In the first part of this series on how estuaries really work we talked a little about some of the magic involved.  It revolved around the presence in an estuary of three totally different and independent plant (producer) communities.  Actually, there are four, if you separate out the seagrasses from the drift algae community.

 

No other ecosystem on earth has this advantage.

 

Now it's time to talk a little about the power sources for the estuary.  And again, there is no other ecosystem on earth which has this combination of sources of power to drive life.

 

When biologists talk about the power that drives ecosystems, they start (of course!) with the sun.  It powers the magical biochemistry of photosynthesis which allows plants to store energy in a form animals can use, and it powers the plant communities of an estuary.

 

But there is another source of power available in estuaries which is not found in most other ecosystems.  The exception is the coral reef -- but the estuary uses this power in ways the critters of the reef cannot.

 

I'll let you wonder for a little bit, while I digress into food chains and webs, which are really energy relationships:  who eats who?

 

In the world of science, we recognize a pair of rules which work every time.  They are called the Laws of Thermodynamics (thermo = heat, dynamics = movement) and they describe how energy (heat) is moved through chemical reactions to produce life. 

 

The First Rule (and that's really what it's called) says "you can't get somethin' for nothin'."  In other words, you can't create energy from nothing.  A corollary to this says you can't destroy energy, either.  You can change it from one form to another, but you can't destroy it. 

 

The Second Rule says "Not only can't you get somethin' from nothin', you can't even break even."   In other words, any time you change energy from one form to another, most of the energy involved is lost (as heat).

 

Think about your car and the Second Rule.  You put gas in the tank, and then you burn it in the engine.  That's a change of energy from one form to another; In burning inside the engine, the gas allows the engine to power the wheels, which move the car.

 

Question:  When it is running, does your engine get hot?  WHY?  The Second Rule!

 

Now let's apply this idea of the Second Law to a living thing:  you.

 

How do you get the energy to play soccer?  Or to work out an algebra problem?  Or just to stay alive?

 

You eat, right?

 

Let's say your eat one pound of food per day.  Yeah, I know - some of you can eat that at just one meal, and you eat more than once a day.  But let's stick with just that one pound of food per day.

 

How much do you weigh?  And one year ago today, how much did you weigh then?  But in the meantime, you ate 365 pounds of food!  Do you now weigh 365 pounds more than a year ago?

 

So where did all that food-energy go?  Well, you lost some as sweat, a lot more to the toilet.  But even that doesn't add up to 365 pounds.  So where did the rest go?

 

Some of that energy you used in playing soccer or using your brain, but even that doesn't add up. 

 

What's your temperature?  And what does that have to do with food?  The Second Law, again.  Much of the energy we take in as food goes only to keep our body temp at about 37C (99F, give or take).  We here in the USA live in the temperate zone; it takes about 2500 Calories per day to keep us going.  If you were an Aleut or Inuit, though, living in extremely cold conditions, you would need at least 5,000 Calories per day just to stay alive (and keep your body temperature at +37C when it is -40C outside).

 

So what's all this stuff about the Second Law have to do with estuaries?

 

Only everything.  We're talking food, after all.  And that means food chains and food webs in the estuary.  And now things get a little complex; not a lot, just a little.  Remember that there are at least three, maybe four different communities of producers in an estuary, and that means that many more food chains and webs.  Just for example, a food chain involving mullet which feed at the roots of the grass beds would have no relationship to a plankton-based food chain which involves herrings, sardines and anchovies.  Except that a hungry predator won't really care whether it's a mullet or a herring; they are both food. 

 

Let's follow a food chain which starts with emergent plants:  cord grass in the temperate zone, mangroves in the tropics.  These plants live at the edge of the estuary, with their leaves in the air and their roots under water in the mud.  In both cases, the energy they store in their leaves, stalks and roots only becomes available when those parts of the plant die; year-round for mangrove leaves in the tropics, winter for cord grass in the temperate zone.  Once these plant parts actually die, they become available as stored food for other critters. 

 

Now we eat dead plant stuff, too.  I happen to love mashed potatoes, especially mixed with peas or green beans.  They've all been cooked before I eat them, so they are dead plant material.  And dead plant stuff is where this food chain begins. 

 

A mangrove leaf or a cord grass stem (leaves still attached) dies and falls to the mud.  Now what?

 

Well, that leaf or stem is stored energy from the sun.  It's FOOD!  And the first critters to take advantage of this energy source is a community of bacteris and viruses which begin their attack within minutes.  Soon - several days or weeks - that leaf or stem is covered with a slime coat of bacteria and fungi, and they in turn become food for the next set of critters up the chain.  These guys - amphipods, ostracods, isopods and more - graze their way across the surface of the leaf or stem, eating the slime coat of bacteria and fungi. 

 

So now this leaf or stem is covered with a bunch of things which are rich in proteins, carbohydrates, lipids (oils and fats) and nucleic acids, and new characters arrive to chow down.  These new guys include baby lobsters, shrimps of many species, crabs of many species - and they all carry a tool which they can use to cut a leaf up into manageable pieces.  They all have some kind of pincer claw. 

 

So they grow.  And soon other predators find them, and feast.  But remember what they are really feasting upon:  leaves and stems. 

 

What's the most common bait used by fishermen in an estuary?  Shrimp!  Not to mention small crabs and baby lobsters.  And how come those shrimp are there?  That food chain, powered by the sun. 

 

The last three steps in this food chain are easy to figure.  Little fish eat shrimp, bigger fish eat the littler fish, and I eat the biggest striper or snook I can catch -- and I don't share!

This food chain is typical of an estuary.  Let's compare it to a corn field.  Corn is used for two different purposes by humans.  We eat it as food, or we feed it to livestock.

If we eat it as food, it's a two-step food chain.  Sun (energy), corn, you (or me).  If we use it to feed livestock, then the chain is one step longer:  sun, corn, cow, me. 

 

But no other ecosystem on earth has food chains as long as those found in the estuary.  And that's part of the Magical Power of Estuaries.  The longer the food chain, the more steps it has, the more productive the ecosystem.

 

Uh-oh.  I told you there was a whole 'nother source of power for an estuary, other than the sun.  But I have not yet given you an answer to the question.  Can you make an educated guess?  And can you figure out why it's important to the estuary?

 

Test Lesson 5