The dwarf seahorse (''Hippocampus zosterae'') is a species of
seahorse
A seahorse (also written ''sea-horse'' and ''sea horse'') is any of 46 species of small marine fish in the genus ''Hippocampus''. "Hippocampus" comes from the Ancient Greek (), itself from () meaning "horse" and () meaning "sea monster" or ...
found in the
subtidal aquatic beds of the
Bahamas
The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the a ...
and parts of the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. It is threatened by
habitat loss
Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
. According to ''
Guinness World Records
''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...
'', it is the slowest-moving fish, with a top speed of about per hour.
Guinness Book of World Records
''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...
(2009)
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
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
.
Description
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 , with a maximum length of .
The dwarf seahorse can live up to 2 years, but most commonly live around 1.
It can be found in colors of beige, yellow, green, and black and may have white speckles, dark spots or protrusions and is well-
camouflage
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
d, 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
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
, reaction to an attack, due to an illness, during
mating…
''H. zosterae'' can be distinguished from other western
Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
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.
File:Hippocampus zosterae skeleton.jpg, 3D computed tomography (CT) scan of dwarf seahorse skeleton
Habitat
''H. zosterae'' are found on the western end of the Atlantic Ocean, precisely in the coastal
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
, Bahamas,
Bermuda
)
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, the
Florida Keys
The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
,
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
’s east coast,
Old Tampa Bay,
Lemon Bay,
Pensacola, and
Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
.
They are restricted almost totally to
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...
microhabitats in shallow water, particularly in association with the seagrass
Zostera
''Zostera'' is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass, and also known as seaweed by some fishermen and recreational boaters including yachtsmen. The genus ''Zostera'' co ...
. They are most common in bays during periods of high salinity, in
coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
s, floating vegetations, and between roots in
mangrove
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...
swamps.
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.
Diet
The dwarf seahorse is a lie-in-wait predator, feeding on living prey, including small
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s such as
amphipods, small
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
s, other small
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s, 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
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
s 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.
Reproduction
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
Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
dance that begins each morning until
copulation
Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
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
A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...
. The male pumps his tail toward his body and eventually the pair intertwine their tails. The female inserts her
ovipositor
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
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.
Males carry between 3 to 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.
Although females could technically mate with several males, seahorses form strict
monogamous
Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
pair bonds for an entire season at least, a rare sight in fish species. 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.
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
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...
. The breeding season starts in mid-February and ends in late October, depending on day length and water temperature.
Development
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.
During their growth in the brood pouch, dorsal fin rays develop first, followed by
anal fins
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as seen ...
. 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.
Season and water temperature disproportionately influences the
sex ratio
The sex ratio (or gender ratio) is usually defined as the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. Many species dev ...
of developing seahorses.
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.
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
Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definit ...
of the male can be determined by the presence of its brood pouch.
Predation
Dwarf seahorses’ predators include
tuna
A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...
s,
dorados,
skates and
rays,
crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s, 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
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s is vital, as they regulate populations of their marine preys, but also help their predators by becoming the prey themselves.
In captivity
The dwarf seahorse only reaches up to in length and is not an aggressive feeder. Therefore, it is typically kept in small aquariums (). The dwarf seahorse can be fed
brine shrimp
''Artemia'' is a genus of aquatic crustaceans also known as brine shrimp. It is the only genus in the family Artemiidae. The first historical record of the existence of ''Artemia'' dates back to the first half of the 10th century AD from Urmia L ...
nauplii, although it will also eat
copepods
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
and other
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
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
An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
. 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. The tank water must be renewed regularly, once, or twice a day. The survival rate of dwarf seahorses in captivity is around 20%.
Interest for humans
This species was particularly popular in the 1960s when mail order companies commonly sold them as the ‘perfect pets’.
Due to its tiny size, the dwarf seahorse remains very popular in the aquarium market. Several
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
located fisheries’ core business lay around dwarf seahorses capture and trade.
Chinese medicine
Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of action ...
is one of the biggest consumers of seahorses, as an estimated 20 million seahorses are used each year. The supposedly have
cholesterol
Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
decrease virtues, preventing
atherosclerosis.
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.
Conservation
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 spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into t ...
s, and
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
.
The
IUCN
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
Red List of Threatened Animals classified ''H.'' ''zosterae'' as vulnerable in 2000.
As of 2016, it is classified as
least concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. ...
.
It is also listed in appendix II of
CITES
CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of intern ...
, as the whole other ''hippocampus'' species.
References
External links
Keeping Dwarf Seahorses as Petspeteducation.com Page on Dwarf Seahorses
{{Taxonbar, from=Q302378
dwarf seahorse
Fauna of the Southeastern United States
Fauna of the Bahamas
Fish of the Gulf of Mexico
Taxa named by David Starr Jordan
Taxa named by Charles Henry Gilbert
dwarf seahorse
Taxonomy articles created by Polbot