Seahorses Are Monogamous, Have Long Courtships, Males Carry The Eggs To Term
Seahorses are monogamous, have long courtships and males carry the eggs to term. Seahorses have captured the interest of both scientists and the public because the male is the one who becomes pregnant and gives birth to the offspring. Curiosity about this phenomenon explains why currently more is known about their reproduction than about seahorse behavior. This lack of scientific knowledge about seahorses is thought to be the reason 10 seahorse species are listed as ‘Vulnerable’ or ‘Endangered’ and have been placed on the List of Threatened Species.
Seahorses have captured the interest of
both scientists and the public because the male is the one who becomes pregnant and gives birth to the offspring.
Curiosity about this phenomenon explains why
currently more is known about their
reproduction than about seahorse behavior.
This lack of scientific knowledge about
seahorses is thought to be the reason 10
seahorse species are listed as ‘Vulnerable’ or
‘Endangered’ and have been placed on the List of Threatened Species.
Seahorses Have One Mate and a Long Courtship
All seahorse species appear to be monogamous within a single breeding cycle, and the male
will accept eggs from only one female. This is seen in both captive and their natural
environment.
Studies have suggested that the reason seahorses are monogamous is because this exclusive
behavior increases reproductive efficiency. Researchers found that because seahorses mate
with the same partner they have larger broods and a reduced time spent on courtship.
Seahorses seem to reinforce their monogamous relationships by daily greetings. In the wild, Hippocampus whitei female seahorses are seen traveling each morning to greet her male mate and they continue to interact for 6–10 min to practice
the first few movements of courtship.
Morning interactions will continue through the seahorse pregnancy, and seems to help fertility from female egg preparation to the end of male pregnancy.
Given their inferred dependence on camouflage, it is interesting that seahorse courtships in the wild are colorful, active and lengthy, lasting up to 9 hours. Males may brightened in color from a dark brown or grey to a pale yellow or off-white during these interactions.
Interestingly, after this long courtship and mating, neither sex within an established pair of seahorses will respond to dangers or threats from other fish.
Male Pregnancy and Development of Young
The eggs of the seahorse are pear-shaped or oval, with a semi-transparent, orange appearance. The color comes from the crustaceans they eat which are high in carotenoids.
Seahorses invest heavily in the development of each of their young. As seahorses mate, the female places her eggs into the brood pouch of the male where the eggs become fertilized. The male then seals the brood pouch shut.
Both male and female seahorses exhibit visible evidence of having mated, as the female girth
diminishes and the male pouch fills Seahorse embryos develop in a marsupium that acts much like the mammalian uterus. The developing embryos are protected and provided with oxygen through a capillary network, while the pouch acts as an adaptation chamber with the osmolarity of the fluid inside the pouch changing from that of body fluids to that of salt water as pregnancy progresses.
After fertilization, the pouch becomes spongy, vascularized and distended. The eggs induce
pits in the wall of the pouch which become compartmentalized and then are enveloped in
epithelial tissue until the end of yolk absorption.
The duration of the male’s pregnancy (gestation duration) ranged from approximately 9 to 45
days, Males of all species studied to date went through several pregnancies in a single
breeding season, the number of pregnancies depending on the length of brooding and the
length of the season: individual male H. comes were observed.
The Male Seahorse is Impregnated, Carries the Eggs and Gives Birth
At the end of pregnancy the male went into labor (usually at night), actively forcing the brood
out of his pouch for hours. Young resembled miniature adult seahorses, complete with
hardened fin rays, trunk rings and Pigmentation. They were independent from birth and
received no further parental care. Known newborn sizes ranged from approximately 2 mm to
20 mm, depending on the species.
Males of most seahorse species produced about 100–300 young per pregnancy, although
smaller species released only about five offspring per cycle.
