Seahorses are a very strange animal

They have the head of a horse; the prehensile tail of a monkey and the males even have a pouch like a kangaroo. But what are they? And what habitat do they live in?

Seahorse in a water habitatWhat is a seahorse?

Seahorses are actually fish. They live in water, breathe with gills, swim with fins and have a swim bladder. However, unlike normal fish, they do not swim around large areas within the ocean habitat. They tend to stay in one location throughout their entire lives. They swim around their little patch using dorsal fins on their backs and small pectoral fins behind their eyes. Their dorsal fins can beat between 30-70 times per second! Despite this, they are not great swimmers, so they grip on to vegetation with their tail to avoid being swept away by the current.

At the end of the snout, they have their mouth. The snout acts as a little tube that they use to suck up small zooplankton, invertebrates and even larval fish. They can eat up to 30-50 tiny shrimp in one day! This makes them important predators of bottom-dwelling species while also acting as prey for larger fish and crabs. For this reason, they hold an important place in healthy ecosystems. To avoid predators, seahorses can change colour to match their surroundings and stay camouflaged. They have even been seen turning fluorescent colours to match floating materials!

Do they live in an Irish habitat?

There are 45-65 species around the world. People all over the world love seahorses due to their unique, almost mythical, appearance. It may come as a surprise to many people that there are two species of seahorse in Ireland. We even have a word for seahorse in Irish – EachUisce, meaning water spirit.  Our two wonderful seahorse species are the short-snouted seahorse (Hippocampus hippocampus) and the spiny seahorse (Hippocampus guttulatus) also known as the long-snouted seahorse.

Seahorse Habitat

Seahorses exist in shallow tropical and temperate waters all over the world, where they live in sheltered habitats. The short-snouted seahorse is known to prefer rocky reefs along harbours and areas of open sediment. The spiny seahorse prefers seagrass meadows. They will stay in these shallow areas during the warmer months of the year and move out to deeper water in autumn when storms begin to disturb the shallow water. They return from February onwards, when the water is calmer and warmer1.

Seahorses are known to exist all around the coast in Ireland. In Cork, there have been sightings at Youghal Beach, Lough Hyne and Berehaven Harbour2.

Do male seahorses actually get pregnant?

You may have heard about seahorses due to their unique form of parental care. And it’s true! Seahorses (and their close relatives) are the only species in the animal kingdom where the male experiences true pregnancy. 

Seahorses are seasonally monogamous, meaning that a pair will stay together for a full season. Males hold a territory of about 1m2 while females roam an area up to 100m2. This means that the females need to approach the males to establish a relationship.  Once they have formed a pair, the female will visit the male every day and they will perform a greeting ritual, which involves changing colours, holding each other’s tails and dancing around each other. This can last from several minutes up to a full hour! This relationship is very important to the seahorses and they have been observed to remain alone for a full breeding season if they are separated from their partner.

When they are ready to breed, they perform a similar ritual for several hours to communicate with each other. The female will deposit her eggs into the males “brood pouch” (imagine a kangaroo’s pouch) where they will be fertilized by the male. Gestation lasts from two weeks up to 24 days. Throughout the pregnancy, the female will continue to visit the male daily to perform the greeting ritual and she will produce more eggs. The male gives birth to up to 1000 fully developed babies (called fries) which will then drift away in the current. But he isn’t done there – immediately after the birth, the female will return and mate with him again. Male seahorses can get pregnant multiple times within the warmer months of the year – the Seahorse Trust even recorded one male who gave birth five times in one season1!

This strange system occurs for a good reason. By taking over the pregnancy, the male allows the female time to produce more eggs and increase the number of offspring that the pair can have per season. This is important because it is thought that only 1 in every 1000 fries will survive to adulthood!

What is their conservation status?

In Ireland, little is known about the number of wild seahorses in our waters or how their population is doing. Both Irish species are listed as ‘data deficient on the IUCN Red List as of the 2017 survey by the IUCN SSC Seahorse, Pipefish & Seadragon Specialist Group. This means that very little is known about how many of them are living in the wild. It is likely that they are suffering due to habitat loss and disturbances. Seahorses are very sensitive to stress so changes to their habitat can have a large impact on them3. Due to their sensitivity, they are also very difficult to breed in captivity. However, marine biologist Kealan Doyle did successfully breed seahorses as part of a conservation programme in Connemara called EachUisce Éireann Teo (Seahorse Ireland as Gaeilge).

Globally, seahorses’ main threat is the Chinese medicine trade and curio trade. Seahorses are listed on Appendix II of CITES (Convention on International Trade in Endangered Species). This means that they are not threatened with extinction, but their trade must be controlled and monitored to ensure the survival of the species. The Seahorse Trust estimates that more than 20 million seahorses are killed each year for the Chinese medicine trade. Similarly, at least one million seahorses have turned into souvenirs annually and sold on beaches, along with starfish, conches, snails and many other species. These are collectively known as curio, and although these souvenirs may seem innocent, they pose a serious threat to seahorse populations.  If you see them being sold, please report them to The Seahorse Trust!

Fun Seahorse facts:

  • Seahorses are closely related to pipefish and sea dragons;
  • Seahorses can live from one to five years in the wild;
  • The smallest seahorse is the Satomi’s pygmy seahorse (Hippocampus satomiae) at 13.8 mm and the largest is the Big Bellied seahorse (Hippocampus abdominalis) that can grow up to 35 cm;
  • The Each-Uisce is also a Celtic mythological sea creature that can appear as both a horse and man;
  • Fota Wildlife Park in Cork has a group of pot-bellied seahorses living in the tropical house;
  • There is a pediatric ward in Cork University Hospital named the Seahorse Day Ward!

If you are a diver or fisherman in Ireland and you have come across seahorses, please report your sightings to the Irish National Biodiversity Data Centre (https://records.biodiversityireland.ie/record/marine) and let the Seahorse Trust know about your sighting through their World Seahorse Survey (https://www.theseahorsetrust.org/conservation/world-seahorse-survey/). Please also ensure that you do not stress them out or use a flash to take photos as this can kill them. 

 Thank you to Neil Garrick-Maidment and the Seahorse Trust for their help with this article.

 

Written by Rebecca O’Sullivan

References:

  1. Seahorse Trust Special Newsletter (Summer/Winter 2019). The Seahorse Trust. Accessed: 8 April 2021 https://www.theseahorsetrust.org/wp-content/uploads/2018/01/MCZ-special-newsletter-summerwinter-2019-1.pdf
  2. Green, Marianne J. (2004) Food production for juvenile seahorse culture. Masters Thesis, Galway-Mayo Institute of Technology
  3. Curtis, J.M.R., Ribeiro, J., Erzini, K. and Vincent, A.C.J. (2007), A conservation trade‐off? Interspecific differences in seahorse responses to experimental changes in fishing effort. Aquatic Conserv: Mar. Freshw. Ecosyst., 17: 468-484. https://doi.org/10.1002/aqc.798