Long-term effect of coral transplantation: Restoration goals and the choice of species.
Journal of Theoretical Biology 280 (2011) 127–138
As the health of many coral reef ecosystems is declining, coral reef restoration is growing increasingly important. A common method of restoration is transplantation, or the transference of healthy coral to failing reef communities. However, research conducted by Soyuka Muko and Yoh Iwasa provides evidence that in some cases, transplantation can be detrimental to restoration efforts. When fast-growing coral was introduced to a population of Pocillopora, an endangered coral species with limited larvae dispersal, the native Pocillopora population was unable to recover and was replaced by the new coral species over the long-term. Such a result would lower the biodiversity of a community and make it more susceptible to collapse. Muko and Iwasa demonstrate that the benefits of a transplantation can be roughly ensured by assessing available larvae supply from existing adult specimen and by using a mathematical model to calculate an appropriate transplanted-coral density. They suggest that the potential of transplantation should be carefully evaluated case-by-case in order to avoid unwanted results.
Great Barrier Reef Concerns
Skeptical Science doi:2011
The Great Barrier Reef has survived past climate changes with higher carbon dioxide rates and warmer temperatures than today. Even so, there should be concerns about ocean acidification currently effecting the Great Barrier Reef.
In the past, during glacial periods, sea levels were 100 m lower than they are today. The Great Barrier Reef was left exposed, and after the glaciers melted, the reefs were covered with soil.
The changes during the melting of glaciers, occurred over a span of 10-20,000 years. Today, temperatures change by 5-8 degrees Celsius by 100 ppm, over a time span of less than 100 years. The rate of change is significantly 100-200 times faster than in the past. The northern end is more adjusted to warm temperatures, and animals cannot cross 2500 km within 100 years, or 25 km per year, to the southern end.
Humans depend ecologically, and economically due to tourism, on the Great Barrier Reef. Unfortunately, rapid changes are occurring with very little time to adjust.
Coral reefs constitute a very important component of many ecosystems across the world’s oceans. Although such reefs occupy less than one tenth of a percent of the oceans’ surface, these diverse ecosystems house twenty-five percent of the world’s marine organisms. The rigid structures that compose coral reefs are formed by a process known as calcification performed by polyps, small marine organisms, which then die and leave behind their calcified shells. However, with increasing carbon dioxide levels in the ocean, calcification can be negatively affected, thereby harming the whole of the world’s coral reef ecosystems.
Under normal conditions, the process of calcification begins with the combination of carbon dioxide and water to form carbonic acid. The carbonic acid subsequently dissociates into a hydrogen ion and a bicarbonate ion, which then breaks down into another hydrogen ion and a carbonate ion. Finally, calcium combines with the carbonate to form a hard calcium carbonate shell. However, when extra carbon dioxide comes into the process, the process shifts so that fewer quantities of calcium carbonate form, causing weaker, smaller calcium carbonate complexes to form reefs. These smaller, weaker reefs inherently cannot house as many organisms as their larger counterparts, and as the oceans continue to acidify, the reefs will continue to wane smaller and weaker. Ocean acidification also slows the growth of reefs, makes coral more susceptible to bleaching and disease, reduces the tolerance of reefs to ultraviolet radiation, and accelerates bioerosion; the combination of such negative effects on reef formation could lead to an eventual disappearance of the structures from the world’s oceans.
Multiple laboratory studies have shown substantial declines in reef growth associated with ocean acidification. In such studies, a doubling of the amount of atmospheric carbon dioxide has led to a decline of three to sixty percent in the rate of calcification. Likewise, calcification rates of brain corals in Bermuda have decreased by twenty-five percent during the last fifty years due in part to increasingly acidic ocean waters. In another study by the United States Geological survey, crustose coralline algae, another important part of reef building, also becomes much less effective in more acidic waters. In water tanks with decreased pH, crustose coralline algae covered ninety-two percent less area than in the tanks with normal ocean water. In addition, non-calcifying algae increased in area by fifty-two percent, showing its ability to outcompete the important crustose coralline algae in acidified ocean environments. A study at the University of Hawaii showed that dominance in reef building could shift from stony corals to fleshy algae in acidified oceans. This shift would lead to not only changes in the reefs themselves but also in neighboring coastlines, thereby drastically changing the ecosystems of the area.
