Seahorse populations are declining mainly due to large quantities collected and sold for the aquarium trade and for traditional Chinese medicine. Chinese medicine alone is the largest consumer of seahorses, with an estimate of 20 million seahorses used per year for this economic market. Evidence from the year 2000 showed that more than 50 tons of dried seahorses were collected for the trade in Asia alone. Research has estimated that populations are declining at rates of anywhere between 15 to 50% over 5 year periods, depending on the species. Hippocampus was listed in Apendix II of CITES in November 2002, which became effective in May 2004 (Lourie et al., 2004).
Hippocampus zosterae was listed in 2000 as vulnerable on the IUCN Red List of Threatened Species. One major threat to dwarf seahorses is habitat degradation due to extraction from subsistence, artisanal uses, and large-scale fisheries as well as infrastructure development such as industry, human settlement, and tourism. Harvesting for local, national, and international trade and accidental mortality as bycatch in fishing nets are also threats to this population. Due to the small size of dwarf seahorses, they are popular in the aquarium trade. Hippocampus zosterae is ranked second of the ten top fishes exported from Florida for the aquarium trade (Foster, Marsden, and Vincent, 2003).
Much effort is being made to educate people about declining seahorse populations throughout the world. Many countries have formed their own conservation groups and have developed ways to regulate and recognize threats to seahorses. The listing of all seahorses in CITES also helps to regulate the level of trade and export to ensure that it is not detrimental to wild populations. Indonesia, Japan, Republic of Korea, and Norway were directly affected by the CITES listing and are also required to restore the habitats of the species of seahorses affected (Lourie et al., 2004).
US Federal List: no special status
CITES: appendix ii
IUCN Red List of Threatened Species: data deficient
Predators of H. zosterea include tunas, dorados, skates and rays, penguins, crabs, and water birds (Lourie et al., 2004). However, young are at the greatest risk of predation. Adults protect themselves from predation with their amazing camouflage abilities. Seahorses in general have the ability to change color to blend in with their surroundings and acquire freckles, spots, or even branchy protrusions in some species. For example, it was shown that a seahorse acquires freckles when showered with bubbles in an aquarium. Seahorses are extremely slow swimmers. Instead they have a sedentary lifestyle, holding tightly to holdfasts, swaying in rhythm with the sea grass, and looking almost invisible among their surroundings for protection from their predators (Thompson and Lewis, 1997). Also, adult seahorses have bony plates and spines that smaller predators find unappealing to eat (Biology of Seahorses, 2003).
The most significant predators of H. zosterae are humans. Dwarf seahorses are extremely popular in the aquarium trade because of their small size. Some fisheries off the coast of Florida have built their business around the capture of live dwarf seahorses in shallow grass beds for the aquarium trade. Tens of thousands of H. zosterae each year go to the aquarium trade (Foster, Marsden, and Vincent, 2003). However, they are difficult to breed as well as keep alive in captivity because they need an abundance of live food and are susceptible to diseases (Vincent, 1997).
Known Predators:
Anti-predator Adaptations: cryptic
Seahorses have a head at a right angle to their body and swim upright, propelled by their dorsal fin. They steer with their pectoral fins, which are located on both sides behind the head (Indivigio, 2002). Seahorses also are distinctive in their possession of a prehensile tail that lacks a caudal fin and is used to anchor the animal to sea grass, coral, or any suitable holdfast (Randall, 1996). Instead of scales, seahorses have a thin layer of skin covering several bony plates that appear as rings around the trunk and tail. Seahorses can be distinguished by the number of trunks rings they possess and by the coronet on the top of the head, which is as unique as a human thumbprint (Vincent, 1997). The young, in comparison to their parents, have larger heads compared to their bodies, higher coronets, and more spines.
Seahorses are sexually dimorphic. Males have longer bodies and tails, whereas females have longer trunks. In addition, males possess a brood pouch, which is absent in the females (Lourie et al., 2004).
