Seahorses: A Life-Size Guide to Every Species - Hardcover

Lourie, Sara A.

Hardcover

ISBN 10: 022633841X ISBN 13: 9780226338415

Publisher: University of Chicago Press, 2016

Synopsis

Absolutely captivating creatures, seahorses seem like a product of myth and imagination rather than of nature. They are small, elusive, and are named for their heads, which are shaped like miniature ponies with tiny snouts. They swim slowly upright by rapidly fanning their delicate dorsal fin, coil their tails to anchor themselves in a drift, and spend days in a dancing courtship. Afterward, it is the male who carries the female’s eggs in his pouch and hatches the young. Seahorses are found worldwide, and they are highly sensitive to environmental destruction and disturbance, making them the flagship species for shallow-water habitat conservation. They are as ecologically important as they are beautiful.

Seahorses celebrates the remarkable variety of seahorse species as well as their exquisiteness. 57 species, including seadragons and pipefish, are presented in lush, life-size photographs alongside descriptive drawings, and each entry includes detailed and up-to-date information on natural history and conservation. Sara Lourie, a foremost expert on seahorse taxonomy, presents captivating stories of species that range from less than an inch to over a foot in height, while highlighting recent discoveries and ecological concerns. Accessibly written, but comprehensive in scope, this book will be a stunning and invaluable reference on seahorse evolution, biology, habitat, and behavior.

Masters of camouflage and rarely seen, seahorses continue to be a fascinating subject of active research. This visually rich and informative book is certain to become the authoritative guide to these charming and unusual wonders of the sea, beloved at aquariums the world over.

About this title

About the Author

Sara Lourie is a research associate with Project Seahorse. She has identified multiple new pygmy seahorse species and is the author of several books and articles on seahorse taxonomy.

Excerpt. © Reprinted by permission. All rights reserved.

Seahorses

A Life-Size Guide to Every Species

By Sara Lourie

The University of Chicago Press

Copyright © 2016 The Ivy Press Limited
All rights reserved.

ISBN: 978-0-226-33841-5

Contents

INTRODUCING SEAHORSES, 
What are Seahorses?, 
Morphology, 
Life History and Behavior, 
Courtship and Reproduction, 
Distribution, 
Fossil Seahorses, 
Evolution, 
Trade, 
Conservation, 
SEAHORSE SPECIES, 
SEAHORSE RELATIVES, 
References and Further Reading, 
Index, 
Acknowledgments, 

CHAPTER 1

WHAT ARE SEAHORSES?

HORSES OF THE SEA

Seahorses are among the most charismatic marine creatures. They are so unlike typical fishes that they were once considered to be marine insects. With their upright posture, strange body-shape and features, and incredible camouflage, it is no wonder that people used to think that seahorses were mythological beings and assigned them such roles as bearing sea nymphs and pulling Poseidon's chariot. The scientific name for the seahorse genus, Hippocampus (in this book shortened to H.), is derived from the Greek words hippo (meaning horse) and kampos (meaning sea monster).

Today we know that seahorses are in fact real fish, albeit most unusual ones, and that there are at least 40 different species. Like other fish, they have gills, fins, and a swim bladder. However, they swim vertically, propelled by a fin on their back, unlike typical fish, which swim horizontally and move by waving their tail fin. Seahorses lack scales — instead their bodies are covered by skin stretched across bony plates. The junctions of these plates protrude into ridges, bumps, and spines, the form of which can help distinguish the different species. They have prehensile tails that can literally hold your hand (or at least your finger), and males possess a marsupial-like pouch within which the young develop. Their curious lobe-like gills resemble miniature bunches of grapes, and they have eyes that can move independently of one another, like those of chameleons. The seahorse snout is tubular, with a tiny toothless mouth at its tip, through which the animal sucks hapless prey (mostly small crustaceans) from the water column or off the surface of vegetation. Food passes through a short and simple gut that lacks even a differentiated stomach.

Perhaps one of the most remarkable things about seahorses is the fact that it is the male who bears the young. Female seahorses still produce the eggs, and the male produces the sperm. However, when the eggs are ripe, the female deposits them in the male's brood pouch, and she plays no further role in the development of the young. The male, meanwhile, fertilizes the eggs inside his pouch, and undergoes an extensive pregnancy during which the young are nourished by the yolk-sac provided with each egg, bathed in a liquid that gradually changes from being like body fluids to resembling seawater over the course of a pregnancy. The seahorses grow until they are ready to be released into surrounding waters.

