Seahorses

This topic submitted by Crystal Hansen ( hansencl@muohio.edu) at 12:44 PM on 6/8/02.

Susan found a "Treasure Chest" in Fernandez Bay, San Salvador, Bahamas. See other beautiful phenomena from the Bahamas.

Tropical Field Courses -Western Program-Miami University

Crystal Hansen
Dr. Hays Cummins
Tropical Marine Ecology
8 June 2002

Seahorses

Seahorses are curious and unique bony fishes in the same family as pipefishes, sea dragons, and pipehorses. All seahorses are of the genus Hippocampus, but classification of individual species has been difficult because they can change color and grow skin filaments to blend in with their surroundings. Seahorses rely on camouflage to capture prey and to avoid predators. They are capable of long-term dramatic color changes to match their background better. Most seahorses are neutral colors ranging from beige to brown to black, but they can also change to fluorescent orange and deep purple, depending on the species. Seahorses can also grow long skin filaments that help them to blend in with their surroundings. Because of this, more than 120 species names have been proposed for seahorses in the last two hundred years, but today most scientists recognize 30-35 different species worldwide.
The anatomy of the seahorse is very interesting. It has a coronet that is nearly as distinctive as a human thumbprint, and each of its two eyes moves independently. It has a horse-like head, a fully prehensile tail, and instead of scales, skin that is stretched over bony plates. The seahorse’s snout is good for sucking up its prey, and its dorsal fins are used for propulsion. The pectoral fins are for stabilization and steering. Although every species of seahorse shares the same basic shape, sea horses can range in length from under one inch to over a foot.
Seahorses live in complex habitats that favor maneuverability over speed. They tend to move slowly across the sea bottom using their dorsal fins for propulsion and their ear-like pectoral fins for stabilization and steering. They don’t have pelvic or caudal fins, and they only have a tiny anal fin. Their slow movement means that camouflage is very important in avoiding predators. Most seahorses are more active during the day than at night. However, the Tiger-tail seahorse, found in some parts of the Philippines, is now nocturnal, possibly in response to heavy fishing pressure.
In nature, young seahorses are very vulnerable to predators (mostly fish-eating fish). Adult seahorses do not have many natural predators, probably because they are difficult to find and are relatively undesirable because of their bony plates and spiny structure. However, they have been found in the stomachs of large fishsuch as tuna and red snapper. Crabs and seabirds are also known to take some. In addition, storms can seriously disrupt their populations, casting some ashore and others adrift, causing many to die and others to be dispersed.
Seahorses establish small home ranges, with a central holdfast that the seahorse wraps its tail around. They appear faithful to their holdfasts, and are repeatedly found on the same blade of seagrass, coral branch, or sponge. However, their dispersal abilities are unknown, and so is the role of currents in facilitating their movement.
Sea horses live in the range between 45Ľ North to 45Ľ South, with most species habitating in the IndoPacific and West Atlantic regions. They live among seagrasses, mangroves, corals, and estuaries. There is a great threat to these habitats due to degradation and destruction. Seagrasses are often dredged or covered as the sea is filled for new land, mangroves are cut down by loggers or flooded with freshwater, corals are silted or dynamited, and estuaries are polluted and canalized. Such circumstances put a great strain on the seahorse’s ability to survive.
In addition to the threat posed by declining seahorse habitats, they are heavily exploited for use as traditional medicines, aquarium fishes, souvenirs, and tonic foods. Traditional Chinese medicine (TCM) is the largest direct market for seahorses. They are used to treat a wide range of ailments, including incontinence, arteriosclerosis, impotence, and asthma. They also provide remedies for skin ailments, heart disease, high cholesterol levels, goiters, excess throat phlegm, and lymph node disorders. Over 46 countries have been identified as being involved in trading seahorses recently, but many others are likely active as well. The largest exporters of seahorses appear to be India, the Philippines, Thailand, and Vietnam. Most dead seahorses are probably imported to China, Hong Kong, and Taiwan; while the USA is the primary importer of live seahorses.
