MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Short snouted seahorse (Hippocampus hippocampus)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.

Summary

Description

The seahorse has a very distinctive shape with the head set at an angle to the body. The trunk of the body is short and rather fat whilst the tail is tapering, curled and prehensile. Hippocampus hippocampus can be up to 15 cm in length. The snout is short and upturned, and less than one third the length of the head. There is a prominent spine above each eye. The dorsal fin has 16-18 rays, usually with a dark stripe running parallel to the margin. The pectoral fins have 13-15 rays. Body rings carry bony tubercles, giving a knobbly, angular appearance. The body is variable in colour: brown, orange, purple or black, sometimes with pale blotches.

Recorded distribution in Britain and Ireland

Distributed along the south coast of England, with substantial populations around the Channel Islands and Ireland (Garrick-Maidment & Jones, 2004).

Global distribution

Reported from the Netherlands, Belgium, the east Atlantic coast of Europe, Algeria, Italy, Malta and Greece.

Habitat

Found in shallow muddy waters, in estuaries or inshore amongst seaweed and seagrasses, clinging by the tail or swimming upright. Hippocampus hippocampus can also be found in rocky areas.

Depth range

77 m

Identifying features

  • Body up to 15 cm in length.
  • Short, upturned snout.
  • Prominent spine above each eye.
  • Dorsal fin has 16-18 rays with a submarginal stripe.
  • Pectoral fin has 13-15 rays.
  • Lacks a mane
  • Bony tubercles on body.

Additional information

Hippocampus hippocampus is one of two species of seahorses found in the British Isles, the other is Hippocampus guttulatus, which has a longer snout and elongated protuberances along the back of the neck, giving the impression of a 'horses mane'.

The exact size and distribution of the population of seahorses around the British Isles are not known at present. The British Seahorse survey is collating records currently and can be found at the Seahorse Trust.

Please note: the biology of seahorses is poorly known and little information on Hippocampus hippocampus was found. Therefore, the following review is based in part on reviews of the biology of seahorses by Vincent (1996), Garrick-Maidment (1997) and Lourie et al., (1999). See also the British Seahorse Survey Report 2004 (Garrick-Maidment & Jones, 2004).

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Biology review

Taxonomy

PhylumChordata
ClassActinopterygii
OrderSyngnathiformes
FamilySyngnathidae
GenusHippocampus
Authority(Linnaeus, 1758)
Recent Synonyms

Biology

Typical abundanceLow density
Male size range15 cm
Male size at maturity
Female size rangeMedium(11-20 cm)
Female size at maturity
Growth formSee additional information
Growth rateSee additional information
Body flexibilitySee additional information
MobilitySwimmer
Characteristic feeding methodPredator
Diet/food sourceCarnivore
Typically feeds onOrganic debris, plankton, brine shrimp, small crustaceans and small fish
SociabilityNo information
Environmental positionDemersal
DependencyNo information found.
SupportsNo information
Is the species harmful?No

Biology information

Growth form
All seahorses have the same basic body shape, that is, a horse-like head held at right angles to an erect body.

Body flexibility
The tail is highly flexible although it cannot bend directly backwards very far (N. Garrick-Maidment, pers. comm.).

Abundance
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.

Camouflage
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).

Mobility
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
Growth rates have not been investigated in any detail but young fry are known to exhibit growth inflexion 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).

Feeding
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 are swallowed whole and pass rapidly through the digestive system.

Predators
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 gulls and penguins eating seahorses of which the former appear to eat them commonly (N. Garrick-Maidment, pers. comm.).

Habitat preferences

Physiographic preferencesEstuary, Offshore seabed, Strait / sound
Biological zone preferencesLower eulittoral, Mid eulittoral, Sublittoral fringe, Upper eulittoral
Substratum / habitat preferencesBedrock, Macroalgae, Mud, Seagrass
Tidal strength preferencesVery Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferencesExtremely sheltered, Moderately exposed, Sheltered, Ultra sheltered, Very sheltered
Salinity preferencesVariable (18-40 psu)
Depth range77 m
Other preferences

None found

Migration PatternNon-migratory / resident

Habitat Information

Seahorses are often found in water less than one metre deep. Most species of seahorse live at depths between 1-15 metres and as deep as 77 m when they move out into deeper waters over winter (Garrick-Maidment, 1998) but the depth varies throughout its range according to habitat (N. Garrick-Maidment, pers. comm.). In the Channel Islands, they are found in much deeper water because here they have a wide tidal range and deep gullies (N. Garrick-Maidment, pers. comm.). On the whole, Hippocampus hippocampus is found below 5 m whereas Hippocampus guttulatus is found in shallower depths (N. Garrick-Maidment, pers. comm.). They occupy only certain parts of seemingly suitable habitats, for example sticking to the edge of seagrass beds leaving large areas unoccupied. These microhabitats have not been investigated but it has been suggested that seahorses find more food in areas of good water exchange (Vincent, 1996). Habitat/substratum preferences may be seasonal and related to seasonal migration (N. Garrick-Maidment, pers. comm.).

