Knysna seahorse

The Knysna seahorse
iHashe Yolwandle

Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Syngnathiformes
Family: Syngnathidae
Hippocampus capensis Boulenger 1900

Seahorses are found in shallow seas from Tasmania to the United Kingdom, and they feature in myths and legends from around the world (think of how they’re usually depicted drawing Poseidon’s chariot, he the Greek god of the sea) - but none is as rare, none is as endangered, and none has so small a range as the Knysna seahorse.

It’s also the only seahorse that’s known to live in estuaries, and it’s found only in dense vegetation in the Keurbooms, Swartvlei, and Knysna Lagoons.

... And the presence of the Knysna seahorse is just one of the reasons why Mission Blue has decided to declare the Knysna Hope Spot (Hope Spots are defined as special conservation areas that are critical to the health of Earth’s blue heart - our oceans).

Seahorses range from about 15 mm (the New Caledonian seahorse, Hippocampus bargibanti) to 400 mm in length (the Eastern Pacific seahorse, Hippocampus ingens), so at about 7 cm on average - and up to 12 cm at maximum - the Knysna seahorse is pretty much your run-of-the-mill citizen of the sea.

Except that it isn’t: it’s an indicator species that acts as a proxy for the health of its environment, and like all of its cousins, it has a fascinating and unusual biology.

Like the chameleon, the seahorse can change colour to blend in with its surroundings, and like the chameleon, it’s able to move its eyes independently, and to wrap its strong and prehensile tail around holdfasts like sponges or sea-grasses - and when once it’s gripped, it’s almost impossible to dislodge.

Seahorses are true fishes - with backbones, gills, swim bladders and fins - but their bodies are enclosed by insect-like armour of bony plates covered by skin.

Although the idea that seahorses mate for life is just another one of the many myths that surround this little relative of the pipe-fish, it is true that pregnancy occurs in the male, which carries his brood in a pouch in his belly.

Knysna seahorses becomes sexually mature at between six to nine months of age - depending on food availability and water temperature - and they mate after a three-day-long courtship ritual during which they dance around each other in graceful displays, or swim together from holdfast to holdfast in tight parallel formation. Finally the female will insert her ovipositor into the male's pouch, where she’ll deposit her eggs - after which she'll have nothing more to do with the young.

The male fertilises the eggs in the pouch, and the young are born live after about 14 to 21 days (depending again on water temperature). And giving birth is a difficult process, too: it may take the big guy up to two days to deliver as many as 190 babies of between 9 and 10 mm in length.

Seahorses feed on tiny crustaceans (zooplankton), which they suck into their mouths from their positions on their holdfasts - although they may occasionally swim after their prey if the need arises.

The Knysna estuary is a fragile system and one that must be protected as part of the greater whole. The continued presence of strong populations of our favourite seahorse clearly shows that the Lagoon is safe.

For the moment....

The Knysna seahorse has been categorised as ‘Threatened’ on the IUCN Red List of Threatened Species since 1994.