Hippocampus zosterae is one of the smallest of the many different seahorse species, ranging in size between 2 to 2.5 cm. The maximum reported size was a male of 5.0 cm (Jordan and Gilbert, 1882). This species of seahorse can be distinguished from other western Atlantic seahorse species by the presence of 10 to 13 dorsal and pectoral fin rays (Daswon and Vari, 1982). Also, dwarf seahorses possess 9 to 10 trunk rings, a high knob-like coronet that lacks spines or projections, knob-like spines on the body, a short snout that is one-third the length of the head, and skin covered in tiny warts (Lourie et al., 2004). Hippocampus zosterae also has a dorsal fin with a submarginal band (Dawson and Vari, 1982). Dwarf seahorses are found in colors of beige, yellow, green, and black, and may have white speckles or dark spots (Lourie et al., 2004).
Range length: 2 to 5.0 cm.
Average length: 2-2.5 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: male larger; sexes shaped differently
The lifespans of seahorses in the wild are generally unknown because of the difficulty in tracking large numbers of these animals. The majority of estimates are from laboratory or captive observations. The known lifespan for Hippocampus is on average 1 to 5 years, depending on the size and species (Biology of Seahorses, 2003).
Hippocampus zosterae, being a smaller species, is expected to live on average one year in the wild and in captivity (if given proper care) (Lourie et al., 2004). The maximum reported lifespan is 1 year for dwarf seahorses (Jordan and Gilbert, 1882).
Range lifespan
Status: captivity: 1 (high) years.
Typical lifespan
Status: wild: 1 (high) years.
Typical lifespan
Status: captivity: 1 (high) years.
Hippocampus zosterae lives in seagrass beds of shallow tropical waters, generally in areas where eelgrass (Zostera marina) is abundant (Foster et al. 2003). They also are found among floating vegetation, mangrove roots, and coral reefs (Lourie et al., 2004)
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: reef ; coastal
Other Habitat Features: estuarine
Hippocampus zosterae, commonly known as the dwarf seahorse, inhabits coastal waters of the western Atlantic Ocean, including the Caribbean sea, the Gulf of Mexico, and the continental shelf of the southeastern United States (Jordan and Gilbert, 1882).
Biogeographic Regions: atlantic ocean (Native )
The diet of Hippocampus zosterae consists of living prey, including small crustaceans such as amphipods, small shrimps, other small invertebrates, and fish fry.
Seahorses are opportunistic hunters that sit anchored by their tail and wait, while camouflaged with their surroundings, for prey to be close enough to eat without leaving the anchor. Once prey is sighted, the seahorse stretches toward the prey and sucks it through snout. The small mouth cavity is widened by the retraction of the hyoid bone that drops the lower jaw and helps to increase the concentration and expulsion of water from the snout by the siphon at the top of the gills. Seahorses lack teeth and a stomach. Also, food progresses through the digestive system so rapidly that all the nutrients are often not absorbed. This is the reason that seahorses require large quantities of food to survive in the wild and in captivity (Indiviglio, 2002). Seahorses are able to consume up to 3,000 brine shrimp per day.
Animal Foods: fish; aquatic crustaceans; other marine invertebrates
Primary Diet: carnivore (Eats non-insect arthropods)
Hippocampus zosterae plays a vital role in the ecosystems in which they live, first as predators that help regulate populations of their marine prey. As prey for other animals, dwarf seahorses help to maintain other species by providing them with a source of food. For example, consumption of small crustaceans by H. zosterae and other predators helps to keep the population numbers balanced (Biology of Seahorses, 2003). Also, H. zosterae is a source of food for pelagic fishes, skates, rays, penguins, crabs, and water birds (Lourie et al., 2004).
A huge economic market surrounds the capture and selling of Hippocampus as pets, ornaments, and for use as ingredients in traditional Chinese medicine. It is believed by practitioners of Chinese medicine that these animals cure impotency and asthma, lower cholesterol, and prevent arteriosclerosis (Vincent, 1997). None of these uses has been tested for efficacy, however.