Seahorses are found in all tropical, subtropical, and temperate waters, meaning that extensive dispersal must have occurred over time, despite lacking a long planktonic dispersal phase. How that dispersal has been achieved may have something to do with the young grasping floating mats of vegetation with their prehensile tails, and rafting to far-off places. These secrets are starting to be unraveled as scientists begin to decode seahorse genetics.

As well as their strange shape and their unusual biology, seahorses are also highly prized for medicinal purposes, particularly in Asia. An estimated 15–20 million seahorses are traded every year to satisfy the demand for traditional Chinese medicine. Live seahorses are also traded for aquaria, and dead (dried) ones sold as souvenirs. This exploitation rate, coupled with extensive trawling and destruction of their habitats has raised conservation alarm bells worldwide. Seahorses were among the first marine species to be listed by the Convention on the International Trade in Endangered Species (CITES). Many countries have national laws that help protect them, and volunteer divers in a number of countries have been recruited to help collect information on seahorse populations in the hope that this information and heightened awareness of the plight of these creatures will help save them.

It is becoming increasingly clear that the world beneath the waves (more than 70 percent of the Earth's surface) is suffering hugely from overexploitation, habitat destruction, pollution, and climate change. We can no longer claim complete ignorance of what is going on, and continuing with the status quo will only lead down a path of further destruction and disruption of the biosphere. However, if we can mobilize efforts to save the charismatic seahorse — and who doesn't love seahorses? — it would go a long way toward addressing many of the issues that are causing problems in coastal areas of the world's oceans.

THE FAMILY SYNGNATHIDAE

Seahorses are members of the teleost (bony fish) family Syngnathidae, most commonly known as pipefish. The family name, derived from Greek, refers to these fishes' tube-like snouts (syn = joined/fused, gnathos = jaws), and the family shares other similarities such as a bony external skeleton, reduced number of fins, and male brooding of the eggs (and young in seahorses). Within the Syngnathidae there are a variety of body forms, ranging from straight, unornamented pipefish, to half-bent pygmy pipehorses, to fully curled seahorses and highly ornamented and camouflaged seadragons. Surprisingly, however, these features do not necessarily mirror their evolutionary relatedness. For example, the seahorses (subfamily Hippocampinae) are closely related to pygmy pipehorses, and also to pipefish (such as Trachyrhamphus) that are straight and look very "normal." Genetic research has shown that some features, such as a grasping (prehensile) tail, or dermal flaps that increase a species' camouflage, may have evolved independently in different groups on a number of separate occasions (known as convergent evolution) and do not necessarily reflect a single common ancestor.

Within the family, the major division is between those species that brood their eggs on the front of their trunk region (the Gastrophori) and those that brood them on the underside of their tail (the Urophori). This distinction was first described by Herald in 1953, but has recently been supported by genetic evidence. Seahorses, pipehorses, pygmy pipehorses, and seadragons along with many straight pipefishes all fall into the second group, while the flag-tail pipefish and others that are straight and lack tail fins are in the first. Overall there are about 230 species of pipefishes distributed across 55 genera, however, this figure is only an estimate since there has been little taxonomic research done on the group since Dawson published his book on Indo-Pacific pipefishes in 1985.

The family Syngnathidae is a part of a higher order group, or order, called Syngnathiformes, which includes other families such as the Fistulariidae (cornet fishes), Aulostomidae (trumpet fish), Solenostomidae (ghost pipefishes), and Centriscidae (bellows fish). The majority of the species in these families occur in the Indo-Pacific, particularly in the Coral Triangle area, between the Philippines, Indonesia, and Papua New Guinea, as is the case for many other marine families.

MYTHS AND LEGENDS

The earliest depictions of what could be considered a seahorse (or a close relative such as a Ribboned Pipefish) were on cave walls in Arnhemland, northeast Australia. These images may have represented the Rainbow Serpent, or creator god, of the Aboriginal Dreamtime. The timing of their execution (about 6,000–8,000 years ago) coincided with rising sea-levels at the end of the last ice age, and it has been suggested that it was the encroachment of the sea, and flooding of the shallow continental shelf, that gave people increased opportunities to witness marine life of the shallows (such as seahorses), which in turn gave artists their inspiration for the Rainbow Serpent.

