Hippocampus capensis 

Scope: Global

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Syngnathiformes Syngnathidae

Scientific Name: Hippocampus capensis
Species Authority: Boulenger, 1900
Common Name(s):
English Knysna Seahorse, Cape Seahorse

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(i,ii,iii,iv)c(ii)+2ab(i,ii,iii,iv)c(ii) ver 3.1
Year Published: 2012
Date Assessed: 2010-07-01
Assessor(s): Czembor, C.A. & Bell, E.M.
Reviewer(s): Teske, P. & Whitfield, A.

Hippocampus capensis is assessed as Endangered (EN B1ab(i,ii,iii,iv)c(ii)+2ab(i,ii,iii,iv)c(ii)) because it has an extent of occurrence (EOO) of 300 km², an area of occupancy (AOO) of 27 km², and it is only found in three locations. Also, the species is experiencing continuing decline in the extent of occurrence, area of occupancy, quality of habitat, and number of locations in which it is found. The species is also experiencing extreme fluctuations in its area of occupancy. Additional monitoring is needed to determine population trends for this species.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

Hippocampus capensis is thought to currently be found in the Knysna, Swartvlei, and Keurbooms estuaries in South Africa (M. Cherry pers.comm., T. Meintjes pers. comm., P. Joubert pers. comm.). Historical and anecdotal records indicate that this species could previously be found in Klein Brak, Groot Brak, Goukamma, Groot, Kromme, Kabeljous and Gamtoos estuaries (Bell et al. 2003, Lockyear et al. 2006), but surveys carried out between 2001 and 2003 could only locate individuals in the Knysna, Swartvlei, and Keurbooms estuaries (Lockyear et al. 2006).

The Knysna estuary (estuarine mouth: 34°04′ S, 23°03′ E) is by far the largest of the three estuarine systems, covering a water surface area of 19–21 km² (Geldenhuys 1979 in Teske et al. 2003). However, extensive sandbanks mean that the subtidal area covers only 10 km² (Bell et al. 2003). The Keurbooms estuary (estuarine mouth 34°02′ S, 23°23′ E) is located approximately 42 km east of the Knysna Estuary, and is much smaller, at 2.7–3 km² (Duvenage and Morant 1984 in Teske et al. 2003, Oudegeest and Laterveer 2005). The third and smallest estuary, Swartvlei estuary (34° S, 22°46′ E), is located approximately 26 km west of the Knysna estuary, with a total water surface of 2–3 km² (Liptrot 1978 in Teske et al. 2003, Oudegeest and Laterveer 2005). The combined water surface of these estuaries is approximately 27 km².

The area of occupancy for H. capensis was estimated to be less than 50 km² in 2000 (Lockyear 1999, Hilton-Taylor 2000), but the total surface area of estuaries currently containing known populations of H. capensis is 27 km². Considering that this species’ abundance within the estuaries is low and distributions are patchy (Teske et al. 2007), that significantly more H. capensis are found at sites characterized by high vegetation cover and vegetated sites are limited in these estuaries (e.g., only approximately 11% of Knysna estuary, Teske et al. 2007), and that sandbanks and other structures reduce available habitat for this species, the actual area of occupancy is likely to be much less than 27 km².

Dispersal within the Knysna estuary is probably accomplished passively through tidal currents, and it is likely that some juvenile seahorses may be flushed out to the sea before finding suitable habitat (Teske et al. 2003). This may provide the two smaller estuaries, Keurbooms and Swartvlei, with an infrequent but continuous input of new colonists from the Knysna estuary (Teske et al. 2003). Channel nets deployed to catch ichthyoplankton in the Swartvlei estuary yielded a net movement of 4,091 juvenile H. capensis out of the estuary mouth in October 1986 and a net movement into the estuary of 250 juveniles in November 1986, over a 24-hr period (Whitfield 1989). The total extent of occurrence for this species may include the three estuaries with known populations as well as the inshore coastal areas connecting the estuaries – a total area certainly no more than 300 km² – but the rates of re-entry into estuaries by juveniles is unknown; thus, according to the precautionary principle, the actual extent of occurrence may be little more than that area of occupancy (A. Whitfield pers. comm.).

