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(dramatic music) NARRATOR: yet, insatiable predators, and delectable prey.

They are prehistoric relics, More than 3600 species of inhabit North America's an inlet with a meandering the entire West Coast of The brackish waters of some of the most extreme of all of the world's Here, freshwater from with an influx of seawater The result, that changes based on even the weather.

Those adapted to these surroundings are iconic, and often, quite charming.

* They are creatures...of (waves crashing) Geologically speaking, It's only been around, for about ten millennia.

The oldest fossils of Calvert Cliffs predate 20 million years.

But the bay's beginnings to the moment a meteor in a fiery collision Ancient rivers--including one the Susquehanna-- began drawn to the massive crater.

Fast forward millions of of the last ice age, a relatively recent The planet was warming, and seas were rising.

The thaw flooded the freshwater mixing with the and the modern (crashing waves) Ever since, to a menagerie of As one of the nation's most it's something of with a little something Like your water on Check.

Not as salty?

We've got that too.

Want plenty of food Try the shallow Or be a part of the action where life lurks in And for the thrill seekers, there's always In a place this unique the residents are full (soft music) * Even amongst the diverse the Chesapeake Bay community, stands out as just Maybe it's the long snout, or the lithe prehensile tail.

or the fact that for a fish, it's an awfully awkward swimmer.

There's a theory that the from its cousin, which, by the way, like a proper fish.

But if you're lucky enough to bobbing in the bay grass you'll understand why this suited for life in the * That flexible little tail?

Perfect for grabbing aquatic or another seahorse, lest the and that snout?

Just right for with a satisfying "snap."

The lined seahorse is, who waits until prey A smart strategy for It scans for prey with each moving independently One thing it doesn't have?

A real stomach.

Food goes right through it.

Perpetually hungry, more than 50 times a day, small shrimp, plankton, anything that will fit Instead of scales, has skin stretched over It's signature lined markings into its environment.

But what's more, master of disguise can to match its surroundings, or, when it's trying to (waltz) When a seahorse chooses a it stays with that mate A daily mating dance lets these two are taken.

In true maverick fashion, into a pouch on the front called a "brood sack."

Essentially, The eggs hatch inside.

And get this, it's the seahorse father to thousands of teeny tiny A new generation of these (typing sound) (soft music) If you know anything about undoubtedly you're familiar most cherished crustacean.

This vibrant blue stunner the water column, scooping the water in in fact, the Chesapeake Callinectes sapidus, (creepy music) but how well do you really most famous creature?

* If you picture a simple scurrying through searching for scraps, these tough guys are stealthy predators.

For a soft shell clam, a smaller blue crab, coming face-to-bug-eyed is downright...terrifying.

But despite those crabs don't always rely on they also use a network Tiny hairs on their mouth, help them sense chemicals Longer, chemosensory antennae creating microcurrents find a meal as it moves the bottom of the bay.

As good as they are at their hiding game is Crabs are known to bury just eyes and antennae exposed.

It's a way to feel safe but they've also been known on an unsuspecting fish.

A-ha!

She's got something!

Those red tips on the claws, mean this crab is a female.

She holds her prey in her to her mouth.

She uses these-- mandibles-- Teeth -- called "ossicles," inside the gut.

They grind the food Some of the other movement and those chemoreceptors keeping tabs on her (soft music) Until recently, weren't all that interested too difficult to crack that But scientists at the Virginia Institute of recently discovered that's if the oysters are injured Check it out.

Researchers captured this on an oyster reef.

The crab expertly uses one of "the crusher" to gently Then it goes in with the sharper of the two, to cut the muscle * The blue crab is a cultural a part of the bay ecosystem But even the most familiar (typing sound) (upbeat music) Four centuries ago, three ships carrying 104 arrived at the shallow become known as As they explored their in search of a place their colony--Jamestown... they were struck by the It's hard to overstate just are to the bay's ecosystem.

They're food...habitat, natural filters that give your a run for its money.

And make no mistake--these busy nothing like stones.

At least, In fact, the Eastern oyster is actually Come on, open up...look, Those horizontal white layers an organ essential for feeding, and filtering.

Here's how it works-- in through the left valve, they of the particles suspended in weight...texture, What's that?

...algae!

The gills are like they catch tiny and move the good stuff for ingestion.

Anything that doesn't taste sand...or silt...gets and ejected.

These "pseudofeces," sink...a feast for All that's left is clean, Nutrients from the algae help build their own shells.