Additionally, many seahorses are caught in the wild and sold to people for home aquariums. Many people believe that buying seahorses and rearing them in captivity will help conserve the species, but seahorses are actually extremely difficult to maintain and only the most experienced aquarists have been able to keep them alive. As a result, many people continue to buy new seahorses to replace the ones that die, and thus contribute to the decline of seahorse populations.
It is common for captive seahorses to encounter buoyancy problems due to gas bubbles. The bubbles show up in the male’s brood pouch, under the skin, or internally. The seahorse needs to be poked by a small, sterile syringe needle and then massaged until the bubbles come out. This is a dangerous and difficult procedure that most people are not qualified to perform.
Many seahorses are labeled as “Vulnerable” on the 1996 IUCN’s Red List of Threatened Animals. There are marked declines in the number and size of seahorses in many populations, but most species are not considered to be in immediate danger of extinction. This means there is still time to develop some ways to maintain seahorse habitats while continuing to satisfy the people who depend on seahorses.
There are still many unanswered questions about the seahorse. Currently, scientists believe their lifespan to range from 1 to 4 years. They are difficult to find and hard to study because they are so good at camouflaging themselves. Seahorses are voracious predators who rely wholly on live, moving food. They catch moving food by sucking it through their bony snout with a rapid snap of the head. They consume up to 3,000 brine shrimp per day by swallowing them whole because they have no teeth. They must consume such large quantities to compensate for their rapid and inefficient digestion.
The most fascinating fact about seahorses is the way they reproduce. Only the male becomes pregnant. It is known that the pregnant animal is the male because he produces sperm and the female produces eggs (thus satisfying the basic biological definitions of the two sexes). The length and timing of the reproductive season varies with location, and will be influenced by light, temperature, and turbulence from monsoon rains or high winds. The female uses an everted egg duct to insert ripe eggs into the male’s brood pouch. The eggs are fertilized in the pouch, in which they are embedded, and then tissue envelops them. The pouch seals shut after one mating and the male then broods the developing embryos. Oxygen diffuses from capillaries in the pouch tissue that envelops the eggs.
The pregnancy lasts ten days to six weeks, depending on the species and water temperature. The male then goes into labor, pumping and jack-knifing for many hours as he expels the young seahorses. The young are miniature replicas of their parents, 7-11 millimeters long, and are able to fend for themselves immediately upon birth. They are fully independent and do not return to the pouch after birth. In species that have been studied, male seahorses become pregnant again shortly after giving birth. One Australian species experiences about seven consecutive 21-day pregnancies per year.
Seahorses of most species form strictly monogamous pairs where the male and female mate repeatedly and exclusively with one another in and between reproductive seasons. The bond is reinforced by elaborate greeting dances soon after dawn each day. The female swims in to the male and they both change color to “dance” together. This dance lasts up to ten minutes, and afterwards the pair separates for the rest of the day. Greetings continue throughout the male’s pregnancy until he gives birth. The next morning the greeting is elaborated into a full courtship, lasting up to nine hours, and remating. The bonded partners ignore all other seahorses for the rest of their partnership, and are slow to seek a new partner if their mate disappears. However, there are a few species that may not be pair-bonded. Scientists speculated that the limited rate of male reproduction might force females to compete for opportunities to mate, but research showed that males compete more to get pregnant than females do to give their eggs away. Thus, seahorses are not sex-role reversed in any sense. The explanation seems to lie in their strict fidelity to one partner.
Seahorses are extremely unique from other fish. Their monogamous relationships and different way of life sets them apart in the vast ocean. For these reasons, many scientists are fascinated and mystified by seahorses. There is still much to learn about these creatures and their habits.

Works Cited

www.pbs.org/wgbh/nova/seahorse

www.seahorse.mcgill.ca/intro.htm

www.seahorseaquaculture.com/au/frame.htm

www.seahorsetales.com

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