Abstract
South Africa's endemic Knysna seahorse, Hippocampus capensis Boulenger 1900, is a rare example of a marine fish listed as Endangered by the IUCN because of its limited range and habitat vulnerability. It is restricted to four estuaries on the southern coast of South Africa. This study reports on its biology in the Knysna and Swartvlei estuaries, both of which are experiencing heavy coastal development. We found that H. capensis was distributed heterogeneously throughout the Knysna Estuary, with a mean density of 0.0089 m−2 and an estimated total population of 89 000 seahorses (95% confidence interval: 30 000–148 000). H. capensis was found most frequently in low density vegetation stands (≤20% cover) and grasping Zostera capensis. Seahorse density was not otherwise correlated with habitat type or depth. The size of the area in which any particular seahorse was resighted did not differ between males and females. Adult sex ratios were skewed in most transects, with more males than females, but were even on a 10 by 10 m focal study grid. Only three juveniles were sighted during the study. Both sexes were reproductively active but no greeting or courtship behaviours were observed. Males on the focal study grid were longer than females, and had shorter heads and longer tails, but were similar in colouration and skin filamentation. The level of threat to H. capensis and our limited knowledge of its biology mean that further scientific study is urgently needed to assist in developing sound management practices.
Similar content being viewed by others
References cited
Ansari, Z.A., C.U. Rivonker, P. Ramani & A.H. Parulekar. 1991. Seagrass habitat complexity and macroinvertebrate abundance in Lakshadweep coral reef lagoons, Arabian Sea. Coral Reefs 10: 127-131.
Bayer, R.D. 1980. Size, seasonality, and sex ratios of the Bay Pipefish (Syngnathus leptorhynchus) in Oregon. Northwest Sci. 54: 161-166.
Bell, J.D. & M. Westoby. 1986. Abundance of macrofauna in dense seagrass is due to habitat preference, not predation. Oecologia 68: 205-209.
Berglund, A.G., G. Rosenqvist & I. Svensson. 1986. Reversed sex roles and parental energy investment in zygotes of two pipefish (Syngnathidae) species. Mar. Ecol. Prog. Ser. 29: 209-215.
Buxton, C.D. & M.J. Smale. 1989. Abundance and distribution patterns of three temperate marine reef fish (Teleostei: Sparidae) in exploited and unexploited areas off the Southern Cape coast. J. Appl. Ecol. 26: 441-451.
Chmelik, F.B. 1975. Economic model for estuarine evaluation. Pretoria Department of Planning and the Environment Bulletin 2. 105 pp.
Cowley, P.D. & A.K. Whitfield. 2001. Ichthyofaunal characteristics of a typical temporarily open/closed estuary on the southeast coast of South Africa. Ichthyol. Bull. J.L.B. Smith Inst. Ichthyol. 71: 1-19.
Dauwe, B. 1992. Ecologie van het zeepaardje Hippocampus reidi (Syngnathidae) op het koraalrif van Bonaire (N.A.): Habitatgebruik, reproductie en interspecifieke interacties. (Ecology of the seahorse Hippocampus reidi on the coral reefs of Bonaire (N.A.): habitat use, reproduction and interspecific interactions.). M.Sc. Thesis, Rijksuniversiteit Groningen, the Netherlands. 65 pp.
Day, D.H. (ed.) 1981. Estuarine ecology with particular reference to South African estuaries. Balkema, Cape Town. 411 pp.
Day, L. 1997. Drifting into danger: Seahorses. Africa-Environment and Wildlife 5: 66-71.
Day, J.H., N.A.H. Millard & A.D. Harrison. 1952. The ecology of South African estuaries. Part III Knysna: A clear open estuary. T. Roy. Soc. S. Afr. 33: 367-413.
Efron, B. & R. LePage. 1992. Introduction to bootstrap. pp. 3-10. In: R. LePage and L. Billard (ed.) Exploring the Limits of Bootstrap, John Wiley & Sons, New York.
Efron, B. & R.J. Tibshirani. 1993. An introduction to the bootstrap. Chapman & Hall, New York. 436 pp.
Fourie, D. 1997. Sex-roles and the influence of size on mating competition in the Knysna seahorse, Hippocampus capensis. Honours Thesis, University of Stellenbosch. 15 pp.
