Name: The Insane Biology of: The Seahorse
Uploaded: 2024-11-17T15:44:06.000Z
Duration: 17 min 10 s
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The sea is filled with incredibly unique lifeforms, coming in a variety of shapes, sizes, colors, and appendages.

Relative clauses (Restrictive vs. nonrestrictive)

Many of such creatures are incredible predators who lurk in the far reaches of the cold, dark ocean.

From the terror-inducing great white shark, to the insidiously clever killer whale, to the snapping jaws of the powerful leopard seal, to the outrageously fast marlin.

Creatures like this strike fear into the hearts of many, but the biggest and scariest predators aren't necessarily the deadliest.

For great white sharks, only about 48% of surface attacks on seals result in successful kills.

Leopard seals only catch their fish prey in 64% of their attempts.

To find one of the most effective predators, you need to set your sights on something much smaller and in much shallower waters.

Residing in coastal regions around the world is the oddly shaped sea creature known as the seahorse.

Seahorses belong to the Cygnathid family of fish, which includes pipefish and sea dragons.

There are about 50 seahorse species ranging in size from 2 to 35 centimeters, each resembling a Frankenstein-like creation with bits and pieces taken from various animals combined to make one extraordinary fish.

Seahorses are one of the most effective hunters in the sea, with a success rate of over 90%.

That's 2 to 3 times higher than other predatory fish, and it's all thanks to their unusual design.

From their chameleon-like eyes that move independently of one another, allowing them to view both what's in front of them and behind them at the same time, to their monkey-like prehensile tails that securely anchor them to objects, to their incredibly flexible and strong body armor, seahorses are built for battle.

But seahorses are strange in more than just their appearance, and they are impressive even beyond their hunting skills.

Their adaptations for survival are among the strangest in the animal kingdom.

And seahorses, however cute and quirky, are a survival powerhouse of the sea.

Seahorses and their relatives are the only known vertebrate animals where pregnancy and birth are performed by the males.

While other animal dads may house and protect fertilized eggs, such as water bugs, cardinal fish, and many bird species, male seahorses do much more.

After an elaborate courting dance, a mating pair of seahorses will entwine their tails and line up the female's egg duct, called the ovipositor, with the male's brood pouch opening.

The female then deposits her eggs into the pouch.

Scientists once believed the eggs were fertilized inside the pouch through an internal sperm duct.

However, dissections have disproved this theory, with a study on the yellow seahorse finding instead that the sperm duct opening is located 4.5 millimeters above the pouch opening.

This means that the sperm travels outside the male seahorse's body, meeting with the eggs as they are deposited into the brood pouch.

Videos of this event have found that the yellow seahorse's pouch stays open for just six seconds, making them uniquely efficient at fertilization, since in this incredibly small window, they produce between 100 and 1,000 embryos.

And once inside, the brood pouch itself becomes rather extraordinary, functioning similarly to a mammalian placenta by providing oxygen and nutrients to the growing seahorse embryos.

Compared to eggs that develop externally, eggs that are incubated internally come with different challenges.

One in particular is a means for respiratory gas exchange.

In order to survive, embryos need a constant exchange of respiratory gases, oxygen and carbon dioxide.

However, being in an enclosed space makes this difficult.

In mammals, this exchange is accomplished through the blood flow from the mother to the placenta to the umbilical cord to the fetus and back again.

In seahorses, scientists believe it happens nearly the same way, through blood flow from the father to the embryos and back.

By examining the brood pouches of the big belly seahorse, researchers even found that they remodel throughout gestation to accommodate the growing embryos.

After fertilization, seahorse embryos become embedded in the lining of the brood pouch, which contains numerous blood vessels.

As the embryos develop and require more oxygen, the lining becomes thinner and more wrinkled, providing the surface area needed for even more blood vessels.

As these changes to the brood pouch mirror the growth of the seahorse fetuses, their findings indicate that the pouch is acting in just the same way as a placenta, providing a means to exchange oxygen and carbon dioxide and even nutrients through blood flow.

The whole gestational process of a male seahorse takes anywhere between 10 days to six weeks, depending on the species.

Then, through a series of muscle contractions, as many as 1,000 fully developed babies are shot from the pouch into the sea.

With these functions performed by the females in nearly every other animal, scientists are left wondering, why in this case is it the males?

Some theorize that male pregnancy leads to more seahorse babies, since without having to carry out the pregnancy, the females are free to start making more eggs right after they deposit them in the males.

And when only 0.5% of seahorse offspring survive to become reproducing adults, making a lot of babies is crucial for the survival of this one-of-a-kind fish.

When you're as small as a seahorse, protection from predators is another survival necessity.

And here, seahorses once again evolved a unique solution.

For most sea creatures, hard, rigid structures such as scales, shells, and exoskeletons act as an armor against predators.

But seahorses took a different approach, with an armor that is instead highly deformable and flexible.

