ENDANGERED CORAL REEFS
Elizabeth Kolbert wrote in National Geographic, “Coral reefs are already threatened by a wide array of forces. Rising water temperatures are producing more frequent "bleaching" events, when corals turn a stark white and often die. Overfishing removes grazers that keep reefs from being overgrown with algae. Agricultural runoff fertilizes algae, further upsetting reef ecology. In the Caribbean some formerly abundant coral species have been devastated by an infection that leaves behind a white band of dead tissue. Probably owing to all these factors, coral cover in the Caribbean declined by around 80 percent between 1977 and 2001. [Source: Elizabeth Kolbert, National Geographic, April 2011]
According to the Environmental Defense Fund, reefs in 93 of the 109 countries where reef are found have been damaged by human activity. A report by the United Nations estimated that 30 percent of the world's reefs have been damaged by human activity. Another report put the figure at 58 percent. Others sources have estimated that 10 percent of three world's reefs have been wiped out. A forth are regarded as degraded beyond recovery.
According to some pessimistic estimates if the pace of damage continues half of the world’s coral reefs might be lost by 2050 and another 30 percent could be seriously depleted. Optimists point out that coral reefs have survived more than 250 million years and disturbance and renewal is common among reef ecosystems and they are so vast and scattered they will survive.
In the Caribbean the amount of reef surface covered by live coral has fallen about 80 percent in the last three decades according to the Global Coral Reef Monitoring Network. In the Pacific Ocean between Hawaii and Indonesia, reefs have lost about 1 percent of their coral coverage annually over the last 25 years.
Some reefs corals that were bright purple are now dull brown. Groupers living there are 60 percent smaller than they were 50 years ago and their population has declined by 95 percent. As much as 20 percent of the world’s coral reefs have effectively been destroyed by pollution, overfishing, diseases and bleaching. In some places 90 percent of the coral reefs have been lost. A survey published in Science in 2008 found that half the coral reefs in U.S. territory are in fair or poor condition.
storm damaged coral Sources: Reefs at Risk a report by the World Resources Institute; the International Coral Reef Action Network; the Global Coral Reef Monitoring Network.
Websites and Resources: National Oceanic and Atmospheric Administration noaa.gov/ocean ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Ocean World oceanworld.tamu.edu ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Montery Bay Aquarium montereybayaquarium.org
Websites and Resources on Fish and Marine Life: MarineBio marinebio.org/oceans/creatures ; Census of Marine Life coml.org/image-gallery ; Marine Life Images marinelifeimages.com/photostore/index ; Marine Species Gallery scuba-equipment-usa.com/marine
Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Wikipedia article Wikipedia ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Coral Reef Pictures squidoo.com/coral-reef-pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.
Hurricanes and Other Natural Threats to Coral Reefs
Corals and reefs are very sensitive. Water that is too muddy, warm, salty or fresh will kill them. Natural threats to reefs include warm waters produced by the El Niño climate phenomena, storms such as typhoons and hurricanes, too much plankton, polyp-eating predators like the crown of thorn starfish and diseases.
Researchers from NOAA have suggested that hurricanes and typhoons may actually be beneficial to coral reefs in the face of global warming as they long as they don’t strike the reef directly with heavy damaging waves. The logic behind the idea is that winds mix cold deep water and warm surface water, reducing the temperature of the damaging water around the reef that is too warm. NOAA researchers studied two bleached coral reefs—one in the Florida Keys and another in the Virgin Island. The one in the Florida Keys rebounded after the passing of Hurricanes Rita and Wilma in 2005, while the one in the Virgin Islands, which was not affected by any hurricanes, did not.
Human Threats to Coral Reefs
diseased coral Reefs are threatened 1) global warming; 2) pollution caused sewage and fertilizer; 3) coral mining; 4) industrial and agricultural run off; 5) sediment from deforestation; 6) dredging of harbors and channels; 6) the use of poisons and dynamite by fishermen; 7) commercial fishing; 8) sport fishing, scuba diving and tourism; 9) sediments from coastal development; and 10) the commercial exploitation of fish, corals, giant clams and other species.
If too many grazing fish are caught, algae grows unchecked and the coral polyps are deprived of sunlight. Careless thrown anchors and misplaced hands or fins day after day by scuba divers and snorkelers can also seriously damage fragile corals. Once destroyed by a carelessly tossed anchor, a reef needs 20 to 30 years to repair the damage.
Sediments from erosion block life-sustaining sunlight, choke the pores of sponges and causes corals to weaken and be overpowered by algae. Nitrogen and phosphorous from fertilizer causes suffocating algae blooms and increases plankton growth which can lead to population explosions of coral-damaging star fish. In some places conditions are so bad that the emphasis has shifted from documenting damage to accessing if and how the reef might be restored.
