Coral Bleaching Research Paper

Climate change: it has become a touchy subject in today’s society. Some claim that it “isn’t real or isn’t happening” despite the overwhelming evidence that proves it is affecting the planet. Human activity has led to a startling increase in atmospheric carbon dioxide levels. For the past 650,000 years, the atmospheric level of carbon dioxide had been relatively steady, never reaching above 300 parts per million. In the past 50 or so years, the rate has skyrocketed from 315 to 400 parts per million. The rate in which carbon dioxide is increasing will prove to be catastrophic if it continues on its current path as it has already affected many ecosystems, and in particular, the ocean. The increase in carbon dioxide has two major effects on the

Like most organisms, corals survive best within certain environmental conditions. In her article about marine biodiversity, Patrice Descombes explains how the range of environmental conditions is very restricted for corals, who often live in temperatures close to their temperature limit. The temperature limit is not so important to the coral itself, but to the symbionts living in the coral. When the corals experience high stress, what results is a phenomenon is known as coral bleaching. Coral bleaching “results from the expulsion of symbiotic dinoflagellate microalgae (zooxanthellae) from the cells of the coral, leaving the host without the color afforded by zooxanthellate pigments. A bleached white skeleton can then be observed through the now translucent coral tissue.”(Pandolfi). Generally, corals die from these events and result in massive mortality events across the reef. In recent weeks, a massive coral bleaching event has occurred in the northern section of the Great Barrier Reef in Australia and scientists have determined the cause to be warmer seawater temperatures. Temperature also accelerates the timing of larval settlement of several coral species. In their article about animal behavior and climate change, Ivan Nagelkerken and Phillip L. Munday found that a 2 °C increase in temperature has resulted in corals settling on crustose coralline algae rather than on the bare

This causes the seawater to become more acidic and carbonate ions in the water to be less abundant. Emma V. Kennedy notes in an article that carbonate is essential for the generation of coral skeletons, which are composed of calcium carbonate, aka limestone. Coral reefs provide a breakwater for many tropical islands against strong waves. Due to ocean acidification, the level of carbonate in the water is much lower than the corals need, effectively stunting their ability to grow. Models have shown that “in general, calcification rates, which are a function of the product of [the] linear extension rate and skeletal density, decline with decreasing aragonite saturation state. However, rates and curves differ substantially among taxa”(Pandolfi). Different species react to the changes in acidity at different rates, but nevertheless, a decline in growth can be seen overall. Hoegh-Guldberg et al. performed studies in which the pre-industrial concentration of atmospheric carbon dioxide was doubled to 560 parts per million. When coral was exposed to this level of carbon dioxide, the coral calcification and growth decreased by up to 40 percent. This occurred because aragonite, the crystalline form of calcium carbonate, would not form with low carbonate ion