Pygmy Seahorses

On the 1st April 2011 my PhD was officially awarded.  I am the first person to have completed a PhD on the biology of pygmy seahorses and I’m excited to share some of my findings.  My thesis is entitled ‘The Biology and Conservation of Gorgonian-Associated Pygmy Seahorses’.  I will be publishing the findings from my thesis in the scientific literature in the coming months so keep checking back or sign up to my blog updates for details.  Until then I wanted to share some information and facts about pygmy seahorses:

• What is a pygmy seahorse?

Pygmy seahorses are a group of seven species of miniature syngnathids (technical name for seahorses and pipefish) fish that live in the Coral Triangle region of southeast Asia. They range in length from 1.4 – 2.7 cm between the tip of the tail to the end of the snout.

• How many species of pygmy seahorse are there?

Within the first decade of the 21st century six of the described total of seven species of pygmy seahorse were officially named.  Before that only Bargibant’s pygmy seahorse was known to science, having been described in 1970. Since then two species have been synonymised with others (Severn’s pygmy joined Pontoh’s and Walea Soft Coral Pygmies joined Satomi’s – although I strongly believe the latter should again be separated).

Follow the links below to the image galleries for each of the pygmy seahorse species where there is more information about them individually:

Bargibant’s Pygmy Seahorse (Hippocampus bargibanti)

Bargibant's Pygmy Seahorse

Bargibant’s pygmy seahorses (Hippocampus bargibanti) inhabiting a gorgonian (Muricella sp), adult Bargibant’s pygmy seahorses reach a maximum size of 2.6 cm, southeast Sulawesi, Indonesia.

Denise’s Pygmy Seahorse (Hippocampus denise)

Pontoh’s Pygmy Seahorse (Hippocampus pontohi) (which also now includes Severn’s pygmy seahorse Hippocampus severnsi)

Pontoh’s pygmy seahorses (Hippocampus pontohi), courting pair of seahorses, female in fore, pregnant male behind, southeast Sulawesi, Indonesia.

Satomi’s Pygmy Seahorse (Hippocampus satomiae)

Satomi's pygmy seahorse (Hippocampus satomiae)

Satomi’s pygmy seahorse (Hippocampus satomiae), the world’s smallest species of seahorse, West Papua, Indonesia.

Walea Soft Coral Pygmy Seahorse (Hippocampus waleananus) – has recently been synonymised with Satomi’s Pygmy Seahorse due to a poor quality holotype specimen.  Hopefully this will be readdressed soon, as this is likely to be the most endangered species of pygmy seahorse.

Walea soft coral pygmy seahorse (Hippocampus waleananus), this seahorse is an obligate associate of Nephthea sp soft corals and is endemic to the Togean Islands, Togean Islands, Sulawesi, Indonesia.

The final described species of pygmy seahorse, Coleman’s pygmy seahorse (Hippocampus colemani), is thought to be restricted to Lord Howe Island off the east coast of Australia although there are unconfirmed reports from eastern Papua New Guinea and Taiwan.  I am yet to observe this species in the wild but hopefully one day I will have the opportunity!

There are likely to be new and undescribed species of pygmy seahorse yet to be discovered.  One such species that awaits a name is the Japanese pygmy seahorse.

Japanese pygmy seahorse (Hippocampus sp.) – I am in the process of investigating this species and working on a possible description.

• How do pygmy seahorses differ from the larger seahorses?

Pygmy seahorses are morphologically distinct from all other seahorses.  Apart from their extremely small size, they have a single gill opening on the back of the head (all other seahorses have a pair of gill openings either side of the head) and the young are brooded within the male’s trunk rather than a pouch on the tail.

Several other small seahorses are sometimes referred to as pygmy seahorses, but lack the true pygmy’s single gill opening and trunk brooding.  These include some recently discovered species such as the endemic Red Sea soft coral pygmy seahorse (Hippocampus debelius) and a pair of deepwater, apparently closely related, southern Australian seahorses: the southeast Australian Bullneck seahorse (Hippocampus minotaur) and the southwestern Paradoxical seahorse (Hippocampus paradoxus).

• Where do pygmy seahorses live?

