Seahorses and their relatives take many remarkable forms and can be considered among the ornatest and most endearing marine creatures on Earth.
Today we’ll take a closer look at two members of this unique family…
Leafy Sea Dragon
Size: 20-24 cm (8-9.5 in) long.
There are two kinds of sea dragon: the Leafy Sea Dragon and the Weedy Sea Dragon, of which the Leafy is the more spectacular. This wonderful marine species is found along the southern and western coasts of Australia and is the marine emblem of the state of South Australia. Aussies refer to them by the endearing nickname of leafies.
The eastern end of their habitat is Wilson’s Promontory in Victoria and from here it extends westwards and northwards as far as Jurien Bay, 220 km (140 miles) north of Perth. You will find them in the shallow coastal waters up to 30 m deep among rocky reefs and protective marine plants.
Leafy sea dragons propel themselves using an almost transparent pectoral fin on a ridge on their necks, and a dorsal fin on the lower back. Their whole body is covered with leaflike protrusions making these delicate and delightful creatures experts in the art of camouflage. As they pass on their slow, graceful and regal course they resemble a piece of floating seaweed. They also have the chameleonesque ability to change colour, dependent on their age, diet, location and level of stress. Their ability to survive among potential predators is dependent on their unique ability to hide in plain sight.
They have unusual circular gill openings covering tufted gills.
They are vulnerable to a number of threats, including pollution and industrial runoff. They are illegally caught by collectors and sometimes used for alternative “medicinal” purposes. Unlike seahorses, they can’t grasp plants with their tails, so are often washed up onto beaches following storms.
Luckily they are now a legally protected species in all the Australian states where they are found. They also enjoy protection under federal law per the Environment Protection and Biodiversity Conservation Act of 1999.
Sea dragons have never been successfully bred in captivity. Specimens are only usually found in public aquaria. Due to their specialist needs it is not at all easy to keep them without an intimate knowledge of their specific needs. Buying a sea dragon is expensive – around $10 000 – $15 000, a deterrent to most would-be private collectors. The law also makes it nearly impossible to obtain one privately.
Divers can be fortunate enough to observe them in their natural habitat around Adelaide, especially at Rapid Bay, Edithburgh and Victor Harbour. If you are not a diver, you can see them in aquariums at Sydney, Melbourne and the Aquarium of Western Australia. There are also several aquariums in the US which have leafy sea dragons on display.
Like seahorses, the Leafies have an unusual sex life. The female sea dragon produces from 120 – 250 bright pink eggs which she proceeds to dump onto a spongy brood patch on her husband’s tail using her ovipositor. These eggs change colour to purple or orange as they ripen to begin hatching after about nine weeks. Daddy shakes and pumps his tail until the young emerge – this process can take an exhausting 24-48 hours. Only about 5% of eggs survive to this stage, but once they are hatched the little sea dragon who is about 20 mm in length is totally independent and can feed on zooplankton until old enough to hunt for himself. They are partial to small crustaceans such as mysid shrimps (sea lice) and amphipods, as well as plankton and larval fish. They will be ready to breed at two years of age, which only around 5% will reach in their natural surroundings.
They are usually loners apart from the breeding season from October to March when some romance enters their lives.
Aussies are justly proud of these unique inhabitants of their coastal waters and they are an integral part of the cultural life of southern Australia.
An animated short movie featuring a sea dragon was released in 2006 to increase awareness among children of the need to preserve them.
Every two years an arts festival called the Leafy Sea Dragon Festival is held on the Fleurieu Peninsula, South Australia.
Seahorses have been around for about 40 million years. Seahorses vary in length from 3 – 35cm long. Like fish, they breathe through gills.
As with their cousins the sea dragons, these little “marine equines” have an unusual sex life: the female lays her eggs in a kangaroo-like pouch which is found on the male, from which the little ones will hatch out into the water.
During summer months they brood their young for 14-45 days (dependant on the water temperature which is usually around 20C) and produce from 7-120 young per brood.
Just like a kind of aquatic chameleon, their eyes can swivel independently to observe their surroundings so that they can grab a meal while keeping an eye for would-be predators. Another feature they share with chameleons is their ability to change colour to blend into the background rather than attract the attention of a hungry meal-seeker. They don’t tend to move around more than they have to, and can spend lengthy time in one spot, making them quite difficult to see.
There are 36 recognized species of seahorse, of which five are found in Southern African waters. The Knysna Seahorse (Hippocampus capensis) is the only fully estuarine species – they aren’t found in the open ocean but in the sheltered saline waters of three lagoons. They are only found naturally in the Keurbooms Estuary at Plettenberg Bay, the Knysna Lagoon, and Swartvlei Lake in the town of Sedgefield in the Western Cape Province of South Africa. All these habitats are within urbanized or developed areas. The Keurbooms and Swartvlei estuaries both have very dense marine plant cover, abounding in their favourite species. However, only about 11% of the Knysna lagoon bed is covered in plants.
They are found in varying hues of green to brown or purplish-black and are usually about 12 cm in length. Their colour depends a lot on their surroundings as well as their mood. So if they are very dark and blotchy you may be observing one very angry seahorse, who emerged from the wrong side of the water weed and has an axe to grind with his or her spouse!
They use their monkey-like tail to grasp plants and for their aquatic courtship dances when in a romantic mood.
They can be found at depths from 50 cm to 8 metres, among the safety of their favourite marine plants around which they can wrap their tails and watch for their next meal without becoming one.
During high tide, experienced Knysna divers can take you to see the fairytale creatures in their peaceful marine sanctuary.
I’ve had the privilege of peering down into the shallows from the shore to view these fantasy animals in their placid, unhurried home environment. This was on Thesen’s Island where they seem to like the shallow waters near the jetties, where these were some weeds for them to shelter among. It is certainly possible for them to thrive side by side with human development provided their basic needs are met.
Swimming regally upright like the Lilliputian royal horses they resemble, they use their small pectoral fins to guide them as they search for tiny fish and shellfish for lunch.
Due to their limited natural range they are vulnerable to threats such as development and any other significant changes to their environment. They are the most endangered seahorse species, but fortunately ongoing efforts are being made and legislation (part of the Marine Living Resource Act of 1998) is in place to protect them and their habitat. Unfortunately not all seahorse species are as lucky and many are killed and used for “medicinal” purposes in some countries. In addition around a million of them are caught every year for display in home and public aquaria due to their whimsical appearance.
It is only in recent years that research dedicated specifically to the study and preservation of the Knysna seahorse has been initiated. These three estuaries need to be properly managed and monitored in order to ensure their survival. As they share their habitat with the famous Knysna oysters, which love the “beds” built around Thesen Islands in the Knysna lagoon for them to facilitate their breeding, the two species should be part of a holistic management effort together with the lagoon itself.
Their population in the three lagoons tends to fluctuate considerably. They are quite tolerant of differing salinity levels, but flood conditions in 2007 and 2011 temporarily reduced their numbers.
Strictly controlled under a permit system, they can be safely kept in captivity and can be seen at the Two Oceans Aquarium in Cape Town, the SANParks reception office on Thesen Island in Knysna, as well as the Antwerp Zoo in Belgium. Due to their appealing beauty they are also bred for the ornamental fish industry.
It is vital that every possible resource be utilized to ensure the continued future of Knysna’s famous little residents, and that development always bear in mind the health of the lagoon and their other two natural homes.
It would be a great pity if the time came that the only place we could see them was in the glassy, artificial environment of an aquarium.