And as the seahorse moves, the plates slide over one another, allowing for a wider range of motion compared to fish with scales.

These plates aren't as hard as the armor of other sea animals, which means that when they experience a force, like a bite from a large fish, the plates deform instead of fracture.

But it's the orientation of the plates themselves that allow the seahorse to survive most attacks.

Unlike typical animal tails, which are cylindrical, a seahorse tail has a square cross-section.

To explore the benefits of a square tail and how it compares to a traditional cylindrical tail, a group of researchers made a 3D printed model of a seahorse tail, composed of 36 square segments, each with four L-shaped bony plates, as well as a similarly segmented cylindrical tail.

They found that, while the cylindrical tail became squished and damaged when crushed, the square tail flattened out and deflected damage away by a central column inside, allowing it to absorb more energy before breaking.

Mechanical tests have found that, under compressive loads, they can deform up to 50% without harming the vertebrae inside.

With this strength and flexibility allowing for agile movement as well as protection, scientists are exploring its potential use as flexible armor in fracture-resistant structures and in robotics.

Scientists also determined that flat sides provide more attachment points when gripping onto objects, which, due to their poor swimming ability, is how seahorses spend most of their time.

Their terrible swimming skills are a result of their upright position as well as their lack of pelvic fins and tail fins.

Their movement is limited to a small dorsal fin on their back that propels them forward and a pectoral fin on either side of their head that steers them where they want to go.

These poor swimming skills make them one of the slowest fish in the sea.

It also explains their mostly sedentary lifestyle, clinging to seagrass or coral.

And while their upright stature may seem disadvantageous, it actually helps them with their protection.

Like many animals, seahorses evolved to fit their environment.

And when their ocean habitat changed dramatically about 25 million years ago, they did just that.

During this period, tectonic events across the Indian and Pacific Oceans transformed the open sea, creating many shallow water, grassy regions.

Scientists believe that this shift is what caused seahorses to diverge from their ancestor, the pygmy pipehorse, eventually emerging as the upright swimmer we know today.

That's because swimming upright has two main advantages in grassy environments.

Swimming upright allows them to move through the blades of grass easier than if they swam horizontally.

In addition to a color-changing ability that many fish and other sea animals possess, a seahorse's upright posture helps them hide in their environment.

Vertical blades of grass and coral can more easily hide a vertical fish.

So seahorses cling to them using their prehensile tail.

And this hidden position doesn't just provide them protection from predators, it provides them stealth for hunting.

In fact, researchers have found that the denser the vegetation, the more successful seahorses are at capturing their prey.

One study found that adult seahorses had over an 80% success rate in highly dense habitats compared to just 30% in habitats with low or no vegetation.

And for seahorses, a high success rate in hunting is particularly important considering they're missing a key component of the digestive system, their stomach.

Without a stomach, food passes through them rather quickly.

This means that they have to eat all the time.

But luckily for them, they are among the most impressive ambush predators in the world.

Being bad at swimming makes it impossible for seahorses to chase down their prey.

Instead, hidden within the seagrass or coral, they very, very slowly get close to their unsuspecting target, snap their head around, and quickly suck them up through their tube-like snout.

This technique is known as pivot feeding and seahorses have perfected it.

They're able to score a meal in record time.

It happens so fast, your eyes can barely comprehend that anything has happened at all.

To rotate their head with such lightning speed, elastic energy is stored in the large tendons of the apaxial muscle, a muscle associated with head rotation, and then quickly released.

This rotation brings their mouth closer to their prey.

Then, with a widening of their snout, a suction force is created that pulls the food into their mouths.

In less than five milliseconds once they begin to pivot, they're already enjoying their meal, making them one of the fastest-feeding vertebrate animals.

But being highly skilled at pivot feeding isn't enough.

Seahorses first have to get within striking distance without being detected, and the typically calm waters of their habitat don't make that easy.

Any motion could send a ripple through the water, cluing their prey in to their approach.

One of their main food sources, copepods, are especially sensitive to hydrodynamic disturbances.

They can respond in three to four milliseconds and make a quick escape at a velocity of 300 meters per second.

And for the pivot-feeding technique to work, seahorses need to get within close range, within about one millimeter.

Luckily, seahorses have another trick up their sleeves, their long snout.

One group of researchers took a closer look at how the dwarf seahorse sneaks up on and captures its prey.

Using high-speed digital recordings, they measured the 3D motions of seahorses, copepods, and the surrounding water during an attack.

They found that the seahorse's elongated snout creates a quiet zone, where fluid motion doesn't exceed 0.8 millimeters per second compared to the 4.1 millimeters per second in the surrounding area.

This region is located right above the end of the snout, in the striking zone, allowing the seahorse to sneak up on their prey undetected.

In contrast, the striking zone of a related fish without an elongated nose, the three-spined stickleback, had the highest fluid motion compared to the surrounding area.

With this oddly-shaped head, the unassuming seahorse is one of the most remarkable hunters of the ocean.