Humans have considered seahorses valuable and powerful for decades based on the magical myths surrounding these exotic creatures, and because males incubate eggs and give birth to their young (Thompson and Lewis, 1997).
Seahorses are important in education and research. The unique reproduction and mating system of seahorses, in which the father provides oxygen and nutrients to the developing young and protects them in his brood pouch, provides humans with an interesting and valuable model of parental investment. This model is of interest because it is the opposite of what is found in many mammalian species. Also, seahorses, which form monogamous pairs, provide a rare model of pair bonding in fish for scientific study (Biology of Seahorses, 2003). Significant scientific research has been devoted to testing the theory that parental investment determines sex-based courtship roles and whether this is reversed in seahorses because males provide parental care (Masonjones and Lewis, 1996).
Positive Impacts: pet trade ; source of medicine or drug ; research and education
There are no known adverse affects of Hippocampus zosterae, or seahorses in general, on humans.
There are many features that mark the development of young seahorses within the brood pouch. For example, dorsal fin rays develop first, followed by anal fins. Both of these structures form before the complete growth of the mouth apparatus. During the larval stage of seahorse development external feeding is not necessary because the brood pouch provides larvae with nutrients. Also, the yolk sack, which provides the young with nutrients, is preserved throughout the postembryonic period and disappears only moments before birth. Therefore, the mouth apparatus does not become functional until young are released from the brood pouch (Kornienko, 2001). Compared to an adult seahorse, offspring within the brood pouch have a rounded tail instead of tetrahedral tail, a wider and shorter snout, a dorsal fin that is closer to the tail, and pectoral fins that are closer to the back of the head (Kornienko, 2001). In addition, the season and the environment, such as water temperature, disproportionately influences the sex ratio of developing seahorses (Dawson and Vari, 1982).
Development - Life Cycle: temperature sex determination
Hippocampus zosterae and other seahorse species produce a rapid clicking sound as a form of communication. These clicking sounds have been observed during courtship and copulation, inter-male competition, feeding, and stress produced, for example, by moving a seahorse from one tank into another. Dwarf seahorses produce these clicking sounds by stridulation, which is the production of sound through the grinding together of hard, usually bony structures. In this case the skull grinds against the vertebrae. More specifically, H. zosterae produces these sounds by the grinding of a bony articulation between the supraoccipital ridge of the neurocranium and the grooved anterior margin of the coronet. When dwarf seahorses lift their head, the ridge of the neurocranium slides under the medial groove of the coronet resulting in the clicking noise that is most likely used as a form of communication. The feeding clicks of H. zosterae range from 5 to 20 milliseconds in length and are between 2.65 and 3.43 kHZ. Also, as size of the seahorse increases the peak frequencies of the clicking sounds decrease (Colson et al., 1998).
The ability of seahorses to change color in many social situations is most likely a form of communication about the state or mood of the seahorse to its mate or other members of its species (Indiviglio, 2002). Mates also communicate with nose pointing and body vibrations.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Seahorses form strict monogamous pair bonds for an entire breeding season, if not longer. This is a unique behavior that is not often seen in other fish species. Although female seahorses have the ability to mate with additional partners during the pregnancy of their mate, they refuse additional partners if they are offered (Vincent, 1995).
Although male seahorses become pregnant, seahorses do not display sex role reversal. Males compete for access to a mate. For example, males will tail wrestle and snap their heads toward each other, and make clicking sounds during competition for access to a female (Milius, 2000).
Hippocampus zosterae display an eloquent courtship dance that begins each morning until copulation takes place. Females initiate courtship behavior by entering into the male’s territory. Once she has entered the territory, the male initiates the actual behavior. In the first courtship phase the male and female change color and take turns quivering. This consists of alternating side-to-side vibrations while the pair is attached to the same holdfast. In addition, both the male and female circle around their common holdfast. This phase lasts for one to two mornings before copulation (Masonjones and Lewis, 1996). The second, third, and fourth phases of courtship behavior occur on the day of copulation. During the second phase the female displays a pointing posture with the head pointed upward. In return the male displays quivering and pumping behaviors in response to the females pointing. In the third phase the male assumes the pointing posture in response to the female’s pointing. Finally, in the last phase of the courtship behavior the pair repeatedly rise in the water column. The male pumps his tail toward his body and eventually the pair intertwine their tails. The female inserts her ovipositor and transfers the eggs into the male’s brood pouch during the final rise in the water column (Masonjones and Lewis, 1996). After eggs are deposited, the male rocks back and forth, most likely to settle the eggs in his pouch (Indiviglio, 2002).