On the opposite side of the world, seahorse-like creatures were frequently depicted in Roman, Greek, and Etruscan mythology and art from the 6th century bce onward. The Hippocampus (or Greek [TEXT NOT REPRODUCIBLE IN ASCII.]) was a mythological creature that was half horse and half fish, possibly inspired by real seahorses. A pair of Hippocampi drew the chariot in which Poseidon (the Greek god of the sea) or Neptune (his Roman counterpart) rode. Hippocampi were often steeds for nereids (sea goddesses) or Triton (the son of Poseidon and Amphitrite), and they frequently adorned tombs, amphorae, and coins. A hoard of 30 silver coins was discovered in the Yizreel Valley in Lower Galilee in 1981. These are believed to have been minted in the 4th century bce, and showed the local god, Melqart, riding on a Hippocampus. In Greece, a Hippocampus statue, topping the Temple of Poseidon in Helikos, apparently caused damage to fishermen's nets for many years following the submergence of the city in about 373 bce (as a result of a tidal wave and ground liquefaction). Mosaics portraying Hippocampi decorated the Roman Baths at Aquae Sulis in Bath, UK, and in Rome, and Hippocampi are represented on the Great Dish (or Neptune's Dish) that forms part of the 4th century Roman Mildenhall Treasure, found in Suffolk, UK, in 1942.

The meaning of funerary art incorporating Hippocampi has been the subject of much debate. It has been suggested that Hippocampi had a role to play in conveying the dead on their watery journey to the Underworld. However, some Etruscan, Roman, and Lucanian depictions suggest an alternative interpretation. The armed warriors in these portrayals, apparently doing battle with Hippocampi, suggest that Hippocampi were in fact monstrous obstacles that the soul must overcome on its way to the Afterworld.

Discovered near Sardis (in today's Turkey), a tiny gold Hippocampus brooch became the center of a great controversy over illegal looting of burial mounds. It was part of an incredible Lydian hoard, from the 6th century bce, that ended up in the Metropolitan Museum of Art in New York, after being smuggled out of the country and sold by unscrupulous dealers in the early 1960s. The full story did not come to light, however, until the 1980s, after which Turkey sued the museum for its return. The case seemed to come to a conclusion in 1993 when the Hippocampus and other artifacts were returned to Turkey. However, the Hippocampus was stolen again in 2006, since when its whereabouts have been a mystery. The brooch now on display at the Usak Museum (near where the hoard was found) is a replica, and the original may no longer even exist.

Other times and cultures have also incorporated the strange-looking seahorse into their mythology. A male god holding two seahorses is found on one of the outer plates of the 1st century bce Gundestrup Cauldron, the largest surviving European Iron Age silverwork, found in a peat bog in Himmerland, Denmark, in 1891. Stone carvings from the 3rd and 4th century in Scotland may represent seahorses, or loch-dwelling water kelpies. In 2009, an Anglo-Saxon seahorse was discovered among the intricately filigreed weapon decorations found as part of the 4,000+ item Staffordshire Hoard. Only about 1 ½ inches (4 cm) tall, this piece shows a complexity and intricate craftsmanship that defies belief — three of the tiny metal spirals fit into the length of a single grain of rice.

During Medieval times, Hippocampi appeared on heraldic charges. Hippocampi persisted through the Renaissance and Baroque Periods, adorning paintings, and statues. Britannia (the female personification of Britain) is pulled through the waves by a team of strong (sea) horses on British stamps issued between 1913 and 1939, as well as on medals for naval service to Britain. Finally, a winged Hippocamp (hippocampe ailé, affectionately referred to by employees as la crevette) was adopted in 1933 as the logo for Air Orient (and its successor Air France). The front half of the hippocampe ailé represented Pegasus, the Greek winged horse (in reference to speed and air), and the back half represented the Dragon of Annam (depicting the link with French Indochina and, being fish-like, the company's use of flying boats). Another story is that the original idea for the hippocampe ailé came from the founder of Air Orient's crash into the Bay of Naples (full of seahorses) in the 1920s, though this may, or may not, have any truth to it.