See those little hair-like They're part of an organ It pulls minerals from and uses them to make which makes up the shell.

Flakes of new growth But depending on the type of you might see a hint like this pretty purple.

(soft upbeat music) Speaking of algae, has way too much of it-- by excess nitrogen nutrient pollution.

Thanks to overfishing there aren't nearly enough to consume it all.

Which is a real problem, can filter 2-3 liters See for yourself...keep an eye It takes just over an hour to clear the water.

* (water cascades) That's why boosting is a big part of the plan Artificial reefs, like these, at the University Horn Point laboratory can help clear the water Here they've planted baby in hopes they grow.

The 17th century Chesapeake Just enough nutrients to nurture young creatures that spend in the shallow waters, to keep those nutrients and the water clear.

We may never again see but when it comes down to it, hinges on these, and a comeback for the ages.

(sea bubbles sounds) (typing sound) * One sign of a healthy oyster A bottom-dweller, out-of-the way locale a mother could love.

Meet the oyster toadfish.

Shy...secretive.

(foghorn sound) But not-so-silent.

The toadfish is known for Like most good animal sounds, the sound is produced an internal organ known as the It does this really fast-- than a hummingbird can It's message to females "Hey, I've made a nest, These dedicated dads protect and even afterwards This classic softie with a tough exterior.

A wide mouth packed and eleven hidden spines and dorsal fin make this to mess with.

a stealth predator, covered in mucus and flaps which helps it to camouflage like small crabs, But it's what's on And as it turns out, of an oyster toadfish is and spacing to our own.

(rocket booster liftoff) WOMAN: Booster ignition and NARRATOR: That's why, NASA decided to send to study how gravity affects the inner ear's Researchers actually on two separate space flights.

In fact, they shared when he became the oldest The study helped space sickness, struggling with vertigo.

Despite its out-of-this-world the toadfish remains humble.

A creature most comfortable waiting, unseen, (sea bubbles sounds) (soft orchestra music) Stare too long at this and you might forget You might even feel like, to the moon.

The aptly-named is the largest of the growing to nearly a foot But-fortunately-their sting the same can't be said other jellyfish, Atlantic Bay Nettle, a brush with one of Well, (soft music) Moon jellies do have stinging They're too small to see, on their fringe-like and on these longer appendages, called "oral arms."

The jelly uses both that's the orange and move it to its mouth.

Look closely, and you can and slowly uncurl, reacting, when they come into contact in the water called Jellies are about so it's easy to see what's as food moves through when it comes to they're mostly at the mercy but they can propel by expanding and contracting gliding through the water They can speed up or slow down from small sensory organs spread along the edge of organs help them keep like, an inner ear system.

On each rhopalium, you can for sensing light.

Jellies are beautifully that can tolerate conditions As oceans warm and coastal jellyfish are thriving.

More and more, we're seeing known as "jellyfish blooms," a sign that the ecosystem The trouble with too many they gobble up all the tiny of the food chain.

That makes it tough for Proof too much of anything even creatures as elegant (sea bubbles sounds) (eerie music) The horseshoe crab the prehistoric seas That's 390 million years walked the earth.

And from what paleontologists the horseshoe crab of today as it did back then.

We call this living fossil but don't break out the old bay It's not really a crab, it's not even a crustacean.

A peek under its smooth shell see those legs?

This creature is an arachnid, closer in relation to Each of its five pairs in bristles that allow it to Two front legs are mostly in its mouth, in the middle of all It breathes through these, Named because they look like, (soft piano music) See that scary-looking Some people think but it's closer to a tail, Horseshoe crabs use them against predators, they can be used as for when they find themselves upside down position.

Now, that's better.

* On the top of the shell, that's where it gets Believe it or not, there are The two compound eyes they have multifaceted lenses, like a fly's eye, The darker it gets, to light they become.

the other "simple" eyes they sense u-v light from off the moon.

For a creature that spawns all of these specially As spring transitions to summer, hundreds of horseshoe crabs in the moonlit surf.

Timing that works well that rely on the eggs to help We humans rely on But, it's their bright This unique copper-based for pharmaceutical companies.

It contains a special protein into contact with called "endotoxins," very useful in medical Up to a third of can be harvested before hopefully, For an individual that can be more than Of course, in a legacy that (water rippling) (soft orchestra music) Chesapeake Bay is (boat engine noise) an economic engine, teeming with life and energy.

Eighteen million people watershed...home.

* But the bay would be nothing, extraordinary species that and amaze, within its waters.

These spectacular creatures *