Only in South Africa: The Knysna Seahorse
Galloping About in Estuaries
The first unique thing about the Knysna, or Cape Seahorse, is that they're the only seahorses that live exclusively in estuaries. Unfortunately, this quirk places them in the direct path of river floods, poachers, pollution and swimmers. They also have the smallest territorial range of any known species — a mere three estuaries. Located in the southern Cape of South Africa, three populations bob about in the Knysna Lagoon, Swartvlei and the Keurbooms estuaries. A fourth clan once existed within the Klein Brak estuary but by 2002, this group was gone.
Profile of the Species
When feeling fancy, this seahorse goes by the scientific name of Hippocampus capensis. They may be medium-sized, stretching between 8 – 12 centimeters long, but have a colourful wardrobe to choose from. That's right, the Knysna Seahorse doesn't stick to one shade. The most common colour is a sensible mottled brown, which provide excellent camouflage. However, individuals can also range from white, yellow, green, orange, beige and black. A dark purple has also been recorded.
A trademark of the species is a reduced crown and short snout. The muscular tail is perfect to anchor the fish to vegetation and also to wrap around a partner during courtship and mating. The males have a ridge above their egg pouches, which is located at the front of the fish.
Speaking of Boys and Their Eggs
It's a well-known fact that seahorses switch things around in the maternity ward (make that paternity ward). The Knysna branch of the family is no different. When about a year old and measuring around 6.5 centimeters, Hippocampus capensis becomes sexually mature. It chooses and then remains with a single mate. A lingering misconception holds that after the couple mates, the female deposits fertilized eggs inside the male's pouch, and he just carries them around until they hatch. The truth is more remarkable.
The male seahorse experiences a true pregnancy. After receiving the clutch from his mate, the male fertilizes the eggs inside himself. The brood pouch, much like a womb, nourishes the young with oxygen and fluids. The length of the pregnancy is linked to temperature and depending on how warm it is, can last between two weeks and 45 days. When the happy day arrives, the family grows with up to two hundred babies. These adorable new arrivals are small, barely measuring a single centimeter. Right after the birth, the female often deposits a second batch of eggs in Dad's pouch.
A Sad First
The Knysna Seahorse holds the tragic honour of being the first seahorse species to be declared as endangered. As the most threatened seahorse in the world, it's protected under South African law but their numbers continue to fall. Unlike most other kinds, the Cape Seahorse doesn't fight a losing battle against being harvested as traditional medicine. However, they are poached for the ornamental fish industry, accidentally trapped in fishing nets, poisoned by pollution and bothered by recreational activities such as swimming and boating. In addition to all these troubles and human interference aside, natural causes can also kick a seahorse when its down.
Having just three estuaries to nurse an entire species is never a good idea for the future. The seahorse appears to flourish between thick aquatic vegetation but one area, the Knysna Lagoon, is sparsely planted compared to the other two habitats. In terms of safety, its waters are not ideal for this vulnerable fish.
The small range already poses a problem, as do crabs and bigger fish that prey on the seahorses. In addition, some of the biggest obstacles standing in the way of their survival are floods and currents experienced by all of the estuaries involved.
A head count between 2002 and 2003 showed how badly flooding affected all of the populations except, perhaps ironically, the group in the Knysna Lagoon. Another survey in 2003 dredged up a frightening moment for conservationists. At the Keurbooms estuary in Plettenberg Bay, there were no seahorses. More surveys continued to comb the area for over a decade. During this time, not a single seahorse turned up and everybody's worst fears seemed to be confirmed — The Keurbooms herd was extinct.
Giving Nature a Hand
ORCA to the Rescue
Incredibly, the extinction didn't last. In 2014, the ORCA Foundation send divers to search the Keurbooms estuary once more and found the elusive seahorses alive and well. However, this particular population appeared to have been thinned out by subsequent river currents and floods. All considered, it may have been the damaging currents that repopulated Keurbooms by sweeping away a splinter group from the Knysna Lagoon. Researchers suspect this scenario but cannot say for certain why the fish reappeared after such a long absence.
Another hopeful step forward involves the captive breeding of South Africa's only seahorse. They have honeymoon suites at the Two Oceans Aquarium in Cape Town and Belgium's Antwerp Zoo. The ornamental aquarium industry is also making the effort to sustain captive bred stock instead of purchasing seahorses caught in the wild.
Did You Know?
- The rare Knysna Seahorse is closely related to the abundant Indo-Pacific seahorse Hippocampus kuda
- Seahorses evolved 40 million years ago and studies suggest their anatomy changed little over time
- Back in the day, some people believed the seahorse was a mythical creature that existed only in stories
- Seahorses have no stomach and digests food so quickly that they're forced to eat almost non-stop
- Just like chameleons, their eyes can move in two different directions at the same time
Questions & Answers
© 2018 Jana Louise Smit