Adults may disperse during short-range migrations but most movement to new areas happens when adults are cast adrift by storms or carried away while grasping floating debris (Vincent, 1999). They can cope with strong tidal strength for varying periods of time (N. Garrick-Maidment, pers. comm.).

Life history

Adult characteristics

Reproductive typeGonochoristic (dioecious)
Reproductive frequency Annual episodic
Fecundity (number of eggs)See additional information
Generation timeInsufficient information
Age at maturity6-12 months
SeasonApril - November
Life spanSee additional information

Larval characteristics

Larval/propagule type-
Larval/juvenile development Viviparous (Parental Care)
Duration of larval stageNot relevant
Larval dispersal potential See additional information
Larval settlement periodNot relevant

Life history 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 vary with location, and is 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 that 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 male's 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 as 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).

Sensitivity reviewHow is sensitivity assessed?

Resilience and recovery rates

Hippocampus hippocampus are benthic and spend most of their time ‘holding onto’ a variety of substrata such as seaweeds, plants, hard rock and artificial surfaces (Garrick-Maidment, 2007). They anchor themselves via their tails and, although able to swim, locomotion is relatively weak (Palma et al., 2019). The species’ distribution is somewhat dependent on indirect movement, due to adults having weak mobility and small home ranges. Dispersal is sporadic and unpredictable as adults may distribute during short-range migrations but most movement to new areas occurs when adults are cast adrift by storms or carried away while grasping floating debris. It is suggested that young fry are more likely to colonize new or depleted areas compared to adults because they are often carried away from their natal habitats (Vincent, 1996). Therefore, it is probable that water flow and wave action may be important for dispersal although no evidence was found.

Hippocampus hippocampus is dioecious but unusual in that the males carry the eggs in a brood pouch until they hatch and 50-100 (up to 250) live fry are released. Pregnancy lasts 20-21 days after which mated pairs can mate again so that they might have more than one broad per year if conditions allow. The mortality of fry is probably higher than adults, depending on the availability of refuges from predators within the substratum (e.g. macroalgae, seagrass). However, there is little information on natural mortality (Vincent, 1996).

Pair bonding between individuals is also seen. Male and female reproductive states change so they become synchronized, reinforcements of bonds are seen through daily greetings (Vincent, 1996). If one half of a bonded pair is separated, reproduction will be reduced, as partners are not quickly replaced and this species if found in low densities (Lourie et al., 1999; Curtis & Vincent, 2005).

Resilience assessmentHippocampus hippocampus is an annual episodic breeder with limited mobility and a short home range.  Adults pair bond and produce a small number (50-250) of fry at a time, although they may be able to have more than one brood per year. Brooding of eggs and the release of a small number of developed fry may reduce their mortality compared to the spawning of eggs and larvae. The mortality of fry is probably higher than adults, depending on the availability of refuges from predators within the substratum (e.g. macroalgae, seagrass). However, there is little information on natural mortality (Vincent, 1996).

Overall, they have the potential for good local recruitment and recovery due to their short generation time, rapid growth rate, and early maturity (with one year) (Woodall, 2017.) However, their small home range, limited mobility, and poor dispersal limit their ability to colonize new areas, recolonize existing areas or move out of areas that become unfavourable (Woodall, 2017). Therefore, where the population is reduced and adults survive (resistance is ‘Medium’) resilience is probably ‘High’ (within 2 years) but where the population is significantly reduced (resistance is ‘Low’ or ‘None’) and recovery is dependent of recruitment from outside the area, resilience is probably ‘Moderate’ (2-10 years). However, recovery may be dependent on stochastic events such as storms and could take longer.

The resilience assessment is based on evidence on Hippocampus hippocampus as a whole, but a scarcity of information on the ecology of this species, and a scarcity of any direct evidence of recovery in the field. Therefore, the confidence in the assessment is 'Low'.