Coral Trade and Reef Diseases
bleached coral Pink and red corals are among the most valued corals for jewelry. A singles necklace made with them can sell or $25,000, with a kilogram of polished coral costing up to twice that. In Japan and other places red and pink coral is harvested in water about 100 meters deep. In Japan, the red and pink coral industry employs about 3,000 people and is worth about $100 million a year. It also employs large numbers of people in North Africa, where it’s the basis of a cottage industry.
Harvests of red and pink coral have declined by 85 percent since 1980. In March 2010,The United Nations Convention on International Trade on Endangered Species (CITES), the United Nations wildlife trade body, proposed controlling the trade of red and pink coral. The measure, which was sharply opposed by Japan, targeted seven species, one in the Mediterranean and six in waters off Japan and Taiwan, along with 24 “lookalike” species to prevent accidental harvesting. But the proposal was rejected out of concerns over job losses and economic damage.
Bleached coral Reef diseases caused by natural and manmade forces include white-band disease, a slow-moving infection that causes coral tissues to peel off their skeleton and is believed to be caused by a rod-shaped bacterium; yellow-ban disease, characterized by algae loss and yellow patches on the reef; and black-band disease, an infection caused by sulphur-oxidizing and sulphur-reducing bacteria that marches across patches of coral in black band, leaving behind bleached coral.
Other reef diseases found in the Caribbean include patch necrosis, white pox, white plague and rapid wasting disease. In some places unusually arm waters lead to a proliferation of coral-eating spiral shells.
Coral bleaching is a phenomena characterized by the changing of coral color from brown, green and pink to bleached white caused by the death of algae within the coral. If algae starts covering the coral, the coral is considered dead.
Reefs all around the world are plagued by coral bleaching. Damage has been particularly bad in the Indian Ocean, where 70 percent of the coral reefs whitened or died in 1998 and 1999. The year 1998 was particularly bad for coral bleaching. About 16 percent of the world’s coral became bleached or died. Not coincidently 1998 was the second warmest year on record up to that time. In 1998 and 2002 the Great Barrier Reef suffered major bleaching that was blamed on El Nino-related warming. Though much of damaged coral recovered about five percent was permanently damaged.
Coral bleaching generally occurs in waters that become warmer than 30 degrees C (85 degrees F). When waters get too hot the coral polyps become stressed and expel its algae. A temperature rise of 1.8 to 3.6 degrees F can trigger coral bleaching in many places.
Causes of Coral Bleaching
healthy coral and bleached coral The whitening is caused by loss of symbiotic zooxanthellare (a kind of algae) from the tissues of the coral polyps. Sometimes healthy corals can become completely white in two or three weeks. If algae returns to the coral within a month the white coral can revive itself. But if the conditions continues for more than two months most of the coral dies.
Coral bleaching occurs because stress has prompts the polyps to expel its dark algae symbionts. Bleaching is not only bad in its own right it also destroys important fisheries and contributes to global warming. Algae in coral and the sea absorb a lot of carbon dioxide.
Among the causes of high water temperatures are the El Niño effect and an absence of storms. Abnormal salt densities can also cause algae to die. Storms like hurricanes and typhoons help keep the water cool by churning up the water so that cooler subsurface layers of water mix with the warmer surface layers.
Many scientists believe that bleaching is a natural phenomena. Others believe it is caused at least in part by human activities. They blame global warming, overfishing and pollution for contributing to the problem.
Recovery from Coral Bleaching Caused by El Nino
Describing what he saw after a sudden increase in water temperatures around Kanton Island in the Phoenix Islands, a tiny archipelago in the central Pacific five days by boat from Fiji, Gregory Stone, wrote in National Geographic, During the El Niño of 2002-03, a body of water more than 1̊C (1.8̊F) warmer than usual had stalled for six months around the Phoenix Islands. We'd heard that the hot spot had severely bleached the region's corals. [Source: Gregory Stone, National Geographic, January 2011]
Settling down beside the reef, I saw dead coral everywhere. What had been flourishing, overlapping, overflowing brown and auburn plates of corals were now ghostly, broken reminders of their former beauty. When I'd first visited the Phoenix Islands a decade ago, these reefs had supported numerous species of hard corals, as well as giant clams, sea anemones, nudibranchs, and great populations of fish, from blacktip reef sharks to parrotfish to bohar snappers. Because the islands have remained undisturbed for so long, they'd largely avoided overfishing, pollution, and other harmful impacts of modern civilization. But they hadn't been able to avoid climate change, which most scientists believe amplifies El Niños.