Female seahorses remain faithful during the pregnancy by returning to the male’s territory each day for an early morning greeting. During the greeting the pair change colors and dance together for about 6 minutes. This greeting plays an important role in reinforcing the strong monogamous bonds between seahorses (Vincent, 1995).
Mating System: monogamous
The breeding season for H. zosterae starts in mid-February and ends in late October, depending on day length and water temperature (Dawson and Vari, 1982). As few as 3 to as many as 55 fully independent young are released from the males brood pouch into the environment after approximately 10 days of gestation (Masonjones and Lewis, 1996; Lourie et al., 2004). The young are expelled from the brood pouch by muscular contractions of the male’s body and pouch (Dawson and Vari, 1982). During the breeding season, pairs of dwarf seahorses will remate within 4 to 20 hours after the male has released the young from his brood pouch (Masonjones and Lewis, 1996). Egg diameter of H. zosterae averages 1.3 mm and the length of young averages 8 mm at birth (Lourie et al., 2004). Seahorses in general reach maturity in about 4 months to 1 year, depending on the species. Smaller species of seahorses like H. zosterae reach maturity within about 4 months. Male sexual maturity can be determined by the presence of a brood pouch (Lourie et al., 2004).
Breeding interval: Dwarf seahorses remate within 4 to 20 hours after the young have been released from the brood pouch. This may occur throughout the breeding season.
Breeding season: Hippocampus zosterea breeds between mid-February and late October.
Range number of offspring: 3 to 55.
Average gestation period: 10 days.
Average time to independence: 10 days.
Average age at sexual or reproductive maturity (female): 4 months.
Average age at sexual or reproductive maturity (male): 4 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
Average age at sexual or reproductive maturity (male)
Sex: male: 118 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 118 days.
Male seahorses provide unique paternal care by carrying the offspring in his brood pouch until they are ready to be released into the environment, completely independent of their parents. Once deposited in the male’s brood pouch, each baby grows and develops in its own tissue pocket that is surrounded by a network of blood vessels. The brood pouch is a kind of “pseudoplacenta” because after the eggs are deposited the walls of the pouch thicken and become more porous (Kornienko, 2001). The brood pouch also provides protection, oxygen, nourishment, waste removal, and osmoregulation to the developing young (Vincent, 1995; Masonjones, 2001). Before the male gives birth to his young, the osmolarity, or salt concentration, of the fluid in the pouch gradually is equalized with the outside environment, possibly to reduce the shock to the young (Kornienko, 2001). Once the offspring are released from the brood pouch into the environment they do not receive any further parental care (Lourie et al., 2004).
Male seahorses invest substantial amounts of energy into the developing offspring. However, they only invest half as much energy into the offspring compared to the energy female seahorses invest into the production of the eggs. This most likely explains why seahorses still display traditional sex roles in which the females choose and the males compete for access to females (Milius, 2000).
Once released from the brood pouch, young seahorses look like minatures of their parents and can swim and eat independently of their parents. Newborns disperse freely into the marine environment. However, survival is not great in the juveniles due to weak swimming ability and large predation risks.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Male, Protecting: Male)
The dwarf seahorse (Hippocampus zosterae) is a species of seahorse found in the subtidal aquatic beds of the Bahamas and parts of the United States. It is threatened by habitat loss. According to Guinness World Records, it is the slowest-moving fish, with a top speed of about 5 feet (1.5 m) per hour.[4]
It is most often white in color but can range from tan, brown, yellow and green. In the wild, it often has small skin growths called cirri that resemble algae.