Hydrological Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

No evidence on the temperature tolerance of Hippocampus hippocampus was found. However, it is a predominantly southern species in British waters and is recorded from a temperature range of 10-30°C. It is recorded in the North Atlantic Ocean and ranges from the North Sea, the Mediterranean and West Africa (Pinnegar et al., 2008; Lourie 2016; OBIS 2017). Therefore, it is likely to resist a 2 °C change in temperature for a year in UK waters.

Its European relative, Hippocampus guttulatus is reported to withstand short-term acute temperature change of 5°C with minor physiological impairment (metabolic and ventilation rate) and no change in behaviour (swimming, foraging and activity) (Aurélio et al., 2013). Therefore, inferences can be made on the effect of short-term acute temperature change for Hippocampus hippocampus although at low confidence.

Sensitivity assessment. Therefore, Hippocampus hippocampus is probably resistant to a 2°C change in temperature for a year in UK waters or a 5°C increase for a month and a resistance of 'High' is recorded, albeit with 'Low' confidence. Hence, resilience is assessed as 'High' and the species is recorded as 'Not sensitive' at the benchmark level.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

No evidence on the temperature tolerance of Hippocampus hippocampus was found.  However, it is recorded in British waters as low as 5°C or 6°C in the winter, and ranges from the North Sea to the Mediterranean and West Africa (Pinnegar et al., 2008; Lourie, 2016; OBIS 2017). Therefore, it is likely to resist a 2°C change in temperature for a year in UK waters.

No information was found on the effect, if any, of short-term acute temperature change (e.g. by 5°C).  However, it is considered a southern species within the UK suggesting that Northern populations may see a population decline with temperature decrease.

Sensitivity assessment. Therefore, it is probably resistant to a 2°C change in temperature for a year in UK waters but a short-term temperature decrease of 5°C may impact population abundance at its northern range.  Therefore, resistance is assessed as ‘Low’ is recorded, albeit with 'Low' confidence. Hence, resilience is assessed as ‘Medium’ and sensitivity is assessed as ’Medium’ at the benchmark level.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Hippocampus hippocampus is recorded from variable salinity conditions. It is generally associated with areas of oceanic influences such as tidal inlets which may experience temporary localised increases in salinity (Curtis & Vincent, 2005). It is unlikely to be exposed to hypersaline (>40) conditions but hypersaline effluents are probably detrimental. It is also mobile species and may, therefore, move to other areas to avoid localized hypersaline conditions. However, no evidence was found on which to base an assessment.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Hippocampus hippocampus is recorded from variable salinity conditions. It has been recorded in estuarine waters within the UK such as that in the river Thames, Tamar and Dart (Garrick-Maidment, 2020; NBN, 2017). It is also recorded in brackish Tunisian waters (Ben Amor et al., 2011) and brackish lakes such as Lake Faro in Italy (Spinelli et al., 2020).

The gill structure of Hippocampus hippocampus allows them to cope with brackish waters, showing a tolerance for a slight decrease in salinity (Garrick-Maidment, pers. comm., February 2004). It is also mobile species and may therefore move to other areas of ideal habitat. Decreased salinity may become detrimental when it occurs over large scales as its poor swimming ability is a restriction to its recoverability. However, no evidence of salinity tolerance of the adult or other life stages was found.

Its recorded presence in estuarine and brackish waters suggests that it could tolerate an occasional salinity decrease in UK waters. But a change from ‘variable’ salinity to ‘low’ could be detrimental. Therefore, a resistance of 'Low' is suggested, with 'Low' confidence. Resilience is probably 'Medium' so sensitivity is assessed as 'Medium'.

Medium High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Hippocampus hippocampus is generally found in sheltered to moderately exposed areas with weak flow and an incoming oceanic influence (Curtis & Vincent, 2005).  A change in water flow may be detrimental to the maintenance of local population structure as it is vital in aiding the distribution of seahorse fry (N. Garrick-Maidment, pers. comm). For example, Correia et al. (2013) reported that young Hippocampus guttulatus juveniles had a low tolerance to an increased current regime from 0.1 m/s to 1 m/s and showed a decrease in holdfast grasping. This may carry young juveniles away from their home ranges and disrupt synchronized pair bonds. However, Qin et al. (2014) recorded different results in Hippocampus erectus, which was more likely to attach themselves to holdfasts or objects in response to an increased current regime reaching 0.2 m/s. Negative impacts were also seen for ventilation, feeding and growth rates.  

