The Knysna Sea Horse occurs only in South Africa and is unusual because it occurs in estuaries. It has the most limited distribution of all seahorse species and is listed as the most threatened seahorse species in the world.
Seahorses are found in most of the world's shallower seas - from Tasmania in the south to the English Channel in the north. All seahorses belong to the genus Hippocampus, from the Greek words for horse (hippos) and sea monster (campus) and all have similar breeding habits.
There are between thirty and forty known species. The largest is the Eastern Pacific Sea Horse, which measures up to 40cm and the smallest is the New Caledonian Sea Horse, which is only 15mm.
Although specimens of up to 12cm in length have been recorded, the average Knysna seahorse is about 7cm long. It is the world's only known estuarine seahorse species and is found in the Keurbooms, Swartvlei and Knysna estuaries.
Although the Knysna Sea Horse has a limited distribution in the estuary, their numbers fluctuate. They are found in quiet waters among eelgrass, commonly seen along the length of the estuary, and algae, which attaches itself to rubble on the substratum.
Their strong tails coil around these underwater plants or any other holdfast, even fishing nylon, from where the seahorse cannot be pried loose easily.
Seahorses are known as the chameleons of the sea because of their ability to change colour to blend in with their surroundings. Their eyes can move independently in much the same way as chameleons.
The tail is strong and prehensile (adapted to seize and grasp) and a seahorse that has wound its tail around a holdfast of plant material, sponge or rope can be almost impossible to dislodge.
Although seahorses appear unusual they are in fact true fishes with backbone, gills, swim bladder and fins. Their bodies are enclosed by an insect-like armour of bony plates covered by skin. The unusual arrangement of their fins makes them slow swimmers and seahorses rely on camouflage to escape detection by predators.
Enemies of the seahorse include crabs, larger fishes and man. And because they tend to live at shallow depths, storms can also contribute to their morality by dislodging their holdfasts and throwing them ashore.
It is thought that most species mate for life and their reproductive habits are quite unusual. Pregnancy occurs in the male. He has a brood pouch in his belly and can easily be distinguished from the female because her belly is much slimmer than his is.
The male goes through a difficult birth process which may last for up to 2 days. Between 5 and 190 babies are delivered. They receive no further care from the parents. The adults usually begin mating again just hours after birth.
Seahorses feed on zooplankton. Their toothless mouths are used to suck on prey, which can be up to 12mm long and 2mm wide.
The Knysna estuary is a fragile system and, like all natural systems, constantly seeks to maintain its environmental balance. The impact of human activities such as farming and property development as well as excavation in the estuary may threaten the balance.
The Knysna seahorse has been formally recognized as endangered by the IUCN -The World Conservation Union - whilst nine other seahorse species are listed as vulnerable.