Ocean acidification has many negative effects on coral and other crucial components of the calcification and the reef building process. Such adverse effects could lead to the eventual disappearance of reefs from the ocean, greatly impacting the lives of many marine organisms inhabiting reef-based ecosystems. Changes in reefs also cause changes in nearby coastlines, which will disturb the living conditions of even more organisms. If ocean acidification continues, the effects on coral reefs will snowball and disrupts a sizeable portion of the world’s marine organisms.
Carbon dioxide is a compound with extremely important biological connotations. It is a reactant in photosynthesis, the chemical process by which plants produce energy. Carbon dioxide is also, however, a byproduct of many industrial reactions, and the earth is struggling to try to find a place to put all this excess anthropogenic carbon dioxide. In particular, some of the carbon dioxide is being sopped up by the world’s oceans. Nonmetal oxides such as carbon dioxide are acid anhydrides in water, and as a result of this absorption, the oceans are becoming more acidic and the average pH of the earth’s oceans has dropped by a quantifiable margin. This phenomenon has aptly been entitled ocean acidification, and it has some rather grave implications. However, the additional carbon dioxide may, to some degree, improve the photosynthetic output of some marine plants, given the compound’s aforementioned role in the reaction.
Diatoms are unicellular algae that are significant producers in many marine food chains. The effects of ocean acidification on diatoms have been a hot topic of research within the past seven years given their importance. In one study, scientists bubbled varying levels of carbon dioxide into colonies of the coastal phytoplankton skeletonema costatum. The colony that received 350 ppm of carbon dioxide grew 1.6 times as much as the control group. A colony given 1000 ppm grew 2.1 times as much. The 1000 ppm culture produced more chlorophyll than the 350 ppm group, and the effectiveness of photosynthesis was enhanced by the additional carbon dioxide as well.
Another experimented conducted entailed the creation of an equilibrium of atmospheric carbon dioxide with bubbled aqueous carbon dioxide. When the carbon dioxide was made to be twice that of normal conditions, consumption increased by 27%. When the carbon dioxide was tripled, the diatoms’ consumption was 39% higher. Estimates say that such carbon dioxide consumption as that described here may in have kept atmospheric levels to 90% of what they would be otherwise since start of the industrial revolution. In yet another study, it was found that certain species of diatoms grow 20% faster when exposed to increased carbon dioxide.
This potentially positive consequence of the increase in atmospheric carbon dioxide is not nearly enough to outweigh the negative results of anthropogenic carbon dioxide. Some algae do not, in fact, benefit from increased levels of carbon dioxide. Zooxanthellae, for example, exist symbiotically with coral reefs. If the zooxanthellae colonies grow too large, then they will be doing so at the expense of their coral homes. Some species of phytoplankton may react poorly to the increased acidity. Then we must factor in things such as coral bleaching, coastal erosion, decalcification, and the loss of biodiversity. Indeed, for every possible upside that comes from ocean acidification, it seems that there are two potentially devastating ramifications.
Kleypas, Joan, Richard Feely, Jean-Pierre Gattuso, and Carol Turley. “FAQs about Ocean Acidification : OCB-OA.” Home : Mobile WHOI.edu. 6 Oct. 2010. Web. 05 Sept. 2011. <http://www.whoi.edu/OCB-OA/FAQs/>.
“Ocean Acidification (Effects on Marine Plants: Phytoplankton, Diatoms) — Summary.” CO2 Science. 7 July 2010. Web. 05 Sept. 2011. <http://www.co2science.org/subject/o/summaries/acidificationdiatoms.php>.