Countries occurrence:
South Africa
FAO Marine Fishing Areas:
Atlantic – southeast
Additional data:
Estimated area of occupancy (AOO) - km2:27Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):YesEstimated extent of occurrence (EOO) - km2:300
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:3Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:No
Lower depth limit (metres):20
Upper depth limit (metres):1
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The total population estimate for Hippocampus capensis in the Knysna estuary (mean, with range representing 95% confidence intervals) was 89,000 seahorses (range 30,000–148,000) in 2000 (Bell et al. 2003) and 62,000 (range 41,000–82,000) in 2001. In 2002, the Swartvlei and Keurbooms supported 995,000 (range 390,000–1.7 million) and 836,000 (range 242,000–1.7 million) seahorses, respectively. In 2003, the Swartvlei estuary supported only 176,000 (range 83,000–280,000) seahorses, and no seahorses could be found in the Keurbooms estuary (Lockyear et al. 2006).

As of 2003, assuming the total population of H. capensis in the Knysna estuary remained relatively constant at 62,000 individuals between 2001 and 2003, the estimated total population in all estuaries was 238,000 seahorses, range 124,000–360,000, down from 1.9 million seahorses, range 675,000–3.5 million, between 2001 and mid-2002 (Lockyear et al. 2006). Juveniles typically constitute 5–20% (average 13%) of individuals sampled (Lockyear et al. 2006), resulting in an estimated mean population size of approximately 207,000 mature individuals as of 2003.

In 2005, the Knysna and Swartvlei population sizes appeared to be healthy (M. Cherry pers. comm.) and, in 2010, populations were reported anecdotally to be seen in abundance in many of the marinas in the Knysna estuary and as being present in the Swartvlei estuary (T. Meintjes pers. comm., P. Joubert pers. comm.). Similar to the 2003 surveys, preliminary surveys of the Keurbooms estuary in 2011 found no seahorses, despite the availability of suitable habitat (Appleby 2011). However, anecdotal evidence indicates individuals may occasionally be seen in this estuary (T. Meintjes pers. comm.; Appleby 2011).

Recently constructed artificial habitats (e.g., marinas/boat harbours) appear to act as protective habitat for H. capensis (P. Joubert pers. comm.) and, as relatively large numbers of individuals are seen in these habitats (B. Allanson pers. comm.), they may have a beneficial effect on population size.

It is unknown whether extreme fluctuations of population size occur in this taxon. In 2002, seahorse densities were high in the Swartvlei and Keurbooms estuaries but, in 2003, seahorses were absent from the Keurbooms estuary and the population size in the Swartvlei estuary had decreased by more than 80% (Lockyear et al. 2006). The population size in the Knysna estuary declined approximately 30% between 2000 and 2001 (Bell et al. 2003, Lockyear et al. 2006). Since 2003, individuals have been seen in abundance in the Knysna and Swartvlei estuaries, although population size has not been quantified recently (M.Cherry pers. comm., T. Meintjes pers. comm., P. Joubert pers. comm.). Populations may not yet have recovered in the Keurbooms estuary, according to preliminary 2011 surveys (Appleby, 2011). These results suggest that populations may occasionally undergo extreme fluctuations in the smaller estuaries, but experience fluctuations to a lesser degree in the larger Knysna estuary. It is expected that fluctuations are not due to changes in life stages or dispersal, but rather that individuals are susceptible to being washed out of the smaller estuaries as a result of floods and increased stormwater run-off from developments (Marker 2003, Lockyear et al. 2006). With H. capensis’ poor swimming ability and reliance on plant holdfasts, strong currents could sweep animals and plants out into the sea and silt depositions could result in the smothering of habitat and the clogging of gills. Individuals remaining in small pockets of water in the drained estuaries after floods may be subject to mortality from increased water temperatures (Russell 1994) and predation (P. Joubert pers. comm.). The larger Knysna estuary thus may act as an infrequent but continuous exporter of colonists to the smaller estuaries (Teske et al. 2003). The rates of recolonization are after large population declines are unknown (M. Cherry pers. comm.). However, anecdotal evidence indicates that the populations in the Knysna, Swartvlei, and Keurbooms estuaries have increased in numbers since the 85% decline in population observed in 2003 (T. Meintjes pers. comm., P. Joubert pers. comm.).
Current Population Trend:Unknown
Additional data:
Number of mature individuals:207000Continuing decline of mature individuals:Unknown
Extreme fluctuations:UnknownPopulation severely fragmented:Yes
Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:YesAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:Hippocampus capensis are found at depths between 0.5–20 m (Toeffie 2000 in Bell et al. 2003) in association with submerged aquatic plants. Within Knysna, H. capensis are associated with five dominant aquatic plants: Zostera capensis, Caulerpa filiformis, Codium extricatum, Halophila ovalis and Ruppia cirrhosa (Teske et al. 2007), though they are most likely to be found grasping Zostera capensis eelgrass holdfasts (Bell et al. 2003). This species is also associated with Pyura stolonifera (a large ascidian) and sponges, but significantly more adult and juvenile seahorses are found at sites characterized by high vegetation cover (75%) than at sites with lower cover (Teske et al. 2007). Vegetated sites make up approx 11% of Knysna estuary (Teske et al. 2007), thus large areas of habitat in the Knysna estuarine system may be unsuitable for H. capensis because of the absence of submerged vegetation (Toeffie 2000 in Lockyear et al. 2006). H. capensis can also tolerate a wide range of environmental conditions (Lockyear et al. 2006), such as salinities ranging from 1–59 g/kg (Whitfield 1995).