Little evidence was found for the effects of a decrease in water flow.  Caldwell & Vincent (2012) reported a population decline in Hippocampus hippocampus in Ria Formosa lagoon, Portugal resurveyed after seven years.  They reported a weak relationship between a decrease in current speed and population decline.  They suggested, with low confidence, that decreased current speed may have been associated with prey availability.  However, Kitsos et al. (2008) reported that the ambush feeding seahorse has a diverse and flexible diet due to its mobility.  However, a decrease in water flow would also reduce the risk of young fry or one individual from a bonded pair being carried away to another home range.  

Sensitivity assessment.  Hippocampus hippocampus is a mobile species and may, therefore, move to other areas of ideal habitat when exposed to local increased or decreased water flow depending on the scale of the change.  Large scale change, increase water flow, coupled with this species' poor swimming ability may interfere with mating and/or remove individuals, especially juveniles from the site. Quin et al. (2014) suggested that holdfast grasping increased in Hippocampus erectus as current speed reached 0.2 m/s but that Hippocampus guttulatus was unable to maintain grasping as the current increased by an order of magnitude from 0.1 to 1 m/s.  Although no clear information on Hippocampus hippocampus was found, the evidence suggests that seahorses are probably sensitive to small changes in water flow, depending on location.  Therefore, resistance is assessed as 'Medium' to represent to possible loss of some individuals in the population due to an increase in current flow at the benchmark level, albeit with 'Low' confidence.  Hence, resilience is assessed as 'High' and sensitivity as 'Low'. 

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant. This pressure is considered applicable to species that are only found in habitats at the littoral and shallow sublittoral fringe. Hippocampus hippocampus is found in the sublittoral and will, therefore, not be affected by a change in emergence and is also mobile enough to swim to deeper waters.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Hippocampus hippocampus is recorded within sheltered and moderately exposed areas attached to seaweed, seagrass and other floating debris. Therefore, a significant change in wave action (e.g. to very exposed) may be detrimental as species could be removed from their habitat and ideal substrata for tail anchoring could be reduced or lost.

However, a 3-5% change in significant wave height (the benchmark) is not likely to be significant. Therefore, a resistance of 'High' is recorded so that resilience is 'High' and the species is probably 'Not sensitive' at the benchmark level.

Chemical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This pressure is Not assessed.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This pressure is Not assessed.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This pressure is Not assessed.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found to base an assessment.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This pressure is Not assessed.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

No evidence of hypoxia tolerance for Hippocampus hippocampus was found but evidence has been reported for other benthic macrofauna. For example, in a systematic review by Diaz & Rosenberg (1995) it was reported that when exposed to low oxygen most fish first experience an increase in respiration rate, some then show avoidance behaviour and move to other areas of ideal habitat whilst, others which are immobile begin to suppress metabolic demands.  Migration and spawning play a large role in the recoverability of a population and as Hippocampus hippocampus is a poor swimmer with a small home range hypoxia is probably detrimental to the species.

Sensitivity assessment. Therefore, resistance is assessed as ‘Low’ albeit with ‘Low’ confidence. Hence, resilience is assessed as 'Medium' and sensitivity as ‘Medium’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence for Hippocampus hippocampus was found. 

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence for Hippocampus hippocampus was found. 

Physical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very low’). Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’. Although no specific evidence is described, confidence in this assessment is ‘High’ due to the incontrovertible nature of this pressure.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Hippocampus hippocampus is commonly found on the sandy bottom in the British Isles; however, it has been recorded in variety habitats including in sea grass, on rocky surfaces, on mud and on artificial material (Garrick-Maidment, 2007). A change to the seabed type from sedimentary to hard rock may decrease the levels of some available habitat and be unsuitable for seahorse colonization. It may decrease its ability to avoid a predator and/or decrease the relative availability of food. However, Hippocampus hippocampus is mobile and potentially able to relocate and find another substratum to recolonize. In addition, other habitats such as rocky surfaces and artificial surfaces would increase. Woodall et al. (2018) found that artificial holdfast such as rope, tyres, pier supports and fishing gear were the most commonly occupied holdfast when presented.