In Chinese cultures, seahorses were believed to be some kind of sea dragon. They were revered as symbols of power and good luck. These attributes have continued to be applied to them, and no doubt contribute to the medicinal value they are believed to possess. The good luck they are said to bring makes seahorses popular among seafarers. Captain Cook's second ship, The Resolution, had a seahorse as a figurehead, and fishers in Southeast Asia commonly keep dried seahorses as protection and to bring them good luck in their fishing expeditions.

The symbolic meanings and values associated with seahorses reflect their biology and nature, and are said to include high perception, patience, protection, inflexibility, persistence, perspective, friendliness, contentment, and generosity, as well as imagination, creativity, good luck, fatherhood, vigilance, grace, and the power of the ocean.

Whatever symbolic, cultural, and mythological relationships humans have with seahorses, it is clear that they have captured people's imaginations for centuries. Today they appear in children's books (such as Eric Carle's Mr Seahorse, and Graham Base's The Sign of the Seahorse), and in role playing games (for example the Pokémon seahorse character, Seadra). Two commemorative coins displaying seahorses (from Canada and the British Virgin Islands) were minted in 2014 and seahorses have been portrayed on many postage stamps (from nations including Palau, USA, Vietnam, Bermuda, the Philippines, and Bulgaria). Seahorses are also charismatic icons and ambassadors for marine conservation. The hope is that people's love of seahorses is strong enough to motivate them to do what they can to help ensure that these remarkable animals (and their marine habitats) persist indefinitely into the future.

MORPHOLOGY

ADAPTATIONS OF THE HEAD

One of the most unusual features of seahorses is the fact that they orient themselves vertically in the water column, with their head bent at a right angle to their body so they are still looking forward. It is a non-trivial evolutionary change to have gone from a "normal" horizontal-swimming fish (like most pipefishes) to a vertical seahorse, and one that necessitates all kinds of anatomical modifications. In particular, changes to the spinal column are needed, and several of the vertebrae closest to the head have become modified so that the holes, through which the spinal cord pass, no longer line up, but instead are off-set in order to accommodate the right-angle bend.

The seahorse head has other unusual features. Most prominently, the snout is extremely elongated. From a morphological point of view it is not technically the jaw bones that are elongated, but other bones that are normally found toward the main part of the skull which have become extended during seahorse evolution. The jaws themselves are the tiny "lips" at the end of the snout, which open and close to allow the entry of small crustaceans and other prey.

The long, tube-like snout enables seahorses (and pipefish) to suck their prey rapidly out of the water. They are experts at the technique. Hippocampus erectus and H. reidi have been recorded as sucking up passing plankton in fewer than 6 milliseconds, and juveniles are even faster (2.5 milliseconds). This is the fastest recorded suction feeding among all teleost fishes. To provide this rapid suction, syngnathids have developed a specialized technique called pivot-feeding. This is initiated by depression of the hyoid bone (or "trigger") under the snout, followed almost instantaneously by the rotation of the head, elevation of the front of the skull (neurocranium), and expansion of the cheeks. This causes a large pressure difference between the mouth cavity and mouth opening, and creates a flow of water into the mouth, along with the intended prey item. It also causes a large pressure differential between the mouth cavity and the gills, which in turn necessitates some special modifications of the gill cavity. One of these is the reduction of the slit-like opercular opening behind the gills (as found in most fishes), to a small hole (near the pectoral fin in most seahorses, but right behind the coronet in pygmy seahorses). Another modification is the extra strong bony gill cover, which is convex in shape, and thus able to withstand the pressure.

On top of the seahorse's head is a bony projection, called the coronet (or crown). This too may have a role to play in the feeding mechanism. Depending on the species, the coronet may be more or less developed (it is basically flat in H. capensis and H. minotaur). When the neurocranium is elevated during feeding it articulates with the bones that make up the front of the coronet and produces a clicking sound. Seahorses have been reported to produce clicking sounds at other times as well (for example, after being moved to a new tank, or when under stress), and it may be that clicking is not only a by-product of feeding, but also a means of communication.

(Continues...)

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Edition details

• Publisher: University of Chicago Press
• Publication date: 2016
• Language: English
• ISBN 10: 022633841X
• ISBN 13: 9780226338415
• Binding: Hardcover
• Edition number: 1
• Number of pages: 160