The Knysna Seahorse

A Special Estuarine Resident


Knysna seahorse
The Knysna seahorse in the most famous estuarine resident in Knysna.


Did you know that our Knysna Estuary boasts the highest biodiversity in comparison to any other estuary in South Africa? It’s a literal treasure trove of flora and fauna. Of  all the critters that reside in the estuary, it is the little Knysna seahorse (Hippocampus capensis) that is the most celebrated.

Seahorses belong to the genus Hippocampus, which comes from the Ancient Greek word ‘hippos’ (meaning horse) and ‘campus’ (meaning sea monster). The Knysna seahorse is just one of more than 45 different species found worldwide, but it’s particularly special because it is the only known true estuarine seahorse species in the world and is very rare indeed.

Its distribution is extremely fragmented. Knysna seahorses are endemic to the Garden Route and have only ever been found in three local estuaries, namely, the Keurbooms River estuary in Plettenberg Bay, the Knysna Estuary, and the estuarine portion of the Swartvlei system in Sedgefield. Owing to this limited geographical range, its small overall population size and the fact that Knysna seahorses are particularly vulnerable to adverse shifts in their natural environment, it is the first seahorse to be classified as endangered by the International Union for the Conservation of Nature (IUCN). This makes the protection of this local fish species and the Knysna Estuary as a whole, so critical. (Yip, believe it or not, these little cuties are fish – they breathe through gills and have a swim bladder).


Knysna seahorse
A beautiful seahorse housed in a tank at the SANParks offices on Thesen Island for environmental purposes.

Seahorses are pretty extraordinary. For one, they have shown a dogged resilience as a species. They have been hanging around in our oceans for at least 40 million years, surviving all this time with only minor evolutionary adaptations. They have a distinctive ‘armoured’ body with an extended abdomen and a head that resembles that of a horse; hence its name. Its muscular tail winds forward in a spiral and is used to grasp a mate during courtship ritual or to anchor itself to a substrate. Colour varies amongst individuals, ranging from mottled brown, yellow and green. Some are just plain brown or black. The eyes of seahorse move independently (like those of a chameleon), one scouring the surrounds for food and the other keeping an ‘eye’ out for predators. They are not movers and shakers. In fact, they are one of the world’s slowest swimmers. But despite this lack of swimming prowess, they are incredibly efficient predators, which is a good thing because they need to eat ALL the time due to the fact that don’t have a stomach.

Knysna seahorses
A herd of Knysna seahorses

One particularly unusual characteristic of this species is that it is the males who gives birth. The female impregnates the male with up to 1,500 eggs and, during the gestation period the male hardly moves at all, while the female brings him food (nothing new there, haha).  After a few short weeks. when it’s time for the babies to be born, the male experiences strong contractions that serve to expel the teeny tiny young out of his pouch.

Knysna seahorses are small and extremely well camouflaged, which makes viewing them in their natural environs really difficult. They are found in particularly dense concentrations throughout the Thesen Island marina, so, if you head over to the jetty at a low tide, lie on your stomach and peer into the murky depths, you can sometimes spot them clinging onto the reno-mattress structures which make up the artificial walls of the marina. But if you really want to spend some time viewing them clearly, we recommend you head over to the SANParks offices on Thesen Island where they have a tank full of seahorses and other small marine life, including the pipefish, a family relative of the seahorse.

Knysna seahorse
A Knysna seahorse seen alongside a pipefish, a member of the same family. Can you spot the newly born seahorse in this picture??

Marine scientists from the Knysna Basin Project are dedicated to researching and protecting this rare and vulnerable species. The study of seahorses is extremely important because they serve as an indicator species, due to the fact that they are extremely sensitive to variations in their natural environment. A flourishing Knysna seahorse population could therefore, be indicative of a healthy estuarine system, or vice versa.  Not only do we need to protect this rare and endangered endemic species but also all the other critters that are sustained by this rich estuarine system.

Our graphic designer at Ocean Odyssey designed a sign to educate visitors on our most famous estuarine resident, pop by and have a look!!

Seahorse signage at the offices of Ocean Odyssey on Thesen Island.