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Website home>Newsletters>September 2007>Diving with Seahorses

Seahorse Newsletter

Diving with Sea Horses

The seahorse is among one of the most loved and photographed underwater creatures. It is one member of the 4 families in the syngnathiform family order which includes seadragons and pipefish.

Seahorse - photo courtesy of Edge of the Reef

Seahorses are well camouflaged creatures and seek out areas of shelter to stay out of harm's way. Many can change colour quickly to camouflage themselves in their surroundings. Additional tools they use to obscure their appearance are allowing encrusting organisms to settle on them, and the growth of long skin appendages to match their environs. However, the easiest way to spot them is to look out for their distinctive tail, which is the only prehensile tail in the fish world.

Sea horses swim in a more or less upright position with their heads up and their tails down. They move forward using their dorsal fins and steer and turn with their pectoral fin.

A relatively recently discovered relative of the common sea horse is the Pygmy Seahorse, which is the one divers consider most sought after. You may need plenty of deco time and a magnifying glass to seek out these cryptic critters. They are approximately 15mm long although some are even smaller, and since their tail is always curled around a seafan, the amount of this cute little critter visible to the naked eye is reduced even further!

Very little is known about the life cycle of pygmy sea horses in the wild. They are believed to consume the same zooplankton as the seafans that they cling to, and they seem to prefer the company of seafans to that of other seahorses since few fans contain more than 1 or 2 members of the species.

Seahorse Fact Sheet

Family name: Hippocampinae
Order name: Syngnathidae
Common name: Sea horse
Scientific name: Hippocampus

Distinguishing Features

Close up of a commom Sea horse

The main characteristics of a seahorse are an elongated body which is encased in a series of bony rings. Unlike fish that have scales, sea horses have a thin layer of skin that stretches over bony plates which resemble rings running across the trunk of the body. Without pelvic fins they use their small pectorals and a single dorsal fin for motion and grasp using their prehensile tails. The sea horse's mouth is a tube-like structure with no teeth and they have small gill openings. Their eyes are capable of independent motion allowing them a greater level of defence against the approach of a possible predator. They also have the equivalent of a human thumb print - a coronet on the top of their head - which is distinctive in every single seahorse. Sea horses range in size from about 10 mm to 35 cm, with the Pacific Seahorse being the largest.

Feeding habits

Sea horses are believed to eat small crustaceans in the form of zooplankton, which they catch by remaining motionless and lying in wait. When suitable prey ventures into range, they open their mouths to create a vacuum that sucks prey in. Without chewing, they swallow their prey whole and allow their digestive juices to do the rest. Seahorses can consume up to 3,000 brine shrimp per day.

Reproduction

Sea horse reproduction is very unusual. Firstly, they are monogamous creatures (surely not normal!) and pursue a long courtship period prior to mating (definitely not normal!). Monogamy is quite unusual in all animals, but this is certainly the case for fish. Evidence suggests that the longer a pair of seahorses remains together, the more successful they are in offspring production. In fact, a male sea horse that is deeply involved in an intimate relationship can be find himself being pregnant for up to 7 months in a single year. Often the male will become pregnant as soon as he has given birth.

It is very unusual that it should be the male of the species that becomes pregnant, but the seahorse follows few of nature's rules. It is common in the fish world for males to take care of the eggs by guarding them or fanning them to ensure cleanliness and adequate oxygenation. However, sea horses take paternal care to an extreme unknown elsewhere in the animal kingdom.

The male carries the eggs in a belly pouch after they have been deposited there by the female. She presumably goes shopping thereafter. The eggs are fertilised by the male in his pouch and he incubates them until hatching. The period of incubation normally lasts between 10 days and 4 weeks, depending on species and the temperature of the surrounding water. A capillary system provides nutrients to the young during this period. When the momentous day of hatching arrives the male gives birth to fully developed but tiny versions of its species in a series of expulsive spasms. Science is not fully aware of the natural lifespan of seahorses in the wild, but estimates range from a single year for small species to around 5 years for a larger species.

Distribution

Seahorses can be found all over the world and typically inhabit sea grass beds and coral reefs. Pygmy sea horses are typically found in sea fans.

The Barbigants Pygmy Seahorse (hippocampus barbiganti) is present all over Indonesia in a variety of colours and at all depths. They can also be found in the muricella sea fans of Papua New Guinea, Malaysia and the Philippines. These fans have bulbous red polyps and their appearance is mimicked by the pygmy sea horses that they host. This camouflage, coupled with their small size, is what makes them so difficult to find.

Hippocampus Denise - the plucked chicken pygmy seahorse

A new pygmy seahorse species was recently found in Indonesia by Denise Hackett and it now officially bears her name, hippocampus Denise. Sadly for Denise it is often called the 'plucked chicken pygmy seahorse' because of its unusual appearance with a lack of the typical bumps (tubercles). Hippocampus Denise can normally be spotted on light yellow gorgonian fans which, as with the sea horse, have smaller polyps and are less bulbous than their close relatives.

An even newer discovery is the weedy pygmy seahorse. It was first recorded in the Banda Sea in 2000, and is now spotted regularly at Wakatobi and in the Lembeh Strait. The Raja Ampat area is another place where you can go to find them. This is the smallest and most cryptic species. They seem to move about considerably more than other species, which can make them even more difficult to pin point.

There are many other spots where you can dive with seahorses generally, such as Mabul Island and Kapalai in Malaysia, Phi Phi Islands and Phuket in Thailand, Rocky Peaks in Burma and Bali and Komodo in Indonesia.

Ecological Threats and Protective Measures

Pygmy sea horses and common seahorses like the tigertail, are very sensitive to stress, and too much attention from excited divers is definitely not good for them. They are particularly averse to bright lights and will turn their heads away if a diver shines a dive light upon them. Divers would be advised to place a red filter on to a dive torch. This will give a softer more diffuse light which should cause less irritation and enable photographers to take superior pictures.

Around the world sea horse numbers are falling. In many Asian cultures they are used in traditional medicine. They are dried and used for afflictions such as asthma and skin complaints but are also commonly used to 'treat' erectile dysfunction - a hard way for the seahorse to 'end up'. Despite there being no scientific data to support any such remedial properties, Asian countries consume around 45 tons of dried seahorses, which amounts to an unbelievable 16 million sea horses.

Another growing trend is that seahorses are being collected for aquariums in the USA, Europe and Japan. Further still, the habitat of sea horses is under threat with declining zones of sea grass areas, coral reefs and mangroves throughout the world.

Seahorses are currently red flagged as 'threatened' on many conservation lists, which act as warnings without actually enforcing restrictions on their trade, but they are not yet officially deemed endangered.

However, some more enlightened countries have put unilateral protective measures in place. South Africa has outlawed the capturing of sea horses, partly as a result of the near total collapse in numbers of the endemic Knysna Seahorse.

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