Not ready to accept this setback, I was heartened to see lots of reef fish and vibrant corals growing up through the rubble—early signs of recovery. Was it possible that the reefs of the Phoenix Islands, like their mythical namesake, were rising from the ashes of a terrible warming?
In 2010 Stone returned to Kanton. He wrote: “The bleaching had killed all the coral on the lagoon floor, but almost half appeared to be growing back—the fastest recovery any of us had ever seen. The reason seemed clear: abundant fish. When coral bleaches, seaweed can grow out of control, stifling reef recovery. But fish eat the algae, keeping it from smothering the coral. Because fish populations had been protected here, the reefs remained surprisingly resilient even after suffering one of the worst bleaching events ever recorded.
Global Warming and the Sea
bleached corals Global warming is causing ocean temperatures as well as air temperatures to rise. A 2005 report by a team headed by Tim Barett of Scripps Institution of Oceanography found that between 1955 and 2000, the oceans warmed by 0.7 degrees F. Because the oceans are so vast the energy needed to warm them even smalls amount is huge.
Scientist have been surprised how even water at great depths is warming up. Water surface temperatures in the tropical Northern hemisphere have increased at ten times the rate of global warming in the air since 1984. Increases of .5 degree to 1 degree F have occurred in the major hurricane and typhoon breeding areas in the Atlantic and Pacific Oceans since 1906.
Carbon dioxide moves freely between the air and sea in a process known as molecular diffusion and tend to go where concentrations are the lowest. When carbon dioxide of levels are high in the air it flows into the sea. It is thought that carbon dioxide used moved from the seas to the air but now the situation is reserved and its flowing from the air to the seas.
Some people have proposed pumping excess carbon dioxide into the deep sea but these plans were dropped when it was discovered that large doses of carbon dioxide kill marine life immediately
Some have asked is it possible for heat from inside the Earth to heat up the seas, If that was happening the seas would heat up from the bottom up. There is no indication that that is happening. Most of the warming occurs at the surface.
Oceans Absorb Carbon Dioxide
giant jellyfish off Japan
maybe connected to global warming The oceans have acted as a large sponge for much of the carbon dioxide created by human activity. If it wasn’t for the oceans the Earth could be two degrees warmer rather than one degree it is now. Not only that it has produced much of the oxygen we breath.
Ocean absorb about a third of the carbon dioxide that humans produce. A study published in Science in July 2004 that involves analyzing 70,000 samples taken from around the globe in the 1990s reported that 48 percent of carbons dioxide produced by humans from 1800 and 1994—467 billion tons of the gas—had been absorbed by seawater.
By some estimates carbon dioxide is entering the ocean at a rate of 1 million tons an hour, ten times the natural rate. There is a large concentration of carbon dioxide in the Atlantic Ocean between North America and Europe and North Africa. The concentrations of carbon dioxide here are around 1.2 kilograms per meter, double or quadruple the amounts in most other seas. The North Atlantic Ocean holds the most because that is where cooled surface water sinks, filling more of the water column with carbon.
Global Warming and Sea Life
Marine life absorbs about 2 billion tons of carbon dioxide from the atmosphere a year. Much of the world’s carbon stocks are held in plankton, mangroves, salt marshes and other marine life. Algae in the sea absorbs some of the excessive carbon dioxide but most of it never reach the seabed to become a permanent store. Mangrove forest, salt marshes and sea grass bed cover less than 1 percent of the world’s seabed but they lock away well over half of all carbon absorbed by marine life.
Some underwater creatures such as mussels and freshwater snails emit nitrous oxide, better known as laughing gas—a powerful greenhouse gas that is 310 times more potent than carbon dioxide in trapping heat in the atmosphere.
See Mangrove Swamps
Impact of Global Warming on the Sea and Sea Life
giant jellyfish off Japan Carbon dioxide in the air and the seas and warmer sea temperatures result in less oxygen near the surface of the sea and produce oxygen poor zones that extend vertically. The massive dead zones like the on off the west coast of the United States are believed to be caused by global warming and warming sea temperatures and changes between the wind and sea that deprive the water of oxygen. The lack of oxygen will be especially tough on large sea creatures that need lots of oxygen to move around and hunt.
High temperatures have already resulted in the bleaching of coral and disappearance of Arctic ice cover. The high temperatures also stunt growth, reduce food supplies and can force fish to breed in or move to cooler water for which they are not adapted.
