One more thing to worry about!
Global warming is a very publicized issue, however there are many off-shooting issues that are not given their fair share of the public limelight. Ocean warming and acidification is an increasing problem, as 30% of the carbon dioxide which we (humans) produce is absorbed by the sea! So, not only is the sea being warmed but it is becoming less basic as the extra carbon dioxide dissolves in to the sea to form carbonic acid, which then interacts with chemicals in the sea and is slowly overcoming the buffering power of the sea.
One offshoot of the oceanographic warming/acidification issue is species having access to areas of the benthic (sea bed in water of depth <100m) which were previously inaccessible to them. These warmer water animals usually have faster metabolisms and greater propensity to fast movement than cold-water animals. One specific example of this is the advancement of shell crushing (durophagous) king crabs up the sea shelf surrounding the Antarctic. King crabs have heavily calcified chelae (claws), and are fiercesome predators, however they cannot survive in water below a certain temperature and so have been kept off the benthic area for physiological reasons, and nothing else. Now the water temperature is on the increase, the area of seabed available to the crabs is slowly increasing.
For the past 40 million years, roughly, the animals living on the Arctic Peninsula have lived in a habitat where there are very few durophagous predators and so these animals have devolved any sort of protection they once had prior to the Eocene period. They have adapted to live in an incredibly cold climate by developing very slow metabolisms, and some species, for example various isopods, are now gigantic. These specialties are a huge benefit to life on the Antarctic Peninsula as it currently is, however, if the king crabs invade the area then none of the indigenous species stand any chance of survival and there may be a mass extermination of the original animals as the population of the crabs will no doubt explode given their newfound access to a brand new source of food, in an environment in which they themselves are relatively free from predation. This invasion will obviously radically change the food chains of the Antarctic waters and will contribute to the gradual homogenization of the global marine population as certain species monopolize on the changes that are currently taking place globally.
If we, humans, wish to conserve anything of the incredible, diverse and beautiful seas that we take so much for granted, we have to start acting radically, and most importantly, soon! Once alien species have taken over it can be nearly impossible to restore the ecosystem to its previous state so clearly the aim has to be not to create the environment where an invasion can happen in the first place.
Based on the work done by Aronson, R.B., S. Thatje, A. Clarke, L.S. Peck, D.B. Blake, C.D. Wilga, and B.A. Seibel. 2007. Climate change and invasibility of the Antarctic benthos. Annual Review of Ecology, Evolution, and Systematics 38: 129-154.
Ocean absorption of CO2 has helped alleviate some of the potential effects of increasing atmospheric CO2 levels, but in doing so has changed the chemistry of the seawater. The chemical reaction from CO2 absorption decreases the water’s pH levels, making the water more acidic. Since the Industrial Revolution, the pH has dropped .1 units and is expected to drop another .3 units if CO2 emissions continue the way they are now. It is uncertain how marine organisms are going to adapt to increased acidity, making the potential threat of ocean acidification alarming. One of the main processes seriously affected by the change is calcification, which enables organisms to produce their shells or skeletons. Increased levels of CO2 in the ocean will shift the carbonate system equilibrium towards higher concentrations of CO2 and lower carbonate ion concentrations. Carbonate ions are essential in order to produce calcium carbonate, which is needed to develop the shells of oysters and mussels.
The change in pH, affecting coral reefs and other calcifying organism, particularly imperils oysters and mussels. Studies have shown that the calcification rates of the edible mussel and Pacific oyster are strongly correlated with increasing concentrations of CO2.If the pH levels continue to decrease as projected, the ability of these mussels and oysters to produce shell material will decrease by 25% and 10% respectively by the year 2100. Oysters are less sensitive to increased levels of CO2, due to their differing shell composition. Mussel shells are composed of mostly calcite, while oyster shells contain a large amount of aragonite. Currently, calcium carbonate is readily available to these organisms so that they can create their shells, but soon it will become harder, requiring greater expenditures of energy, for these organisms to produce shells.
