Fish
Leafy Seadragon
Phycodurus eques · also called leafy seadragon, Glauert's seadragon
The leafy seadragon looks less like a fish than like a sprig of seaweed that has come loose and started to swim. It is a relative of the seahorse from the cool waters of southern Australia, and it is one of the most complete examples of camouflage in the sea.
Overview
Leafy seadragons live only along the southern coast of Australia, over rocky reef, kelp forest, and seagrass from the shallows down to about 50 metres. They stay in the same small area for long periods, moving slowly among the weed and feeding almost constantly. They are not common anywhere in that range, and encountering one is a highlight for divers.
Built to disappear
The seadragon’s body carries dozens of leaf-shaped lobes of skin along its back, belly, and tail. They match the shape, colour, and movement of the surrounding algae so well that a motionless seadragon in kelp is effectively invisible, and it can slowly change hue to fit a new background. When it does move, it is pushed along by two tiny transparent fins — one behind each eye, one on the back — beating too fast to see, so it appears to drift like a detached frond.
No anchor
Seahorses grip seaweed and coral with a coiling tail. The seadragon cannot — its tail is not prehensile. This makes it vulnerable to rough weather: storms regularly wash seadragons out of their habitat and strand them, sometimes carrying them far offshore.
Feeding
The long, pipe-like snout works as a pipette. The seadragon drifts up to a cloud of mysid shrimp or other tiny crustaceans and sucks individuals in one at a time with a sharp flick, swallowing them whole. It has no teeth and no stomach, so it must feed very frequently.
Male pregnancy
As in all members of the family, the male carries the eggs. The female deposits around 250 eggs onto a soft brood patch under his tail; tissue grows up around each one to deliver oxygen. After about nine weeks the male releases a batch of fully formed young, which fend for themselves from the first moment.
Status
The leafy seadragon is listed as Least Concern, but its tiny range, low numbers, weak swimming, and dependence on healthy kelp and seagrass make it fragile. It is fully protected in Australia, collection from the wild is prohibited, and it is the marine emblem of South Australia. Habitat loss, coastal pollution, warming seas, and illegal collection are the standing threats.
Leafy Seadragon: common questions
How is a leafy seadragon different from a seahorse?
They are close relatives in the same family, but the seadragon has taken camouflage much further. Its body is fringed with long, leaf-shaped flaps of skin that break up its outline so completely that, drifting among seaweed, it is nearly impossible to spot. It is also larger than most seahorses, it holds its body more horizontally, and — importantly — it lacks a prehensile tail, so it cannot anchor itself to a holdfast the way a seahorse can. It also lacks the seahorse's fully enclosed brood pouch; the male carries eggs exposed on the underside of his tail.
Do the leaf-like parts help it swim?
No. The leafy appendages are pure disguise and are not muscled. All of the seadragon's propulsion comes from two small, translucent, fast-beating fins — a pectoral fin on each side of the neck for steering and a dorsal fin along the back for drive. Because these fins are almost transparent and move in a blur, a swimming seadragon appears to glide along with no visible means of movement, like a piece of weed carried by the current.
Which parent carries the babies?
The male, as in all seahorses and seadragons. When a pair is ready to breed the female produces around 250 bright pink eggs and presses them onto a specialised spongy "brood patch" on the underside of the male's tail, where cups of tissue form around each egg and supply it with oxygen. The male carries them for roughly nine weeks and then releases fully independent miniature seadragons over several days. There is no further parental care, and only a small percentage survive to adulthood.
Is the leafy seadragon endangered?
It is currently listed as Least Concern, but it is a special case. It lives only along the southern coast of Australia, it is never abundant, it is a weak swimmer that cannot recolonise an area quickly, and it depends on healthy kelp and seagrass. It is fully protected under Australian and state law, collection is banned, and it is the marine emblem of South Australia. The main concerns for its future are habitat loss, pollution runoff, warming water pushing its cool-water habitat southward, and illegal capture for the aquarium and traditional-medicine trades.