Scientists have even found deep-sea corals off the coast of Antarctica. For a long time, because deep-sea corals were so inaccessible, no one had any idea how many species existed. Now, by studying specimens collected on research expeditions, ocean scientists are starting to come up with a count.
Because so many species of deep-sea corals look alike, marine researchers may do DNA testing to confirm the results. So, how many species of deep-sea corals are there? It is still too soon to say because new species are continually being discovered. To date, however, more than 3, species of deep-sea corals have been identified. And the numbers keep climbing. Not only are deep-sea corals more diverse than ocean scientists ever imagined, they are also amazingly old.
According to scientific estimates, one particular colony of gold coral Gerardia sp. Marine researchers determined that another deep-sea coral colony in Hawaii—this one a black coral Leiopathes sp. These coral colonies are the oldest marine organisms on record. Due to the continuous regeneration of new polyps, some deep-sea coral reefs have been actively growing for as long as 40, years. And there may very well be even older deep-sea coral reefs or colonies out there—in Hawaii or elsewhere.
Deep-sea corals come in a virtual paint box of colors—yellow, orange, red, purple, and more. Their shapes are equally varied and include branching, fan-shaped, and feather-shaped forms, to name a few.
When it comes to size, the range among deep-sea corals is tremendous. Scientists have discovered single polyps as small as a grain of rice, tree-like coral colonies that tower as tall as 10 m 35 ft , and massive coral reefs that stretch for 40 km 25 mi. But the ocean is a vast realm.
There may be even bigger deep-sea corals out there still to be discovered. Invertebrates like worms, starfish, and lobsters as well as vertebrates like fishes depend on deep-sea corals.
The corals offer food, places to hide from predators, nurseries for juveniles, and a solid surface where invertebrates can take hold. Among the diverse species that depend on deep-sea corals are ones that are commercially important to humans—including shrimp, crabs, groupers, rockfish, and snappers.
Some organisms that live in deep-sea coral habitats produce chemicals that have enormous potential for use as new medicines. For example, scientists recently discovered that two sponges that grow in deep-sea coral ecosystems have compounds with anti-inflammatory and anti-viral properties.
A compound from another deep-water sponge, Discodermia dissoluta , displays potent anti-tumor activity against human lung and breast cancer cells. As deep-sea corals grow, they form layers or bands—similar to tree rings.
The chemical composition of the bands reflects the changing ocean conditions under which the corals formed. By measuring and examining the thickness of each band, marine scientists can estimate how much the corals grew during a given time period. This information sheds light on what ocean conditions existed during that period.
By conducting more complex analyses of deep-sea corals, ocean scientists can gather valuable information about changes in water temperature, nutrients, and ocean circulation over time. They are less tasty once they settle down and secrete a skeleton, but some fish, worms , snails and sea stars prey on adult corals.
Crown-of-thorns sea stars are particularly voracious predators in many parts of the Pacific Ocean. Population explosions of these predators can result in a reef being covered with tens of thousands of these starfish, with most of the coral killed in less than a year.
Corals also have to worry about competitors. They use the same nematocysts that catch their food to sting other encroaching corals and keep them at bay. Seaweeds are a particularly dangerous competitor, as they typically grow much faster than corals and may contain nasty chemicals that injure the coral as well. Corals do not have to only rely on themselves for their defenses because mutualisms beneficial relationships abound on coral reefs.
The partnership between corals and their zooxanthellae is one of many examples of symbiosis, where different species live together and help each other. Some coral colonies have crabs and shrimps that live within their branches and defend their home against coral predators with their pincers. Parrotfish, in their quest to find seaweed, will often bite off chunks of coral and will later poop out the digested remains as sand.
One kind of goby chews up a particularly nasty seaweed, and even benefits by becoming more poisonous itself. The greatest threats to reefs are rising water temperatures and ocean acidification linked to rising carbon dioxide levels. High water temperatures cause corals to lose the microscopic algae that produce the food corals need—a condition known as coral bleaching.
Severe or prolonged bleaching can kill coral colonies or leave them vulnerable to other threats. Meanwhile, ocean acidification means more acidic seawater, which makes it more difficult for corals to build their calcium carbonate skeletons. And if acidification gets severe enough, it could even break apart the existing skeletons that already provide the structure for reefs. Scientists predict that by ocean conditions will be acidic enough for corals around the globe to begin to dissolve.