Global warming is blamed for causing warmer sea temperatures in the North Sea which in turn have causes many species of fish including cod, sole and whiting to migrate further north in search of cooler water. In the Americas global warming has caused an oyster-infecting bacterium that causes food poisoning in humans to spread from the Gulf of Mexico to waters off Alaska.
Research by Australia’s Commonwealth Scientific and Industrial Research Organization indicates that climate change is affecting fish growth, with species living in warmer, shallow water growing faster and those living in cooling deep ocean waters growing slower. Ron Thresher, an oceanographer involved with the study told Reuters, “Fish growth rates are closely tied with water temperature s, so warming surface waters mean the shallow-water fish are growing more slowly than they were a century ago. The finding was made by examining 555 fish specimens aged between 2 and 128 born between 1861 and 1992 and comparing that with changes in sea temperatures obtained from 60-year-old records and data obtained from 440-year-old deep water coral.
Carbon Dioxide and the Sea
Extra carbon dioxide molecule in sea water alters the pH level of sea water, making it slightly more acidic. In some places scientists have observed rises in acidity of 30 percent and predict 100 to 150 percent increases by 2100.
Carbon monoxide concentrations off coast of China,
indicative of carbon dioxide releases
Elizabeth Kolbert wrote in National Geographic, “The air and the water constantly exchange gases, so a portion of anything emitted into the atmosphere eventually ends up in the sea. Winds quickly mix it into the top few hundred feet, and over centuries currents spread it through the ocean depths. In the 1990s an international team of scientists undertook a massive research project that involved collecting and analyzing more than 77,000 seawater samples from different depths and locations around the world. The work took 15 years. It showed that the oceans have absorbed 30 percent of the CO2 released by humans over the past two centuries. They continue to absorb roughly a million tons every hour. [Source: Elizabeth Kolbert, National Geographic, April 2011]
For life on land this process is a boon; every ton of CO2 the oceans remove from the atmosphere is a ton that's not contributing to global warming. But for life in the sea the picture looks different. The head of the National Oceanic and Atmospheric Administration, Jane Lubchenco, a marine ecologist, has called ocean acidification global warming's "equally evil twin."
During the long history of life on Earth, atmospheric carbon dioxide levels have often been higher than they are today. But only very rarely—if ever—have they risen as quickly as right now. For life in the oceans, it's probably the rate of change that matters.
To find a period analogous to the present, you have to go back at least 55 million years, to what's known as the Paleocene-Eocene Thermal Maximum or PETM. During the PETM huge quantities of carbon were released into the atmosphere, from where, no one is quite sure. Temperatures around the world soared by around ten degrees Fahrenheit, and marine chemistry changed dramatically. The ocean depths became so corrosive that in many places shells stopped piling up on the seafloor and simply dissolved. In sediment cores the period shows up as a layer of red clay sandwiched between two white layers of calcium carbonate. Many deepwater species of forami—nifera went extinct.
Surprisingly, though, most organisms that live near the sea surface seem to have come through the PETM just fine. Perhaps marine life is more resilient than the results from places like Castello Aragonese and One Tree Island seem to indicate. Or perhaps the PETM, while extreme, was not as extreme as what's happening today.
The sediment record doesn't reveal how fast the PETM carbon release occurred. But modeling studies suggest it took place over thousands of years—slow enough for the chemical effects to spread through the entire ocean to its depths. Today's rate of emissions seems to be roughly ten times as fast, and there's not enough time for the water layers to mix. In the coming century acidification will be concentrated near the surface, where most marine calcifiers and all tropical corals reside. "What we're doing now is quite geologically special," says climate scientist Andy Ridgwell of the University of Bristol, who has modeled the PETM ocean.
Ph (Acid) levels in the ocean
The mixture of carbon dioxide and seawater creates carbonic acid, the weak acid in carbonated drinks. The increased acidity reduces the abundance of carbonate ions and other chemicals necessary to form calcium carbonate used make sea shells and coral skeletons. To get an idea what acid can due to shells remember back to high school chemistry classes when acid was added to calcium carbonate, causing it to fizz.
