Treasures of the Laguna Madre Bay: On the Texas Gulf Coast, the Mother Lagoon, one of three hypersaline estuaries in the world, is causing scientists to re-examine what makes bays so productive.

On The Bay

January 16, 1998|By Tom Horton | Tom Horton,SUN STAFF

CORPUS CHRISTI, Texas -- If there's one thing I thought I knew something about, it is estuaries -- the bays, sounds, seas, fjords and lagoons that occur at the lap of land and oceans.

That includes Texas, whose coastline is favored with at least seven estuaries, and whose Department of Parks and Wildlife once sent a film crew to Maryland, for whom I expounded on the similarities between the Chesapeake and Galveston bays.

So it was a revelation, this month, to spend some time with Scott Hedges on another Texas bay that he promised would make me reconsider what I thought about such places, that in fact is causing scientists to re-examine what makes estuaries so incredibly productive.

Hedges manages coastal bird sanctuaries for the National Audubon Society along the length of the Texas Gulf Coast, and even if he didn't know so much about the outdoors, is my ideal host.

I am about 6 feet 6, and he is taller, so kayaks always have legroom, beds are always long enough, rearview mirrors in the truck never need readjusting, and borrowed boots are a perfect 14D.

Our venue was the Laguna Madre, or Mother Lagoon, which stretches 125 miles behind Padre Island National Seashore, from Corpus Christi almost to the Mexican border near Brownsville.

It is nearly unique among the world's estuaries, one of only three that are hypersaline. The only others are a sister lagoon of the same name that begins across the border in Mexico, and something called the Sivash, or "Putrid" Sea, in the Crimea in Ukraine.

Hypersalinity means a salt content greater than that of the oceans to which the Laguna Madre is connected. Historically, in droughts, it has been as high as 113 parts of salt per thousand parts of water (ocean water is about 34 parts per thousand), though salinities of about 40 to 60 are more common.

Though the Laguna Madre is nothing like most bays, it was in one respect like a trip back in time on the Chesapeake. Floating in rafts of several thousand, stretching half a mile or more, and thickly peppering the horizon as our skiff scared them up, were redhead ducks.

This classic North American diving duck was a fixture of Chesapeake winters until recent decades, when declining habitat virtually banished them from Maryland and Virginia waters.

The Laguna Madre and adjacent waters support close to 800,000 redheads, the bulk of the species' world population, which is estimated at 900,000.

There, it seemed, the similarities ended. "You will almost have to reorient your self to appreciate this place," Hedges said, as he led me across what appeared to be a wasteland, a vast expanse of waterless flats, scummed over with thick, leathery mats of algae.

The Laguna Madre has none of the lush tidal marshes that one associates with the Chesapeake and most North American coastal waters. It is too salty for salt marsh to grow, and virtually tideless.

Instead, it has these great, scummy mats of blue-green algae. From a distance, long reaches of the shoreline on the backside of Padre Island have a distinct, bluish cast, though up close it just looks brown.

But even here there is life. For more than an hour we watched one of the rarer sights in coastal bird-dom, a flock of reddish egrets, milling in circles, flapping their wings, herding minnows where the water edged up on the algae flats to no more than a few inches in depth.

These large, elegant egrets are the most restricted member of all the world's herons. Specialists that feed where few other birds do, they exist mainly on one type of minnow that ranges the Laguna, where most of their world population is centered.

The algal "wastelands" might also hold one of the keys to a paradox of the Laguna Madre that has long intrigued scientists -- why is the place so productive.

By most standards of what is known about estuaries, the place shouldn't work nearly as well as it does. It is the mix of fresh and salt, the inflow of abundant nutrients from rivers and marshes that makes estuaries such marvels of natural productivity.

The Laguna Madre has no marshes, and has virtually no river inflow. It is so shallow -- average depth about 3 feet -- that cold weather causes fish kills.

And yet, it produces half the commercial finfish catches of the Texas coast, even though it is only 20 percent of its estuarine acreage. It is host to nearly 400 species of birds in a given year, including vast numbers of waterfowl and wading birds. Two years ago, ornithologists trapped and banded nearly 800 endangered peregrine falcons migrating down the Laguna.

The algae that grows on the flats fixes its nitrogen from the air, and might be a primary energy source underpinning the Laguna's unexpected ability to support life.

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