They are commonly also found in estuaries where the water may be quite brackish or even experience intermittent freshwater floods. Seahorses are sparsely distributed in most populations, found at 0.06 per m2 or one seahorse per 16.67 m2, for example. They do, however, occur in higher densities at particular times and places, especially in lagoons. The highest density of seahorses – up to 0.66 per m2 (one seahorse every 155 m2) – has been found in a tidal lake in the Bahamas that is isolated from the ocean.1 A lagoon in Portugal also had high densities of about 1.5 per m2 when first studied in the early 2002, although densities had declined by 94% by 2008.
Seahorses occupy a huge diversity of shallow water habitats: seagrasses, mangroves, corals, sponges, seaweeds, and shallow dips in mud and sandy bottoms.
Most species settle down onto the bottom, anchored to a holdfast of an emergent plant, animal or seaweed. Some pygmy seahorses are found only in association with gorgonian corals or sea fans and will spend their entire life on a single sea fan. In contrast, at least four species have been encountered several kilometres offshore and have been recorded at depths greater than 100 m. The discovery of seahorses in the stomachs of open ocean predators – e.g. yellowfin tuna, trevally and dolphinfish – confirms that some might even occur far offshore.
Jayakar’s seahorse (Hippocampus jayakari). Photo by Ronny De Pesseroy / Seahorses of the World
Camouflage
Most seahorses are very camouflaged, matching their habitats closely. They change colours to blend into their background – even including matching fluorescent survey tape – and grow skin filaments to hide even better. By using their prehensile tail to grip a holdfast tightly and staying immobile, they become almost invisible to the casual (and even the determined) seeker. Seahorses also brighten during elaborate pair bond and courtship displays but these short term colour changes serve to make the seahorses more visible. Speaking of brightening, recent work has been exploring how biofluorescence in seahorses can be used to spot them at night.2,3
Migration
Some seahorse species engage in migration, moving long distances, for at least three reasons: juveniles move to adult habitats; adults move on a seasonal basis; and seahorses go rafting. With respect to rafting, seahorses from a number of species have been found tucked into sargassum and other seaweed clumps, drifting long distances. Given that such travel creates the potential for long distance dispersal, much more needs to be learned about migrations and rafting.
Masonjones, H., Rose, E., Elson, J., Roberts, B. and J. Curtis-Quick. 2019. High density, early maturing, and morphometrically unique Hippocampus erectus population makes a Bahamian pond a priority site for conservation. Endangered Species Research 39:35-49.
De Brauwer, M., Hobbs, J-P.A. Ambo-Rappe, R., Jompa, J., Harvey, E.S. and J.L. McIlwain. 2018. Biofluorescence as a survey tool for cryptic marine species. Conservation Biology 32(3): 706-715.
Vaccani, A.C., Freret-Meurer, N.V., Bertoncini, A.A. and L.N. Santos. 2019. Shining in the dark: First record of bioflurescence in the seahorse Hippocampus reidi. PLoS ONE 14(8): e0220561
We present the first synthesis of the life history and ecology of seahorses, compare relationships for seahorses with other marine teleosts and identify research needs. Seahorses occurred primarily amidst temperate seagrasses and tropical coral reefs. Population densities were generally low, ranging from 0 to 0·51 individuals m−2, but reached 10 m−2 in some patches. Inferred life spans … Read more Life history and ecology of seahorses: implications for conservation and management
Seahorses are marine fish with several life history characteristics hypothesized to make them resilient but are of conservation concern because of their international trade and habitat loss. Surveys of two unexploited European seahorse species (Hippocampus guttulatus and Hippocampus hippocampus) in Ria Formosa lagoon, Portugal, were repeated seven years after their populations in the lagoon were … Read more Revisiting two sympatric European seahorse species: apparent decline in the absence of exploitation
Kleiber, D., Blight, L.K., Caldwell, I.R. and A.C.J. Vincent
A review of 135 accounts of predation on seahorses and pipefishes identified 82 predator species, with nine species of seahorses and 25 of pipefishes recorded as prey. These cryptic fishes were generally depredated in low numbers. Where syngnathids formed a high proportion of predator diets, predation occurred on (1) a single abundant species during a … Read more The importance of seahorses and pipefishes in the diet of marine animals