Sensitivity review. Therefore, it is probably resistant to a change from sedimentary to artificial substrata so resistance is assessed as 'High', albeit with 'Low' confidence. Hence, resilience is assessed as 'High' and the species is recorded as 'Not sensitive' at the benchmark level.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

This pressure is not 'Not relevant' where Hippocampus hippocampus occurs on hard rock habitats.  This species is also found on a variety of habitat types such as eelgrass, micro- and macro-algae to silt, mud and rocky substrata including artificial substrata (Garrick-Maidment & Jones, 2004; Garrick-Maidment, 2007). Therefore, it is probably ‘Not sensitive’ to a change in the sediment type. 

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Hippocampus hippocampus is found on a variety of habitat types such as eelgrass, micro- and macro-algae to silt, mud and rocky substrata including artificial substrata (Garrick-Maidment & Jones, 2004; Garrick-Maidment, 2007). It is also mobile species and may be able to avoid the area impacted by the pressure. The pressure will become detrimental when it occurs over larger scales as its poor swimming ability is a restriction to its recoverability.

Therefore, it is probably ‘Not sensitive’ to the extraction of substratum due to its mobility and ability to utilize a variety of substrata. This pressure is not 'Not relevant' where Hippocampus hippocampus occurs on hard rock substratum.  

Low Medium Medium
Q: High
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

No evidence on the effects of abrasion on this species was found. However, it is associated with eelgrass and seagrass beds that are likely to be damaged or removed by abrasion and which may cause a decrease in local abundance of the resident seahorse populations. For example, these habitats are reported to be sensitive to abrasion due to the dropping of pots or creels, cables and chains associated with fixed gears, mooring and the anchoring of recreational vessels (Collins et al., 2010). A reduction in the abundance of eelgrass and seagrass may result in the loss of available substratum for this species. However, as Hippocampus hippocampus is mobile it may move to other areas of ideal habitat within the site of interest. However, abrasion may be detrimental if it occurs over large areas as its poor swimming ability will restrict recoverability. 

Furthermore, individual seahorses or their habitats were reported to be damaged by trawling particularly by the prawn trawling industry and as bycatch in gillnets, beach seines and traps (Hiscock et al., 2005; Cisneros-Montemayor et al., 2016; Lawson et al., 2017). The numbers of individuals taken can accumulate quickly due to industry demand and may impact population structure. For example, there may be shifts in reproduction due to pair bond disruption, imbalances in sex ratio and the removal of fertile males.

Sensitivity assessment. The sensitivity of Hippocampus hippocampus to abrasion can be linked to the sensitivity of its preferred substratum and the impact of anthropogenic exploitation. Therefore, abrasion may cause a significant reduction in the abundance of the seahorse population or its habitat of available substratum and resistance is assessed as ‘Low’. A resilience of ‘Medium’ (2-10 years) is suggested to account for the return of suitable substratum and subsequent recovery of the relevantly poor swimming resident population from the surrounding area.  Hence, sensitivity is assessed as ‘Medium’.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Hard rock is resistant to sub-surface penetration. Therefore, where this species' preferred substratum is hard rock the pressure is recorded as 'Not relevant'.  In sedimentary habitats penetrative gear are likely to cause more damage than abrasion (see above). For example, seagrass shoots and rhizomes may be removed from the impacted area (see SS.SMp.SSgr.Zmar).

Therefore, penetrating gears may cause a significant reduction in the abundance of the seahorse population or its habitat of available substratum and resistance is assessed as ‘Low’. A resilience of ‘Medium’ (2-10 years) is suggested to account for the return of suitable substratum and subsequent recovery of the relevantly poor swimming resident population from the surrounding area. Hence, sensitivity is assessed as ‘Medium’.

Medium High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Hippocampus hippocampus can be associated with seagrass and are commonly found near tidal inlets on substrata including silt and mud where some sediment may accumulate (Curtis & Vincent, 2005; Garrick-Maidment & Jones, 2004). But, no evidence on the direct effects of suspended sediments on the seahorse was found.

However, evidence in syngnathids has shown that reduced light intensity, which is a consequence of high turbidity as suspended particles scatter and absorb light (Voichick et al., 2018), can impact prey capture rates. For example, James & Heck (1994) reported that a visual predator such as Hippocampus erectus uses ambient light to feed. When ambient light was reduced via increased shading prey capture rates decreased. Furthermore, in fish, high turbidity levels were reported to reduce mate choice for those who use visual cues in sexual signalling (Candolin et al., 2007; Seehausen et al., 1997). As seahorses have been seen to use visual cues in clear water (Felício et al., 2006) and evidence into other sensory pathways is limited it suggests that an increase in turbidity may be detrimental to mate reinforcement and reproduction. 