Juvenile H. capensis are often found in low frequencies during surveys, likely because they spend time in the plankton, at least initially, and older juveniles may use different habitat from the adults sampled (Bell et al. 2003). Juvenile length is strongly dependent on temperature and photoperiod, with higher temperatures and longer photoperiods resulting in juveniles being smaller in captivity (Lockyear et al. 1997).

H. capensis adults feed predominantly on small crustaceans which are sucked from submerged leaf surfaces or from the water column (Whitfield 1995).

Breeding occurs in the austral summer, when water temperatures approach 20°C and sexual maturity is attained in about one year at 65 mm standard length (Whitfield 1995). In captivity, H. capensis are diurnally active and have an elaborate courtship and mating ritual involving brood pouch inflation, tail grasping and ‘face-to-face’ positioning (Grange and Cretchley 1995).
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):1-3
Congregatory:Congregatory (and dispersive)

Use and Trade [top]

Use and Trade: As this species is protected, it is not commercially traded or used for subsistence. Small numbers of specimens, however, were previously provided to researchers (McPherson and Vincent 2011). Historically, individuals were taken for the aquarium trade (Skelton 1987 in Whitfield 1995).

Threats [top]

Major Threat(s): Hippocampus capensis is the only seahorse species thus far inferred to be primarily at risk from habitat damage (Lockyear 2000, Bell et al. 2003). This species’ primary habitat, the Knysna estuary, is among the most heavily used water bodies in South Africa (Bell et al. 2003) and human settlements and associated industrial, domestic, and recreational activities are increasing around all estuaries where this species has been recorded (Skelton 1987 in Whitfield 1995).

The area is under threat from urban expansion and land-use changes in the catchment; stormwater runoff has increased in volume and peak flows carry suspended sediment into the estuary (strong currents sweep animals and plants out into the sea and silt depositions result in the smothering of habitat and the clogging of gills); rising population and equity development, to provide piped water for all, threatens freshwater inflow; and waste water disposal brings in chemical and biological pollutants (Marker 2003). Development surrounding the estuary is known to deposit trace metals, hydrocarbons, pesticides and organic wastes into the estuary (Chmelik 1975 in Bell et al. 2003). Within the estuary, the cumulative impact of boats may significantly affect the seagrass habitats of this species (Lockyear et al. 2006). Pollution events or other disturbances which affect the submerged plant beds of these estuaries will have a direct and indirect impact on H. capensis populations (Skelton 1987 in Whitfield 1995), yet construction developments and pollution continue (Lockyear et al. 2006, Teske et al. 2007).

