The

Knysna Knysna () is a town with 76,150 inhabitants (2019 mid-year estimates) in the Western Cape province of South Africa. and is one of the destinations on the loosely defined Garden Route tourist route. It lies at 34° 2' 6.3168'' S and 23° 2' 47. ...

seahorse or Cape seahorse (''Hippocampus capensis'') is a species of

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

in the family Syngnathidae. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the south coast of

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

, where it has been found in only three brackish water habitats: the estuary of the

Keurbooms River The Keurbooms River ( af, Keurboomsrivier) is a river in the Western Cape Province in South Africa. The river has its sources south of Uniondale in the Langkloof and flows in a roughly southeastern direction. It passes De Vlugt and the Prince A ...

in Plettenberg Bay, the

Lagoon, and the estuarine portion of the

Swartvlei Sedgefield is a coastal town on the Garden Route in the Western Cape province of South Africa. It is situated on the N2 national road, between George and Knysna. The town was proclaimed in 1929 on the farm Sedgefield, which in turn was named in 1 ...

system in

Sedgefield Sedgefield is a market town and civil parish in County Durham, England. It had a population of 5,211 as at the 2011 census. It has the only operating racecourse in County Durham. History Roman A Roman 'ladder settlement' was discovered by C ...

. The limited range of this seahorse puts it at great risk of extinction.

Description

The Knysna seahorse is a small, delicate creature with a standard length of up to 12 centimetres. 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.
Hippocampus capensis
' FishBase. Retrieved 2011-08-27.

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 ''Zostera capensis'' is a species of dwarf eelgrass growing along the shores of the Indian and Atlantic oceans on the African coast. Its range extends from southern Kenya, through Tanzania, Mozambique, Madagascar, and South Africa up to Angola ...

'', ''

Caulerpa filiformis ''Caulerpa filiformis'' is a species of seaweed in the '' Caulerpaceae'' family. It has been recorded at coastal sites in Australia and South Africa. References filiformis Species described in 1841 {{Green algae-stub ...

'', '' Codium extricatum'', ''

Halophila ovalis ''Halophila ovalis'', commonly known as paddle weed, spoon grass or dugong grass, is a seagrass in the family Hydrocharitaceae. It is a small herbaceous plant that occurs in sea beds and other saltwater environments in the Indo-Pacific. The fir ...

'' 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.

Population structure

Genetic data from the mitochondrial control region indicate that, even though each of the three populations of ''Hippocampus capensis'' has a unique combination of

haplotype A haplotype ( haploid genotype) is a group of alleles in an organism that are inherited together from a single parent. Many organisms contain genetic material ( DNA) which is inherited from two parents. Normally these organisms have their DNA or ...

s, there is no support for the hypothesis that each represents a distinct

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

. This finding was recently confirmed with more variable

microsatellite A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...

data. 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.

Population sizes

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.

Evolution

''Hippocampus capensis'' is closely related to the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

population of the widespread

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

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.

Experimentation

Seahorses were taken from the coast and put in sections of Thesen Islands Marina. Hydrolab in the KEMP (Knysa Estuarine Mornitorings Platform) replicated the springs and fences and left there so that it can grow and maturation to see which they prefer. The cages were all test to see where they would go.

Captive breeding

Captive bred populations of ''Hippocampus capensis'' are held at the

Two Oceans Aquarium The Two Oceans Aquarium is an aquarium located at the Victoria & Alfred Waterfront in Cape Town, Western Cape, South Africa. The aquarium was opened on the 13 November 1995 and comprises several exhibition galleries with large viewing windows: ...

Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...

and at Antwerp Zoo. Knysna seahorses are also bred and sold for the ornamental fish industry.

Sources

External links

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IOL News: Single seahorse dad mourns loss of wife
{{Taxonbar, from=Q2673571 Hippocampus (genus) Fish of South Africa Endemic fauna of South Africa Taxa named by George Albert Boulenger Fish described in 1900 Taxonomy articles created by Polbot