>Since the turn of the millennium, there has been a flurry of new pygmy seahorse discoveries. We now have seven named species across the Indo-Pacific. Georges Bargibant, a researcher in New Caledonia, discovered the first pygmy seahorse when he was collecting a gorgonian coral for the Noumea museum and found a pair of tiny seahorses on its surface. Bargibant's pygmy seahorses are extreme habitat specialists that live only on the surface of Muricella gorgonians. Also known as sea fans, these corals can reach monumental sizes, measuring a couple of meters across.
>My involvement in the naming of Hippocampus japapigu came about after I visited Hachijo-jima, a tiny island just a 45-minute flight from Tokyo. In 2013 I was in Okinawa for a fish biologist conference, but I also planned a side trip to look for an odd pygmy seahorse that I had seen in a picture. Japapigu looks similar enough to Pontoh's pygmy seahorse that no one had further investigated the odd fish in the photo; having seen many pygmies over the years, I was sure this seahorse was a different species. Not being a taxonomist, I was thwarted for a few years until I met seahorse taxonomist Graham Short at another conference, and we started talking about this unusual pygmy. On much closer inspection, Japapigu turned out to be quite different: Genetic analysis showed that it split off from all other pygmies around 8 million years ago.
>Like all other seahorses, pygmies have the reproductive quirk of male pregnancy. In a process known as egg hydration, females internally ready a clutch of eggs about four days before they are due to mate. Daily dances and behavioral rituals with their partners allow pairs to synchronize their reproductive cycles, minimizing the time between broods to produce as many young as possible. When a pair mates, the female transfers her unfertilized eggs into the male's brood pouch. The male fertilizes the eggs as they go into his pouch, as such he can be certain that he is the father of each baby he carries, which is almost unique in the animal kingdom. For this reason the male seahorse becomes pregnant and puts so much effort into raising the fry.
>Over six months I dived several times a day to study different groups of Denise's pygmies, discovering that once settled on a gorgonian as a tiny juvenile, they wouldn't leave it again. After I selected a group at a suitable depth that enabled me to visit frequently, I began to collect data. I took close-up images under the trunk of each pygmy, which allowed me to identify the sex of the animals: Females have a tiny raised circular pore, and males have a slit-like opening from where the babies will eventually emerge.
>After two months of recording every interaction for several hours each day, I found that pygmies are somewhat more risqué than their larger cousins. In their battles over the female, the three males were quite pugnacious and would frequently attempt to strangle each other with their tails. One epic battle involved all three males and resulted in one of them having a sprained tail for several days afterward. Like giraffes, the males also tried to use their necks to push each other over in displays of dominance.
>Like many marine creatures, pygmy seahorses have a precarious place in our oceans. I found them to have some of the lowest population densities of any seahorses yet studied. Furthermore, the species that directly rely on gorgonians or soft corals for their existence require a healthy host. Reefs throughout their ranges are heavily degrading, destroying the fragile hosts for pygmies. Divers can help through thoughtful and careful interactions with these delicate creatures. Do not touch the animal or its habitat, and avoid disturbing them with bright lights and excessive use of strobes.
>As is the case with many marine animals, we still have much to learn about pygmies. My colleagues and I are working on naming yet another new species of pygmy seahorse, which appeared in a most unexpected location. Keep your eyes open while diving — most pygmies have been found by eagle-eyed recreational divers and dive guides, revealing new species to the scientific community at an unprecedented rate.
>See the new species of pygmy seahorse, Hippocampus japapigu, in this video.
>© Alert Diver — Q1 2020