The ocean has absorbed carbon dioxide (CO2) from the atmosphere since the beginning of time. The ocean is known as a carbon dioxide sink because of its absorption capabilities. This has been viewed as a positive in the past few decades since global warming has become a pressing issue. The ocean absorbs CO2 from the atmosphere, which helps lessen the threat of global warming to the earth. Carbon dioxide levels have risen since the Industrial Revolution due to automobile emissions, cement production, industrial power plants and other contributing factors. Now, with the oceans absorbing absorbing about 1/3 of the earth’s carbon dioxide, the sea chemistry is being affected. The ocean cannot handle such high levels of CO2 as a result, its pH is becoming more acidic. This effect is known as ocean acidification.
Before the Industrial Revolution, the ocean’s pH levels were stable. Since then, the pH has dropped 0.1 units. Though this may seem like a relatively small change, the world’s ocean has a very high buffering, or acid neutralizing, ability so the fact that the pH has declined to this extent is very startling. PH levels are predicted to drop even more in the next century.
Like all ecosystems, marine ecosystems are comprised of a vast array of interactions between different species and different types of organisms (both alive and dead) and the physical environment. Therefore, a change in any of these aspects will lead to a plethora of changes throughout the rest of the ecosystem. Because of the sheer quantity of life present and the significant interactions between species, coral reefs are prime candidates to be affected greatly by ocean acidification. These reefs provide food and shelter to hundreds of thousands of marine organisms so when the reef is harmed by acidification, so are all of the organisms that interact with it. When global warming, one of the world’s most alarming environmental threats directly affects the coral reef, one of the ocean’s most important ecosystems, the ramifications are dire.
Coral reefs are created by large calcium carbonate colonies known as coral. These reef structures are the home and feeding grounds to a wide array of organisms. Coral reef ecosystems have been called “cradles of evolution” because more marine organisms evolve from coral reefs than from any other ecosystem.
Ocean acidification may actually alter the physical structure of coral reefs. Acidification affects the organisms that build the reef because it lowers calcification rates and pH, inhibiting the creature’s skeletal growth. Without these reef-building organisms, coral reefs cannot exist.
Aside from hindering the organisms that physically build the reefs, ocean acidification also increases the probability that existing reef structures may dissolve. Reef erosion is likely, given the vulnerability inevitable with increased acidification.
Acidification raises the possibility of coral mortality. It can cause coral bleaching, which can cause the coral to die. As the coral tries to survive and is in a weakened state, they become vulnerable to encroachment by other marine organisms. Some species can benefit from higher water acidity, like macroalgae. As these algae thrive, they block sunlight from getting to the coral and they may be abrasive to coral structures as they move through the water in the current. Both low light and abrasive contact can weaken the coral, or even kill the reef structure.
Dissolving and eroding coral reefs, as well as coral that is lost because of displacement by other organisms that can survive better in the high acidity all lead to what is known as “reef flattening”. This is a phenomenon that creates a loss in the “architectural complexity” of the reef. This affects all of the organisms that live within and rely on the reef as a key part of their survival methods. Reef flattening diminishes reef structure and habitats, and reduces organism populations and biodiversity.
Coral reefs are home to over 25% of all known species of fish and exhibit the highest biodiversity of any ecosystem in the entire ocean. Threats to coral reefs are a threat to thousands of other organisms, so as we see ocean acidification harming our world’s coral reefs, we should be very concerned. Ocean acidification does not mean that the oceans will die, but the survivors may be algae and jellyfish. For the ocean to be sustainable in its present form, with coral reefs the prominent sanctuaries for marine life, the pH of the ocean has to maintain acidity within relatively narrow boundaries. With the alarming increase in CO2 being absorbed into our great carbon dioxide sink known as the ocean, the coral reef is in jeopardy.
“Chapter 4.” Ocean Acidification: a National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. Print.
Eilperin, Juliet. “Growing Acidity of Oceans May Kill Corals.” The Washington Post: National, World & D.C. Area News and Headlines – The Washington Post. 5 July 2006. Web. 04 Sept. 2011. <http://www.washingtonpost.com/wp-dyn/content/article/2006/07/04/AR2006070400772.html>
Studies conducted in the waters of Florida and the Caribbean have shown that there have been declines in the coral populations which have coincided with increases in the presence of macroalgae. The causes of this decline still aren’t agreed upon. Various things, some of human influence and some of natural occurrence, such as water quality and diseases, or storms and temperature rises, have been suggested as possible reasons for the decreasing numbers in coral populations.