Elizabeth Kolbert wrote in National Geographic, The pH scale, which measures acidity in terms of the concentration of hydrogen ions, runs from zero to 14. At the low end of the scale are strong acids, such as hydrochloric acid, that release hydrogen readily (more readily than carbonic acid does). At the high end are strong bases such as lye. Pure, distilled water has a pH of 7, which is neutral. Seawater should be slightly basic, with a pH around 8.2 near the sea surface. So far CO2 emissions have reduced the pH there by about 0.1. Like the Richter scale, the pH scale is logarithmic, so even small numerical changes represent large effects. A pH drop of 0.1 means the water has become 30 percent more acidic. If present trends continue, surface pH will drop to around 7.8 by 2100. At that point the water will be 150 percent more acidic than it was in 1800. [Source: Elizabeth Kolbert, National Geographic, April 2011]
The acidification that has occurred so far is probably irreversible. Although in theory it's possible to add chemicals to the sea to counter the effects of the extra CO2, as a practical matter, the volumes involved would be staggering; it would take at least two tons of lime, for example, to offset a single ton of carbon dioxide, and the world now emits more than 30 billion tons of CO2 each year. Meanwhile, natural processes that could counter acidification—such as the weathering of rocks on land—operate far too slowly to make a difference on a human time-scale. Even if CO2 emissions were somehow to cease today, it would take tens of thousands of years for ocean chemistry to return to its pre-industrial condition.
Affects of Ocean Acidification on Sea Life
Acid-affected pteropod Elizabeth Kolbert wrote in National Geographic, “Acidification has myriad effects. By favoring some marine microbes over others, it is likely to alter the availability of key nutrients like iron and nitrogen. For similar reasons it may let more sunlight penetrate the sea surface. By changing the basic chemistry of seawater, acidification is also expected to reduce the water's ability to absorb and muffle low-frequency sound by up to 40 percent, making some parts of the ocean noisier. Finally, acidification interferes with reproduction in some species and with the ability of others—the so-called calcifiers—to form shells and stony skeletons of calcium carbonate. These last effects are the best documented ones, but whether they will prove the most significant in the long run is unclear. “[Source: Elizabeth Kolbert, National Geographic, April 2011]
High acidity makes it difficult for some species of mollusks, gastropods and corals to produce their shells and poisons the acid-sensitive eggs of some species of fish such as amberjack and halibut. If populations of these organisms collapse then populations of fish and other creatures that feed on them could also suffer.
Elizabeth Kolbert wrote in National Geographic, “Meanwhile, scientists are just beginning to explore the way that ocean acidification will affect more-complex organisms such as fish and marine mammals. Changes at the bottom of the marine food web—to shell-forming pteropods, say, or coccolithophores—will inevitably affect the animals higher up. But altering oceanic pH is also likely to have a direct impact on their physiology. Researchers in Australia have found, for example, that young clownfish—the real-life versions of Nemo—can't find their way to suitable habitat when CO2 is elevated. Apparently the acidified water impairs their sense of smell. [Source: Elizabeth Kolbert, National Geographic, April 2011]
In Waters Where Ocean Acidification Is Already Taking Place
shells that experienced
heavy acidification Elizabeth Kolbert wrote in National Geographic, “Owing to a quirk of geology, the sea around Castello Aragonese —a tiny island in the Tyrrhenian Sea 17 miles west of Naples— provides a window onto the oceans of 2050 and beyond. Bubbles of CO2 rise from volcanic vents on the seafloor and dissolve to form carbonic acid. Carbonic acid is relatively weak; people drink it all the time in carbonated beverages. But if enough of it forms, it makes seawater corrosive. "When you get to the extremely high CO2, almost nothing can tolerate that," Jason Hall-Spencer, a marine biologist from Britain's University of Plymouth, explains. Castello Aragonese offers a natural analogue for an unnatural process: The acidification that has taken place off its shore is occurring more gradually across the world's oceans, as they absorb more and more of the carbon dioxide that's coming from tailpipes and smokestacks. [Source: Elizabeth Kolbert, National Geographic, April 2011]
Hall-Spencer has been studying the sea around the island for the past eight years, carefully measuring the properties of the water and tracking the fish and corals and mollusks that live and, in some cases, dissolve there. On a chilly winter's day I went swimming with him and with Maria Cristina Buia, a scientist at Italy's Anton Dohrn Zoological Station, to see the effects of acidification up close. We anchored our boat about 50 yards from the southern shore of Castello Aragonese. Even before we got into the water, some impacts were evident. Clumps of barnacles formed a whitish band at the base of the island's wave-battered cliffs. "Barnacles are really tough," Hall-Spencer observed. In the areas where the water was most acidified, though, they were missing.