Mussels and oysters are an integral part of the fishing economy and the predicted decrease in calcification due to ocean acidification will lead to significant economic losses. Global shellfish production has had an annual increase of 7.9% over the last 30 years, which corresponds to a commercial value of 10.5 billion US dollars. The Pacific oyster was the most cultivated species in 2002 and represented 10.8% of the total world aquaculture production, while mussels represented 3.6% of total production. There are fishermen whose livelihoods depend on the sale of shellfish. Although a much more sudden example, many fishermen were put out of work and incapable of providing for their families after the oil spill in the Gulf of Mexico. A similar thing could happen if ocean acidification continues to make calcification increasingly difficult. Any decline in these species will cause considerable damage to the fishing market as well as have major consequences for coastal biodiversity.
Mussels and oysters serve an important purpose in coastal ecosystems. They both regulate energy and nutrient flow, as well as provide habitats for other species. If the population of mussels and oysters diminishes because of their inability to calcify and make shells, there will be huge repercussions for biodiversity and the function of the ecosystem.
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>
The Loss of Coral Reefs
The increased acidification of the world’s oceans is beginning to pose a great threat to the many life forms that inhabit them. One ecosystem in which this threat is particularly prevalent is the coral reefs. Between the broad array of corals and sponges that make up reefs and the many other organisms that depend on reefs for shelter, they are the most biodiverse ecosystem in the ocean. However, based on some models these reefs may lose a great deal of that amazing biodiversity in the near future.
The base of the problem of ocean acidification comes from the vast amount of CO2 that is being absorbed by seawater. Once the CO2 is in the seawater it quickly goes through a series of chemical reactions creating carbonic acid and bicarbonate. In the creation of these two compounds the carbonate ion (CO32-) is removed from the calcium carbonate (CaCO3), which was previously present in the seawater. This process can be observed by measuring the pH of the water, as the amount of carbonic acid in the ocean increases, the pH of the seawater drops. Since the dawn of the Industrial Revolution the amount of CO2 in the air has been rapidly increasing, this has caused the average pH of the ocean surface to drop from 8.2 to 8.1. While 0.1 may seem like an insignificantly small number, there has not been a change in ocean pH this intense in hundreds of thousands of years (Ocean Studies Board). Since corals rely on taking calcium carbonate from the water and the drop in pH has reduced the concentration of calcium carbonate in the water, this change is having a negative impact on the reefs. Studies show that important groups of reef building corals begin to struggle and in some cases die as they attempt to carry on the calcification process. After observing the CO2 seeps in Milne Bay, Papua New Guinea a group of scientists concluded that falling pH causes a decrease of up to 40% in coral diversity with mainly boulder corals surviving. The same group found that if the pH of the ocean falls below 7.7, all reef growth will come to a halt (Katharina E. Fabricius). Another experiment predicts that by the middle of the century seawater conditions will cause many coral groups to have calcification rates 10-50% less than the pre-industrial average (Joan A. Kleypas and Kimberly Yates). The coral reefs of the world are on the brink of destruction if the current trend of ocean acidification continues.
When people talk about the effects of the huge amounts of CO2 that people produce every day the destruction of coral reefs is rarely at the forefront of the discussion. After my research I would argue that coral reefs should be a huge part of the argument about CO2 and global warming. Coral reefs are the most vibrant, diverse, and arguably important ecosystem in the oceans which happen to take up most of the Earth’s surface. Considering ocean acidification and rising water temperatures these reefs are undoubtedly in danger that people cannot continue to ignore. Whether we like it or not humans rely on sea-life as a supply of food and coral reefs are just the first ecosystem in a long line that we could lose if we stand by and do nothing.
Fabiricius, Katharina E. “Ocean Acidification and Coral Reefs.” PhysOrg.com – Science News, Technology, Physics, Nanotechnology, Space Science, Earth Science, Medicine. Nature Climate Change, 29 May 2011. Web. 04 Sept. 2011. .
Kleypas, Joan A., and Kimberly K. Yates. “Coral Reefs and Ocean Acidification.” Oceanography 22.4 (2009). The Oceanographic Society. Web. 4 Sept. 2011. .
Ocean Studies Board. Ocean Acidification: a National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. Print.
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