Seahorses Look Like Horses With Googly Eyes
The seahorse has the ability to move his eyes in different directions at the same time. This maximizes his ability to search for moving prey. He will eat most any organism that is small enough to fit into their snout. These are usually tiny amphipods or other crustaceans but they also enjoy invertebrate fish fry.
Seahorses have a horse-like head positioned at a right angle to an erect body; eyes that swivel independently; a long tubular snout (no teeth) that sucks food; a digestive tract without a differentiated stomach; skin without scales, stretched over a series of
bony plates visible as obvious rings around the trunk and tail; and a prehensile tail.
Adult seahorses do not have pelvic or caudal fins, only one dorasal fin for propulsion and two small stabilizating pectral and anal fins used for steering. Most Hippocampus species have have a reduced caudal fin which disappears in adulthood. Seahorses ranged in size from the tiny Hippocampus denise (<20mmHt) to the large Hippocampus abdominalis (>300mmHt). Male and female seahorses are about the same size.
However, males do have a longer tail and females have a longer body trunks. A longer tail may
enable a male to support a large caudal pouch while still grasping a holdfast (an object to hang
onto), or may give males an advantage in the tail-wrestling exhibited during mating
competition. In some species males have shorter snouts (H. abdominalis and Hippocampus fuscus) than the females. The use of snouts to snap at competitors may explain the shorter and thicker snouts in some males.
Seahorses have excellent camouflage techniques, with traits that give them the ability to
avoid their enemies. Their disquise also helps them capture prey for food as they avoid being captured by those that prey on them. They remain virtually immobile for much of the time
and can change color over a few days or weeks to match the background if it has changed.
Most seahorses are beige, brown or black, but some species can make color changes that
include bright orange or dark purple. For example, Hippocampus capensis seahorses
are mostly mottled in color with brown or darker patches, but they can be found in green, white, black, and yellow colors forms.
Hippocampus bargibanti mimics in color and form the stalks and polyps of the gorgonian coral
(Muricella sp.) to which it clings using its tail. Encrusting organisms sometimes grow on the skin of a seahorse, which improves the fish’s camouflage. Seahorses often changed color rapidly when interacting with each other. Both sexes of Hippocampus whitei brightened in color from a dark brown or grey to a pale yellow or off-white during pair-wise encounters in the wild.
On an Australian algal reef, Hippocampus breviceps were observed to brighten their pouches
and body front to a flashing silver or white when approaching another seahorse. Similarly, some have observed H. fuscus males, Hippocampus guttulatus and Hippocampus
hippocampus males brighten in color when courting females.
Endangered Species
Seahorses have joined the many species whose life history have made them vulnerable to capture. Their habitats have also been polluted or destryed making them candidates for species who make become extinct. They are found to have a very low population density in their chosen areas of habitation. The traits that add to their low population includes, staying in a small habitat area, remaining immobile for long peroids, having a long parenting period and being monogamous.
Seahorses are exclusively marine, generally living in coastal habitats in shallow temperate
and tropical waters. Temperate species of seahorses predominantly inhabite seagrasses and algae, while tropical species are mostly found among the pacific coral reefs.
Seahorse Behavior and Ecology
Most seahorses grasped holdfasts with their tail, although individuals in some populations,
such as that of H. abdominalis, are found distant from any structure, nestled in small
depressions in the substratum. Generally, holdfasts can be anything from a sponge to a
branching coral, a piece of seagrass or a submerged tree branch. Most seahorse species studied by researchers are active during the day (diurnal). These include H. breviceps, H. capensis, H. erectus, H. guttulatus, H. hippocampus, H. kuda, H. whitei and H. zosterae.
Nocturnal species included Hippocampus ingens, while Hippocampus abdominalis is reportedly both active during the day and night. Hippocampus comes may also be active during both day and night, but most are commonly seen to be active at night. Most seahorse species studied by researchers have been found to remain on individual home ranges, mostly in the breeding season. This has enabled the seahorses to evolve the best camouflage for their environment, and to maintain a stable social structure.