In ocean acidification the increase in the quantities of Carbon Dioxide (CO2) present in the water decreases the amount of Calcium Carbonate (CaCO3) available. Because Calcium Carbonate is used by various organisms to make skeletons, ocean acidification affects the calcification rates in corals. This subsequently interferes with their skeletal growth and sometimes even results in the dissolution of their skeletons in conditions where pH levels were lower than what the organisms were accustomed to. Decreased rates of skeletal growth can have negative effects on coral survival. For instance, thinner more fragile skeletons decrease coral ability to resist erosion. Decreases in skeletal growth also changes the age at which they reach sexual maturity.
Coral and macroalgae compete for space. So a decrease in coral population is beneficial for their main competitors. Macroalgae thrive in environments with no herbivores, high quantities of nutrients and slow coral growth. Ocean acidification slows coral growth and therefore favors the spread of macroalgae over coral.
Further studies have shown that increase in contact and interaction between corals and macroalgae increased the rates of disease spread in coral populations. One particular infection known as the white plague which has spread from colonies in the Florida Keys all throughout the Caribbean. Results of an experiment conducted to test the veracity of this claim demonstrated that after two weeks of exposure to Halimeda Opuntia, a type of algae, coral colonies tested on displayed symptoms of infection. And after a month, they had fully contracted the disease.
The effects of decrease in coral populations and increases in macroalgal populations have repercussions on other species as well. The presence of coral reefs provides physical protection to the creatures that inhabit shallower coastal waters. Their erosion would leave these creatures and their homes exposed to the elements.
Lower coral presence can also lead to decline in biodiversity, as the coral reefs become unable to offer adequate habitat for the species to which they provide shelter. While a direct relation has yet to be demonstrated, large fish presence in various areas has usually corresponded with low quantities of macroalgae. And large quantities of macroalgae tend to coincide with low coral population. “As soon as they move in, there goes the neighborhood.”
D. Lirman, Competition between macroalgae and corals: effects of herbivore exclusion and increased algal biomass and growth. 9/4/2011
Nancy Knowlton, Jeremy B.C. Jackson, Shifting baselines, Local impacts, and Global Change on coral reefs. 9/4/2011
Maggy M. Nugues, Garriett W. Smith, Ruben J. Von Hooidonk, Maria I. Seabra, Rolf P. M. Bak, Algal contact as a trigger for coral disease. 9/4/2011
Deep-sea ecosystems have potential to be seriously impaired by ocean acidification. The organisms in the deep-sea live in cold-water climates that are far more stable than climates in shallow water. Thus, the organisms that inhabit the deep sea do not adapt well to change and the impacts of acidification are extremely severe for them.
Ocean acidification is the process in which excess carbon dioxide from the atmosphere is absorbed into the oceans, changing their chemistry significantly. The pH of the waters is reduced, making them far more acidic. When the oceans acidify, carbonate ion concentrations and saturation states for calcium carbonate minerals decrease. Skeletons and shells of many marine organisms depend on calcium carbonate minerals. Therefore, change in saturation states can seriously harm and even wipe out species.
The deep-sea ecosystem is a cold and dark environment. Ocean acidification occurs more slowly in deep-sea ecosystems, but the organisms are highly sensitive. They have low metabolic rates, which make for a low capacity gas exchange and reduced enzyme function. Deeper in the sea, organisms are more vulnerable to acid-base disturbance.
Many deep-sea species have calcium carbonate in their bodies. Shells and skeletons of these organisms are eaten away at when the water they live in acidifies. 55 years ago, a mass extinction of marine species occurred; shelled creatures in the deep oceans nearly vanished. The disappearance of these organisms is rooted back to a drastic drop in the pH of the ocean. Hundreds of thousands of years later the oceans recovered, but the seas are now acidifying ten times faster than they did at the time of the extinction. Scientists are concerned that the deep waters may once again experience a similar situation. Even if only select species are eliminated, the entire ecosystem will suffer as a result.
