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 present 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.
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)
Denise’s pygmy seahorse (Hippocampus denise)
Pontoh’s pygmy seahorse (Hippocampus pontohi)
Satomi’s pygmy seahorse (Hippocampus satomiae)
Severn’s pygmy seahorse (Hippocampus severnsi)
Walea soft coral pygmy seahorse (Hippocampus waleananus)
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.)
• 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.
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.
I have just arrived in Okinawa, Japan for the 9th quadrennial Indo-Pacific Fish Conference. I presented at the last meeting four years ago in Freemantle with my talk ‘First field studies of the obligate gorgonian-associated pygmy seahorses, Hippocampus bargibanti and H. denise‘. This time round I decided to do a poster presentation for a change, on another aspect of my PhD research.
If you happen to be attending, my poster session is on Thursday afternoon so come and say ‘hi’. The poster is about the polygamy that I observed in Denise’s pygmy seahorses. There is a downloadable version of my poster below and the abstract for the poster is as follows:
A wide range of mating systems have been recorded in syngnathids; however, despite some social promiscuity and mate switching, all studies of seahorse reproduction to date have revealed ubiquitous genetic monogamy. Denise’s pygmy seahorse (Hippocampus denise) is among the smallest (maximum standard length 24 mm) and most habitat-specific of all seahorses, with individuals spending their entire adult life isolated in small groups on a single gorgonian coral host. We investigated whether the reproductive strategies and social interactions of this species align with those of its congeners. During 217 thirty-minute observation periods we recorded the reproductive and social behaviour of 18 adult H. denise in four groups of differing sex ratio in a wild population of seahorses in southeast Sulawesi, Indonesia. We found social polygamy and sequential polyandry to feature in the species’ reproductive strategies, although monogamy was dominant. Social and reproductive behaviours were described for the first time and characterised by daily interactions between reproductively active partners at dawn and dusk conducted in a core area. The use of core areas, a term used for protected regions of the gorgonian host shared for the most part by reproductively active individuals, may have been pivotal in enabling a stable polyandry to develop. Conventional sex roles were observed, with males competing for access to females. The ecology of H. denise appears to have favoured the evolution of mating system plasticity and the maximisation of reproductive output, which may be explained by the species’ small size, skewed sex ratios and density of individuals sharing a single host.
As part of my PhD research I visited a small resort in central Sulawesi. It is scarcely known to non-Italians, but an absolute gem. I was in search of the amazing Walea soft coral pygmy seahorse (Hippocampus waleananus), which is known only from the reefs of the Togian Islands.
The diving is outstanding, with some of the best hard coral I have seen and many interesting critters, including bumblebee shrimp, boxer crab, tiger shrimp, four species of pygmy seahorse and the rare Kyonemichthys rumengani found in abundance.
My article about the area is featured in the new issue (159) of Sport Diving magazine, available now throughout Australasia.
I’m excited to have the cover image and a feature article in the spring issue of Marine Conservation Society’s magazine. MCS is a UK based charity that does great work throughout the British Isles, protecting our amazing marine life.
The cover shot is an image of Denise’s pygmy seahorse on a whip coral taken at Wakatobi Dive Resort in Indonesia. My article ‘Protecting the Pygmy’ is about pygmy seahorses and the threats they face, from habitat loss and destruction to accidental damage by overzealous divers. There is information about the Code of Conduct for observing and photographing pygmies that I created based on my PhD research. For more about the code, check out my information page.
Visit the MCS website to join up and show them some support!
I am pleased to announce that this issue (Volume 2: Issue 1) I have the cover image and a feature article ‘The Sex Life of Seahorses’ in 72 & Rising Magazine, which is a magazine focusing on marine and freshwater environments and their conservation.
Check out the article here:
The Sex Life of Seahorses by Richard Smith (© Richard Smith 2012)
It’s easy to list any number of unusual features about seahorses: a horse-like head ending in a puckered mouth, a monkey-like prehensile tail and eyes that move about independently. Even stranger than all of this is their reproduction where extraordinarily devoted fathers and strict monogamy are unique in the animal kingdom.
The most well-known and fascinating aspect of seahorse reproduction is male pregnancy. Male seahorses aren’t the only fish that put a great deal of effort into raising their young, but they are the only ones that become truly pregnant and even get stretch marks. Whilst male cardinalfish mouth brood and some male frogs carry tadpoles around, the male seahorse nurtures his young inside a fully enclosed pouch full of blood vessels, which bring nourishment and oxygen, whilst carrying away waste products. Paternal care is found across the entire family Syngnathidae, whose members include pipefishes, pipehorses and of course seahorses. Less advanced forms, such as the pipefishes, merely adhere eggs to a patch of skin on the belly whilst the more highly evolved pipehorses, as their name suggests, are an intermediate form and have a semi-enclosed brood area.
Over time the role of the brood pouch has grown beyond the protection of young and has driven the evolution of mating systems in the family. The brood surface on the belly of pipefishes is open to the environment but also potential mates, meaning that males are able to accept eggs from several females at a time. This has driven the females of some species to compete for the attentions of males and in a surprise twist it is the females rather than males that develop sexual ornamentation, much like the peacock’s tail but in reverse. This situation contrasts with seahorses, where the male’s brood pouch is sealed immediately following the transfer of eggs. In this case, a male can only accept eggs from one female for the entire gestation period. Females on the other hand are prevented from mating with other males by the scarcity of mates and the cost of egg production. The result is ubiquitous monogamy in seahorses for the duration of at least each distinct brood. The advent of DNA testing highlighted the exceptionality of this as virtually all other species previously believed to be monogamous, including many birds and even humans, were actually discovered to have produced young by multiple partners.
