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USF Marine Scientists Analyze Mysterious New ‘Death Zone’ in Northern Gulf of Mexico

Green hazy water, white coatings on coral and sponges causing die-off on reef usually full of color and active marine life.

TAMPA, Fla.  (Aug. 16, 2016) – University of South Florida (USF) College of Marine Science researchers are working with the federal government, colleagues at Texas A&M University and Roffer's Ocean Fishing Forecasting Service to search for answers about why marine life is unexpectedly dying on a normally colorful and vibrant coral reef in the Gulf of Mexico, 100 miles off the shores of Texas. So far, the culprit appears to be an unusually large amount of turbid coastal water, which was identified by satellite imagery and analyzed by USF marine scientists.

A huge patch of hazy green water, dead marine life and corals covered by a strange, thick white coat, were first noticed by sport divers in the area known as the East Flower Garden Bank, near buoy number four on the outer continental shelf off Texas.  The region, part of a National Marine Sanctuary, is generally considered one of the healthiest coral reefs in the Gulf.  The divers notified the National Oceanic and Atmospheric Administration (NOAA) and the Bureau of Ocean Energy Management (BOEM), which then alerted the U.S. Integrated Ocean Observing System (IOOS).  

These federal organizations are working on various other projects with Dr. Frank Muller-Karger, professor of biological marine science at USF and director of the USF Institute for Marine Remote Sensing (IMaRS), and asked the university to help identify the causes for the sudden die-off of marine creatures in the sanctuary.  The objective of IMaRS is to provide a better understanding of the world’s oceans, specializing in coastal processes of highly variable regions such as the Gulf of Mexico.  The Institute has been collecting and analyzing satellite images of marine areas, including Cuba, Mexico, and the USA since the late 1970’s.

“A quick search through our satellite image archives shows that this is a very unusual event for the Flower Garden Banks. There seems to have been a similar episode captured in pictures taken by a NASA satellite in 1979, but nothing like what we saw in July and early August has happened since then,” said Muller-Karger.

When the USF IMaRS team, which also includes USF postdoctoral research associate Digna Rueda Roa, reviewed satellite data for the affected region in the northern region of the Gulf, and compared recent images to thousands of images collected in this area in previous years, they identified a highly unusual offshore movement of very turbid coastal water that impacted the area throughout July and the first week of August. 

According to Muller-Karger, at this time of the year ocean water near the affected area can have some turbidity coming from as far as the Mississippi River.  In this region the chlorophyll concentration, an index measured by satellite cameras, is generally low. Not this summer, however.

“This year, from June 22 through August 1, the East Flower Garden Banks have experienced a sustained presence of very high chlorophyll,” explained Muller-Karger. “This is an indication that the coastal plume is particularly strong and is affecting the area.”

The Louisiana and Texas coast have seen heavy rains in the last few months and an unusually large inflow of fresh water moved offshore covering a very sizeable area of the northern Gulf, carrying the water over reefs. Winds and ocean circulation patterns have pushed the water farther offshore than is typical and the corals in the Sanctuary have experienced low salinity and high turbidity, which means they are getting less light and more organic matter deposited than normal. 

“My suspicion is that what we see at the surface is also an indication that the large area of low dissolved oxygen that forms every summer of Louisiana was much larger this year and that it stretched along the coast of Texas, and all this water was pushed offshore in this unusual pattern,” said Muller-Karger. “The unusual pattern also means that bacteria from decaying organic matter are present. This helps to create a low oxygen, or hypoxic, environment that can suffocate and kill marine life on the reefs.”

According to a report by NOAA, twelve miles away from the affected area reefs on the West Flower Garden Bank “remain vibrant, bathed in clear blue water and free of the problem, for now.”

NOAA has recommended that the public avoid diving, fishing and boating in the region.

As many questions remain unanswered, Muller-Karger and colleagues are conducting a study to see if anything similar has occurred in the past and to find a more definitive cause to explain the event.

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