Mar. Ecol. Prog. Ser. 388, 235-242 (2009)
Increased atmospheric CO2 concentrations may pose a greater threat to some species of fish than previously predicted because of the combined effects of ocean acidification and increased temperature.
Philip Munday at James Cook University and his colleagues tested the aerobic scope (resting and active O2 consumption) of two species of Australian coral reef fishes, Ostorhinchus doederleini and O. cyanosoma, in waters that modeled 2100 projections for temperature and pH.
In both species, aerobic scope declined over 30% in both above-average temperatures (29 to 32oC) and in acidified water (pH 7.8 and ~1000 ppm CO2). Mortality rates increased dramatically above 33oC.
Reduced aerobic capacity in tropical fish species will likely affect feeding, growth and reproduction, threatening the stability of fish populations. Compounded effects of increased temperature and increased pH on non-calcifying marine organisms had been largely unknown, but this study indicates that some fish populations could be at significant risk if carbon emissions continue at the current rate.
In the documentary A Sea Change, retired educator Sven Huseby travels the world examining the effects of ocean acidification on the worlds various marine ecosystems. Throughout the film, the focus remains on only the negative effects of the increasing ocean acidity, entirely ignoring any possible fixes and conveying a sense of helplessness to the viewer. However, as the film concludes, the rhetoric changes in favor of creating hope and giving the human race a call to action to save the world’s oceans from acidification.
The first major example of positive, hopeful rhetoric comes is the appearance of an eco-friendly foreign hotel that institutes a heating and cooling system that emits no carbon. Such as system drew on nearby ocean water in order to provide heat and air conditioning for the entire building without releasing any anthropogenic carbon. In the conversation between Sven and the hotel representation, the film makes clear that such technology could be used in many coastal areas in the United States of America, thereby giving Americans hope that they can implement such technologies to help save the oceans and spurring them to action.
Likewise, Sven visits a very windy area on the coast of Norway and meets with a pair of experts on wind energy. They discuss turbines that will convert the energy in the wind into clean energy used to power large areas. As with the hotel, the film makes a point of naming specific locations in the United States where such turbines could operate highly efficiently, once again using rhetoric that will spur Americans to take action in the hopes of reducing carbon dioxide emissions.
Finally, Sven visits the headquarters of the corporation Google, famous for its search engine. While receiving a tour of the grounds, the documentary prominently features the myriad arrays of solar panels. In addition, the conversation between Sven and his guide strongly emphasizes that the solar panels provide for one third of Google’s power consumption. This rhetoric strongly influences people to believe that by investing in solar panels themselves they can cut down on carbon dioxide emissions and therefore do their part to save the world’s oceans.
After implementing mostly despairing rhetoric through the majority of A Sea Change, the documentary changes to a style which inspires hope in the viewer. This hope coupled with the possible solutions the film provides to the carbon dioxide emission problem intends to spur the film’s viewers to action. Ideally, the ending would influence every viewer to do his or her utmost to reduce carbon emissions and save the oceans.
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.