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Seahorses: Flagships of Our Coasts
(Released May 2003)

 
  by David Lindsay  

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With their whimsical charm, seahorses inspire an almost universal reaction of wonder and delight. They have been favored in fairytales as friendly denizens of the deep, the mythical steeds of mermen, and have been prized as aquarium specimens and sought after for medicinal uses. Their unusual body form evokes comparisons to other animals; seahorses have been said to have the snout of an aardvark, the spines of a puffer fish, the pouch of a kangaroo, the independent eyes of a lizard, the prehensile tail of a monkey, the armor-plated body of a stegosaurus, and the color-changing capability of a chameleon. But it is the remarkable resemblence of the head to that of a miniature horse that makes these creatures so immediately recognizable and popular [Davis].

The National Aquarium in Baltimore is running an exhibit, "Seahorses: Beyond Imagination", that provides a live display of 18 species of these exquisite creatures [NatAqu]. The exhibit runs through December 2003 and is intended to educate the public about the biology and conservation of seahorses around the world.

Seahorse Anatomy
http://www.pbs.org/wgbh/nova/
seahorse/basics
The survival of seahorses in the wild is threatened by many anthropogenic factors, including loss of habitat, pollution, and overfishing, that also threaten less well-known species living in the same habitats. Seahorses are harvested for medicinal purposes, as souvenirs, and for the aquarium trade, often at unsustainable levels. However, the attractive appearance and popularity of seahorses make it more likely that efforts will be made to preserve them, and these measures can benefit many other creatures living in their ecosystems. Biologists call a species that functions in such a protective role a flagship species [Sreepada].

Physical Description

Seahorses are a saltwater vertebrate fish belonging to the order Perciformes, family Syngnathidae, meaning "with jaw", genus Hippocampus, literally "horse of the sea". The family includes seadragons, pipefishes, and pipehorses, and has existed for at least 40 million years [Ireland]. All 32 species are characterized by a hard bony body and a narrow two-jawed mouth. They live in temperate and tropical salt waters, in depths from .5 to 30 m. Seahorses average about 15 cm in length, but can range from .6 cm to 30 cm [Davis]. Four species live off American coasts, ranging in size from the 2.5 cm long dwarf seahorse (Hippocampus zosterae) to the 30 cm Pacific seahorse (Hippocampus ingens) [WGBH2]. A full lifespan is about four years, but only a few seahorses in thousands will reach maturity [WGBH3].

The body of a seahorse consists of plates joined together in rings that provide limited articulation. The number of rings is a characteristic of the species. Some rings carry protective spines. Their armor ensures their natural enemies are confined to the larger predators [Davis].

Seahorses can be white, yellow, red, brown, black, gray, green, or gold in color, and the pattern can be spotted or banded. They have the ability to change color and pattern almost instantly to match their surroundings, from sea grasses to speckled gravel. Some species have skin appendages that make them resemble kelp, or carry encrusting organisms that make them resemble coral or rocks. This camouflage can make it difficult to spot a seahorse even when it is in plain view; field workers learn to look for the unique feature of the curled tail [WGBH2]. They have distinctive coronets on the tops of their head, which allow experienced observers to distinguish individuals [WGBH].

Behavior

Seahorses can be found in sea grass beds, mangrove areas, coral reefs, and estuaries [WGBH3]. They feed on small crustaceans, plankton, worms, and other small invertebrates, and can consume up to 3000 brine shrimp per day [WGBH]. They are able to see microscopic prey, which they suck into their mouths by lowering their mouth floors and swallowing whole [Davis].

Seahorses generally hold their bodies in an upright position and appear to move mysteriously without apparent effort. In fact they propel themselves forward by beating a dorsal fin 20 to 30 times per second, fast enough for it to appear invisible [WGBH]. They use their pectoral fins to provide steering, and can control the amount of gas in their bodies to move up and down. They spend most of their time anchored to coral or grass with their prehensile tails, and sway in the current to resemble sea grasses or drifting kelp. They are slow swimmers, and rely on armor and camouflage for protection [Davis].

Reproduction

Hippocampus breviceps mating
http://www.pbs.org/wgbh/nova/
seahorse/roundup
The mating characteristics of seahorses reveal some of their most extraordinary features. The male has a pouch he may inflate with water to attract females, who may compete to win him. A pair performs a mating ritual that may last anywhere from a few hours to several days, during the time of a full moon. The ritual involves synchronized swimming, head lifting, and color changes [WGBH2]. During mating the female impregnates the male, depositing 200-600 pinkish eggs from .5-1.5 mm in diameter into the male pouch. The eggs are fertilized in the pouch and incubate in 2-6 weeks, depending on species and water temperature [Davis].

The term pregnancy is appropriate, for the male's pouch functions as more than a depository. It provides nourishing fluid and oxygen through a capillary network. As the babies mature, the fluid gradually changes to salt water, and when they reach about 1 cm in length the father expels them in a series of convulsions, appearing exhausted by the effort. Males are usually impregnated again soon after they give birth [WGBH].