Grange, N. & R. Cretchley. 1995. A preliminary investigation of the reproductive behaviour of the Knysna seahorses, Hippocampus capensis Boulenger 1900. S. Afr. J. Aquat. Sci. 21: 103-104.
Grindley, J.R. & G.A. Eagle. 1978. Environmental effects of the discharge of sewage effluent into Knysna Estuary. University of Cape Town, School of Environmental Studies. 62 pp.
Grindley, J.R. & C.S. Snow. 1983. Environmental effects of the discharge of sewage effluent into Knysna Lagoon. University of Cape Town, School of Environmental Studies. 55 pp.
Groombridge, B. (ed.) 1993. 1994 IUCN Red List of Threatened Animals. IUCN, Gland. 286 pp.
Harris, S., W.J. Cresswell, P.G. Forde, W.J. Trewhella, T. Woollard & S. Wray. 1990. Home-range analysis using radio-tracking data-a review of the problems and techniques particularly as applied to the study of mammals. Mammal Rev. 20: 97-123.
Hilton-Taylor, C. (compiler) 2000. 2000 IUCN Red List of Threatened Species. IUCN/SSC, Gland, Switzerland & Cambridge, U.K. http://www.redlist.org.
IUCN. 1995. Guidelines for re-introductions. Gland, Switzerland. http://www.iucn.org.
Jones, A.G., C. Kvarnemo, G.I. Moore, L.W. Simmons & J.C. Avise. 1998. Microsatellite evidence for monogamy and sex-biased recombination in the Western Australian seahorse Hippocampus angustus. Mol. Ecol. 7: 1497-1505.
Kok, H.M. 1981. Knysna seahorse distribution poses a problem. African Wildlife 35: 9.
Kramer, D.L., R.W. Rangeley & L.J. Chapman. 1997. Habitat selection: Patterns of spatial distribution from behavioural decisions. pp. 37-80. In: J.-G.J. Godin (ed.) Behavioural Ecology of Teleost Fishes. Oxford University Press.
Kvarnemo, C., G.I. Moore, A.G. Jones, W.S. Nelson & J.C.Avise. 2000. Monogamous pair bonds and mate switching in the Western Australian seahorse Hippocampus subelongatus. J. Evol. Biol. 13: 882-888.
Le Cheminant, J. 2000.Aninvestigation to establish the suitability of Opalithplattchen (Bee Tag), Fly andVisible Implant Fluorescent Elastomer (VIFE) tagging systems for marking the Knysna seahorse, Hippocampus capensis. M.Sc. thesis, Bournemouth University. 83 pp.
Lockyear, J.F., H. Kaiser & T. Hecht. 1997. Studies on the captive breeding of the Knysna Seahorse (Hippocampus capensis). Aquar. Sci. Conserv. 1: 129-136.
Lourie, S.A., A.C.J. Vincent & H.J. Hall. 1999. Seahorses: An identification guide to the world's species and their conservation. London, U.K. 214 pp.
Masonjones, H.D. & S.M. Lewis. 1996. Courtship behavior in the dwarf seahorse, Hippocampus zosterae. Copeia 3: 634-640.
Matsumoto, K. & Y. Yanagisawa. 2001. Monogamy and sex role reversal in the pipefish Corythoichthys haematopterus. Anim. Behav. 61: 163-170.
Middleton, M.J., J.D. Bell, J.J. Burchmore, D.A. Pollard & B.C. Pease. 1984. Structural differences in the fish communities of Zostera capricorni and Posidonia australia seagrass meadows in Botany Bay, New South Wales. Aquat. Bot. 18: 89-109.
Naylor, R.L., R.J. Goldburg, J.H. Primavera, N. Kautsky, M.C.M. Beveridge, J. Clay, C. Folke, J. Lubchenco, H. Mooney & M. Troell. 2000. Effect of aquaculture on world fish supplies. Nature 405: 1017-1024.
Nijhoff, M. (1993) Voortplantingsecologie van het zeepaardje Hippocampus reidi op het koraalrif van Bonaire. (Reproductive ecology of the seahorse Hippocampus reidi on a Bonaire coral reef.). M.Sc. thesis, Rijksuniversiteit Groningen, the Netherlands. 49 pp.
