About Hippocampus trimaculatus Leach, 1814
Nomenclature
The longnose seahorse, whose scientific name is Hippocampus trimaculatus, also has multiple common names: flat-faced seahorse, low-crowned seahorse, and three-spot seahorse.
Distribution
This species is primarily found in shallow seas surrounding Australia and Asia.
Diet
It feeds on plankton and small crustaceans, which it sucks in through its snout.
Feeding Behavior
Like typical seahorse behavior, this species anchors itself to seagrass while feeding to save energy.
Body Morphology
While its appearance can vary across individuals, the species typically has a flat body, sharp hook-shaped cheek and eye spines, a narrow head, and no nose spines.
Coloration
Its body color can be golden orange, sandy, or completely black; some individuals even have brown and white zebra-like stripes.
Sexual Size Dimorphism
On average, males of this species are slightly longer than females.
Depth Range
Longnose seahorses are usually found at depths between 10 and 100 meters.
Juvenile Depth Observation
Recently, however, juvenile flat-faced seahorses were observed at a depth of less than 0.1 meters in the Malacca Strait.
Migration Evidence
This observation may be the first record of drifting juvenile seahorses in this area, and it provides potentially strong evidence that this species performs passive long-distance migration.
Habitat
This seahorse generally lives on gravel or sand bottoms around coral reefs, in muddy estuaries, and near mangroves, and it can also survive in brackish water.
Conservation Status
The flat-faced seahorse is classified as a vulnerable species and is threatened by habitat loss.
Vulnerability Drivers
Several factors contribute to its vulnerability.
Harvest and Trade Threats
Large numbers of this species are part of the millions of seahorses traded internationally each year, and they are also frequently caught as bycatch.
Harvest Uses
Harvested seahorses are commonly used in traditional Chinese medicine, dried and sold as souvenirs in the United States, and sold as pets worldwide.
CITES Trade Restrictions Proposal
These unsustainable harvesting and trade practices led the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to propose restrictions on seahorse trade.
Restriction Enforcement
While these restrictions are not legally binding, traders must follow them to earn sustainable certification.
Size Restriction Rule
The key restriction prohibits harvesting any seahorse smaller than 10 cm.
Size Restriction Relevance
This size restriction is particularly relevant because of how flat-faced seahorses reach sexual maturity.
Sexual Maturity Predictor
For this species, sexual maturity is predicted more accurately by size than by age.
Regional Maturity Variation Example
For example, populations in the South China Sea and North China Sea both reach sexual maturity at the same size, but South China Sea individuals reach maturity at 3 months old, while North China Sea individuals reach maturity at 5 months old.
Maturity Size Trait
Unlike many other seahorse species that reach maturity after growing larger than 10 cm, flat-faced seahorses reach sexual maturity before they reach 10 cm in length.
Mating Reproduction Strategy
During mating, female flat-faced seahorses transfer their eggs to males, who carry the eggs and give birth to live young.
Gestation Period
The gestation period for this species ranges from 11 to 20 days, with an average of 16 days.
Gestation Temperature Correlation
The length of gestation varies with water temperature: the species has a 19-day gestation period at 22.5°C, 16 days at 24°C, and 11 days at 28.5°C, which matches the pattern seen in other Hippocampus genus members.
Breeding Season
While captive flat-faced seahorses can reproduce year-round, wild populations in the China Sea have a peak breeding season from March to May.
Breeding Season Variation Driver
Their peak breeding season may vary by location, because the species’ reproduction depends on consistent water temperature.