Seahorses bond monogamously, and a pair seems to become more productive with successive births. Monogamous bonding is relatively rare among animals, and although there are examples of male assistance with parenting, primarily in birds, it is usually limited to feeding and guarding [WGBH2]. The reproductive service provided by male seahorses and their kin is unique in the animal kingdom.

Threats to Seahorses

Seahorses are slow swimmers and defenseless, and are at the mercy of larger predators, such as crabs, tuna, skates, rays, birds, and sea turtles. They also face dangers from storms, which can tear them loose from their moorings and leave them stranded or exhausted [WGBH3]. Their habitats may be damaged by dredging or pollution. They are often caught inadvertently in the nets of shrimp trawlers.

Seahorse babies
http://www.pbs.org/wgbh/nova/
seahorse/hssurvival
A few hundred thousand seahorses per year are captured for the home aquarium market. The US is the leading consumer of live seahorses [PNN]. Unfortunately most of these die, as seahorses are difficult to keep alive in captivity, due to their susceptibility to disease in a closed environment and their constant need for food [Garrick]. A few hundred thousand more per year are consumed by the ornament trade to make souvenirs and decorative objects, such as keychains, jewelry, and paperweights. Some of this demand is met by seahorse breeding farms.

But by far the greatest consumption is by the medicinal market. For the past 400 years, the Chinese have believed seahorses can not only enhance virility, but can cure impotence, asthma, high cholesterol, arteriosclerosis, incontinence, thyroid problems, skin ailments, heart disease, and even broken bones [WGBH3]. The dried bodies are often ground into a powder for consumption.

Around the world, 39 countries are involved in the seahorse trade. The market is lucrative: low quality seahorses sell for $440/kg, large ones for $1200/kg, and rare specimens can reach $2600/kg. Each kilogram contains approximately 400 dried seahorses [Vincent2]. The largest seahorse exporter is India, selling at least 1.3 million seahorses per year, followed by the Philippines, Thailand, and Vietnam. The US is also an exporter: in 1994, 112,000 seahorses were brought ashore in Florida, and most were exported to Taiwan. Indonesia, Filipino groups, Japan, Korea, Malaysia and Singapore are heavy consumers. The total market is estimated at 20-24 million seahorses per year [WGBH2].

Conservation Measures

Many biologists fear that native populations will be exterminated by such a level of consumption. Definitive data is not available, but some populations are estimated to have declined 25-50% within a five-year period. Seahorses have been listed in the 1996 International Union for the Conservation of Nature red flag category [WGBH2], and protection is being urged by field conservation efforts such as Project Seahorse and global programs such as the Marine Aquarium Councils certification scheme [Hall]. Recently, the Convention on International Trade in Endangered Species (CITES) announced protection of all seahorses. So far no animal species has become extinct due to trade once protected by CITES, but much work remains to protect the seahorse [PNN].

It is possible the perceived medicinal benefits of seahorses could be supplanted by Western medicines. Some folk remedies have proven to be effective, often by providing a key substance that can be isolated and produced artificially. However, the medicinal benefit of seahorses beyond the psychological placebo effect has not been demonstrated by objective experiments or rigorous double-blind testing [WGBH2]. Some conservationists hope that demand for seahorse remedies could be transferred to demand for Western pharmaceuticals with proven effects.

In addition to global programs, there have been efforts to work directly with native harvesters. Oxford biologist Amanda Vincent has worked with native Barangay fishermen in Handumon village in the Philippines since 1995. For the Barangay, the seahorse represents a critical source of income. Vincent was able to convince some of them of the need to practice conservation of their resource. The Barungay now abide by self-administered quotas, set aside protected areas, reseed depleted areas, and practice measures such as placing pregnant males in a special enclosure that allows the babies to be born before the male is harvested. Developing alternative industries for the fishermen would also relieve pressure on seahorse populations [Vincent].

Public aquariums and zoos are visited by over 600 million people per year, representing 10% of the world's population [Hall]. These institutions can play an important role in raising public awareness about the plight of seahorses and assisting in conservation efforts. The Baltimore Aquarium's Conservation Department operates a seahorse breeding laboratory that supplies seahorses not just to the "Seahorses: Beyond Imagination" exhibit, but to other aquariums worldwide [PNN].

Conclusion

Preservation of the seahorse presents a challenge at many levels. Continued survival of seahorses is important to humans, because of their aesthetic appeal, their biological value, their market value to marginal island economies, and the role they play in ecosystems around the world.

Unfortunately the very popularity of seahorses could lead to their own destruction. Their salvation must rest upon trade protection to restrain the frivolous consumption of these extraordinary creatures, critical examination of the medicinal benefits and promotion of alternatives, encouragement of alternative enterprises for people who depend on the seahorse harvest, development of captive breeding programs, and management of threats to habitat and water quality.

The fate of the seahorse rests in human hands.

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