Like other seahorses, the dwarf seahorse has a head angled at right angles to its body and swims upright using its dorsal fin to propel it and its pectoral fins to steer. It grows to an average length of 2 and 2.5 cm (0.8 and 1.0 in), with a maximum length of 5.0 cm (2.0 in).
The dwarf seahorse can live up to 2 years, but most commonly live around 1.[5]
It can be found in colors of beige, yellow, green, and black and may have white speckles, dark spots or protrusions and is well-camouflaged, the coloring usually matching the gorgonian on which it is typically found. It can change color.
It has been observed that this seahorse changes color for various reasons such as camouflage, reaction to an attack, due to an illness, during mating...[6]
H. zosterae can be distinguished from other western Atlantic species such as H. reidi and H. erectus thanks to its number of fin rays. This species possesses from 10 to 13 dorsal and pectoral fin rays, and 9 to 10 trunk rings. Fully grown H. zosterae adults are usually smaller than these 2 other species.[5][6]
3D computed tomography (CT) scan of dwarf seahorse skeleton
H. zosterae are found on the western end of the Atlantic Ocean, precisely in the coastal Gulf of Mexico, Bahamas, Bermuda, the Florida Keys, Florida’s east coast, Old Tampa Bay, Lemon Bay, Pensacola, and Texas.[5][6][7]
They are restricted almost totally to seagrass microhabitats in shallow water, particularly in association with the seagrass Zostera. They are most common in bays during periods of high salinity, in coral reefs, floating vegetations, and between roots in mangrove swamps.[5][6]
They often live as a pair, sometimes alone. Males are rather sedentary and live in a small home range of about 1 square meter, whereas females roam on other males’ territory, around a hundred times larger than theirs.[6]
The dwarf seahorse is a lie-in-wait predator, feeding on living prey, including small crustaceans such as amphipods, small shrimps, other small invertebrates, and fish fry. Once their target is fixed, the hunter stretches towards it and sucks it through its snout. Food progresses through the digestive system rapidly, causing the nutrients to be ill-absorbed. This is the reason seahorses require large amounts of food to survive. These creatures can consume up to 3,000 brine-shrimps per day.[6]
Although, as every other seahorse species, it is the male that carries the offspring, they must still compete to access a mate. Males will tail wrestle and snap their heads toward each other and make clicking sounds during competition for access to a female. They display an eloquent courtship dance that begins each morning until copulation takes place.
Females initiate courtship behavior by entering the male's territory. Once she has entered his territory, the male initiates the actual behavior. In the first courtship phase the male and female change color and take turns quivering. This phase lasts for one to two mornings before copulation. The following phases of courtship behavior occur on the day of copulation. During the second phase the female displays a pointing posture with the head pointed upward. In return the male displays quivering and pumping behaviors in response to the females pointing. In the third phase the male assumes the pointing posture in response to the female's pointing. Finally, in the last phase of the courtship behavior, the pair repeatedly rise in the water column. The male pumps his tail toward his body and eventually the pair intertwine their tails. The female inserts her ovipositor and transfers the eggs into the male's brood pouch during the final rise in the water column. After eggs are deposited, the male rocks back and forth to settle the eggs in its pouch.[6][8]
Males carry between 3 and 55 soon-to-be younglings in their brood pouch for around 10 days before releasing them. Just born dwarf seahorses are 7 to 9 mm long, while the diameter of the eggs in the pouch was around 1.3 mm.[6]
Although females could technically mate with several males, seahorses form strict monogamous pair bonds for an entire season at least, a rare sight in fish species.[9] Female seahorses remain faithful during the pregnancy by returning to the male's territory each day for an early morning greeting. During the greeting, the pair change colors and dance together for about 6 minutes. Adult dwarf seahorses are iteroparous, meaning that they have multiple reproductive cycles in the course of their lifetime, in this case 2 per month.[5][6]
Dwarf seahorses remate within 4 to 20 hours after the young have been released from the brood pouch. This may occur throughout the breeding season. The breeding season starts in mid-February and ends in late October, depending on day length and water temperature.[6][10]
Each larva grows and develops in its own tissue pocket which is surrounded by a network of blood vessels. The brood pouch is comparable to a “pseudoplacenta”: after the eggs are deposited, the walls of the pouch thicken and become more porous. The pouch provides protection, oxygen, nourishment, and waste removal.[6]
During their growth in the brood pouch, dorsal fin rays develop first, followed by anal fins. The mouth apparatus's development follows, but it is not functional until juveniles are released from the brood pouch.