Acidification in cold-water communities is cause for alarm in Alaskan waters. These areas host countless cold-water coral species, many of which are endemic. The coral colonies serve as important habitats for many organisms, which may not be able to survive if the coral reef population is destroyed. The coral species in Alaska and across the world are diverse and vital to their environments. Many of the species are unique to specific areas; their extinction would pose a great threat to the deep-sea ecosystems that they inhabit.
The deep oceans are at serious risk with the current of acidification. The deep-water corals may experience serious ecological changes. Carbonate-based organisms may be the root of a monumental change in the marine food chain.
With the accelerating phenomenon of ocean acidification caused by increased atmospheric CO2 levels, there is a pressing need for evidence delineating the effects on different types of oceanic ecosystems. The majority of on-site studies to date on ocean acidification have been on coral reef ecosystems. Researchers from the University of Miami examined three coral reef sites in Papa New Guinea. At each site, there were volcanic fissures on the seabed that constantly poured out CO2, simulating the effects of atmospheric CO2 dissolving into the ocean. The pH level dropped from the normal level of 8.1 to 7.7, a more than 250% increase in the concentration of hydrogen ions. An oceanic pH of 7.7-7.8 is projected for the year 2100 in the business-as-usual model, where humans do nothing to curb the rates of CO2, being emitted into the atmosphere.
The glimpse into what our coral reefs could become in less than a century was certainly shocking. The coral diversity at the sites dropped by a staggering 40 percent, due to the marked decline of the key calcifiers such as the zooxanthellate corals and macroalgae. These species suffer when greater amounts of CO2 are dissolved into the ocean because the gas reacts with H2O to produce greater concentrations of hydrogen ions, driving the pH down. As pH decreases, CO3- (Carbonate ion), a key ingredient for calcification, becomes more scarce. As a result, many corals suffer a decreased rate of calcification, eventually dying off because they are unable to adapt to the changing ocean chemistry. Though, it has to be noted that not all species are harmed from ocean acidification, namely sea grasses and non-calcifying macroalgae. In fact, the researchers discovered that sea grasses extended their area on the seabed by three or four times after the volcanic leakage of CO2, demonstrating that unaffected species capitalize on the decline of calcifying organisms. Access to sunlight is crucial for the survival many coral reef species, explaining why the sea grasses were quick to colonize into the recently vacated areas. The changes in the coral reef ecosystem are better described by a “regime-shift” of species rather than mass extinction.
Still, the losers from an acidified ocean greatly outnumber the winners. As calcifying organisms begin to disappear, the complexity of coral structures also diminishes, leaving a more flattened habitat. This then cascades into the decline of other aquatic organisms such as schools of fish or bottom-dwelling crabs that rely on the coral structures to live in, hide, or hunt from. The level of diversity across the board dwindles significantly from the adverse effects of increased amounts of CO2 released into the environment that eventually dissolves into the ocean. If this trend continues for rest of the century, perhaps coral reefs will no longer be described as the “rainforest” among oceanic ecosystems.
Tropical coral reefs are one of many ecosystems that are affected by ocean acidification as well as a changing global climate. These ecosystems are home to countless species of fish and marine organisms. Many of these animals depend on the corals for not only shelter, but also a source of food. Without healthy and living corals, the diverse life in the ecosystem would virtually disappear.
Ocean acidification is the process in which excess carbon dioxide from the atmosphere dissolves into the ocean and shifts the chemical equilibrium of seawater. Under normal circumstances, the carbon dioxide binds with the water to form carbonic acid. The carbonic acid then breaks down into both bicarbonate and carbonate molecules. The carbonate molecules combine with free calcium ions in the water to form calcium carbonate, the chemical that many marine organisms, including corals, need in order to build their calcium skeletons. However, ocean acidification causes an increase in the carbon dioxide levels causing a shift in equilibrium to more carbonic acid and bicarbonate and less carbonate molecules. The result is a shortage of carbonate molecules to react with the calcium ions and thus a shortage in general of calcium carbonate for marine organisms to utilize for structural use.