Perante, N.C., M.G. Pajaro & A.C.J. Vincent. 1998. Demographics of the seahorse Hippocampus comes in the Central Philippines. pp. 439-448. In: B. Morton (ed.) The Marine Biology of the South China Sea. Proceedings of the Third International Conference on the Marine Biology of the South China Sea, Hong Kong, 28 October-1 November, 1996. Hong Kong University Press.
Perante, N.C., M.G. Pajaro & A.C.J. Vincent. 2002. Biology of a seahorse species, Hippocampus comes, in the central Philippines. J. Fish Biol. 60: 821-837.
Plumstead, E.E. 1990. Changes in ichthyofaunal diversity and abundance within the Mbashe Estuary, Transkei, following construction of a river barrage. S. Afr. J. Mar. Sci. 9: 399-407.
Russell, I.A. 1994. Mass mortality of marine and estuarine fish in the Swartvlei andWilderness Lake systems, Southern Cape. S. Afr. J. Aquat. Sci. 20: 93-96.
Smith, M.M. 1981. The Seahorse of the Knysna Lagoon. African Wildlife 35: 6-9.
Smith, M.M., P.C. Heemstra & J.L.B. Smith (ed.) 1986. Smith's Sea Fishes, 6th edn. Springer-Verlag, Berlin. 1047 pp.
Strawn, K. 1958. Life history of the pigmy seahorse, Hippocampus zosterae Jordan and Gilbert, at Cedar Key, Florida. Copeia 1958: 16-22.
Toeffie, Z. 2000. A preliminary examination of the morphology and genetic structure within populations of the Knysna seahorse, Hippocampus capensis (Pisces: Syngnathidae), from two South African estuaries. M.Sc. thesis, University of the Western Cape. 102 pp.
Tops, S. 1999. An investigation into the effects of habitat complexity and food types on the behaviour of the Knysna Seahorse-Hippocampus capensis. Honours Thesis, University of St. Andrews. 53 pp.
Vincent, A.C.J. 1990. Reproductive ecology of seahorses. Ph.D. Thesis, University of Cambridge. 109 pp.
Vincent, A.C.J. 1994. Seahorses exhibit conventional sex roles in mating competition, despite male pregnancy. Behaviour 128: 135-151.
Vincent, A.C.J. 1995. A role for daily greetings in maintaining seahorse pair bonds. Anim. Behav. 49: 258-260.
Vincent, A.C.J. 1996. The International Trade in Seahorses. TRAFFIC International, Cambridge, UK. 163 pp.
Vincent, A.C.J. & L.M. Sadler. 1995. Faithful pair bonds in wild seahorses, Hippocampus whitei. Anim. Behav. 50: 1557-1569.
Whitfield, A.K. 1989a. Ichthyoplankton interchange in the mouth region of a southern African estuary. Mar. Ecol. Prog. Ser. 54: 25-33.
Whitfield, A.K. 1989b. Fish larval composition, abundance and seasonality in a southern African estuarine lake. S. Afr. J. Zool. 24: 217-224.
Whitfield, A.K. 1995a. Threatened fishes of the world: Hippocampus capensis Boulenger 1900 (Syngnathidae). Environ. Biol. Fish. 44: 362.
Whitfield, A.K. 1995b. Threatened fishes of the world: Syngnathus watermeyeri Smith, 1963 (Syngnathidae) Environ. Biol. Fish. 43(2): 152.
Whitfield, A.K., L.E. Beckley, B.A. Bennett, G.M. Branch, H.M. Kok, I.C. Potter & R.P. Van der Elst. 1989. Composition, species richness and similarity of ichthyofaunas in eelgrass, Zostera capensis, beds of Southern Africa. S. Afr. J. Mar. Sci. 8: 251-259.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Bell, E.M., Lockyear, J.F., McPherson, J.M. et al. First Field Studies of an Endangered South African seahorse, Hippocampus capensis . Environmental Biology of Fishes 67, 35–46 (2003). https://doi.org/10.1023/A:1024440717162
Issue Date:
DOI: https://doi.org/10.1023/A:1024440717162