Many Miami environmental science graduate students take the Ecology Field Courses each year.
Seahorses: Fish of the Sea
Sara E. Waits
Seahorses: Fish of the Sea
Seahorses are a one of a kind animal that can be found in temperate and tropical bodies of water all over the world. With a head shaped like a horse, fins like a fish, and a prehensile tail, similar to a monkey, this fish is definitely out of the ordinary. If these characteristics were not enough, seahorses are monogamous and one of the only species in the world where the male becomes ŇpregnantÓ (National Geographic Society [NGS], 2007). They are members of the Syngnathidae family and the Hippocampus genus. There are 35 species, but only 3 of these species can be seen in the Florida Keys and the Bahamas (Restrepo, 2004).
Overview of Seahorses
Seahorses are a type of fish, despite what most people think. A long time ago, people thought they were insects, due to their strange combination of physical features. Seahorses come in all different sizes and colors. The Pygmy seahorse (Hippocampus bargibanti) is the smallest seahorse reaching a maximum height of .6 inches. On the other end of the height spectrum, the Pacific Seahorse (Hippocampus ingens) can grow to as many as 12 inches (Restrepo, 2004).
Seahorses can be found all over the world: the Pacific Ocean, Atlantic Ocean, Mediterranean Sea, Indian Ocean, off the coasts of the Philippines, Australia, South Africa, Thailand, Taiwan, Japan, and China. These are just a few locations seahorses have been spotted. They can also be seen in commercial settings, such as aquariums, pet shops, and zoos (Casey, Hall, Stanley, & Vincent, 2003). In the wild, they reside in shallow, temperate and tropical waters and use their prehensile tails to attach to corals and seagrasses in mangroves, estuaries, and coral reefs (Sheng, Lin, Chen, Gao, Shen, & Lu, 2006). This means they can be found along the coastlines, usually in waters ranging from depths of one meter to 15 meters, although some seahorses have been found living in depths of up to 60 meters. Seahorses do not require much territory however. Research done on the Hippocampus whitei, an Australian species, showed that males only inhabit a range of about one square meter and females live in a range of about 100 square meters (Restrepo, 2004).
Males and females differ in size, shape, and color. Males tend to be slimmer and less spiny. They also can change color during and after mating (Restrepo, 2004). All seahorses have a few characteristics in common. They have a horse-like head that is bent and ends with a long, slender snout used for sucking up food. They have two eyes, one on each side of their head, which move independently of each other, and a prehensile tail. Seahorses have one dorsal fin that is used to propel them forwards and backwards which flutters up to 35 times a second, two pectoral fins located near the head which are used for stabilization, steering, and moving up and down, and a tiny, clear (almost invisible) anal fin. Only male seahorses have a pouch that is used to hold the eggs until they hatch. Unlike most other fishes, seahorses do not have scales. They do have a structure skeleton though, which has not changed very much throughout evolution (Taylor, 1992). Their bodies are encased in bony rings that form distinct ridges. The number of rings and different shaped ridges are important in distinguishing among different species. Many seahorses also have a crown, or coronet, on the top of their head, which can also be using in identifying different species (Sadovy, 2000).
Seahorses use their long, slender snout to suck up food. They are carnivores and for their size, eat an impressive amount of food. They eat fish, plankton, and small crustaceans by ambushing their prey and then inhaling rapidly. They are very noisy eaters and the clicking sound they make when sucking up food can be heard some distance away. They also eat all day because they have no stomach to store the food in (Taylor, 1992). They depend on camouflage to be able to hunt, as well as hide from predators. They can change their appearance to blend into their background, similar to octopi and chameleons (Vincent, 1994). Seahorses can also grow additional body parts, such as tendrils and skin filaments to blend in even more to their surroundings (Curtis, 2006).
Due to their small size and lack of fast mobility, seahorses have many predators. They depend on camouflage to hide from larger fishes such as tunas, flatheads, perch, trumpeters, skates, cods, rays, and snappers. Water birds, penguins and crabs occasionally prey on seahorses as well. Like most species, seahorses are most vulnerable to predators when they are young. Seahorses of any age can also be killed by strong storms that tear them away from the corals or seagrasses and wash them onto the shore (Restrepo, 2004). Damage and loss of habitat, as well as overfishing are also causing a decrease in the number of seahorses (Sadovy, 2000).
Despite the fact that seahorses live in the sea, they are not very good swimmers. They can die due to fatigue from swimming, especially in stormy waters. They tend to stay rooted in one place, or drift with the tides. They can swim for short distances but swimming is not their preferred method of movement (Restrepo, 2004).