We all dived in. Buia was carrying a knife. She pried some unlucky limpets from a rock. Searching for food, they had wandered into water that was too caustic for them. Their shells were so thin they were almost transparent. Bubbles of carbon dioxide streamed up from the seafloor like beads of quicksilver. We swam on. Beds of sea grass waved beneath us. The grass was a vivid green; the tiny organisms that usually coat the blades, dulling their color, were all missing. Sea urchins, commonplace away from the vents, were also absent; they can't tolerate even moderately acidified water. Swarms of nearly transparent jellyfish floated by. "Watch out," Hall-Spencer warned. "They sting."
diatom walls broken down by acids Jellyfish, sea grass, and algae—not much else lives near the densest concentration of vents at Castello Aragonese. Even a few hundred yards away, many native species can't survive. The water there is about as acidified as the oceans as a whole are forecast to be by 2100. "Normally in a polluted harbor you've got just a few species that are weedlike and able to cope with widely fluctuating conditions," Hall-Spencer said once we were back on the boat. "Well, it's like that when you ramp up CO2."
Elizabeth Kolbert wrote in National Geographic, “Will organisms be able to adapt to the new ocean chemistry? The evidence from Castello Aragonese is not encouraging. The volcanic vents have been pouring CO2 into the water for at least a thousand years, Hall-Spencer told me when I visited. But the area where the pH is 7.8—the level that may be reached oceanwide by the end of the century—is missing nearly a third of the species that live nearby, outside the vent system. Those species have had "generations on generations to adapt to these conditions," Hall-Spencer said, "yet they're not there. [Source: Elizabeth Kolbert, National Geographic, April 2011]
"Because it's so important, we humans put a lot of energy into making sure that the pH of our blood is constant," he went on. "But some of these lower organisms, they don't have the physiology to do that. They've just got to tolerate what's happening outside. And so they get pushed beyond their limits."
Coral Reefs, High Acidity and Global Warming, See Coral Reefs
Affects of Ocean Acidification on Coral Reefs
Oa-sami, ocean acid
measuring devise Elizabeth Kolbert wrote in National Geographic, “Ocean acidification adds yet another threat, one that may be less immediate but ultimately more devastating to hard, reef-building corals. It undermines their basic, ancient structure—the stony skeleton that's secreted by millions upon millions of coral polyps over thousands of years....To make calcium carbonate, corals need two ingredients: calcium ions and carbonate ions. Acids react with carbonate ions, in effect tying them up. So as atmospheric CO2 levels rise, carbonate ions become scarcer in the water, and corals have to expend more energy to collect them. Under lab conditions coral skeleton growth has been shown to decline pretty much linearly as the carbonate concentration drops off. [Source: Elizabeth Kolbert, National Geographic, April 2011]
Slow growth may not matter much in the lab. Out in the ocean, though, reefs are constantly being picked at by other organisms, both large and small. (When I went snorkeling off One Tree Island, I could hear parrotfish chomping away at the reef.) "A reef is like a city," said Ove Hoegh-Guldberg, who used to direct the One Tree Island Research Station and now heads the Global Change Institute at Australia's University of Queensland. "You've got construction firms and you've got demolition firms. By restricting the building materials that go to the construction firms, you tip the balance toward destruction, which is going on all the time, even on a healthy reef. In the end you wind up with a city that destroys itself."
By comparing measurements made in the 1970s with those taken more recently, Caldeira's team found that at one location on the northern tip of the reef, calcification had declined by 40 percent. (The team was at One Tree to repeat this study at the southern tip of the reef.) A different team using a different method has found that the growth of Porites corals, which form massive, boulderlike clumps, declined 14 percent on the Great Barrier Reef between 1990 and 2005.
Ocean acidification seems to affect corals' ability to produce new colonies as well. Corals can, in effect, clone themselves, and an entire colony is likely to be made up of genetically identical polyps. But once a year, in summer, many species of coral also engage in "mass spawning," a kind of synchronized group sex. Each polyp produces a beadlike pink sac that contains both eggs and sperm. On the night of the spawning all the polyps release their sacs into the water. So many sacs are bobbing around that the waves seem to be covered in a veil of mauve.
Selina Ward, a researcher at the University of Queensland, has been studying coral reproduction on Heron Island, has found through her research that lower pH leads to declines in fertilization, in larval development, and also in settlement—the stage at which the coral larvae drop out of the water column, attach themselves to something solid, and start producing new colonies. "And if any of those steps doesn't work, you're not going to get replacement corals coming into your system," Ward said.
Once a reef can no longer grow fast enough to keep up with erosion, this community will crumble. "Coral reefs will lose their ecological functionality," Jack Silverman, a member of Caldeira's team at One Tree, told me. "They won't be able to maintain their framework. And if you don't have a building, where are the tenants going to live?" That moment could come by 2050. Under the business-as-usual emissions scenario, CO2 concentrations in the atmosphere will be roughly double what they were in preindustrial times. Many experiments suggest that coral reefs will then start to disintegrate.”