The direct transfer of eggs into the male’s brood pouch also affords him a certain confidence in his fatherly duties. Unlike other animals where promiscuity is rife, the male seahorse can be one hundred per cent sure that each of the offspring he carries is his own, with no risk of cuckoldry. This explains the extreme lengths that male seahorses are willing to go to in raising their young. It is certainly in his best interests to raise as many young as possible, in order for his genes to be passed on to the next generation.
The reproductive cycle of a seahorse begins with locating a mate, which can be easier said than done as they live at very low densities. If there is opportunity to be picky, seahorses will preferentially chose a partner of a similar size. This means that neither brood pouch space nor eggs will be wasted through a partner being too large or small for the clutch of eggs. Once an unpartnered male and female have found each other, the pair begin to dance. Courtship rituals are very important for the bonding pair as it allows them to synchronise their reproductive cycles. Pair bonding provides the female with the assurance needed to hydrate a clutch of eggs, a necessary step before they are ready to be transferred to her mate. Egg hydration is an irreversible process once it has begun, so it is important for the female to be confident that her partner is willing and able to accept them. If she does not transfer the clutch at the end of the few days it takes to hydrate them, they can go bad and damage her reproductive organs and she must expel them, which wastes precious energy reserves. Synchronisation is beneficial as it increases the pair’s overall productivity, making monogamy a more stable option and switching mates between broods more inefficient.
After egg hydration is complete, the pair carry out an extended ritualised courtship involving colour changes and specific body movements, which culminate in the pair raising up together into the water column. A heart shape is formed from the two seahorse’s bodies as the two fish grasp each other’s tails and their snouts meet in the middle whilst eggs are passed between them. The eggs are transferred directly into the pouch, which is immediately sealed to prevent the intrusion of harmful seawater. The male’s pregnancy then lasts between ten days and six weeks, depending on species and water temperature. Daily courtship continues throughout the gestation, allowing the female to gauge when her mate will give birth and to allow her to hydrate eggs accordingly, thus maximising the number of young they are able to produce. This synchronisation is such that I have seen pairs remate within thirty minutes of the male giving birth!
The birth itself is slightly less traumatic than our own but the male is clearly exerted by the contractions that expel the babies. The number of young produced varies between half a dozen for the smallest species and over a thousand for the largest seahorse, the pot-bellied seahorse, which reaches 30 cm in length. Once they are born, the tiny seahorses, which are miniature fully formed copies of their parents, exploit ocean currents in a planktonic phase to be swept away to settle in a new area. The juvenile seahorses are then ready to find a partner of their own and begin the cycle again.
Seahorses have fascinated humans since the Ancient Greeks but only in the last few decades have the true mysteries of these enigmatic creatures been revealed. Male pregnancy and strict monogamy evolved over millions of years; however, loss of habitat and the Traditional Chinese Medicine trade pose significant threats to seahorse populations around the world.
PYGMY SEAHORSES are a fascinating group of miniature seahorses, measuring 1.4 – 2.7 cm as adults, depending on the species. Six of the seven described species were described in the first decade of the 21st Century and
as a result very little is known about them. Although they belong to the genus Hippocampus, along with all other seahorses, they have several adaptations for their small size. Among these unique morphological attributes is the brooding of young within a pouch located inside the body cavity of the diminutive fish, rather than a pouch located on the tail, as is the case in other seahorses. This is thought to be an adaptation for their extremely small size as a tail pouch would hinder their movement. Among other aspects of their biology and conservation, pygmy seahorse reproductive behaviour comprised part of my PhD studies.
I am extremely pleased to announce that my image of mating Denise’s pygmy seahorses (Hippocampus denise) taken at Wakatobi Dive Resort is the ‘Parting Shot’ in the new issue (Winter 2012) of Alert Diver magazine (see attachment below).
Alert Diver, as many of you will know, is the quarterly publication of the Divers Alert Network (DAN) in the USA and regularly features the biggest names in underwater photography. I am honoured to have my image in print alongside the work of Brian Skerry, Flip Nicklin, Ned and Anna DeLoach, Michelle Westmorland, Keri Wilk and Amos Nachoum – all under the editorial eye of Stephen Frink!
The image of mating Denise’s pygmy seahorses was taken during my PhD research on the biology and conservation of pygmy seahorses. I spent hundreds of hours observing and recording the social and reproductive behaviours of these animals for one part of my study and was lucky enough to watch them giving birth and mating on several occasions.
One pygmy birth that I witnessed was particularly memorable due to a pair of titan triggerfish choosing to lay their own clutch of eggs at the exact same time that the pygmies were giving birth. Triggers are notorious for their bad temper when nesting and I can confirm that their excitement is amplified when actually laying their eggs. Somehow I managed to scribble down my notes during the incessant onslaught, with my buddy acting as a bodyguard, and witnessed the 3 mm baby pygmies being released into the world.
Another focus of my research was the interaction between divers and pygmy seahorses. By observing many such interactions I was able to pinpoint certain diver actions that resulted in the seahorses exhibiting stressed behaviours. This culminated in Code of Conduct guidelines to help educate divers on which actions to avoid whilst photographing and observing these amazing animals. You can read more about the code and a download a version in various languages by following this link.
Attachment: Alert Diver Parting Shot Mating Pygmy Seahorses.pdf