Genetics have been used to trace the evolution of seahorses, yet there is not one widely accepted theory to explain where they originally evolved. Some studies have shown that the first species of seahorses probably originated from the Atlantic biome. This theory is supported because the only fossils of seahorses ever found were located in Italy and seahorses are most closely related to pipefish, which definitely originated in the Atlantic biome. Others support the theory that seahorses evolved in the Indo-West Pacific region, because this is where the greatest concentration of seahorses (more than 27 species) are today. A third theory supports the idea that tropical shore species migrated around the Cape of Good Hope and established themselves in the Atlantic region (Teskes, Cherry, & Matthee, 2003).
The oldest fossils of seahorses date back to the Eocene, which is about 40 million years ago during the Cenozoic Era. Seahorses are members of the Syngnathidae family. Other members include pipefishes, pipehorses, seadragons, and flag-tail pipefishes. Seahorses have a couple distinguishing features that make them unique, including a prehensile tail and brood pouch (Teskes et al, 2003).
In todayŐs society, seahorses have become very important to humans. Some like to keep them in aquariums as pets. Unfortunately, seahorses donŐt often survive the transition from the wild to an aquarium, due to the stress of being shipped, changes in habitat, and problems with feeding and nutrition (Sadovy, 2000).
In Asia, seahorses are being used more and more for medicinal purposes. There are many traditional Chinese medicines that require seahorses and with the economic growth since the mid 1980Ős, the demand for seahorses in China has been increasing quickly. Subsidence fishers and small-scale fishers in Asia have come to depend on fishing for seahorses as their annual income. At least 32 nations worldwide are involved in the seahorse trade and in Asia alone, 45 dried tons of seahorses are consumed per year. This increased demand for seahorses is causing a rapid decrease in the seahorse population and if the demand does not decrease any time soon, the seahorses may be in danger of becoming extinct (Vincent, 1994). Seahorses are also becoming a valuable commodity for curios; they are used to make jewelry and ornaments (Sadovy, 2000).
Seahorses are very unique when it comes to mating for several reasons. They are monogamous, which means they stay with the same partner for life. This is very rare in fish of any species. Another oddity is that the male seahorse becomes pregnant. The female deposits her eggs in the brood pouch in the male. He then fertilizes the eggs and nourishes, protects, and oxygenates them until they hatch. After ten days to six weeks, the male will give birth during the night (Vincent, 1995). Once the babies are born, they are miniature versions of their parents and completely independent. Depending on the species, the size of broods varies from just five babies to up to 1,500 offspring per pregnancy. Seahorses also mate and reproduce several times a year. In the tropical seas, seahorses mate year round. In cooler waters they mate in the spring and summer. Mating for all seahorses usually coincides with a full moon. Seahorses have a relatively short life span of one to five years, depending on the species (Vincent, 1994).
Species Commonly Found in the Atlantic Ocean
There are three species of seahorses that are commonly found in Atlantic Ocean that may be seen during our class trip. Hippocampus erectus is one of two species native to the Florida Keys and the Bahamas. The Lined Seahorse comes in several different colors- olive-brown, yellow, or orange, and it usually has large pale blotches and dark lines that run lengthwise on the neck and back. Some may also have fleshy tabs and 18-21 dorsal fin rays. They are about six inches in length. Some have bony protuberances and fleshy tabs that serve as camouflage to protect them from predators (Robins & Ray, 1986).
The Dwarf Seahorse, Hippocampus zosterae, usually has a tan colored body and is typically unpatterened. The dorsal fin has a dark stripe and 11-13 dorsal-fin rays. The Dwarf Seahorse is only about two inches in length and can be found Bermuda, Southern Florida, the Bahamas, and the Gulf of Mexico and lives in shallow seagrasses and floating vegetation (Lourie, Foster, Cooper, Vincent, 2004).
The Longsnout Seahorse, Hippocampus reidi, has many dark spots evenly scattered over a brownish colored body. It has a long snout, 16-19 dorsal fin rays and is about six inches in length. It can be found in the Bahamas to Northern South America, but is rare in the United States (Lythgoe & Lythgoe, 1992).
Seahorses are amazing animals with many characteristics that make them truly unique. They are very hard to find in the wild so seeing one is a rare treat. They are becoming harder and harder to find due to increasing demand for them by humans, whether they are being used in medicine, for jewelry and ornaments, or for consumption. Destruction of their habitats is also causing a decrease in their population. Since these animals are hard to keep in captivity, the only hope we have of saving these precious creatures is by decreasing the demand humans have put on them and by putting a stop to the destruction of their habitats. By working together with scientists, marine biologists, and fisherman, hopefully this goal can one day be accomplished before itŐs too late.
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