Biology

The taxonomy of pipefishes and pipehorses is in great need of revision. The last significant summary at the species level was in 1985.¹ At present, there are about 278 species of syngnathids across 54 genera. About 80% of the species in about 49 genera are the long slender linear pipefishes. Eleven of the species (4%) in two genera are pipehorses, with the head bent ventrally relative to the trunk. A further three species 1% in two genera are seadragons, which have a very distinctive shape and long, elaborate skin filaments.

Syngnathid fishes are fascinating in their evolutionary history.² You can see increasing specialisation for male parental care across the genera of syngnathids: some just glue the eggs onto their tail or abdomen with no pouch; some have a slight walling to protect the embryos; some have full flaps over the brood of young; some have a long pouch that more or less zips over the embryos to envelop them fully; then the seahorses have a fully sealed pouch with a small sphincter opening. Amazingly the various forms of paternal brooding appear to have arisen several times independently within the lineage.³

Pipefishes are found in temperate and tropical waters of more than 150 countries, and even in the open ocean. These species generally live in shallow coastal seas (even in less than one metre deep water) but some pipefishes have been found in waters at least 400 m deep.⁴ Some pipefish species live in freshwater, most notably the genera Microphis (18 species), Hippichthys (6 species), Doryichthys (5 species), Pseudophallus (3 species), Enneacampus (2 species) and Ichthyocampus (1 species).

Pipehorses have a smaller distribution. Pygmy pipehorses are restricted to shallow tropical and sub-tropical waters in the western Atlantic, Indian and Pacific oceans up to 40 m in depth. The larger pipehorses tend to prefer deeper waters of up to 200 m deep. They are found in about 30 countries in the western Pacific and Indian oceans.

The three seadragon species are all endemic to southern and eastern Australia, from western Australia to New South Wales, including Tasmania. The newly discovered ruby seadragon is found in seas more than 50 m deep⁵ while the common (also known as weedy) and leafy seadragons occur in shallower waters.

In total, pipefishes, pipehorses and seadragons occur off six continents and many parts of the world’s ocean:

• Western Atlantic – from New Brunswick in Canada to Patagonia in Argentina, and throughout the Caribbean Sea.
• Eastern Atlantic – from Norway to South Africa, and throughout the Mediterranean Sea.
• Indian Ocean – from Kenya to Australia, throughout the Middle East, South Asia and Southeast Asia.
• Western Pacific – from South Korea to New Zealand and Tasmania in Australia, and some Pacific islands.
• Eastern Pacific – from Alaska in the USA to Chile.

Habitats

Pipefishes, pipehorses and seadragons are found primarily in marine habitats, but about 10% of pipefish species inhabit brackish or freshwater habitats. In the ocean, pipefishes and pipehorses are found in similar habitats to seahorses, among seagrasses, corals, sponges, seaweed and rocky areas. Densities of pipefishes are similar to those seen in seahorses, exhibiting patchy distributions.⁶ The most threatened pipefish in the world, the Critically Endangered Syngnathus watermeyeri, lives in only two or three lagoon systems of South Africa. This extremely cryptic species is found in low densities from 0.05 to 0.2 individuals m² but new research on the species may change this estimate.⁷

Seadragons generally occur in sandy or rocky reefs in association with kelp and other seaweeds. The few assessments for seadragons that exist indicate low population densities in the range of 0.001 to 0.007 individuals per m². They display high site fidelity with adults moving between 50 to 500 m over the year.⁸

Crypsis

Many pipefishes and pipehorses are highly cryptic, probably in response to predation. Some greenish species hang vertically, blending in wonderfully with seagrass habitats,⁹ for example, while other species are brown and lie among leaf detritus. Still others are a reddish hue that allows them to camouflage in red algae,¹⁰ their tails clasped around the frond.  Some species change colour to match their background or grow skin filaments, as seahorses do. The extraordinary decorative skin filaments of the seadragons create remarkable camouflage in seagrass and algal habitat.

Movement

Some pipefish species stay in shallow seagrass beds throughout the year¹¹ while others make seasonal migrations, similar to that of seahorses, by moving to deeper waters in winter months.¹² For example, Syngnathus abaster will migrate seasonally to estuaries for breeding. ¹³ Little to nothing is documented about pipehorse behaviour or movement. Seadragons tend to remain in a small area in well-defined home ranges,¹⁴ without seasonal migration. That said, some pregnant male seadragons move to shallow sheltered waters to release their young at the end of the breeding season.¹⁵

Parental care

As in seahorses, the males of pipefishes, pipehorses and seadragons brood developing embryos, either in a pouch or on their trunk or tail. A wide diversity of brooding structures are seen within the Family Syngnathidae, ranging from simple gluing on the ventral surface to complex sealed structures.¹⁶ There is some evidence that the as brood pouch complexity increases across species, so too does egg size.¹⁷ After mating the eggs are organized in rows and are covered in a thick sticky mucus that act as a glue to attach eggs to the brood patch.  Within a brooding structure, epithelial tissue forms a cup around each egg, providing osmoregulation to the developing embryos.¹⁸

Mating and pair bonding

Pipefish species exhibit a range of mating patterns, from faithful and enduring monogamy by both sexes through to polygamy by one or both sexes.  Male and female pipefish tend to differ more in size, colour and ornamentation in polygamous species than in monogamous species.¹⁹ Some pipefish species are role reversed in that females tend to compete more for access to mates, and males are more selective than females when it comes to mate choice.  Males prefer larger females, with brighter colours and more elaborate ornamentation.²⁰ In at least one species, female flamboyance is indeed known to reflect offspring quality.²¹ Many species of pipefishes and pipehorses form pair bonds (of differing durations) and will engage in elaborate courtship displays.  That said, males of some species will minimise investment in a current brood when a better potential mate is available, a new female that might transfer a superior brood.²² The normal pattern is for one male and one female to rise to the surface together during mating, similar to the seahorses.²³

Common seadragons appear to be monogamous during a single breeding event although they may be polygamous during a breeding season.²⁴ During courtship and just before mating, the brood pouch of the male common seadragon becomes soft swollen and turns red.²⁵