Texas Parks & Wildlife Magazine   


Dead Zone

When fertilizer-laden runoff from the Mississippi River empties into the gulf, algae thrives — and marine animals die.

By Wendee Holtcamp

I'm in the middle of the Gulf of Mexico on a modified shrimp boat, the R/V Sabine Lake, and a trawl net's worth of ocean catch has just been unceremoniously dumped on board. A pile of slimy, silvery things squirm and flip around a square tray, but the large iridescent eyes of a dozen or so little squid enthrall me. I watch as small dots on their whitish-clear bodies pulse and expand as they turn rust-red. The pulsating dots are called chromatophores, TPWD biologist Kirk Blood tells me as he picks through the catch, counting and measuring each organism.

We've arrived at the first stop of eight on an all-day research excursion. Rain or shine, wind or waves, the TPWD upper coast fisheries biologists take this trip twice monthly and year-round to sample a 300-square-mile wide region of the gulf for sea creatures and water quality. If the weather doesn't cooperate, the crew roughs it in sloppy seas under the careful guidance of Captain Robert Martinez Jr. — who is with us today. They haven't missed a sampling in 23 years.

"Catch data for these different species helps us judge whether these organisms need special attention through regulation changes," Terry Stelly, TPWD ecosystem biologist, explains. "Our samples are for fishery management, but we do encounter the dead zone in our routine sampling."

The dead zone? Is that like the Bermuda Triangle? The Dragon's Triangle? Area 51? Being the mildly paranoid seafarer that I am, I already fear the Perfect Storm arising from nowhere, and now we are talking about a dead zone? And then out of nowhere, Captain Martinez asks if I brought a banana on board. He looks worried. "No," I say, "I ate one this morning, though. Why?"

"Every time someone brings a banana on board, we have bad luck."

Winds have picked up, turning glassy seas to 3-foot swells, and there's a dead zone? Maybe I have banana remnants on my pants. I put on a brave face, and even though not a single cloud mars the blue sky, I swallow a Dramamine just in case.

It turns out the dead zone cannot suck our boat into the watery abyss, but as for sea creatures, they are not so lucky.

"From the Mississippi to the Sabine River, you have an area of essentially dead water on the bottom," Blood says.

Also known as a zone of hypoxia, the dead zone is an amoeba-like blob of oxygen-deprived water that stretches down the Louisiana and Texas coastline and has blighted the Gulf of Mexico for at least the past half-century. Hypoxia sounds like a Harry Potter killing curse to extinguish ocean life — Hypoxia kedavra! A pox on your ocean! A pox on your fish! All those things that lie on the ocean floor — your clams and sea stars and polychaete worms and freakishly colored nudibranchs — death to them all! And that is pretty much what it means.

Water containing less than 2 milligrams of oxygen per liter of water is considered hypoxic and can not support life.

"Species that are not fast enough or mobile enough, perish," Blood explains. He's been working with TPWD for 13 years, and has seen this firsthand. Ocean organisms that can swim will leave the area if they can swim fast enough, but if the low-oxygen zone lasts too long, ocean-floor creatures have no options. They die. "If this persists, you can lose whole species that are endemic and live in just this specific area."

We motor on to the next few sampling locations in the gulf, and in each one, the crew collects water on the ocean floor using a "water catcher" — a tube that snaps shut once it reaches the bottom. They test the water for salinity or saltiness, turbidity or cloudiness, temperature, and dissolved oxygen which reveals whether or not they have entered the dead zone — even though the main purpose of their research is to help govern TPWD regulations on fisheries — the shrimp, crab and finfish fisheries.

At each stop the guys also throw a 20-foot trawl net overboard which sinks to the ocean floor some 12 to 39 feet below. Martinez then motors the boat in a straight line for about a half-mile. Next, they haul the trawl net back on board and dump everything out. Catch after catch on our eight stops, we find shrimp galore.

"This is the Bubba Gump shrimp boat," Martinez says with a laugh. He rattles out the names: white shrimp, brown shrimp, pink shrimp, mantis shrimp, broken-back shrimp and seabob shrimp. We also catch some cool and creepy creatures, including blue crabs, longnose spider crabs, pink purse crab, Florida lady crab, a brittle star, sand seatrout, croaker and lookdowns — thin fish whose eyes make them appear they're looking down. But the coolest catch besides the squid? Bighead searobins — which have huge fins and fingerlike rays which they use to walk along the sea floor.

Blood recalls fondly a vivid experience that catalyzed his love of the sea when he was just 15. "My dad took me out and we were diving off a rig," he says. "I saw a whole school of lookdowns and I was like, 'wow' and then they disappeared! They're about 1 centimeter wide so the whole school looks like it disappears when they turn. Then I couldn't find my dad or the rig." He headed to the surface and had to swim against strong current to make it back. But his appreciation for marine life has never waned. He's not the only one. Martinez keeps repeating how much he loves it out here at sea.

There's so much life squirming on board after each trawl that I start to wonder if that gulf dead zone really exists. "Our critters and our data are being affected. Sometimes we're not catching anything at all," says Stelly. "When we take those measurements at the bottom, many times in the month of April through about September or so, we end up getting [oxygen] values right near two, sometimes less than two." Apparently, the dead zone can last up to six months out of the year, but doesn't typically appear during winter months. That explains why we're catching critters in February.

