Saltwater from the sea and freshwater from land come together here.

And there are very few places on earth as rich with different kinds of life.

Music This is an estuary.

As in most estuaries, life is everywhere, above and below the surface.

This is how nature works!

Theme Music Music Water covers more than three fourths of the earth, and 99% of that water is salty.

All kinds of different creatures live together in the ocean and in estuaries, where freshwater and saltwater mix organisms that live together and naturally interact with each other are a community.

Communities in or on water are called aquatic.

Aquatic communities can exist where the water is fresh, places like ponds and streams, or they can be where the water is salty or brackish, such as in estuaries or in the ocean.

Those in saltwater are called marine communities.

The seas are the largest environments on Earth.

The Pacific, Atlantic, and India Oceans are all connected and together they support a huge variety of life.

The great variety comes partly from all the different conditions in the sea.

Organisms are adapted not just to waves at the beach, but also the different amounts of salt, water, pressure, heat and cold, sunlight, and water movement.

Out in the ocean, there are three zones of life, each home to different communities.

The sunlit, shallower area, down about 660 feet, is called the euphotic zone.

The darker deep water below 660 feet is called the dysphotic zone.

The very deep ocean where it is completely dark is called the aphotic zone.

Most of the ocean's water is in the aphotic zone.

This area is barely explored and new life forms are discovered there every year.

Water pressure there is extremely high and the temperature is near freezing.

Aphotic communities often live near cracks in the Earth's crust that give off minerals and heat.

As you rise up from the deep aphotic zone to the dysphotic zone, the ocean is still cold and pressure is still extreme, but very dim light filters through.

Only about 1% of all marine life is here, and the animals that live here tend to be small.

Above 660ft and all the way to the surface, there is an area called the euphotic zone, where life thrives on sunlight and the nutrients washed from land.

In these euphotic communities, sun and nutrients feed microscopic single-celled plants called phytoplankton.

Directly or indirectly, most marine animals depend on these plants for food.

More than 90% of all marine organisms live in the euphotic communities.

Places where saltwater from the sea mixes with freshwater from rivers and streams are called estuaries.

All these conditions make a lot of different habitats.

There are saltwater marshes, beaches, mud and sand flats, rocky shores, oyster reefs, mangrove forests, river deltas, tidal pools, seagrass and kelp beds, and wooded swamps.

Lots of different organisms live, feed, and reproduce in the different habitats.

There are so many different habitats in and around salt water, with different communities in each one.

Some of the most beautiful communities are in a place called the intertidal zone, where the sea meets the land.

Let's go meet Dave at the Seacoast Science Center and see what type of animals we can find there.

Molly, look what I found.

Music This water's cold.

How do animals survive in such cold water?

Well, it might seem cold to us, but actually to the animals that live in here, they're perfectly well adapted to it.

In fact, one of the factors that they have to deal with is the variable temperatures in tide pools.

Because in the wintertime, the freezing, subzero temperatures can make the water icy cold.

But in the summertime, the hot sun can actually warm the water up in a tide pool fairly quickly.

And temperature is one of the most important factors in determining where life in a tidal zone lives.

What other things do they contend with?

Well, one of the things they have to contend with is the fact that they get exposed to the sun and the air twice a day when the tides come in and out.

Other things include the pounding surf, you know, the waves come crashing up against them, and that happens year round.

But in the wintertime, the ice forms and that can actually scrape against the rocks as well.

When rain falls into a tide pool, that reduces the salinity or salt content.

And you add in all the predators that live in the tide pool, you can begin to understand this is a pretty tough community to live in.

What do tide pool creatures eat?

Well, to start with, the barnacles there, they're scoopers.

They have bristles on their legs that they fan through the water and kind of scoop out the plankton that are there.

And mussels, they're plankton feeders, too, but they actually suck the water into their shells or siphon it in along with the plankton.

And periwinkles, they're grazers.

They're actually scraping the algae off the rocks and the rock weed or even the mud.

And sea urchins, they're munchers.

They actually have five triangular teeth in here that allow them to kind of scrape and munch the little algae up, along with little animals that's living in the algae.

And sea stars, they're mostly predators.

They use their long legs and their tube feet to wrap around a shellfish, and then they pry open the shell and thrust their stomach inside.

Where are the greatest threats to life in tide pools?

Well, without a doubt, the two biggest threats are pollution and people who just ravage tide pools looking for food, or sometimes even doing it just for fun.

That's one thing everybody can do.

If you visit a tide pool and explore, that's great.

But when you're done, make sure you put those little tidal creatures back in there and treat the tide pool with respect.

You know, tide pools are a really special communities where the ocean meets the rocky coast.

But, you know, Patrice, there's another neat marine environment where the land and the ocean come together along with rivers.

Those are the estuaries.

Music An estuary is a place where freshwater from the land mixes with saltwater from the ocean.