No seahorses have been seen to take on a territorial defense of the home range, which is
unlike most fish with limited home ranges. It is believed that this is because they do not
need to defend sites where eggs have been deposited, since the male seahorse carries the
eggs in his pouch.
Sometimes seahorses are dispersed over large distances only when they are cast adrift by
storms or carried away while grasping floating debris. Otherwise they remain stationary. The life spans for the seahorse species is short, ranging from about 1 year in the very small species H. zosterae to an average of 3 to 5 years for larger species.
Predator or Prey- Both
Sub-adult and adult seahorses have few natural predators. This is believed to result from
their camouflage capabilities, and unpalatable bony plates and spines.
However, seahorses were found in the stomachs of large pelagic fishes such as red snapper,
dorado, rays, skates, tuna and dolphin fish, and are also preyed upon by anglerfish, flatheads
and sea urchins. Seahorses are sometimes captured by bird species such as cormorants,
penguins, and other water birds.
Seahorse as Predator
Seahorses are ambush predators, and consume primarily live, mobile prey. When feeding within the water column, they wait until prey come close to the mouth, then draw the prey up into their long snout with a rapid intake of water. Wild seahorses do not appear to eat plants or algae, but pieces of seagrass were found in the stomachs of some species. Researchers think that the seagrass may have been indirectly ingested when eating small prey such as mollusks which were attached to the grass blades.
Hippocampus zosterae were credited with eating sufficient ocean invertebrate prey to
affect the structure of at least some benthic invertebrate communities. Hippocampus erectus appears capable able to obtain prey over a wide range of habitat complexities, although they prefer to grasp a holdfast when feeding.
Types of Food Selected
Studies have shown that Hippocampus abdominalis consumes a greater proportion of
amphipods in the wild, while larger consume more caridean shrimp. It is believed that if given a choice of amphipods and smaller copepods, Hippocampus erectus will eat both prey types. Some researchers have found that large H. erectus eat mostly amphipods in the wild.
Growth Rates and Breeding Season
Smaller seahorse species, such as Hippocampus zosterae, appeared to mature at 3 months,
while Hippocampus barbouri, Hippocampus fuscus, and Hippocampus ingens reached maturity at 4 or 5 months, while other species are believed to reach maturity at 6 months to 1 year. In the wild, the timing and length of the breeding season for seahorses varied with ocean
location, and this is probably influenced by environmental parameters such as light,
temperature and food availability.
The breeding season for Hippocampus zosterae appears to be correlated more with day length than with temperature. The duration of the breeding season is longer in tropical than temperate waters, with the apparent exception of H. abdominalis. Diseases that reduce seahorse numbers include bacteria, cestodes, icrosporidians, fungi, ciliates, trematodes and marine leeches.
The survival of the seahorse has come into question in recent years. Public interest in this strange, interesting creature, pollution of his habitat and his life history combine to preclude a rapid comeback. Public agencies must help to save the seahorse from extinction.
References
Foster, S. J. & Vincent, A. C. J. (2004). Life history and ecology of seahorses: implications for
conservation and management. Journal of Fish Biology, vol. 64.
Jones, A. G. & Avise, J. C. (2001). Mating systems and sexual selection in male-pregnant
pipefishes and seahorses: insight from microsatellite-based studies of maternity. Journal of
Heredity, vol. 92.
Kuiter, R. H. (2009). Seahorses, Pipefishes and Their Relatives: A Comprehensive Guide to
Syngnathiformes. Southend-on-Sea: Aqua Press.
Vincent, A. C. J. (1994). Seahorses exhibit conventional sex roles in mating competition,
despite male pregnancy. Behaviour, vol. 128.
Woods, C. M. C. (2000). Preliminary observations on breeding and rearing the seahorse
Hippocampus abdominali in captivity. New Zealand Journal of Marine and Freshwater
Research, vol. 34.
