Ancient Black Coral in the Gulf of Mexico

Black corals are a group of deep water, tree-like corals related to sea anemones. Though black coral's living tissue is brilliantly colored, it takes its name from the distinctive black or dark brown color of its skeleton. For the first time, scientists have been able to validate the age of deep-sea black corals in the Gulf of Mexico. They found the Gulf is home to 2,000 year-old deep-sea black corals, many of which are only a few feet tall. These slow-growing, long-living animals thrive in very deep waters—300 meters (984 feet) and deeper—yet scientists say they are sensitive to what is happening in the surface ocean as well as on the sea floor.


"The fact that the animals live continuously for thousands of years amazes me,”� said Dr. Nancy Prouty of the U.S. Geological Survey Pacific Coastal and Marine Science Center, who analyzed the coral samples that were collected by the USGS and colleagues as part of several ongoing deep-sea coral ecosystem studies between 2003 and 2009. “Despite living at 300 meters and deeper, these animals are sensitive to what is going on in the surface ocean because they are feeding on organic matter that rapidly sinks to the sea floor. Since longevity is a key factor for population maintenance, recovery from a disturbance to these ecosystems, natural or man made, may take decades to centuries."

Reliably age dating the corals, as done in the recent study, is a critical step in using them as natural archives of environmental change.

Like shallow-water coral reefs, deep-sea coral-reef ecosystems are among the most diverse and productive communities on Earth, providing shelter and feeding grounds for commercial and non-commercial fish species and their prey, as well as breeding and nursery areas. Activities that affect both the seafloor and the surface ocean, such as certain methods of petroleum exploration and commercial fishing, can impact these ecosystems.

The skeletons that these animals secrete continuously over hundreds to thousands of years offer an unprecedented window into past environmental conditions. Age dating used in combination with emerging technologies, such as sampling skeletal material with a laser to determine its chemical composition, enables scientists to reconstruct environmental conditions in time slices smaller than a decade over the last 1,000 to 2,000 years.

Black corals grow in tree- or bush-like forms. Scientists confirmed that black corals are the slowest growing deep-sea corals. They grow 8 to 22 micrometers per year as compared to the shallow-water reef-building coral, typically found in tropical areas like Hawaii, which grows about 1 mm per year, or 65 times as fast as black coral. Human fingernails grow about 3 mm per year, or 200 times faster than black coral.

Black corals can capture and record in their skeletons the history of changing concentrations of carbon in surface waters and the atmosphere. Unlike the skeletons of most shallow-water corals, which consist of calcium carbonate, black coral skeletons are composed mainly of organic matter: successive layers of protein and chitin (a long molecule containing carbon, oxygen, hydrogen, and nitrogen) glued together by a cement layer. These skeletons are very similar to insect cuticles in that they are quite flexible and can thus bend in water currents.

Like trees, black corals exhibit radial growth, with the oldest skeletal material found in the center and successfully younger material building out toward the edge. Viewed in a horizontal cross section, the black coral’s growth bands resemble tree rings.

In 2008 some black coral off the coast of Hawaii was found to be as old as 4000 years. Located on the floor of the Pacific Ocean, off Hawaii, the 3 meters tall, (extremely) long-lived "black coral" could yield some valuable clues about past incidents of climate change; specifically, it could better scientists' understanding of how oceans draw down carbon dioxide - and of ocean acidification in general. Brendan Roark of Texas A&M University, had led a research expedition in 2006 to study the corals' climate records.

A full copy of the present study can be found online in the Feb. 10, 2011, edition of “Marine Ecology Progress Series.”

Source: www.enn.com