Ocean Observing Tools Support Investigation of Mysterious Die Off in Flower Garden Banks SanctuaryAug 3, 2016 • 9:26 am
Since July, officials with the Flower Garden Banks National Marine Sanctuary (FGBNMS/NOAA) have been investigating the deaths of “unprecedented numbers of dying corals, sponges, sea urchins, brittle stars, clams and other invertebrates” on the East Flower Garden Bank (EFGB), one of two coral reefs within the sanctuary, located on the outer continental shelf about 100 miles off the Texas coast.
According to Emma Hickerson, FGBNMS research coordinator, and Steve Gittings, chief scientist in the Office of National Marine Sanctuaries: “Sport divers aboard the M/V Fling, diving in the Gulf of Mexico 100 miles offshore of Texas and Louisiana, were stunned to find green, hazy water, huge patches of ugly white mats coating corals and sponges, and dead animals littering the bottom on the East Flower Garden Bank, a reef normally filled with color and marine life. The reef, which is part of Flower Garden Banks National Marine Sanctuary, is considered one of the healthiest anywhere in the region.”
To assess the extent of the water quality problems and potential factors, Hickerson and Gittings reached out to a team of scientists, including Frank Muller Karger, Director of the Institute for Marine Remote Sensing (IMaRS) at the University of South Florida, a GCOOS Member and data provider.
The IMaRS team immediately analyzed a month of satellite data for the northern region of the Gulf of Mexico and compared it to previous years. They identified a highly unusual offshore movement of coastal water that affected the Sanctuary throughout much of July.
Water quality satellite images are an integral dataset that are being integrated into a new portal that is part of the Marine Biodiversity Observation Network (MBON). The MBON is a partnership between the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), the Bureau of Ocean Energy Management (BOEM) and the U.S. Integrated Ocean Observing System (IOOS). GCOOS is a partner in the MBON, along with the Sanctuary program, the University of South Florida, and the Florida Fish and Wildlife Research Institute.
The divers who first spotted the die-off on EFGB buoy No. 4 reported their findings to NOAA and BOEM scientists who were conducting long-term monitoring just 900 feet away, on EFGB buoy No. 2, where the corals were unaffected by the mortality event.
The comparison images provided by IMaRS show the NASA MODIS Chlorophyll-a (Chl) product “climatology” (June-July 2003-2010) vs. some of the MODIS Chl- individual passes collected between June and August 2016. The images were created by Digna Rueda Roa and Frank Muller-Karger in the IMaRS lab for the regional MBON effort being undertaken in conjunction with the Office of National Marine Sanctuaries, including the FGBNMS and the Florida Keys National Marine Sanctuary.
The images were used by the FGBNMS and Texas A&M University’s Geochemical and Environmental Research Group to plan a rapid response research trip to investigate the Sanctuary die-off at the end of July. In the images, the location of the East Flower Garden Bank portion of the Sanctuary is marked with a red star and the areas with chlorophyll higher than 0.5 mg/m3 are masked in white.
According to IMaRS Director Dr. Frank Muller-Karger, the satellite chlorophyll concentration image is a very good tracer of land discharge and coastal waters, especially as the plume from the Mississippi River and coastal waters disperses. Typically, chlorophyll concentration offshore in the Gulf of Mexico during summer is very low (less than 0.1 mg/m3). Coastal values can be much higher, between 1-10 mg/m3, especially off the delta of the Mississippi River and the mouths of the various estuaries in the region.
“Typically for this time of the year, the FGBNMS is near the edge of the coastal water plume,” Muller-Karger said. “The FGBNMS area gets some brackish water but is not totally immersed in it. This year, from June 22 through August 1, the East Flower Garden Banks had a sustained presence of high chlorophyll. The coastal plume is particularly affecting the East Flower Garden Bank. This has been an ongoing issue.”
The normally high chlorophyll concentration along the coast of the Louisiana-Texas coast are accentuated by the heavy rains in the Texas, Louisiana and Mississippi watershed over the past several months, Muller-Karger said. What is most unusual is the large inflow of fresh water moving offshore from this region, carrying this water over the reefs. Winds and ocean circulation patterns have pushed the water farther offshore than is typical.
“That means the corals in the Sanctuary have experienced several anomalies for an entire month, including lower salinity and higher turbidity — which means they’re getting less light and the deposition of more organic matter. This also means exposure to higher bacterial counts created by the decay of the organic matter and most likely hypoxic (low-oxygen) conditions. It is possible that part of the coastal hypoxic zone that develops west of the Mississippi Delta every summer also moved offshore with this massive offshore movement of coastal waters.”
Researchers are now engaged in a large collaborative effort investigating potential causes for the mortality event, which could be caused by poor water quality, disease pathogens or chemical spills. Sanctuary officials say no known spills have occurred.
Banner photo courtesy of FGBNMS/G.P. Schmahl.