Affects of Ocean Acidification on Calcium-Producing Organisms
Oa-buoy There are concerns that global warming could deplete the oceans of calcifying plankton, including small snails call pteropods. These small creatures (usually about 0.3 centimeters in size) are a critical part of the chain in polar and near polar seas. They are a favorite food of herring, pollock, cod, salmon and whales. Large masses of them are a sign of a healthy environment. Research has shown that their shells dissolve when placed in water acidified by carbon dioxide.
Shells with large amounts of the mineral aragonote—a very soluble form of calcium carbonate—are particularly vulnerable. Pteropods are such creatures, In one experiment a transparent shell was placed in water with the amount of dissolved carbon dioxide expected to be in the Antarctic Ocean by the year 2100. After just two days the shell becomes pitted and opaque. After 15 days it becomes badly deformed and had all but disappeared by day 45.
Elizabeth Kolbert wrote in National Geographic, “Corals, of course, are just one kind of calcifier. There are thousands of others. Crustaceans like barnacles are calcifiers, and so are echinoderms like sea stars and sea urchins and mollusks like clams and oysters. Coralline algae—minute organisms that produce what looks like a coating of pink or lilac paint—are also calcifiers. Their calcium carbonate secretions help cement coral reefs together, but they're also found elsewhere—on sea grass at Castello Aragonese, for instance. It was their absence from the grass near the volcanic vents that made it look so green. [Source: Elizabeth Kolbert, National Geographic, April 2011]
The seas are filled with one-celled calcifying plants called coccolithophores, whose seasonal blooms turn thousands of square miles of ocean a milky hue. Many species of planktonic forami—nifera—also one-celled—are calcifiers; their dead shells drift down to the ocean floor in what's been described as a never ending rain. Calcifiers are so plentiful they've changed the Earth's geology. England's White Cliffs of Dover, for example, are the remains of countless ancient calcifiers that piled up during the Cretaceous period.
Acidification makes all calcifiers work harder, though some seem better able to cope. In experiments on 18 species belonging to different taxonomic groups, researchers at the Woods Hole Oceanographic Institution found that while a majority calcified less when CO2 was high, some calcified more. One species—blue mussels—showed no change, no matter how acidified the water.
"Organisms make choices," explained Ulf Riebesell, a biological oceanographer at the Leibniz Institute of Marine Sciences in Kiel, Germany. "They sense the change in their environment, and some of them have the ability to compensate. They just have to invest more energy into calcification. They choose, 'OK, I'll invest less in reproduction' or 'I'll invest less in growth.'" What drives such choices, and whether they're viable over the long term, is not known; most studies so far have been performed on creatures living for a brief time in tanks, without other species that might compete with them. "If I invest less in growth or in reproduction," Riebesell went on, "does it mean that somebody else who does not have to make this choice, because they are not calcifying, will win out and take my spot?"
A 2009 study by Alex Rogers of the International Programme on the State of the Ocean warned that carbon emission levels were on track to reach 450 parts per million by 2050 (there are around 380 parts per million today), putting corals and creatures with calcium shells on a path to extinction. Many scientists predict levels won’t start leveling off until they reach 550 parts per million and even to each that level will require strong political will which thus far does not seem to present.
Concern Over Ocean Acidification
Bleached_coral In May 2010, the Nation Research Council reported that the world’s oceans are becoming more acidic as the fastest pace in hundreds of thousands of years. Ocean acidification eats away at coral reefs, interferes with some fish species ability to find their homes and can hurt commercial shellfish like mussels and oyster and keep them from forming protective shells. Some scientists predict the seas could be so acid to coral that reefs will only survive behind acid-free barriers.
Elizabeth Kolbert wrote in National Geographic, “In 2008 a group of more than 150 leading researchers issued a declaration stating that they were "deeply concerned by recent, rapid changes in ocean chemistry," which could within decades "severely affect marine organisms, food webs, biodiversity, and fisheries." Warm-water coral reefs are the prime worry. But because carbon dioxide dissolves more readily in cold water, the impact may actually show up first closer to the Poles. Scientists have already documented significant effects on pteropods—tiny swimming snails that are an important food for fish, whales, and birds in both the Arctic and the Antarctic. Experiments show that pteropod shells grow more slowly in acidified seawater. [Source: Elizabeth Kolbert, National Geographic, April 2011]
It's still possible to avert the most extreme acidification scenarios. But the only way to do this, or at least the only way anyone has come up with so far, is to dramatically reduce CO2 emissions. At the moment, corals and pteropods are lined up against a global economy built on cheap fossil fuels. It's not a fair fight.
