The mysterious world of seadragons

By Richard Wylie 22 June 2012
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They are little-known but incredibly fascinating creatures of the ocean. Meet our endemic seadragons.

Richard Wylie is a marine biologist and director of the Euakafa Island Research Centre in Vava’u, Tonga.

LIKE MANY PEOPLE IN Australia, I hadn’t really thought much about our temperate marine environment, instead considering the Great Barrier Reef the pinnacle of marine life in our waters.

When I moved to Victoria seven years ago, however, I found I couldn’t be more wrong. Being a tropical marine biologist, I was amazed to learn that 85-90 per cent of all life found in Australia’s southern seas are completely unique to the region, compared to only 10 per cent of all the animals and plants found on the Great Barrier Reef.

Australia’s cooler waters also contain one of my all-time favourite fish: seadragons.

The wonderful world of seadragons

Weedy seadragons (Phyllopteryx taeniolatus) are found in relatively shallow, coastal waters from Port Stephens in NSW, through Victoria, Tasmania, South Australia, and up to Geraldton in Western Australia. In addition, we also have leafy seadragons (Phycodurus eques), which are generally found in South Australia and Western Australia.

Both species are distantly related to seahorses but seadragons are in fact more closely related to pipefish. Zoological classification places them in the syngnathidae family (along with seahorses, pipe-horses and pipefish), as the Latin ‘syngnathid’ refers to the fused jaws that form their distinctive, tube-like snouts.

Seadragon dads incubate young

Like their seahorse and pipefish relatives, the male seadragons are responsible for rearing their young. Every year around spring, males and females perform an elegant dance before mating, at which point the fertilised eggs are transferred to the male.

The bright pink eggs are attached to the seasonally adapted, highly vascularised (increase blood flow) and pulpy area beneath his tail so that his blood can enrich the eggs during incubation – which usually lasts for approximately 8 weeks.

Upon hatching the fully formed, very small, baby seadragons swim off to fend for themselves, and take sustenance from the remains of their egg sack until they are able to catch their own food.

Sea dragons: camouflage keeps them out of view

Living primarily off tiny crustaceans called mysids, seadragons also eat fish larvae and plankton. Using powerful suction caused by expanding a small joint at the base of their fused jaw, they suck food through their mouth located at the tip of their snout. Interestingly, they don’t have a proper stomach and are forced to constantly forage for food to survive.

I’ve often wondered why seadragons aren’t more widely known in Australia. They’re incredibly beautiful and are so distinct that they are – at least in my mind – the marine equivalent to other iconic species such as the kangaroo, platypus and echidna. Victorians seem to have realised this and have made the weedy seadragon their marine emblem – though few would know it.

I believe, however, the seadragons’ low public profile is a result of their camouflage being too good – they’re literally invisible to the untrained eye and are consequently out of mind.

Seadragons are uniquely adapted to their marine environment and have evolved delicate, leaf like structures that enable them to blend seamlessly into the marine vegetation that they prefer to inhabit.

Seadragons on the endangered species list

Their only method of propulsion is via small pectoral fins behind their heads and a long caudal fin along their back. Unable to move quickly, they use their fins to sway rhythmically –  which makes them resemble  the waving, leafy seaweed they derive their names from.

Their camouflage is so effective that once they reach their adult size of approximately 40-46 cm they are no longer at risk of natural predators. However, the IUCN still lists them as Near Threatened due to their relatively limited geographical range and the damage to their natural environment through pollution and habitat destruction.

Their risk highlights the need to value the unique and precious species that reside in our temperate and sub-temperate waters. We must remember the southern shores of Australia contain species – like seadragons – every bit as wonderful as anything found in the tropics.