour (usually at night), which can last for hours. The brood pouch opens and fully formed young are pushed out by vigorous pumping movements. Male seahorses have relatively small broods (TRAFFIC, 2002). Brood size depends largely but not entirely on the size of the adults (Lourie et al., 2002). The number of young produced by Hippocampus hippocampus can range from 50-100 (Garrick-Maidment, 1998) although recent information shows that the number can be as high as 250 (N. Garrick-Maidment, pers. comm.). Fecundity depends on the age of the male, older males producing a larger number of offspring (N. Garrick-Maidment, pers. comm.). In pairs that are familiar with each other the male is able to mate again within a few hours of emptying his brood pouch without any decline in his physical condition (Carcupino et al., 2002)

Dispersal potential
It has been suggested that young fry are more likely to colonize new or depleted areas because they are often carried away from natal habitats despite attempts to settle into the substrata (Vincent, 1996). The extent of dispersal by this mechanism is unknown (Vincent et al., 1999).
Longevity
The natural lifespan and mortality rates of seahorses and the parameters that define them are virtually unknown and in need of research (Anon, 1990a; cited in Vincent, 1996). It has been suggested that the lifespan is only about 1 year in very small species such as Hippocampus zosterae (~ 2.5 cm) (Strawn 1953; cited in Vincent, 1996) whereas larger seahorses, such as Hippocampus hippocampus, have a lifespan of 1-5 years (Lourie et al., 1999). Hippocampus hippocampus has been regularly recorded living up to 5-6 years in captivity (N. Garrick-Maidment, pers. comm.).

Natural adult mortality rates are likely to be low but the data on mortality rates is very limited (Vincent, 1996). Fry are released at an advanced stage of development, which probably gives them a higher chance of survival than in many other species (TRAFFIC, 2002). However, it has been suggested that mortality is probably highest in young fry, as they are highly vulnerable to piscivorous fish (Vincent, 1996).

Reproduction References

Dipper, 2001, Vincent et al., 1992, Vincent, 1994a, Vincent, 1994b, Garrick-Maidment, 1998, Carcupino et al., 2002, Lourie et al., 1999, Vincent, 1996, TRAFFIC, 2002, Garrick-Maidment & Jones, 2004, FishBase, 2000,