| Leafy seadragon | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Syngnathiformes |
| Family: | Syngnathidae |
| Subfamily: | Syngnathinae |
| Genus: | Phycodurus Gill, 1896 |
| Species: | P. eques |
| Binomial name | |
| Phycodurus eques (Günther, 1865) |
|
The leafy seadragon or Glauert's seadragon,[1] Phycodurus eques, is a marine fish in the family Syngnathidae, which also includes the seahorses. It is the only member of the genus Phycodurus. It is found along the southern and western coasts of Australia. The name is derived from the appearance, with long leaf-like protrusions coming from all over the body. These protrusions are not used for propulsion; they serve only as camouflage. The leafy seadragon propels itself by means of a pectoral fin on the ridge of its neck and a dorsal fin on its back closer to the tail end. These small fins are almost completely transparent and difficult to see as they undulate minutely to move the creature sedately through the water, completing the illusion of floating seaweed.
Popularly known as "leafies",[2][3] they are the marine emblem of the state of South Australia and a focus for local marine conservation.
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Much like the seahorse, the leafy seadragon's name is derived from its resemblance to another creature (in this case, the mythical dragon). While not large, they are slightly larger than most seahorses, growing to about 20–24 cm (8–10 in). They feed on plankton and small crustaceans.
The lobes of skin that grow on the leafy seadragon provide camouflage, giving it the appearance of seaweed. It is able to maintain the illusion when swimming, appearing to move through the water like a piece of floating seaweed. It can also change colour to blend in, but this ability depends on the seadragon's diet, age, location, and stress level.
The creature feeds by sucking up small crustaceans, such as amphipods and mysid shrimp, plankton and larval fish through its long, pipe-like snout.[2]
The leafy seadragon is related to the pipefish and belongs to the family Syngnathidae, along with the seahorse. It differs from the seahorse in appearance, form of locomotion, and its inability to coil or grasp things with its tail. A related species is the weedy seadragon, which is multi-coloured and grows weed-like fins but is smaller than the leafy seadragon. Current research at the Scripps Institution of Oceanography is investigating the evolutionary relationships of the Syngnathidae[4] and the DNA variation of the two seadragon species across their ranges.[5]
As with seahorses, the male leafy seadragon cares for the eggs. The female produces up to 250 bright pink eggs, then deposits them on to the male's tail via a long tube. The eggs then attach themselves to a brood patch, which supplies them with oxygen. It takes a total of nine weeks for the eggs to begin to hatch, depending on water conditions. The eggs turn a ripe purple or orange over this period, after which the male pumps its tail until the infants emerge, a process which takes place over 24–48 hours. The male aids in the babies hatching by shaking his tail, and rubbing it against seaweed and rocks. Once born, the infant seadragon is completely independent, eating small zooplankton until large enough to hunt mysids. Only about 5% of the eggs survive. Leafy seadragons take about 28 months to reach sexual maturity.[6]
The leafy seadragon uses the fins along the side of its head to allow it to steer and turn. However, its outer skin is fairly rigid, limiting mobility.
Individual leafy seadragons have been observed remaining in one location for extended periods of time (up to 68 hours) but will sometimes move for lengthy periods. Tracking of one individual indicated it moved at up to 150 metres (490 feet) per hour.[7]
Leafy seadragons are subject to many threats, both natural and man-made. They are caught by collectors, and used in alternative medicine. They are vulnerable when first born, and are slow swimmers, reducing their chance of escape from a predator. Seadragons are often washed ashore after storms, as unlike their relative the seahorse, seadragons cannot curl their tail and hold onto seagrass to stay safe.[8]
They have become endangered through pollution and industrial runoff as well as collection by fascinated divers who are entranced by their unique appearance. In response to these dangers they have been officially protected by the Federal Government of Australia.
The leafy seadragon is found only in southern Australian waters, from Kangaroo Island at the eastern end of its range, westward to Jurien Bay[9], 220 km (140 mi) north of Perth. It was once thought that individuals had very restricted ranges; however, further research has discovered that seadragons will actually travel several hundred metres from their habitual locations, returning to the same spot using a strong sense of direction. They are mostly found over sand patches in waters up to 50 metres (164 feet) deep, around kelp-covered rocks and clumps of sea grass.[2] They are commonly sighted by scuba divers near Adelaide, especially at Rapid Bay and Edithburgh.[10]
Due to being protected by law, obtaining seadragons is often an expensive and difficult process as they must be from captive bred stock, and exporters must prove their broodstock were caught before collecting restrictions went into effect, or that they had a license to collect seadragons. Seadragons have a specific level of protection under federal fisheries legislation as well as in most Australian states where they occur.[11] Seadragons are difficult to maintain in aquaria. Success in keeping them has been largely confined to the public aquarium sector, due to funding and knowledge that would not be available to the average enthusiast.
To date, only the Tennessee Aquarium [12] in Chattanooga, Tennessee has been able to breed the leafy seadragon. It first succeeded in doing so in 2003. Other aquaria which feature leafy seadragons include the New England Aquarium;[13] the Monterey Bay Aquarium;[14] Long Beach California's Aquarium of the Pacific.[15] and the Aquarium of Western Australia;[16]
The leafy seadragon is the official marine emblem of the state of South Australia.[17] It also features in the logo of the Marine Life Society of South Australia Inc. [18]
A biennial Leafy Sea Dragon Festival is held by the District Council of Yankalilla, South Australia. It is a festival of the environment, arts and culture of the southern Fleurieu Peninsula, with the theme of celebrating the leafy seadragon. The inaugural festival in 2005 attracted over 7,000 participants and visitors.[19]
In 2006 an animated short film, The amazing adventures of Gavin, a Leafy Seadragon, was made on behalf of several South Australian organisations involved in conserving the marine environment, including the Coast Protection Board, the Department of Environment and Heritage and the Marine Discovery Centre.[20][21][22] Made through a collaboration of The People's Republic of Animation, Waterline Productions and the SA Film Corporation,[23] the film is an introductory guide to marine conservation and the marine bioregions of South Australia suitable for 8-12 year olds,[24] and copies were distributed on DVD to all primary schools in the State. An educator's resource kit to accompany the film was released in 2008.[25][26]
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