Pygmy Seahorse Facts and Images

On the 1^st 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 published various findings from my thesis in the scientific literature but wanted to share some more accessible information and facts about pygmy seahorses from my research:

My new book ‘The World Beneath‘ has a chapter about my pygmy seahorse research and the soap opera that is the lives of pygmies sharing a seafan together. MORE HERE 

• What is a pygmy seahorse?

Pygmy seahorses are a group of eight species of miniature syngnathids (technical name for seahorses and pipefish) fish that live in the Coral Triangle region of southeast Asia.

• What is the size of a pygmy seahorse?

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 21^st century seven of the described total of eight 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 – Severn’s and Pontoh’s pygmy seahorses are now known to represent a single species, so the name Hippocampus severnsi has been dropped.

Follow the LINK to more information and images of each of the pygmy seahorse species individually:

Bargibant’s Pygmy Seahorse (Hippocampus bargibanti) – 1970

Denise’s Pygmy Seahorse (Hippocampus denise) – 2003

Pontoh’s Pygmy Seahorse (Hippocampus pontohi) (which also now includes Severn’s pygmy seahorse Hippocampus severnsi) – 2008 

Satomi’s Pygmy Seahorse (Hippocampus satomiae) – 2008

Walea Soft Coral Pygmy Seahorse (Hippocampus waleananus) – 2009

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! Colleagues and I are investigating the Taiwanese species and it’s inclusion under the name H. colemani.

In 2019, colleagues and I named this new species of pygmy seahorse from Japan. Read more about it HERE

Japanese pygmy seahorse (Hippocampus japapigu) – 2019

Finally, I described the latest new pygmy seahorse species in 2020! The Sodwana Pygmy Seahorse (Hippocampus nalu)

• How do pygmy seahorses differ from the larger seahorses?

Pygmy seahorses are morphologically distinct from all other seahorses, which are adaptations for their extremely small size.  In addition to 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, southern Australian syngnathids: 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. Pygmy seahorses have amazing camouflage to match their immediate surroundings.

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 (also known as seafans).  Bargibant’s lives only on one genus of gorgonian coral, Muricella spp, whilst Denise’s pygmy seahorse is known from at least ten 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.

• 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 are 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.  Of the five species of pygmy seahorses listed on the IUCN World Conservation Unions Red List of Threatened Species, four are recorded as ‘Data Deficient’.  This classification means that not enough is known about their population sizes to make an informed assessment of their conservation requirements. Only Pontoh’s pygmy is listed as ‘Least Concern’. Walea, Japanese and Sodwana pygmies are not yet recorded on the list.

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.

• Is a pygmy seahorse the same as a pygmy pipehorse?

In addition to the pygmy seahorses, there are some other pygmy syngnathids. One of these is the pygmy pipehorses, which are close relatives of the seahorses and pipefishes but belong to a different evolutionary branch. Some pygmy pipehorses look so similar to seahorses, that they have even been named as seahorses incorrectly. An example is Hippocampus tyro, which was classified in the genus Hippocampus along with all seahorses, but it is now known to be a pygmy pipehorse. Four years ago I was lucky enough to be in New Zealand and saw a pygmy pipehorse, which at the time was undescribed. It was named in September 2021 as Cylix tupareomanaia or the New Zealand Manaia pygmy pipehorse. I am working with colleagues to name another new pygmy pipehorse too!