Sensitivity assessment. Therefore, a resistance of ‘Medium’ is recorded, albeit with 'Low' confidence. Hence, resilience is assessed as ‘High’ and the species is recorded with ‘Low’’ sensitivity at the benchmark level.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

‘Light’ deposition of fine material to the seabed is unlikely to impact Hippocampus hippocampus as it is a mobile species and is able to swim away to avoid deposition. Therefore, the pressure is considered ‘Not relevant’ to this species at the benchmark level.

Medium High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

No evidence into the impact of ‘heavy’ deposition of fine material to the seabed for Hippocampus hippocampus was found. However, as it is up to 15 cm in length, and can swim away it would probably avoid localized deposition. However, some adults and smaller juveniles may be trapped by deposition.

Therefore, a resistance of ‘Medium’ is recorded, albeit with 'Low' confidence. Hence, resilience is assessed as ‘High’ and sensitivity assessed as Low’ at the benchmark level but with ‘Low’ confidence.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This pressure is Not assessed.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found on which to base an assessment.

Medium High Low
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

No evidence of underwater noise tolerance for Hippocampus hippocampus was found but evidence has been reported for other Hippocampus species.

Palma et al. (2019) found that when Hippocampus guttulatus was subjected to short-term (63.4–127.6 dB) and constant (up to 137.1 dB) motorboat noise there was an immediate physiological and behavioural response. Opercular movements increased and seahorses were much more likely to abandon their holdfasts. Abandonment can be detrimental to a cryptic species like Hippocampus hippocampus that have a poor swimming ability (Garrick-Maidment, 2007) and may lead to increased predation, poor local l recruitment and fragmentation in the population at a larger scale. Research into Hippocampus erectus (Anderson, 2009; Anderson et al., 2011) and Hippocampus capensis (Classens & Hodgson, 2018) also recorded similar findings in response to noise exposure.

Sensitivity assessment. As Hippocampus hippocampus inhabits shallow coastal habitats underwater noise especially from anthropogenic sources such as dredging, fishing activity and boat traffic is likely to have a significant effect on physiology and behaviour like that seen in Hippocampus sp. Therefore, a resistance of 'Medium' is recorded to represent the possible alteration in recruitment and predation.  Resilience is assessed as 'High' and sensitivity as ‘Low’ sensitivity at the benchmark level.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Palnas et al. (2013) reported that female Hippocampus hippocampus responded to different photothermic conditions. For example, low photoperiods (10L:14D) and a low temperature increase from 15-18°C decreased egg production (total eggs, clutch size and clutches per female). However, under high photoperiods (16L:8D) with the same low temperature egg production increased. Therefore, it was established that light regime was the initial controlling factor for female maturation and that temperature had a later influence. These results imply that shading, which has the potential to lower photoperiods, may have a detrimental effect of recruitment however, as it is a mobile species Hippocampus hippocampus would most likely be able to move away from shaded areas, and could, therefore, be seen as resistant.

Other research into Hippocampus sp. has shown similar results. For example, increasing light intensity from 500-3000 lx decreased the survival rate of juvenile Hippocampus erectus. Explanations include detrimental energy expenditure due to the high activity of the seahorse and its prey Artemia (Lin et al., 2009). In addition, Sheng et al (2006) recorded significant relations between different aged Hippocampus trimaculatus juvenile groups, light intensity and feeding time throughout the day. As feeding can be associated with growth an absence of this light intensity may cause a stunt in growth, which can impact sexual maturity and later reproduction for the species (Curtis et al., 2017). However, Wong & Benzie (2003) showed no impact of light intensity on growth in juvenile Hippocampus whitei. More research is needed to understand the effect of anthropogenic sources or light.

In addition, as Hippocampus hippocampus occupies areas of seagrass especially Zostera marina within the UK (Garrick-Maidment and Jones, 2004). Changes to light can impact the flowering plant density. For example, Zostera marina beds are seen to reduce growth rates under shading conditions (Ochieng et al., 2010). A decrease in habitat availability may influence the degree of crypsis, the ability to attach for stabilisation and the harbouring of food sources such as small crustaceans (Howard & Koehn 1985; Tipton & Bell 1988; Foster & Vincent 2004).

Nevertheless, resistance is assessed as ‘High’ as the seahorse could avoid areas of localized shading. Therefore, resilience is 'High' and the species is probably 'Not sensitive' at the benchmark level.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found on which to base an assessment.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant to Hippocampus hippocampus due to their anchoring and close proximity to the seabed. Collision by interaction with bottom towed fishing gears and moorings are addressed under ‘surface abrasion’.

