August 23, 2012 | 3
When the Mississippi River flows into the Gulf of Mexico, its odyssey doesn’t end. It enters an underwater valley called the Mississippi Canyon, a world where nutrients from the river nourish some fantastical forms of life. One part of this canyon looks like this:
The graceful white sculptures sprouting from carbonate outcrops are Lophelia coral. These corals are not the sort you may be familiar with from tropical reefs. They have no photosymbiont, or algal partner, to help them make food from light. Instead, Lophelia will eat much of what it can get its tentacles on — living zooplankton like chaetognaths, krill, tiny crustaceans, or even dead fish particles (Doesn’t sound so appetizing. Perhaps the coral prefers to think of them as “manna sushi”).
According to lophelia.org, the name Lophelia comes from the Greek “lophos” and “helios”, meaning “a tuft of suns”, which, in the image at left, I think you can see.
Living with them are brittlestars coiled like snakes around sea fans, black corals (which I wrote about here), sea pens, sea whips, squat lobsters, and urchins, feeding likewise on whatever passes within their grasp. I love how the jointed, robotic natural arms of that squat lobster foreshadow, in the very next shot, the robotic constructed arms of the ship we use to sample its world.
Lophelia is a part of the deep water coral community, one so pervasive and important that more than 50% of known coral species are found in such places. It was judged so important to some scientists that they created an entire website about it — lophelia.org — complete with an introduction from the great David Attenborough himself.
And recently, scientists on a NOAA project looking for Lophelia growing on the legs of oil platforms in the Gulf of Mexico — the same team that took the video of the Mississippi Canyon — discovered the deepest yet found in the Gulf, though not in the world, as cold-water corals are found around the world. Using ROV-mounted camera, scientists found Lophelia growing at 2620 feet on the Ram Powell platform, built in 1997. It is one of the deepest platforms in the gulf. The previous Gulf record was 2066 feet.
Unlike the glittering, turquoise tropical seas, coldwater corals live in perpetual darkness and frigid water colder than 12 C. In the Gulf of Mexico, Lophelia pertusa often occurs with Madrepora oculata, the delightfully and aptly named zigzag coral.
Both of them are scleractinian corals, which are known for making hard skeletons out of calcium carbonate — the white hard part of Lophelia — and for having tentacles in multiples of six. Lophelia is a primary reef-framework building species. It grows robust, bushy colonies.
Madrepora oculata grows finer branches on top of pre-existing Lophelia reefs, forming a secondary reef framework more hospitable to creatures who prefer their nooks and crannies to be nookier and crannier than those provided by Lophelia.
Although hundreds of tropical coral species can produce hard, extensive skeletons that form reefs, there are only six known cold-water corals that can do the same. That makes these particular species particularly important.
Because the age of oil platforms is known, scientists can take samples from corals found growing on them to calculate growth rates accurately and test the radiocarbon methods they have been using on corals of unknown age. Other manmade reefs — like this wreck of the USS Gulfpenn, sunk while carrying 90,000 barrels of gasoline by German U-Boat 506 on May 13, 1942 (there were U-Boats in the Gulf of Mexico? Wow!), are also of known age and can help with the task on a longer scale:
The NOAA scientists were part of the Lophelia II project, a four-year mission to study cold-water coral communities on oil platforms in the Gulf of Mexico to understand, in addition to their growth rates, their temperature tolerances and associated microbial communities, among other things.
But they also wanted to know about what scientists refer to as “gene flow” — essentially, interbreeding among distinct populations. On Lopehelia I, the scientists on this team collected samples of Lophelia from three different sites in the Gulf and determined they were interbreeding and dispersing across distances of at least 370 km.
These scientists wonder whether oil platforms might further increase that connectivity. Although oil and gas exploration also has the power to damage Lophelia populations — as do deep-sea trawl nets with metal doors and rollers that are drug along the bottom to harvest fish — it is possible that fortuitously-located platforms may help otherwise distant populations interbreed, increasing genetic diversity. That can help the coral survive environmental jolts from climate change or other disturbances. By studying the DNA of Lophelia found on rigs, they can find out if this is, indeed, happening.
To end, I’ll leave you with a few moments of zen in this video of a Lophelia community in the western North Atlantic, in a place called the Garden Banks, taken during the Lophelia I expedition. Watch for the closeup of Lophelia polyps at the end. Enjoy.