H. capensis also appears to be vulnerable to water temperature increases. In 1991, 3,000 dead seahorses were found along the shores of the Swartvlei estuary after heavy rainfall and flooding caused a breach in the estuarine mouth and partially drained the estuary, leaving many individuals trapped in small pockets of remaining water. Mortality was attributed to the sudden increase in water temperature following the reduction in water level (Russell 1994). When the water levels drop and individuals are restricted to smaller pools, they are also susceptible to high levels of predation (P. Joubert pers. comm.). Furthermore, large-scale flooding may substantially alter the estuaries in which this species is found (C.A.P.E. Estuaries Management Programme 2010). The present rate at which construction developments and other human activities are increasing along the estuary is alarming; the resulting habitat degradation may make recovery of populations after a naturally occurring disaster, such as a freshwater flood, increasingly difficult (Teske et al. 2003).

Furthermore, recently observed specimens of H. capensis also appear to be infected with lesions; the disease appears most often in individuals using artificial habitats (P. Joubert pers. comm.).

Conservation Actions [top]

Conservation Actions: Hippocampus capensis is protected by law in the Knysna estuary (Sea Fisheries Act of 1973) and both the Swartvlei and Knysna estuaries fall under the protection of the National Parks Board (Whitfield 1995).

A conservation breeding program was started in 1998 to help mitigate the natural and anthropogenic threats to this species (Galbusera et al. 2007). Offspring of this founding stock was transferred from the Zoological Society of London to the Royal Zoological Society of Antwerp (RZSA), currently the only zoo in Europe where this species is being bred in captivity (Galbusera et al. 2007).

This species is listed on Appendix II of CITES.

Classifications [top]

9. Marine Neritic -> 9.9. Marine Neritic - Seagrass (Submerged)
suitability:Suitable  major importance:Yes
9. Marine Neritic -> 9.10. Marine Neritic - Estuaries
suitability:Suitable  major importance:Yes
1. Land/water protection -> 1.1. Site/area protection
1. Land/water protection -> 1.2. Resource & habitat protection
2. Land/water management -> 2.1. Site/area management

In-Place Research, Monitoring and Planning
  Action Recovery plan:No
  Systematic monitoring scheme:No
In-Place Land/Water Protection and Management
  Conservation sites identified:Yes, over part of range
  Occur in at least one PA:Yes
  Area based regional management plan:No
  Invasive species control or prevention:Not Applicable
In-Place Species Management
  Harvest management plan:No
  Successfully reintroduced or introduced beningly:No
  Subject to ex-situ conservation:Yes
In-Place Education
  Subject to recent education and awareness programmes:Unknown
  Included in international legislation:Yes
  Subject to any international management/trade controls:Yes
1. Residential & commercial development -> 1.1. Housing & urban areas
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.3. Indirect ecosystem effects

1. Residential & commercial development -> 1.2. Commercial & industrial areas
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation

1. Residential & commercial development -> 1.3. Tourism & recreation areas
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.1. Ecosystem conversion
  • 2. Species Stresses -> 2.2. Species disturbance

5. Biological resource use -> 5.4. Fishing & harvesting aquatic resources -> 5.4.3. Unintentional effects: (subsistence/small scale)
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.1. Species mortality

6. Human intrusions & disturbance -> 6.1. Recreational activities
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.1. Ecosystem conversion
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.2. Species disturbance

7. Natural system modifications -> 7.2. Dams & water management/use -> 7.2.1. Abstraction of surface water (domestic use)
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.3. Indirect ecosystem effects

9. Pollution -> 9.1. Domestic & urban waste water -> 9.1.1. Sewage
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation

9. Pollution -> 9.1. Domestic & urban waste water -> 9.1.2. Run-off
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Unknown ⇒ Impact score:Unknown 
→ Stresses
  • 2. Species Stresses -> 2.1. Species mortality

11. Climate change & severe weather -> 11.4. Storms & flooding
♦ timing:Ongoing ♦ scope:Unknown ♦ severity:Very Rapid Declines ⇒ Impact score:Unknown 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation
  • 2. Species Stresses -> 2.1. Species mortality
  • 2. Species Stresses -> 2.2. Species disturbance

1. Research -> 1.2. Population size, distribution & trends
1. Research -> 1.3. Life history & ecology
2. Conservation Planning -> 2.2. Area-based Management Plan
3. Monitoring -> 3.1. Population trends
3. Monitoring -> 3.4. Habitat trends

Bibliography [top]

Appleby, C. 2011. Presence/absence surveys for the Knysna Seahorse, Hippocampus capensis in the Keurbooms Estuary, Plettenberg Bay. Orca Foundation. Plettenberg Bay, South Africa.

