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Knysna Seahorse in dire straits

The Knysna seahorse Hippocampus capensis is an endemic seahorse species to the Western Cape, found in only three estuarine systems: Swartvlei Estuary, Knysna Estuary, and Keurbooms Estuary. Historically this species was also found in Klein Brak, Groot Brak, Goukamma, Groot, Kromme, Kabeljous, and Gamtoos estuaries but they have not been seen in these systems for many years. Knysna seahorses are a curious blend of creatures:  they have the head of a horse with a thin snout; they have the prehensile tail of a monkey; males have the pouch of a kangaroo; they have the gills and fins of a fish; and they have the ability to change colour, and independently moving eyes of a chameleon. The Knysna seahorse measures 12cm in length, and ranges in colour from pale green to brown to purplish black. The Knysna seahorse is found at depths between 50cm and 20m, and is most likely found grasping Cape eelgrass Zostera capensis holdfasts in sites characterised by high vegetation cover. Adults feed predominantly on small crustaceans which are sucked from submerged leaf surfaces or the water column. Breeding occurs in summer, and males and females have an elaborate courtship and mating ritual which involves the male inflating his brood pouch, tail grasping, and face-to-face positioning. The female seahorse deposits her eggs into the male’s brood pouch and after about 4 weeks gestation they hatch out into the water, miniature replicates of their parents. Unfortunately Knysna seahorses, and seahorses in general, have life histories which are characterised by a sparse distribution, low mobility, small home ranges, low fecundity, and mate fidelity. These make seahorses particularly vulnerable to habitat degradation, incidental bycatch, and overexploitation. Of these the Knysna seahorses is primarily at risk from habitat degradation. The species primary location is the Knysna estuary, one of the most heavily used water bodies in South Africa, with human settlements and associated industrial, domestic and recreational activities increasing.

 

Written by: Minke Witteveen

 

For further reading:

  • Bell, E.M., Lockyear, J.F., McPherson, J.M., Marsden, A.D. & Vincent, A.C.J. 2003. First field studies of an Endangered South African seahorse, Hippocampus capensis. Environmental Biology of Fishes 67: 35-46.
  • Czembor, C.A. & Bell, E.M. 2012. Hippocampus capensis. The IUCN Red List of Threatened Species 2012. Accessed: 2017-05-20. URL: http://www.iucnredlist.org/details/10056/0.
  • Foster, S.J. & Vincent, A.C.J. 2004. Life history and ecology of seahorses: implications for conservation and management. Journal of Fish Biology 65: 1-61.

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