High High Not sensitive
Q: High
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

No evidence was found on the impact of visual disturbance on Hippocampus hippocampus specifically. However, evidence for Hippocampus sp. suggests that visual cues such as flash photography has no significant impact on retinal anatomy, feeding, or behaviour (Harasti &Gladstone, 2013; De Brauwer et al., 2019). Therefore, a resistance of 'High' is recorded, albeit with 'Low' confidence. Hence, resilience is assessed as 'High' and the species is recorded as 'Not sensitive'.

Biological Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence of translocation, breeding or species hybridization in Hippocampus hippocampus was found so an assessment could not be made. 

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found to suggest a positive or negative interaction between non-indigenous invasive species and Hippocampus hippocampus.

None Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Diseases in Hippocampus sp. are associated with breeding, captivity and aquaculture (Vincent & Clifton-Hadley, 1989; Koldewey & Martin-Smith, 2010; Sanaye et al., 2013). Diseases such as ectoparasites, endoparasites, exophthalmia, pouch emphysema and flesh-erosion disease are all associated with seahorses in home aquaria and are treatable or preventable (Wooten, 2004; Seahorse Savvy, 2019). Some diseases such as those caused by Vibrio sp. can be detrimental to species survival with nearly 90% mortality for captive bred Hippocampus sp. (Alcaide et al., 2001).

In captivity, seahorses are prone to gas bubble disease which can manifest itself in two forms. The first form can be caused by stress and bacteria. Visible symptoms include:

  • Gas bubbles under the skin of the tail.

  • Gas bubbles under the skin on the snout.

This type of gas bubble disease is very destructive. It may be accompanied by fungus and will eventually cause death (Garrick-Maidment, 1997). The second type of gas bubble disease may be caused by decaying embryos but there is a suggestion that high levels of dissolved oxygen from protein skimmers can cause similar problems in aquaria (Garrick-Maidment pers. comm., February 2004). An internal injury in the pouch may also be responsible (Garrick-Maidment, 1997). Gaseous build can see seahorses lose control of their buoyancy and hang upside down in the water and not be able to anchor themselves (Garrick-Maidment, 1997). This form of the disease can be cured (Garrick-Maidment, 1997).

No specific effects of microbial pathogens or parasites could be found for Hippocampus hippocampus, however, inference may be drawn from other species of Hippocampus sp. For example:

  • An abundant growth of parasitic hydroids (believed to be Serialia lendigera) on the head, neck, and anterior body parts in an aquarium held Hippocampus ramulosus was reported but no specific effects were observed (Newman, 1873; cited in Lauckner, 1984), and

  • In a New York aquarium, the ciliate Uronema marinum was found in the musculature and skin in seahorses. The ciliates also invaded the kidneys, urinary bladder, neural canal, blood vessels and gills and was highly destructive to the host's tissues, ingesting blood cells and tissue debris (Cheung et al., 1980).

Evidence of diseases in the wild is scarce. However, during census dives, divers recorded white spots on the body of Hippocampus hippocampus and recorded it as the onset of disease (Curtis et al., 2017).

Sensitivity assessment. Therefore, resistance is assessed as ‘None’ to represent a potential loss of species abundance like that caused by Vibrio sp, while resilience is assessed as ‘Medium’. Hence, sensitivity is assessed as ‘Medium’ albeit with ‘Low’ confidence.

Low Medium Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

Seahorses including Hippocampus hippocampus are targeted for trade worldwide. The main reasons for their trade are for traditional medicines and for aquariums. It is estimated that one million seahorses worldwide are taken each year for the purpose of the aquaria trade with records in 1994 suggesting that the UK imported 4000 live seahorses for distribution into aquariums (Wilson, 1995; cited in Vincent, 1996). Predictions for seahorse extraction from UK waters is said to be of increasing interest with a small but significant number of animals being taken in Weymouth Bay in Dorset commercially (price reported as £65 per fish) and a handful of animals being taken by divers and fishermen particularly around the Channel Islands of Jersey and Guernsey (JNCC, 2002; Garrick-Maidment & Jones, 2004).

Specifically, the targeting of Hippocampus hippocampus may have detrimental impacts on population abundance and structure as they are commonly found in low densities compared to other Hippocampus sp. (Curtis & Vincent, 2005; Gristina et al., 2015). Therefore, the loss of a small proportion of the population could be enough to dislodge sexual relations and alter community structure.