Pygmy seahorses live in different habitats from their larger cousins.  Larger seahorses are rarely found on tropical corals reefs, particularly current prone walls.  Pygmy seahorses have evolved several adaptations to fill this niche perfectly.  

Three species of pygmy seahorse have evolved a special association with sessile coral reef invertebrates.  Two, Bargibant’s and Denise’s pygmy seahorses, are only found living on gorgonian corals.  Bargibant’s lives only on one genus of gorgonian coral, Muricella spp, whilst Denise’s pygmy seahorse is known from at least nine genera of gorgonians.  The third species, the Walea pygmy seahorse, is found living in association with soft corals.

• What do pygmy seahorses eat?

The diet of pygmy seahorses consists of small crustaceans.

• Can you distinguish between male and female pygmy seahorses?

Male pygmy seahorses have a tiny slit at the base of the abdomen and females have a tiny round, raised pore.

Distinguishing between male and female pygmy seahorses

Female pygmy seahorse on the left hand image (a) with a raised circular urinogenital pore and a male right (b) with a slit-like opening to the brood pouch.  Scale bars are 5 mm.

• How do pygmy seahorses reproduce?

Like all seahorses the male is responsible for all post-fertilisation care of the developing young.  Eggs are transferred, unfertilised, to him from his mate into his brood pouch.  They remain within the pouch, which is full of blood vessels, until they are born 11-14 days later.  The blood vessels bring nourishment and oxygen to the developing offspring.  Between 6 and 34 young have been recorded from a single clutch of eggs.

• What happens to the baby pygmy seahorses after they’re born?

The young are released with some force from the male’s brood pouch and are swept away by the current into the ocean.  They then have a planktonic phase where they feed and grow in the water column until settling onto the reef.  They are dark in colour until settling onto the reef, where they change to suit their immediate surroundings.

Satomi’s pygmy seahorse on the other hand, is reported to give birth to young that settle immediately to the reef around their parents.  This observation does however seem at odds with the relatively large geographic distribution of the species.  Without a pelagic phase for young pygmies to drift with ocean currents and reach new reefs they would be unlikely to have a distribution stretching from east to west Indonesia.

For more information on the birth of pygmy seahorses in the wild follow this link to my paper from the journal Coral Reefs.

• Are pygmy seahorses endangered?

Mine has been the first study on the population sizes of pygmy seahorses.  Currently all seven species of pygmy seahorse are classified as ‘Data Deficient’ by the IUCN World Conservation Union.  This classification means that not enough is known about their population sizes to make an informed assessment of their conservation requirements. 

I studied the populations of Bargibant’s and Denise’s pygmy seahorses around Wakatobi Dive Resort, southeast Sulawesi, Indonesia.  The resort has gone to great lengths to protect their reefs for the last fifteen years, which provided a rare opportunity to estimate pygmy seahorse populations in a near pristine environment.  I found that the population sizes of these two pygmy seahorse species are naturally low.  They were in fact among the lowest for any unexploited seahorse population yet studied.  Their habitat specificity and small population sizes mean that conservation measures may need to be taken to protect them in some areas.

For more information on my pygmy seahorse population paper published in the scientific journal Marine Ecology Progress Series, please follow this link.

• Do pygmy seahorses have any predators?

The small size and amazing camouflage of pygmy seahorses mean they do not suffer heavy rates of predation.  Occasionally however, they may be opportunistically be taken by one of the reef’s general predators.  There are also reports of long-nose hawkfish eating pygmy seahorses but there is no truth to the myth that the presence of a hawkfish on a gorgonian means there will be no pygmies present.

• Can you keep pygmy seahorses as pets in an aquarium?

The habitat specialisation of pygmy seahorses, their extremely delicate nature and small size all prevent the true pygmy seahorses from being kept as pets in aquaria.  Unsuccessful attempts have been made by national aquaria in the past and resulted in the death of the animals and their gorgonian coral host. Confusion can arise as the Dwarf seahorse, Hippocampus zosterae, is also known as a pygmy seahorse.  Unlike the true pygmies, this species is slightly larger, has paired gill openings and males have a brood pouch located on the tail.  The care of these dwarf seahorses can be quite challenging and it is recommended only for experienced aquarists.

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