Leafy Seadragon

(Phycodurus eques)

Amazingly, Phycodurus eques are actually fish. They have small, transparent fins; a dorsal fin on the back and pectoral fins on the neck. These help the dragons move through the water. They also have a bony skeleton. (In fact, its spine is why it is classified as a vertebrate.) Instead of scales their slender trunks are protected by a bony plates. And, they breath under water with tiny gills.

Despite having dorsal and pectoral fins, Phycodurus eques lack a caudal fin on their tails to help with propulsion. This means they can’t swim very well. Instead, their swim bladder holds gas that allows them to float in place. Sometimes they will rock back and forth amongst the seaweed, kelp beds, and sea grasses. Unlike their sea horse brethren, Phycodurus eques do not have prehensile tails (tails that can grip on to things). This means they can be tossed about by rough waters or other fish.

Natural history

The Phycodurus eques eats small shrimplike animals called mysids that live among the algae and seagrasses. A sea dragon’s tubelike mouth works like a drinking straw; a hungry dragon waits until its prey ventures near, then slurps it up. Each day, a single Phycodurus eques may slurp up thousands of mysid shrimp.

Habitat and Distribution

Phycodurus eques have been recorded at depths of about 20-30 meters off the southern coasts of Western Australia, South Australia, and Victoria. They make their home near rocky reefs and sandy meadows where seaweed, kelp, and sea grasses grow.

One of the most fascinating things about Phycodurus eques is how effective they are at hiding. They look like the leafy kelp where they make their home. Other animals mistake them for kelp when they’re floating in the water among the macroalgae (seaweeds). But, not only do they blend in because of their shape, they can also change colour to match their surroundings. This amazing camouflage keeps them safe from carnivorous fish. Young Phycodurus eques are less effective at camouflage and are sometimes preyed upon by other fish, crustaceans, and sea anemones.

Life Cycle, Reproduction, and Society

One of the most amazing things about Phycodurus eques, and other pipefish species, is that the father carries the eggs. Unlike sea horses, who carry eggs in a pouch, Phycodurus eques have a soft, spongy brood patch under their tail. In Summer, when the male is ready to mate he’ll turn bright yellow. The female sea dragon then lays about 200 bright pink eggs on the male’s brood patch where they become fertilised. Daddy dragon then carries the young for four to six weeks. When the babies are ready, they begin to hatch over several days. The father helps this process by gently shaking the babies from their eggs.

When the babies first hatch they are just 20mms long. Phycodurus eques live rather solitary lives and adult sea dragons don’t care for their young, so the babies are on their own in the dangerous waters. Because they are so small they can be picked off by predators. Only about one in twenty young survive. In their first year they’ll grow to about 20cm in length. By two years of age they are fully grown. Adults sea dragons will be between 30cm and 45cm in length. Phycodurus eques live about five to ten years.

Newly hatched Phycodurus eques feed from a yolk sac for the first few days of life. When they are big enough, they begin hunting zooplankton, such as copepods (a microscopic crustacean) and rotifers (tiny aquatic animal). As they mature they begin eating larger zooplankton, such as mysids (a tiny crustacean) and sea lice (the larvae of jellyfish and other ocean stingers). A Phycodurus eques hunts its food by snapping its head forward and sucking the shrimps and larvae into its long, tubular, toothless snout before swallowing them whole. They eat up to 1000 little sea creatures a day!

Facts

• As with its seahorse kin, a male Phycodurus eques carries its mate’s eggs until the eggs hatch.
• But unlike seahorses, male sea dragons don’t have a pouch. Instead, a male sea dragon carries the eggs on the underside of its tail in a brood patch that develops as mating season approaches. The brood patch contains capillaries that deliver oxygen-rich blood to the cuplike tissue.
• The female sea dragon transfers up to 300 eggs to the male’s brood patch, where the male fertilizes the eggs. The male cares for the eggs until their birth approximately four weeks later. Newborns, equipped with enough yolk to sustain them for two to three days, are on their own from the start. Once they deplete their yolk, the new-borns must find their own food sources such as zooplankton and baby mysids.
• At birth, Phycodurus eques are only around 8 inches (20 mm) long. Within one year, they can grow up to 7.9 inches (20 cm). They reach their mature length within their first two years of life.