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Dwarf Seahorse: the tiniest sea monster

The Dwarf Seahorse (Hippocampus zosterae) is a species we commonly encounter on our Seagrass Wading Trips.

Seahorses and pipefish belong to a family of fishes called Sygnathidae, which means "fused jaws". This refers to their long straw-like snout, which they use to suck up any nearby zooplankton, like amphipods, fish fry, and crustacean larvae. They're pretty terrible at digesting their food though, so they have to constantly eat throughout the day to gain enough energy. In captivity, seahorses can eat upward of 3000 brine shrimp in a day!

Seahorses are ambush predators, using their prehensile tail to hold on to a piece of vegetation as they eat any unfortunates that drift past. Since they can lie in wait, they don't need to be strong swimmers; in fact, the dwarf seahorse holds the Guinness World Record as the slowest swimming fish, with a max speed of about 5 feet per hour. They only grow to about two inches long, so moving their max speed of five feet per hour is equivalent to a six foot tall human taking an entire hour to round the bases on a baseball field. So yeah, they're pretty terrible swimmers, but they still might have been able to beat Babe Ruth around the bases!

Photo Credit: Sanibel Sea School

The males and females actually form monogamous bonds with each other, which is extremely unusual for fish. The male dwarf seahorse only covers a territory of about one square meter, while the female roams a bigger area and will come to visit his tiny territory. An individual staying put in a small, restricted area like this is known in the science world as having a high "site fidelity"; just as their faithful to their mate, they also faithfully stay in their territory as well.

Each morning, the female visits the males patch of turf and initiates a courtship dance. This may or may not lead to copulation, in which the two will rise from the bottom and intertwine tails before the female deposits her eggs into the male's brood pouch on his abdomen, similar to the pouches that marsupials like kangaroos have. This means that the male seahorses are the ones that get pregnant! He will fertilize and incubate the eggs for about 10 days before giving birth to up to 50 tiny babies. These young are not not called sea ponies unfortunately, but are actually called fry.

The fry are completely self-sufficient once born and will venture off to find their own new territories somewhere else in the seagrass. The parents will often mate again just hours after the father gives birth, but the males in some species of seahorse are known to fill their brood pouch with water after giving birth so they still look pregnant and can get a brief respite before the female comes to give him more of her eggs. Everyone needs a break!

The etymology of this species is a lot of fun too. Their genus name, "Hippocampus", is a Latin word derived from two Greek words: "hippos", meaning a horse, and "kampos", meaning a sea monster. The hippocampus in mythology was a part-dolphin, part-horse creature, and groups of them were often depicted pulling Neptune's chariot. Their species name, "zosterae", stems from the Latin word, "zoster", meaning a men's belt or girdle. This doesn't refer to the seahorses being belted, but rather to Zostera, a genus of seagrass commonly known as eelgrasses that the dwarf seahorse often lives in. So the scientific name of this miniscule, slow as molasses pipsqueak is "the sea monster horse in the eelgrass". We hope they know that the giant scary pink apes that catch them think they're sea monsters.

Gerald Thompson

Education Coordinator

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