Habitat and Ecology
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).
Recorded at 20 meters.
Habitat: demersal. Found in bays and estuaries (Ref. 4281).
Life History and Behavior
Molecular Biology and Genetics
Barcode data: Hippocampus capensis
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Hippocampus capensis
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
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.
- 1996Vulnerable(Baillie and Groombridge 1996)
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
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.).
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.).
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.
Relevance to Humans and Ecosystems
The Knysna // seahorse or Cape seahorse (Hippocampus capensis) is a species of fish in the family Syngnathidae. It is endemic to the south coast of South Africa, where it has been found in only three brackish water habitats: the estuary of the Keurbooms River in Plettenberg Bay, the Knysna Lagoon, and the estuarine portion of the Swartvlei system in Sedgefield. The limited range of this seahorse puts it at great risk of extinction.
The Knysna seahorse is a small, delicate creature with a standard length of up to 12 centimeters. Colouration is strongly influenced by the surrounding environment and a particular individual's mood. It varies from pale green to brown (often with darker speckles) to purplish black. The body is encased in a series of bony rings, the snout is relatively short, and the neck arches in a smooth curve without a crown. The tail is muscular and is used to grasp a mate during courtship or to anchor the fish to the substrate.
Habitat and Ecology
The Knysna seahorse occurs mostly in areas with high vegetation cover (at least 75%), and is associated with five dominant aquatic plants: Zostera capensis, Caulerpa filiformis, Codium extricatum, Halophila ovalis and Ruppia cirrhosa. While the Keurbooms and Swartvlei estuaries both have very dense plant cover, vegetated sites only make up approximately 11% of the Knysna Lagoon. Large areas of habitat in this system may thus be unsuitable for H. capensis.
The fish is well adapted to estuarine habitat and can tolerate a wide range of environmental conditions, such as salinities ranging from 1–59 ‰.
Breeding occurs in the austral summer, when water temperatures approach 20°C. Sexual maturity is attained in about one year at 65 mm standard length.
Genetic data from the mitochondrial control region indicate that, even though each of the three populations of Hippocampus capensis has a unique combination of haplotypes, there is no support for the hypothesis that each represents a distinct subspecies. There is thus no compelling reason not to translocate individuals between estuaries, should this become necessary. Low genetic diversity in the Swartvlei estuary suggests that this population is partially isolated from the other two populations.
Census data from 2002 and 2003 (WWF-SA) indicated that the population sizes of Hippocampus capensis in the Keurbooms and Swartvlei estuaries can at times far exceed that in the much larger Knysna Lagoon. However, they fluctuate considerably. In the Keurbooms estuary, a period of strong river flow may even have resulted in the temporary extinction of the species, suggesting that this estuary has no permanent seahorse population and merely provides habitat when conditions are favourable. Hippocampus capensis was found again in the estuary during more recent surveys conducted by the ORCA Foundation, but it was also found that this population diminished as a result of floods during 2007 and 2011.
Hippocampus capensis is closely related to the Indian Ocean population of the widespread Indo-Pacific seahorse H. kuda. The Knysna seahorse's smaller size, shorter snout, and reduced coronet are likely adaptations to improve manoeuvrability in the dense seagrass habitats typical of South African estuaries.
This article incorporates text from the ARKive fact-file "Cape seahorse" under the Creative Commons Attribution-ShareAlike 3.0 Unported License and the GFDL.
- Czembor, C. A. & E. M. Bell. 2012. Hippocampus capensis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. Downloaded on 27 May 2013.
- Hippocampus capensis FishBase. Retrieved 2011-08-27.
- Teske, P.R., Lockyear, J.F., Hecht, T. & 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. doi:10.3377/1562-7020(2007)42[23:dteksh]2.0.co;2.
- Whitfield, A.K. (1995). "Threatened fishes of the world: Hippocampus capensis Boulenger, 1900 (Syngnathidae).". Environmental Biology of Fishes 44: 362. doi:10.1007/bf00008251.
- Teske, P.R., Cherry, M.I., Matthee, C.A. (2003). "Population genetics of the endangered Knysna seahorse, Hippocampus capensis.". Molecular Ecology 12: 1703–1715. doi:10.1046/j.1365-294x.2003.01852.x.
- Lockyear, J.L., Hecht, T., Kaiser, H. & Teske, R.P. (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. doi:10.2989/16085910609503897.
- Teske, P.R., Hamilton, H., Palsboll, P.J., Choo, C.K., Gabr, H., Lourie, S.A., Santos, M., Sreepada, M., Cherry, M.I. & Matthee, C.A. (2005). "Molecular evidence for long-distance colonization in an Indo-Pacific seahorse lineage.". Marine Ecology Progress Series 286: 249–260. doi:10.3354/meps286249.
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