Scuba divers have long been fascinated by these often extremely tiny critters. Seahorses are illusive photo subjects as they camouflage themselves by changing colour quickly to blend in with their surroundings. They also allow encrusting organisms to settle on them and they can grow long skin appendages to match their surroundings even better. During mating their skin will lighten and darken. Generally the easiest part of the seahorse to spot is the tail.
The seahorse is 1 of 4 families in the syngnathiform family order which also includes pipefish, flag tail pipefish and seadragons. They swim in an upright position with their tails down and their heads up. Their dorsal fin moves them forward and the pectoral fin controls steering and turning.
The pygmy seahorse is a recently discovered relative of the common sea horse and one of the divers most sought after finds. A lot of deco time and a magnifying glass will help in the search for these cryptic critters. They are roughly 15mm in length although some are smaller, and as their tail is always curled around a seafan, they appear even smaller.
Very little is known about their life cycle. They are thought to eat the same zooplankton as the seafans that they inhabit and they seem to prefer seafans to other family members, as there are normally few other inhabitants on a pygmy’s seafan.
Sea horse Fact Sheet
Family name: Hippocampinae
Order name: Syngnathidae
Common name: Seahorse
Scientific name: Hippocampus
They are characterised by an elongated body encased in bony rings. Instead of scales that are found on most fish, seahorses have a thin layer of skin stretched over a series of bony plates. These plates show themselves as the bony rings along their body’s trunk. They have no pelvic fins but most have small pectoral fins and a single dorsal fin. They have a prehensile tail (able to grasp) and a tube-like mouth with no teeth, and small gill openings. Unlike (most) humans but similar to chameleons, seahorses can move their eyes independently of each other. They range in size from 10mm to 35cm, the largest species being the Pacific seahorse. Seahorses also have a coronet on the top of their head which is distinctive in all seahorses, in the same way that a thumb print is in humans.
Seahorses eat small crustaceans which they catch by staying still and lying in wait. When prey comes near they snap them up. Their tube like mouth creates a vacuum that sucks prey in and they swallow their food whole. They can eat up to 3,000 brine shrimp per day.
Sea horses are unusual in a couple of ways. One is that they are monogamous and have long courtship periods when mating. Monogamy is unusual in all animals but especially in fish. There is some evidence to suggest that the longer a couple of seahorses stick together, the better they are at producing babies. Indeed, a male seahorse that is involved in an intimate relationship can be pregnant for as many as 7 months of the year. Once the male has given birth, he often becomes pregnant again right away.
Another unusual aspect of the sea horse is that it’s the male of the species that becomes pregnant and carries the eggs in a pouch on his belly, after the eggs have been deposited there by the female. The eggs are fertilised in the pouch and incubated until they hatch. Incubation lasts between 10 days and 4 weeks, depending on the species and water temperature.
At hatching, the male gives birth to fully developed but tiny versions of its species. The natural lifespan of seahorses is not known, but believed to be from 1 year for small species to 5 years for a larger species.
It is common in the fish world for the males to take care of the eggs by guarding them or fanning them to keep them clean and provide enough oxygen. But seahorses take parental care to an extreme unknown elsewhere in the animal kingdom. A capillary system provides nutrients to the young.
Want to Know Where to Scuba Dive with Seahorses?
The Barbigants pygmy seahorse (hippocampus barbiganti) can be found all over Indonesia in various colours and at all depths. They can be found in the muricella sea fans in Papua New Guinea, Philippines and Malaysia. These sea fans have bulbous red polyps as do the pygmy seahorses. This, along with their small size, is what makes them so difficult to spot.
Denise Hackett recently discovered a new pygmy seahorse species in Indonesia. It’s named after her, hippocampus Denise, but it’s often called the ‘plucked chicken pygmy seahorse’ due to its unusual appearance with a lack of the typical bumps (tubercles). Hippocampus Denise is normally found in light yellow gorgonians which, like the pygmy, are less bulbous with smaller polyps.
The weedy pygmy seahorse is an even newer discovery. First recorded in the Banda Sea in 2000, they are now regularly seen at Wakatobi and the Lembeh Strait. The Raja Ampat area is another good place to find them. This species is the smallest and most cryptic. They seem to move around more than other species making them even harder to pin point.