June 6, 2010 Thousands of barrels of oil are leaking out of the Deepwater Horizon site each day. The oil ascends from depths of approximately 1502 m. (4928 ft.), but not all of it reaches the sea surface. The stratified seawater of the Gulf of Mexico captures or slows the ascent of the oil, and the addition of dispersants near the oil source produces tiny droplets that float for a considerable time in the water column and may never reach the surface.
According to Drs. Gregor Eberli, Mark Grasmueck, and Ph.D. candidate Thiago Correa of the Marine Geology & Geophysics division of the University of Miami (UM), the oil that remains in suspension in the water column and creates plumes poses a serious risk for the planktonic and benthic (sea floor) life throughout the region, including the deep-sea reefs they study.
"The deep water communities within the Gulf of Mexico and in the Straits of Florida are well hidden from us, but they include many species of cold-water corals that live in water at depths of 600 -- 1500 m. (1969 -4921 ft.) in waters as cold as 3° Celsius (37.4°F)," said Eberli. "Unlike their more familiar shallow-water counterparts, these corals do not live in symbiosis with unicellular algae called zooxanthellae, but are animals that feed on organic matter floating through the water column. We know that most of the food consumed by the cold-water corals is produced in the surface waters and eventually sinks down to the corals."
The large plumes being created by the oil spill, some of which are reported to be several miles long, sit in the water column situated between this source of food and these deep-water corals. As organic material sinks through the water column it passes through the oil plumes and is contaminated by micron-sized oil droplets.
"It is most likely that the delicate cold-water corals are not able to digest these oil-laden food particles and will perish in large numbers," said Eberli. "We are especially concerned because the migrating oil plumes have the potential to destroy or greatly diminish these deep-sea coral communities as they are carried by the currents. These corals are important because they are the foundation of a diverse ecosystem that at last count includes over 1,300 marine species, according to Dr. Thomas Hourigan at NOAA."
There is also a danger that these plumes are carried by the Loop Current from the Gulf of Mexico to the Atlantic Ocean. Deep-sea coral ecosystems are common at numerous sites from the eastern Gulf of Mexico through the Straits of Florida and northward to the Blake Plateau off North Carolina. This distribution matches the path of the Loop Current that forms from the water masses in the Gulf of Mexico, and enters the Straits of Florida to form the Florida Current and further north the Gulf Stream.
Particularly vulnerable to disturbance are deep-sea fish that form part of this ecosystem because of their late maturation, extreme longevity, low fecundity and slow growth. Deep-water coral reefs in Florida waters are the habitat of the economically valuable grouper, snapper and amberjack. These and other species inhabit hundreds of deep-water coral reefs off the coast of Florida at depths of about 300 -915 m. (1000 to 3000 feet), which were explored by Dr. John Reed from Harbor Branch Oceanographic Institute some thirty years ago. This includes the 59,500 sq. m. (~23,000 sq. mi.) of deep-water reefs off the east coast of Florida, which is now proposed as the Oculina Habitat Area of Particular Concern.
There is no known technique to clean the water column from these oil plumes, and as a consequence the hidden oases of corals in the deep, cold waters of the Gulf of Mexico, the Straits of Florida and the Blake Plateau are in severe danger of being decimated by this oil spill.
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The above story is based on materials provided by Rosenstiel School of Marine & Atmospheric Science, University of Miami.
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