Compared to an adult seahorse, offspring within the brood pouch have a rounded tail instead of tetrahedral tail, a wider and shorter snout, a dorsal fin that is closer to the tail, and pectoral fins that are closer to the back of the head.[6]
Season and water temperature disproportionately influences the sex ratio of developing seahorses.[6][11]
Once the offspring are released in the environment, they are completely independent of their parents. They are able to swim and feed immediately, but their weak swimming ability and high predation diminishes their rate of survival.[6]
The growth of H. zosterae is relatively rapid, especially during the summer season; both male and female are fully grown after 3 to 4 months. Sexual maturity of the male can be determined by the presence of its brood pouch.[6]
Dwarf seahorses’ predators include tunas, dorados, skates and rays, crabs, and water birds. Although the adults can protect themselves with their camouflage abilities, the young are not capable yet and are thus at a greater risk.
The seahorse's role in the ecosystems is vital, as they regulate populations of their marine preys, but also help their predators by becoming the prey themselves.[6]
The dwarf seahorse only reaches up to 2 inches (51 mm) in length and is not an aggressive feeder. Therefore, it is typically kept in small aquariums (5 to 10 US gallons (19 to 38 L)). The dwarf seahorse can be fed brine shrimp nauplii, although it will also eat copepods and other shrimp larvae. Because of its short digestive tract, food must be available to them all day, making it a difficult species to keep. Unlike most marine fish, it will readily breed in the aquarium. The seahorse fry can be kept in the same aquarium as the adults in a dwarf seahorse dedicated tank. The dwarf seahorse has a gestation period of 10–14 days and can live up to over 2 years in captivity. The water temperature in the aquarium must place between 20 and 28 °C, with a pH ranging around 8-8.5.[12] The tank water must be renewed regularly, once, or twice a day. The survival rate of dwarf seahorses in captivity is around 20%.[5]
This species was particularly popular in the 1960s when mail order companies commonly sold them as the ‘perfect pets’.[5]
Due to its tiny size, the dwarf seahorse remains very popular in the aquarium market. Several Florida located fisheries’ core business lay around dwarf seahorses capture and trade.[6]
Chinese medicine is one of the biggest consumers of seahorses, as an estimated 20 million seahorses are used each year. The supposedly have cholesterol decrease virtues, preventing atherosclerosis.[6]
Humans have considered seahorses valuable and powerful for decades based on the magical myths surrounding these exotic creatures, and because males incubate eggs and give birth to their young.
Seahorses are important in education and research. The unique reproduction and mating system of seahorses, and the fact that they form monogamous pairs, a rare model of pair bonding in fish, makes them important for scientific study.
Before 1970, this species was regarded as common. However, numbers have decreased over subsequent years, most likely due to a reduction in the extent of seagrass beds, pollution, oil spills, and ocean acidification.[5][13]
The IUCN Red List of Threatened Animals classified H. zosterae as vulnerable in 2000.[6][5] As of 2016, it is classified as least concern.[14][10] It is also listed in appendix II of CITES, as the whole other hippocampus species.[15]
The dwarf seahorse (Hippocampus zosterae) is a species of seahorse found in the subtidal aquatic beds of the Bahamas and parts of the United States. It is threatened by habitat loss. According to Guinness World Records, it is the slowest-moving fish, with a top speed of about 5 feet (1.5 m) per hour.
It is most often white in color but can range from tan, brown, yellow and green. In the wild, it often has small skin growths called cirri that resemble algae.