Bell, E.M., Lockyear, J.F. and McPherson, J.M. 2003. First field studies of an endangered South African seahorse, Hippocampus capensis. Enviornmental Biology of Fishes 67: 35–46.

C.A.P.E. Estuaries Management Programme. 2010. Keurbooms/Bitou Estuary Management Plan: Situation Assessment. In: Eviro-fish Africa (pty) Ltd. (ed.). Grahamstown, South Africa.

Galbusera, P.H.A., Gillemot, S., Jouk, P., Teske, P.R., Hellemans, B. and Volckaert, F. 2007. Isolation of microsatellite markers for the endangered Knysna seahorse Hippocampus capensis and their use in the detection of a genetic bottleneck. Molecular Ecology Notes 7(4): 638-640.

Grange, N. and Cretchley, R. 1995. A preliminary investigation of the reproductive behaviour of the Knysna seahorse Hippocampus capensis Boulanger, 1900. South African Journal of Aquatic Science 21: 103-104.

Hilton-Taylor, C. (compiler). 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN. 2012. IUCN Red List of Threatened Species (ver. 2012.1). Available at: (Accessed: 19 June 2012).

Lockyear, J. 1999. Abundance and distribution of the Knysna Seahorse, Hippocampus capensis.

Lockyear, J. 2000. Hippocampus capensis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. .

Lockyear, J., Hecht, T., Kaiser, H., Teske, P.R. 2006. The distribution and abundance of the endangered Knysna seahorse Hippocampus capensis (Pisces: Syngnathidae) in South African estuaries. African Journal of Aquatic Science 31: 275-283.

Lockyear, J., Kaiser, H. and Hecht, T. 1997. Studies on the captive breeding of the Knysna seahorse, Hippocampus capensis. Aquarium Sciences and Conservation 1: 129-136.

Marker, M.E. 2003. The Knysna Basin, South Africa: geomorphology, landscape sensitivity and sustainability. Geographical Journal 169: 32-42.

McPherson, J.M. and Vincent, A.C.J. 2011. Trade in seahorses and other syngnathids in Africa. In: A.C.J. Vincent, B.G. Giles, C.A. Czembor, S.J. Foster (ed.), Trade in Seahorses and other Syngnathids in non-Asian Countries (1998-2001), pp. 7-38. Fisheries Centre, University of British Columbia, Canada.

Oudegeest, T. and Laterveer, M. 2005. Project Hica (Nov 2003-Jan 2005): Management report on the conservation of a marine fish species. Rotterdam Zoo, Rotterdam.

Russell, I.A. 1994. Mass mortality of marine and estuarine fish in the Swartvlei and Wilderness Lake Systems, Southern Cape. South African Journal of Aquatic Science 20: 93-96.

Teske, P.R., Cherry, M.I. and Matthee, C.A. 2003. Population genetics of the endangered Knysna seahorse, Hippocampus capensis. Molecular Ecology 12: 1703-1715.

Teske, P.R., Lockyear, J., Hecht, T. and Kaiser, H. 2007. Does the endangered Knysna seahorse, Hippocampus capensis, have a preference for aquatic vegetation type, cover or height? African Zoology 42: 23-30.

Whitfield, A.K. 1989. Ichthyoplankton interchange in the mouth region of a southern African estuary. Marine Ecology Progress Series MESEDT 54: 25-33.

Whitfield, A.K. 1995. Threatened fishes of the world:Hippocampus capensis Boulenger, 1990 (Syngnathidae). Environmental Biology of Fishes 44: 362.

Citation: Czembor, C.A. & Bell, E.M. 2012. Hippocampus capensis. The IUCN Red List of Threatened Species 2012: e.T10056A495994. . Downloaded on 29 July 2016.
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