Coral Bleaching Coral reefs are the most biodiverse ecosystem on the planet. There are more than 25,000 known species of organisms and countless others that have yet to be identified. Reefs thrive on the shallow edge of tropical seas, most often on the eastern edge of continents along warm water currents that brush the coasts. Reefs cannot live in cold waters and are limited by ocean depth and available sunlight. Coral is the foundation of the reef community, providing a three-dimensional structure where thousands of species of vertebrates and invertebrates live and feed. Some species of coral are hard, while others soft.
Coral are very old animals that have evolved over millions of years to become reef-building organisms. On Earth, coral reefs are among the most biologically diverse places to be found. They may only cover a small percent of the ocean, about .2 percent, but more than 25 percent of the marine life resides there. The two main types of coral are hard coral and soft coral. Hard coral is the major species that build reefs. Similar to tropical rainforests, coral reefs are usually located within 30 degrees latitude of the equator. Water temperatures for the reefs are between 16 and 30 degrees Celsius, though there are coral outside these regions with somewhat colder temperatures. The ideal development waters for reefs are tropical waters which are low in nitrogen, phosphorous and other nutrients, stable temperatures, as well as stable salt content. The coral reefs we see today are a result of thousands of years of production and cycling through life and death. Coral only contribute a smaller portion of life found in the reefs, though they create a habitat for various amounts of other species. There are three main types of coral reefs: barrier reefs, fringing reefs, and atolls. Respectively, these reefs are offshore, separated by water from land, continuous with land, and islands made of coral that flank lagoons. Though there are different types, the general coral makeup is the same. After years of mystery, we now know that coral is very complex in its design. Coral is a symbiotic relationship with the small animals that make up coral called polyps, and the microscopic algae called zooxanthellae that live inside the coral. Coral reefs lives in colonies consisting of many polyps using living tissues to connect to each other. Each polyp resembles a cupcake shape with a circle of tentacles near the opening. To capture zooplankton for food, the tentacles are equipped with stinging cells for trapping. The small polyps secrete limestone, also known as calcium carbonate. The exoskeleton of the coral is made of these secretions, just like the shell of a snail. Reefs are able to grow from the stone. The algae that live in the corals use the process of photosynthesis, taking sunlight to converts water and carbon dioxide into sustenance. The polyps receive most of their energy this way, although they are carnivorous. For providing the corals with energy, the algae are provided shelter to live, taking the coral waste for their own growth. A situation where two organisms live together gaining benefit is called mutualistic symbiosis.
In 2003, the Australian government identified the link between poor water quality and the outbreak of crown-of-thorns starfish and is committed to enhancing water quality (Sweatman et al., 2013). The poor water quality is attributed to the inflow of chemical effluents that pollute the water and endanger the lives of most organisms. In addition, they raise nutrient levels necessary for the growth of crow-of-thorn starfish. Coral cover within the Great Barrier Reef is evidently declining, and thus fast mitigation is necessary to safeguard the listed World Heritage area in Australia. Given the procedural work in enforcing such measures, it is unlikely to have impacts in the short term (Veron, 2008). However, direct action is not only necessary but also required to minimize the growth of crown-of-thorns starfish and extra loss of corals. Nevertheless, with or without improved mitigation, the coral cover will continue to decline mainly because past activities have majorly increased ocean temperatures and seawater acidity. Marine life may not necessarily decline, but the severe conditions will compel the living organisms to adjust to new modes of survival since the food web will be distorted. This situation will tamper with the atmospheric cycle. Carbon entering the atmosphere will no longer be sufficiently absorbed in the water bodies, thus increasing air and water pollution (Watson, 2011).
Definitely, ocean temperatures will continue to rise over the next few decades unless mitigation measures are taken to reduce the rapidly increasing greenhouse gases. Coral reefs will be affected by the temperature rise and bleaching events will occur at a greater rate. In light of the rapidly increasing temperatures, coral species face an uphill struggle to adapt, evolve and survive. Although corals and their symbionts have the abilities to resist the temperature changes, one can only wonder the extent and effectiveness of these strategies.
De’ath, G., Fabricius, E., Sweatman, H., & Puotinen, M. (2012). The 27–year decline of coral cover on the Great Barrier Reef and its causes. PNAS, 109 (4), 17995-99.
Pyers, G. (2011). Biodiversity of coral reefs. New York, NY: Marshall Cavendish Benchmark.
Sweatman, H., Delean, S., & Syms, C. (2011). Assessing loss of coral cover on Australia’s Great Barrier Reef over two decades, with implications for longer-term trends. Coral Reefs, 30, 521–531.
Veron, J. (2008). A reef in time: The Great Barrier Reef from beginning to end. Cambridge, MA: Belknap Press of Harvard University Press.
Watson, M. (2011). Coral Reefs. Encyclopedia of Environmental Issues, 1(4), 317-319.