Sensitivity assessment. Therefore, resistance is assessed as ‘Low’. Hence, resilience is assessed as 'Medium' and sensitivity as 'Medium'.

Low Medium Medium
Q: High
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

Individual seahorses or their habitats are reported to be damaged by trawling particularly by the prawn trawling industry and as bycatch in gillnets, beach seines and traps (Hiscock et al., 2005; Cisneros-Montemayor et al., 2016; Lawson et al., 2017). The numbers of individuals taken can accumulate quickly due to industry demand and may impact population structure. For example, there may be shifts in reproduction due to pair bond disruption, imbalances in sex ratio and the removal of fertile males.

Sensitivity assessment. Therefore, resistance is assessed as ‘Low’. Hence, resilience is assessed as 'Medium' and sensitivity as 'Medium'.

Importance review

Policy/legislation

Berne ConventionAppendix II
CITESAppendix B
Wildlife & Countryside ActSchedule 5, section 9
UK Biodiversity Action Plan Priority
Species of principal importance (England)
OSPAR Annex V
IUCN Red ListData Deficient (DD)
Features of Conservation Importance (England & Wales)

Status

Non-native

Importance information

To date, few conservation strategies have been implemented for Hippocampus hippocampus. However, seahorses are listed for protection under UK statutes, EU directives and international conventions.

  • The entire genus Hippocampus was listed in Appendix II of the IUCN Red List in November 2002 but the implementation of the listing was delayed until 2004.
  • Hippocampus hippocampus was previously listed in 1996 as vulnerable (VU A2cd) under the 1994 criteria. This assessment was based on suspected past declines in occupancy, occurrence and habitat, as well as on potential levels of exploitation. The IUCN reported that there is no appropriate data on the biology and ecology, habitat, abundance or distribution of Hippocampus hippocampus. As a result, Hippocampus hippocampus has been reassessed as 'data deficient' under new criteria (Marsden et al., 2003).
  • The European Union regulate and/or monitor the use of dried and live syngnathids but without management requirements (TRAFFIC, 2002).
  • In the UK, the Seahorse Trust submitted Hippocampus hippocampus and Hippocampus guttulatus for full protection under section 5 of the Wildlife and Countryside Act 1981 in February 2000 (Garrick-Maidment & Jones, 2004). This proposal is still under review and is awaiting consultation by the Government with a wide range of organisations and individuals concerned with the review process.
  • In 2002, JNCC supported this proposal and recommended that both species be given full legal protection under section 5 of the Wildlife and Countryside Act.

The seahorse trade
Seahorses of Hippocampus spp. are globally exploited for use as medicines, aquarium fishes, curios and even foods. The majority of seahorses go to traditional Chinese medicine and its derivatives (e.g. Japanese and Korean traditional medicines) (Vincent, 1996). Treatments including seahorses are believed to benefit a range of conditions including respiratory disorders such as asthma, sexual dysfunctions, general lethargy and pain (Lourie et al., 1999).

The statistics on the seahorse trade are limited and the few that have been published suggest that the annual consumption within the Asian nations alone may amount to 45 t of dried seahorse (about 16 million individuals). The largest users appear to be the Chinese (estimated 20 t), Taiwan (11.2 t), and Hong Kong (10 t) (Vincent, 1996). These figures are underestimates as they include only the trade that passed through China, Hong Kong and Singapore. Therefore, the total global consumption of seahorses will be much greater, and as of yet no statistics are available (Vincent, 1996).

The British Isles is now being targeted for collection for the aquarium trade, with a small but significant number of animals being taken in Weymouth Bay in Dorset commercially (price reported as £65 per fish) and a handful of animals being taken by divers and fishermen particularly around the Channel Islands of Jersey and Guernsey (JNCC, 2002). It has been suggested that as stocks of Hippocampus hippocampus diminish in other countries and as more unusual species of seahorse are sought after, then this lucrative trade is bound to increase in UK waters, which could lead to a larger scale fishery (JNCC, 2002).

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Datasets

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Citation

This review can be cited as:

Sabatini, M., Nash, R.A. & Ballerstedt, S. 2021. Hippocampus hippocampus Short snouted seahorse. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28-10-2021]. Available from: https://www.marlin.ac.uk/species/detail/1788

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Last Updated: 16/06/2021

Tags: sea horse