Addressing Global Warming and Improving Conditions of the Sea
Boris Worm of Dalhousie University in Halifax said, the problem “is not too large to turn around. It can be done, but it must be done soon. We need to shift from single species management to ecosystem management. It just requires a big chunk of political will to do it.” His team called for new marine reserves, better management to prevent overfishing and tighter controls on pollution.
Some see the Reducing Emissions from Deforestation and Forest Degradation (REDD) agreement, a global warming agreement hammered out in Copenhagen in December 2009, as a model tackling problems related to climate change and the sea. One of the key components of the program is the compensation of developing countries for preserving forests, peat soils, swamps and fields that absorb carbon dioxide. An similar a agreement that would address global warming and the sea would offer compensation to developing countries for protecting coral reefs. Mangrove swamps and other oceanic environment.
Progress has been made reducing the amount sewage and other pollution entering the sea.
New Satellite to Measure Sea Saltiness and Gain Insights Into Climate Change
In June 2011, an Argentine-built spacecraft carrying instruments from the United States and other nations was launched from the Vandenberg Air Force Base in California aboard a Delta 2 rocket. Its mission: to chart the saltiness of the ocean – from outer space and get better insight into how global warming affects the world’s oceans. AP reported: “The craft will circle 408 miles above the Earth and will use a NASA-built instrument to map weekly changes in the levels of brine in the sea. NASA's Aquarius instrument is so sensitive that it can detect changes down to a dash of salt in a gallon of water.” [Source: Alicia Chang, AP, June 6 2011]
satellite images of coccoliths
in the Celtic Sea The spacecraft will measure the concentration of salt in the topmost layer of the sea, which varies around the globe. Understanding how brackish the sea surface is will help researchers better predict future climate change and short-term climate phenomena such as El Nino and its alter ego La Nina, which can have profound effects on weather around the world.
A fleet of Earth-orbiting satellites routinely provides updates on sea surface temperatures, sea level changes and ocean winds. But measurements of dissolved salts in the ocean so far have been limited, sporadically measured by ships and buoys. "There are vast tracts of the ocean where salinity has never been collected – ever," NASA's Eric Lindstrom said at a pre-launch news conference.
The $287 million Aquarius – Latin for water-bearer and named after the constellation – is designed to measure microwave energy emitted by the ocean, giving scientists an idea of the saltiness. To prevent interference from radio, radar and other noise, another instrument will doublecheck the data and correct for any wrong readings.Aquarius is expected to provide scientists with monthly maps depicting ocean salt variations over its three-year mission.
The project is a joint venture between NASA and Argentina's space agency CONAE. Other participating countries include Brazil, Canada, France and Italy, which will collect environmental data. It's not the first to do ocean remote sensing of salt levels. Once in orbit, the spacecraft will join a dual-purpose European satellite that has been collecting data on ocean salt and soil moisture since 2009. Unlike the European mission, the new project is dedicated to the ocean and uses different technology to make measurements. It's not unusual to have several overlapping Earth-observing satellites.
Reefs Could Perish by 2100 Experts Warn
In July 2009, Reuters reported: Increasingly acidic oceans and warming water temperatures due to carbon dioxide emissions could kill off the world's ocean reefs by the end of this century, experts told a meeting in London, saying the predicted pace of emissions means a level of 450 parts per million of carbon dioxide (CO2) in the atmosphere will be reached by 2050, putting corals on a path to extinction in the following decades. The experts were comprised of two dozen coral reef specialists and climate change experts representing universities, government research offices and the Intergovernmental Panel on Climate Change. [Source: Michael Kahn, Reuters, July 6, 2009]
"The kitchen is on fire and it's spreading around the house," Alex Rogers of the Zoological Society of London and the International Program on the State of the Ocean, said in a statement. "If we act quickly and decisively we may be able to put it out before the damage becomes irreversible."
"If CO2 is allowed to reach 450 ppm, as is currently widely regarded as being the most optimistic threshold target for world leaders to agree at Copenhagen, we will have put the world's reefs on a path to major degradation and ultimate extinction," John Veron, the former chief scientist of the Australian Institute of Marine Science, told the meeting. "Such a catastrophe poses a dire threat to the future wellbeing of all humanity."
The scientists agreed that governments should strive for a level of 320 parts per million of carbon dioxide, saying 360 was a breaking point for reefs to survive. At the current level of 387 parts per million of carbon dioxide, reefs are in serious decline, they said. This will have a future knock-effect that threatens other marine and coastal ecosystems.
Image Source: National Oceanic and Atmospheric Administration (NOAA) noaa.gov/ocean and Wikimedia Commons, except giant jellyfish from Hector Garcia blog
Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
© 2009 Jeffrey Hays
Last updated March 2011