At high tide, seawater takes over estuaries, flooding creeks and marshes with saltwater.

And when the tide goes out, freshwater from the land continues to flow into the estuary, diluting the saltwater.

Sandbars, barrier reefs, and islands shelter estuaries from the full force of the ocean.

Because of this protection, they're great places for an incredibly diverse group of organisms to live, find food, and reproduce.

The soil is rich in nutrients from decaying plants and animals.

Nutrient-rich soil supports lots of different species of plants.

Because there so many plants, animals are attracted to estuaries.

Birds are common in estuaries because there's so many fish, worms, crabs, and clams for them to eat.

And many migratory birds use estuaries as places to rest during their journeys.

Mainstays along the shores of the estuary are birds like herons and sandpipers.

Their long legs and toes are perfect for wading in the water and walking through the mud, hunting for fish, worms, and invertebrates.

When they find their prey, they snap them up with their long beaks.

Some people call estuaries the nursery of the sea, because so many species of fish and shellfish rely on their sheltered waters as safe places to spawn.

Estuaries are more than just places for plants and animals to live.

They also help control pollution.

Water from upland areas carry sediments and pollutants.

When this water flows through fresh and saltwater marshes, sediments and some pollutants are filtered out.

Plants and soils absorb flood water and storm surges, protecting upland areas.

Human development can damage or destroy estuaries.

Some pollution from upland areas can run off into estuaries and damage habitats, and dams can block natural stream routes in estuaries.

When stream routes are blocked, fresh water can't flow into the estuary, causing a change in the balance of fresh and salt water, which can harm the life living there.

People are working to stop pollution, helping to ensure that the estuaries continue to function as healthy ecosystems.

Maintaining the delicate balance of an estuary can be challenging, especially when something uninvited arrives.

Jessica and Daniel are going to spend a day in an estuary at the Wells Reserve, monitoring soft shell clams and green crab experiments with Caitlin Mullen and Lindsay Whitlow.

Music Now is your chance to get muddy.

Yeah.

Be careful with this first step.

It's a big one.

There you go.

There's a good one.

This guy’s a little more feisty.

He’s active.

Why are we doing this, and, like, what is, what happens to the crabs after they've gotten, like, scooped up?

Well, what we're trying to do is figure out what the crab population is like here in the little river.

When - This area is a really good place for clams to live.

So the crabs eat the clams?

Yeah, exactly.

Do the crabs eat fish too?

The crabs’ll eat just about anything they feel like.

They are omnivorous, which means they can eat plants and animals.

Okay, so you guys get a sense of what the crabs are actually going after, what we're trying to protect.

We’ll dig up a clam for you.

Do they try and hang on to the ground that they’re in?

No, that's another thing.

I mean, these clams are really not, not at all well adapted for any sort of predator that digs, whether it's a crab or us.

And so you can pull them right out.

So this is a soft-shelled clam.

And what you can see, this is the back end here where it's spitting at you.

The widest spines there on the top of the carapace are the two you want.

It's 51.3.

The shell’s really thin and brittle.

So if the crab can get it out, it can eat it, no problem.

And not really depending on the size of the crab, that a small crab - You can see that the two sides of the shell don't even close all the way.

And so you could just pick the meat right out.

Good crab, That's a good crab.

Flip it over.

He's a male.

Which claw’s bigger?

That one, the left.

Clams are important in the community.

Not only for, you know, people like us to eat them but they also, they filter a lot of the algae and stuff that'll build up whenever you have nutrients that come in from any sort of outflow from farms or things like that.

Filter feeders do a lot of important cleaning of the water, and so if we lose a lot of the clams, then our water may not be as clean as it once was.

So what's going to happen to the clams?

Well, a lot of that has to do with education and awareness in our communities and getting, getting this knowledge out there.

And even though there aren't any native predators here on the crabs anymore, hopefully the clams will be able to survive.

The more we learn about crab biology, the more we learn about clam biology.

Thanks a lot for your help today, guys.

Good day.

Thank you.

What have we learned today?

Marine communities are found in the salt water of oceans and estuaries.

Oceans are the largest environments on Earth, and they support a huge variety of life.

Conditions like the amount of salt, water pressure, temperature, sunlight, and water movement all help determine the type of life found in an aquatic community.

Now you know how nature works!

Music Theme Music Major funding for Nature Works was provided by American Honda Foundation.

Additional funding was provided by Alice Freeman.

Muchnic, Alice J. Reen Charitable trusts, Cogswell Benevolent Trust, the Finisterre Fund, Greater Piscataqua Community Foundation, Morgridge Family Trust, the Natural Areas Wildlife Fund, Rawson L. Wood.

Support for this episode of Nature Works provided by Greater Piscataqua Community Foundation.

Alice Freeman Muchnic, Laudholm Trust.

(animal sounds)