Ocean acidification poses a problem to coral by weakening the reefs in a number of different ways. Acidification slows down coral growth as well as reproduction. It contributes to the erosion of existing reefs and coral bleaching as well.
One of the organisms affected by ocean acidification is an alga called Zooxanthellae. They are vital in the reef-building process. The algae have a symbiotic relationship with the coral in which the coral is depends upon the algae to conduct photosynthesis and to supply nutrients. In order for reefs to grow, the Zooxanthellae must supply the coral the aforementioned calcium carbonate (CaCo3), which makes up the majority of the skeletal structure of coral. In many studies, high carbon dioxide levels have been attributed to a decrease in calcification rates. In turn, lower calcification rates lead to slow or nonexistent growth in corals. This is worrisome for the future of coral reefs. If something were to happen and a large portion of the reefs were damaged, because of the slow calcification rates, the reefs would not be able to repair themselves at a fast enough pace.
Another pressing issue is the erosion and dissolution of the reefs. The dissolution rate is a measure of how fast the existing reefs are eroding. According to one study, acidification has been shown to increase dissolution rates sharply. In different study done by Silverman, the combined effect of increased dissolution rates and decreased calcification rates will cause corals to start shrinking instead of growing at a certain carbon dioxide level in the water.
Coral bleaching is another alarming effect of a lower pH ocean. Corals expel the Zooxanthellae when under stress. The algae are what make up most of the color of the corals; so expelling the algae results in just a white skeleton being left behind (hence bleaching). Bleached coral are weak and prone to erosion and dissolution and are not ideal habitats for other marine organisms.
Coral reefs have much to lose from ocean acidification. If the oceans keep following the “business-as-usual” scenario, it is quite likely that by 2050, the majority of the coral reefs will have disappeared. Steps must be taken to preserve what is left and to ensure the survival of the coral reefs of our oceans.
Although there exists a plethora of hypotheses on how ocean acidification will affect marine life, many argue that these are, in fact, just theories, made by over-zealous scientists trying to scare the population into living more sustainably. However, during a recent research study on the effects of low pH levels on coral reefs, scientists were able to observe these effects in a completely natural environment, making their conclusions more real and alarming than ever.
Coral reef ecosystems are known for their vivid colors and majestic aura, and as a result, the tourism industry racks up billions of dollars in hotel and tour revenue from people eager to experience them. However, the amount of healthy coral reefs has been decreasing rapidly. Although many hypotheses exist about why this is happening, ocean acidification is usually near the end of this list, apparently being only a small threat and playing only a minimal rule in destructing this ecosystem. Recent research, however, has found the opposite to be true.
The basis of a coral reef is calcium carbonate. Calcium carbonate is a precipitate only in slightly basic environments such as marine waters, and when placed in a more acidic environment, starts to dissolve. So naturally, one would think that the acidification of the ocean would be a crucial problem for the coral reefs. However, so far, the acidity of the ocean has decreased by only .1 pH unit. What would happen if marine pH were to decrease even more? By studying volcano fissures on the ocean floor, scientists were able to see the answer to this question firsthand. These fissures released CO2 into the water and consequently lowered the water pH by .4 units, causing temporary ocean acidification. In such an environment, nearby coral reefs were completely unable to grow and function, becoming completely crippled and lifeless.
In this scenario, healthy reefs that were less affected by the volcano fissures were eventually able to supply the underdeveloped coral reefs with calcifying macroalgae (or reef builders) and bring them back to a standard degree of vitality. However, what would happen if acidification prevailed throughout the entire ocean? Coral reefs would have no “back-up” reefs to save them. The continued acidification of the ocean will definitely have a disastrous effect on the world’s reefs, slowing disabling this beautiful yet delicate ecosystem until its complete decline.
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Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. Print.