Survival, growth, and home ranges

Newborn seahorses get eaten lots as they drift around, but adults have few predators and tend to stay close to home.

Long-snouted seahorse (Hippocampus guttulatus), Portugal. ©Rui Palma/Guylian Seahorses of the World

Fun fact: Seahorses are voracious carnivores, eating a wide variety of live mobile prey.

Generally seahorses have rapid growth rates, early age of maturity, and short generation times.

Seahorses live for a year to about five years, depending on the species, with smaller species having shorter lifespans. The longest known lifespan for a wild seahorse is seven years for a White’s seahorse in Port Stephens, Australia1.

Their highest risk of mortality comes as planktonic young, with much higher survival after settlement.

Young seahorses settle to the bottom after several days to weeks, according to the species – 14 to 18 days for a pygmy seahorse and four to six weeks for the largest species – and then may not move much thereafter.

Seahorses are voracious carnivores, eating a wide variety of live mobile prey. Their lack of stomach means they need to eat constantly, and poop a lot.

They are ambush predators, who wait motionless for some small organism to pass. They most commonly eat small shrimp-like creatures and other crustaceans but will also take nematodes, polychaetes or baby fishes such as gobies. Indeed, they will try to inhale most passing animals that might fit into their snouts and even a few that won’t; seahorses have been spotted choking on too big a prey item as they try to dislodge it from their snout. In the end, snout shape and size probably largely explains what they eat.

Seahorses eat a great deal, so much that they help structure communities on the ocean floor.2

Juvenile seahorses grow rapidly in size, depending on the habitat and water temperature. In some species, males grow larger than females.

Seahorses start reproducing at about seven months to one year old, with size influencing age at maturity.

Species with longer snouts have larger brains. Females tend to have larger brains, as well.3

Once they are settled, seahorses fall prey to relatively few predators. Their excellent ability to camouflage and their unappetizing / unpalatable bony plated and spines protect them well.

Seahorses are really not considered important prey species in marine food webs but they may be useful alternative prey. They have been eaten by species such as crabs, octopus, sharks, stingrays, tuna, marine turtles, striped anglerfish, black seabass, ling, sea-perch, cod… and even penguins, gulls, and other birds.

We think that most predation on seahorses is opportunistic rather the result of active searches.

Project Seahorse discovered that adult seahorses tend to have small home ranges (say 5-50 m2), and remain faithful to one location. A pygmy seahorse may remain on just one branching coral all its adult life.

In contrast, a seahorse from a medium size species that is monogamous might move in a radius of only several metres. In turn, seahorses from a large polygamous species may move hundreds of metres in day.

In monogamous species, partners maintain strongly overlapping home ranges for several reproductive seasons. Males are essentially anchored onto one tiny patch of seagrass or branching coral for months while the female may roam a bit farther around her partner.

  1. David Harasti (per obs.) Nov 26, 2019
  2. Tipton, K. and S. Bell. 1988. Foraging patterns of two syngnathid fishes: importance of harpacticoid copepods. Marine Ecology Press Series 47:31-43.
  3. Tsuboi, M., Lim, A.C.O., Ooi, B.L., Yip, M.Y., Chong, V.C., Ahnesjö, I. and N. Kolm. 2017. Brain size evolution in pipefishes and seahorses: the role of feeding ecology, life history and sexual selection. Journal of Evolutionary Biology 30: 150-160.