According to predictions made by a team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University, and the University of Michigan, the Gulf of Mexico “dead zone” is likely to become record big this summer. If there predictions are true, we will see a dead zone the size of New Jersey (7,450 to 8,456 square miles). Additional flooding of the Mississippi River since May can however increase these numbers even further.

What is the Gulf of Mexico ‘dead zone’?

The dead zone is an area off the coast of Louisiana and Texas in the Gulf of Mexico where the oxygen level seasonally drops so low that most life forms living in and close to the bottom dies.

Dead zones are the result of large amounts of nutrients reaching the water, e.g. through waterways polluted by sewage and agricultural runoff. The excess nutrients stimulate rapid and massive algae growth in the affected area, a so called algae bloom. When the algae die, they sink to the bottom where oxygen dependant bacteria begin to break them down. The decomposition process consumes vast amounts of oxygen and soon the bottom and near-bottom waters become so oxygen depleted that all sorts of oxygen breathing organisms begin to die. This so called hypoxic area (an area where the oxygen levels are low to non-existent) is not just a problem for wildlife; it can also damage the economy of nearby states since it destroys habitat necessary for commercial and recreational Gulf fisheries.

The largest dead zone on record appeared in 2002 and measured 8,484 square miles.

Mississippi and Atchafalaya Rivers too rich in nutrients

During April and May this year, the Mississippi and Atchafalaya Rivers experienced heavy water flows that were 11 percent above average.

“The high water volume flows coupled with nearly triple the nitrogen concentrations in these rivers over the past 50 years from human activities has led to a dramatic increase in the size of the dead zone,” said Gene Turner, Ph.D., a lead forecast modeler from Louisiana State University.

“As with weather forecasts, this forecast uses multiple models to predict the range of the expected size of the dead zone“, said Robert Magnien, Ph.D., director of NOAA’s Center for Sponsored Coastal Ocean Research. “The strong track record of these models reinforces our confidence in the link between excess nutrients from the Mississippi River and the dead zone.”

Hundreds of thousands of tourists visits Green Island each year to enjoy scuba diving and snorkelling among its beautiful reefs, but no sewage treatment exists so an average of 1,500 tons of untreated sewage is flushed into the sea on a daily basis.

According to The China Post , no sewage treatment project has been prepared for the island since land can’t be procured for a sewage plant. Researchers now fear that the untreated sewage is to blame for the spread of the so called “Black Death” among the corals.

Chen Jhao-lun, a senior research fellow at the Academia Sinica who has studied the coral
reefs, describes the affected colonies as being covered slowly with a piece of black cloth.
“As this black sponge which multiplies itself covers the colonies, it shuts off sunlight to stop
photosynthesis by coral polyps,” Chen explains. The polyps die and no new corals are formed.

The “Black Death”, a type of necrosis, typically manifests in the form of black lesions that gradually spread across the surface of an infested colony.

However, very little is known about the Black Death and some researchers think that other factors, such as changing water temperatures or overfishing, might be to blame – not the untreated sewage. It is also possible that a combination of unfavourable factors have tipped the balance of the reef, causing the disease to go rampant. Temperature does appear to be a key variable associated with outbreaks, but it remains unknown if a temperature change alone is capable of causing this degree of devastation.

Molecular studies on lesions have not been able to identify a likely microbial pathogen, and according to Chen, the black layer might actually be an opportunistic second effect rather than the causative agent of the coral mortality. Montipora aequituberculae corals seem to be especially susceptible to the disease, but at least five other coral species from three different genera have been affected as well.

When Chen surveyed the water of Green Island last year, only four colonies off Dabaisha or Great White Sand showed signs of Black Death. In April this year, Chen found 24 affected colonies – six times as many as last year. If nothing is done to remedy the problem, Great White Sand near the southernmost tip of Green Island may have only dead colonies in five to six years, Chen predicts.

Green Island
Green Island is known as one of the world’s best spots for scuba diving and snorkelling. Located roughly 16 nautical miles southeast of Taitung on east Taiwan, Green Island used to house a concentration camp for political prisoners. Today, it is instead famous for its rich coral reefs.

(The picture is not from the green island but rather the great barrier reef)