Beyond the Reaches of Sunlight

It was 1843 when British naturalist Edward Forbes declared life in the ocean cannot exist below 300 fathoms (1800 feet).  Ten years later American naturalist Louis F. de Pourtales of the U.S. Coast Survey found indications of life in depths over 1000 fathoms (6000 feet).  It was 1867 when Louis F. de Pourtales found conclusive evidence of deep-sea life while conducing dredging operations off the southern coast of Florida.  Thanks to new technology and deep-sea submersibles we have discovered so much more about the ocean floor such as hydrothermal-vent communities, bioluminescent organisms, the Giant Squid, and deep-water corals.

At one time it was believed coral polyps only lived in the shallow-waters of the tropical regions of the world.  More than 250 years ago fisherman discovered evidence of coral living below the euphotic zone.  The past few decades scientists are discovering the true value of these deep-water corals as they explore below the euphotic zone of the ocean in their deep-sea submersibles.  Just recently scientists discovered an 85-mile stretch of deep-water coral off the coast of South Carolina.

Deep-water corals are also known as cold-water corals compared to the shallow-water or warm-water corals of the tropics.  Deep-water corals are found all over the world including Antarctica and have been found up to 20,000 feet below the surface of the ocean (that is more than 3 miles).  Deep-sea submersibles have discovered deep-water coral living in water as cold as -1oC (30.2oF).  Half of all known coral species in the world are from deep water.

Unlike their “cousins”, the shallow-water corals, deep-water corals do not have zooxanthellae which provide them food as part of a mutualistic relationship.    Deep-water coral obtains their energy needs by trapping tiny organisms and detritus (marine snow) as it drops from above and is passed along in the deep ocean current.  These sessile organisms can capture food floating by because they are fan-shaped and have increased their surface-area.

Besides providing habitat for important ecologically and economically fish, deep-water coral and the sponge communities they support may be a source of compounds for the development of new drugs and medical treatments.  The green Latrunculia austini sponge found living along side deep-sea corals contains molecules which specifically target and kill pancreatic tumor cells.

Deep-water corals are just as affected by ocean acidification as shallow-water corals.  Other threats to deep-water coral is bottom-trawling, mineral extraction, oil and gas exploration, and cable trenching.  One can imagine the damage done by bottom-trawling by observing what a forest looks like after they bulldoze the trees to put in a subdivision or shopping mall.

There is so much more we must learn about the deep-sea.  What will be discovered next and how will it benefit humans? 

Do you want to know more?