The dead zone's seasonality became a vital clue to determining its cause. Although first documented in the 1970s, scientists have systematically studied and mapped the phenomenon only since 1985. They soon discovered that fertilizers applied to America's breadbasket — the farm belt that stretches across the Great Plains — were affecting the ocean thousands of miles away. The fertilizers get washed off the land during rainstorms, drain into the Mississippi and out into the Gulf of Mexico. Major landscape changes over the past two centuries, including deforestation, development and concretization, have increased the volume of water flowing into the Mississippi River by 20 to 30 percent, and as the largest river in North America, the Mississippi watershed drains 41 percent of the contiguous United States. The loss of coastal wetlands further exacerbates the problem, because they otherwise would allow some of the nutrients and fertilizers to settle out before reaching the ocean.

Fertilizer-laden river flow contains nitrogen- and phosphorus-based compounds, and once this water enters the bay, it spreads out and "fertilizes" naturally occurring ocean algae. The algae explode into riotous blooms at the sea surface. These algae blooms actually produce oxygen through photosynthesis at the surface, but as algae cells die, they sink toward the ocean bottom where mass quantities of oceanic bacteria decompose them. This decomposition consumes so much oxygen that it depletes the ocean for thousands of miles, giving rise to a dead zone that follows currents down the coast.

Besides the fact that farmers apply fertilizer in spring, a couple of other factors cause the dead zone to occur during warmer months. Just as hot air rises, so also does warm water rise above colder water. In addition, fresh water is less dense than salt water so it tends to stay near the surface. The result? Warm, fresh, oxygenated water on top and cold, salty, oxygen-deprived water below.

"When you have these two layers, oxygen in the surface layer doesn't get down to the bottom," says Nancy Rabalais of the Louisiana Universities Marine Consortium and one of the world's leading dead zone experts. "Like a tequila sunrise cocktail, with layers of orange juice and grenadine, until you mix it up, the layers are going to be separate." Anything that churns up the ocean will bring some of the oxygen down below, reducing the size and extent of the dead zone, so whenever hurricanes and tropical storms sweep through, the zone shrinks.

Stelly tells me about how in 2005, Hurricanes Katrina and then Rita mixed up the gulf, decreasing the dead zone temporarily although it re-emerged after the hurricanes. But in December, when the TPWD crew normally would not catch many shrimp, they were catching boatloads. The most likely explanation, says Stelly, is that the temporary increase in oxygen caused by the hurricanes gave shrimp a small window in time needed to reproduce — so the crew caught an extraordinary amount in December.

The dead zone lasts up to six months of the year, but is that the extent of its damage? According to scientists, it affects the marine ecosystem year-round. Rabalais and her colleagues found dramatic declines in marine biodiversity and the total abundance of marine organisms in regions of the gulf affected by severe hypoxia. "A healthy community will have a diversity of fauna — snails and clams, plants, starfish, sea urchins, small shrimp that live in the sediment," says Rabalais. Within the dead zone, "none of those are there anymore. There's mostly small worms and bacteria."

Dead zones occur around the world, not just in the Gulf of Mexico. In 2004, the United Nations identified 146 such zones, ranging from less than 1 square mile to 45,000 square miles in the Baltic Sea. Other dead zones around the United States include Chesapeake Bay and a new one off the Pacific Coast from California to Oregon, which scientists attribute to rising ocean temperatures due to climate change. Since warmer ocean temperatures cause more intense stratification and more algae blooms, climate change will inevitably intensify dead zone phenomena. Dead zones can reverse if steps are taken, but unfortunately sometimes the necessary actions are drastic. A massive dead zone in the Black Sea disappeared after the collapse of the Soviet Union made fertilizer use unaffordable.

So what, if anything, is being done to breathe life back into the gulf dead zone? An interagency Mississippi River/Gulf of Mexico Watershed Nutrient Task Force formed in 1997 and set a goal to reduce the dead zone to less than 1,900 square miles by 2008. But in 2007, it extended for 7,900 square miles, roughly the size of Massachusetts.

"There's not a concerted, well-funded effort to make a difference. That's what the task force is supposed to be doing," says Rabalais. "In 2001, the task force forwarded an action plan to [the president]. The five-year reassessment still isn't done. A lot of people call it the No Action Plan."

It's a basic tenet of ecology that you can't change one part of the web of life without affecting a dozen other parts. What happens in middle America affects organisms on the bottom of the sea, which have no say in the matter. We live on land, but we impact our oceans, and it is foolish to believe that our lives are unaffected by the state of our oceans. People make a living from shrimping or marine fisheries along the coast. People take their kids fishing in the bays and along the coast on weekends.

"The right solution is to try to figure out better land management. If you can get all the farmers on the same page for 3,000 river miles and all the tributaries, that's going to require major effort between different user groups to get this accomplished," says Stelly. "With the push for corn [for biofuel and ethanol], it's going to make the battle even harder."

And so, as we finish up our sampling in the eighth sampling spot and head toward shore, the beauty of the sun setting over the open ocean leaves a sinking feeling in my heart. Even though we caught some fascinating ocean creatures today, below those waves a dead zone has zapped the life from a large expanse of the gulf. At the present time, Texas does not serve on the interagency task force, and although the dead zone affects more of Louisiana's coastal water, it stretches into Texas waters every summer. Texans need to get involved in order to ensure that the marine life that has inspired awe in so many people — and indeed has led these biologists to dedicate their lives to sampling, studying and saving it — does not continue to decline, die and disappear.

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