Science and society: Eels point to suffocating the Gulf floor

Eerie eel by moonlightNormally slum dweller settlements including the eel has been spied on the surface of the Gulf in July, escaping, suffocating bottom waters.N. Rabalais/LUMCON

In June, scientists predict that the annual Gulf of Mexico dead zone-the region's underwater where the water contains too little oxygen to preserve life — may turn into the biggest ever. In fact, not uncommon. Due to the fortuitous arrival of stormy weather, the dead zone that year debuted on approximately 6,800 square miles, the researchers report Aug. 1 — large, but far from the behemoth record 9,500 square miles that were mentioned explicitly as soon as possible.

This is a good message. The bad: a substantial part of the Gulf region affected should not be so low in oxygen, but practically ornamentu it from the surface to seafloor. And researchers literally could smell problem, not Nancy Rabalais, Executive Director of the Louisiana universities marine Consortium, based in Chauvin. In the case where the loss of oxygen occurs at seafloor sediment, she reports, gurgles up hydrogen sulfide — gas, which transfers the egg to the rotten stench.

It was not the only character environment very perturbed.

As in previous years and her colleagues spent Rabalais time at sea this summer mapping an oxygen level (see below) from different depths of North Bay. In July, the long walk Rabalais witnessed eels swimming at the surface. Usually they live in the sediment of the Gulf. Some crabs living in seafloor also propelled each tens of feet to the surface to avoid suffocating.

Bay in 2011 dead zoneDark red represents the area of the Gulf, and the place where Dead Zone July--a region with less than 2 parts per million (2 mg/l) of dissolved oxygen--expanded.N. Rabalais/LUMCON

"I have seen the brown shrimp (not on this cruise) is the same. They live in the mud, as well as ' he says. And for them to fly up to 65 feet to avoid suffocating bottom waters, desperate, he says, because they would have been an essential food all along the way.

Such monuments are evidence of the validity of the depletion of oxygen, or hypoxia, developed in some regions this year, the dead zone waters. As the concentration of oxygen in the seafloor approach zero, chemistry including sediment water interface transfers, releasing hydrogen sulfide. This is a double whammy for aquatic life, explains Rabalais: not only is there little or no oxygen present, but hydrogen sulphide may itself to kill organisms that cannot fly away.

Even those that can be moved may develop subtle reproductive toxicity, Rabalais adds, pointing out at work by Peter Thomas, University of Texas at Austin Marine Science Institute, its in port Aransas.

His team began studying croakers, a genus of fish that may be living in the waters of the depleted of oxygen. Initially, the team reported absence of spawning-because the affected croakers lacked mature eggs or sperm. Recently, Rabalais notes, his band "showed that low oxygen has led to some changes in sex in the croakers, who live in the area — turning females males."

Links for farm runoff

Dead zones require two-factor usposabiajacy: a surfeit of nutrients and the stratification of water on two solid, unmixing zones. Whether Rabalais the Mississippi River is responsible for both, explains.

Provide a spring of fresh water, which is less dense than brine, can lead to stratification of the water. The river also deposits of fertilizer — mainly nitrate — who the source of growth of algae and phytoplankton. According to these organisms die, their bodies instilled into the lower zone and decompose. But the microbes responsible for the degradation of oxygen consumption, which, owing to the separate layers of water by levels of salinity, will not easily become completed. This leads to a growing loss of oxygen at depth. If the situation through long enough oxygen can be found of water, practically to the surface.

Excessive flooding this spring, upper Midwest and years fueled the Gulf with fresh water and nitrogen, so the anticipated dead zona Monster. However, along the Don, Invest, in July (it made landfall in Texas 29). The oxygen-rich monk churning butter whisked surface waters to depths suffocating, limiting growth and ultimate size of this year, Dead Zone, Rabalais said.

But this has not been jeopardised, Anna adds. I also quite lucky because the evidence is building is an indication of "the Gulf is becoming less resistant to impurities of nitrogen," she observes. Over time, is made of smaller nitrogen inputs to create large areas of low oxygen. And "this is clearly not good news," he says.

Found in: Chemistry, Ecology and environment

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