For one reef in Hawaii this is already a reality. Unfortunately, warming and more acid seas are not the only threats to coral reefs. Overfishing and overharvesting of corals also disrupt reef ecosystems. If care is not taken, boat anchors and divers can scar reefs. Invasive species can also threaten coral reefs. The lionfish , native to Indo-Pacific waters, has a fast-growing population in waters of the Atlantic Ocean. With such large numbers the fish could greatly impact coral reef ecosystems through consumption of, and competition with, native coral reef animals.
Even activities that take place far from reefs can have an impact. Runoff from lawns, sewage, cities, and farms feeds algae that can overwhelm reefs. Deforestation hastens soil erosion, which clouds water—smothering corals.
Without their zooxanthellae, the living tissues are nearly transparent, and you can see right through to the stony skeleton, which is white, hence the name coral bleaching. Many different kinds of stressors can cause coral bleaching — water that is too cold or too hot, too much or too little light, or the dilution of seawater by lots of fresh water can all cause coral bleaching. The biggest cause of bleaching today has been rising temperatures caused by global warming. Temperatures more than 2 degrees F or 1 degree C above the normal seasonal maximimum can cause bleaching.
Bleached corals do not die right away, but if temperatures are very hot or are too warm for a long time, corals either die from starvation or disease. In , 80 percent of the corals in the Indian Ocean bleached and 20 percent died. There is much that we can do locally to protect coral reefs, by making sure there is a healthy fish community and that the water surrounding the reefs is clean.
Well-protected reefs today typically have much healthier coral populations, and are more resilient better able to recover from natural disasters such as typhoons and hurricanes. Fish play important roles on coral reefs, particularly the fish that eat seaweeds and keep them from smothering corals, which grow more slowly than the seaweeds.
Fish also eat the predators of corals, such as crown of thorns starfish. Marine protected areas MPAs are an important tool for keeping reefs healthy. Smaller ones, managed by local communities, have been very successful in developing countries. Clean water is also important. Erosion on land causes rivers to dump mud on reefs, smothering and killing corals. Seawater with too many nutrients speeds up the growth of seaweeds and increases the food for predators of corals when they are developing as larvae in the plankton.
Clean water depends on careful use of the land, avoiding too many fertilizers and erosion caused by deforestation and certain construction practices. In the long run, however, the future of coral reefs will depend on reducing carbon dioxide in the atmosphere, which is increasing rapidly due to burning of fossil fuels. Carbon dioxide is both warming the ocean, resulting in coral bleaching, and changing the chemistry of the ocean, causing ocean acidification.
Both making it harder for corals to build their skeletons. The coral collection housed at the National Museum of Natural History may be the largest and best documented in the world.
Its jewel is a collection of shallow-water corals from the U. South Seas Exploring Expedition of —one of the largest voyages of discovery in the history of Western exploration. The expedition brought back many unknown specimens that scientists used to name and describe almost all Pacific reef corals.
These are known as type specimens in the collection. Altogether, the collection includes specimens of about 4, species of corals , and about 65 percent of those species live in deep water. In the late s, several Smithsonian scientists set themselves an ambitious goal: understanding the inner workings of Caribbean coral reefs.
To study this complex ecosystem, they needed a field station where they could conduct research in one location, from multiple disciplines, over a long period of time. In they came across a tiny island with three shuttered buildings. It was the perfect spot. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank the Coral Reefs of the High Seas Coalition for providing invaluable support to this effort, and in particular A.
McGowern, A. Smith, A. Khoo, A. Hedlund, A. Miller, C. White, C. Hicks, E. Karan, G. Farmer, G. Cid, I. Irigoyen, J. Custopulos, J. Weller, L. Barrera, L. Van der Meer, M. Gianni, M. Wassum, M. Conathan, N. Clark, N. Ludlow, S. Earle, T. Thomas, T. Mackey, and W. Benchley for all their thoughtful contributions to this work. We further thank S. Cairns and B. Hoeksema for providing invaluable taxonomic guidance.
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