The Weedy Sea Dragon, one of the most beautiful creatures in the sea, is usually seen by divers in the waters off southern Australia; however, little is known about this fascinating marine species with a remarkable reproductive behaviour.
Weedy Sea Dragons, known to science as Phyllopteryx taeniolatus, are fish related to the Leafy Sea Dragons (Phycodurus eques) and to the Seahorses (Hippocampus). Sea dragons’ distribution is restricted to Australian temperate marine waters, ranging from the central New South Wales coast, around the south coast of Australia, to the southern coast of Western Australia. They are also found around the coast of Tasmania.
The Leafy Sea Dragon is a "cousin" of the Weedy Sea Dragon. This fish is also an "expert" at camouflage.
The common name denotes the leaf-like appendages on the body that help weedy sea dragons to blend with their natural habitat and camouflage among the seaweeds. Their general appearance resembles the seahorses.
They have a bony-plated body, elongated snout and a long tail, which contrarily to the seahorses, is not prehensile. The adult weedy sea dragons may reach a length of about 40-45 cm. They are reddish with yellow dots and purple-blue side bars; they have several short spines for protection, a long dorsal fin along the back for propulsion, and small pectoral fins on either side of the neck, which provide balance. The females are slightly lighter and thicker than the males.
A Weedy Sea Dragon swims in front the sea grass. Note the leaf-like camouflage appendages and the brilliant dotty pattern and colouration.
An unusual reproductive strategy
Weedy sea dragons have a highly distinctive way of reproducing. It is the male who incubates the eggs in a fairly complex system of small pouches in its tail. The fish usually pair and mate in the spring (see mating dancing ritual in the video above). The female develops about 250 - 300 orange eggs in the abdominal cavity. At the same time, the male begins to form fine blood vessels and small “egg cups” near the surface of the underside of the tail. The eggs are then transferred from the female into the male’s brood pouches and are fertilized and incubated.
The male carries the eggs for about 4-5 weeks (see video above). The eggs hatch and leave the small pouches over several days, which allows for dispersal and minimizes competition among the hatchlings. The young sea dragons grow fast, reaching about 20 cm within one year. They are sexually mature in their second year, and their life span extends to about 6-7 years.
A couple of Weedy Sea Dragons swimming next to a seaweed forest. (Courtesy of Jason Shelley).
Research on distribution and conservation measures
Until recent years, there was insufficient knowledge about the species abundance, life cycle and population dynamics. Studies carried out by researchers of the Sydney Institute of Marine Science (SIMS) have made significant contributions on the home range, site fidelity, growth and reproductive cycle of the weedy sea dragon. This knowledge has contributed to the design of management, protection and conservation measures, since the species is listed as “Near-Threatened” in the IUCN Red List as the result of habitat degradation caused by discharge of industrial waste into coastal waters.
A Weedy Sea Dragon fish swims slowly over a sandy bottom (Courtesy of Jason Shelley).
A jewel for divers and photographers
Because their “armored” body and the lack of a caudal fin, sea dragons are weak swimmers and slow moving fish. They are usually present among the coastal fish fauna and are frequently seen and photographed by divers.
Jason Shelley is an enthusiastic diver based in Sydney, New South Wales, Australia. Jason contributed some of his own photographs of sea dragons for this report and answered some questions about his experience in searching for, observing and photographing these fascinating animals.
Digital Journal: Where do you usually find sea dragons?
Jason Shelley: One of the best places in Sydney to see sea dragons is at the entrance to Botany Bay. They are often found at the southern side of the bay’s entrance, close to Kurnell, in diving sites known as Inscription Point and The Monuments (Captain Cook Memorial Obelisk and Captain Cook’s Landing Place monument).
DJ: What are the sea dragon’s preferred habitats?
JS: They seem to prefer areas located between sandy bottom and rocky reefs, where there is an abundance of kelp and other seaweeds.
Detail of the head of a Weedy Sea Dragon showing the fine pectoral fins on each side of the "neck" (Courtesy of Jason Shelley).
DJ: Do you have to dive very deep to find them?
JS: Around Botany Bay (Kurnell, The Monuments) they can occasionally be found at shallow depths of between 2 to 4 meters, but more often in deeper areas, around 12-18 meters, where the kelp is more abundant; however, I have also found them as deep as 18-22 meters.
DJ: When is the best time to observe the sea dragons reproducing?
JS: At Botany Bay, the best period when the males are incubating eggs is between September and December. The time when most males are “pregnant” seems to coincide with the increase in water temperature.
Additional pictures of underwater creatures can be seen in Jason Shelley's Facebook page.